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STEP 1 (4) > Biochemistry- Metabolism > Flashcards

Biochemistry- Metabolism Flashcards

1
Q

What metabolic processes occur in the mitochondria?

A

fatty acid oxidation (B-oxidation)

acetyl-CoA production

TCA cycle

oxidative phosphorylation

ketogenesis

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2
Q

What metabolic processes occur in the cytoplasm?

A

glycolysis

fatty acid synthesis

HMP shunt

protein synthesis (RER)

steroid synthesis (SER)

cholesterol synthesis

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3
Q

What metabolic processes occur both in the cytoplasm and mitochondria?

A

heme synthesis

urea cycle

gluconeogenesis

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4
Q

What does a kinase do?

A

uses ATP to add a high energy phosphate onto a substrate (e.g. phosphofructokinase)

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5
Q

What does a phosphorylase do?

A

adds inorganic phosphate onto substrate without using ATP

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6
Q

What does a phosphatase do?

A

removes phosphate groups

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7
Q

What does a dehydrogenase do?

A

catalyzes redox rxns

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8
Q

What does a hydroxylase do?

A

adds hydroxyl group (-OH) onto substrates

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9
Q

What does a carboxylase do?

A

transfers Co2 groups with the help of biotin

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10
Q

What does a mutase do?

A

relocates a functional group within a molecule

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11
Q

What is the rate determining step of glycolysis?

A

phosphofructokinase-1 (PFK-1)

Stimulate: AMP, fructose-2,6-bisphosphate

Inhibit: ATP, citrate

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12
Q

What is the rate determining step of gluconeogenesis?

A

fructose-1,6-bisphosphatase

Stimulates: ATP, acetyl-CoA

Inhibits: AMP, fructose-2,6-bisphosphate

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13
Q

What is the rate determining step of the TCA cycle?

A

isocitrate dehydrogenase

Stimulates: ADP

Inhibits: ATP, NADH

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14
Q

What is the rate determining step of glycogenesis?

A

glycogen synthease

+: glucose-6-phosphate, insulin, cortisol

-: epi, glucagon

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15
Q

What is the rate determining step of glycogenolysis?

A

glycogen phosphorylase

+: epi, glucagon, AMP

-: glucose-6-phosphate, insulin, ATP

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16
Q

What is the rate determining step of HMP shunt?

A

Glucose-6-phosphate dehydrogenase (G6PD)

+: NADP+

-: NADPH

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17
Q

What is the rate determining step of de novo pyrimidine synthesis?

A

carbamoyl phosphate synthetase II

+: ATP

-: UTP

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18
Q

What is the rate determining step of de novo purine synthesis?

A

glutamine-phosphoribosylphosphate (PRPP) amidotransferase

+: none

-: AMP, IMP, GMP

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19
Q

What is the rate determining step of the urea cycle?

A

carbamoyl phosphate synthetase I

+: N-acetylglutamate

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20
Q

What is the rate determining step of fatty acid synthesis?

A

acetyl-CoA carboxylase (ACC)

+: Insulin, citrate

-:glucagon, palmitoyl-CoA

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21
Q

What is the rate determining step of fatty acid oxidation?

A

carnitine acyltransferase I

-: Malonyl CoA

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22
Q

What is the rate determining step of ketogenesis?

A

HMG-CoA synthase

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23
Q

What is the rate determining step of cholesterol synthesis?

A

HMG-CoA reductase

+: insulin, thyroxine

-: glucagon, cholesterol

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24
Q

Describe ATP production

A

Aerobic metabolism of glucose produces 32 net ATp via malate-aspartate shuttle (heart and liver), 30 net ATP via glycerol-3-phosphate shuttle (muscle)

Anaerobic gycolysis produces only 2 net ATP per glucose molecule (arsensic causes glycolysis to produce 0 zero ATP)

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25
Q

What are some universal electron acceptors?

