as aqa biology summary diagram
DESCRIPTION
BIOLOGY AQA A LEVEL DIAGRAMTRANSCRIPT
EMBED PBrush
EMBED PBrush
EMBED PBrush
Carbohydrates:
Monosaccharides: sweet, water soluble, reducing sugars
Disaccharides: sweet, water soluble, most are reducing (not sucrose)
Sucrose: Glucose + Fructose
Lactose: Glucose + Galactose
Maltose: Glucose + Glucose
Polysaccharides: long chains of repeating subunits (monosaccharides) joined by condensation reactions
Isomers: same molecular formula but a different structural formula
EMBED PBrush
EMBED PBrush
EMBED PBrush
Triglycerides
Fatty acid chains can be saturated (no C=C) or unsaturated (have C=C bonds). The more unsaturated the fatty acid the lower the melting point. Fats are insoluble ion water. A phospholipid has a fatty acid replace with a phosphate group. This means it has a hydrophilic region (phosphate head) and hydrophobic regions fatty acid tail. It is integral in the cell membrane.
EMBED PBrush
General fatty acid
Glycerol
Formation of a triglyceride
EMBED PBrush
Proteins
Polymers made up of amino acids.
EMBED PBrush
EMBED PBrush
Globular Proteins
The vast majority of proteins are globular, i.e. they have a compact, ball-shaped structure. This group includes enzymes, membrane proteins, receptors and storage proteins. The diagram below shows a typical globular enzyme molecule. It has been drawn to highlight the different secondary structures.
Globular Proteins
Have complex tertiary and sometimes quaternary structures.
Folded into spherical (globular) shapes.
Usually soluble as hydrophobic side chains in centre of structure.
Roles in metabolic reactions.
E.g. enzymes, haemoglobin in blood.
Fibrous (or Filamentous) Proteins Fibrous proteins are long and thin, like ropes. They tend to have structural roles, such as collagen (bone), keratin (hair), tubulin (cytoskeleton) and actin (muscle). They are always composed of many polypeptide chains. This diagram shows part of a molecule of collagen, which is found in bone and cartilage.
Fibrous Proteins
Little or no tertiary structure.
Long parallel polypeptide chains.
Cross linkages at intervals forming long fibres or sheets.
Usually insoluble.
Many have structural roles.
E.g. keratin in hair and the outer layer of skin, collagen (a connective tissue).
How the shape of the enzyme/protein molecules is suited to its function
Each enzyme/protein has specific primary structure (amino acid sequence)this sequence determines where the H-bonds will form during development of the secondary structure Proteins have a unique tertiary structure (further folding of the secondary structure) held by ionic and hydrogen bonds and if amino acids containing cysteine are present, disulphide bridgesGlobular proteins have an active site with unique structure;shape of active site complementary to/ will only fit that of substrate
Enzyme substrate complexes can form
Describe how enzymes break down substances
Lowering the activation energy
Substrate with a complementary shape to the active enters the active site
An enzyme substrate complex is formed
Active site changes shape to mould around the substrate (induced fit)
This weakens the bonds in the substrate (lowering activation energy) by stretching and distorting them
The bonds are broken
Products leave the active site
Enzyme remains unchanged
Describe how an enzyme catalyses a condensation reaction
Enzyme active site has a complementary shape to the substrate
An enzyme substrate complex is formed
The reactive groupshydroxyl, hydroxyl/ amino, and carboxylic / hydroxyl and carboxylic are brought close together
Change in the shape of the active site (induced fit) lowers the activation energy
Water is removed and a glycosidic, peptide or ester bond forms
Products leave the active site
The enzyme remains unchanged
The effect of temperature on the rate of an enzyme reaction
As temperature increases so does the rate of the reaction as
Substrate and enzyme gain K.E and collide more frequently
More enzyme substrate complexes form
Further increases in the temperature cause bonds (ionic, disulphide, hydrogen) holding the tertiary structure of the enzyme in place begin to break
The enzyme denatures,
The active site no longer complements the substrate
No enzyme substrate complexes can form
The effect of pH on the rate of enzyme activity
Changes in the pH affect the charges on the R groups of the amino acids at the active site
Interactions between the substrate and enzyme are disrupted
Enzyme substrate complexes are less likely to form
More extreme pH conditions can cause the bonds (ionic, Hydrogen) holding the tertiary structure to break
The enzyme denatures (active site is no longer complementary to the substrate)
No enzyme substrate complexes can form
Explain how inhibitors affect enzyme activity
There are two types of inhibitor, competitive and non-competitive
Competitive inhibitors have a similar shape to the substrate
They can enter and bind with the active site
Prevents enzyme substrate complexes forming
The problem can be overcome by increasing the substrate concentration
Non-competitive inhibitors
Have a different shape to the substrate
Bind at a point other than the active site
They cause a change in the shape of the active site
Prevent formation of enzyme substrate complexes
Explain how the small intestine is adapted to its function in the digestion and absorption of the products of digestion.
