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NBDE PART 1 BIOCHEM/PHYSIOLOGY > Enzymes > Flashcards

Flashcards in Enzymes Deck (209):
1

what enzyme controls glycolysis

phosphofructokinase (PFK)-1

2

what is the rate limiting step of glycolysis

step 3: fructose 6 phosphate ==> fructose
1, 6 bisphosphate via phosphofructokinase (PFK)

3

phosphofructokinase (PFK)-1 is inhibited by (4)

ATP, H+, and citrate, glucagon

4

phosphofructokinase (PFK)-1 is upregulated by

ADP and AMP

5

phosphofructokinase (PFK)-1 is most active when the energy of the cell is high/low

low = ADP and AMP are high

6

does insulin promote or inhibit glycolysis

promote/stimulate

7

fructose 2,6 bisphosphate is the __ of glycolysis

supercharger

8

fructose 2,6 bisphosphate is made using what enzyme

PFK-2

9

is fructose 2,6 bisphosphate an enzyme?

NO! it is an allosteric activator of PFK-1

10

fructose 2,6 bisphosphate (F2,6BP) is an allosteric inhibitor of?

fructose 1,6 bisphosphotase in gluconeogenesis

11

what enzyme converts F1,6BP to DHAP and GAP

aldolase converts fructose 1, 6 bisphosphate to two 3 carbon metabolites: dihydroxyacetone phosphate and glyceraldehyde-3-phosphate

12

the aldose rxn is called the

aldolytic reaction of glycolysis

13

aldolase is plentiful in what tissues

heart and skeletal tissue

14

glycolysis occurs in the _ in the _ of oxygen

cytoplasm in the absence of oxygen

15

what is formed in glycolysis

2NADH and 2ATP net

16

how many ATP from substrate level phosphorylation in glycolysis

4

17

fluoride inhibits bacterial __

enolase = decreases pyruvate synthesis and in turn decreases acid production

18

under ANAEROBIC CONDITIONS, pyruvate is converted to lactic acid by what enzyme

lactate dehydrogenase = this reaction regenerates the NAD+ bc uses NADH.

19

all of these are useful enzymes for diagnosis of acute myocardial infarction except one:
a. creatine kinase (CK)
b. lactate dehydrogenase (LDH)
c. alanine transaminase (ALT)
d. aspartate transaminase (AST)

ALT

20

ECG is good to locate the site of the myocardial infarction but cannot distinguish

bw old and recent infarcts

21

it distinguish bw old and recent infarcts we looks at

enzyme elevations

22

the first enzyme to appear in blood after a heart attack is?

creatine phosphate (CK-2 and CK3)

23

the second and third enzymes to appear in blood after a heart attack is

aspartate transaminase (AST)
lactate dehydrogenase (LDH)

24

if you find alanine transaminase (ALT)
and aspartate transaminase (AST) in th blood = _ damage

liver. these enzymes should not be in the blood.

25

in the heart 3 enzymes that shouldn't be in the blood = myocardial infarct are

aspartate transaminase (AST)
lactate dehydrogenase (LDH)
creatine kinase

26

levels of lipase and amylase are elevated in

acute pancreatitis

27

Creatine kinase (CK) is used for diagnosis of

muscle disease

28

elevated LDH with more or less normal AST and CK levels means

pulmonary infarction

29

elevated glutamyl transferase (GGT) =

biliary obstruction

30

acid phosphatase and prostate specific antigen =

tumor markers for prostate cancer

31

which two amino acids are NOT transaminated

serine and threonine

32

serine and threonine are oxidatively deaminated (release NH3) by a _ enzyme to form?

dehydratase enzyme
serine ==> pyruvate
threonine ==> propionyl coA

33

the first step of catabolism of most amino acids is the removal of the

alpha amino group

34

nitrogen is transferred from one amino acid to another by

transamination reactions which always involve 2 different pairs of amino acids and their corresponding alpha keto acids

35

all transaminase require the coenzyme

pyridoxal phosphate PLP Ithe coenzyme form of pyridoxine/vit B6)

36

oxidative deamination liberates a free ammonia (NH3). these reactions occur in all tissues, but mostly in the

liver and kidney

37

oxidative deamination provides the alpha ketoacid for _ and the ammonia for

energy
ammonia for urea synthesis

38

glutamate dehydrogenase is used for

oxidative deamination of glutamate

39

histidase is used for oxidative deamination of

histidine

40

serine dehydratase is used for

oxidative deamination of serine and threonine

41

pyridoxal phosphate PLP is the aldehyde form that can accept an amino group. this changes it into its aminated form, __ which can donate its amino acid to an alpha keto acid

pyridoxamine phosphate (PMP)

