The structure and function of membranes

Question 1

What does compartmentalisation mean

Answer 1

The formation of separate membrane-bound areas in a cell

Question 2

Why is compartmentalisation necessary

Answer 2

It allows for the different and specific environments for the chemical reactions to exist even if they are not compatible with one another

Question 3

What is the name for the cell surface membrane?

Answer 3

The plasma membrane

Question 4

What is the main function of the plasma membrane?

Answer 4

It separates the cell from its external environment

Question 5

What are membranes formed from?

Answer 5

Phospholipid bilayer

Question 6

Describe and draw how the phospholipids create a bilayer (and thus the cell wall)

Answer 6

The many phospholipids aramge themselves in a way in which the hydrophilic phosphate heads are both on the inner and outer surface of the membrane, sandwiching the hydrophobic, fatty acid tails in the middle

Question 7

What type of environment do cells normally live in?

Answer 7

An aqueous environment

Question 8

What evidence in 1950s arose which supported the theory of the lipid bilayer?

Answer 8

The invention of the electron microscope showed the cell membrane as two black lines.

Question 9

During 1972 what did the two scientists Singer and Nicolson propose?

Answer 9

The fluid-mosaic model

Question 10

Why was it called the fluid-mosaic model?

Answer 10

Because the phospholipids are free to move within the layer relative to each other and because the proteins within the layer vary in shape,size and position.

Question 11

Where are intrinsic proteins located on the membrane?

Answer 11

Through both layers of the membrane

Question 12

Draw a diagram of an intrinsic protein

Answer 12

e

Question 13

What is anther name for an intrinsic protein?

Answer 13

An integral protein

Question 14

How do intrinsic proteins keep themselves in place?

Answer 14

Hydrophobic R-groups on their external surfaces of the protein interact with the hydrophobic core of the membrane, keeping them in place

Question 15

What are the three different types of intrinsic proteins?

Answer 15

Channel, carrier proteins, glycoporoteins

Question 16

What are channel and carrier proteins both evolved with?

Answer 16

Transport across the membrane

Question 17

How do channel proteins allow the movement of polar molecules and ions into the cell?

Answer 17

They provide a hydrophilic channel that allows passive movement of polar molecules and ions down a concentration gradient through the membrane

Question 18

What type of molecule does channel proteins allow through?

Answer 18

polar molecules and ions

Question 19

What is the function of the carrier protein?

Answer 19

It plays a role in both passive and active transport into cells.

Question 20

What is the structure of glycoporoteins?

Answer 20

They are proteins with attached carbohydrate chains

Question 21

What do glycoproteins play a role in?

Answer 21

cell adhesion and as receptors for chemical signals

Question 22

What is meant by cell signaling?

Answer 22

When the chemicals bind to the receptor on a cell membrane which causes either a direct response or sets of a cascade of events inside of the cell.

Question 23

What is the structure of a glycolipid?

Answer 23

They are lipids with attached carbohydrate chains

Question 24

What are other names for glycolipids?

Answer 24

Cell markers or antigens

Question 25

What is the function of glycolipids?

Answer 25

They can be recognised by the cells of the immune system as self or non-self

Question 26

What are extrinsic proteins?

Answer 26

They are proteins which are only present on one side of the bilayer

Question 27

Draw a diagram of ab extrinsic protein

Answer 27

d

Question 28

What is another name for an extrinsic protein?

Answer 28

Peripheral proteins

Question 29

How are extrinsic proteins kept in place?

Answer 29

They have hydrophilic R-groups on their outer surfaces which interact with the polar heads of the phospholipids or intrinsic proteins.

Question 30

What is the structure of cholesterol?

Answer 30

They are a lipid with a hydrophilic end and a hydrophobic end.

Question 31

What is the function of cholesterol?

Answer 31

It regulates the fluidity of membranes

Question 32

How does cholesterol add stability to the membrane without making it too rigid?

Answer 32

The cholesterol molecules are positioned between two phospholipids with the hydrophilic end interacting with the heads and the hydrophobic ends interacting with the tails, pulling them together

Question 33

What do the cholesterol molecules act to prevent?

Answer 33

The membranes from becoming too solidly stopping the phospholipid molecules from grouping too closely and crystallising