3.4 Flashcards
stages of cellular respiration
- glycolysis
- pyruvate oxidation
- citric acid cycle
- electron transport chain/ATP synthesis
in the presence of O2
pyruvate oxidation
occurs in the mitochondrial matrix
pyruvate is oxidized to form acetate and CO2, and acetate then binds to coenzyme A to form acetyl CoA
pyruvate oxidation is exergonic: one NAD+ is reduced to NADH
pyruvate oxidation products
from ONE pyruvate (glycolysis produces 2)
1 acetyl CoA
1 NADH
1 CO2
citric acid cycle
completely oxidizes the acetyl group to two molecules of CO2
completes the oxidation of glucose to CO2
cyclic metabolic pathway consisting of 8 steps
acetyl CoA is the starting point
energy is captured by NAD+, FAD, GDP
oxaloacetate is regenerated in the last step
malate oxidation
the oxidation of malate is highly exergonic, and the released energy is captured by NAD+, forming NADH
products of the CAC
from ONE turn (pyruvate oxidation produces 2)
3 NADH (3, 4, 8)
1 FADH2 (6)
1 GTP/ATP (5)
2 CO2 (3, 4)
complete oxidation equation from glycolysis to CAC
C6H12O6 + 10NAD+ + 2FAD + 4ADP + 4Pi + O2 –> 6CO2 + 10NADH + 2FADH2 + 4ATP
NAD+ replenishment
oxidized electron carriers (NAD+) must be replenished so that another carbon molecule can be catabolized/oxidized
O2 serves as the final electron acceptor in aerobic conditions, so fermentation regenerates NAD+ in the absence of O2
NAD+ is needed for fermentation to occur
lactic acid fermentation
regenerates NAD+ using pyruvate as an electron acceptor without O2
takes places when O2 is scarce in muscle cells
lactate dehydrogenase reduces pyruvate to lactate
glucose is only partially oxidized
C6H12O6 + 2ADP + 2Pi —> 2 lactate + 2ATP
alcoholic fermentation
regenerates NAD+ by using acetylaldehyde as an electron acceptor without O2
takes places in yeast and some plants
pyruvate decarboxylase converts pyruvate to acetylaldehyde and O2
alcohol dehydrogenase reduces acetylaldehyde to ethanol
glucose is partially oxidized
C6H12O6 + 2ADP +2Pi –> 2EtOH + 2CO2 + 2ATP
catabolic interconversions
polysaccharides –> glucose –> glycolysis
lipids –> fatty acids –> glycerol
a). glycerol –> DHAP –> glycolysis
b). fatty acids –> acetyl CoA – CAC
proteins –> amino acids –> glycolysis or CAC
anabolic interconversions
pyruvate –> glucose –> polysaccharide synthesis
acetyl CoA –> fatty acids –> lipid synthesis
regulation of metabolic pathways
regulation of gene expression
regulation of enzyme activity (reversible inhibition, covalent modification, allosteric regulation)
regulation of glycolysis and CAC
controlled by allosteric regulation
enzymes are regulated by:
molecules signaling the energy state in the cell
a). inhibition by high energy molecules: ATP, NADH
b). activation by low energy molecules: ADP, AMP, NAD+
inhibition by final products: ATP, NADH
activation by substrate
control point in glycolysis
enzyme phosphofructokinase
PFK is inhibited by high levels of ATP or citrate
PFK is activated by high levels of ADP or AMP
control point in CAC
enzyme isocitrate dehydrogenase
inhibited by high levels of ATP or NADH
activated by high levels of ADP, NAD+, or isocitrate
