Structure of the cell membrane

Question 1

All membranes around and within all cells have the same structure, including cell organelles. What is this structure known as?

Answer 1

The plasma membrane also known as the cell surface membrane

Question 2

What is the plasma membrane?

Answer 2

The plasma membrane is the membrane found in all cells that forms the boundary between the cell cytoplasm and the environment

Question 3

What is the plasma membrane described as?

Answer 3

The plasma membrane is described as the fluid - mosaic model

Question 3

Why is the plasma membrane described as the fluid - mosaic model?

Answer 3

Described as fluid: because the individual phospholipid molecules can move relative to one another, giving the membrane a flexible structure that constantly changes shape

Described as mosaic: because the proteins that are embedded in the bilayer vary in shape, size and pattern the same way the stones/tiles of a mosaic

Question 4

The phospholipid bilayer is a partially permeable membrane. How is this partially permeable membrane formed?

Answer 4

All these molecules are arranged within the phospholipid bilayer to create a partially permeable membrane, that is the cell surface membrane

Question 5

What are the key components of the plasma membrane?

Answer 5

1. Phospholipids
2. Cholesterol
3. Proteins (integral/peripheral proteins and protein channel/carrier proteins)
4. Glycoproteins
5. Glycolipid

Question 6

How is the phospholipid bilayer formed?

Answer 6

The phospholipids align as a bilayer due to the hydrophilic heads being attracted to water and the hydrophobic tail being repelled by water

Question 7

What does the “bilayer” refer to?

Answer 7

The bilayer refers to the two layers of phospholipids arranged to form the phospholipid bilayer

Question 8

What is the positioning of the hydrophobic tail in the phospholipid bilayer?

Answer 8

The hydrophobic tails point facing the centre of the cell surface membrane

Question 9

What is the positioning of the hydrophilic head in the phospholipid bilayer?

Answer 9

The hydrophilic heads point outside of the cell surface membrane

Question 10

What are the functions of the phospholipid in the membrane?

Answer 10

The phospholipids allow lipid soluble substances to enter and leave the cell. They prevent water soluble substances entering and leaving the cell. Lastly making sure the membrane stays flexible and self sealing

Question 11

Where are cholesterol molecules located, involving the phospholipid bilayer?

Answer 11

Cholesterol molecules are located within the phospholipid bilayer of the cell surface membrane

Question 12

How does cholesterol restrict te lateral movement of other molecules in the membrane?

Answer 12

Cholesterol pulls together the fatty acid tails of the phospholipid molecules, limiting their movement and that of other molecules but without making the membrane as a whole too rigid. Therefore the more cholesterol within a membrane, the less fluidity, the more rigid the membrane is

Question 12

What is the function of cholesterol molecules?

Answer 12

Cholesterol molecules strengthen the membrane. They restrict the lateral movement of other molecules in the membrane

Question 13

How is cholesterol useful in the membrane because of its function?

Answer 13

Cholesterol makes the membrane less fluid at higher temperatures. This prevents the possibility of the gaps between the phospholipid bilayer becoming too big, due to increased temperature, causing water and dissolved ions to leak in or out the cell. In the long run, potentially causing dehydration or cells bursting

Question 13

What are the functions of cholesterol?

Answer 13

1. Reduce lateral movement of other molecules including phospholipids
2. Make the membrane less fluid at high temperatures
3. Prevent leakage of water and dissolved ions from the cell

Question 14

What are peripheral proteins?

Answer 14

Peripheral proteins provide mechanical support. They can also connect to proteins or lipids to make glycoproteins or glycolipids acting as receptors for cell recognition

Question 14

Proteins are embedded within the cell surface membrane. There are two ways proteins are embedded, what are these two ways?

Answer 14

Proteins are imbedded either peripherally (proteins that do not completely go through the entire cell surface membrane) or integrally (proteins that span across one side of the membrane to the other)

Question 15

What are integral proteins?

Answer 15

Integral proteins are protein carries or channel proteins involved in the transportation of molecules across the membranes

Question 16

What are protein channels?

Answer 16

Protein channels are water filled tubes that enable water soluble ions to diffuse.

example water soluble ion: sodium

Question 17

What are carrier proteins?

Answer 17

Carrier proteins bind with larger molecules (e.g. glucose and amino acids). Then the carrier proteins change their own shapes to move these molecules across the membrane

Question 18

What is the function of proteins within the membrane?

Answer 18

1. provide structural support
2. act as channels transporting water - soluble substances across the membrane
3. allows active transport across the membrane through carrier proteins
4. forms cell surafce receptors for identifying cells
5. helps cells adhere together
6. acts as receptors for hormones

Question 19

What are glycoproteins?

Answer 19

Glycoproteins are carbohydrate chains that are attached to many extrinsic proteins on the outer surface of the cell membrane

Question 20

What is the function of glycoproteins?

Answer 20

1. Acts as cell surface receptor, more specifically for homrones and neurotransmitters
2. Helps cells attach to one another, to form tissues
3. Allows cells to recognise one another, for example lymphocytes can recognise an organism’s own cells

Question 21

What are glycolipids?

Answer 21

Glycolipids are made up of a carbohydrate covalently bonded with a lipid

Question 22

How are glycolipids located within a cell? What do glycolipids do in this position?

Answer 22

The carbohydrate portion extends from the phospholipid bilayer into the watery environment outside the cell where it acts as a cell surface receptor for specific chemicals

Question 23

What is the function of glycolipids?

Answer 23

1. Act as a recognition site
2. Help maintain stability of the membrane
3. Helps cells attach to one another, to form tissues

Question 24

The cell surface membrane is partially membrane, meaning most molecules do not freely diffuse across it. Why is this the case though? {4pts}

Answer 24

1. Molecules that are not soluble in lipids cannot pass through the phospholipid layer
2. Molecules can be too large to pass through the channels in the membrane
3. Some molecules have the same charge as the protein channels and when attempting to pass through are repelled
4. Some molecules are electrically charged and therefore have difficulty passing through the non - polar hydrophobic tails