42

deamination is a _ reaction

oxidative therefore needs oxygen (aerobic)

43

the amine group in deamination will go into

urea cycle

44

oxidative deamination occurs primarily on _ bc it is the end product of many transamination reactions

glutamic acid

45

when ammonia is released from glutamate, what is formed? is the reaction reversible? what is the enzyme

alpha ketoglutarate.
reversible
glutamate dehydrogenase

46

___ deaminates glutamine to glutamate and ammonium ion

glutaminase = glutamine
(glutamate dehydrogenase = glutamate)

47

asparaginase deaminates asparagine to

aspartate and ammonium ion

48

histidine is deaminated by _ to dorm

histidase ==> urocanate and ammonium ion (NH4+)

49

serine and threonine are deaminated by

serine hydratase.

50

serine is deaminated to form

pyruvate

51

threonine is deaminated to form

alpha ketobutyrate ==> which is decarboxylated oxidatively to form propionyl CoA

52

carbonic anhydrases are _ containing enzymes that catalyze the reversible reaction b/w CO2 hydration and bicarbonate dehydration

zinc

53

which is more soluble in the lipid membrane and therefore can cross easier bicarbonate or carbon dioxide

CO2 (remember bicarb is charged)

54

carbonic anhydrase is a fast or slow enzyme

one of the fastest enzymes known. one molecule processes on million CO2 in one sec!

55

is carbonic anhydrase REQUIRED to convert CO2 and water to carbonic acid

no

56

does carbonic anhydrase work faster in whole blood or plasma

in whole blood since plasma does not contain erythrocytes

57

what part of electron transport chain accepts only electrons

cytochrome b

58

cytochromes accept electrons/H+

all the cytochromes accept only electrons/
the other components accept both electrons and H+

59

electron transport chain aka respiratory chain (oxidative phosphorylation) occurs on the ___ in what cell

inner mitochondrial membrane in all cells in our body that have mitochondria

60

FMN is which complex

complex 1 = NADH oxidoreductase

61

FMN receives _ and transfers them thru Fe-S centers to __

NADH ==> coenzyme Q
NADH ==> NAD

62

FMN is derived from

riboflavin (Vitamin B2)

63

NAD+ is derived from

niacin (vitamin B3)

64

Coenzyme Q receives electrons from

FMN's FeS center and also FADH2 (complex II called succinate)

65

Is coenzyme Q derived from a vitamin

no the body synthesizes it

66

cytochromes b, c, a and a3 receive electrons from the

reduced form of coenzyme Q

67

each cytochrome is made up of

heme and protein

68

cytochrome a +a3 is called

cytochrome oxidase

69

___ is synthesized from glycine and succinyl CoA

Heme

70

is Heme derived from a Vitamin

no

71

oxygen receives the electrons in the chain and is reduced to

water

72

a coenzyme is a protein/non protein substance

non protein substance. it is an organic cofactor

73

a coenzyme combines with an apoenzyme to form

a haloenzyme = catalytically active enzyme

74

A ___is a non-protein chemical compound that is required for the protein's biological activity

cofactor

75

Cofactors can be classified depending on how tightly they bind to an enzyme, with loosely bound cofactors termed ___ and tightly bound cofactors termed __

1. loose = coenzymes
2. prosthetic groups

76

An inactive enzyme without the cofactor is called an ___

apoenzyme

77

while the complete enzyme with cofactor is called a ___

holoenzyme

78

which is not an enzyme classification:
oxidoreductase
ligase
transferase
oxygenase
hydrolase
isomerase

oxygenase. it is an enzyme but not a classification. it belongs to oxidoreductase class

79

which catalyzes redox reactions
oxidoreductase
ligase
transferase
oxygenase
hydrolase
isomerase

oxidoreductase

80

which transfers functional groups
oxidoreductase
ligase
transferase
oxygenase
hydrolase
isomerase

transferase

81

which causes hydrolysis reactions
oxidoreductase
ligase
transferase
oxygenase
hydrolase
isomerase

hydrolase

82

which breaks CO, CC or CN bonds
oxidoreductase
ligase
transferase
oxygenase
hydrolase
isomerase
lyase

lyase

83

which rearranges functional groups
oxidoreductase
ligase
transferase
oxygenase
hydrolase
isomerase

isomerase

84

which joins two molecules
oxidoreductase
ligase
transferase
oxygenase
hydrolase
isomerase

ligase

85

a catalytically inactive protein formed by removal of the cofactor from an active enzyme is called

apoenzyme

86

urokinase

made by kidney. it activates plasminogen --> plasmin

87

plasmin cleaves _

the peptide bond in fibrin

88

fibrinogen is soluble protein essential for blood clotting. it is converted into an insoluble thread like polymer called fibrin by which enzyme

thrombin

89

thrombin is produced from the inactive plasma protein precursor

prothrombin (formed in the liver)

