Glycolysis, Fermentation, Gluconeogenesis Flashcards
Step 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
What is significant about G6P being phosphorylated in Step 1 of Glycolysis?
Whenever G6P is phosphorylated, it cannot pass through the GLUT4 transporter, so it is trapped in cytosol
Step 2
Phosphoglucose Isomerase (PGI)
GABC (occurs through enediol intermediate)
How many ATP are used up during the “Prep Phase” of Glycolysis?
2 ATP used
Step 3
Phosphofructokinase (PFK-1)
Irreversible
ATP used up in this step!
Mg2+ is required for metal ion catalysis by charge shielding
Step 4
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
Step 5
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
Step 6
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
Step 7
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
Step 8
Phosphoglycerate Mutase (PGM)
Changes conformation of Phosphoglycerate to a more useful form
Has a Phosphohistidine residue in active site
Step 9
Enolase
Lyase (EC4)
Step 10
Pyruvate Kinase
Transfer high energy phosphate (from PEP) to ADP, making ATP
Substrate Level Phosphorylation (SLP)
Kinases (EC2 Transferases)
What 3 things do you think of a Dyhydrogenase?
- Hydride Transfer
- EC1 Oxidoreductase
- Look for a Redox Cofactor
How many ATP are produced in the “payoff phase” of glycolysis per glucose, made by Substrate Level Phosphorylation?
4 ATP per glucose
Describe Substrate-Level Phosphorylation (SLP)
Production of ATP (from ADP) by direct transfer of a high energy Pi from a high energy Phosphoryl compound
What is significant about NADH?
Nicotinamide Adenine Dinucleotide
High energy due to Hydride
Carries 2 electrons
Niacin Vitamin makes NAD+
What is significant about PEP?
GOAT of high energy compounds
Enol to KETO tautomerization is the reason why PEP is so high in energy
What are activator/inhibitors of PFK-1 (the main control point of Glycolysis)
Activators: AMP, ADP, Fructose-2,6-Bisphosphate
Inhibitors: ATP, Citrate
What enzyme breaks down glycogen and pushes it into glycolysis? Describe how it is regulated by phosphorylation. What are its other regulators?
Glycogen Phosphorylase
Controlled by phosphorylation (ON with Pi)
ATP is neg. heterotrophic effector
AMP is pos. heterotrophic effector
How does glycolysis influence O2 transport?
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)
Describe the steps of Alcohol Fermentation
(1) Pyruvate Decarboxylase
*Requires Vitamin Thiamine
*Carboxylic Acid on Pyruvate comes off as CO2
(2) Alcohol Dehydrogenase (ADH)
*Requires Zn2+ cofactor
*Regenerates NAD+
Describe the steps of Anaerobic Glycolysis (Homolactic Fermentation)
(1) Lactate Dehydrogenase (LDH)
*LDH catalyzes a prochiral differentiation
*NAD+ is regenerated
Describe what is unique about Cancer Cells, related to how they use up glucose.
Warburg Effect (200x)
Cancer cells only undergo anaerobic Glycolysis
Cancer cells feed on glucose (not efficient)
Why is Methanol poisonous?
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)