Key Enzymes Flashcards
1
Q
What pathway requires Pyruvate Carboxylase?
A
Key regulatory enzyme in Gluconeogenesis
2
Q
What activates and inhibits Pyruvate Carboxylase?
A
Activator: Acetyl-CoA, Inhibitor: ADP
3
Q
What cofactors does pyruvate carboxylase require?
A
ATP, Biotin, Bicarbonate (HCO3)
4
Q
What pathway in the liver and muscle requires glycogen synthase?
A
Key regulatory enzyme in glycogen synthesis
5
Q
What activates liver glycogen synthase?
A
Glucose and Insulin
6
Q
What activates muscle glycogen synthase?
A
Insulin
7
Q
What inhibits liver glycogen synthase?
A
Glucagon and epinephrine
8
Q
What inhibits muscle glycogen synthase?
A
Epinephrine only
9
Q
What pathway is glycogen phosphorylase involved in?
A
Glycogenolysis (use of glycogen)
10
Q
What activates glycogen phosphorylase in the liver?
A
glucagon and epinephrine
11
Q
What activates glycogen phosphorylase in the muscle?
A
Epinephrine, AMP and Calcium
12
Q
What inhibits glycogen phosphorylase in the liver?
A
Insulin
13
Q
What inhibits glycogen phosphorylase in the muscle?
A
Increased ATP and Insulin
14
Q
What cofactor does glycogen phosphorylase require?
A
PLP- Vitamin B6
15
Q
Which enzyme in the pentose phosphate pathway requires thymine pyrophosphate?
A
Transketolase
16
Q
Which enzyme in requires selenium as a cofactor?
A
Glutathione peroxidase
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
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
19
Q
What are the activators of pancreatic lipase?
A
Bile acids, phospholipids, colipase
20
Q
What is the function of phospholipase A2?
A
Break down of phospholipids into lysophospholipids and fatty acids
21
Q
What activates phospholipase A2?
A
Trypsin and Calcium
22
Q
What is the function of cholesteryl ester hydrolase?
A
Break down cholesteryl esters into cholesterol and fatty acids
23
Q
What activates cholesteryl ester hydrolase?
A
Bile acids
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
25
What activates lipoprotein lipase?
apoC-II and phospholipids
26
What enzyme catalyzes the committed step of fatty acid synthesis?
Acetyl-CoA carboxylase
27
What cofactors does Acetyl-CoA carboxylase require?
ATP, Biotin, HCO3 (ABC enzyme)
28
What activates acetyl-CoA carboxylase?
Citrate, dephosphorylation by insulin cascade
29
What inhibits acetyl-CoA carboxylase?
long-chain fatty acids (end-product inhibition), phosphorylation by epinephrine/glucagon cascade
30
What enzyme does the liver have that adipose tissue does not in regards to TAG synthesis?
Liver has glycerol kinase and can use glycerol to synthesize TAGs, adipocytes have to use DHAP
31
What is the function of hormone sensitive lipase?
hydrolysis of TAGs
32
What activates hormone sensitive lipase?
Epinephrine, norepinephrine, glucagon and adrenocorticotropic hormone
33
What inhibits hormone sensitive lipase?
Insulin
34
What inhibits Beta-oxidation?
CPT I inihibited by increased malonyl CoA, 3-hydroxyacyl CoA dehydrogenase inhibited by NADH, thiolase inhibited by acetyl CoA
35
Where is phospholipase A2 found?
In snake venom
36
Decarboxylation of phosphatidylserine to phosphatidylethanolamine requires what cofactor?
SAM-- acts as methyl donor
37
What is the regulatory enzyme in cholesterol biosynthesis?
HMG-CoA reductase
38
What inhibits HMG-CoA reductase?
Allosteric inhibition by sterols, hormonal inhibition by glucagon
39
What enzyme do statin drugs act on?
Inhibit HMG-CoA reductase
40
What activates HMG-CoA reductase?
Insulin
41
What is the regulation point of steroid synthesis?
Desmolase (cholesterol to pregnenolone)
42
What is the key enzyme for protein breakdown in the stomach? What is special about it?
Pepsin, activates itself through autocatalytic cleavage
43
Where can you find trypsin?
Small intestine
44
What is the function of the ubiquitin system?
Tags intracellular proteins for breakdown via the proteasome complex
45
What is the regulated enzyme in urea synthesis?
Carbamoyl phosphate synthase I
46
What activates Carbamoyl phosphate synthase I
Arginine and N-acetylglutamine
47
What enzyme catalyzes teh rate limiting step of heme biosynthesis?
ALA synthase
48
What enzymes in heme biosynthesis are inhibited by lead?