90

what converts prothrombin to thrombin

thromboplastin and calcium ions

91

thrombin acts upon the __ in fibrinogen to produce fibrin monomer

arginyl-glycine linkages

92

a zymogen is converted to its active enzyme form by:
removal of peptide fragment
removal of an amino group

removal of peptide fragment

93

Glycoside hydrolases

aka amylase - break down starch into glucose molecules

94

amylase is aka

ptyalin

95

all amylases act on what bonds

alpha 1, 4-glycosidic bonds

96

alpha amylase acts on amylose to produce

maltotriose and maltose

97

alpha amylase acts on amylopectin to produce

maltose, glucose, and limit dextrin

98

which is faster alpha/beta amylase

alpha

99

in humans both the salivary and pancreatic amylases are alpha/beta

alpha

100

beta amylase works from the _ end, and hydrolyzes the 2nd alpha 1,4-glycosidic bond cleaving off___

non reducing end, 2 glucose units (maltose) at a time

101

gamma amylase cleaves?

the last alpha-1,4 glycosidic linkages at the non reducing end of amylose and amylopectin yielding glucose, and alpha-1,6 glycosidic linkages

102

_ are branched polysaccharide fragments that remain following hydrolysis of starch

limit dextins
(note they are not dextrAns)

103

disaccharides are hydrolyzed at the intestinal brush border by

lactase, sucrase, maltase, and alpha-dextrinase

104

only _ are absorbed in small intestine

monosach

105

isomaltase cleaves

glucose linked 1,6 to another glucose as in branch points in starch and glcogen

106

which predominate in glycogen alpha 1,4 or alpha-1,6

alpha 1,4

107

if patient has von Gierke's disease she is missing enzyme _ that converts _

missing glucose-6-phosphatase
converts glucose-6-phosphate to glucose

108

Gluconeogenesis only occurs

in liver and kidney

109

why does Gluconeogenesis only occur in liver and the kidneys, and not the brain and muscle?

because glucose-6-phosphatase (G6P) is not present in the brain and muscle

110

pyruvate carboxylase (1st step in gluconeogenesis) is only present where

in the liver and kidneys. NOT MUSCLE. Also only in mitochondria

111

gluconeogenesis is a process where glucose is made from molecules that are not

carbohydrates or fatty acids

112

gluconeogenesis makes glucose primarily from

amino acids. typically converts lactic acid and amino acids into pyruvate or phosphoenol pyruvate (PEP)

113

gluconeogenesis
1st reaction: pyruvate ==> via what enzyme

pyruvate ========> oxaloacetate
pyruvate carboxylase (only in mitochondria)

114

gluconeogenesis
2nd reaction: oxaloacetate==> via what enzyme

oxaloacetate ========> PEP (phosphoenol pyruvate) via phosphoenolpyruvate carboxy kinase (PEPCK)

115

gluconeogenesis
Fructose 1,6 bisphoshate ==> via what enzyme

Fructose 1,6 bisphoshate ==> fructose 6 phosphate
fructose 1, 6 bisphosphatase

116

gluconeogenesis
Glucose 6 phoshate ==> via what enzyme
does this require ATP

Glucose 6 bisphoshate ==>glucose
glucose 6 phosphatase
no ATP

117

Km is the substrate concentration at which the enzyme is _

half saturated with its substrate

118

Km is also the substrate concentration at which the reaction is

half maximal

119

Michaelis Menton kinetics assumes 4 things:
1. the reaction has _ substrate
2. the molar concentration of the substrate is much ___ than that of the enzyme
3. only the _ reaction is considered
4. the course of the reaction is observed for only a very __time period

1. only one
2. higher substrate concentration
3. initial
4. short

120

Km has what unit

molarity

121

Km is the substrate concentration at which Vo (initial reaction velocity) is _

one half Vmax

122

most Km value lies between

10-1 and 10-6

123

the lower the Km the _ the enzyme affinity for substrate

higher

124

Km increases/decreases in presence of competitive inhibitor

increase

125

Km is not affected in presence of

non competitive inhibitor

126

what change in presence of non competitive competitor

Vmx is reduced

127

when is the max rate (Vmax) attained for enzyme

when all enzyme sites are saturated with substrate

128

___ enzymes are enzymes that change their conformational ensemble upon binding of an effector, which results in an apparent change in binding affinity at a different ligand binding site. This "action at a distance" through binding of one ligand affecting the binding of another at a distinctly different site,

