Enzyme classes + membrane proteins

Question 1

What do enzyme classes depend on?

Answer 1

The type of reaction they catalyse

Question 2

What are some enzyme classes?

Answer 2

-oxidoreductases (dehydrogenases)
-transferases
-hydrolases
-lyases (synthases)
-isomerases
-ligase (synthetases)

Question 3

Describe oxidoreductases

Answer 3

-often use a cofactor e.g NAD(P)H, FAD
-carry out redox reactions of substrates

Question 4

Describe transferases

Answer 4

-chemical group transfer between molecules - nucleophilic substitutions
-group transfer reactions involve transfer of an electrophilic group from 1 nucleophile to another

Question 5

Describe hydrolases

Answer 5

-cleavage reaction via addition of water
-special form of transfer reactions using water as acceptor

Question 6

Describe lyases

Answer 6

-addition or removal of groups to form a double bond

Question 7

Describe isomerases

Answer 7

-interconversion of isomeric forms of compounds

Question 8

What is the process called when interconverting L-amino acids to D-amino acids?

Answer 8

-racemization
-catalysed by a racemase enzyme
-need 4 different groups around carbon (not glycine)

Question 9

Describe ligases

Answer 9

-joining of 2 molecules requiring a chemical energy store, usually ATP

Question 10

In ligase reactions, what does pyruvate carboxylase require?

Answer 10

-a biotin cofactor
-binds CO2 via use of ATP + releases it to react with pyruvate

Question 11

What is the function of cell and organelle membranes?

Answer 11

-separate cells from external environment
-form boundaries for organelles within cells

Question 12

What are key properties of biological membranes?

Answer 12

-high selective permeability
-fluid + asymmetric organisation
-highly variable lipid + protein composition

Question 13

What are biological membranes permeable to?

Answer 13

-gases
-small uncharged polar molecules

Question 14

What are biological membranes slightly permeable to?

Answer 14

Small uncharged polar molecules (water)

Question 15

What are biological membranes impermeable to?

Answer 15

-large uncharged polar molecules
-ions
-charged, polar molecules

Question 16

What can having different types of lipids in the membrane influence?

Answer 16

-curvature
-fluidity
-thickness

Question 17

In cholesterol, which parts are hydrophobic and which are hydrophilic?

Answer 17

-OH is hydrophilic
-rest of molecule is hydrophobic

Question 18

Is bilayer formation favourable or not?

Answer 18

It’s a favourable spontaneous process

Question 18

What is a biomolecular sheet formed from?

Answer 18

-from glycolipids + phospholipids in aqueous media
-hydrophilic part faces solvent, hydrophobic parts in middle
-one side = a leaflet

Question 18

What parts of cholesterol interact with which parts of the phospholipid?

Answer 18

-hydroxyl at C3 interacts with phospholipid head
-steroid rings + tail interact with fatty acid chains

Question 18

What is bilayer thickness influenced by?

Answer 18

-lipid composition
-shorter tail = thinner bilayer
-longer tail = thicker bilayer

Question 18

What can thicken the bilayer membrane?

Answer 18

Cholesterol

Question 19

What can make the bilayer membrane thinner?

Answer 19

-lipid tails can overlap
-cholesterol prevents this

Question 20

What determines the membrane fluidity and how?

Answer 20

-fatty acid composition + cholesterol content
-cholesterol packs alongside fatty acid chains, stiffening the structure