Kreb's Cycle Flashcards
What are the other two names for the Kreb’s cycle?
TCA cycle
Citric acid cycle
What can enter the Kreb’s cycle?
Fatty acids, glucose as pyruvate, amino acids
What is the purpose of the Kreb’s cycle?
Biosynthesis and energy production
What are the products of the energy production of Kreb’s cycle?
3 NADH, FADH2, 2 CO2, GTP
What stimulates fatty acid production?
High carb diet with no exercise
What two amino acids are the easiest to make?
Aspartate and glutamate
What intermediate in the Kreb’s cycle is required to make hemoglobin?
Succinyl CoA
What needs heme?
Hemoglobin, cytochromes
What must the Kreb’s cycle be paired with to make energy?
Electron transport chain
What is the starting molecule of Kreb’s cycle?
Acetyl-CoA
What is the first equation of the Kreb’s cycle?
Oxaloacetate + acetyl-CoA (+H2O) -> citrate
(enzyme: citrate synthase)
How do carbs enter the Kreb’s cycle?
Glycolysis
What do carbs enter the Kreb’s cycle as?
Pyruvate
What is the pre-Kreb’s step for pyruvate?
Pyruvate to acetyl CoA
What coenzymes are needed for pyruvate to acetyl CoA?
B1 (TPP), B2 (FAD), B3 (NAD), B5 (CoAsh), lipoic acid
How do fatty acids enter the Kreb’s cycle?
Beta oxidation into acetyl CoA
What is the purpose of the aconitase enzyme in step two?
prevent acetyl-CoA -> glucose
citrate -> isocitrate
(aconitase)
What two minerals support the function of the aconitase enzyme?
Iron and sulfur
What food are rich in iron?
Spinach, red meat, raisins, dried apricots
What foods are rich in sulfur?
Cruciferous vegetables, eggs, asparagus, onions
What is the allosteric enzyme in the TCA cycle?
Isocitrate dehydrogenase
isocitrate + NAD -> a-ketoglutarate + NADH+H + CO2
(isocitrate dehydrogenase)
What two compounds, if they build up, inhibit isocitrate dehydrogenase?
NADH and ATP
What is the name of the enzyme that uses all the same co-enzymes as pyruvate dehydrogenase?
Alpha-ketoglutarate dehydrogenase
Name the enzyme that converts pyruvate to OAA, and its coenzymes
Pyruvate carboxylase
ATP + biotin
Name the high energy compound made in the step succinyl CoA -> succinate
GTP
(enzyme: succinate thiokinase)
What complex in the cytochrome chain contains the enzyme succinate dehydrogenase?
Complex II
What is the location in the mitochondria of most Kreb’s cycle enzymes?
Mitochondrial matrix
What is the coenzyme for the enzyme fumarase?
H2O (in)
What is the name of the enzyme that converts malate to OAA?
Malate dehydrogenase
What coenzyme is needed for malate dehydrogenase to convert malate to OAA?
NAD+
What do ketogenic compounds enter Kreb’s cycle as?
Acetyl CoA
Name the amino acids that are ONLY ketogenic
lysine, leucine
Name the amino acids that are both ketogenic and gluconeogenic
Phenylalanine, isoleucine, tyrosine, tryptophan
Where do gluconeogenic amino acids enter the Kreb’s cycle?
Other intermediates
What amino acids enter as pyruvate?
Alanine, glycine, cysteine, serine, threonine, tryptophan
What amino acids enter as alpha ketoglutarate?
Histidine, arginine, proline, glutamate, glutamine
What enzyme is used for the amino acids entering as alpha ketoglutarate?
SGPT
What amino acids enter as succinyl CoA?
Valine, isoleucine, methionine
What amino acids enter as fumarate?
Phenylalanine, aspartate, tyrosine
What amino acids enter as oxaloacetate?
Aspartate, asparagine
What enzyme is used for amino acids entering as oxaloacetate?
SGOT/aspartate transaminase
What is the energy yield for 1 acetyl CoA when Kreb’s and ETC are combined without accounting for heat?
12
What is the energy yield for 1 acetyl CoA when Kreb’s and ETC are combined with accounting for heat?
10
What is the total energy yield for aerobic glycolysis (depending on shuttle) without accounting for heat?
36 or 38
What is the total energy yield for aerobic glycolysis (depending on shuttle) accounting for heat?
30 or 32
What three substances decrease the action of pyruvate dehydrogenase by end product inhibition?
NADH, acetyl CoA, ATP
What type of diet increases the concentration of OAA?
High carbohydrates
What is the impact of high carbohydrates in the diet on the rate of the TCA cycle?
Increases the rate
Why does a high alcohol diet slow the rate of the Kreb’s cycle?
Lots of NADH with alcohol dehydrogenase
What is the impact of high levels of citric acid on glycolysis?
Shuts off phosphofructokinase
What pathway is turned on by high levels of citrate in the cytoplasm
Fat synthesis
What is the impact of lack of exercise on the Kreb’s cycle?
Increases ATP which turns off the cycle
What cycle in the liver is connected with the Kreb’s cycle?
Urea cycle
