What are some key differences between glucokinase and hexokinase?
Glucokinase is specific for glucose, has a high Km and no inhibitor. Hexokinase is nonspecific, has a low Km and inhibitors.
How does the low Km of hexokinase affect glucose distribution throughout the body?
Hexokinase has a very high affinity for glucose, so very low glucose concentration gets you to Vmax. This allows the brain and muscle to "dibs" glucose over the liver.
What makes the liver altruistic?
The high Km restricts uptake of glucose only when blood glucose levels are pretty high.
What is the key inhibitor of hexokinase?
Glucose-6-phosphate. When the glycolytic pathway gets saturated, you don't want to continue burning ATP making Gluc-6-P from glucose.
What does the liver do with glucose-6-phosphate?
1st it routes excess to glycogen and 2nd if there is still excess once glycogen stores are full it will route it to fat.
What are the activators and inhibitors of PFK-1?
Activators: F26BP (activated in liver in response to insulin) and AMP (muscle). Inhibitors: ATP, Citrate
What hormones control the fed and fasted states?
Fed state: insulin increase leads to increase in F26BP. Fasting state: glucagon increase leads to decrease in F26BP.
Why do AMP levels rise as ADP levels rise?
Adenylate kinase catalyzes this reaction to generate another ATP to use.
How do ATP, ADP and AMP levels change going from rest to exercise?
Relative amounts of AMP jump during exercise due to adenylate kinase because ATP levels start going down. This makes it a good signaling molecule.
How does ATP regulate the kinetics of Fruc-6-P?
When ATP levels are low, ATP fills up the active site of the enzyme to push glycolysis forward. Once all of the ATP active sites are full, ATP fills an allosteric site that will eventually inhibit PFK-1 by 99%. PFK-1 will not become activated again until it is hit by AMP.
How does the body prevent lactic acidosis in metabolism?
The H+ produced in lactate synthesis binds to PFK-1 and slows its reactions so you stop producing so much pyruvate. Citrate also goes back and inhibits PFK-1 as it builds up.
How does yeast recycle NAD?
Pyruvate is decarboxylated to form Acetaldehyde and CO2. The NADH then reduces acetaldehyde to ethanol