Chemical Nature of Cells

Property of Water How it helps life existSolubility All polar substances can be dissolved in water.

Water acts to transport solutes around the organism.High heat capacity Water acts as a thermal buffer minimising temperature changes due

to the environment.Provides a stable external and internal environment.

High latent heat of vaporisation Exploited by animals in cooling mechanisms.As sweat goes from liquid to vapour, heat is removed from the animal, cooling the body.

High latent heat of fusion Doesn’t turn into a solid very easily, doesn’t damage cells except in extreme temperatures.

Density Bottom of lakes rarely freeze allowing animals to still be able to live in that area.

Cohesion and surface tension Cohesion – strong attraction of water molecules to one another.Surface tension – forms a skin on the surface.Exploited for animals to live on and for some animals to hold onto the skin.Polar molecules bind to xylem walls, using cohesion and adhesion to create a continuous column of water.

Reagent Acts as a source for many processes.

The 4 most common elements in living things are;o Hydrogeno Carbono Oxygeno Nitrogen

All organic molecules contain complex carbon.

Biomolecule Elements Examples UseCarbohydrates C, H, O Glycogen Stores energyLipids C, H, O, (N, P) Phospholipid Cell membraneProteins C, H, O, N Haemoglobin TransportNucleic Acids C, H, O, N, P DNA Genetic Material

Chapter 1.1

Water is the most abundant compound in organisms and cells. 75% - 85% of a cell weight is water. Water is made up of one oxygen atom and two hydrogen atoms, linked by covalent bonds. Water molecules most important feature is its dipole nature, meaning it has two charges. Positive charge in hydrogen atoms and negative charge on oxygen atoms. Water molecules are highly cohesive (form hydrogen bonds with each other because of dipole nature) Hydrogen bonds explain properties seen in water, because they are weak and continually breaking. At 4˚, there is no sufficient movement to break hydrogen bonds (turns to ice), water molecules form a

lattice structure that is less dense than liquid water. At 100˚, movement increases to the point where hydrogen bonds can’t hold together anymore, water is

converted to a gaseous state. Water is a versatile solvent because of the polarity of water molecules (universal solvent) Substances that can dissolve in water are hydrophilic or soluble (e.g. salts, etc.) Substances that cant dissolve in water are hydrophobic or insoluble (e.g. fats, oils, petrol, etc.)

Many chemical reactions within cells produce acidic or alkaline/basic substances. Level of hydrogen ions in solution can be measured using the pH scale. Pure water is neutral (7), acidic (0-6.9), basic (7.1-14) Vital that blood pH is maintained at steady level at mean 7.4 Cells maintain a relatively constant internal pH by using cytosols as buffers, removing and releasing

hydrogen.

Chapter 1.2

Water is not always pure, it may contain other substances. The molecules that make up organisms are;

o Carbohydrateso Proteinso Lipidso Nucleic acidso Water

Large molecules are called macromolecules, classified as nucleic acids, complex carbohydrates, lipids and organic proteins.

Large biomacromolecules are synthesised on site inside the cell. Polymerisation - single units (monomers) link to form polymers. Carbohydrates are made up of carbon, hydrogen and oxygen in the ratio 1:2:1. Carbohydrates are important structural components and in energy storage. Monosaccharides are used as structural components and in energy storage. Disaccharides are double – sugar molecules joined with a glycosidic bond. Disaccharides provide a convenient way to transport glucose, sucrose, maltose and lactose. Polysaccharides – glycogen used to store energy in animals, more soluble in water, many insoluble in

water. Polysaccharide – starch is a polymer of glucose, energy storage in plants, insoluble. Polysaccharide – cellulose, glucose polymer, important structural material in plants. Glycoproteins – a molecule made up of carbohydrates and proteins. Glycolipids – a molecule made up of carbohydrates and lipids. Carbohydrates used in energy production, energy storage, structural communication and genetic

components. It is advantageous for starch and glycogen to be large and insoluble because they are used to store

energy. They are large and insoluble, they can form solid grains inside cells that don’t affect the other parts of the cell.

Condensation – Monosaccharides join and water is released. Hydrolysis – Monosaccharides are broken down and water is added.

Chapter 1.3

18% of a cell is protein. The whole set of proteins produced by the cell is called proteomes. Proteins contain large complex molecules. Motility – allow movement of cells and their organelles (tubulin). Structural – provides support and protection (collagen, keratin). Enzymes - catalyse biochemical reactions (catalase). Transport – carry molecules from one location to another or across all membranes (haemoglobin). Hormones – signalling between different cell types, stimulation or inhibition. Cell surface receptors – label cells as targets for hormones, viruses, growth factors, recognition of ‘self’,

transmission of nerve impulses. Neurotransmitters – signalling between neurons. Immunoglobins – recognition of foreign substances. Poisons or toxins – chemicals for defence and to aid in capture of food. Amino acids are basic units which proteins are made.

