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Biochemistry > Key Enzymes > Flashcards

Key Enzymes Flashcards

1
Q

What pathway requires Pyruvate Carboxylase?

A

Key regulatory enzyme in Gluconeogenesis

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2
Q

What activates and inhibits Pyruvate Carboxylase?

A

Activator: Acetyl-CoA, Inhibitor: ADP

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3
Q

What cofactors does pyruvate carboxylase require?

A

ATP, Biotin, Bicarbonate (HCO3)

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4
Q

What pathway in the liver and muscle requires glycogen synthase?

A

Key regulatory enzyme in glycogen synthesis

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5
Q

What activates liver glycogen synthase?

A

Glucose and Insulin

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6
Q

What activates muscle glycogen synthase?

A

Insulin

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7
Q

What inhibits liver glycogen synthase?

A

Glucagon and epinephrine

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8
Q

What inhibits muscle glycogen synthase?

A

Epinephrine only

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9
Q

What pathway is glycogen phosphorylase involved in?

A

Glycogenolysis (use of glycogen)

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10
Q

What activates glycogen phosphorylase in the liver?

A

glucagon and epinephrine

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11
Q

What activates glycogen phosphorylase in the muscle?

A

Epinephrine, AMP and Calcium

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12
Q

What inhibits glycogen phosphorylase in the liver?

A

Insulin

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13
Q

What inhibits glycogen phosphorylase in the muscle?

A

Increased ATP and Insulin

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14
Q

What cofactor does glycogen phosphorylase require?

A

PLP- Vitamin B6

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15
Q

Which enzyme in the pentose phosphate pathway requires thymine pyrophosphate?

A

Transketolase

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16
Q

Which enzyme in requires selenium as a cofactor?

A

Glutathione peroxidase

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17
Q

Where are gastric lipase and lingual lipase released from? What is their function?

A

Pancreas; break down of TAGs to free fatty acids and monoglycerides and glycerol

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18
Q

What is the function of pancreatic lipase? What are its products?

A

Function: removal of fatty acids at C1 and C3 of TAGs,
Products: 2 FFAs and 2-monoacyl glycerol

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19
Q

What are the activators of pancreatic lipase?

A

Bile acids, phospholipids, colipase

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20
Q

What is the function of phospholipase A2?

A

Break down of phospholipids into lysophospholipids and fatty acids

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21
Q

What activates phospholipase A2?

A

Trypsin and Calcium

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22
Q

What is the function of cholesteryl ester hydrolase?

A

Break down cholesteryl esters into cholesterol and fatty acids

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23
Q

What activates cholesteryl ester hydrolase?

A

Bile acids

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24
Q

Where is lipoprotein lipase found? What is its function?

A

In the capillary endothelial cell surface of adipose tissue and muscle capillaries, removes fatty acids from TAGs

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25
Q

What activates lipoprotein lipase?

A

apoC-II and phospholipids

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26
Q

What enzyme catalyzes the committed step of fatty acid synthesis?

A

Acetyl-CoA carboxylase

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27
Q

What cofactors does Acetyl-CoA carboxylase require?

A

ATP, Biotin, HCO3 (ABC enzyme)

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28
Q

What activates acetyl-CoA carboxylase?

A

Citrate, dephosphorylation by insulin cascade

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29
Q

What inhibits acetyl-CoA carboxylase?

A

long-chain fatty acids (end-product inhibition), phosphorylation by epinephrine/glucagon cascade

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30
Q

What enzyme does the liver have that adipose tissue does not in regards to TAG synthesis?

A

Liver has glycerol kinase and can use glycerol to synthesize TAGs, adipocytes have to use DHAP

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31
Q

What is the function of hormone sensitive lipase?

A

hydrolysis of TAGs

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32
Q

What activates hormone sensitive lipase?

A

Epinephrine, norepinephrine, glucagon and adrenocorticotropic hormone

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33
Q

What inhibits hormone sensitive lipase?

A

Insulin

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34
Q

What inhibits Beta-oxidation?

