Plasma Membranes!

Question 1

What is compartmentalisation?

Answer 1

The formation of separate membrane bound areas in a cell

Question 2

What is a plasma membrane?

Answer 2

The cell surface membrane which separates the cell from its external environment

Question 3

Which way do the hydrophilic heads face?

Answer 3

Outwards

Question 4

Why do the hydrophobic tails remain inside the bilayer?

Answer 4

To create a hydrophobic core, membranes are usually located in aqueous environments

Question 5

What is the fluid mosaic model?

Answer 5

Proteins occupy various layers within the membrane. Called the fluid mosaic model as the phospholipids are free to move within the layer relative to eachother, giving the membrane flexibility. Proteins in membrane vary in size shape and position

Question 6

What is a glycoprotein?

Answer 6

Branching carbohydrate portion of a protein that acts as a recognition site for chemicals eg hormones

Question 7

What is a glycolipid?

Answer 7

Acts as a recognition site eg for cholera toxins

Question 8

Why is the role of cholesterol in the membrane?

Answer 8

For stability / flexibility

Question 9

What is an extrinsic protein?

Answer 9

Protein molecule partly embedded in the membrane

Question 10

What is an intrinsic protein?

Answer 10

Protein molecules spanning the phospholipid bilateral

Question 11

What are the 2 types of intrinsic protein?

Answer 11

Channel proteins

Carrier proteins

Question 12

How are intrinsic proteins adapted to function?

Answer 12

Embedded through both layers of membrane.

They have amino acids with hydrophobic R groups on their external surfaces, which interact with the hydrophobic core of the membrane keeping them in place.

Question 13

What is the role of a channel protein?

Answer 13

Provide a hydrophilic channel that allows the passive movement of polar molecules and ions down a concentration gradient through membranes. Held in position by interactions between hydrophobic core of the membrane and hydrophobic R groups on outside of the proteins.

Question 14

What is the role of a carrier protein?

Answer 14

Involved in Passive transport down a concentration gradient and active transport into cells. This often involves the shape of the protein changing.

Question 15

How are glycoproteins adapted to function?

Answer 15

Embedded in the cell surface membrane with attached carbohydrate chains of varying lengths and shapes. Glycoproteins Play a key role in cell adhesion ( when cells join together to form tight junctions in certain tissues) and as receptors for chemical signals

Question 16

What is cell signalling?

Answer 16

When a chemical binds to a receptor or elicits a response from the cell. This may causes direct response or set off a cascade of events inside the cell.

Question 17

Name some examples of cell signalling?

Answer 17

Receptors for neurotransmitters such as acetylcholine at a nerve cell synapse. The binding of neurotransmitters triggers or prevents an impulse at the next neurone.

Receptors for peptide hormones including insulin and glucagon, which affect the uptake and storage of glucose by cells.

Question 18

What are glycolipids and what do they do?

Answer 18

They’re lipids with starches carbohydrate (sugar) chains. These are called cell markers or antigens which can be recognised by the cells of the immune system as self or non self.

Question 19

What features to extrinsic proteins normally have?

Answer 19

Hydrophilic R groups on their outer surfaces and interact with the polar heads of the phospholipids or with intrinsic proteins. Can be present in either layer and some can move between the layers.

Question 20

What is the role of cholesterol within membranes?

Answer 20

Regulating the fluidity and stability of membranes.

Question 21

How are cholesterol molecules positioned in the membrane?

Answer 21

Cholesterol molecules are positioned between phospholipids in the bilayer, with the hydrophilic end interacting with the heads and the hydrophobic end interacting with the tails pulling them together.

Question 22

How does cholesterol prevent the membrane from becoming too solid?

Answer 22

By stopping the phospholipid molecules from grouping too closely and crystallising.

Question 23

How does temperature affect plasma membranes?

Answer 23

As temperature increases the phospholipids will have more kinetic energy and will therefore move more. This makes a membrane more fluid and it will begin to lose its structure, if this temperature continues to increase, the cell will break down completely.

At higher temperatures the cell is more permeable to particles due to the increase in permeability.

At very high temperatures the carrier and channel proteins work denature, meaning the membrane permeability will be affected once again.

Question 24

Why does water not disrupt cell membranes?

Answer 24

Charged phosphate heads (hydrophilic) interact with water keeping the membrane in tact. Non polar tails are oriented away from the water forming a bilayer with the hydrophobic core.

Question 25

Why do organic / less polar molecules dissolve / disrupt the membrane?

Answer 25

Organic solvents can dissolve the membranes, therefore disrupting the cell.

Question 26

Why are pure or strong alcohols toxic?

Answer 26

Because they can destroy the cells within the body.

Question 27

How do alcoholic drinks affect the membranes?

Answer 27

Non polar alcohol molecules enter the cell membrane and the presence of these between the phospholipid disrupts the membrane. When disrupted, the membrane becomes more fluid and more permeable.

Many cells need intact membranes for specific functions eg nerve impulse transmission in nerve cells.