Protein structure

o Primary – sequence of amino acids joined together by peptide bonds in polypeptide chains.

o Secondary – repeated twisting and folding of polypeptide chains forming hydrogen bonds (3D)

o Tertiary – final folded 3D shape, by hydrogen bonds, ionic bonds, disulphide bonds, Van der Waal forces and hydrophobic interactions.

o Quaternary – more than one polypeptide chain bonded to make a complete protein.

When proteins denature, their bonds in tertiary and quaternary structure is broken.

Chapter 1.4

Large macromolecules consist of monomers, called mononucleotides. 2 groups of bases

o Pyrimidines – thymine (urasil in RNA) and cytosineo Purines – adenine and guanine

Polymerisation – nucleotides can be joined by a sugar phosphate linkage. During polymerisation, a bond forms between C3 and C5 called a ‘3-5 sugar

phosphate linkage’ RNA is single stranded. DNA is double stranded. DNA is comprised of two nucleotide strands running anti-parallel to each other. The base sequence in one strand determines the base sequence in the

complimentary strand (law of base pairing). 2 strands are held together by hydrogen bonds between the bases. Each bond is weak and easily broken. Adenine pairs with Thymine. Guanine pairs with Cytosine.

Chapter 1.5

Lipids are fats, oils and waxes. They are all made of Carbon, Hydrogen and Oxygen. Lipids can carry more energy than carbohydrates and proteins. Fats are insoluble in water making carrying energy around the body

easier. Adipose cells are cells that are used to store fats.

Polymer Monomer Complex Carbohydrates

Simple sugars

Lipid Triglycerides & Fatty acids

Protein Amino acids Nucleic Acid Nucleotides

There are two types of nucleic acids, DNA and RNA. Function of Nucleic Acids

o Messenger RNA – read by ribosome to produce functional protein.o Ribosomal RNA – makes ribosomes.o Transfer RNA – transports amino acids from cytoplasm to ribosome.o DNA – the code from which all proteins are synthesised.

Proteoglycans are molecules that contain both carbohydrates and proteins.

Membranes and cell organelles

Chapter 2.1

Apoptosis is ‘programmed cell death’. Controlled by signals and receptors on the plasma membrane. Important because if more cells are created than the number being destroyed, tumors form. Body wasting diseases, cancers (not enough apoptosis), degenerative diseases. Two main pathways of apoptosis

o Signals from inside a cell – the mitochondrial pathways.o Signals from outside a cell – the death receptor pathways.

Necrosis occurs in cells that are seriously damaged (e.g. by infection). Necrosis is the death of a portion of tissue or an organ in the body. Tissue death occurs when not enough blood is supplied to the area. Necrosis is irreversible. Eukaryotic Cells have an outer boundary called the plasma membrane. Cells produce substances that need to be modified and stored in organelles. Inside the cell is a fluid called the cytosol. Organelles are held in place by the cytoskeleton. Cytosol – fluid inside cells Cytoplasm – cytosol + organelles excluding nucleus Protoplasm – cytosol +ALL organelles Cells vary in shape and contents to match their environment and biological function. Unicellular organisms remain unspecialised and carries out a range of biological functions. Prokaryotic Cells have a cell membrane and cytosol. Prokaryotic cells lack membrane bound organelles and no nuclear membrane with just one circular

chromosome. Every living cell of every part of an organism needs matter and a source of energy to keep it alive. Multicellular organisms have specialised body systems. Unicellular organisms have large surface area to volume ratio so that materials can diffuse into the cell

quickly.

Chapter 2.2

The plasma membrane selectively controls the movement of materials into and out of the cell. It is responsible for cell-cell recognition. Plasma membrane is described as selectively permeable, allowing only some and not other substances

through. Function of the Plasma membrane

o Encloses cell contento Regulates movement of materials into and out of the cello Helps maintain shape and communication with neighbouring cells

Lipid structure of the membrane gives it the unique property of being flexible and able to repair itself. Specialised protein molecules are embedded in the bilayer. Phosphobilipid layer has a hydrophilic head and hydrophobic tail. Function of cell membrane components

o Glycoprotein – cell recognition and triggers an immune responseo Glycolipid – helps cells adhere together to make tissueo Protein channels – control movement of specific substanceso Cholesterol – keeps membrane fluid

Membrane proteinso Transport proteins – channel and carrier – allow some ions to move througho Receptor proteins – hormones and other substances bind to these – affects cell activityo Glycoproteins – acts as markers, antigens, enables immune system to distinguish self from non-

selfo Adhesion proteins – connects cells to multicellular organisms

Chapter 2.3

The main processes in which substances pass through the membrane areo Diffusion (passive)o Osmosis (passive of water)o Facilitated diffusion (passive via transport proteins)o Active transport (requires energy)o Exocytosis (bulk movement requiring energy)o Endocytosis (bulk movement requiring energy)

Chapter 2.4

Diffusion is the net movement of particles from a region of high concentration to an area of low concentration not necessarily across a membrane not requiring energy.

