Biochemistry II Quiz 9 Flashcards
What is done in order to conserve energy in all these metabolic pathways (futile cycles)?
-activating both reactions wastes cellular energy continuously
-minimize energy loss by having the reaction only going in one direction should be active at a time (glycolysis vs gluconeogenesis)
-liver utilizes this too with glucose and glucose-1-phosphate as a buffer to maintain blood glucose levels
Describe the glucose transporters
GLUT-1: basal non-insulin-stimulated glucose uptake (exists on virtually any cell and participates in passive uptake)
GLUT-2: glucose sensing; B-cell in pancreas, forms the B cells glucose sensor (with glucokinase) and allows glucose to enter the b-cell at a rate proportional to the extracellular glucose level
GLUT-3: non-insulin-mediated glucose uptake into brain neurons
GLUT-4: responsible for insulin-stimulated glucose uptake in muscle and adipose tissue, and hypoglycemic action of insulin results
Describe Glycolysis
Location: Cytosol
Input: Glucose
Output: 2 Pyruvate
Energy Harvested: 2 ATP and 2 NADH
priming- 3 steps
splitting- 2 steps
energy extraction- 5 steps
-the production of fructose-1,6-bisphosphate is the COMMITMENT STEP of glycolysis
How does AMP work as a signaling molecule?
-concept of small percent decrease in ATP concentration—>large percent increase in AMP concentration
-therefore, useful as a sensor
-high AMP activates PFK-1 and pyruvate kinase
-high ATP inhibits Hexokinase, PFK-1 and pyruvate kinase
What does lactate do in relation to glycolysis?
-decreases the intracellular pH which inhibits glycolysis at PFK-1
-can be used as a substrate for gluconeogenesis via the cori cycle
-overproduction/underutilization of lactate can decrease blood pH and cause lactic acidosis
Describe Gluconeogenesis
-liver produces glucose through gluconeogenesis
-same enzymes used in glycolysis are used in gluconeogensis except for three irreversible steps
-utilize phosphatases instead (Glucose-6-phosphatase, Fructose biphosphate phosphatase)
How is Oxaloacetate important in gluconeogenesis?
-key intermediate from Pyruvate to PEP
-also intermediate in TCA cycle
-the step catalyzed by PEP carboxykinase is the rate-limiting step
Describe the Alanine Cycle
-Pyruvate in muscle is converted to alanine and released into blood
-alanine is transaminated back to pyruvate and reconverted to glucose in the liver
-glutamate is most common amino acid used in this reaction
Describe the Cori Cycle
-lactate is release from red blood cells, into the blood stream
-highly exercised muscle can also release lactate into blood
-in liver lactate is converted back into glucose through gluconeogenesis
What are the fates of Glucose-6-phosphate?
- Gluconeogenesis (LIVER)
- Glycogen Synthesis
- Glycolysis
- Pentose Phosphate Pathway
What is important about glycogen synthesis and breakdown?
-excess glucose is stored as glycogen
-liver regulates blood glucose levels using glycogen
-allosteric and hormonal regulation
Glycogenesis-forms glycogen
Gycogenolysis- glycogen is broken down into glucose and glucose-1-phosphate
What does the Pyruvate Dehydrogenase complex do?
-converts pyruvate to acetyl coA
-reaction is irreversible in cells
-produces CO2
-uses E1,E2 and E3
-3 reactants (Pyruvate, NAD+, CoA)
-3 products (CO2, Acetyl-Coa, NADH+H)
What does Coenzyme A do?
-purpose is to capture acyl groups from other intermediates and carry it without getting degraded (oxidized)
What does Acetyl CoA do?
-produced fro glucose, fatty acids and some animo acids
-fuel of TCA cycle
-cannot be used to make glucose
-can be used for ketogenesis, fatty acid synthesis
What do Ketone bodies do?
-Ketogenesis reduced the need for gluconeogenesis (reduced protein wasting)
-can be used as brain/skeletal muscles as fue;
-produced by liver during fasting or ketogenic diet
-is converted to acetyl-CoA in nonhepatic tissues(liver can not use ketone bodies)
