Glycolysis 1 Flashcards
Briefly Describe glycogen conversion to lactate
- glycogen undergoes glycolysis to become glucose in the bloodstream
- glucose in the bloodstream undergoes glycolysis to become lactate
Briefly describe how lactate is concerted to glycogen
- lactate undergoes gluconeogenesis to become glucose in the blood
- glucose in the blood undergoes glycogenesis to become glycogen
What are the glucose consuming processes?
- Glycogenesis
- glycolysis
What are the glucose producing processes?
- Glycogenolysis
- gluconeogenesis
Outline the function of glucose transporters/ glucose uptake
Glucose is taken into the cell through trans membrane proteins called GLUT transporters
It is taken up along its concentration gradient
-uses facilitated diffusion (requires no ATP)
Where are GLUT 1 transporters located?
Brain and erythrocytes
Where are GLUT 2 transporters located?
Liver
Where are GLUT 3 transporters located?
Neurons, placenta and testes
Describe the GLUT 4 transport protein
Adipocytes, skeletal and cardiac muscle
- insulin dependent - increases in number with the presence of insulin
Describe SGLT as glucose transport proteins
SGLT: intestinal cells, renal tubules
- secondary active transport - Uses sodium gradient for glucose absorption, maintained by the Na- K ATPase channel
Describe the tissue specific metabolism of glucose in the brain
Glucose is completely metabolized to CO2 in the brain
Describe the tissue specific metabolism of glucose in the liver
Liver: completely metabolized to CO2, lactate , divert to fat, deliver glucose to blood
Describe the tissue specific metabolism of gluc9se in adipose tissue
Adipose: metabolized to Acetyl CoA, then fat
Describe the tissue specific metabolism of glucose in the muscle
Muscle: completely metabolized to CO2, lactate
Describe tissue specific metabolism of glucose in erythrocytes
Erythrocytes: glucose metabolized to lactate
What is glycolysis?
One of the principal pathways for ATP generation- considered as a catabolic pathway
In brain; erythrocytes and actively contracting skeletal muscle
Why does red blood cells contain mitochondria?
Because glycolysis is the only source of ATP they have
Where are glycolysis enzymes present?
Present in the cytosol
Glycolysis can generate ATP in the presence and absence of __________ and __________
Oxygen
Mitchondria
What are the input and output of glycolysis?
Glycolysis consumes 2 ATP but produces 4 ATP (net gain of 2)
Also converts 2 NAD+ to 2 NADH
What is the difference between aerobic glycolysis and anaerobic glycolysis ?
Aerobic glycolysis: NADH produces from conversion of Glyceraldehyde 3-P to 1,3-bisphosphoglycerate is used for oxidative phosphorylation
Anaerobic glycolysis: NADH produced from conversion of Glyceraldehyde 3-P to 1,3 bid-phosphoglycerate is used in the conversion of Pyruvate to lactate(reversible)
What is the overall yield of one molecule of glucose in aerobic glucose?
2 ATP and 2 NADH
What is the overall yield of of anaerobic glycolysis?
Anaerobic glycolysis
-2 ATP (NADH is used to convert Pyruvate to lactate)
What is the energy investment stage of glycolysis?
- preparatory phase
- phosphorylation of glucose and it’s conversion to Glyceraldehyde 3-phosphate
- net loss of 2 ATP
Describe the first of step of glycolysis
Step 1: formation of glucose 6-phosphate
- Glucose is phosphorylated to glucose 6-phosphate by ATP and Hexokinase/Glucokinase
- this reaction traps glucose as glucose 6-pohosphate as phosphorylated molecules cannot easily cross membranes
- irreversible reaction; exergonic
Differentiate Glucokinase and Hexokinase
Glucokinase- in liver and beta cells of pancreas, high Km and high Vmax and NO product inhibition of glucose 6-phosphate
Hexokinase- located in all other tissues, has low Km and low Vmax and HAS product inhibition of glucose 6-phosphate
Describe the second step of glycolysis
Step 2: formation of fructose 6-phosphate
- Phosphoglucose isomerase catalyzes the conversion of glucose 6-P (aldose) to fructose 6-P(ketose)
- Aldo-keto interconversion ; reaction is reversible
Describe the 3rd step of glycolysis
Step 3: formation of fructose 1,6-bisphosphate
Fructose 6-phosphate is phosphorylated to fructose 1,6-bisphosphate
-this is done by Phosphofructosekinase-1 and is the second irreversible reaction of glycolysis and also the most important regulated step(allosteric regulated enzyme)
Is the rate limiting step
What is the rate limiting step of glycolysis ?