The steeper the concentration gradient, the more rapid the rate of diffusion. Diffusion occurs until equilibrium is met. Factors affecting diffusion

o Concentration gradiento Diffusion distanceo Surface areao Physical barriers

Disadvantage is that molecules in the cell that are required may be lost if the external environment has a lower concentration than the internal environment.

Smaller molecules and heat will increase the rate of diffusion. Water is the universal solvent. The solute would be the substance that is added to the solvent, e.g. salt. Osmosis is the net movement of water from a region of high concentration to an area of low

concentration across a semi permeable membrane not requiring energy. Hypotonic is when there a net movement into the cells. Hypertonic is when there is a net movement out of the cells. Isotonic is when there is no net movement.

Facilitated diffusiono Transport proteins in the cell membrane assist the movement of large polar and non polar

molecules that are relatively insoluble in lipids. Transport proteins

o Carrier proteinso Channel proteins

Chapter 2.5

Active transport processes require energy expenditure because material must be moved against their concentration gradient.

Cells engaged in active transport have huge numbers of mitochondria whose function is to make energy available to the cell.

It involves carrier proteins that are similar to those responsible for facilitated diffusion but that the carrier protein is coupled to a source of energy.

Cells make very small containers within them from the plasma membrane itself called vesticles. (their formation and movement is referred as cytosis)

Transport using vesticles into the cell is called endocytosis. Transport using vesticles out of the cell is called exocytosis. Phagocytosis is the endocytic process involves enclosing solid material. Pinocytosis is the endocytic process involves enclosing liquid. Smaller organisms have a large surface area to volume ratio.

Chapter 2.6

Features that are shared by both plant and animal cells include;o Nucleuso Plasma membraneo Ribosomeso Mitochondriao Golgi apparatuso Endoplasmic reticulum (rough and smooth)o Cytoskeletono Vacuoles and vesticles

Organelles are membrane bound structures found in eukaryotic cells which carry out specific functions.

Organelle Function Location Structure DiagramNucleus Contains

genetic material

Cytoplasm Nucleolus in the centre surrounded by chromatin enclosed in a double layer of nuclear membrane perforated with nuclear pores.

Mitochondria Site of cellular respiration

Cytoplasm Cylindrical organelles occurring in large numbers. Bounded by a double membrane, the inner layer is extensively folded to form cristae.

Ribosomes Synthesis of proteins

Free in cytoplasm or bound to rough endoplasmic reticulum

Made up of ribosomal RNA, protein and two subunits. A larger and smaller one.

Rough Endoplasmic Reticulum

Synthesis, folding and modification of proteins. Transportation of proteins throughout the cell. Membrane production

Continuous with the nuclear membrane and extending to the cytoplasm as part of the endomembrane system.

A complex system of membranous tubules studded with ribosomes. Connect to the smooth ER.

Smooth Endoplasmic Reticulum

Synthesis of lipids. Transport of materials throughout the cell. Detoxification of drugs and poisons

Cytoplasm as part of the endomembrane system

A system of membranous tubules similar in appearance to rough ER but lacking ribosomes

Golgi apparatus

Modification of proteins. Sorting, packaging and storage of proteins and lipids to send out of the cell. Transport of materials through vesicles. Manufacture of some macromolecules

Cytoplasm, associated with ER

Stack of flattened membranous sacs called cisternae

Lysosomes Releases intracellular digestive enzymes that destroy macromolecules (e.g. apoptosis). Recycling of cellular components.

Cytoplasm Single membrane bound sac of hydrolytic enzymes. Lysosomes bud off the golgi apparatus

Chloroplasts Site of photosynthesis

Within the cytoplasm of plant leaf

Stacks of thylakoids stacked together as grana

Cellulose cell wall

Protects the cell. Maintains

- Cellulose fibres.

cell shape. Prevents excessive water uptake.

Between the walls of adjacent cells is the middle lamella.

Plastids Chloroplasts – site of photosynthesisChromoplasts – attractants and identifiersAmyloplasts – storage of starch and fats

Cytoplasm Double membrane structure bound structures

Centrioles Organizing microtubule assembly but not essential

Cytoskeleton Found as a pair, each composed of nine sets of triplet microtubules arranged in a ring

Vacuoles and Vesticles

Food vacuoles. Contractile vacuoles. Central vacuole

Cytoplasm Membrane bound sacs. (vacuoles are larger)

Cell Cytoskeleton

Shape and mechanical support for the cell. Regulation of cellular activities. Motility

Network throughout the cytoplasm

Dynamic system of protein microtubules, microfilaments and intermediate filaments

