Lesson 15 - Structure and function of membranes

Question 1

Compartmentalisation

Answer 1

The formation of separate membrane-bound areas in a cell. It is vital to a cell as metabolism includes many different and often incompatible reactions. Allows for specific conditions, maintains chemical gradients and protects vital cell components

Question 2

Name of cell-surface membrane

Answer 2

Plasma membrane

Question 3

Describe phospholipid bilayer:

Answer 3

Phospholipids composed of a phydrophilic phosphate head and hydrophobic fatty acid tails.
Therefore, there is a hydrophobic core of phospholipid tails and the hydrophilic heats interact with water / aqueous solution.

Question 4

When were cell membranes first seeN/

Answer 4

After the invention of the electron microscope.
- Two black parallel lines.
- Theory = Composed of a lipid bilayer

Question 5

Who proposed the fluid-mosaic model?

Answer 5

Singer and Nicolson

Question 6

Fluid-mosaic bilayer:

Answer 6

• Proteins embedded in the bilayer vary in shape, size and position. (particular to each type of cell)
• Phospholipids are free to move within the layer relative to each other. Provides flexibility.

Question 7

Two types of cell-surface membrane proteins:

Answer 7

• Intrinsic
• Extrinsic

Question 8

Intrinsic proteins: (Integral proteins)

Answer 8

• Transmembrane proteins that are embedded in both layers of a membrane.
• Have amino acids with hydrophobic R-groups on their external surfaces, which interact with hydrophobic core of the membrane. This keeps them in place.

Question 9

Types of intrinsic proteins?

Answer 9

• Channel proteins
• Carrier proteins

Question 10

Channel proteins:

Answer 10

• Hydrophilic channel that allows the passive movement of polar molecules and ions down a concentration gradient through membranes. They are held in position by interactions between hydrophobic core of the membrane and the hydrophobic R-groups on the outside of proetins.
• Passive / diffusion gradient

Question 11

Carrier proteins:

Answer 11

Important role in both passive and active transport into cells. This often involves the shape of the protein changing.
- Sodium / potassium pump

Question 12

Glycoproteins?

Answer 12

• Intrinsic proteins.
• Embedded in the cell-surface membrane with attached carbohydrate (sugar) chains of varying lengths and shapes.
• Play a role in cell adhesion and as receptors for chemical signals.

Question 13

Receptors in chemical signals?

Answer 13

• Receptors for neurotransmitters such as acetylcholine at nerve cell synapses. Binding of neurotransmitters triggers or prevents an impulse in the next neurone.
• Receptors for peptide hormones, including insulin and glucagon, which affect the uptake and storage of glucose by cells.
• Drugs: beta blockers (reduce response of the heart to stress.

Question 14

Cell adhesion

Answer 14

When cells join together to form tight junctions in certain tissues

Question 15

Permeability of cell membranes:

Answer 15

• Water can diffuse through lipid bilayer
• Aquaporins (protein channels that allow the passage of water)
• Partially permeable

Question 16

Glycolipids:

Answer 16

Lipids with carbohydrates chains attached.
- Cell markers / antigens and can be recognised by the cells of the immune system as self or non-self.

Question 17

Can large, lipid soluble molecules move through cell membranes?

Answer 17

Yes

Question 18

Extrinsic proteins:

Answer 18

Normally have hydrophilic R-groups on their outer surfaces and interact with the polar heads of the phospholipids or with intrinsic proteins.
- Present in either layer or between.

Question 19

Cholesterol:

Answer 19

Lipid with a hydrophilic end and a hydrophobic end, like a phospholipid.
- Regulates fluidity of membranes.

Question 20

ATPase / ATP synthase

Answer 20

Manufactures ATP - embedded in the mitochondrial membrane.
- Membrane bound

Question 21

Cholesterol in membranes structure:

Answer 21

• Positioned between phospholipids in membrane bilayer
• Hydrophilic end interacting with heads and hydrophobic end interacting with tails. Pulls them together
• Adds stability to membranes (without making too rigid)
• Prevents membranes from becoming too solid by stopping phospholipid molecules from grouping too closely and crystallising.

Question 22

Enzymes in membranes:

Answer 22

Need to be in particular positions for chemical reactions to take place.
- Eg. ATP synthase and electron carriers within the cristae (inner membrane of mitochondrion) for production of ATP in respiration.
- Enzymes in photosynthesis are found on the membrane stacks within the chloroplasts.

Question 23

Cytoskeleton:

Answer 23

Acts as an anchor and maintains the integrity of the membrane (prevents falling apart)