B1.2 Membrane and membrane transport

Question 1

plasma membrane is made of

Answer 1

phospholipids

Question 2

phospholipids are (properties)

Answer 2

amphipathic

Question 3

amphipathic meaning

Answer 3

both hydrophilic and hydrophobic

Question 4

structure of phospholipid

Answer 4

• hydrophilic phosphate head
• two hydrophobic hydrocarbon tails

Question 5

why is phospholipid hydrophilic?

Answer 5

• Oxygen on RHS has a negative charge → hydrogen can bond
• Polar → phosphate head can bond to it

Question 6

Why is phospholipid hydrophobic?

Answer 6

• Double bond oxygen → slightly positive?
• No charge

Question 7

structure of plasma membrane in terms of phospholipids

Answer 7

phospholipid bilayer

heads facing out, tails facing in towards one another

Question 8

the plasma membrane is…

Answer 8

selectively/partially permeable

Question 9

what can pass through using simple diffusion?

Answer 9

• small, soluble + non-polar (e.g. oxygen, CO2)
• small & polar (e.g. water, glucose) but slowly

Question 10

what cannot pass through using simple diffusion?

Answer 10

• large molecules
• charge molecules (repulsion with the hydrophobic tails)

Question 11

what is the fluid mosiac model?

Answer 11

• The structure of the membrane is flexible, adaptable and in motion
• phospholipids have freedom of movement in the horizontal plane → can move around each other, and can flow with pressure, yet do not allow the membrane to break
• The individual phospholipids are attached to each other by weak attractions, the cumulative effect of which is a very strong membrane

Question 12

examples of integral proteins and application of such integral proteins

Answer 12

• enzymes: sites for chemical reactions
• pumps: for active transport of molecules

Question 13

glycoproteins are made up of

Answer 13

carbohydrate + protein

• combine with carbohydrates to make chemical receptors

Question 14

glycolipids are made up of

Answer 14

carbohydrates + lipids

Question 15

Glycocalyx is made up of

Answer 15

many glycoproteins and glycolipids

Question 16

Usage of glycocalyx

Answer 16

prevents plasma cells from binding to capillary wall (if so have blood clot)

Question 17

Use of peripheral proteins

Answer 17

act as receptors to “recognise” other cells

Question 18

Affect of cholesterol

Answer 18

affects membrane fluidity at different temperatures

Question 19

use of channel proteins

Answer 19

carry molecules through the plasma membrane (charged molecules)

For charged molecules to go through, channel proteins (facilitated diffusion) or pump proteins (active transport) are needed.

Some polar molecules also need these to go through faster (e.g. aquaporin for water is osmosis)

Question 20

structure of aquaporin + charge

Answer 20

Aquaporin

• very narrow
• positively charged → ensures that proton (H+) can’t go through as it is repelled

Question 21

How do the channel proteins make sure that it is specific?

Answer 21

the diameter of a pore and the chemical properties of its sides ensure that only one type of particle passes though — e.g. sodium ions/potassium ions, but not both

Question 22

explain what are protein pumps and how they work

Answer 22

• Protein pumps are specific to their molecules
• The molecules binds to the active site of the pump
• The release of energy from ATP results in a conformational change in the shape of the protein pump
• The molecule is pushed to the other side of the membrane

Question 23

active transport (definition)

Question 24

examples of active transport

Answer 24

• nephron (reabsorption of glucose)
• small intestine (to absorb extra nutrients)
• roots in plants (uptake of ions)

Question 25

exocytosis (definition)

Answer 25

export of macromolecules from the cell

Question 25

endocytosis (definition)

Answer 25

import of macromolecules

Question 26

phagocytosis (definition)

Answer 26

ingestion of solid molecules

Question 27

pinocytosis (definition)

Answer 27

ingestion of liquids and solutes