Large surface area provided by villi and microvilli
Thin epithelium gives a short diffusion pathway
The dense capillary network for absorbing amino acids and sugars and the lacteal for the absorption of digested fats; ensures a steep concentration gradient is maintained
The many mitochondria in the epithelial cells supply ATP/ energy for active transportCarrier proteins (in membranes) provide a path for polar molecules to pass through the membrane.
Enzymes built into the epithelial membrane make it more likely for enzyme substrate complexes to form and ensure products for absorption are released close to the carrier and channel proteins
Absorption of glucose in intestines
Glucose moves into the epithelial cell with sodium Via a symport carrier protein;
Sodium is removed from the epithelial cell by active transport at the sodium-potassium pump;
Maintaining a sodium concentration gradient between the lumen and epithelial cell
Glucose moves into blood by facilitated diffusion
And is carried away in the Heaptic portal vein
Digestion of Carbohydrates and Disaccharides
Starch Digestion:
Amylase
Hydrolyses
Glycosidic bonds
Producing maltose
Maltase hydrolyses maltose to glucose
Lactose intolerance
Cause: reduced lactase levels as we age
Symptoms: diarrhoea and gas and cramps
Explanation
Gas comes from bacteria breaking down the sugar
Diarrhoea: sugar lowers the water potential of the lumen compared to epithelial cells, water moves into the lumen by osmosis
Food moves through the digestive system by peristalsis.
Mouth = digestion of carbs
Stomach = digestion of protein
Duodenum = most digestion, receives pancreatic juice from pancreatic duct and bile form gall bladder (produced in liver)
Ileum = most absorption
Colon = absorption of water and minerals
Describe the structure of a cell membrane and phospholipids.
Described as fluid mosaic.
Fluid: molecules within the membrane able to move;Mosaic: mixture of phospholipid and protein
Double layer of phospholipid molecules;Phospholipid consists of glycerol;To which are joined two fatty acids;And a phosphate;formed by condensation reactionPhosphate head is hydrophilic/polar
Fatty acid tail is hydrophobicthe phospholipids are arranged as bilayer in membrane;
Heads on the outside and tails on the inside;
Intrinsic proteins molecules pass through entire bilayer
Some of the proteins have channels/pores;
Some have specific binding sites and are carrier proteins
Extrinsic proteins only in one layer
Those on the outer side often act as receptors for hormonesMolecules can move in membrane/dynamic/membrane containscholesterol;Many of the proteins and phospholipids have carbohydrates attached forming glycolipids and glycoproteins that make up the Glycocalyx
How the membrane regulates the movement of substances into and out of cells.
Non-polar/lipid soluble molecules move through phospholipid bilayer;Small molecules/water/gases move through phospholipid layer/bilayer;Ions/water soluble substances move through channels in proteins;Some proteins are gated;Reference to diffusion;Carriers identified as proteins;Carriers associated with facilitated diffusion;Carriers associated with active transport/transport with ATP/pumps;Different cells have different proteins;Correct reference to cytosis;
How plasma membrane is adapted for its functions.
Phospholipid bilayer (as a barrier);
Forms a barrier to water soluble but allows non-polar substances to pass so maintains a different environment on each side (compartmentalisation)
Bilayer is fluid: can bend to take up different shapes for phagocytosis and form vesicles
Channel proteins (intrinsic): let water soluble/substances through (facilitated diffusion)
Carrier proteins (intrinsic): allow facilitated diffusion and active transport
Extrinsic proteins: act in cell recognition, act as antigens or receptors;
Cholesterol: regulates fluidity / increases stability;
Membrane and Movement
The membrane is a phospholipid bilayer
Where the hydrophobic tails point inwards and the hydrophilic heads face outwards
The membrane contains two types of proteins
Intrinsic proteins (allow transport of water soluble molecules): spanning the entire bilayer
Extrinsic proteins: found on one side of the membrane
Most molecules move across the membrane by diffusion down a concentration gradient
Small molecules (water/gases) and lipid soluble molecules diffuse between the phospholipids
Polar molecules require channel or carrier proteins to move them
Channels are water filled pores that can be open at all times or they can be gated (voltage/ligand gated)
Carrier proteins have a specific binding site for the molecules/ions
This can be facilitated diffusion, a passive (no ATP required) process
Some molecules are actively transported across the membrane (against the concentration gradient)
This requires ATP (released in respiration)
The ATP changes the shape of the protein to move the molecule across the membrane
How proteins are arranged in a plasma membrane and role in transport
1 Some proteins pass right through membrane;
2 Some proteins associated with one layer;
3 Involved in facilitated diffusion;
4 Involved in active transport;
5 Proteins act as carriers;
6 Carrier changes shape / position;
7 Proteins form channels / pores;
8 Protein allows passage of water soluble molecules /charged particles / correct named example;
Describing the fluid-mosaic structure of a membrane
Phospholipids and proteins;Phospholipid bilayer: Arrangement of phospholipid molecules Tails to tails;Molecules can move in membrane;Intrinsic proteins extend through bilayer: Channel and carrier proteins
Extrinsic proteins in outer layer only: Act as antigens, receptors
Glycoproteins and glycolipids form glycocalyx Presence of cholesterol to help regulate fluidity
The phospholipids are arranged in a bilayer (i.e. a double layer), with their polar, hydrophilic phosphate heads facing out towards water, and their non-polar, hydrophobic fatty acid tails facing each other in the middle of the bilayer. This hydrophobic layer acts as a barrier to most molecules, effectively isolating the two sides of the membrane. Different kinds of membranes can contain phospholipids with different fatty acids, affecting the strength and flexibility of the membrane, and animal cell membranes also contain cholesterol linking the fatty acids together and so stabilising and strengthening the membrane.
