Glycolysis-12

Question 1

What is Glycolysis?

Answer 1

Breakdown of glucose by series of connected reactions

Question 2

What is the purpose of Glycolysis?

Answer 2

1. The making of energy carrying molecules such as ATP
2. The making of pyruvate, the end product in glycolysis, to continue further in downstream metabolic pathways (i.e citric acid)

Question 3

Glycolysis

Answer 3

The pathway of Glycolysis occurs in the cytoplasm of the cell

Once pyruvate is generated (the end product of glycolysis) it will be converted into

With oxygen,
Go through aerobic oxidation,
product is Acetyl-CoA, 
Acetyl-CoA go through the citric acid, 
products of Acetyl-CoA go onto the electron transport chain and then oxidative phosphorylation 

Without oxygen,
Go through Anaerobic alcoholic fermentation,
Carbon Dioxide and Ethanol

If there isn’t enough oxygen,
Anaerobic homolactic fermentation occurs
we will form lactic acid

Question 4

What are the Fates of Glucose?

Answer 4

Glucose can either be stored as glycogen, starch or sucrose

2. Go through oxidation via glycolysis to form Pyruvate
3. Go through oxidation via pentose phosphate pathway to form Ribose-5-phosphate

Question 5

You need oxygen for Glycolysis to happen True/False

Answer 5

False

Glycolysis can occur with or without oxygen

Question 6

Nerve cell and glucose

Answer 6

Nerve cells in the brain rely predominantly on glucose as an energy source

Question 7

What are the 2 stages of Glycolysis Metabolism?

Answer 7

1.) Glycolysis

2. ) a.) Fermentation
   - occurs in the absence of O2 in the cytoplasm
   - partial breakdown of glucose

OR

b. ) Cellular Respiration
- occurs in the presence of O2 in the mitochondria
- complete breakdown of glucose

Question 8

Glycolysis Metabolism under anaerobic and aerobic conditions:

Answer 8

Under anaerobic conditions (in the absence of O2) pyruvate is converted by a process known as fermentation, into lactate or ethanol in the cytoplasm

Under aerobic conditions, it may enter the mitochondria where it will be oxidized in the presence of O2 to become CO2 and H2O

Generating an additional 30-34 ATP molecules
-Cellular respiration

Cellular respiration consists of 2 path ways

1. Krebs cycle
2. Oxidative Phosphorylation

Question 9

What are the possible fates of pyruvate produced from glycolysis in the 2nd stage of glucose metabolism?

depending on the availability of O2

In Anaerobic conditions

Answer 9

Pyruvate is fermented in the cytoplasm to

1. Alcohol
2. Lactate

Question 10

What are the 2 stages in cellular respiration?

Answer 10

1. Krebs cycle (citric acid cycle)

2. Oxidative Phosphorylation

Question 11

What are the possible fates of pyruvate produced from glycolysis in the 2nd stage of glucose metabolism?

depending on the availability of O2

In Aerobic conditions

Answer 11

Pyruvate enters the krebs cycle in the mitochondria and be oxidized in the presence of O2 to become CO2 or H2O

Question 12

Definition of Glycolysis:

Answer 12

Glycolysis is a process whereby a glucose molecule is broken down in the absence of O2 (anaerobic respiration) into 2 pyruvate molecules, producing a net yield of 2 ATP molecules in the process

Occurs in the cytoplasm

O2 comes into the picture after glycolysis

Question 13

What occurs in the first stage of glycolysis? How many reactions are there?

Answer 13

Stage 1 investment

1-5 reactions

It is a preparatory stage in which the hexose glucose is phosphorylated and cleaved to yield two molecules of the triose glyceraldehyde-3-phosphate. Stage 1 consumes 2 ATPs

Uses 2 ATPs in a kind of energy investment

Question 14

What occurs in the second stage of glycolysis? How many reactions are there?

Answer 14

Harvest
reactions 6-10

The 2 molecules of glyceraldehyde-3-phosphate are converted to pyruvate, with concomitant generation of 4 ATPs, Stage 2 produces 4 ATPs. Glycolysis therefore has a net profit of 2 ATPs per glucose

Question 15

Overall Glycolysis reaction summary

Answer 15

Glucose + 2NAD + 2ADP +2P –> 2NADH + 2 pyruvate +2 ATP+ 2H2O + 4H+

Question 16

10 reactions of Glycolysis:

Answer 16

1. Phosphorylation of glucose by ATP to make glucose 6-phosphate

2-3 Rearrangement by a second ATP phosphorylation

4-5 The six carbon molecule is split into two three-carbon molecules of G3P

6. Oxidation followed by phosphorylation produces 2 NADH molecules and gives 2 molecules of BPG (1,3-biphosphoglycerate), each with one high-energy phosphate bond
7. Removal of high-energy phosphate by 2 ADP molecules produces 2 ATP molecules and gives 2 3PG (3-phosphoglycerate) molecules

8-9 Removal of water gives 2 PEP molecules (phosphoenolpyruvate)

10. Removal for high energy phosphate by 2 ADP molecules produces 2 ATP molecules and gives 2 pyruvate molecules

Glucose + 2NAD + 2ADP +2P –> 2NADH + 2 pyruvate +2 ATP+ 2H2O + 4H+

Question 17

How is the energy present in glucose harvested in glycolysis?