Biochemical Processes in the Cell

Chapter 3.1

All organisms require energy for metabolism – the overall chemical activity of the cell. It involved the action of enzymes in the manufacture of organic molecules in various energy transforming

and recycling processes, and the breakdown of unwanted substances. Reactants go in the chemical reaction and Products come out. Metabolic reactions are reversible. Chemical reactions will only occur if it has sufficient amount of energy to begin the reaction (activation

energy) Anabolic / Endergonic reactions Reduction involves the removal of oxygen or additional electrons Requires energy input E.G. photosynthesis 6CO2 + 6H2O -> C6H12O6 + 6O2

Small molecules combine to build larger ones Catabolic / Exergonic reactions Oxidation involves the addition of oxygen or electrons Reactions release energy E.G. cellular respiration C6H12O6 + 6O2 -> 6CO2 + 6H2O + Energy Larger molecules break down into smaller, less complex molecules Autotrophs produce their own energy through photosynthesis (light) or chemosynthesis (inorganic). Heteroths cannot produce their own and must consume energy via eating. Glucose stores energy within animals ATP provides the energy for metabolic reactions Adenosine triphosphate structure

ATP works through hydrolysis, losing the end phosphate groupreaction is reversible.

The energy that is released from the lost of the phosphate is immediately ready to be used inside the cell.

3.2

Catalysts speed up reactions without being used up or changed in the reaction Enzymes are protein catalysts that increase the rate of a chemical reaction Substrates are the reactant/s in the enzyme-catalysed reaction

Active site is the area of the enzyme to which the substrate binds to, it is highly specific Enzymes only catalyse one (or very few) types of substrate Enzymes lower the activation energy required and do not change the nature of the reaction or the end

result Enzymes are needed so that reactions occur ata a fast enough rate to support the requirements of the cell

/ organism. Substrates have specific shapes to fit into the active sites (lock and key model) The Amino acid R groups in the active site help the substrate bind Poisons such as cyanide and arsenic can block the active site and stop a reaction Induced Fit model says that the enzyme structure is flexible not rigid and that it adjusts its shape to bind

to the substrate This increases the range of substrate specificity Two types of Inhibitors, competitive and non competitive, both are reversible Competitive inhibitor binds temporarily with the active site preventing the binding of the enzyme and

substrate Non competitive inhibitor binds with the enzyme in another part, not the active site. These inhibitors

change the shape of the enzyme therefore affecting its ability to bind with the substrates. Rate of enzyme catalysed reactions are affected by temperature, pH, cofactors and coenzymes, enzyme

and substrate, and stimulatory and inhibitory effects of the products At low temperature, there is low activity, temporarily inactive The rate increase with the temperature, most active at optimum temp. High temperature denature the enzyme by disrupting the hydrogen bonds, resulting in a loss of tertiary

structure from the unfolding and unwinding of the protein. Different enzymes have different optimum pH. It often depends on the location and type of enzyme. Increasing the substrate concentration increases the reaction rate as it increases the number of collisions

between the enzyme. However eventually all active sites will be occupied at which this point the maximum rate of reaction has been reached and can no longer increase.

Cofactors are non protein molecules that bind to the enzyme (is not changed by the enzyme) and assists in catalysing process. E.g. iron, calcium, copper, zinc, potassium & magnesium

Coenzymes are organic cofactors. E.g. vitamins

3.3 / 3.4

Cellular respiration is the process by which mitochondria break down glucose to make ATP Cellular respiration is a 3 stage process Glycolysis occurs in the cytoplasm and is where the glucose is broken down Glucose breaks down into 2 pyruvate and 2 ATP 1 glucose + 2 atp + enzymes -> 2 pyruvates + 4 ATP (2 gained) + 2 NADH (goes to ETC) Pyruvate is converted to acetyl CoA 2 pyuruvate -> 2 Acetyl CoA + 2 Co2 (waste) + 2NADH (goes to ETC) Krebs cycle breaks down pyruvate into C02 and occurs in the mitochondrial matrix Generates electrons for use in electron transport 2 Acetyl CoA -> 2 ATP + chain6 NADH (goes to ETC) + 2 FADH2 (goes to ETC) + 4CO2 (waste) Electron Transport Chain occurs in inner membrane of mitochondria. ATP is synthesised Electrons are transported through the chain. Electrons are carried to this step by NADH and FADH2, oxygen is used and water is given off 10 NADH + 2 FADH2 + Oxygen -> 34 ATP + Water There is a total of 38 ATP by the end of Cellular Respiration

2 ATP made in glycolysis 2 ATP made in Krebs Cycle34 ATP made in ETC1 NADH = 3 ATP

10 X 3 = 301 FADH2 = 2 ATP

2 X 2 = 4 Anaerobic Respiration (Fermentation) yields 2 pyruvate and 2 ATP, occurs in glycolysis Two types of fermentation, alcoholic and lactic acid

6CO2 +

6H2O

C6H12O6 + 6O2

Chlorophyl

l

Light

Alcoholic – pyruvate converted to ethyl alcohol and carbon dioxide, carried out by yeast and bacteria and is used in producing alcohol and baking

Lactic Acid – pyruvate converted to lactic acid, carried out by muscles when don’t get enough oxygen, causes muscle soreness and cramps

Photosynthesis is carried out by MOST autotrophs, opposite of cellular respiration. 2 steps of photosynthesis, Light dependent and Light Independent Light dependent traps sunlight, produces electrons and ATP required to power the light independent

stage. Oxygen is released. Light independent (aka Calvin Cycle) uses the ATP and electrons from the light dependent stage and

carbon dioxide to make glucose.

