CellsMCD YEAR 1

Anil Chopra

ContentsMCD – Cells 1 – Cells and Organelles.......................................................................1MCD – Cells 2 – Pathogenic Microbes.......................................................................3MCD - Cells 3 – Cell Membranes...............................................................................4MCD- Cells 4 – Blood..................................................................................................7

MCD – Cells 1 – Cells and OrganellesAnil Chopra

1. Understand what constitutes a cell, and the scale of cells and moleculesWhat Constitutes a Cell?

- make up tissues and organs- separated my membranes- if they live independently: protozoa- they can come together to form colonies specialise.- Many cells have polarity.

Scale if CellsSize of cell: 50μmWeight of a cell: (density = 1.06ng)Size of virus: 0.1 μm/100nm

2. Demonstrate the following on a suitable transmission electron micrograph: nucleus; nucleolus; nuclear envelope; mitochondrion; rough endoplasmic reticulum; smooth endoplasmic reticulum; ribosomes; Golgi apparatus; secretory granule; plasma membrane; cytoskeletal components.

1 Nucleus 1a Euchromatin 1b Heterochromatin   2 Nucleolus   3 Nuclear membrane  4 Nucleopore   5 Ribosomes  6 Rough endoplasmic reticulum (with ribosomes)  7 Smooth endoplasmic reticulum8a Longitudinal- and cross-sections of a mitochondrion showing aristae8b Longitudinal- and cross-sections of a mitochondrion showing tubules 8c Longitudinal- and cross-sections of a mitochondrion of the prismatic type 8d Longitudinal- and cross-sections of a mitochondrion showing saccules  9 Longitudinal- and cross-sections of a centriole10 Golgi Apparatusus 11 Golgi vesicles 12 Endopinosomes, endopinocytotic vesicles13 primary lysosomes 14 secondary lysosomes, phagocytosomes 15 tertiary lysosomes16, 17 Multivesicular bodies

18 peroxisomes, microbodies19 Secretory granules 20 Microtubules 21 Actin filaments 22 Intermediate filaments linking to desmosomes24 Glycogen granules 25 Fat droplets 26 Synapse 27 Synaptic body28 Cell membrane with glycocalyx(polysaccharides and glycoproteins)29 Intercellular space 3031 Tight junction32 Adherens junction 33 Fascia Adherens with actin filaments (cardiac) 34 Punctum Adherens 35 Macula Adherens (desmosome) 36 Hemidesmosome (joins cell to basal lamina) 37 Gap junction38 Microvilli with glycocalyx 39 Cilia 40 Basal bodies of microcilia41 Stereocilia42 Basal lamina

3. Identify the essential characteristics of prokaryotic and eukaryotic cells.Prokaryotes Eukaryotes

Kingdoms of Monera and Archea Do not contain organelles May have flagella for locomotion Have 0.001 times DNA as

eukaryote. High degrees of mutation DNA is circular Smaller Ribosomes Contins a single copy of

chromosomes. Contains peptidoglycan. Less defined cytoskeleton.

Kingdoms of Animals, plants and protocists.

Contain organelles inc. nucleus Have a high degree of

organisation Have 1000 times DNA as

prokaryote. Relatively rare mutations DNA chromosomal in nucleus Larger Ribosomes Diploid containing 2 different

chromosomes Contains NO peptidoglycan. Well-defined cytoskeleton.

4. Explain the relationship of individual cells to the organisation of the whole body. 5. Understand that cancer is a disorder of cell divisionRelationships between cells and the whole body:

Cells ---make up tissues ---which make uporgans---which make up systems Many diseases/conditions are caused by problems at a cellular level. Cancer is caused by irregular cell division. Mutations include:

o Cells signalled to divide but then not to stopo DNA copying correction mechanism is haltedo Telomeres are lengthenedo Calls not limited to tissue boundarieso Tumours spread to tother tissueso Cells die due to lack of O2.