The proteins usually span from one side of the phospholipid bilayer to the other (integral proteins), but can also sit on one of the surfaces (peripheral proteins). They can slide around the membrane very quickly and collide with each other, but can never flip from one side to the other. The proteins have hydrophilic amino acids in contact with the water on the outside of membranes, and hydrophobic amino acids in contact with the fatty chains inside the membrane.
EMBED PBrush
EMBED PBrush
EMBED PBrush
EMBED PBrush
EMBED PBrush
EMBED PBrush
Diffusion: net movement of molecules form a high concentration to a low concentration
Lipid soluble molecules can diffuse easily though the phospholipid bilayer along with small hydrophilic molecules like water, carbon dioxide and oxygen
Facilitated diffusion: a passive process, moving large, hydrophilic molecules down the concentration gradient. The molecules cannot pass though the hydrophobic bilayer and must enter/exit the cell through channel proteins or carrier proteins that are specific to the molecules.
Active transport
Moves a molecule against the concentration gradient (low to high)
Requires a specific protein carrier
Energy/ATP is used to change the shape of the protein
Energy is released in respiration
EMBED PBrush
Rate of movement of molecules in facilitated diffusion is limited by the availability of carrier/channel proteins in the membrane. As concentration increase rate will eventually level out as the channels or carriers are working at their maximum rate/ fully occupied.
EMBED PBrush
Mechanism of the heart beat
Cardiac muscle is myogenic
The SAN
Sends a wave of electrical activity (depolarisation) across the atria
This triggers atrial systole
The impulse is relayed to the ventricles through the AVN
Passing down to the apex of the heart along the bundle of His
The impulse spreads along the ventricle walls via the purkyne fibres
The ventricles contract from the bottom
The AVN delays ventricular systole to allow them to fill up with blood
Some key facts to learn
Valves in the heart and blood vessels prevent back flow
Tricuspid valve is on the right side of the heart
Bicuspid valve is on the left side of the heart
These two valves are called the atrioventricular valves
These valves are prevented from inverting as they are attached to the papillary muscle in the ventricle walls, by tendinous cords
Semilunar valves are located between the ventricles and the aorta and pulmonary artery. Rare for arteries to have valves
Pulmonary artery carries deoxygenated blood to the lungs. Rare for arteries to carry deoxygenated blood
Pulmonary vein carries oxygenated blood to the heart from the lung, rare for vein to have oxygenated blood.
Double circulation: blood flows through the heart twice for one circuit of the body, needs re-pumped after losing pressure in the lungs
Deoxygenated blood returns via the vena cava to the RA (1).
Atrium contracts blood through tricuspid into RV (2).
Ventricle contracts and tricuspid shuts so blood enters the pulmonary artery (3)
Blood returns to the LA (4) via the pulmonary vein.
The LA contracts and blood forced through the bicuspid valve into the LV (5).
The LV contracts and the bicuspid shuts and oxygenated blood flows into the aorta (6)
The left ventricle has a thicker, more muscular wall than the right ventricle as it has to pump blood around the whole body, so must generate a higher pressure.