A

Nicotinamides (NAD+ from vitB3 and NADP+) and flavin nucleotides (FAD+ from vitB2)

NAD+ is generally used in catabolic processes to carry reducing equivalents away as NADH and NADPH is used in anabolic processes (steroid and fatty acid synthesis) as a supply of reducing equivalents

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26
Q

What are the functions of hexokinase and glycokinase

A

both are involved in phosphorylation of glucose to yield glucose-6-phosphate (1st step in glycolysis)

At low glucose conc, hexokinase sequesters glucose in the tissue and at high glucose conc, excess glucose is stored in the liver

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27
Q

Describe hexokinase

A

Location: most tissues, except liver and pancreatic B cells

Km: lower (increased affinity)

Vmax: lower (decreased capacity)

Induced by insulin: No

Feedback inhibited by G6P: Yes

Gene mutation associated with maturity onset of the young (MODY): No

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28
Q

Describe glucokinase

A

Location: liver, pancreatic B cells

Km: higher (decreased affinity)

Vmax: higher (increased capacity)

Induced by insulin: Yes

Feedback inhibited by G6P: No

Gene mutation associated with maturity onset of the young (MODY): Yes

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29
Q

net glucolysis eqn

A

Glucose + 2Pi + 2ADP + 2NAD+ -> 2 pyruvate + 2ATP + 2NADH + 2H+ + 2H2O

Eqn not balanced chemically, and exact balanced eqn depends on ionization state of reactants and products

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30
Q

What enzymes in glycolysis require ATP?

A

hexokinase/glucose (glucose to G6P) (glucose-6-P inhibits hexokinase and fructose-6-P inhibits glucokinase)

PFK-1 (+AMP, fructose-2,6-bisphosphate; -ATP, citrate)

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31
Q

What enzymes in glycolysis produce ATP?

A

conversion of 1,3-BPG to 3-PG using phosphoglycerate kinase and

conversion of PEP to pyruvate via pyruvate kinase (fructose-1,6-bisphosphate+; -ATP, alanine)

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32
Q

While PFK-2 catalyzes conversion of fructose-6-P to fructose-1,6-BP in glycolysis, what catalyzes the reverse rxn to promote gluconeogenesis?

A

FBPase-2 (fructose bisphosphatase-2)

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33
Q

FBPase-2 and PFK-2 are essentially the same enzyme whose function is reversed by what?

A

phosphorylation by protein kinase A (= more FBPase-2)

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34
Q

What does fasting promote in relation to glucose?

A

fasting increases glucagon which increases cAMP which increases PKA which promotes increased FBPase-2 and less PFK-2, leading to gluconeogenesis

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35
Q

What does the fed state promote in relation to glucose?

A

increased insulin leading to decreased cAMP= less PKA= less FBPase-2, more PFK-2= glycolysis

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36
Q

Describe the pyruvate dehydrogenase complex

A

Mitochondrial enzyme complex linking glycolysis and TCA cycle. Differentially regulated in fed/fasting states (active in fed state)

Rxn: pyruvate + NAD+ + CoA -> acetyl-CoA + CO2 + NADH

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37
Q

What cofactors are needed for the pyruvate dehydrogenase complex?

A

pyrophosphate (B1, thiamine, TPP)

FAD (B2, riboflavin)

NAD (B3, niacin)

CoA (B5, pantothenic acid)

Lipoic acid

Activated by exercise, which promotes increased NAD+/NADH ratio, increased ADP, and increased Ca2+

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38
Q

What inhibits lipoic acid and how does that present clinically?

A

Arsenic, leading to vomiting, rice-water stools, garlic breath

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39
Q

What does pyruvate dehydrogenase complex deficiency result in?

A

causes a buildup of pyruvate that gets shunted to lactate (via LDH) and alanine (via ALT)

X-linked disease

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40
Q

How does pyruvate dehydrogenase complex deficiency present?

A

neurologic defects, lactic acidosis, increased serum alanine starting in infancy

41
Q

How is pyruvate dehydrogenase complex deficiency tx?