Chapter 4 – Rational Drug Design

Rational drug design involves finding out how the infective agent works against the cell and using that information to design a drug that prevents the infective agent from being able to do what it is supposed to do.

1. Analyse the organism that causes disease and determine the structure of the active site 2. Design a drug that binds to the agent and blocks the active site.

Coordination and Regulation: Endocrine System

5.1

Homeostasis is defined as the maintenance of a constant internal environment, maintained within narrow limits.

The endocrine and nervous systems together control homeostasis. The endocrine system is a ductless gland system that produces hormones into the blood. Hormones are chemical substances that target and excite particular cells. They are slowly released and

have a long lasting effect. Extracellular fluid surround the outside of the cell

o Interstitial / Tissue fluido Blood plasma

Intracellular fluid is inside the cello Cytosol

Exchange between fluids is required to maintain homeostasis. Substances within these fluids are exchanged via

o Vesicular transporto Diffusiono Bulk flow

Variables subject to homeostasiso Body temperatureo Water balanceo Nutrient balance

o Ionso pHo Blood volumeo Blood pressureo Oxygeno Carbon Dioxideo Red Blood Cells

Homeostasis may not occur wheno Infectiono Traumao Toxic exposureo Automimmune diseaseo Genetic disease

Negative feedback system is “negative” because the response to the stimulus reduces the effect of the original stimulus.

5.2

The different cells in the Pancreas respond to the change in blood glucose levels in two ways. o Alpha cells increase production of glucagono Beta cells decrease production of insulin

Diabetes mellitus is a condition characterised by less glucose being absorbed by cells so excreted in urine (lack of insulin activity)

o Type 1 – due to undersupply of insulino Type 2 – due to insulin not binding with its effector cells

Signal transduction involves getting a signal from a target cell’s exterior to the cell’s interior during which the cell converts one kind of signal into another.

Amino acid hormones is a water soluble signal molecule that travels in the bloodstream. It cannot pass through the cell membrane so it uses the second messenger system. The receptor for amino acids is located on the outside of the plasma membrane. The first messenger is the binding between the hormone and the receptor. This stimulates production of a second messenger inside the cell. The second messenger system is rapid is it activates enzymes already present in the cell causing the

response.

Steroid hormones are lipid soluble signal molecules that are carried in the bloodstream and are able to pass through the cell membrane.

Steroid hormones are able to diffuse directly across the plasma membrane and bind to the receptor that is located within the cytosol.

The receptor then moves to the nucleus, interacting with the DNA and thus altering protein production. The action of the steroid hormones is slower than that of amino acid hormones as it takes time to

activate genes and to adjust protein production.

5.3

Pheromones are

chemical signalling molecules secrete by animals, they are not hormones as they are not secreted by ductless glands.

Pheromones can be used for communication purposes, to mark trails or to warn others. Sexual pheromones are secreted by organisms seeking a mate, however they can be misused by

predators who use them to attract prey. Plant hormones are produced in small amounts, act on target cells and cause a response. External factors influencing plant growth

o Light intensityo Gravityo Watero Light directiono Day lengtho Temperature

Plants are able to respond to physical parameters in their environmento Phototropism – growing towards lighto Positive geotropism – growing downwards towards gravityo Negative geotropism – growing upwards against gravityo Vernalisation – response to periods of cold

Plant hormones are transported throughout the plant via the xylem and/or phloem and/or diffusion.

Coordination and Regulation: Nervous System

6.1

6.2

Neurons / nerve cells are the basic unit of the nervous system. A number of neurons bound tougher is called a nerve. There are 3 types of neurons;

o Sensory / affector neuron (PNS > CNS)o Motor / effector neuron (CNS > PNS)o Inter / connecting neuron (in CNS connecting sensory& motor neurons)

Axon lengths and dendrites all vary. The nervous system involves a more direct pathway communication around the body. Neurons do not touch each other. The gap is called synaptic cleft / synapse. Nervous impulse pathway

o Neuron one is stimulatedo The nervous impulse moves along the dendrites of the first neurono The nervous impulse moves along the axon of the first neurono The nervous impulse arrives at the synapse and vesticles release their neurotransmitter into the

spaceo The neurotransmitter diffuses across the synaptic cleft to receptors of the second neurono The neurotransmitter binds with the receptor of the receiving neurono The nervous impulse stimulates the second neurono The neurotransmitter is deactivated by the enzyme in the synaptic cleft

