Plasma membranes

Question 1

What is a Plasma membrane

Answer 1

Basically the cell surface mmebrane of all cells and organelles

Question 2

Why are plasma membranes described as fluid mosaic

Answer 2

This is due to the mixture of different components
The fluid part refers to the movement of the molecules as they can move up and down and side to side

Question 3

What are the different components that make up the plasma membrane (5)

Answer 3

Phospholipids
Proteins- Channel, Carrier, Extrinsic and Intrinsic
Glycolipids
Glycoproteins
Cholesterol

Question 4

How does the phospholipid bilayer affect entry and exit of substances in and out of the cell? (4)

Answer 4

• It allows the movement of lipid soluble and non charged molecules
• Prevents the movement of Water soluble/Polar molecules
• Membrane is partially permeable
• Large molecules do not move through;small molcecules do

Question 5

What is a phospholipid made up of

Answer 5

A glycerol molecule
Phosphate group -hydrohphilic-
Two fatty acids -hydrohphobic-

Question 6

What is the function of cholesterol

Answer 6

It can restrict the lateral movement of other molecules in the membrane (more cholesterol= less fluid or more ridgid)
Provides strength and ridgity

Question 7

What is the importance of cholesterol

Answer 7

• Makes the membrane less fluid at high temps
• Prevents water and dissolved ions leaking out of the cell

Question 8

What is the difference between Peripheral/extrinsic and Integral/intrinsic proteins?

Answer 8

• Peripheral/extrinsic do not extend completely across the membrane
• Integral/Intrinsic spans across from one side of the bilayer to the other

Question 9

What is the function of the peripheral/extrinsic proteins

Answer 9

• To provide mechanical support
• They connect to proteins or lipids to make glycoproteins and glycolipids—> act as receptors,cell recognition,

Question 10

What is the function of integral/intrinsic proteins

Answer 10

Transport molecules across the membrane through carrier and channel proteins

Question 11

What is the function of glycoproteins/lipids

Answer 11

Cell recognition ;act as receptors

Question 12

What do channel proteins do

Answer 12

Form tubes that fill with water to enable water soluble ions to diffuse

Question 13

What do carrier proteins do

Answer 13

Bind with larger molecules, such as glucose and amino acids and change shape to transport them to the other side of the membrane

Question 14

What are the factors allowing substances to pass through the membrane (simple diffusion)

Answer 14

Lipid soluble substances e.g. some hormones: estrogen
Very small molecules e.g. O2 CO2 H2O

Question 15

What are the factors that do not allow molecules to pass through the membrane in Simple diffusion

Answer 15

Water soluble (polar) substances
Sodium ions
Large molecules e.g. glucose

Question 16

What are the limitation imposed by the phospholipid bilayer

Answer 16

Only certain molecules can passively pass through the phospholipid bilayer.
This is due to it being made of phospholipids which have a polar, hydrophilic head and nonpolar, hydrophobic fatty acid tails shielded by the heads. They are arranged closely in the fluid mosaic model too which only allows small molecules to pass through.

Question 17

In a phospholipid bilyaer, what direction do the heads point

Answer 17

Outwards, towards the tissue fluid or cytoplasm

Question 18

What features of a particle would allow it to diffuse directly through the phospholipid bilayer

Answer 18

Small and non polar (uncharged)

Question 19

What structure in the membrane has the function ‘to allow the facillitated diffusion of large or charged particles’

Answer 19

Channel proteins