1. Describe the major steps of glycolysis
Chapt. 22 Glycolysis
Ch. 22 Glycolysis
Student Learning Outcomes:
Explain how glucose is universal fuel, oxidized in every tissue to form ATP
Describe the major steps of glycolysis
Explain decision point for pyruvate utilization depending on oxygen
Describe major enzymes regulated
Explain lactic acidemia and causes

2. Overview of Glycolysis, TCA cycle, electron transport chain:
Glycolysis overview
Overview of Glycolysis, TCA cycle, electron transport chain:
Starts 1 glucose phosphorylated
2 ATP to start process
Oxidation to 2 pyruvates
yields 2 NADH, 4 ATP
Aerobic conditions: pyruvate to TCA cycle, complete oxidation
NADH from cytoplasm into mitochondria
to ETC (waste some)
Complete oxidation total ATP
Fig. 1*

3. In absence of oxygen, anaerobic glycolysis:
Recycles NADH to permit glycolysis continue
Reduces pyruvate to lactate
Only 2 ATP per glucose
May cause lactic acidemia
Fig. 2

4. Glucose phosphorylated Cleaved to 2 triose phosphates Costs 2 ATP
Glycolysis phases
Glycolysis phases:
Preparation:
Glucose phosphorylated
Cleaved to 2 triose phosphates
Costs 2 ATP
ATP-generating phase:
Triose phosphates oxidized more
Produces 2 NADH
Produces 4 ATP
Fig. 3

5. 1. Glucose is phosphorylated by Hexokinase with ATP: Commitment step
Glycolysis step 1
1. Glucose is phosphorylated by Hexokinase with ATP:
Commitment step
G6-P not cross plasma membrane
Irreversible
Many pathway choices
Glycogen synthesis needs G1-P
Many tissue-specific isozymes of hexokinases
Fig. 4

6. 2 ATP convert Glucose to Fructose 1,6 bis-P;
Glycolysis phase I
2 ATP convert Glucose to Fructose 1,6 bis-P;
Fructose 1,6-bis-P split to 2 trioses
Glyceraldehyde 3-P (and DHAP isomerized)
Key enzymes:
Hexokinase
PFK-1
Commits to glycolysis
Regulated step
Fig. 5 top

7. Oxidation, substrate level phosphorylation yield
Glycolysis phase II
Oxidation, substrate level phosphorylation yield
2 NADH, 4 ATP from 1 Glyceraldehyde 3-P
Key enzymes:
Glyceraldehyde 3-P dehydrogenase
High-energy bond
Pyruvate kinase:
Regulated step
Fig. 5 lower

8. **Alternatie fates of pyruvate
Fate of pyruvate depends on availability of oxygen:
Much more ATP from complete oxidation of glucose
Aerobic: shuttles carry NADH into mitochondria; pyruvate can be oxidized to Acetyl CoA and enter TCA
Anaerobic: pyruvate reduced by NADH to lactate, NAD+, H+
Fig. 6*

9. Aerobic: Glycerol 3-P shuttle carries NADH
Aerobic: Glycerol 3-P shuttle carries e- from NADH into mitochondrion; regenerates cytosol NAD+
Glycerol 3-P diffuses across
outer memberane, donates e-
to inner membrane FAD enzyme
Loses some energy
FAD(2H) not NADH
Bacteria not need shuttle since only 1 compartment
Fig. 5 top
Fig. 7

10. Anaerobic:
Anaerobic glycolysis: NADH reduces pyruvate to lactate, regenerates NAD+ to continue glycolysis
1 glucose + 2 ADP + 2 Pi -> 2 lactate + 2 ATP + 2 H2O + 2 H+
Lactate and H+ transported to blood; can have lactic acidosis
Red blood cell, muscle, eye, other tissues
To maintain cell:
Run faster
More enzymes
Use lot glucose
Fig. 9

11. Used to make glucose (liver) – Cori cycle
Fate of lactate
Fate of lactate:
Used to make glucose (liver) – Cori cycle
Reoxidized to pyruvate (liver, heart, skeletal muscle)
lactate + NAD+ -> pyruvate + NADH
Lactate dehydrogenase (LDH) favors lactate, but if NADH used in ETC (or gluconeogenesis), then other direction
Heart can use lactate -> pyruvate for energy
Isoforms of LDH: M4 muscle; H4 heart; mixed others)
Fig. 10

12. II. Other functions of glycolysis
Glycolysis generates precursors for other paths:
5-C sugars for NTPs
Amino acids
Fatty acids, glycerol
Liver is major site of
biosynthesis
Fig. 11

13. III. Glycolysis is regulated
Glycolysis is regulated by need for ATP:
Hexokinase
Tissue specific isoforms
Inhibited by G-6-P
Except for liver
PFK-1
Pyruvate kinase
Pyruvate dehydrogenase
(PDH or PDC)
Fig. 12

14. Levels of AMP in cytosol good indicator of rate ATP utilization
Levels of ATP, ADP, AMP
Levels of AMP in cytosol good indicator of rate ATP utilization
2 ADP <-> AMP + ATP
reaction of adenylate kinase
Hydrolysis ATP -> ADP
increases ADP, AMP
ATP present highest conc:
Small dec ATP -> large AMP
Fig. 13

15. Rate-limiting step, tetramer 6 binding sites:
Regulation of PFK-1
Regulation of PFK-1:
Rate-limiting step, tetramer
6 binding sites:
2 substrates: ATP, Fructose 6-P
4 allosteric: inhibit ATP
Activate by AMP
Activate by fructose 2,6 bis-P (product when excess glucose in blood)
Fig. 14

16. Regulation of glycolysis enzymes
Regulation of pyruvate kinase:
R form (RBC), L (liver); M1/M2 muscle, others
Liver enz allosteric inhibition by compound in fasting;
also inhibited by PO4 from Protein Kinase A
Regulation of PDH (PDC):
By PO4 to inactivate
Rate of ATP utilization
NADH/NAD+ ratio
Fig. 12

17. Lactic acidosis: Lactic Acidemia Fig. 15
Excess lactic acid in blood > 5mM
pH < 7.2
From increased
NADH/NAD+
Many causes ->
Excess alcohol
Hypoxia
Fig. 15

18. Key concepts
Glycolysis is universal pathway by which glucose is oxidized and cleaved to pyruvate
Enzymes are in cytosol
Generates 2 molecules of ATP (substrate-level phosphorylation) and 2 NADH
Pyruvate can enter mitochondria for complete oxidation to CO2 in TCA + electron transport chain
Anaerobic glycolysis reduces pyruvate to lactate, and recycles (wastes) NADH -> NAD+
Key enzymes of glycolysis are regulated: hexokinase, PFK-1, pyruvate kinase, PDH C

19. ATP is formed by oxidative phosphorylation
Review question
Which of the following statements correctly describes an aspect of glycolysis?
ATP is formed by oxidative phosphorylation
Two molecules of ATP are used in the beginning of the pathway
Pyruvate kinase is the rate-limiting enzyme
One molecule of pyruvate and 3 olecules of CO2 are formed from the oxidation of 1 glucose
The reactions take place in the matrix of the mitochondria

20. Glyceraldehyde 3-P dehydrogenase
Glyceraldehyde 3-P dehydrogenase uses covalent linkage of substrate to S of cys to form ~P:
Covalent link to S of Cys; NAD+ nearby
Oxidation forms NADH + H+; ~S bond
NADH leaves, new NAD+
Pi attacks thioester
Enzyme reforemd
Fig. 17