Nervous System

Central Nervous System(Brain & Spinal Cord)

Peripheral Nervous System(nerve cells not part of CNS)

Sensory/Afferent Division(transmit to CNS)

Somatic sensory nerurons(monitors events outside of

body)

Viseral sensory neurons(monitors events inside of

body)

Motor/Efferent Divison(transmit from CNS)

Somatic nervous system(under voluntary/conscious

control)

Autonomic nervous system(involuntary)

Sympathetic nervous system

(brings system into action, increases impulse action in

response to stress)

Parasymthetic nervous system

(system returns to normal, decreses impulse action

after stress)

o The nervous impulse passes along the second neuron Sensory neurons act as different types of receptors

o Chemoreceptorso Mechanoreceptorso Photoreceptorso Thermo-receptorso Pain receptors

Nerve impulse involves a change in a charge across the axon membrane. Nerve impulse is a wave of electrical charge (an action potential) that passes rapidly along an axon. Nerve impulse transmission – Action potential

o As the impulse passes along the nerve, Na+ ions move in and the inside becomes positive and the outside negative.

o As the impulse moves, K+ ions move out and the outside becomes positive once more and the inside negative, taking it back to its original state.

Action potential is the burst of electrical activity caused by the process of depolarisation.

6.3

Neurotransmitters are specialised chemical messengers. Neurons have a large amount of mitochondria to provide energy. The junction between a neuron and a muscle is called a nerve-muscle junction. Neurohormones is any hormone secreted by the nervous system into the bloodstream. Neurohormonal activity is distinguished from that of classical neurotransmitters as it can have an effect

on cells distance from the nerve. Diverging pathways spread out. One cell can influence many others.

Converging pathways come in. One cell can be influenced by many others.

Neurotoxins prevent the transmission of nerve impulses at nerve muscle junctions. Antitoxins react with toxins to destroy their normal abilities.

6.5

Nervous Communication Endocrine CommunicationRapid response to a stimuli (within fractions of a second)

Relatively slow response (within minutes or longer)

Travels electrochemically along axons and chemically across a synapse

Travels as chemicals in the circulation

Response short lived Response usually long lastingResponse is specific in target neuron, muscle or gland

Response often widespread in several target tissue

The nervous system may stimulate glands to correct a change that disturbs homeostasis. Osmoregulation is controlled largely by the kidneys.

Thermoregulation

Infection and Disease

Chapter 7

Disease describes a condition where a change impairs the normal functioning of an animal.

Infectious Disease – any illness caused by the invasion of the body by pathogens Non-infectious Disease – any disease NOT caused by a pathogen Transmission of Infectious disease by;

o Direct contact

Categories of Disease

Infectious Non-infectious

Environmental Social Genetic Deficiency Degenerative Mental

o Ingestiono Aerosolso Vectors

Stages of infectious disease;o Entry of pathogeno Incubation periodo Symptoms

Pathogens may be cellular or non cellular. Prions are non-cellular pathogenic agents. Prions are unenclosed proteins that can infect plants but mostly affect animals. Prions are not destroyed by heat (that usually destroy virus) but are destroyed by procedures that destroy

proteins. Prion Proteins are capable of self-replication and of being infectious. Prions are abnormal forms of a normal cell protein. They are produced by mutations in the gene that codes

for a normal cell protein. A shape change transforms the harmless protein into its infectious prion form. Prions are unique in that they are both infectious and a hereditary disease. Viruses are non-cellular pathogens, they contain DNA or RNA and can only reproduce inside a hot cell. Stages in viral infection are;

o Attachment to host cello Penetrationo Uncoating and replication of genetic material

Viruses can only be killed by destroying the host cell.

Treatment of viral infections;o Antiviral drugs

It is more difficult to treat a viral infection than a bacterial infection sine the virus is contained within host cells

Some antiviral drugs have been developed that specifically act on enzymes important to the virus without damage to the host cell

o Interferon – protein chemical secreted by host cell that is infected by the virus Help the uninfected cells to resist the virus.

Viroids are non-cellular. They are the smallest particle that is able to replicate, made of a short single strand of RNA with no “cell wall”. Like viruses, viroids need a host to make protein coat.

