B2.1 Membranes and membrane transport

Question 1

Function of membrane (2)

Answer 1

separate cytoplasm from external environment

separate interior of organelles from each other + from cytosol

Question 2

Structure of phospholipids (3)

Answer 2

same as triglyceride but phosphate joins to 3rd OH instead of fatty acid

2 non-polar fatty acid chains

amphipathic molecules - hydrophilic phosphate head, hydrophobic fatty acids

Question 3

Define amphipathic molecules

Answer 3

molecules with both hydrophobic and hydrophillic properties

Question 4

Reasons for formation of phospholipid bilayer or micelle (2)

Answer 4

hydrophobic tails point inward + away from water/aqueous environment

hydrophilic heads point outward + towards aqueous environment

Question 5

Lipid bilayers as barriers (3)

Answer 5

lipid-soluble non-polar molecules are permeable

ions are impermeable

large uncharged polar molecules (glucose) are mostly impermeable

Question 6

Why are ions impermeable to a lipid bilayer (2)

Answer 6

ions have + and - charges so will interact will polar water

hydrophobic tails of bilayer repel hydrophilic ions

Question 7

Why are large uncharged polar molecules mostly impermeable to a lipid bilayer (2)

Answer 7

mostly hydrophillic due to being polar

hydrophobic tails of bilayer repel hydrophillic molecules

Question 8

Why are lipid-soluble non-polar molecules permeable to a lipid bilayer

Answer 8

no polarity = not repelled by hydrophobic tails

Question 9

Factors which affect permeability of biological membranes (2)

Answer 9

size of molecule - smaller molecules more likely to pass

hydrophobic nature - hydrophobic molecules more likely to pass through instead of polar molecules

Question 10

Define simple diffusion

Answer 10

movement of molecules from a region of high concentration to a region of low concentration down a concentration gradient

Question 11

Movement of oxygen in body as an example of simple diffusion (3)

Answer 11

red blood cells transport oxygen from lungs to body’s cells

oxygen diffuses from alveoli to RBCs in capillaries surrounding alveoli

tissues - oxygen diffuses from high concentration in RBC to low concentration in cells

Question 12

Movement of carbon dioxide in body as an example of simple diffusion (3)

Answer 12

CO2 diffuses from cells (high CO2 concentration) to blood (lower CO2 concentration)

CO2 reaches lungs

CO2 diffuses from blood (high CO2 concentration) to alveoli (low CO2 concentration)

Question 13

2 types of membrane proteins (2)

Answer 13

integral proteins

peripheral proteins

Question 14

Features of integral proteins (4)

Answer 14

embedded in lipid bilayer (both layers) - difficult to isolate

amphipathic molecules - hydrophillic amino acids interact with hydrophillic head, hydrophobic amino acids interact with hydrophobic tail

channel proteins - hydrophilic interior + hydrophobic exterior allows charged particles to pass through by diffusion

carrier proteins - involved in active + passive transport by changing shape

Question 15

Features of peripheral proteins (3)

Answer 15

hydrophilic

found on surface of membrane

interact with hydrophilic regions of integral proteins + phospholipid heads

Question 16

Functions of membrane proteins (4)

Answer 16

Transport

Recognition

Receptors

Enzymes

Question 17

Transport as a function of membrane proteins (2)

Answer 17

facilitate movement of molecules inside + outside cell

channel + carrier proteins

Question 18

Recognition as a function of membrane proteins (2)

Answer 18

help in cell-cell recognition

distinguishes immune system from self and non-self cells

Question 19

Receptors as a function of membrane proteins (2)

Answer 19

bind to signaling molecules like hormones + neurotransmitters

binding triggers a chain of intracellular reactions

Question 20

Enzymes as a function of membrane proteins

Answer 20

catalyse reactions