ALA dehydratase and Ferrochelatase
49
What cofactor does ALA synthase require?
Pyridoxal phosphate (Vitamin B6)
50
What enzyme is required for conjugation of bilirubin? Where is it?
Liver UDP glucouronyl transferase
51
What is the rate limiting step of catecholamine synthesis catalyzed by?
Tyrosine hydroxylase
52
What enzyme in catecholamine biosynthesis requires PLP as a cofactor?
DOPA decarboxylase
53
What are the two enzymes involved in catecholamine breakdown?
COMT: Catechol-O-methyltransferase
MAO: monamine oxidase
54
Which enzyme is inhibited in treatment of depression? What is its effect?
MAO by MAO inhibitors, reduces the breakdown of serotonin in the synaptic cleft
55
What are the cofactors required for serotonin synthesis?
Tryptophan, tetrahydrobiopterin, PLP
56
What are the cofactors required for melatonin synthesis from serotonin?
Acetyl-CoA and S-adenosyl methionine (SAM)
57
What enzyme catalyzes histamine synthesis?
PLP-dependent decarboxylase
58
What catalyzes the rate limiting step of purine synthesis?
Amidophosphoribosyl transferase
59
What inhibits glutamine phosphoribosyl amidotransferase?
AMP and GMP synergistically inhibit the enzyme, when AMP is high GMP synthesis is reduced or vice versa
60
What enzyme is involved in the salvage pathway synthesis of adenine?
Adenine phosphoribosyltransferase
61
What enzyme is involved in the salvage pathway synthesis of guanine?
Hypoxanthine-guanine phosphoribosyl transferase
62
What is the function of ribonucleotide reductase?
Reduce ribose sugars to deoxyribose sugars, form dNTPs from NTPs
63
What is required for the regeneration of ribonucleotide reductase?
thioredoxin (which is reduced by NADPH)
64
What is the function of the activity site of ribonucleotide reductase?
binding of dATP decreases the catalytic activity of the enzyme and prevents DNA synthesis
65
What is the function of the substrate specificity site of ribonucleotide reductase?
Binding of any NTP increases the conversion of NTPs to dNTPs
66
What effect does hydroxyurea have on ribonucleotide reductase?
It destroys the free radical in the active site and inhibits the enzyme
67
What enzyme in purine metabolism contains iron and molybdenum?
Xanthine oxidase
68
What drug inhibits xanthine oxidase? What disorder does it treat?
Allopurinol, treats Gout
69
What inhibits carbamoyl phosphate synthase II?
UDP, UTP, dUTP, CTP
70
What activates carbamoyl phosphate synthase II?
ATP & PRPP regulated by end products
71
What inhibits aspartate transcarbamoylase? What kind of inhibition?
Glycine, via competitive inhibition
72
What inhibits orotidylate decarboxylase?
UMP and CMP
73
What activates CTP synthetase?
GTP
74
What inhibits CTP synthetase?
CTP
75
What cofactor does thymidylate synthase require?
N5-N10 methylene tetrahydrofolate
76
What enzyme does fluorouracil target? What mechanism?
Irreversibly inhibits thymidylate synthase, suicide inhibition
77
What does methotrexate inhibit?
Dihydrofolate analog, competitively inhibits dihydrofolate reductase
78
What does aminopterin inhibit?
dihydrofolate analog, competitively inhibits dihydrofolate reductase
79
What does trimethoprim inhibit?
Folate analog; binds to bacterial dihydrofolate reductase
80
What enzymes require vitamin B12?
methionine synthase and methylmalonyl CoA mutase (involved in homocysteine pathway)
81
What cofactor is required for cobalmin absorption?
Intrinsic factor
82
What enzymes require biotin?
Carboxylation enzymes (think ABC enzymes)
83
What enzymes require pantothenic acid (B5)?
CoA and Acyl carrier proteins in fatty acid synthesis
84
What vitamin is the precursor to tetrahydrofolate?
Folate
85
What enzymes require vitamin C?
Prolysl and Lysyl hydroxylase in procollagen formation
86
What reactions is pyridoxal phosphate (B6) required in?
Transamination, Decarboxylation, Deamination, Condensation, Glycogen phosphorylase
87
What enzymes is riboflavin required for?
Complex II of the ETC, Xanthine oxidase
88
What enzyme converts retinal to retinol?
Intestinal retinaldehyde reductase
89
What enzyme activates vitamin D?
Alpha-1-hydroxylase
90
What enzyme regenerates vitamin K? What drug blocks this enzyme?
Epoxide reductase, Warfarin blocks it
91
What is the mechanism of action of glucagon?
