Biological Membranes

Question 1

Intrinsic proteins

Answer 1

Proteins which span the whole bilayer

Question 2

Extrinsic proteins

Answer 2

Proteins which are partially embedded inside or outside the bilayer

Question 3

Glycoprotein

Answer 3

Protein + carbohydrate

Question 4

Glycolipid

Answer 4

Phospholipid + carbohydrate

Question 5

Carrier and channel proteins are _____

Answer 5

Intrinsic

Question 6

Channel proteins

Answer 6

• Provide a hydrophilic channel that allows the passive movement of polar molecules and ions down a concentration gradient
• they are held in position by interactions between the hydrophobic core of the membrane and the hydrophilic R groups on the outside of the protein

E.g. diffusion, osmosis

Question 7

Carrier proteins

Answer 7

• have an important role in passive and active transport (against conc gradient) into cells
• this often involves the shape of the protein changing

Question 8

Glycoprotein role

Answer 8

• embedded in the cell surface membrane
• play role in cell adhesion and as receptors for chemical signalling

Question 9

Glycolipid role

Answer 9

• cell markers or antigens and can be recognised by the cells of the immune system

Question 10

Cholesterol

Answer 10

• a lipid that regulates the fluidity of membranes
  -restricts too much movement within phospholipid bilayer

Question 11

Actin Microfilaments

Answer 11

Helps anchor proteins and stop them moving around too much

Question 12

Cohesion (in water)

Answer 12

Molecules of water are attracted to each other

Question 13

Adhesion (in water)

Answer 13

Water molecules are attracted to cell walls e.g. xylem

Question 14

Diffusion

Answer 14

The net movement of molecules from a area of higher concentration to an area of lower concentration, down a conc gradient

Question 15

Simple diffusion

Answer 15

Few substances can pass directly across the bilayer:
- lipid based molecules- fat soluble so dissolve and diffuse readily across the bilayer e.g. steroid hormone
- very small molecules- e.g. oxygen and carbon dioxide are small enough to pass between phospholipid molecules. Water and urea are very small but because they are polar (charged) they pass across the bilateral much slower

The smaller and less polar a molecule, the quicker it will diffuse across a membrane
SMALL & NON POLAR

Question 16

Factors affecting diffusion

Answer 16

• temperature
• stirring/moving
• SA
• distance / thickness
• size of molecule
• concentration gradient

Question 17

Facilitated diffusion

Answer 17

Diffusion across a membrane through a protein channel

Channel Proteins
- forms pores in membranes
- hydrophilic conditions inside pore are specific to certain small water soluble molecules or ions e.g. sodium or calcium ions
- allow diffusion in or out of cell

Carrier Proteins
- carries larger molecules e.g. glucose and amino acids
- shaped for specific molecules to bind to
- the molecule binding changes the shape of the carrier protein
- causes the molecule to be carried and released on the other side of the membrane
- allow diffusion in or out of cell
- no energy required for facilitated diffusion

Question 18

Osmosis

Answer 18

The passive movement of water from an area of higher water potential to an area of lower water potential, down water potential gradient, across a partially permeable membrane

Question 19

Pure water

Answer 19

0kPa
- highest possible value for WP

Question 20

Water potential

Answer 20

The pressure exerted by water molecules as they collide with a membrane

Question 21

Flaccid

Answer 21

Plant tissue where there is no turgur

Question 22

Crenated

Answer 22

A shrivelled animal cell
- water lost by osmosis

Question 23

Cytolysis

Answer 23

When an animal cell bursts, the plasma membrane breaks because of too many water molecules entering cell

Question 24

Plasmolysed

Answer 24

Plant cell where the contents have shrunk due to loss of water by osmosis
- plasma membrane has separated from the cell wall

Question 25

How does water potential affect osmosis

Answer 25

Water will move by osmosis towards the more negative water potential

Question 26

Active transport

Answer 26

the movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration

Question 27

Why does active transport require ATP

Answer 27

particles are being moved against the concentration gradient

Question 28

Process of active transport

Answer 28

1. The molecule or ion to be transported binds to receptors in the channel of the carrier protein on the outside of the cell
2. On the inside of the cell ATP binds to the carrier protein and is hydrolysed into ADP and phosphate
3. The binding of the phosphate molecule to the carrier protein causes the protein to change shape
4. The molecule or ion is released into the cell
5. The phosphate molecule is released from the carrier protein and recombines with the ADP to form ATP
6. The carrier protein returns to its original shape

Question 29

Endocytosis

Answer 29

1. molecule binds to a receptor
2. This causes the cell surface membrane to fold in- invaginates
3. This requires ATP
4. cell surface membrane fuses with itself to form a vesicle
5. Vesicle e.g. moves through cytoplasm to where it is needed in the cell

Question 30

Exocytosis

Answer 30

1. Vesicle moves towards the cell surface membrane on microtubules, using ATP
2. the vesicle fuses with the cell surface membrane- requires ATP
3. molecules are ejected from the cell via exoxytosis