2.1 (b) - Cell Membrane

Question 1

What is the cell membrane?

Answer 1

• The cell membrane, also known as the plasma membrane, is a double layer of lipids and proteins that surrounds a cell and separates the cytoplasm

Question 2

What is the structure of the cell membrane?

Answer 2

• Cell membranes consist of: Two layers (bi-layers) of phospholipid molecules; also know as the phospholipid bilayer.
• Very thin
• Fluid-mosaic model
• Proteins molecules embedded or attached.

Question 3

What is the function of the cell membrane?

Answer 3

• The cell membrane separates the cell from it’s surroundings and controls the exchange of materials in and out of the cell, as well as having a range of other important roles in cell communication, cell adhesion and the binding of hormones.
• Separate contents of cell from external environment
• Regulate passage of substances in/out of cell
• Cell recognition (e.g. other cells and hormones)
• Enable attachment of cytoskeleton

Question 4

What are Phospholipids?

Answer 4

• single molecules made up of two parts: a hydrophilic tail and two hydrophobic heads.

Question 5

What are the two types of membrane proteins?

Answer 5

• Integral Proteins

- Peripheral Proteins

Question 6

What are Integral proteins?

Answer 6

• Proteins which are permanently in the bilayer.

Question 7

What are Peripheral proteins?

Answer 7

• Proteins which tend to move more temporarily and are not a permanent part of the membrane.

Question 8

Where is Cholesterol located?

Answer 8

• Usually found positioned between the phospholipids (only in animal cells)

Question 9

What are Glycoproteins?

Answer 9

• Membrane proteins with carbohydrate chains attached.

Question 10

What are Glycolipids?

Answer 10

• Phospholipids with carbohydrate chains attached.

Question 11

What is the Fluid Mosaic Model?

Answer 11

• Used to describe the cell membrane, and contains, large proteins and glycoprotein molecules embedded in the phospholipid bilayer.
  The molecules are able to move relative to each other.

Question 12

What does Permeable mean?

Answer 12

• Anything can pass through the cell membrane.

Question 13

What does Semi-Permeable mean?

Answer 13

• Only some things can pass through the cell membrane.

Question 14

What does Selectively Permeable mean?

Answer 14

• The cell membrane can regulate what passes through it.

Question 15

How is the Phospholipid Bilayer arranged?

Answer 15

• The phospholipid bilayer consists of two layers of lipid molecules which are arranged with their phosphate groups (Hydrophobic Tail) on the outside eg. Facing the outside of the cell and towards the cytoplasm and the lipid tails projecting inwards.

Question 16

What is the phosphate head called?

Answer 16

• The phosphate head of the phospholipid are known as Hydrophilic and have a
  ‘polar’ charge associated and therefore, they can interact with (or attract water molecules)

Question 17

What is the phosphate tail called?

Answer 17

• The phosphate tail are know as Hydrophobic and have a ‘non-polar’ charge associated and therefore do not interact with water (or they repel water.)

Question 18

What types of proteins are associated with the cell membrane?

Answer 18

• Channel proteins that are throughout the membrane which transport substances.
• Receptor proteins that are bound to the surface of the membrane and communicate to other parts through cellular communication.
• Proteins on the underside of the membrane with transfer message through intracellular signalling.

Question 19

What are the five functions of membrane proteins?

Answer 19

1. Hormone Binding Site
2. Cell Communication
3. Cell Adhesion
4. Channel Proteins and Pump Proteins
5. Cholesterol

Question 20

What is the Hormone Binding Site?

Answer 20

• Hormones are molecules that carry messages to cell. some hormones are proteins and therefore, cannot cross the cell membrane.
• Many hormones transported in the blood can only bind and act on cells with complementary protein receptors on the outside of their membranes. Eg. A growth hormone molecule will only bind to a specific growth hormone receptor.

Question 21

How does Hormone binding occur?

Answer 21

• Protein receptors on the outside of the cell membrane have a shape which is complementary to the hormone. Eg. Lock and key fit.
• The binding of the hormone to the receptor triggers a signal sent inside the cell.
• This initiates cellular changes and gene activity. Eg. Human growth hormone stimulates growth, especially in childhood, strengthening bones and increasing muscle mass.

Question 22

How does Cell Communication occur?

Answer 22

• Cell communication can occur via direct contact between cell membrane proteins of adjacent cells or via hormones or nerve transmitter chemicals (called neurotransmitters)
• Proteins on the cell surface can send a signal to other cells when there is direct contact between the cells.

Question 23

How does Cell Adhesion occur?

Answer 23

• Integral proteins can stick out and bind to specific protein molecules on adjacent cells or attach to the cytoskeleton.

Question 24

What is the Cytoskeleton?

Answer 24

• The cytoskeleton is a framework of tiny protein tubules and filaments that extend throughout the cytosol.
• Its function includes attachment and movement of organelles, and movements of the cell membrane and chromosomes.

Question 25

What are Channel Proteins and Pump Proteins?

Answer 25

• These proteins can either allow movement of molecules by proteins by diffusion or use energy to actively move molecules in and out of cells (active transport.) and allows the movement of molecules which are unable to diffuse through the phospholipid bilayer to diffuse through the protein (eg. Water molecules moving through a type of protein channel called aquaporin, where the channel regulates the flow of water in and out of the cell by a process called osmosis.

Question 26

What is Cholesterol?

Answer 26

• Cholesterol is NOT a protein.
• The cell membranes within animal cells contain a lipid called cholesterol which is an important molecules in regulating the fluidity of the phosphates.