PFK-1 and ATP phosphorylates fructose 6-phosphate to fructose 1,6-bisphosphate
What are steps 4 and 5 of glycolysis?
- Aldolase (step 4)cleaves fructose 1,6 bisphosphate into two trioses(3C) glyceraldehyde 3-phosphate and dihydroxyacetone phosphate
- The triose phosphate isomerase (step 5) converts to dihydroxyacetone phosphate to glyceraldehyde 3-phosphate to to enable it to be further metabolized by glucolysis.
- both reactions are reversible
Describe the energy generation phase of glycolysis
- “payoff phase”
- oxidative conversion of glyceraldehyde3-phosphate to pyruvate and the coupled formation of ATP and NADH
- gain of 4 ATP and 2 NADH
Describe the 6th step of glycolysis
Step 6: formation of 1,3-bisphosphoglycerate
- Glyceraldehyde 3-phosphate dehydrogenase results in the formation of 1,3 Bisphosphoglycerate (high energy compound ) and NADH
- Oxidation reaction
- Addition of phosphate(not by ATP)
How does arsenic effect glycolysis?
- Pentavelent arsenic (arsenate) is a substrate for Glyceraldehyde 3-PDH (competing with Pi)
- Arsenate bond is Labile, and easily breaks, - non-enzymatic—
- Arsenate: bypasses the Biphosphoglycerate intermediate, and loss of ATP production
Describe the 7th step of glycolysis
Phosphoglycerate kinase removes phosphate from 1,3-bisphosphoglycerate(high energy intermediate) to convert ADP to ATP (substrate phosphorylation without involvement of mitochondrial electron transport chain
Reversible
Where and when are substrate level phosphorylation reactions important?
Important during periods of low oxygen(hypoxia) and in RBC (which lack mitochondria)
Describe the 8th step of glycolysis
Step 8:
Phosphoglycerate mutate catalyzes the reversible isomeration of 3-P-glyceraldehyde( 3PG) to 2-P-glycerate (2PG)
Describe step 9 of glycolysis
Step 9: dehydration reaction to form a high energy enol phosphate compound
2-phosphoglycerate(2PG) converted to phosphoenolpyruvate(PEP) (High energy compound) by enolase
How does fluoride affect glycolysis? What are the applications?
Enolase catalyzes 2PG —> PEP
Enolase is inhibited by fluoride- so… 1) NaF is added to tubes when collecting blood samples for glucose assays
2) addition of fluoride to water reduces lactate production by mouth bacteria, decreasing tooth decay
What is the 10th step of glycolysis?(last step)
- Pyruvate kinase(step 10) results in the formation of the 2nd ATP
- Pyruvate kinase is an irreversible reaction
- Phosphoenolpyruvate(PEP) is converted to Pyruvate by Pyruvate kinase, Mg2+ and K+
- From a molecule of glucose(6C), 2 molecules of Pyruvate (3C) are formed as a result of glycolysis
What is the net Gibbs free energy of the formation of Pyruvate from PEP?
About -30 kjmol-1
What is the net Gibbs free energy of ATP Hydrolysis in the formation of ATP?
Hydrolysis of ATP. Net G= -30.5 kjmol-1
Describe phosphoenolpyruvate
Phosphoenolpyruvate is a high energy compound that results in the formation of ATP, without the involvement of the ETC in mitochondria (substrate level phosphorylation)
Give an example of a regulated and disorder -related step in glycolysis
The conversion of Phosphoenolpyruvate to Pyruvate
Catalyzes by Pyruvate kinase and converts. ADP to ATP