6. Describe the predominant types of molecules in a cellsolutes include: soluble proteins

ions (K+, Na+, Mg2+, Ca2+, PO42-,

Cl-)sugars

Nucleotides: e.g. ATP, cAMP, GTPamino acidsmRNAtRNALipids, cholesterolPeptides

MCD – Cells 2 – Pathogenic MicrobesAnil Chopra

1. Name the main types of infectious agent causing disease in humans2. List the key differences between prokaryotes and eukaryotes3. Give examples of each type of infectious agent and the disease it causes4. Name the distinguishing features of the different types of infectious agent and

explain how they replicateType Example FeaturesBacteria Mycobacterium

tuberculosis, E. coli, Neisseria meningitides

Prokaryotes that replicated by binary fission, they contain chromosomes, but no nucleus. Their DNA is circular. They inhabit the gut, skin, they stimulate the immune system and aid with metabolism and provision of nutrients. Some are pathogenic and can in the immuno-compromised, cause infections (opportunistic infections).

Viruses HIV, common cold, influenza

Not cells in their own right (obligate parasites), inhibit host cell from replicating. Contain DNA or RNA and use reverse transcriptase to divide. Make use of a host cell nuclear synthetic machinery to replicate and divide by budding out of the host cell. Show host specificity but infect almost all other life forms including bacteria.

Fungi Candida albicans (thrush), aspergillus fumigatus

Single celled eukaryotes that exist as yeasts or filaments. Yeasts bud or divide; filaments (hyphae) which have cross walls or septa.Usually affect immuno-compromised people. Causes mycoses (infection).

Protozoa Malaria, leishmaniasis Single celled eukaryotes, include intestinal, blood and tissue parasites. Replicate in host by binary fission or by forming trophozoites in a cell. Many have complicated life cycle involving 2 hosts. Infection acquired by ingestion or via a vector.

Helminths Tapeworm, fluke, roundworms

Multicellular organisms. Have life cycles outside human host, visible to the naked eye. Complex life cycle including embronation to generations in different hosts.

MCD - Cells 3 – Cell MembranesAnil Chopra

1) Explain the function of phospholipids bilayers in aqueous environment.Constitutes – phospholipid bilayerC=C unsaturated bond causes kink in chain.

Causes them not to pack as tightly as the kinks take up room.

Lipids have a hydrophilic head (polar) and hydrophobic tail. To avoid water, the tails pack together.They suspended in water and form micelles or droplets. They can also arrange themselves into bilayers (a layer two molecules thick). Droplets in cells are called liposomes.

Cholesterol is also found in membranes – acts to increase membrane stiffness. Glycolipids are found on the extracellular side of the membrane with negative

charges inside the cell

The bilayers need to:- Have selective permeability- Be impermeable to macromolecules, biochemical intermediates- Be permeable to nutrients, waste products- Allow transfer of information (= signal transduction)

The Bilayer is DynamicFlip-flop: lipids switch sides in the bilayer - occurs less than once a month for any individual molecule. Diffusion: lipid molecules readily exchange places with their neighbours within a monolayer (~107 times a second). This gives rise to a rapid lateral diffusion, with a diffusion coefficient (D) of about 10-8cm2/sec, which means that an average lipid molecule diffuses the length of a large bacterial cell (~2 µm) in about 1 second.

2) Draw the structure of phosphotidylcholine and identify the component parts.

3) Describe the permeability properties of the phospholipid bilayer.

Bilayer Permeable to: Not permeable to: Some can H2O Cations (K+, Na+, Ca+) & Anions (Cl-, HCO3

-) move by O2 By osmosis/diffusion Small hydrophilic molecules facilitated diff. CO2 down diffusion gradient Macromolecules or active trans.

4) Distinguish between simple diffusion, facilitated diffusion and active transport.

Lipids can exchange places with neighbours – Lateral diffusion, but can rarely “flip flop” i.e. switch sides of the bilayer.