When ventricular pressure > atrial pressure (1) the atrioventricular valves shut to prevent backflow, this is the first sound in the heart beat (lub)
When the ventricular pressure < arterial pressure (3) the semilunar valves shut, this is the second sound of the heart beat (dup)
QRS = electrical activity in the ventricles, occurs just before ventricle pressure increases
P = electrical activity in atria and P(Q = time delay due to AVN
Cardiac Output: is the amount of blood flowing through the heart each minute. It is calculated as the product of the heart rate and the stroke volume:
Cardiac output = heart rate x stroke volume
The heart rate can be calculated from the pressure graph by measuring the time taken for one cardiac cycle and using the formula:
Heart rate (beats/minute) = 60 time for 1 cycle
The stroke volume is the volume of blood pumped in each beat. Both the heart rate and the stroke volume can be varied by the body. When the body exercises the cardiac output can increase dramatically so that
Oxygen and glucose can get to the muscles faster
Carbon dioxide and lactate can be carried away from the muscles faster
Heat can be carried away from the muscles faster
Smokingdecreases conc. of antioxidants in blood: this increases the damage done to artery walls;raises the number of platelets in the blood and makes them more sticky :more blood clots are likely to form;causes constriction of coronary arteries: raises blood pressure and damage to the artery liningcarbon monoxide combines with haemoglobin so less available to transport oxygenblood pressure increased: due to increased heart rate
Fatblood cholesterol level increases;LDLs transport cholesterol in the blood;LDLs deposit cholesterol in arteries
atheroma formedblood pressure increased, turbulence makes clotting more likely
SaltIncreased salt concentration in blooddecreases water potential of the bloodwater moves into the bloodblood pressure increased
How atheroma causes an aneurysm
Fatty material within walls of arteries;Vessels narrow;Blood pressure rises;Weakened blood vessels may burst;
Describe how atheroma may form and lead to a myocardial infarction
Cholesterol deposited in the artery wall
This atheroma narrows lumen of the artery
This creates turbulence and can damage to lining of arteryTurbulence increases risk the of blood clot (thrombus)The blood clot may break off (embolus)And lodge in coronary artery;Reduced blood supply to heart muscle;Reduced oxygen supply;
Reduced respirationLeads to death of heart muscle
Atheroma:
A build-up of cholesterol
in the artery wall
There are thousands of different kinds of cell, but the biggest division is between the cells of the prokaryote kingdom (the bacteria) and those of the other four kingdoms (animals, plants, fungi and protoctista), which are all eukaryotic cells.
Prokaryotic cells are smaller and simpler than eukaryotic cells, and do not have a nucleus.
Prokaryote = without a nucleus
Eukaryote = with a nucleus
To see cells we need microscopes, like a light microscope. To see the ultrastructure of a cell (the organelles inside) we need electron microscopes.
20m
If given a scale bar as below then the formula to use is
Actual length of scale bar
Magnification =
Representative length of the scale bar
Ensure you work in the same units
Cm ( mm ( m ( nm
10
1000
1000
If no scale bar is given then the formula to use is
Image Size
Magnification =
Actual Size of image
Ensure you work in the same units and then convert to the units they want at the end
Resolution: how close 2 points can be to each other and still be distinguished as 2 separate points.
Electron microscopes have a higher resolution than (light microscopes, as they use electrons that have a shorter wavelength than light
Shorter wavelengths (like electrons) allow better resolution than longer wavelengths (like light).
Explain the advantages and limitations of using a transmission electron microscope
Advantages
1 TEM uses (beam of) electrons;
2 These have short wavelength;
3 Allow high resolution/greater resolution/Allow more detail tobe seen/greater useful magnification;
Disadvantages
4 Electrons scattered (by molecules in air);
5 Vacuum established;
6 Cannot examine living cells;
7 Lots of preparation/procedures used in preparing specimens/ fixing/staining/sectioning;
8 May alter appearance/result in artefacts;
9 very thin specimens
10 black and white, images
How to use a microscope to measure the size of an object.
Measure with an eyepiece graticule
Calibrate with the stage mcirometer (an object of a known size)
Repeat and calculate an average
Magnification and Resolution
Magnification simply indicates how much bigger the image is that the original object. It is usually given as a magnification factor, e.g. x100. By using more lenses microscopes can magnify by a larger amount, but the image may get more blurred, so this doesn't always mean that more detail can be seen.
Resolution is the smallest separation at which two separate objects can be distinguished (or resolved), and is therefore a distance (usually in nm). The resolution of a microscope is ultimately limited by the wavelength of light used (400-600nm for visible light). To improve the resolution a shorter wavelength
of light is needed, and sometimes microscopes have blue filters for this purpose (because blue has the shortest wavelength of visible light).
Electron Microscopes
This uses a beam of electrons, rather than electromagnetic radiation, to "illuminate" the specimen. This may seem strange, but electrons behave like waves and can easily be produced (using a hot wire), focused (using electromagnets) and detected (using a phosphor screen or photographic film). A beam of electrons has an effective wavelength of less than 1nm, so can be used to resolve small sub-cellular ultrastructure. The development of the electron microscope in the 1930s revolutionised biology, allowing organelles such as mitochondria, ER and membranes to be seen in detail for the first time.
There are two kinds of electron microscope.
Transmission electron microscopes (TEM) work much like a light microscope, transmitting a beam of electrons through a thin specimen and then focusing the electrons to form an image on a screen or on film. This is the most common form of electron microscope and has the best resolution (