Allosteric

129

which enzymes DO NOT follow Michaelis Menton kinetics

allosteric enzymes bc they show a complex relationship bw velocity and substrate concentration

130

an allosteric enzyme is a regulatory enzyme that has both an _ site for the substrate and an allosteric site for the __ (non active site)

active site = substrate
allosteric site = effector

131

the hallmark of effectors is that when they bind to enzymes the effectors alter the

catalytic properties of an enzymes active site

132

positive effectors _ catalytic activity of the enzyme

increase

133

negative effectors will _ catalytic activity of the enzyme

decrease

134

name an allosteric enzyme in glycolysis

PFK phosphfructokinase

135

negative effectors can be the substrate itself or some other metabolite. t/f

true
ex ATP in PFK can inhibit and act as a substrate

136

name an example of covalent modification of an enzyme. is it reversible

it is reversible. phosphorylation is an example

137

modified enzyme vs unmodified = which is phosphorylated

modified

138

phosphorylation is always catalyzed by ___

ATP dependent protein kinases

139

phosphorylated enzymes are dephosphorylated by

phosphoprotein phosphatases

140

what is the substrate for glycogen synthesis

UDP-glucose and non reducing end of glycogen as the other

141

the synthesis of glycogen from glucose is carried out by enzyme

glycogen synthase

142

glucose enters the cell and is phosphorylated to G-6-P by _ in most tissues except the liver

hexokinase

143

in the liver, glucose enters the cell and is phosphorylated to G-6-P by _

glukokinase

144

to initiate glycogen synthesis, the G6P is reversibly converted into __ by __

G1P by phosphoglucomutase

145

this G1P is then converted to UDP-glucose by

UDP glucose pyrophosphorylase

146

steps in glycogen synthesis

G ==> G6P ==>G1P ==> UDP-glucose
hexokinase ==> phosphoglucomutase ==> UDP glucose pyrophosphorylase

147

phosphorylated = Glycogen synthase A is activated (dephosphorylated) by

insulin - will make it dephosphorylated

148

Glycogen synthase B is the inactivated form. it is inactivated (phosphorylated) by

epinephrine in muscle and liver
and glucagon in the liver

149

Glycogen phosphorylase action

breaks down glycogen

150

Glycogen phosphorylase also has two forms a and b. the phosphorylation of this enzyme forms the active or inactive form

active form (a) = by glucagon
inactive form is dephosphorylated (b). = by insulin

151

therefore insulin always

dephosphorylates. when it dephosphorylates Glycogen synthase b ==> active form a
when it dephosphorylates glycogen phosphorylase ==> inactivates it into b enzyme

152

both glycogen synthase and phosphorylase are phosphorylated at specific _ residues

serine

153

__ is a non competitive inhibitor that can bind only when the substrate is attached

uncompetitive

154

name the reversible inhibitions

competitive, noncompetitive, uncompetitive, mixed

155

___ competitive inhibitor resembles the substrate and binds to the ACTIVE SITE of the enzyme blocking substrate from binding. hallmark is: it can be overcome by increasing the substrate concentration

competitive

156

_- the inhibitor and substrate can bind simultaneously to the enzyme. binding sites do not overlap. do not compete for same site. and CANNOT BE OVERCOME by adding more substrate. IT IS AN ALLOSTERIC INHIBITOR

noncompetitive

157

_= like noncompetitive, the inhibitor and substrate bind at different sites which do not overlap. however it can ONLY BIND once the substrate has already attached (ES)

uncompetitive

158

__= the inhibitor binds to a site other than the active site, but has a different affinity for the lone enzyme vesus the ES complex

mixed inhibition

159

non competitive inhibitor binds to either

a free enzyme or the ES complex

160

___ inhibitors are those that combine with or destroy a functional group on the enzyme needed for its activity.

irreversible

161

COX cyclooxygenase is inhibited by acetylsalicylate (aspirin). what kind of inhibition is this

irreversible bc acetylates the active site serine residue

162

mnemonic for competitive and non competitive inhibition

Kompetitive Inhibition: Km Increases; no change in Vmax.

163

Non-kompetitive inhibition:

No Km change, but Vmax decreases.

