Cell processes.

Question 1

What does amphipathic mean?

Answer 1

Has both polar and non polar regions

Question 2

Cell membrane controls the passage of substances into and out of the cell; this allows for (4)

Answer 2

Concentration gradients
Spatial organisation of chemical and physical processes within the cell
Controlled uptake of nutrients and discharge of waste
Development of a membrane potential

Question 3

The two basic classes of membrane proteins

Answer 3

Intergral (transmembrane): Extend into or completely across the cell membrane.
Peripheral: Attached to either the inner or outer surface of the membrane, easily removed.

Question 4

Functions of membrane proteins (6)

Answer 4

Receptors
Cell identity markers
linkers
Enzymes
Channels
Transporters

Question 5

Cell membrane is permeable to?

Impermeable to?

Answer 5

Permeable:
nonpolar uncharged molecules (O2, N2, benzene)
Small uncharged polar molecules (H2O, urea, glycerol, O2)
Impermeable:
Large uncharged polar molecules (glucose, amino acids)
Ions (Na+, K+. Cl-, Ca2+, H+)

Question 6

Factors influencing diffusion

Answer 6

Concentration
Temperature
Surface area
Size of molecule
Distance

Question 7

Membrane potential is influenced by…?

Answer 7

Concentration and electrical gradients; electrochemical gradient.

Question 8

Describe osmotic pressure

Answer 8

The hydrostatic pressure applied to oppose osmosis. A colligative property, i.e. depends on the numbers and not the types of particles in solution.

Question 9

Osmolarity depends on…?

Answer 9

Concentration and ionisation properties of solutes

Question 10

Define tonicity

Answer 10

The effect a solution has on cell volume (thus includes membrane permeability of the solute)

Question 11

Describe ion channels

Answer 11

Water filled pore that span lipid bilayer
Rapid transfer rate (~1 million ions/sec)
Exhibit ion selectivity

Question 12

What opens and closes ion channels

Answer 12

Voltage
Ligands
Phosphorylation
Cell volume (stretch)
pH

Question 13

Two classes of carrier proteins and common features

Answer 13

Passive or active

Exhibit: Specificity, saturation, inhibition, and competition

Question 14

Describe passive carriers

Answer 14

Substrates move down their concentration gradients via the transport protein which undergoes a conformational change as the substrate move through.
Eg GLUT which move glucose into the cell down it’s concentration gradient.

Question 15

Describe primary active transport

Answer 15

Energy used by hydrolysis of ATP to move a substrate against its concentration gradient.

Question 16

How much of the cells energy is used in primary active transport?

Answer 16

30%

Question 17

Describe the features of the Na+/K+ ATPase

Answer 17

Primary active transport that maintains low Na+ and high K+ inside the cell. Three Na+ are pumped out of the cell for every 2 K+ pumped in.

Question 18

What does the Na+K+ ATPase facilitate (6)?

Answer 18

Resting membrane potential
Electrical excitability
Contraction of muscle
Maintenance of steady state cell volume
Uptake of nutrients via secondary active transporters
Maintenance of intracellular pH by secondary active transport.

Question 19

Describe secondary active transport

Answer 19

Uses the energy stored in the ion gradient to facilitate movement of substrate against their concentration gradient through substrates moving though channels alongside ions moving down their conc. gradients. Eg. glucose and aa move into the cell alongside Na+ ions.

Question 20

Describe three forms of endocytosis

Answer 20

Phagocytosis- Carried out primarily by macrophages and neutrophils, foreign particle binds with the membrane receptor protein. Pseudopods extend and form a vesicle around it (phagosome); phagosome binds with lysosome and foreign particle degraded.
Pinocytosis- same as phagocytosis but not pseudopod
Receptor mediated endocytosis. Substance binds to receptor protein in specific clathrin coated region. Cathrin comes off and vesicle binds with endosome. Ligands digested by lysosomal enzymes or transported across cell.

Question 21

Exocytosis

Answer 21

Substances exit the cell through fusion of their carrier vesicles with the cell membrane

Question 22

Process of glucose absorption

Answer 22

1) Na+K+ATPase located in basolateral membrane creates electrochemical gradient
2) Na+ glucose cotransporter moves glucose from the lumen into the cell via secondary active transport
3) glucose moves out of the cell into the blood via passive facilitated diffusion through the GLUT transport protein
4) movement of ions and glucose across the cell induces H2O and Cl- movement across the paracellular pathway into the blood.
5) Na+ exits cell via the Na+K+ ATPase pump

Question 23

What is the maximum transport rate of glucose

Answer 23

375 mg/min

Question 24

Steps of chloride secretion

Answer 24

1) Na+K+ATPase located in basolateral membrane creates electrochemical gradient
2) NaKCl simperer uses energy of Na gradient to move Cl into the cell actively accumulating it above its concentration gradient.
3) Cl- leaves the cell in apical membrane through facilitated passive diffusion via the CFTR gated channel
4) Na exits via NaK ATPase pump and K exits through K channel
5) Transport of Cl across the epithelium induces paracellular H2O and Na fluxes

Question 25

Describe 2 steps of CFTR channel gating

Answer 25

1) phosphorylation of the regulatory domain
2) Results in binding of ATP to the nucleotide binding site channel opened.
3) hydrolysis of ATP is required for the closing of the CFTR channel

Question 26

Describe pathology in sweat secretion in CF patients

Answer 26

In sweat gland there is primary secretion of isotonic solution; there is then secondary reabsorption to create a hypotonic solution. The reabsorption is affected in CF as CFTR channels not working

Question 27

What is the fluidity of the membrane determined by?

Answer 27

The amount of cholesterol and the number of double bonds in the fatty acid tails (each puts a kink in the tail which increase fluidity by preventing lipid molecules from packing too tightly).

Question 28

Relating to intra and extracellular ion concentrations which ion wants to move into the cell

Answer 28

Na+

Question 29

Describe the three kinds of endocytosis

Answer 29

1) Phagocytosis carried out mainly by phagocytes uses pseudopods
2) Pinocytosis cell drinking a vesicle forms and substance ingested
3) Receptor mediated endocytosis. For specific substances substance binds to receptor protein in clathrin coated region, vesicle forms and becomes uncoated and binds with endosome