This can occur by: - Facilitated diffusion: charged pores, vary in size, shape and other characteristics.- Co-transport: coupled transporters, symporters, e.g. sugars and amino acids with

Na+ or antiporters e.g. Na+/K+ exchange.

5) Functions of membrane proteinsProteins in the membrane increase the cell fluidity. They are also used for transport, receptors, recognition and adhesion of cells, electron carriers.

Membrane Potential and Potassium Gradients

The Na+-K+ pump exchanges 3 Na+ ions from inside the cell for two K+ ions on the outside. There are two consequences:o Ionic gradients are created: less Na+ and more K+ inside the cell than outside.o A charge gradient is created, as more positive charges are pushed out than are

coming in. This results in the inside of the cell being at a more negative potential than the outside.

- [K+]i is high inside the cell- There is a therefore a tendency for K+ to move out of the cell- This is counterbalanced by the electric potential which opposes the movement of

positive charges out of the cell, as this would accentuate the voltage difference across the cell.

- An equilibrium will be reached when the rate of inward movement of K+ ions down the electrochemical gradient equals the rate of outward movement down the concentration gradient

- Thus the electrical imbalance caused by the sodium pump will not quite be compensated by K+ movement

- The end result is a membrane potential, with a voltage difference across the membrane (inside negative).

- This is important for signaling in nerves, muscles, etc

6) Explain the movements of ions across a cell membrane against a concentration gradient.

Movement of ions:- Cl- ions move into the cell down the concentration gradient.- As proteins usually have a negative (-) charge, there is a high conc. of K+ ions

to balance out; and usually low Cl- ion concentration.- Na+ ions are low in conc. in the cell.- The Na+/K+ exchange pump, pumps 2K+ ions in for every 3Na+ ions pumped

out.- This requires ATP ADP + Pi

7) Explain the entry of glucose and amino acids against a conc. Gradient.The Na/K exchange pump aids glucose transport. Glucose moves down its concentration gradient into the cell, binds to glucose transporter and flip-flops along with the Na ion moving down the concentration gradient.

8) Explain how external Chemical signals can be sensed at the interior of the cell

Signalling: Secretion of hormones – exocytosis: substances packed into intracellular vesicles toward

extracellular space by fusion with cell membrane. External messengers cause entry: e.g. messenger like neurotransmitter binds to

membrane-bound Ca2+ ion channel protein causing it to open. External messenger brings about other change e.g. endocytosis: engulfment of

extracellular substance by intracellular, membrane-bound vesicles or hormone binds to receptor on membrane causing substrate within the cell to send off second messenger to other parts of the cell e.g. nucleus.

The Neuromuscular Junction Depolarisation of the muscular post-synaptic membrane results in a propagated

action potential. The wave of depolarization extends into the t-tubules (invaginations of the cell

membrane) to transmit the activation signal into the core of each muscle cell in the motor unit.

Close contact with the sarcoplasmic membrane via triadic junctions involving the dihydropyridine (t-tubule membrane) and ryanodine receptors (sarcoplasmic reticulum membrane) results in calcium release from the sarcoplasmic reticulum.

Calcium diffusion into the myofilaments lattice and calcium binding the troponin on the thin filaments (actin) in skeletal and cardiac muscle result in activation of the contractile machinery and contraction.

MCD- Cells 4 – BloodAnil Chopra1) List the main functions of the blood. Respiratory function, ie transport of O2 and CO2 pH buffering, ie stabilisation of acidity/alkalinity status Nutritional, ie transport of glucose, fats etc. Excretory, ie transport of waste products eg urea Hormone transport Haemostasis ie clotting to stop blood loss Defence against infection Temperature control Maintenance of fluid balance

2) List the major components of the blood. Plasma and the formed elements: erythrocytes (RBCs), leukocytes (WBCs),

thrombocytes (platelets) There is approximately 5-6l of blood in males and 4-5l of blood in females

3) Explain the difference between plasma and serum. When plasma is allowed to clot and the clot removed, the liquid that remains is

called serum. Serum is plasma minus fibrinogen.