Bacteria are of many different shapes. Reproduce by binary fission. Some are aerobic and some are anaerobic. Bacteria causes disease by entering hosts and reproducing in hosts. Bacteria have many different structures

o Flagella to moveo Spores to protect themselveso Capsule that determines the degree that it can cause diseaseo Polysacharide cell wall

Disease can be transmitted in three wayso Contact transmission

Airborne droplets Sexual contact Direct contact

o Vehicle transmission Food and waterborne Carried in blood

o Vector transmission Arthropod borne

Incubation period is the most infectious period. There are two types of toxins

o Exotoxinso Endotoxins

Pathogen Cellular/Non-cellular

Mode of Transmission

Means of Action Disease Caused

Prion Non-cellular Infectious and hereditary

Mutates proteins to become prions

Degenerative neurological disease

Non-cellular DNA enters host cell and replicates

Vector (mosquito) MalariaRNA Virus Airborne spores InfluenzaParasidic protozoa & Worms

Primary and secondary host

Tapeworm

Bacteria

Immunity: Defence against Disease

Self: materials made by the body’s cells Non-self: materials foreign to the body Immune system is a group of lymphoid tissue and organs and lymphatic vessels that assist the body to

resist infection and disease through specialised cells. Non-specific (innate) immunity

o Levels 1 & 2o Acts in the same way for every infectiono Has no ‘memory’ of a prior infectiono Cannot adapt

Specific (acquired) immunity

o Level 3o Involves production of specialised cells and chemical substances known as antibodieso Has a ‘memory’ so when another infection from the same organism occurs, an increased

response is obtainedo Targets specific pathogenso Is adaptive and acquired

1 st Line of defence prevents entry of the pathogeno Mucus secretions and ciliated linings line respiratory, reproductive, urinary and gastrointestinal

tracts.o The sticky mucus traps foreign substances which are then removed by cilia.o Intact skin forms a physical barrier that mot pathogens cannot pass through.o Secretions include tears, sweat, saliva, urine and gastric juices.o Gastric juices have a pH that is unfavourable to micro-organisms.o Saliva, tears and urine flush micro-organisms away.o Tears and sweat contain chemicals that destroy the bacterial cell walls.o Natural flora are the usually harmless populations of bacteria that exist on the outer surfaces

whose presence inhibits the ability of pathogens to colonise these surfaces. 2 nd Line of defence is responsible for destroying and inhibiting pathogens

o Phagocytosis is the process where phagocytes engulf and destroy micro-organisms and foreign materials.

o Phagocytes are produced in the bone marrow and include neutrophils and macrophages.o Complement proteins are continually present in the blood, they stick to microbes so that they can

be recognised by phagocytes.o They stimulate phagocytes to become more active, attract phagocytes to the site of infection and

others destroy the membranes of invading micro-organisms.o Interferons are secreted by some virally infected cells.o They induce resistance to the viral infection in the surrounding cells, act as a warning signal from

the infected cell and causes changes in the surfaces of the surrounding cells, making it more difficult for the virus to infect, prevents viral protein synthesis and plays an important role in reducing and slowing down the development of the pathogen and minimising symptoms.

o Cytokines are a group of proteins and peptides that are produced by all cells as signalling molecules to send messages between cells.

o They are similar to hormones and neurotransmitters in allowing cells to communicate with another, they are involved in a variety of immunological, inflammatory and infectious diseases and each cytokine binds to a specific cell-surface receptor.

o Inflammation is a defensive response caused by physical agents, chemical agents or microbial infection when there is damage to the body’s tissues.

o Inflammation causes dilation of nearby arterioles to allow more blood to reach the affected area, increasing the blood flow allows a greater number of platelets, macrophages, mast cells and additional substances to reach the affected area.

o The blood vessels become more permeable which allows response agents to leave the bloodstream and move into the damaged tissue and phagocytes release histamines to attract more phagocytes to the infection site.

o Fevers are caused by bacterial or viral infections. It raises the body temperature and metabolic rate, increases speed of blood flow including delivery of white blood cells to the site of the infection, increases effective of interferon and the release of interleukin-1 which speeds up the immune system.

o Stages in a fever; Pathogen or toxin is taken into the body.

Macrophages ingest the foreign substance releasing interleukin into the bloodstream.

Interleukin-1 causes the body’s thermostat to reset to a higher temperature.

Fever is initiated.o Blood Clotting occurs when a blood vessel is torn or ruptured.o Sequence of events include;

Collagen fibres are exposed to blood. Platelets stick to the fibres, making the other platelets

sticky to form a platelet plug sealing the wound. Fibrin traps blood cells, causing blood to coagulate and

produce a more permanent seal for the wound. Fibres form a crusty scab as they dry and falls off when tissue underneath has healed properly.

3 rd Line of defence occurs inside the body when the foreign antigen has been identified.o Third level of defence is acquired, specific and adaptive. o It is produced by the lymphocytes – T cells and B cells.o T cells are responsible for T mediated immunity.o B cells are responsible for antibody mediated immunity and memory of the antigen.o The humoral immune system involves B cells, which produce antibodies. The humoral system is

associated with serum, the non-cellular part of the blood.o The cell mediated immune system Is associated with the production of specialised lymphocytes

called T cells.o B cells produce specific antibodies which are produced against specific antigens.o T cells target pathogens directly.o The Major Histocompatibility Complex (MHC) markers are attached to the surface of body cells so

that the immune system can recognise its own and foreign material. o Foreign MHC molecules are antigenic which cause T cells to lyse the foreign cells, macrophages to

engulf the foreign cells, antibodies are released to attack the foreign cells and injure the blood vessels that supply the transplant organ with blood.

o B cells and T cells recognise and ignore cells that have the same MHC markers as themselves. o Antigens are foreign substances that cause the formation of antibodies.o Two membrane-bound receptor molecules for antigens are found in the immune system.

