Block 2 Glycolysis Flashcards
Where does glycolysis occur, and what are its major products?
In the cytosol; ATP and pyruvate
What are the 2 phases of glycolysis?
1: preparative phase; 2: ATP-generating phase
What happens in the preparative phase of glycolysis?
Glucose is P by ATP and cleaved into 2 triose phosphates
What happens in the ATP-generating phase of glycolysis?
Triose phosphate oxidized by NAD+ and P by Pi. The phosphates are rearranged into high energy bonds so they can form ATP.
What is the net yield of glycolysis?
1 mole glucose -> 2 mol ATP, 2 NADH, 2 pyruvate
What are the irreversible reactions of glycolysis?
Glucose -> G-6P by gluco/hexokinase; F-6P -> F-1,6-bisP by PFK-1; phosphoenolpyruvate -> pyruvate by pyruvate kinase
What is hexo/glucokinase?
Convert glucose to glucose-6-phosphate. *Irreversible.
How does glucose-6-phosphate affect hexo/glucokinase?
Inhibits hexokinase, no effect on glucokinase
What is phosphoglucose isomerase?
Converts G-6P to open chain form, then open chain F-6P, then fructose-6-P
What is PFK-1?
Converts F-6P + ATP to F-1,6-BP + ADP + H+. *Irreversible, key allosterically regulated enzyme
What is aldolase A?
Converts F-1,6-BP to dihydroxyacetone-P or glyceraldehyde-3-P
What is triose phosphate isomerase?
Converts between dihydroxyacetone-P and glyceraldehyde-3-P
What is glyceraldehyde-3-phosphate dehydrogenase?
Catalyzes conversion of GA-3-P to 1,3-BP-glycerate
What is 3-phosphoglycerate kinase?
Converts 1,3-BPG to 3-PG. *Substrate level P
What is phosphoglyceromutase?
Converts 3-PG to 2-PG
What is enolase?
Converts 2-PG to phosphoenolpyruvate
What is pyruvate kinase?
Converts phosphoenolpyruvate to pyruvate. *Irreversible, substrate level P
What is arsenate (AsO4 3-)?
Similar to P in structure and reactivity, can replace P in attack of thioester intermediate; uncouples oxidation and phosphorylation by forming acyl arsenate. *Potent poison b/c resembles phosphate!
How does NADH get reoxidized to NAD+ to be recycled in glycolytic pathway?
1) e- transported back into mito by glycerol-3-P or malate-aspartate shuttle & passed to O2 in ETC
2) Lactate DH
What is anaerobic glycolysis?
NADH from glycolysis re-oxidized in cytosol by reducing pyruvate to lactate with LDH
Why are pyruvate levels lower in the blood than lactate?
Equilibrium for LDH favors lactate
What tissues depend on anaerobic glycolysis for ATP?
RBC, lymphocytes, leukocytes, kidney medulla, eye, skeletal muscles
What determines the ratio of glucose oxidized to CO2 vs. anaerobic glycolysis?
Mitochondrial oxidative capacity and O2 supply to tissue
What is the Cori cycle?
Lactate produced by exercising muscle, RBCs, etc. converted to glucose by gluconeogenic pathway in liver
What pathway do fructose-6P, glucose-6P, and glyceraldehyde-3P feed into?
Become ribose-5P in pentose pathway, which provides ribose and deoxyribose for nucleotides
What amino acids can 3-phosphoglycerate help make?
Serine, cysteine, glycine
What amino acid can pyruvate be converted to? What can it become in the liver?
Alanine, when transaminated. In liver, pyruvate/AcCoA is a substrate for FA biosynthesis
What can dihydroxyacetone phosphate become?
Glycerol-3P, backbone of TAGs and PLs
What is 2,3-BPG?
A detour from glycolytic pathway; an intermediate between 1,3-BPG and 3-PG
Why does glycolysis need to be regulated?
So rate of ATP generation matches rate of utilization
What are the activators and inhibitors of PFK?
Activator: AMP, F-6P-BP
Inhibitor: ATP, citrate
How does AMP activate PFK?
Binds allosteric site, induces conformational change to increase affinity for F-6P (separate binding site from F-2,3-bisP)
How is hexokinase regulated?
Decreased flux through PFK increases G-6P levels and inhibit hexokinase
How does the pentose phosphate pathway influence the activity of hexokinase?
G-6P can be converted to glycogen and enter PPP, so the rate of use of G-6P can influence its inhibition of hexokinase
How is glucokinase regulated?
Insulin increases synthesis of GK. GKRP in nucleus binds to inhibit GK in absence of glucose. High F-6P increases GK-GKRP, but glucose inhibits this interaction.
How does F-2,6-bisP affect PFK-1?
Mediates effects of insulin and glucagon. Increase in ins/gluc ratio increases levels, which activate PFK-1
How does pyruvate kinase regulate glycolysis?
Increase in glucagon/decrease in ins/gluc ratio during fasting activates PKA, PK-P = inactive. Increase in insulin or ratio after high carb meal activates phosphatase and activates PK.
What are three ways to regulate pyruvate kinase?
Insulin/glucagon ratio and activation of kinase/phosphatase; feed forward fructose-1,6-BP activation (liver); allosteric regulators ATP, alanine inhibit with gluconeogenesis is active
What is the Pasteur effect?
In aerobic conditions/increased respiration, levels of citrate and ATP increase, which inhibit PFK-1 (both) and PK (ATP)
What are the most common inherited enzyme deficiencies of glycolysis?
95% patients - pyruvate kinase; 4% - phosphoglucose isomerase
Where are PL and hexokinase deficiencies expressed?
Erythrocytes only
Where is triose phosphate isomerase deficiency seen?
Erythrocytes, leukocytes, muscle, CNS
What condition do most patients with glycolytic enzyme deficiency exhibit, and how are severe cases treated?
Hemolytic anemia; severe hemolysis treated with folic acid supplements
How does a PK deficiency lead to hemolytic anemia?
Decrease in enzyme = decrease in glycolysis rate = decreased ATP -> instability of PM of RBCs -> phagocytosis by macrophages in spleen
What is lactic acidosis?
Accumulation of LA in blood due to increased rate of production vs. metabolism, decreasing pH below 7.2
What deficiencies may lead to lactic acidosis?
Impaired ox of pyr by PDH (B1 def), TCA cycle, inability to re-ox NADH efficiently, pry carboxylase, exercise, MI
How does excessive NADH lead to lactic acidosis?
Drives lactate DH reaction in the direction of lactate
How does an MI cause lactic acidosis?
Absence of O2 for OXPHOS decreases ATP levels, increases AMP, activating PFK-1. Increase ATP, low O2 -> lactate, lower pH, inhibits PFK-1, inhibiting ATP generation
What is the ATP yield from aerobic/complete oxidation and anaerobic glycolysis of glucose?
Aerobic: 30-32 moles ATP/mole glucose
Anaerobic: 2 moles ATP