A

increase intake of ketogenic nutrients (e.g. high fat content or more lysine and leucine)

Lysine and Leucine are the only purely ketogenic AAs

42
Q

What 4 things can primarily happen to pyruvate?

A
43
Q

What is the purpose of the Cahill cycle? What cofactor is needed for ALT?

A

Alanine carries amino groups from muscle to the liver

needs B6

44
Q

What cofactor does pyruvate carboxylase use?

A

biotin

45
Q

What cofactors does pyruvate dehydrogenase use?

A

B1, B2, B3, B5, and lipoic acid

46
Q

What cofactor does lactic acid dehydrogenase (LDH) use?

A

B3 (note that conversion of pyruvate to lactic acid is the end of the anaerobic glycolysis (the major pathway in RBCs, WBCs, kidney medulla, lens, cornea, and testes)

47
Q

What are the products of the TCA cycle?

A

3NADH, 2Co2, 1GTP, 10ATP, 1FADH2 per Acetyl-CoA (2x per glucose molecule)

Occurs in the mitochondria

48
Q

1st step in TCA cycle

A

conversion of pyruvate (3C) to acetyl-CoA via PDH (-ATP, Acetyl-CoA, NADH)

49
Q

2nd step in TCA cycle

A

conversion of oxaloacetate (4C) to citrate (6C) by adding acetyl CoA (2C) and via citrate synthase

50
Q

3rd step in TCA cycle

A

conversion of citrate (6C) to cis-aconitate to isocitrate (6C)

51
Q

4th step in TCA cycle

A

conversion of isocitrate to a-KG (5C) via isocitrate dehydrogenase (giving off Co2+ NADH) (-ATP, NADH; +ADP)

52
Q

5th step in TCA cycle

A

conversion of a-KG (5C) to succinyl-CoA (4C) via a-KG dehydrogenase (giving off NADH +CO2) (-succinyl CoA, NADH, ATP)

53
Q

6th step in TCA cycle

A

conversion of succinyl CoA (4C) to succinate (4C) giving off GT + CoA

54
Q

7th step in TCA cycle

A

conversion of succinate to fumarate giving of FADH2

55
Q

8th step in TCA cycle

A

conversion of fumarate (4C) to malate (4C)

56
Q

9th step in TCA cycle

A

conversion of malate (4C) to oxaloacetate (4C) giving off NADH

57
Q

Describe the electron transport chain and oxidative phosphorylation

A

NADH electrons from glycolysis enter mitochondria via the malate-aspartate of glycerol-3-phosphate shuttle. FADH2 electrons are transferred to complex II (at a lower energy level than NADH).

The passage of electrons results in the formation of a proton gradient that, coupled to oxidative phsophorylation, drives the production of ATP

58
Q

How many ATP are produced per NADH? per FADH2?

A

NADH: 2.5ATP

FADH2: 1.5ATP

59
Q

What drug inhibits complex I of the ETC? complex III? IV?

A

I: Roterone

III: Antimycin

IV: Cyanide, CO

60
Q

Oxidative phosphorylation poisons: Electron transport inhibitors

A

directly inhibit electron transport, causing a decreased proton gradient and block of ATP synthesis

Rotenone, cyanide, antimycin A, CO

61
Q

Oxidative phosphorylation poisons: ATP synthase inhibitors

A

directly inibit mitochondrial ATP synthase, causing an increased proton gradient.

Oligomycin

62
Q

Oxidative phosphorylation poisons: Uncoupling agents

A

Increase permeability of membrane, causing a decreased proton gradient and increased O2 consumption. ATP synthesis stops, but electron transport continues. Produces heat

2,4-Dinitrophenol (used for weight loss), aspirin (fever often occur after aspirin OD), thermogenin in brown fat

63
Q

What are the irreversible enzymes of gluconeogenesis?

A

Pyruvate carboxylase

Phosphoenolpyruvate carboxykinase

Fructose-1,6-bisphosphatase

Glucose-6-phosphatase

64
Q

What does Pyruvate carboxylase do?