Bound to G-coupled receptors, activates adenylate cyclase which converts ATP--> cAMP, activates phosphorylase kinase A which phosphorylates other enzymes
92
What is the mechanism of action of insulin?
binds to tyrosine kinase receptors--> phosphorylates IRS, SHC, PLC, activate protein phosphatase which dephosphorylates a bunch of enzymes
93
What histone proteins are involved in the nucleosome structure?
2 of each: H2A, H2B, H3, H4
94
What is the function of prokaryotic DNA Pol III?
Main replicating enzyme for DNA replication
95
What is the function of prokaryotic DNA Pol I?
Fills in gaps, joins strands together, removes primers, repair, recombinant DNA synthesis
96
What is the function of prokaryotic DNA Pol II?
Repair of DNA
97
What is the function of DNA helicases?
Utilize ATP to unwind DNA, to allow ssDNA to be accessible to other enzymes and begin DNA synthesis
98
What is the function of single-stranded binding proteins?
trap single strands of DNA in a bracelet like structure (stabilizes them)
99
What enzyme forms the RNA primer?
Specialized RNA polymerase
100
What are three special features of DNA polymerase III?
High catalytic potency, fidelity and processivity
101
What do DNA topoisomerases do?
Relieve torsional stress caused by DNA unwinding
102
What are the two types of DNA topoisomerases and what do they do?
Type I: breaks one strand and reseals it
| Type II: breaks both strands and reseals them
103
What drugs target Bacterial topoisomerase II?
Novobiocin, nalidixic acid, ciprofloxacin
104
What does camptothecin do?
Inhbits human topoisomerase I, anti-cancer drug
105
What does etoposide do?
Inhibits human topoisomerase II, anti-cancer drug
106
What does DNA polymerase I do?
Removes RNA primers and replaces them with DNA
107
What do DNA ligases do?
Seal the gaps left by DNA pol I, uses ATP as an energy source
108
What are the functions of DNA pol alpha?
Eukaryotic DNA, acts as primase and initiates replication
109
What are the functions of DNA pol beta?
Repair of DNA
110
What are the functions of DNA pol gamma?
Replication of mitochondrial DNA, also has proof reading ability
111
What are the functions of DNA pol delta?
Elongates DNA, also has proof reading ability, completes DNA synthesis on leading and lagging strands
112
What are the functions of DNA pol epsilon?
Repair of DNA, acts as proof reader
113
What do telomerases do?
Telomerases maintain the ends of chromosomes in eukaryotes by forming an overhang that ensures that all the DNA is replicated
114
What enzyme deficiency is implicated in aging?
Telomerases
115
What does reverse transcriptase do?
Synthesizes DNA from an RNA template, seen in retroviruses (HIV)
116
What is an exinuclease?
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
What are N-glycosylases?
They recognize and remove the bases that have undergone DNA depurination
118
What enzymes are involved in base excision repair?
AP endonucleases: deoxyribose phosphate lyase, DNA poymerase and DNA ligase
119
What is the step where transcription is regulated?
Initiation of transcription
120
What is the function of the sigma unit of RNA polymerase?
It finds the promoter site
121
What subunits make up the core enzyme of RNA Polymerase?
Alpha-2, Beta and beta'
122
What is euchromatin?
Transcriptionally active DNA (accessible) in interphase
123
What is constitutive heterochromatin?
DNA that is always condensed and transcriptionally inactive (near the centromere and telomeres)
124
What is facultative heterochromatin?
DNA that is condensed at times but also active at times
125
What is the process of conversion between euchromatin and heterochromatin?
Chromatin remodelling
126
What is the function of promoters?
Direct RNA polymerase to the transcription start site, on the same strand, recognized by transcription factor 2F
127
What is the most important promoter?
TATA box (and CAAT box)
128
What is special about enhancers?
They can be on any part of the DNA, they greatly increase the activity of promoters
129
What do snRNPs do?
Cleave the RNA at the 5' end, join to the branch point, cleaves the 3' end and joins the exons together
130
What is the function of the consensus sequence?
help snRNPs recognize splice sites?
131
Where do trans-acting factors bind?
On cis-acting elements
132
What is an operon?
Prokaryotic regulatory unit of a set of clustered genes
133
What are hormone responsive elements?
enhancer-like sequences that allow for global regulation of metabolic pathways by increasing or decreasing the level of transcription
134
Where do members of nuclear-receptor super family of hormones bind?
Intracellular hormones, bind to zinc-finger motif of DNA
135
Where do large hormones bind?
Bind to extracellular receptors, start a cascade and phosphorylate CREB which binds to CRE via a leucine-zipper motif
136
Where does gene rearrangement occur in adults?
Immunoglobulins (B Cells)