A

CPT I inihibited by increased malonyl CoA, 3-hydroxyacyl CoA dehydrogenase inhibited by NADH, thiolase inhibited by acetyl CoA

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35
Q

Where is phospholipase A2 found?

A

In snake venom

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36
Q

Decarboxylation of phosphatidylserine to phosphatidylethanolamine requires what cofactor?

A

SAM– acts as methyl donor

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37
Q

What is the regulatory enzyme in cholesterol biosynthesis?

A

HMG-CoA reductase

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38
Q

What inhibits HMG-CoA reductase?

A

Allosteric inhibition by sterols, hormonal inhibition by glucagon

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39
Q

What enzyme do statin drugs act on?

A

Inhibit HMG-CoA reductase

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40
Q

What activates HMG-CoA reductase?

A

Insulin

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41
Q

What is the regulation point of steroid synthesis?

A

Desmolase (cholesterol to pregnenolone)

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42
Q

What is the key enzyme for protein breakdown in the stomach? What is special about it?

A

Pepsin, activates itself through autocatalytic cleavage

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43
Q

Where can you find trypsin?

A

Small intestine

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44
Q

What is the function of the ubiquitin system?

A

Tags intracellular proteins for breakdown via the proteasome complex

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45
Q

What is the regulated enzyme in urea synthesis?

A

Carbamoyl phosphate synthase I

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46
Q

What activates Carbamoyl phosphate synthase I

A

Arginine and N-acetylglutamine

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47
Q

What enzyme catalyzes teh rate limiting step of heme biosynthesis?

A

ALA synthase

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48
Q

What enzymes in heme biosynthesis are inhibited by lead?

A

ALA dehydratase and Ferrochelatase

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49
Q

What cofactor does ALA synthase require?

A

Pyridoxal phosphate (Vitamin B6)

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50
Q

What enzyme is required for conjugation of bilirubin? Where is it?

A

Liver UDP glucouronyl transferase

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51
Q

What is the rate limiting step of catecholamine synthesis catalyzed by?

A

Tyrosine hydroxylase

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52
Q

What enzyme in catecholamine biosynthesis requires PLP as a cofactor?

A

DOPA decarboxylase

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53
Q

What are the two enzymes involved in catecholamine breakdown?

A

COMT: Catechol-O-methyltransferase
MAO: monamine oxidase

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54
Q

Which enzyme is inhibited in treatment of depression? What is its effect?

A

MAO by MAO inhibitors, reduces the breakdown of serotonin in the synaptic cleft

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55
Q

What are the cofactors required for serotonin synthesis?

A

Tryptophan, tetrahydrobiopterin, PLP

56
Q

What are the cofactors required for melatonin synthesis from serotonin?

A

Acetyl-CoA and S-adenosyl methionine (SAM)

57
Q

What enzyme catalyzes histamine synthesis?

A

PLP-dependent decarboxylase

58
Q

What catalyzes the rate limiting step of purine synthesis?

A

Amidophosphoribosyl transferase

59
Q

What inhibits glutamine phosphoribosyl amidotransferase?

A

AMP and GMP synergistically inhibit the enzyme, when AMP is high GMP synthesis is reduced or vice versa

60
Q

What enzyme is involved in the salvage pathway synthesis of adenine?

A

Adenine phosphoribosyltransferase

61
Q

What enzyme is involved in the salvage pathway synthesis of guanine?

A

Hypoxanthine-guanine phosphoribosyl transferase

62
Q

What is the function of ribonucleotide reductase?

A

Reduce ribose sugars to deoxyribose sugars, form dNTPs from NTPs

63
Q

What is required for the regeneration of ribonucleotide reductase?

A

thioredoxin (which is reduced by NADPH)

64
Q

What is the function of the activity site of ribonucleotide reductase?

A

binding of dATP decreases the catalytic activity of the enzyme and prevents DNA synthesis

65
Q

What is the function of the substrate specificity site of ribonucleotide reductase?

A

Binding of any NTP increases the conversion of NTPs to dNTPs

66
Q

What effect does hydroxyurea have on ribonucleotide reductase?