Answer 17

First energy investment
-2 ATP molecules is used to convert glucose to the highly reactive fructose-1, 6-bisphosphate

-Fructose-1, 6-biphosphate splits into 2 smaller molecules of glyceraldehyde-3-phosphate (G3P)

Question 18

What is the enzyme that catalyzes the 1st step of glycolysis?

Answer 18

Hexokinase enzyme
(transferase)

transfer of phosphate from ATP to glucose to make glucose-6-phosphate

There is a conformation change upon glucose binding

“closing” of two lobes draws the substrates glucose and ATP together

After the product glucose-6-phosphate is formed, the conformation goes back to starting state

Question 19

What are the enzymes and their products involved in the 10 reactions of Glycolysis? Investment and Harvest stages

Answer 19

Investment
1. Hexokinase
Function: Transfer of a phosphoryl group from ATP to glucose
Products: From glucose to Glucose-6-phosphate

2. Glucose-6-phosphate isomerase
   Function: Isomerization (changing of the structure of the chemical)
   Products: Glucose-6-Phosphate to Fructuose-6-phosphate
3. Phospho-fructose kinase
   Function: Transfer of a phosphoryl group from ATP to fructose 6-phosphate
   Products: Fructose-6-phosphate to Fructose 1,6 bisphosphate

4- Aldolase
Function: C-3-C-4 bond cleavage, yielding two triose phosphates
Products: Fructose 1,6 bisphosphate to Dihydroxy acetone phosphate and Glyceraldehyde 3 phosphate

5-Triose phosphate isomerase (rapidly Isomerized)
Function: Rapid interconversion of triose phosphates
Products: From Dihydroxyacetone Phosphate to Glyceraldehyde 3 phosphate (because Dihydroxyacetone phosphate cannot be readily degraded like Glyceraldehyde, not in the useable form)

6-Glyceraldehyde 3-phosphate dehydrogenase
Function: Oxidation and phosphorylation, yielding a high energy mixed-acid anhydride
Products: Glyceraldehyde 3 phosphate to 1,3-Bisphosphoglycerate

Harvest
7-Phosphoglycerate kinase
Function: Transfer of high energy phosphoryl group to ADP, yielding ATP (Made one ATP)
Products: 1,3-Bisphosphateglycerate to 3 Phosphoglycerate

8-Phosphoglycerate mutase
Function: Intramolecular phosphoryl-group transfer
Products: 3-phosphoglycerate to 2-phosphoglycerate

9-Enolase
Function: Dehydration to an energy-rich enol ester
Products: 2-Phosphoglycerate to Phosphoenolpyruvate

10- Pyruvate kinase
Function: Transfer of high energy phosphoryl group to ADP yielding ATP
Products: Phosphoenolpyruvate to pyruvate

Question 20

When in glycolysis does the reaction use up ATP?

Answer 20

During the investment stage

In the 1st reaction, when hexose kinase converts glucose into glucose-6-phosphate by transfer of a phosphoryl group from ATP to glucose

In the 3rd reaction, when Phospho-fructose kinase transfer a phosphoryl group from ATP to Fructose 6-phosphate to form Fructose 1,6 bisphosphate

Question 21

When in glycolysis does the reaction makes ATP?

Answer 21

During the Harvest stage

In the 7th reaction, when Phosphoglycerate kinase converts 1,3-Bisphosphoglycerate to 3-Phosphoglycerate. A phosphoryl group is transferred to ADP yielding ATP

In the 10th reaction, when Pyruvate kinase converts Phospho enoyl pyruvate to pyruvate .A phosphoryl group is transferred to ADP yielding ATP

Question 22

Function of Phosphoglucose isomerase (Glucose-6-phosphate isomerase):

Answer 22

During the 2nd step of glycolysis:
Glucose-6-phosphaye-> Fructose-6-phosphate

Molecular changes of glucose-6-phosphate in the active site of phosphoglucose isomerase

Question 23

How is the energy present in glucose harvested in glycolysis?

