Lec 15 - Membrane structure and function

Question 1

What is a leaflet of the plasma membrane?

Answer 1

One individual layer of phospholipids

Question 2

How thick is the cell membrane?

Answer 2

8nm

Question 3

What is the major function of the cell membrane?

Answer 3

To separate the inside from the outside of the cell, and to mediate transport of wanted substances into and unwanted substance out of the cell.

Question 4

Structure of the cell membrane according to the fluid mosaic model?

Answer 4

50% lipid and 50% protein
‘sea of lipids in which proteins float like icebergs’

Question 5

Function of the lipid part of the lipid bilayer?

Answer 5

Acts as a barrier against entry or exit of polar substances

Question 6

Function of the proteins in the lipid bilayer?

Answer 6

Proteins are gatekeepers and regulate traffic

Question 7

What is a glycolipid?

Answer 7

A sugar group attached to a hydrophobic lipid molecule (looks like a phospholipid with a carbohydrate head)

Question 8

What is cholesterol?

Answer 8

A lipid that can insert in the phospholipid backbone and can control the properties of the lipid bilayer

Question 9

Which direction do the leaflets face in the lipid bilayer?

Answer 9

One faces towards the inside of the cell, one faces towards the outside of the cell.

Question 10

Are phospholipids amphipathic?

Answer 10

Yes

Question 11

Is a phopholipid primarily lipid or phosphate?

Answer 11

They are 75% lipid

Question 12

Can a lipid bilayer form in water from oil?

Answer 12

Yes, when oil/fat is added to water, it will form a lipid bilayer

Question 13

Are the hydrophillic surfaces charged or uncharged?

Answer 13

The phosphate heads are polar, so yes they are charged

Question 14

What are the features of membrane fluidity?

Answer 14

Lipids can move around freely in one leaflet of the membrane. They rarely flip flop.

Question 15

What is the benefit of lipid composition being asymmetrical in the bilayer?

Answer 15

Can assist in cell signalling and other cellular pathways/properties of cells

Question 16

How does lipid tail length effect the fluidity of the cell membrane?

Answer 16

Longer the tail, the lower the fluidity

Question 17

How does number of double bonds in the lipid tails effect the fluidity of the cell membrane?

Answer 17

The more double bonds, the higher the fluidity

Question 18

How does the amount of cholesterol effect the fluidity of the lipid bilayer?

Answer 18

More cholesterol = lower fluidity (cholesterol makes arteries less fluid)

Question 19

What is an example of a fat with more double bonds?

Answer 19

Polyunsaturated fats

Question 20

What are integral proteins

Answer 20

Embedded in the membrane (transmembrane span the entire membrane)

Question 21

What are peripheral proteins

Answer 21

Easily moved, attached to either the inner or outer surface of the cell membrane

Question 22

How can peripheral proteins be easily removed?

Answer 22

They tend to be protein-protein interactions, so you can separate it (break the bonds) using a high salt concentration

Question 23

How do you remove integral proteins from the lipid bilayer?

Answer 23

ONly detergent can. Because it breaks the interaction between the protein and the lipid bilayer.

Question 24

What can change the shape of the cell? (think about peripheral and integral proteins)

Answer 24

Integral proteins binding to peripheral proteins that are joined to the cytoskeletal filaments

Question 25

Where is the hydrophobic region of an intergral protein and what is the structure?

Answer 25

The hydrophobic regions span the core of the lipid bilayer. these regions consist of non-polar amino acids coiled into a helix

Question 26

What do the hydrophillic parts of the protein interact with?

Answer 26

The aqueous solution

Question 27

Membrane proteins can act as?

Answer 27

Receptor
enzyme
transporter
channel
cell-linking (junctions)
cell identity markers (hey don’t attack me bro)

Question 28

What does the lipid bilayer allow in without assistance of tranport proteins?

Answer 28

nonpolar, uncharged, small molecules
lipid soluble molecules
permeable to some polar molecules: H2O, urea, CO2

Question 29

What doesn’t the lipid bilayer allow through?

Answer 29

Large molecules
Polar molecules
Ions

Question 31

What effects the rate of diffusion?

Answer 31

Steepness of concentration gradient
temperature
surface area
size of molecule
distance of diffusion

Question 31

What determines the selective permeability of the lipid bilayer?

Answer 31

Its molecular organisation

Question 31

What is a typical cell’s membrane potential?

Answer 31

8 millivolts

Question 31

What is the term we use for the movement of ions down its gradient?

Answer 31

Electrochemical gradient

Question 31

Why is the cell size limit a thing and what is the limit?

Answer 31

20 micrometres
If the cell was too large, diffusion would not be able to occur efficiently. diffusion is very fast over small distances (blood capilaries to cells)

Question 31

What diffuses down a concentration gradient?

Answer 31

non-charged molecules will diffuse down their concentration gradient

Question 31

What diffuses down an electrochemical gradient and how does it work?

Answer 31

ions move down it, and will be influenced by membrane potential in addition to their concentration gradient

Question 32

What allows a difference in concentration across a membrane?

Answer 32

the selective permeability of the membrane

Question 33

Can gradients act as stored energy?

Answer 33

Yes

Question 34

Which physical element can a lipid bilayer act as and why?

Answer 34

It can act as a capacitor, because it can store charge and release it quickly (can seperate and store charge)

Question 35

How can we generate electricity with an electrochemical gradient?

Answer 35

By allowing the flow of ions through an ion channel into the cell

Question 36

State whether, inside a cell if each of these are high or low: K+, Na+ and Cl-

Answer 36

K+ = high
Na+ = low
Cl- = low

Question 37

State whether, outside a cell if each of these are high or low: K+, Na+ and Cl-

Answer 37

K+ = low
Na+ = high
Cl- = high

Question 38

Why is potassium considered to have a bungee cord on it?

Answer 38

Because even though it leaves the cell down it’s electrochemical gradient, the negative membrane potential holds it back.