Lecture 11 Overview of CHO Metabolism II Part B Flashcards
What is a major gateway molecule driving the CAC?
pyruvate
How is pyruvate made accessible in the mitochondria?
It is converted to Acetyl-CoA by the pyruvate dehydrogenase (PDH) complex.
What is the metabolic fates of pyruvate?
- aerobic conditions
- anaerobic conditions (homolactic fermentation)
- alcoholic fermentation
What happens to pyruvate under aeorobic conditions?
pyruvate carbons are converted to Acetyl-CoA via PDH and then oxidized to CO2 by the CAC and the electrons are eventually transferred to yield H2O in oxidative phosphorylation.
What happens to pyruvate under anaerobic conditions?
pyruvate is reversibly converted to lactate & alanine. During situations of exerting muscles beyond the VO2max glycolysis is being asked to work faster than the CAC forming a build up of pyruvate which turns into lactate or alanine in order to get rid of it.
What substrates are increased in working muscle to cause lactate?
NADH, Pi and ADP (AMP) are ↑ in working muscle, stimulating glycolysis and ↑ pyruvating leading to lactate formation, regenerating NAD+
homolactic fermentation
What happens to pyruvate in yeast?
fermentation → converted to CO2 and ethanol
What substrate is central to pyruvate reaction?
nicotinamide adenine dinucleotide + hydrogen (NADH and NAD+) are central to these reactions for electron movement
How is pyruvate converted to lactate?
Via the enzyme lactate dehydrogenase and uses the conenzyme NADH to regenerate NAD+
What is the purpose of converting pyruvate to lactate?
Essentially when the body is in a high energy need, glycolysis and CAC become uncoupled and the high rate of glycolysis leads to a desparation for NAD+. The NADH which is generated in step 6 of glycolysis can be converted back to NAD+ in the reaction that generate lactate from pyruvate. This reaction assures a steady supply of NAD+ which allows for the continued operation of step 6 and the continued production of ATP even under conditions of redcued oxygen availabilty.
What is the amount of ATP produced in anaeorbic vs. aerobic conditions?
rate of ATP formation via glycolysis is about 100x faster than ox. phos.. thus the need for more NAD+ when glycolysis and CAC are uncoupled
What is the primary conversion of pyruvate?
Cori cycle
Lactate from anaeorbic metabolism of glucose is taken to the liver because where it may be used for gluconeogensis to replenish plasma glucose. so the lactate is converted right back into pyruvate which also regenerate NADH for gluconeogenesis
What is the secondary conversion of pyruvate?
alanine cycle (protein source of energy)
with high energy demand muscle protein gets broken down to amino acids so the pyruvate and amino acids will leave the tissue as alanine and be taken up by the liver where the pyruvate may be used for gluconeogensis and the amino group converted to urea for excretion (detoxification of NH4)
Where are lactate and alanine generated?
peripheral tissue
What is the ultimate purpose of the cori cycle and alanine cycle?
The lactate and alanine produced from pyruvate in the peripheral tissue can be converted back into glucose in the liver and recycled back to the tissue via blood.
Main purpose of CAC
Acetyl CoA → 2 CO2
Acetyl groups derived from CHO, aa, FAs enter the CAC where they are oxidized to CO2
Regulation of the CAC
- points of inhibition
- central role of NAD+ requirements can inhibit if not available
- excess NADH will also suppress
- ADP and Ca2+ are activators
What happens in the ETC?
oxidative phosporylation chain of rxs located in the inner mitochondrial membrane (ADP + Pi = ATP)
* Free energy from electrons is used to pump H+ into inter-membrane space = electrochemical gradient (low to high) ⇝ energy created from H+ coming back used to form ATP bond
general summary of ox. phos.
How does PPP reconnect with glucose?
Excess R5P is converted to glycolytic intermediates by a sequence of reactions that can operate in reverse to generate additional R5P if needed
