The structure of Cell Membrane

Question 1

Cell membranes are most made of

Answer 1

Lipids

Question 2

What two types of membrane can you have in eucaryotic cells

Answer 2

Cell membrane/ Plasma membrane

Internal membranes

Question 3

Cell Membrane/ Plasma membrane

Answer 3

Boundry between the cell and internal environment
The absolute barrier for eucaryotic cells
Surrounded by cell wall
About 5nm thick
Interface to the external world.
Contains many proteins used for good function

• Receiving info
• Import and export of molecules

Question 4

Internal Membrane

Answer 4

Membranes that separate the organelles from the cytoplasm

Question 5

What is the structure of the membrane

Answer 5

Lipid Bilayer
Combination of lipids and proteins
This is intersperses with intercalated proteins- These proteins control the membrane functions

Question 6

What is special about the lipids in the membrane

Answer 6

They are phospholipids
Amphipathic property
Both hydrophobic and hydrophilic

Question 7

What is special about the lipids in the membrane

Answer 7

Amphipathic property
Both hydrophobic and hydrophilic
This helps membranes assemble spontaneously. Don’t need enzymes/ enzyme catalysis to bring them together

Question 8

Which ends of the lipids face where

Answer 8

Hydrophilic ends face the water
(either the external environment or the cytoplasm)
Hydrophobic ends face the inside
This is why the lipid layer is a double layer
This is the most energetically favourable conformation

Question 9

Hydrophilic

Answer 9

Dissolve readily in water due to charged atoms or polar groupd that form electrostatic/ hydrogen bonds with water molecules

Question 10

Hydrophobic

Answer 10

Insoluble because their atoms are uncharged.

They force water molecules to form a cage like structure around the molecule.

Question 11

The tails can be either

Answer 11

Saturated or Unsaturated (contains double bonds )

Therefore the hydrophobic end can either be saturated or unsaturated

Question 12

What is and what causes a self sealing layer

Answer 12

Forces involved in bilayer formation
Membrane damage is energetically unfavourable and leads to repair of vesicle formation

Repair occurs to small damages

Large damage is fixed by creating a vesicle

Question 13

Membrane movement

Answer 13

They are in constant motion and are said to be fluid

Question 14

What are each of the layers in the lipid bylayer called

Answer 14

Leaflets

Question 15

Lipids move constantly within their own leaflet. How do they move between leaflets (flip flop)

Answer 15

Flip flop occurs spontaneously very rarely

Axis rotation and lateral diffusion are common and frequency is related to temperature

Question 16

Why is having high blood cholesterol bad

Answer 16

Cholesterol as a molecule can integrate itself into the lipid bilayer within blood vessels. Stops lipid movement –> blood vessels loose their fluidity and become more rigid and start to get inflamed

Question 17

Are the leaflets symmetrical

Answer 17

There is asymmetry in the leaflets.

Question 18

Glycolipids

Answer 18

Lipids that have short stretches of carbohydrates attached to them.
Never found in the inner lipids only in the outer lipids

Question 19

Leaflet that faces the extra cellular environment

Answer 19

Predominance of phosphotodile prolein
single myline
Cholesterol

Have glycolipids

Question 20

When does asymmetry in lipids arise

Answer 20

Arises during manufacture
Lipids are manufactures in the endoplasmic reticulum. This has enzymes that produce lipid components. These are first integrated into the leaflet that faces the cytoplasm.
Scramblases flip some of the lipids
The bilayer then leaves the endoplasmic reticulum and moves as vesicles to the golgi apparatus. In the golgi apparatus the flippases move the specific lipids either to the cytoplasmic to extracellular sides

Question 21

Scramblases

Answer 21

Facilitate the flip flop so the bilayer grows evenly

Present in the endoplasmic reticulum
More random
Only faciliate extention of the lipid membrane

Question 22

The different lipids are differentiated how

Answer 22

Separated based on what their different polar groups are

Question 23

Flippases

Answer 23

Present in the golgi apparatus

More to do with which specific membrane faces which way

Question 24

there are three ways proteins can be localised on membranes

Answer 24

Transmembrane
Lipid attached
Protein attached

Question 25

Transmembrane proteins

Answer 25

Proteins that spanned the entire membranes

Question 26

Lipid Attached Protein

Answer 26

Proteins that face either the internal or external environment. Attached to the lipids in the lipid bilayer

Question 27

What are the two types of membrane protein

Answer 27

Integral - Have to use a harsher treatment and break open the lipid membrane
Peripheral - Easily extracted, leave the membrane in tact

This is dependent on how hard it is to extract from the membrane

Question 28

What are the two types of membrane protein

Answer 28

Integral - Have to use a harsher treatment and break open the lipid membrane
Peripheral - Easily extracted, leave the membrane in tact

This is dependent on how hard it is to extract from the membrane

Question 29

The extremely hydrophobic nature of the space between the leaflets means what for proteins

Answer 29

The water molecules in the proteins are repelled so the proteins are forced to fold in specific ways. Forming alpha helixes and beta barrels

Question 30

What are the differences between alpha helixes and beat barrels

Answer 30

Alpha helixes are tighter wound and beta barrels are larger.
Alpha helixes tend to be receptors- Don’t allow movement of molecules across a membrane but have a role in sensing the internal environment.
Beta barrels are larger and allow the movement of molecules across a membrane

Question 31

How do we disrupt a bilayer

Answer 31

Use detergents e.g. SDS –> Form mycells

Breaks lipids apart

Question 32

Cell Cortex

Answer 32

The membrane is very fluid and fragile
The cell cortex provides the shape.
Protein framework that is attached to the lipid membrane
Fibrous meshwork of proteins attached to the cytosolic side

Question 33

Within the membrane can proteins move

Answer 33

Yes
The cells have a specific way of controlling this movements.
Cells restrict the movement of proteins by creating barriers . Especially in the gut

Question 34

How to cells control protein movement

Answer 34

1.Tethering proteins to the cell cortex
2. Tethering to the extracellular matrix proteins
3. Tethering to proteins on the surface of another cell
By falling within a diffusion barrier