A

in mitochondria, converts pyruvate to oxaloacetate

requires biotin, ATP

Activated by acetyl-CoA

65
Q

What does PEP carboxylkinase do?

A

In cytosol. converts oxaloacetate to PEP (requires GTP)

66
Q

What does fructose-1,6- bisphosphatase do?

A

in cytosol. converts fructose-1,6-bisphosphate to fructose-6-phosphate

+citrate; -fructose-2,6-bisphosphate

67
Q

What does glucose-6-phosphatase do?

A

In ER. converts G6P to glucose

68
Q

Where does gluconeogenesis occur?

A

primarily in the liver and serves to maintain euglycemia during fasting

Enzymes are also found in the kidney and intestinal epithelium (muscle cannot participate in gluconeogenesis because it lacks G6P)

69
Q

More about gluconeogenesis

A

Odd-chain fatty acids yield 1 propionyl-CoA during metabolism which can enter the TCA as succinyl CoA, and serve as a glucose source

Even-chain fatty acids cannot produce new glucose, since they yield only acetyl-CoA equivalents

70
Q

What is the HMP shunt (pentose phosphate pathway)?

A

Provides a source of NADPH from abundantly available glucose-6-P (NADPH is required for reductive rxns, e.g. glutathione reduction inside RBCs, fatty acid and cholesterol biosynthesis)

Additionally, this pathway yields ribose for nucleotide sytnhesis and glycolytic intermediates. 2 distinct phases (oxidative and nonoxidative), both of which occur in the cytoplasm. No ATP is need or produced.

71
Q

What are some body sites where the HMP shunt (pentose phosphate pathway) occurs?

A

lactating mammary glands, liver, adrenal cortex, (sites of fatty acid or steroid synthesis)

72
Q

Describe the oxidative (irreversible) part of the HMP shunt (pentose phosphate pathway)

A

G6P to Co2, 2NADPH, and ribulose-5-P via glucose-6-P dehydrogenase

73
Q

Describe the nonoxidative (reversible) part of the HMP shunt (pentose phosphate pathway)

A

ribulose-5-P to ribose-5-P, glucose-3-P, and fructose-6-P via phosphopentose isomerase transketolases (requires B1)

74
Q

What does G6PD deficiency result in?

A

NADPH is needed to keep glutathiona reduced, which in turn detoxifies free radicals and peroxides. Decreased levels of NADPH in RBCs leads to hemolytic anemia due to poor RBC defense against oxidizing agents, (e.g. fava beans, sulonamides, primaquine, antiTB drugs)

Infection can also precipitate hemolysis (free radicals generated via inflammatory response can diffuse into RBCS and cause oxidative damage)

75
Q

Describe the glutathione pathway

A

G6PD conevrts G6P to 6-phosphogluconate as NADP+ is reduced to NADPH

glutathione reductase then reduces GSSG to 2GSH as NADPH is oxidized back to NADP+

Glutathiona peroxidase then reduces H2O2 to 2H2O as GSH is oxidized back to GSSG

76
Q

What are the main findings of G6PD deficiency

A

x-linked recessive disorder; most common enzyme deficiency

offers increased malarial resistance

Heinz bodies (denatured hemoglobin precipitates within RBCs due to oxidative stress) (below)

Bite cells- result from the phagocytic removal of Heinz bodies by splenic macrophages

77
Q

What causes essential fructosuria?

A

involves a defect in fructokinase. AR

described as a bening, asymptomatic condition, since fructose is not trapped in cells

78
Q

How does essential fructosuria present?

A

fructose appears in blood and urine

79
Q

What causes fructose intolerance?

A

AR inherited deficiency of aldolase B

80
Q

What happens with aldolase B deficiency in fructose intolerance?

A

Fluctose-1-P accumulates, causing a decrease in available phosphate, which results in inhibition of glycogenolysis and gluconeogenesis. Symptoms then present following consumption of fruit, honey, or juice and consist of hypoglycemia, jaundice, cirrhosis, and vomiting

81
Q

How is fructose intolerance diagnosis and tx?

