glycolysis

Question 1

what is anabolism?

Answer 1

smaller molecules coveted to macromolecules
requires energy

macromolecules include polysaccharides, proteins, lipids and nucleic acids

smaller = sugars, amino acids, fatty acids

Question 2

what is catabolism?

Answer 2

macromolecules converted to smaller molecules
releases energy

Question 3

purpose of starch degradation

Answer 3

break down starch storage to glucose to get energy for growth during germination

series of hydrolysis reactions

Question 4

process of starch degradation

Answer 4

a-amylase cleaves alpha 1,4 bonds
- breaks them internally (endohydrolase)

limit dextrinase cleaves alpha 1,6 branch linkages

b-amylase releases maltose
cleaves alpha 1,4 from non-reducing end (exohydrolase)

maltase hydrolyses maltose to 2 glucose molecules

Question 5

outline glycolysis

Answer 5

major pathway where monosaccharides are oxidised
aerobically or anaerobically

occurs in cytoplasm and chloroplasts

starts with glucose (or other monosaccharides)
produces 2 pyruvate molecules per glucose

Question 6

why does glycolysis occur in a pathway and not a single reaction?

Answer 6

pathway is more efficient
in a single reaction, lots of energy wasted

energy released in several smaller steps
multiple reactions coupled to ATP formation
more chemical opportunities
more versatile and flexible

Question 7

step one

Answer 7

phosphorylation of glucose
- irreversible reaction

catalysed by hexokinase
cofactor = magnesium

1 ATP hydrolysed and used per glucose = ADP

= glucose 6 phosphate

Question 8

step 2

Answer 8

isomerisation of G6P to fructose-6-P
isomers of each other - same atoms arranged in a different way

reversible isomerisation reaction

catalysed by phosphoglucose isomerase

= fructose-6-phosphate

Question 9

step 3

Answer 9

phosphorylation of fructose-6-phosphate
irreversible

1 ATP hydrolysed

catalysed by phosphofructose kinase
cofactor = magnesium

= fructose-1,6bisphosphate

Question 10

step 4

Answer 10

cleaving fructose 1,6 bisphosphate
reversible

splitting bond between carbon 3 and 4
two 3 carbon molecules formed (2 triodes)

= ketose phodphate - dihydroxyacetone phosphate
= aldose phosphate - glyceraldhyde-3-phosphate

Question 11

step 5

Answer 11

isomerisation of DHAP to G3P
reversible

interconverting 3 trioses

catalysed by triose phosphate isomerase

= 2 G3P molecules for 2nd stage

1 from fructose 1,6 bisphosphate
1 from DHAP

Question 12

step 6

Answer 12

oxidation and phosphorylation of G3P
reversible

catalysed by glyceraldehyde-3-phosphate dehydrogenase

G3P oxidised and phosphorylated to 1,3-bisphosphoglycerate

H+ removed during oxidation transferred to the H+ carrier
= reduced NAD

Question 13

step 7

Answer 13

substrate level phosphorylation
reversible

catalysed phosphoglycerate kinase
cofactor = magnesium

1 ATP per 1,3bpg made = total 2 ATP

= 3-phosphoglycerate

Question 14

step 8

Answer 14

isomerisation reaction
reversible

catalysed by phosphoglycerate mutase
cofactor = magnesium

3-phosphoglycerate isomerised

= 2-phosphoglycerate

Question 15

step 9

Answer 15

dehydration reaction
reversible

catalysed by enolase
cofactor = magnesium

2-phosphoglycerate converted

= phosphoenolpyruvate

Question 16

step 10

Answer 16

substrate level phosphorylation
irreversible

catalysed by pyruvate kinase

1 ATP per PEP = total 2 ATP

= pyruvate

Question 17

why is glycolysis controlled?

Answer 17

operates at a rate that meets cellular needs for
energy
metabolites for anabolic processes

major point in step 3 - phosphofructokinase

Question 18

role of phosphofructokinase

Answer 18

major control point in glycolysis
regulated by ATP

activity inhibited by ATP

Question 19

how does ATP inhibit phosphofructokinase

Answer 19

ATP binds at 2 sites
- catalytic site - phosphoric transfer to fructose 6 phosphate
- allosteric (regulatory) - different from active site

Question 20

effects of phosphofructokinase inhibition

Answer 20

accumulation of fructose 6P and glucose 6P
inhibition of hexokinase

less glucose phosphorylated into glucose 6P
lower rate of glucose entry into glycolysis

Question 21

what determines inhibition/activation

Answer 21

ATP levels high in cell = inhibited
less glucose into pathway

ATP levels low (AMP high) = activated PFK
so more ATP produced

Question 22

inhibition/activation

Answer 22

inhibition
ATP binding at allosteric sites
lower affinity of catalytic sites for fructose 6P
= lower activity

activation
AMP competes with ATP for binding at allosteric site
AMP reverses effect of ATP
allosteric activation of PFK