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MCAT > Important Biochemistry Concepts > Flashcards

Important Biochemistry Concepts Flashcards

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MCAT flashcards
1
Q

Glycolysis, 3 major steps?

A

Hexokinase converts glucose to glucose-6-p (ATP cost)

Phosofructase(PFK) converts fructose-6-P to fructose-1,6-P2 (ATP cost) (COMMITTED STEP)

Pyruvate kinase converts PEP to pyruvate, produces 2 ATP

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2
Q

Glycolysis, anaerobic or aerobic

A

Anaerobic

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3
Q

Glycolysis, full chemical reaction?

A

Glucose -> Glucose-6-Phosphate -> Fructose-6-Phosphate -> Fructose-1,6-biphosphate (COMMITTED)

-> Glyceraldehyde-3-Phosphate-> 1,3-Bisphosphoglycerate -> 3-Phosphoglycerate -> 2-Phosphoglycerate -> PhosphoenolPyruvate -> Pyruvate

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4
Q

Glycolysis, overall reactants and products?

A

Reactants: Glucose, 2NAD+, and 2ADP,Pi

Products: 2 Pyruvate, 2NADH, and 2ATP, 2H+

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5
Q

Glycolysis, location?

A

Cytosol

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6
Q

Fermentation, purpose?

A

Oxidizes NADH to regenerate NAD+ while reducing pyruvate to lactic acid (or ethanol, yeast)

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7
Q

Pyruvate dehydrogenase complex, definition?

A

Where oxidative decarboxylation of pyruvate occurs to regenerate acetyl-CoA

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8
Q

Pyruvate dehydrogenase complex, location?

A

Mitochondrial matrix

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9
Q

Pyruvate dehydrogenase complex, overall reactants and products?

A

Uses up CoA, NAD+, pyruvate

Creates NADH, CO2, Acetyl-CoA

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10
Q

Importance of thiamine

A

TPP is a prosethetic group that helps with decarboxylation of pyruvate, it is derived from Thiamine (Vitamin B)

Pyruvate Decarboxylation Complex

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11
Q

Pyruvate dehydrogenase complex, allosteric inhibition?

A

ATP and fatty acids inhibit oxidative decarboxylation of pyruvate by the pyruvate dehydrogenase complex, s_ince acetyl-CoA goes to fatty acid and ATP synthesis_

Pyruvate dehydrogenase also creates NADH and Acetyl CoA, high levels of those inhibit the function

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12
Q

Krebs Cycle, purpose?

A

Production of 3 NADH and 1 FADH2 for the electron transport chain

Also produces 2 ATP

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13
Q

Krebs Cycle, location?

A

Mitochondrial Matrix

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14
Q

Krebs Cycle, overall reactants and products?

A

Per 1 turn:

Reactants: Acetyl-CoA (from pyruvate), OAA from previous cycle

Products: 2 CO2, 3 NADH, 1 GTP, 1 FADH2

each glycose does 2 turns

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15
Q

Krebs Cycle, regulation methods?

A

Substrate availability - amino acids can be converted to alpha-ketoglutarate to speed up cycle

Substrates inhibit their enzymes - citrate inhibits citrate synthase; succinyl-CoA inhibits aKG dehydrogenase

Allosteric regulation - ATP, NADH inhibit TCA cycle

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16
Q

Krebs Cycle, full chemical reaction?

A

-> Citrate -> Isocitrate -> alpha-Ketaglutorate -> Succinyl-CoA -> Succinate -> Fumarate -> L-Malate -> OAA -> Citrate

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17
Q

Kreb Cycle, steps that produce NADH?

A

Isocitrate dehydrogenase - Isocitrate to alpha-ketoglutarate

aKG dehydrogenase - alpha-keto glutarate to succinyl CoA

Malate dehydrogenase - malate to OAA

3 per turn, 6 per glucose

Pyruvate Dehydrogenase complex also produces an NADH

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18
Q

Krebs Cycle, steps that produce FADH2

A

Succinate dehydrogenase - Succinate to fumarate

1 per turn, 2 per glucose

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19
Q

Krebs Cycle, steps that produce GTP?

A

Succinyl-CoA synthetase - succinyl-CoA to succinate

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20
Q

What is oxidative phosphorylation?

A

The electron transport chain (Empty electron carriers) + chemiosmosis (ATP production)

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21
Q

Electron transport chain, location?