A

diagnosis: urine dipstick will be negatie

reducing sugar can be detected in the urine (nonspecific test for inborn errors of carb metabolism)

tx: decrease intake of both fructose and sucrose (glucose + fructose)

82
Q

Describe fructose metabolism

A

Fructose is converted to fructose-1-P via fructokinase (producing ADP from ATP)

Fructose-1-P is converted to glyceraldehyde and dihydroxyacetone-P via aldolase B

83
Q

What happens to glyceraldehyde during fructose metabolism?

A

can either:

be converted to glycerol (NADH to NAD+)

or be converted to glyceraldehyde-3-P via triose kinase (ATP to ADP) (simialrly, dihdyroxyacetone-P is converted directly to glyceraldehyde-3-P). this end product then enters glycolysis

84
Q

What would hereditary deficiency in galactokinase cause?

A

galactokinase deficiency, marking accumulating galactitol when galactose is present in the diet

relatively mild condition (AR)

85
Q

How does galactokinase deficiency present?

A

galactose appears in blood and urine, infantile cataracts

may present as failure to track objects or to develop a social smile

86
Q

What does absence of galactose-1-phosphate uridyltransferase cause?

A

Classic galactosemia

87
Q

Describe Classic galactosemia

A

AR syndrome marked by damage induced by accumulation of toxic substances (including glactitol, which accumulates in the lens of the eyes), resulting in symptoms of:

failure to thrive, jaundice, hepatomegaly, infantile cataratcts, intellectual disability, and increased risk of E. coli sepsis i neonates

88
Q

How is Classic galactosemia tx?

A

exclude galactose and lactose (galactose + glucose) from diet

89
Q

Describe galactose metabolism

A

galactose can be converted to either galactitol via aldose reductase or galactose-1-P via galactokinase (ATP to ADP)

Galactose-1-P is converted to glucose-1-P via uridyltransferase as UDP-Glu is converted to UDP-Gal via 4-epimerase

90
Q

Describe the sorbitol pathway

A

glucose converted to sorbitol via aldose reductase (NADPH) and then to fructose via sorbitol dehydrogenase (NAD+)

Note that the schwann cells, retine, and kidneys have only aldose reductase and similar for the lens

91
Q

What is the purpose of making sorbitol?

A

It is an alternative method of trapping glucose in the cell by converting it to its alcohol counterpart, sorbitol, via aldose reductase. Some tissues then convert sorbitol to fructose using sorbitol dehydrogenase and tissues lacking this enzyme are at risk of accumulating sorbitol, which causes osmotic damage (e.g. cataracts, retinopathy, and peripheral neuropathy seen with chronic hyperglycemia in diabetes)

92
Q

What is the result of lactase deficiency?

A

insufficient lactase leads to dietary lactose intolerance (note that lactase is a brush-border enzyme used to break down lactase to glucose and galactose)

93
Q

Primary, secondary, and congenital lactase deficiency

A

Primary: age-dependent decline after childhood (due to absence of lactase-persistent allele), common in Asians, Africans and Native Americans

Secondary: loss of brush border due to gastroenteritis (e.g. rotavirus), autoimmune disease, etc.

Congenital: rare, due to defective gene

94
Q

T or F. Only L-amino acids are found in protein

A

T.

95
Q

What are the essential glucogenic AAs?

A

methionine (met), valine (Val), and histidine (His)

96
Q

What are the essential glucogenic/ketogenic AAs?

A

isoleucine (IlE), phenylalanine (Phe), thronine (Thr), and trptophan (Trp)

97
Q

What are the essential ketogenic AAs?

A

leucine (Leu), lysine (Lys)

98
Q

What are the acidic AAs?

A

aspartic acid (Asp) and glutamic acid (Glu). Negatively charged at body pH

99
Q

What are the basic AAs?

A

arginne (Arg; most basic), lysine (Lys), and histidine (His)

His no charge at body pH

Note: Arg and His are required during growth periods and Arg and Lys are in histones

STEP 1 (4) (18 decks)

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