glycolysis

Question 1

describe glycolysis

Answer 1

its the central pathway for carbohydrate metabolism, because all other sugars can be converted to glucose

its ancient process

its sued by vast array of organisms such as mammals, bacteria and plants

its anaerobic process, as evolved before lots oxygen present in earths atmosphere

Question 2

give a quick overview of glycolysis what it uses and produces

Answer 2

it involves breakdown of glucose (c6) into 2 pyruvate molecules (c3), resulting in 2 molecules of ATP being produced

Question 3

where does glycolysis occur

Answer 3

in cytosol of mammalian cells

Question 4

how many reactions are there in glycolysis

Answer 4

10 which are essentially the same in all cells and are divided into 2 phases

Question 5

summarise the 2 phases of glycolysis

Answer 5

phase 1: converts glucose into two glyceraldehyde 3-phosphate molecules and is energy requiring (catabolic)

phase 2: generates two pyruvate molecules and is energy producing (anabolic)

Question 6

name the products of glycolysis

Answer 6

2 pyruvate
4 ATP
2 NADH
2 water

Question 7

what are the 3 irreversible reactions in glycolysis pathway and why need them

Answer 7

needed as allow process to move forward and progress

1. Glucose —>Glucose-6-phosphate​

Hexokinase​

2. Fructose-6-phosphate—-> Fructose-1,6-bisphosphate​

Phosphofructokinase​

3. Phosphoenolpyruvate —-> Pyruvate​

Pyruvate kinase

Question 8

describe the hexokinase reaction 1

Answer 8

glucose is irreversibly phosphorylated into glucose-6-phosphate, this is powered by ATP hydrolysis (the transfer of a phosphate group from ATP onto other molecule is called phosphate transfer)

its important to trap glucose inside cell

Question 9

describe the phosphoglucose isomerase reaction 2

Answer 9

this is the second step in the isomerisation of glucose-6-phosphate to fructose-6-phosphate

the reaction is the conversion of aldose sugar into ketose sugar
- aldose = aldehyde group
- ketose = ketone group

Question 10

describe the phosphofructokinase reaction 3

Answer 10

fructose-6-phosphate is phosphorylated again to generate fructose-1,6-bisphophate

thus is the 2nd phosphoryl transfer reaction of glycolysis

Question 11

what does allosteric mean

Answer 11

enzymes that have an additional binding site for effector molecules other than the active site.

• ATP is an allosteric effector
• high levels inhibit the enzyme
• low levels activate it

Question 12

how is phosphofructokinase an isoenzyme and allosteric

Answer 12

it exists as a tetramer:
- the tetramer is composed of L and M subunits
- M4, M3L, M2L2, and L4 all exist
- combinations of these subunits are called isoenzymes
- muscles are rich in M4
liver is rich in L4

Question 13

describe aldolase reaction 4

Answer 13

fructose -1,6-bisphosphate is cleaved into two 3-carbon fragments:

• dihydroxyacetone phosphate - a ketose
• glyceraldehyde 3-phiosphate - an aldose

Question 14

describe the triose phosphate isomerase reaction 5

Answer 14

the subsequent reaction uses only glyceraldehyde 3-phosphate.

• dihydroxyacetone phosphate (DHAP) is converted to glyceraldehyde-3-phosphate. when this is used, the equilibrium is restored by conversion of DHAP to glyceraldehyde 3-phosphate

Question 15

describe a summary of phase 1

Answer 15

its a catabolic (energy investing) phase as 2 molecules of ATP have been used

glucose is converted to two molecules of glyceraldehyde 3-phosphate. the key intermediate in this reaction is fructose-1,6-bisphosphate. the enzyme that catalyses the reaction, phosphofructokinase, is subject to allosteric control

Question 16

describe glyceraldehyde 3-phosphate dehydrogenase reaction 6

Answer 16

its the first reaction that begins conversion to pyruvate, involving oxidation of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate. this reaction involves adding an inorganic phosphate group

NAD+ is reduced to NADH

Question 17

describe phosphoglycerate kinase reaction 7

Answer 17

1,3-bisphosphoglycerate is converted to 3-phosphoglycerate by phosphoglycerate kinase

this step involves another reaction where ATP is produced by ADP phosphorylation. As 1,3-bisphosphoglycerate transfers a phosphate group to ADP known as substrate level phosphorylation.
the reaction is catalysed by phosphoglycerate kinase and pays off the ATP dept created by priming reactions in the first place

Question 18

describe phosphoglyceromutase reaction 8

Answer 18

3-phosphoglycerate is isomerized to 2-phosphoglycerate. this is by a mutase catalysing the migration of a functional group within the substrate

Question 19

describe enolase reaction 9

Answer 19

enolase = phosphopyruvate hydrolase

2-phosphoglycerate lose one water molecule, forming phosphenolpyruvate

enolase catalyses the reaction and requires a mg2+ cofactor. this requires 3 isoenzymes:

• alpha alpha or NNE (non-neural enolase), found in tissues such as liver, brain, kidney, spleen, adipose. and is present at some level in normal human cells
• beta beta or MSE (muscle-specific enolase), enzyme largely restricted to muscle where present at very high levels
• gamma gamma or NSE (neuron-specific enolase), in very high levels in neurons and neural tissue, accounting for as much as 3% of total soluble protein. its expressed at much lower levels in mammalian cells

Question 20

describe pyruvate kinase reaction 10

Answer 20

phosphoenolpyruvate contains a high energy bond. as transfers its phosphate group to ADP producing ATP and pyruvate (substrate level phosphorylation)

this reaction is catalysed by pyruvate kinase

Question 21

give a summary of phase 2

Answer 21

its anabolic (energy producing)

2 pyruvate molecules produced for each molecule of glucose entering pathway. these reactions involve production of two NADH molecules and net production of two ATP for each glucose molecule

Question 22

what are the metabolic fates of NADH and pyruvate produced in glycolysis in mammals

Answer 22

NADH can be recycled via aerobic or anaerobic pathways

• aerobic (oxygen present), NAD is reoxidised in electron transport pathway, making ATP in oxidative phosphorylation. three ATP molecules made from one NADH molecule
• anaerobic (no oxygen), NADH is reoxidized by lactate dehydrogenase (LDH) which provides NAD+ for more glycolysis

Question 23

describe the anaerobic metabolism of pyruvate

Answer 23

under anaerobic conditions, such as actively contracting muscle, the most important pathway for regeneration of NAD+ is reduction of pyruvate to lactate by lactase dehydrogenase

Question 24

describe the aerobic metabolism of pyruvate

Answer 24

aims to get pyruvate into citric acid cycle where the products of glucose can be completely oxidised, leading to production of many ATP

the 2 steps required for this are:
- convert pyruvate into acetyl-CoA
- put the acetyl CoA into the citric acid cycle