A

inner Mitochondrial Membrane. (Protons are pumped into the intermembrane space from the matrix)

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22
Q

Electron transport chain, purpose?

A

To create a proton gradient as NADH and FADH2 are oxidized

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23
Q

Electron transport chain, location?

A

Inner mitochondrial membrane

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24
Q

Electron transport chain, pathway?

A

Complex 1 - NADH dehydrogenase enzyme, pumps hydrogen into intermembrane space and transfers electrons from NADH

Complex 2 - Succinate dehydrogenase enzyme, transfers electrons from FADH2, no H+ pumped

Ubinquinone (Q) - Transfers electrons from Complex 1 and 2 to Complex 3

Complex 3 - Cytochrome C reductase enzyme, carries electrons to complex 4, pumps protons into intermembrane space

Cytochrome C - Transfers electrons from Complex 3 to Complex 4

Complex 4 - Cytochrome C oxidase enzyme, oxygen is converted to water, pumps protons into intermembrane space

Onward to Chemiosmosis

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25
Q

Electron transport chain, definition of prosthetic groups?

A

A prosthetic group is a non-protein molecule required for the activity of a protein

26
Q

Electron Transport chain, overall reactants and products?

A

Reactants: Hydrogen ions, oxygen, NADH, FADH2

Products: Water, ATP

27
Q

ATP yield, value of NADH?

A

2.5 ATP

28
Q

ATP yield, value of FADH2?

A

1.5 ATP

29
Q

ATP yield, total eukaryotic and prokaryotic?

A

Eukaryotic = ~30 ATP

Prokaryotic = ~ 32 ATP

30
Q

Gluconeogenesis, purpose?

A

Produces glucose from pyruvate with ATP when glucose is low (fasting) and ATP is high

31
Q

Gluconeogenesis, overall reactants and products?

A

Reactants: 4 ATP, 2 GTP, 2 NADH, 2 pyruvic acid, 6H2O, 2H+

Products: Glucose, 4 ADP, 2 GDP, 2 NAD+, 6HPO42-, 6H+

(Reverse of Glycolysis)

32
Q

Gluconeogensis, location?

A

Mainly liver, also kidneys

33
Q

Gluconeogenesis, how does glucose production differ from glycolysis?

A

Irreversible

Formation of glucose, fructose-6-P, and PEP are irreversible steps that push equilibrium to favor gluconeogenesis

34
Q

Gluconeogensis, what is the alternative mean of raising blood glucose levels?

A

Degradation of glycogen, stored in the liver

35
Q

Gluconeogenesis, pathway and important enzymes?

A

Reverse path of glycolysis, with alternatives for glycolysis’s irreversible steps 1, 3 and 10.

Alternative enzymes:

Pyruvate carboxylase to convert pyruvate to OAA

PEP carboxykinase to convert OAA to PEP

(OAA is unique intermediate, glycolysis has direct transition from pyruvate to PEP)

Fructose-1,6-bisphosphatase to convert Fructose-1,6-bisphosphate to Fructose-6-Phosphate

Glucose-6-phosphatase to convert Glucose-6-Phosphate to Glucose

36
Q

Gluconeogenesis, enzymes that require ATP

A

Pyruvate carboxylase (unique), pyruvate to OAA

PEP carboxykinase (unique), OAA to PEP

Phosphoglycerate kinase (also glycolysis), 3-phosphoglycerate to 1,3-bisphosphoglycerate

6 total per glucose

Steps 10(x2) and 7 of glycolysis, and steps 1 and 5 of gluconeogenesis)

37
Q

Gluconeogenesis, steps that require NADH?

A

1,2-biphosphoglycerate to glyceraldehyde-3-P

2 total per glucose

(Step 4 of glycolysis)

38
Q

Gluconeogenesis, possible starting material?

A

Lactate, pyruvate, glycerol (enters through dihydroxyacetone phosphate), amino acids (enters through pyruvate), any Krebs cycle intermediates (enters through OAA)

39
Q

Glycogenesis, purpose and regulation?

A

Production of glycogen from glycose to store in skeletal muscle and/or liver

Stimulated by insulin and high glucose levels

40
Q

Glycogenesis, enzymes?

A

Hexokinase, phophoglucomutase, glycogen synthase

41
Q

Glycogenolysis, purpose?