164

mixed inhibition Km and Vmax

Km increased and Vm decreased

165

uncompetitive inhibition Km and Vmax

Km and Vm decreased

166

trypsinogen is activated by trypsin or

enteropeptidase

167

the presence of __ in the small intestine (duodenum) stimulates release of cholecystokinin (CCK)

amino acids from protein digestion

168

CCK causes release of __ and contraction of

pancreatic zymogens and gallbladder contraction to deliver bile to duodenum

169

_ can act as an activator for all zymogens of pancreatic proteases

trypsin

170

pepsinogen secreted by _ cells of _ is activated to pepsin by

chief cells of stomach = activated by low pH In stomach OR other activated pepsin molecules

171

Trypsin cleaves peptide chains mainly at the carboxyl side of the amino acids __ or ___, except when either is followed by ___.

lysine or arginine (basic amino acids)

proline

172

chymotrypsin cleaves peptide bonds in which the carboxyl group is contributed by __ amino acids

leucine or aromatic amino acids

173

elastase cleaves at the carboxyl end of which amino acids

hydrophobic small uncharged side chains such as alanine glycine or serine

174

carboxypeptidase B cleaves

basic amino acids Lysine and arginine (like trypsin)

175

___ refers to any of a large group of enzymes that catalyze the hydrolysis of peptide bonds in the interior of a polypeptide or protein molecule

endopeptidase
ie trypsin

176

which enzyme is derived from osteoblasts and its serum level rises in bone conditions with increased osteoblastic activity
alkaline phosphatase
acid phosphatase

alkaline phosphatase
abundant in bone, placenta, intestine and hepatobiliary system

177

the _ and _ are most abundant in normal serum alkaline phosphatase

bone and liver

178

the liver enzyme alkaline phosphatase is raised in patients with

biliary obstruction

179

plasma cholinesterase is used to diagnose __

organophosphate poisoning

180

plasma cholinesterase is __ in liver disease, hepatitis and liver cirrhosis

decreased

181

ALT and AST are most abundant in the

liver

182

are ALT and AST secreted into the blood

no = diagnose liver disease

183

gamma glutamyl transferase present in most tissues but most abundant in kidney and liver. GGT is used to indicate

biliary obstruction

184

acid phosphatase (ACP)

tumor markers prostate cancer

185

PSA prostate specific antigen

tumor markers prostate cancer

186

creatine kinase (CK) CK2 and CK3

first heart enzymes to appear in blood after heart attack. followed by AST and LDH

187

lipase and amylase elevated in

acute pancreatitis = severe abdominal pain of sudden onset

188

__ + ___ = haloenzyme

cofactor + apoenzyme

189

___ are organic molecules (coenzymes) or ions (usually metal ions)

Cofactors

190

what is the cofactor for
glutathione peroxidase

Se

191

what is the cofactor for Dinitrogenase

Mo

192

what is the cofactor for urease

Ni2+

193

what is the cofactor for pyruvate

K+

194

what is the cofactor for hexokinase

Mg2+

195

what is the cofactor for glucose 6 phosphatase

Mg2+

196

what is the cofactor for pyruvate kinase

Mg2+

197

what is the cofactor for carbonic anhydrase

Zn2+

198

what is the cofactor for alcohol dehydrogenase

Zn2+

199

what is the cofactor for cytochrome oxidase

Cu2+ and Fe2+/Fe3+

200

what is the cofactor for pyruvate phophokinase

Cu2+

201

what is the cofactor for catalase

Fe2+/Fe3+

202

what is the cofactor for peroxidase

Fe2+/Fe3+

203

what is the cofactor for ferredoxin

Fe2+/Fe3+

204

what is the cofactor for perxidase

Fe2+/Fe3+whi

205

which coenzyme is vital to tissue respiration

thiamin pyrophosphate (TPP). it is needed for enzyme pyruvate dehydrogenase which catalyzes decarboxylation of pyruvate to form acetyl coA which enters the TCA

206

thiamin pyrophosphate (TPP) is a coenzyme for which pathway

pentose phosphate pathway = alternate pathway for glucose oxidation. coenzyme for tranketolase

207

von Gierke's disease

glycogen storing disease: glucose 6 phosphatase is deficient: The deficiency impairs the ability of the liver to produce free glucose from glycogen and from gluconeogenesis

208

what is the ABC enzyme mnemonic?

ABC = ATP, Biotin, CO2

1. pyruvate carboxylase enzyme:
pyruvate (3C) +CO2 ==> OAA (4C)
2. acetyl-CoA carboxylase
acetylCoA + CO2 ==> malonyl CoA (3C)

209

Pyruvate dehydrogenase mnemonic for cofactors

"Tender Love & Care For Nancy"
1. TPP (from B1)
2. Lipoic acid
3. CoA (from B5)
4. FAD (from B2)
5. NAD (from B3)