Module 1 - Principles of Cell Function

Question 1

Define amphipathic molecules and give and example

Answer 1

Molecules that have hydrophilic and hydrophobic parts e.g. phospholipids of the cellular membrane

Question 2

Explain the fluid mosaic model of membranes

Answer 2

fluid - moving all the time

mosaic - lots of proteins embedded in it

Question 3

Role of cholesterol in cell membrane

Answer 3

hold phospholipids apart when cold and together when hot

Question 4

Saturated vs unsaturated

Answer 4

Saturated - max hydrogens, straight, single carbon carbon bonds, usually solid as can pack together tightly
Unsaturated - at least on double or triple carbon carbon bond, bent, more viscous as cannot pack together as tightly

Question 5

What is a glycoprotein?

Answer 5

A membrane protein with a carbohydrate attached

Question 6

What is a glycolipid?

Answer 6

A lipid with a carbohydrate attached

Question 7

Where are the hydrophilic and hydorphobic regions of the membrane?

Answer 7

Hydrophobic - inside, neutral

Hydrophilic - outside, charged

Question 8

How do we know that membranes are fluid?

Answer 8

Mouse and human cell test - proteins spread over entire cell (not one sided)

Question 9

Six major functions of membrane proteins with examples

Answer 9

• transport (ions)
• enzymatic activity
• signal transduction (receptors)
• cell to cell recognition (antigen-antibody reactions)
• intercaellular joining (to form tissues)
• attachment to the cytoskeleton and extracellular matrix (ECM)

Question 10

Passive vs active vs facilitated diffusion (examples)

Answer 10

Passive - along concentration gradient, no work (small neutral molecules)
Active - against concentration gradient, uses ATP (Na+/K+-ATPase pump)
Facilitated - along concentration gradient, molecules carried by transport proteins to speed up an otherwise passive process (aquaporins, ion channels)

Question 11

What are channel proteins? Examples

Answer 11

Proteins in the cellular membrane that provide corridors that allow a specific molecule or ion to cross the membrane e.g. aquaporins for the facilitated diffusion of water, and ion channels which are gated so that they open and close in response to stimulus

Question 12

Define and provide examples of osmotica

Answer 12

compounds that cause osmosis due to inability to cross the membrane e.g. ions, sugars, proteins

Question 13

What is osomosis?

Answer 13

diffusion of water through a selectively permeable membrane into another aqueous compartment containing solute at a higher concentration

Question 14

Define tonicity, isotonic, hypertonic and hypotonic and their effect on the cell

Answer 14

tonicity - the ability of a solution to cause a cell to gain or lose water
isotonic - inside and outside solute concentration is the same: no change in cell
hypertonic - solute concentration higher outside the cell, so water flows out of the cell causing shrivelling - crenation
hypotonic - solution concentration higher inside the cell, so water flows into the cell causing it to swell and lyse

Question 15

What is crenation?

Answer 15

The shrivelling of a cell in hypertonic solution

Question 16

What is hemolysis?

Answer 16

The bursting of a cell in hypotonic solution

Question 17

Plant cell tonicity vs animal cell tonicity

Answer 17

Plants like hypotonic conditions as their cell wall saves them from lysing. These conditions make the cells turgid, rather than flaccid as in isotonic solution or plasmolysed as in hypotonic solution which is when the plasma membrane seperates from the cell wall

Question 18

Are transport proteins specific for the substance it moves?

Answer 18

Yes

Question 19

What kind of substances do transport proteins allow the pass across the membrane?

Answer 19

hydrophilic as they wouldn’t be able to pass through the membrane otherwise

Question 20

What is an electrogenic pump?

Answer 20

A transport protein that generates voltage across a voltage across a membrane e.g. sodium-potassium pump in animals and the proton pump in plants, fungi and bacteria

Question 21

What is cotransport? Example

Answer 21

When the active transport of a solute indirectly drives the transport of another solute e.g. plants gradient of hydrogen drives active transport of nutrients

Question 22

Types of endcytosis

Answer 22

Phagocytosis - engulfing particles
Pinocytosis - cells drinking (vesicle of extracellular fluid formed)
Receptor-mediated endocytosis - vesicle formation triggered by ligands binding to membrane receptors

Question 23

3 stages of cell signalling

Answer 23

Reception - signalling molecule binds to receptor
Transduction - relay molecules pass on signal
Response - activation of cellular response

Question 24

What is an agonist?

Answer 24

A substance that is similar to a naturally occuring chemical in the body e.g. drugs

Question 25

4 receptor types in families with speed of neurotransmission

Answer 25

Plasma membrane receptors:
Ion channel receptors - fastest (milliseconds)
G protein-coupled receptors (e.g. adrenaline) - second fastest (seconds)
Tyrosine kinase linked receptors (e.g. insulin) - third fastest (minutes)
Intracellular receptors:
Steroid receptors - slowest reaction

Question 26

facts about GPCR’s

Answer 26

• most important receptor types due to abundance
• 7 transmembrane spanning domains (7 helix protein)
• over 1000 types
• activated by numerous stimuli inc. light, ions, odourants, gustative molecules, neurotransmitters, hormones, peptides, proteins

Question 27

Adenylyl cyclase GCPR pathway

Answer 27

Adenylyl cyclase (enzyme) activated
+ ATP produces cyclic AMP (a second messenger)
acts on protein kinase A which initiates cellular response

Question 28

What is a kinase?

Answer 28

An enzyme that transfers phosphates to activate or inactivate target proteins

Question 29

3 roles of phosphorylation

Answer 29

• conformational change in protein
• protein-protein interactions
• change in cellular location

Question 30

What is osmolarity?

Answer 30

The number of particles in water e.g. NaCl = 2 but glucose = 1