A

Breaking down glycogen into glucose to provide immediate energy and to maintain blood glucose levels during fasting

42
Q

Glycogenolysis, regulation?

A

Stimulated hormonally by glucagon and epinephrine

Inhibited hormonally by insulin

Hormonal regulation through cAMP/pKA signalling

Inhibited allosterically by ATP and and glucose

43
Q

Glycogenolysis, enzymes?

A

Glycogen phosphorylase catalyzes the sequential phosphorolysis/breaking down of glycogen (no ATP required)

Other enzymes include phosphoglucomutaseandglu-6-phosphatase

44
Q

Pentose phosphate pathway, purpose and products?

A

2 phase alternative process to glycolysis, glucose oxidation

Produces 2 NADPHs (reducing power in fatty acid synthesis, eliminating free radicals)

and ribose-5-phosphate (nucleotide precursor)

45
Q

Pentose phosphate pathway, location?

A

Cytosol

46
Q

Pentose phosphate pathway, oxidative phase?

A

Glucose-6-phosphate is converted to ribulose-5-P with glucose-6-phosphate dehydrogenase

47
Q

Pentose phosphate pathway, nonoxidative phase?

A

Ribulose-5-phosphate is converted to ribose-5-phosphate and 2 glycolysis intermediates

48
Q

Fatty acid/beta oxidation, purpose?

A

Breaking down fatty acids into NADH, FADH2, and acetyl CoA (for use in Krebs cycle)

Huge source of ATP

49
Q

Fatty acid/beta oxidation, location?

A

Mitochondria for eukarytotic cells

Cytosol for prokaryotic cells

50
Q

Fatty acid/beta oxidation, process?

A

2 carbons removed from fatty acid chain with each round of oxidation, which produce single molecules of acetyl-CoA

Cycle repeats until fatty acid is 2 or 3 carbons long

51
Q

Fatty acid/beta oxidation, enzymes?

A

For saturated fatty acids - dehydrogenase

For unsaturated fatty acids - isomerase

52
Q

Fatty acid/beta oxidation, requirements?

A

ATP to activate, FAD and NAD+ for each 2C to produce FADH2 and NADH

53
Q

Fatty acid/beta oxidation, precursor/enzyme for metabolism?

A

Before oxidation, fatty acids must be activated by addition of S-CoA to carboxylic end (in cytoplasm)

Lipase is an enzyme that breaks down triglycerides

54
Q

Fatty acid ketogenesis, purpose?

A

Under metabolic conditions associated with high rate of fatty acid oxidation (starvation, keto), the liver produces ketone bodies from acetyl-CoA as a source of energy.

These ketone bodies can enter brain or other organisms to be reconverted to acetyl-CoA

55
Q

Fatty acid ketogenesis, ketone bodies?

A

Acetone, Acetoacetate, 3-hydroxybutyrate

(Acetoacetate can split to form the other two)

56
Q

Fatty acid ketogenesis, regulation?

A

Triggered by low blood glucose and low glycogen

OR

Triggered by high blood glucose and low insulin

57
Q

Fatty acid synthesis, purpose and precursor molecules?

A

Creation of fatty acids from activated acetyl-COA and malonyl-CoA

58
Q

Fatty acid synthesis, location?

A

Cytosol

59
Q

Fatty acid synthesis, process?

A

Acetyl-CoA and Malonyl-CoA are activated by ACP (acyl carrier protein) to acetyl-_ACP_ and Malonyl-_ACP_

Acetyl-CoA is converted to Acetyl-FAS (fatty acid attached)

Fatty acid synthase combines malonyl-ACP with acetyl

2 NADPH’s used (per round) to remove ketone and double bond

Cycle repeats, adding activated malonyl-CoA to create fatty acid chain (typically around 16 carbons)

60
Q

Protein catabolism, 3 endpoints?

A

Can be used to construct other proteins

Amino end can be used for nucleotides or urea

Remaining carbon skeleton can be converted to acetyl-CoA or glucose (glycolytic or ketogenic pathways)

61
Q

Protein catabolism, process?

A

Hydrolysis breaks peptide bond to detach amino acid from peptide chain

Amino acid deamination utilizes NAD+ and produces NADH

62
Q

Insulin and Glucagon regulation

A
  • Insulin helps the cells absorb glucose, promotes
  • Glucagon instructs the liver to release stored glucose, promotes

MCAT (10 decks)

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