MODULE 1: Principles of Cell Function

Question 1

Phospholipid

Answer 1

• amphipathic molecule
• lipid tail made of of carbons and hydrogens
• non polar –> hydrophobic
• phosphate head is charged –> hydrophilic

Question 2

Viscous Membrane

Answer 2

• single carbon-carbon bonds
• fits together and packed tightly
• saturated tails
• increasing temp decreases viscosity
• cholesterol stops membrane become too viscous/fluid

Question 3

Fluid Membrane

Answer 3

• double carbon-carbon bonds creating kinks
• not tightly packed
• unsaturated tails
• increasing temp increases fluidity
• cholesterol stops membrane become too viscous/fluid

Question 4

Structure of proteins

Answer 4

• peptide bonds
• alpha helix or beta sheets
• N terminus = NH2 group
• C terminus = COOH group
• additional side chains
• charged/polar chains are hydrophilic
• uncharged/non-polar chains are lipidphilic

Question 5

6 Major Functions of Membrane Proteins

Answer 5

1. transport
2. enzymatic activities
3. signal transduction
4. cell-cell recognition
5. intercellular joining
6. attachment to cytoskeleton and extracellular matrix

Question 6

Selective Permeability

Answer 6

Lipid bilayers NOT permeable to:

• ions
• small hydrophilic molecules (glucose)
• macromolecules (proteins & RNA)

Permeable to:
- hydrophobic, non-polar, uncharged small molecules

Question 7

Passive Transport

Answer 7

Diffusion of a substance across membrane with no energy arrangement

Occurs with time due to random motion of molecules becoming equally distributed

Moves to eliminate concentration gradient

Question 8

Osmosis

Answer 8

Diffusion of water through selectively permeable membrane into another aqueous compartment containing solute with higher concentration

Water wants to reach equilibrium

Sugars, ions, proteins and nutrients are osmotically active

Question 9

Tonicity

Answer 9

Ability of solution to cause cell to gain/lose water

Question 10

Isotonic / Hypertonic / Hypotonic

Answer 10

Isotonic: solute concentration is same as inside cel, no net water movement

Hypertonic: solute concentration is greater than inside cell, cell loses water (shrink)

Hypotonic: solute concentration less than inside cell, cell gains water (swell/pop)

Question 11

Facilitated Diffusion

Answer 11

Passive Transport aided by proteins

Transport proteins speed up passive movement

Channel proteins provide hydrophilic corridors that allow a specific molecule or ion to cross membrane (aquaporins, ion channels)

Question 12

Transport Proteins

Answer 12

Allow passage of hydrophilic substances across membrane

Carrier proteins bind to specific molecule and changes shape to shuttle it across membrane

Question 13

Passive vs Active Transport

Answer 13

passive: down concentration gradient
active: against concentration gradient

Question 14

Electrogenic Pump

Answer 14

• active transport
• transport protein that generates voltage across membrane to pump ions through
• sodium-potassium is major electrogenic pump of animal cells
• plants, fungi and bacteria use proton pump

Question 15

Cotransport

Answer 15

Active transport of a solute indirectly drives transport of another solute

Question 16

Bulk Transport

Answer 16

exocytosis - vesicle fuses with membrane to release contents

endocytosis - vesicle pinches off from membrane containing particles

Question 17

Phagocytosis

Answer 17

• endocytosis

- engulfing large particles by forming food vacuole

Question 18

Pinocytosis

Answer 18

• endocytosis
• absorbing molecules from solution
• cells drinking

Question 19

Receptor-mediated Endocytosis

Answer 19

special coated segment of membrane with specific receptors combine with certain molecules from surroundings

Question 20

Paracrine Signalling

Answer 20

• secreting cells acts on nearby target cell
• discharges molecules of local regulator into extracellular fluid
• local sigalling

Question 21

Synaptic Signalling

Answer 21

• nerve releases neurotransmitters into synapse
• stimulates target cell
• local/long distance signalling

Question 22

Hormonal Signalling

Answer 22

• specialised endocrine cells secrete hormones into blood
• reach all body cells
• long distance signalling

Question 23

Autocrine Signalling

Answer 23

• cells release compound which acts on receptors on same cell
• most localised signalling

Question 24

Stages of Cell Signalling

Answer 24

1. Reception - signalling molecule attaches to receptor
2. Transduction- relay molecules in a signal transduction pathway
3. Response - activation of cellular response (gene activation, enzyme stimulation, rearrange cytoskeleton)

Question 25

G protein coupled receptor

Answer 25

• signal molecule/1st messenger binds to extracellular receptor
• receptor made of amino acid chain
• 7 transmembrane domains
• couples with a G protein attached to inside of membrane
• G protein reacts with something else inside cell to produce large yield of another compound/2nd messenger
• 2nd messenger produces response within cell
• happens within one second
• can control the activity of enzymes, ion channels and intracellular signal transduction pathways

Question 26

Tyrosine Kinase Linked Receptor

Answer 26

• tyrosine is an amino acid
• kinase is an enzyme that initiates phosphorylation
• phosphorylation results in conformational change, protein-protein interactions, change in cellular location
• phosphorylation produces response within cell

Question 27

Steroid Receptors

Answer 27

• steroid moves into cell via diffusion (lipidphilic)
• hormone receptor complex moves into nucleus
• binds to DNA to activate genes
• produces new proteins
• takes hours/days

Question 28

Insulin Receptor

Answer 28

• tyrosine kinase linked receptor
• 1 transmembral domaine
• binds to two receptors to create bridge
• results in phosphorylation
• glucose transporters move outside cell
• glucose taken from blood to cell