TOPIC 1-Cell membranes

Question 1

How do tempratures below 0 degrees Celsius effect plasma membranes?

Answer 1

-The phospholipids do not have much energy so they cannot move/vibrate very much
-They are packed together closely which makes the membrane rigid
-Channel and carrier proteins denature (loose their structure and function)
-Permability of the membrane is increased
-Ice crystals may form and pierce the membrane making it highly permeable when it thaws

Question 2

How do temperatures between 0-45 degrees Celsius effect plasma membrane?

Answer 2

-The phospholipids can move around and aren’t pack as tightly together
-The membrane is partially permeable
-Ad the temprature increases,the phospholipids move as they have more energy which increases permeability

Question 3

How do tempratures above 45 degrees Celsius effect plasma membranes?

Answer 3

-The phospholipid bilateral starts to melt (break down) and the membrane becomes more permeable
-Water inside the cell expands putting pressure on the membrane
-Channel proteins and carrier proteins in the membranes denature
-Therefore they cannot control what comes in and out of the cell

Question 4

Define partially permeable

Answer 4

They let some molecules through but not others

Question 5

What is the function of membranes within cells?

Answer 5

Divides the cell into different components- acts as a barrier between the organelle and the cytoplasm

Question 6

What are cell membranes composed of?

Answer 6

Lipids (mainly phospholipids), proteins and carbohydrates

Question 7

Which model was created in 1972?

Answer 7

Fluid mosaic model

Question 8

How are molecules arranged according to the fluid mosaic model?

Answer 8

-Phospholipid molecules form a bilayer
-Proteins are scattered throughout (mosaic), these include channel and carrier proteins, receptor proteins
-Glycolipids and glycoproteins
-Cholesterol

Question 9

Why is the bilayer fluid?

Answer 9

-The phospholipids are constantly moving

Question 10

What is the function of the carrier and channel proteins?

Answer 10

-To allow large molecules and ions to pass through the membrane

Question 11

What is the function of receptor proteins?

Answer 11

Allow the cell to detect chemical changes released by other cells

Question 12

What are glycolipids and glycoproteins?

Answer 12

glycoproteins= proteins that have a carbohydrate attached
Glycolipids= proteins that have a lipid attached x

Question 13

What is a phospholipid head and tail?

Answer 13

Phospholipid head=hydrophillic
Tail= hydrophobic

Question 14

What is meant by hydrophilic and hydrophobic?

Answer 14

Hydrophillic= attracts water
Hydrophobic= repels water

Question 15

How are molecules arranged in a bilayer?

Answer 15

-The head faces out towards the water on both sides of the membrane
-The centre of the bilayer is hydrophobic so no water-soluble substances diffuse through it
-However small nonpolar substances and water can diffuse through the membrane

Question 16

What is the purpose of cholesterol?

Answer 16

-Provides stability

Question 17

Where is cholesterol found?

Answer 17

-In all cell membranes apart from bacterial cell membranes
-Found between the phospholipids

Question 18

Where does cholesterol bind to?

Answer 18

-Hydrophobic tail of the phospholipid

Question 19

How does cholesterol help to maintain rigidity?

Answer 19

-Causes it to pack more closely
-Restricts the movement of the phospholipids which makes it less fluid and more rigid

Question 20

Why does cholesterol also contain hydrophobic regions?

Answer 20

-Able to create a further barrier to polar substances moving through the membrane