A

It destroys the free radical in the active site and inhibits the enzyme

67
Q

What enzyme in purine metabolism contains iron and molybdenum?

A

Xanthine oxidase

68
Q

What drug inhibits xanthine oxidase? What disorder does it treat?

A

Allopurinol, treats Gout

69
Q

What inhibits carbamoyl phosphate synthase II?

A

UDP, UTP, dUTP, CTP

70
Q

What activates carbamoyl phosphate synthase II?

A

ATP & PRPP regulated by end products

71
Q

What inhibits aspartate transcarbamoylase? What kind of inhibition?

A

Glycine, via competitive inhibition

72
Q

What inhibits orotidylate decarboxylase?

A

UMP and CMP

73
Q

What activates CTP synthetase?

A

GTP

74
Q

What inhibits CTP synthetase?

A

CTP

75
Q

What cofactor does thymidylate synthase require?

A

N5-N10 methylene tetrahydrofolate

76
Q

What enzyme does fluorouracil target? What mechanism?

A

Irreversibly inhibits thymidylate synthase, suicide inhibition

77
Q

What does methotrexate inhibit?

A

Dihydrofolate analog, competitively inhibits dihydrofolate reductase

78
Q

What does aminopterin inhibit?

A

dihydrofolate analog, competitively inhibits dihydrofolate reductase

79
Q

What does trimethoprim inhibit?

A

Folate analog; binds to bacterial dihydrofolate reductase

80
Q

What enzymes require vitamin B12?

A

methionine synthase and methylmalonyl CoA mutase (involved in homocysteine pathway)

81
Q

What cofactor is required for cobalmin absorption?

A

Intrinsic factor

82
Q

What enzymes require biotin?

A

Carboxylation enzymes (think ABC enzymes)

83
Q

What enzymes require pantothenic acid (B5)?

A

CoA and Acyl carrier proteins in fatty acid synthesis

84
Q

What vitamin is the precursor to tetrahydrofolate?

A

Folate

85
Q

What enzymes require vitamin C?

A

Prolysl and Lysyl hydroxylase in procollagen formation

86
Q

What reactions is pyridoxal phosphate (B6) required in?

A

Transamination, Decarboxylation, Deamination, Condensation, Glycogen phosphorylase

87
Q

What enzymes is riboflavin required for?

A

Complex II of the ETC, Xanthine oxidase

88
Q

What enzyme converts retinal to retinol?

A

Intestinal retinaldehyde reductase

89
Q

What enzyme activates vitamin D?

A

Alpha-1-hydroxylase

90
Q

What enzyme regenerates vitamin K? What drug blocks this enzyme?

A

Epoxide reductase, Warfarin blocks it

91
Q

What is the mechanism of action of glucagon?

A

Bound to G-coupled receptors, activates adenylate cyclase which converts ATP–> cAMP, activates phosphorylase kinase A which phosphorylates other enzymes

92
Q

What is the mechanism of action of insulin?

A

binds to tyrosine kinase receptors–> phosphorylates IRS, SHC, PLC, activate protein phosphatase which dephosphorylates a bunch of enzymes

93
Q

What histone proteins are involved in the nucleosome structure?

A

2 of each: H2A, H2B, H3, H4

94
Q

What is the function of prokaryotic DNA Pol III?

A

Main replicating enzyme for DNA replication

95
Q

What is the function of prokaryotic DNA Pol I?

A

Fills in gaps, joins strands together, removes primers, repair, recombinant DNA synthesis

96
Q

What is the function of prokaryotic DNA Pol II?

A

Repair of DNA

97
Q

What is the function of DNA helicases?

A

Utilize ATP to unwind DNA, to allow ssDNA to be accessible to other enzymes and begin DNA synthesis

98
Q

What is the function of single-stranded binding proteins?

A

trap single strands of DNA in a bracelet like structure (stabilizes them)

99
Q

What enzyme forms the RNA primer?

A

Specialized RNA polymerase

100
Q

What are three special features of DNA polymerase III?

A

High catalytic potency, fidelity and processivity

101
Q

What do DNA topoisomerases do?