Antibodies are found on B cells and T cell receptors are found on T cells.o An antibody molecule has 4 polypeptide chains. The hinge area allows the antibody to bend if

needed to bind better with the antigen. 5 different kinds of heavy chains result in 5 different classes of antibodies / immunoglobulins.

o

B cells defend against bacteria and viruses outside the cell and toxins produced by bacteria. Each B cell only has one type of antibody. It is helpful having a small number of each antibody because it means there is more chance of ‘recognising’

the antigen. The humoral response begins when an antigen activates a particular B cell. The particular B cell multiplies

using colonal expansion to form plasma cells. Plasma cells make antibodies make antibodies specifically designed to attack and kill the indentified pathogen. Some B cells differentiate into long lived memory cells.

B cells originate in the bone marrow and differentiate into memory cells and plasma cells. When memory cells encounter the same antigen again, they will rapidly differentiate into antibody producing plasma cells.

Plasma cells secrete antibodies against antigens. Clonal expansion is when B cells reproduce rapidly so that there is a large number of identical cells.

T cells originate from stem cells and mature in the thymus. They only respond to antigen fragments that have been processed and bound to macrophages.

There are 4 types of T cells;o Helper T cello Suppressor T cello T cell for delayed hypersensitivityo Cytotoxic T cell

Infected cells display antigen-MHC T helper cells are activated and stimulate cytotoxic T cells to destroy the infected cells. Major steps in immunity

o Macrophages engulf pathogens and then display some of the pathogen’s antigens on their surface (antigen-MHC complex)

o T-helper cells are attracted to the macrophages and are activated by the antigen- MHC complexo T-helper cells stimulate B cellso If appropriate B cell is present with the antibody specific to the microbe antigen it will bind to the

antigen-MHC complex on eth macrophage o The B cell divides to form a clone of the plasma cells that produce a specific antibodyo B-memory cells are produced to identify the antigen in the future

Antibodies are also known as immunoglobulins and are made in response to antigens.

Variable regions form the antigen-binding sites. Each antibody can bind two antigen molecules.

Antibody

Light chain (short)

Hinge region connecting the light and heavy chains. This allows the two chains to open and close (like a clothes peg).

Heavy chain (long)

There are 5 classes of antibodies, each has a different function;o IgG – activate complement proteins and can neutralise toxins directlyo IgM – causes agglutination of antigenso IgA – neutralises pathogens in the digestive, respiratory and reproductive tractso IgD – located on surface of B cellso IgE – binds to mast cells and helps initiate inflammation

Monoclonal antibodies are artificially produced antibodies that only neutralises one specific antigen. They are useful as they are totally uniform, can be produced in large quantities and are highly specific.’

Defence Mechanisms in

Humans

Non Specific (Innate)

First line of Defence

Mucus secretions

Ciliated linings

Intact skin

Secretions

Natural flora

Second line of Defence

Phagocytes

Complement proteins

Interferons

Cytokines

Bloodclots

Inflammation

Fever

Stimulate mast cells (release histamines)

Specific (Acquired)

Third line of Defence

Humoral (B cells involved)

MHC recognises self from non

self

Class 1 (human cells)

Class 2 (macrophage B

cells)

B plasma cells (antibodies)

B memory cells

Cell mediated (T cells involved)

T supressor cellsT cells for delayed

hypersensitivity

Cytotoxic (killer T cells) T Helper cells

Activates cytotoxic T cells

Activates B cells

Herd immunity is where majority of the population is vaccinated against a disease and the few people that aren’t rely on the rest of the community being immune as there will be less occurrence of that disease and so they be unlikely to get it.

Failures in the immune system include:

1. Allergies and Hypersens

2. Rhesus incompatibility

3. Auto-immune diseases

4. Rejection of transplanted organs

5. Immune deficiency diseases

6. Acquired immune deficiency syndrome (AIDS)

Mast cells release histamines that cause inflammation.

Allergic reactions can occur by inhalation, ingestion, injection and skin contact.

Blood groups are the marker proteins on the surface of the red blood cells.

Plants prevent entry of pathogens by passive defence that is always present. It includes the cuticle being a mechanical barrier, but the pathogen can still enter from the stomata causing abnormal swelling called a gall.

Active defence is after the pathogen has been identified, it uses chemical barriers, such as oils to act as antibiotics to repel insects, or gum seals infected area.