Answer 23

The 2 G3P molecules undergo a series of reactions that result in the generation of 4 ATP and 2 NADH
Therefore, glycolysis results in a net production of 2 ATP and 2 NADH per glucose molecules

Question 24

What is NADH?

Answer 24

Nicotinamide adenine dinucleotide hydride or also known as coenzyme 1 (NOT co enzyme A)

NADH is a co enzyme without which many enzymes are useless

Question 25

What is the significance of NAD+?

Answer 25

NAD+ (from the glyceraldehyde-3-phosphate dehydrogenase) provides the oxidizing power for glycolysis to occur in the absence of O2. As such, in order for glycolysis to occur continuously, NAD+ must be continuously be regenerated - in the presence of O2, NAD+ would be regenerated via oxidative phosphorylation (later part of cellular respiration) - in the absence of O2, NAD+ would be regenerated via fermentation

Question 26

Energy input and Energy output summary of the Glycolysis reaction:

Answer 26

Energy input: 2 ATP molecules Energy output: 4 ATP molecules- net yield 2 ATP molecules 2 NADH molecules Pyruvate molecules

Question 27

What is the purpose of glycolysis?

Answer 27

To produce ATP (e.g muscle contraction)

Question 28

Can ATP and AMP regulate glycolysis?

Answer 28

- Too much ATP (energy-rich): INHIBIT glycolysis | - Too much AMP (energy-poor): ACTIVATE glycolysis

Question 29

What are the 3 regulatory points at the enzyme level? Regulation of Glycolysis

Answer 29

1. Hexokinase (HK) 2. Phosphofructokinase-1 (PKJ) 3. Pyruvate kinase (PK)

Question 30

What are the molecules that will inhibit or activate glycolysis?

Answer 30

Activate: - too much AMP - too much 2,6-fructose bisphosphate - too much 1,6-fructose bisphosphate Inhibit: - too much ATP - too much citrate - too much Glucose-6-phosphate - No AMP

Question 31

Examples of other sugars that can enter the glycolytic pathway:

Answer 31

1- Fructose 2-Galactose 3-Mannose 4-Glycerol (can be converted to an intermediate molecule in glycolysis)

Question 32

What are the diseases associated with the glycolysis pathway? Glycolysis defects

Answer 32

For patients with deficient levels of hexokinase and pyruvate kinase enzymes, the oxygen binding to their haemoglobin is altered For hexokinase deficient cases, the O2 binding curve is shifted to the left of normal That results in too tight association, so O2 cannot be sufficiently released (bind too much to oxygen and very tightly, cannot release the oxygen from the red blood cell to the rest of the body) For pyruvate kinase deficient cases, the O2 binding curve is shifted to the right of normal. That results in too loose association , so O2 cannot be sufficiently taken up (bind too loosely, loose association, oxygen cannot be taken up efficiently)

Question 33

How does Hexokinase and pyruvate kinase deficiency lead to abnormal O2 haemoglobin binding?

Answer 33

2,3-bisphosphoglycerate (2,3-BPG) is the byproduct of the eight reaction in glycolysis 2,3-BPG directly binds to empty haemoglobin and inhibits O2 binding Low hexokinase levels -> lower 2,3 BPG, so O2 binding to haemoglobin is raised (the production of the products down the reaction will be stopped) Low pyruvate kinase -> Higher 2,3-BPG, O2 binding to haemoglobin is decreased because 2,3-BPG INHIBITS O2.

Question 34

What occurs during the cooperative binding of oxygen?

Answer 34

Uptake of oxygen by a heme subunit results in a shift in the deoxyhaemoglobin structure, and 2,3-DPG is expelled. This structure change facilitates the binding of oxygen by the other 3 heme subunits Binding of oxygen at one site in the haemoglobin tetramer influence the oxygen binding properties at the other sites

Question 35

What is 2,3 DPG (diphosphoglycerate) and its function/ importance?

Answer 35

2,3-DPG is the byproduct of glycolytic pathway (glycolysis) when ATPs are produced in RBCs. -regulates the structure and function of haemoglobin

Question 36

What happens when there is too less 2,3-DPG and too much?

Answer 36

When 2,3-DPG is low (because hexokinase is deficient) then our haemoglobin binds oxygen too tightly and our tissues cannot get oxygen Too high, 2,3-DPG is high (pyruvate kinase is deficient) then our haemogobin binds oxygen too loosely and cannot draw enough of it from the lungs

Question 37

How does 2,3-DPG change the structure of haemoglobin?

Answer 37

B-chain of haemoglobin move closer when oxygenated, 2,3-DPG is pushed out B-chains are pulled apart when O2 is unloaded, permitting entry of 2,3-DPG resulting in lower affinity of O2