lecture 21 Flashcards
many intermediates formed during glycolysis and the CAC serve as
precursors to the production of important molecules like amino acids, nucleotides and fats
what lies at the heart of the metabolic pathway?
glycolysis and CAC
but they only represent a fraction of all the rxns that occur in the cell
the balance between glycolysis and gluconeogenesis is made by?
positive and negative feedback inhibition
gluconeogenesis is energetically expensive! it requires…
4 ATP and 2 GTP for each molecule of glucose produced
why is it important to carefully regulate glycolysis and gluconeogenesis?
so energy is not wasted
glucose can be stored as
glycogen (in the cytoplasm of liver and muscle cells)
how are fats stored?
as triacylglycerols in cells known as adipocytes
plants store fats and starch in
chloroplasts
starch=
a branched polymer of glucose that is similar to glycogen
the controlled, stepwise oxidation of sugar allows the
capture of energy in small portions (captured by activated carriers ATP and NADH)
3 stages of catabolism
- Breakdown of food to subunits
- Breakdown of subunits to acetyl coA
- Oxidation of acetyl coA
Glycolysis 2 phases
preparatory phase= an input of energy (2 ATP) is required to activate the glucose molecule
payoff phase= energy investment pays off in the form of 4 ATP and 2 NADH for each glucose
what is the net result of glycolysis?
glucose –> 2 pyruvate + 2 ATP + 2 NADH
does glycolysis involve any oxidation reactions?
yes!
fermentation
= the breakdown of organic molecules in the absence of oxygen
- Ex. occurs in active muscle cells and in yeast
- Fermentation regenerated the NAD+ needed for glycolysis
why is fermentation especially important in brewing and breadmaking?
The byproducts of fermentation include CO2 and ethanol. CO2 helps bread rise. Ethanol is the key component in most alcoholic beverages.
Citric acid cycle (CAC)
Or the tricarboxylic acid cycle (TCA) or the Krebs cycle
- Takes place in the mitochondrial matrix (does not use O2 directly but depends on it! O2 is used in the ETC which regenerated NAD+)
each turn of the CAC cycle produces
3 NADH, 1 GTP, 1 FADH2 and releases 2 molecules of CO2
and results in regeneration of oxaloacetate
ETC drives the synthesis of
most of the ATP in most cells
(About 30 ATP from 1 molecule of glucose)
ETC takes place using
using proteins embedded in the inner mitochondrial membrane
gluconeogenesis
= the production of glucose from other small molecules (like pyruvate)
glucose can be stored as
glycogen (in cytoplasm of muscle and liver cells)
Why is it important to carefully regulate glycolysis and gluconeogenesis?
So energy is not wasted!
fats can be stored as
triaglycerols in cells known as adipocytes
plants store fats and starch in
chloroplasts