4) Describe the essential features of the erythrocyte and list its major functions. Constitute almost half the volume of blood. Anucleate, biconcave discs – diameter

8.5μm, thickness 2.4μm filled with a concentrated haemoglobin solution surrounded by a membrane. Functions are O2 transport in combination with haemoglobin; CO2 transport – greatly facilitated by carbonic anhydrase which speeds up CO2 + H2O H2CO3

5) Explain the erythrocytic difference between men and women. Females have a lower haematocrit (H) (% of blood which is the RBC), whole

blood Hb (Hb) (conc. of Hb) and red cell count (n). This is because increased testosterone boost the bone marrow into producing more erythrocytes. Females lose RBCs in menstruation.

Also women tend to be small on the whole, and therefore carry less blood and therefore fewer red blood cells.

Red Blood cell parameters: N (or RBC) = number of red blood cells (about 5.1x1012 in males and 4.5x1012 in

females) H (or Hct) = haematocrit – this is the percentage of the volume of a sample of

blood occupied by the red blood cells (46% in males and 41% in females) Hb = concentration of haemoglobin in the blood (15.5g/dl in males and 13.7g/dl in

females) MCV = mean cell volume = Hct/(RBC x 100) (normally around 90fl) MCH = mean cellular haemoglobin (Hb x 10)/RBC (around 30pg) MCHC = mean cell haemoglobin concentration (Hb x 100)/Hct (around 34g/dl) Note that the final three do not depend on gender

6) Define anaemia and list the major causes. Anaemia is a condition in which the Hb falls below the

normal range for the subject. Disturbed production (Fe, B12 or folic acid deficiencies

and kidney disease). Increased destruction eg sickle cell disease. Haemorrhage – loss of red cells and iron.

7) List the major erythrocyctic differences between iron deficiency and vitamin B12 deficiency anaemias. Iron deficiency anaemia – low values for haematocrit,

whole blood Hb, red cell count, mean cell volume, mean cell Hb, mean cell Hb concentration ie all parameters. Essential for haemoglobin production – it occurs due to the lack of intake but more likely due to excessive loss (microcytic- small cells)

Vitamin B12 anaemia – low values of haematocrit, whole blood Hb and red cell count but high values for mean cell volume and mean cell Hb. This is essential for normal DNA synthesis during maturation of primitive erythroid cells (macrocytic-large cells anaemia)

8) List the major differences between the leukocyte and platelet populations of normal blood and the erythrocyte population. Leukocytes have a nucleus and are fewer in number than the RBCs but of a

similar or slightly larger size. Platelets are anucleate and very much smaller than the RBCs.

RBC : WBC = 500 : 1; RBC : Platelet = 12 : 1

9) Explain simply the major functions of the leukocytes and platelets. Leukocytes defend against infection; platelets are important in haemostasis,

stemming the loss of blood after a haemorrhage ie clotting.

10) Explain simply the meaning of phagocytosis, immune reaction, chemotaxis, diapedesis.

Phagocytosis – ingestion of foreign material by engulfing into the cytoplasm. Immune reaction – the role of lymphocytes. Antibodies bind specifically to the

antigen that induced its formation. Chemotaxis – movement of cells up a concentration gradient towards the site of

infection where the infected agent releases a chemical that is detected by the cells. Diapedesis – migration of cells through the walls of blood capillaries into the

tissue spaces.

11) Describe the major requirements, nutritional and otherwise, of normal erythropoiesis.

Iron is essential for haemoglobin production. Vitamin B12 and folic acid are essential for normal DNA synthesis during the

maturation of prmitive erythroid cells.

Erythropoiesis = takes place in red marrow (skull, ribs, sternum), there is a close balance between production and destruction, which keeps RBC count within a small range in health.

RBC production is under the control of erythropoietin (EPO)- which is produced in the kidney and production is increased when renal tissue becomes hypoxic.