Glycolysis Flashcards
GLUT 1 & 3
Low km, high affinity
Unregulated activity
RBC and brain
Constant need, uptake even when blood glucose is low
Digestion and utilization of sugars
Absorption of dietary sugars and carbs from the gut into the blood is only as a monosaccharide
GLUT 4
Low km, high affinity Regulated by insulin Active only in the fed states Muscle and adipose Muscle contraction also activates
GLUT 2
High km, low affinity
Unregulated
Active when blood glucose is high, fed state
Found in cells that regulate glucose levels
Pancreas, liver
Insulin
A time to build up
Fed state hormone
Promotes uptake of glucose by muscle
Stimulates glycogenesis in muscles and liv
Stimulates protein synthesis in muscle
2-4 hours
Amino acids titular insulin release in pancreas
Hexokinase/glucokinase
ATP+ glucose –> glucose-6-P
Activates glucose, primed for metabolism
Hexokinase: most tissues, low km, high affinity. Glucose is phosphorylated even when blood glucose is low. Inhibited by glucose-6-P
Glucokinase: found in liver and beta cells of pancreas. High km, low affinity. Not inhibited by glucose-6-P. phosphorylated only when blood glucose is high.
Glycolysis
Glucose converted to glucose-6-P by hexokinase or glucokinase
Converted to 2 pyruvates (3C)
Cytosol
4 - 2 ATP= 2 ATP out, 2 NADH, 2 pyruvate
Pyruvate can then enter citric acid cycle if mitochondria and oxygen is present, aerobic
Or can be converted to lactate, anaerobic
Phosphofructokinase, PFK
Principal control point for glycolysis
ATP + fructose-6-P –> fructose-1,6-bis-P + ADP
Inhibited by energy rich signal such as ATP, NADH, citrate
Activated by fructose-2,6-bis-P
In liver and adipose, insulin–> increased synthesis
In muscle, epinephrine–> increased synthesis
Pyruvate kinase
Enzyme that makes ATP
Makes 2ATP and 2 pyruvates
Lactate dehydrogenase
Converts pyruvate to lactate
Uses 2 NADH and spits out 2 NAD+
Amplified glycolysis
Amplified when there is no mitochondria (RBC), oxygen limiting (exercise), or tumor cells
Inhibitors of glycolysis are low
Amplified by conditions that increase fructose-2,6-bis-phosphatase levels
Regenerating NAD+ anaerobic
Glycolysis produces NADH which inhibits glycolysis
Shortage of NAD+ slows or stops glycolysis
Anaerobic conditions, RBC or exercising muscle reduce pyruvate to lactate using lactate dehydrogenase,n producing NAD+
Cori Cycle
RBC needs to make new ATP
Make lactate out of pyruvate to regenerate NAD+
Lactate spills out and goes to the liver which converts lactate to pyruvate, used to make glucose
Get rid of NADH under aerobic conditions
Most tissues NADH can't enter mito Can shuttle them electrons it carries inside and use energy to make ATP Glycerol-P-shuttle Heart and liver malate shuttle