A

Relieve torsional stress caused by DNA unwinding

102
Q

What are the two types of DNA topoisomerases and what do they do?

A

Type I: breaks one strand and reseals it

Type II: breaks both strands and reseals them

103
Q

What drugs target Bacterial topoisomerase II?

A

Novobiocin, nalidixic acid, ciprofloxacin

104
Q

What does camptothecin do?

A

Inhbits human topoisomerase I, anti-cancer drug

105
Q

What does etoposide do?

A

Inhibits human topoisomerase II, anti-cancer drug

106
Q

What does DNA polymerase I do?

A

Removes RNA primers and replaces them with DNA

107
Q

What do DNA ligases do?

A

Seal the gaps left by DNA pol I, uses ATP as an energy source

108
Q

What are the functions of DNA pol alpha?

A

Eukaryotic DNA, acts as primase and initiates replication

109
Q

What are the functions of DNA pol beta?

A

Repair of DNA

110
Q

What are the functions of DNA pol gamma?

A

Replication of mitochondrial DNA, also has proof reading ability

111
Q

What are the functions of DNA pol delta?

A

Elongates DNA, also has proof reading ability, completes DNA synthesis on leading and lagging strands

112
Q

What are the functions of DNA pol epsilon?

A

Repair of DNA, acts as proof reader

113
Q

What do telomerases do?

A

Telomerases maintain the ends of chromosomes in eukaryotes by forming an overhang that ensures that all the DNA is replicated

114
Q

What enzyme deficiency is implicated in aging?

A

Telomerases

115
Q

What does reverse transcriptase do?

A

Synthesizes DNA from an RNA template, seen in retroviruses (HIV)

116
Q

What is an exinuclease?

A

UV specific endonuclease that recognizes dimers formed from UV radiating and cleves the strand at the 5’ and 3’ ends taking a segment of ~30 nucleotides

117
Q

What are N-glycosylases?

A

They recognize and remove the bases that have undergone DNA depurination

118
Q

What enzymes are involved in base excision repair?

A

AP endonucleases: deoxyribose phosphate lyase, DNA poymerase and DNA ligase

119
Q

What is the step where transcription is regulated?

A

Initiation of transcription

120
Q

What is the function of the sigma unit of RNA polymerase?

A

It finds the promoter site

121
Q

What subunits make up the core enzyme of RNA Polymerase?

A

Alpha-2, Beta and beta’

122
Q

What is euchromatin?

A

Transcriptionally active DNA (accessible) in interphase

123
Q

What is constitutive heterochromatin?

A

DNA that is always condensed and transcriptionally inactive (near the centromere and telomeres)

124
Q

What is facultative heterochromatin?

A

DNA that is condensed at times but also active at times

125
Q

What is the process of conversion between euchromatin and heterochromatin?

A

Chromatin remodelling

126
Q

What is the function of promoters?

A

Direct RNA polymerase to the transcription start site, on the same strand, recognized by transcription factor 2F

127
Q

What is the most important promoter?

A

TATA box (and CAAT box)

128
Q

What is special about enhancers?

A

They can be on any part of the DNA, they greatly increase the activity of promoters

129
Q

What do snRNPs do?

A

Cleave the RNA at the 5’ end, join to the branch point, cleaves the 3’ end and joins the exons together

130
Q

What is the function of the consensus sequence?

A

help snRNPs recognize splice sites?

131
Q

Where do trans-acting factors bind?

A

On cis-acting elements

132
Q

What is an operon?

A

Prokaryotic regulatory unit of a set of clustered genes

133
Q

What are hormone responsive elements?

A

enhancer-like sequences that allow for global regulation of metabolic pathways by increasing or decreasing the level of transcription

134
Q

Where do members of nuclear-receptor super family of hormones bind?

A

Intracellular hormones, bind to zinc-finger motif of DNA

135
Q

Where do large hormones bind?

A

Bind to extracellular receptors, start a cascade and phosphorylate CREB which binds to CRE via a leucine-zipper motif

136
Q

Where does gene rearrangement occur in adults?

A

Immunoglobulins (B Cells)

Biochemistry (3 decks)

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