Glycolysis, Fermentation, Gluconeogenesis

Question 1

Step 1

Answer 1

Hexokinase
Kinases - Adds a phosphate! (All kinases EC2 Transferases)
Process is regulated in step 1
Exhibits induced fit - Excludes all water from active site (prevents hydrolysis of ATP)
ATP used up in this step!
Mg2+ is required for metal ion catalysis by charge shielding

Question 2

What is significant about G6P being phosphorylated in Step 1 of Glycolysis?

Answer 2

Whenever G6P is phosphorylated, it cannot pass through the GLUT4 transporter, so it is trapped in cytosol

Question 3

Step 2

Answer 3

Phosphoglucose Isomerase (PGI)
GABC (occurs through enediol intermediate)

Question 4

How many ATP are used up during the “Prep Phase” of Glycolysis?

Answer 4

2 ATP used

Question 5

Step 3

Answer 5

Phosphofructokinase (PFK-1)
Irreversible
ATP used up in this step!
Mg2+ is required for metal ion catalysis by charge shielding

Question 6

Step 4

Answer 6

Aldolase
Lyase (splits F-1,6-P down the middle)
All Lyases (EC4) are reversible
Aldol Cleavage (reverse rxn is aldol condensation)
KNOW MECHANISM - Alternate pathway through formation of a covalent adduct

Question 7

Step 5

Answer 7

Triosephosphate Isomerase (TIM)
To end the prep phase of glycolysis, you will have 2 GAPs
GABC (tautomerization) (occurs through enediol intermediate)
Equilibrium favors DHAP, but GAP is made, thanks to Le’Chatlier’s principle
TIM is a kinetically “perfect” enzyme

Question 8

Step 6

Answer 8

GAP DH
There are 2 GAP molecules that head into “payoff phase”, but we look at the process “per GAP”
GAPDH generates the first high energy intermediate (1,3-BPG), so ATP is made in Step 7 by Substrate Level Phosphorylation (SLP)
Generates NADH per GAP (2 total per glucose molecule)
Arsenic is very similar structurally to Phosphorous, thus Arsenic can poison GAPDH & disrupt ATP formation
Has an unfavorable deltaG (+), thus it is coupled with PGK (step 7)
Know Mechanism! - Cys Thiol in Active site

Question 9

Step 7

Answer 9

Phosphoglycerate Kinase (PGK)
First ATP generation step in glycolysis (2 ATP produced per glucose)
Exhibits induced fit
Coupled to GAPDH (step 6), to give overall process (-) deltaG

Question 10

Step 8

Answer 10

Phosphoglycerate Mutase (PGM)
Changes conformation of Phosphoglycerate to a more useful form
Has a Phosphohistidine residue in active site

Question 11

Step 9

Answer 11

Enolase
Lyase (EC4)

Question 12

Step 10

Answer 12

Pyruvate Kinase
Transfer high energy phosphate (from PEP) to ADP, making ATP
Substrate Level Phosphorylation (SLP)
Kinases (EC2 Transferases)

Question 13

What 3 things do you think of a Dyhydrogenase?

Answer 13

1. Hydride Transfer
2. EC1 Oxidoreductase
3. Look for a Redox Cofactor

Question 14

How many ATP are produced in the “payoff phase” of glycolysis per glucose, made by Substrate Level Phosphorylation?

Answer 14

4 ATP per glucose

Question 15

Describe Substrate-Level Phosphorylation (SLP)

Answer 15

Production of ATP (from ADP) by direct transfer of a high energy Pi from a high energy Phosphoryl compound

Question 16

What is significant about NADH?

Answer 16

Nicotinamide Adenine Dinucleotide
High energy due to Hydride
Carries 2 electrons
Niacin Vitamin makes NAD+

Question 17

What is significant about PEP?

Answer 17

GOAT of high energy compounds
Enol to KETO tautomerization is the reason why PEP is so high in energy

Question 18

What are activator/inhibitors of PFK-1 (the main control point of Glycolysis)

Answer 18

Activators: AMP, ADP, Fructose-2,6-Bisphosphate
Inhibitors: ATP, Citrate

Question 19

What enzyme breaks down glycogen and pushes it into glycolysis? Describe how it is regulated by phosphorylation. What are its other regulators?

Answer 19

Glycogen Phosphorylase
Controlled by phosphorylation (ON with Pi)
ATP is neg. heterotrophic effector
AMP is pos. heterotrophic effector

Question 20

How does glycolysis influence O2 transport?

Answer 20

2,3-BPG is an allosteric inhibitor of Hb
1,3-BPG is an isomer of 2,3-BPG that is made during Glycolysis
BPG Mutase convertes 1,3-BPG to 2,3-BPG in between steps 6 & 7
(2,3-bisphosphoglycerate phosphatase converts 2,3-BPG to 3PG)

Question 21

Describe the steps of Alcohol Fermentation

Answer 21

(1) Pyruvate Decarboxylase
*Requires Vitamin Thiamine
*Carboxylic Acid on Pyruvate comes off as CO2
(2) Alcohol Dehydrogenase (ADH)
*Requires Zn2+ cofactor
*Regenerates NAD+

Question 22

Describe the steps of Anaerobic Glycolysis (Homolactic Fermentation)

Answer 22

(1) Lactate Dehydrogenase (LDH)
*LDH catalyzes a prochiral differentiation
*NAD+ is regenerated

Question 23

Describe what is unique about Cancer Cells, related to how they use up glucose.

Answer 23

Warburg Effect (200x)
Cancer cells only undergo anaerobic Glycolysis
Cancer cells feed on glucose (not efficient)

Question 24

Why is Methanol poisonous?

Answer 24

Ethanol is produced by Alcohol Fermentation, and ADH can work backwards to produce Acetaldehyde (which makes you drunk)
Methanol is very similar in structure to ethanol, and it can be transformed into Formaldehyde by ADH (formadlehyde is very poisonous)

Question 25

What steps differ between glucose and gluconeogenesis?

Answer 25

Step 10, 3, and 1 differ between Glycolysis and Gluconeogenesis

Question 26

Describe the reaction that replaces step 10 (glycolysis) in gluconeogenesis

Answer 26

(1) Pyruvate Carboxylate
*Occurs in the mito matrix
*Biotin is needed for carboxylation reactions
*Forms oxaloacetate (important in the Krebs Cycle)
*Requires ATP
(2) PEPCK
*Occurs in both cytosol and mito matrix
*Requires GTP

Question 27

What reaction replaces step 3 (glycolysis) in gluconeogenesis

Answer 27

Fructose Bisphosphatase (enzyme)

Question 28

What reaction repalces step 1 (glycolysis) in gluconeogenesis

Answer 28

Glucose-6-Phosphatase