BB17 Glycolysis

Question 0

Glycolysis is an

Answer 0

energy conservation pathway

Question 1

Glycolysis

Answer 1

• sequence of reactions that converts glucose into pyruvate

* relatively small amount of ATP produced

Question 2

The chemical intermediates in glycolysis are either

Answer 2

six-carbon units
• derivatives of glucose or fructose

three-carbon units
• derivatives of glyceraldehydes, dihydroxyacetone, glycerate, pyruvate

Question 3

All intermediates are phosphorylated with the phosphoryl groups linked as either

Answer 3

esters
anhydrides
••phosphorylation activates these intermediates

Question 4

Stages of glycolysis

Answer 4

Stage 1 – trapping of glucose and its destabilization

Stage 2 – breakdown of a six-carbon unit to create 2 three-carbon units

Stage 3 – generates ATP

Question 5

Stage 1

Answer 5

• traps glucose, forms a compound easily broken down into phosphorylated 3-C units

1. add phosphate to trap and destabilize (glucose-6-phosphate)
2. isomerization
   (fructose-6-phosphate)
3. further phosphorylation (fructose-1,6-bisphosphate)

Question 6

… adds phosphate to glucose to make glucose-6-phosphate

Answer 6

Hexokinase

Question 7

Isomerization of
glucose-6-phosphate to
fructose-6-phosphate
catalyzed by

Answer 7

phosphoglucose isomerise
• opens 6-membered ring
• catalyzes the isomerisation
• promotes the formation of a 5-membered ring
* still 6 carbons – 1 is a side group

Question 8

Second phosphorylation of fructose-6-phosphate to fructose-1,6-bisphosphate catalyzed by

Answer 8

phosphofructokinase

Question 9

Fructose-1,6-bisphosphate

Answer 9

molecule that’s easily cleaved into two 3-carbon units

Question 10

Stage 2

Answer 10

produces two different 3-carbon units that are interconvertible

Question 11

… cleaves
fructose-1,6-bisphosphate
into two 3-carbon units

Answer 11

aldolase

Question 12

Fructose-1,6-bisphosphate is cleaved into

Answer 12

• glyceraldehydes 3-phosphate (on glycolytic pathway)

* dihydroxyacetone phosphate (not on glycolytic pathway)

Question 13

Glyceraldehyde 3-phosphate and dihydroxyacetone phosphate

Answer 13

• can be interconverted in an isomerisation process
• catalyzed by triose phosphate isomerise
(Tim-barrel)

Question 14

Product of stage 2

Answer 14

2 x glyceraldehyde 3-phosphate

Question 15

Stage 3

Answer 15

produces ATP
2x
4 ATP – 2ATP from stage 1
= 2 ATP gained

Question 16

Stage 3

Answer 16

• 5 steps
1. glyaldehyde 3-phosphate
    =>1,3-bisphosphoglycerate 
     (1,3-BPG)
2. 1,3-BPG      
    =>  3-phosphoglycerate
3. 3-phosphoglycerate     
    => 2-phosphoglycerate
4. 2-phosphoglycerate      
    => phosphoenolpyruvate
5. phosphoenolpyruvate   
     =>   pyruvate   +   ATP

forms 2 ATP but repeated = 4 ATP

Question 17

Oxidation of glyceraldehyde 3-phosphate to

Answer 17

1,3-bisphosphoglycerate
• catalyzed by glyceraldehyde 3-phosphate dehydrogenase
• requires reduction of NAD+ to NADH

Question 18

1,3-BPG is a

Answer 18

high-potential phosphorylated product

• more energy released when losing phosphoryl group than in creating bond to make ATP from ADP

Question 19

A phosphoryl group is transferred from 1,3-BPG to ADP, forming

Answer 19

3-phosphoglycerate and ATP

• catalyzed by phosphoglycerate kinase

Question 20

A phosphoryl shift occurs in the conversion of 3-phosphoglycerate to

Answer 20

2-phosphoglycerate
• catalyzed by phosphoglycerate mutase
• 2-phosphoglycerate is less stable

Question 21

A dehydration converts

2-phosphoglycerate to

Answer 21

phosphoenolpyruvate
• catalyzed by enolase
• phosphoenolpyruvate is another high-potential phosphorylated compound

Question 22

A phosphoryl group is transferred from phosphoenolpyruvate to ADP, forming

Answer 22

pyruvate and ATP
• losing phosphoryl = pyruvate in unstable enol form
• rearranges to pyruvate
• catalyzed by pyruvate kinase
• virtually irreversible reaction

Question 23

The net reaction in the transformation of glucose into pyruvate is

Answer 23

• Glucose
• 2Pi
• 2 ADP
• 2 NAD+
=
• 2 Pyruvate
• 2 ATP
• 2 NADH
• 2H+
• 2 H2O

Question 24

One glucose molecule generates

Answer 24

2 molecules of ATP | 2 molecules of pyruvate

Question 25

The reactions of glycolysis

Answer 25

(energetically favourable) are coupled to the synthesis of ATP (energetically unfavourable) via shared chemical intermediate

Question 26

There are 2 positions where ATP is formed

Answer 26

1) 1,3-Bisphosphoglycerate to 3-phosphoglycerate • 1,3-BPG passes phosphate to ADP = substrate level phosphorylation 2) the phosphoenolpyruvate to pyruvate • loss of phosphate makes pyruvate in an unstable enol form • free energy released on the arrangement of pyruvate into its more stable ketone form is more than is needed to produce ATP

Question 27

Glycolysis regulation reflects its dual role in

Answer 27

* degrading glucose to make ATP | * providing building blocks for biosynthetic reactions (ie formation of long chain fatty acids)

Question 28

In metabolic pathways, enzymes catalyzing... are potential sites of control/regulation

Answer 28

essentially irreversible reactions

Question 29

Reactions catalyzed by...are virtually irreversible

Answer 29

* Phosphofructokinase * Hexokinase * Pyruvate kinase

Question 30

Activities of control sites are regulated by

Answer 30

* reversible allosteric control (ie feedback inhibition) – in milliseconds * reversible covalent modifaction (ie phosphorylation) – in seconds * transcriptional control – in hours

Question 31

The most important controlling element in the glycolytic pathway of mammals is

Answer 31

Phosphofructokinase

Question 32

2 features of the phosphofructokinase enzyme

Answer 32

1) regulation of ATP production | 2) regulation to provision of building blocks

Question 33

Phosphofructokinase regulation of ATP production

Answer 33

• allosteric inhibition by high levels of ATP • allosteric activation by high levels of AMP (glycolysis is stimulated as the energy charge falls) • to prevent excess formation of lactate the enzyme is also inhibited by H+ (low pH)

Question 34

Phosphofructokinase is stimulated by

Answer 34

fructose 2,6-bisphosphate | • a molecule produced only when glucose is abundant

Question 35

Phosphofructokinase regulation of provision of building blocks

Answer 35

the enzyme is inhibited by citrate, an early intermediate in the citric acid cycle

Question 36

Other enzymes that regulate glycolysis

Answer 36

* hexokinase | * pyruvate kinase

Question 37

Hexokinase

Answer 37

inhibited by increased levels of glucose 6-phosphate fructokinase 6-phosphate • ie when phosphofructokinase is inactive

Question 38

Fructose 1,6-bisphosphate

Answer 38

activates pyruvate kinase

Question 39

ATP

Answer 39

allosterically inhibits pyruvate kinase | feed-forward activation