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Flashcards in Exam 3 Deck (126):
1

an inactive enzyme that must be partially digested to attain full enzymatic activity

zymogen

2

How does amylase digest carbohydrates?

cleaning the alpha-1,4 glycosidic bonds of starch

3

Which enzyme activates trypsin?

enteropeptidase

4

The transport of lipids in the lymph is carried out by

chylomicrons

5

______ pathways can be either anabolic or catabolic, depending on the energy conditions of the cell

amphibolic

6

ultimate acceptor of electrons in aerobic organisms

O2

7

the product of oxidation of carbon containing fuels in aerobic metabolism

CO2

8

this compound serves as an acyl carrier in metabolism

acetyl-CoA

9

the chemical currency of metabolism

ATP

10

the type of metabolism where useful energy is harvested

catabolism

11

serves as a reservoir of high potential phosphoric groups that can be readily transferred to ADP to regenerate ATP in vertebrate muscle

creatine phosphate

12

the metabolic pathways that require energy and are often biosynthetic processes are

anabolic

13

metabolic pathways are regulated by

-transcriptional regulation of the amount of enzyme
-allosteric control of enzyme activity
-the accessibility of substrates by compartmentalization

14

Explain how a metabolic pathway can contain an energetically unfavorable reaction yet still occur

the free-energy changes of the individual steps in a pathway are summed to determine the overall free-energy charge. Thus, a step that might not normally occur can be driven if it is coupled to a thermodynamically stable reaction.

15

What is an activated carrier? Provide two examples.

Activated carriers are molecules that are used as the carrier molecules of a particular molecule, atom, electron, or of protons. One example would be ATP, which is the activated carrier of phosphoryl groups. Flavin derivatives (FAD) and nicotinamide derivatives (NAD+) are examples of activate carriers of electrons.

16

stereoisomers that are mirror images of eachother

enantiomers

17

monosaccharides that differs at a single asymmetric carbon

epimers

18

the storage form of glucose in animals

glycogen

19

the enzymes that synthesize oligosaccharides

glycosyltransferases

20

the molecule to which most sugars are attached prior to transfer

UDP

21

a five-membered ring formed from a monosaccharide

furanose

22

formed when tow monosaccharides are linked together via a glycosidic bond

disaccharide

23

in N-linked glycoproteins, the carbohydrate portion is attached to an ____ residue in the protein

asparagine

24

The simplest carbohydrates are

dihydroxyacetone and D- and L-glyceraldehyde

25

an aldehyde and alcohol can react to form a

hemiacetal

26

the nutritional storage forms of glucose in plants

amylase and amylopectin

27

to which amino acid residues in glycoproteins are the sugars commonly linked

serine, threonine, and asparagine

28

Inhibitors against this viral enzyme have potential as anti-influenza agents

neuramidase

29

List three functions of carbohydrates and provide examples

-Fuel: monosaccharides like glucose, fructose and galactose have entry points into basic ATP-generating metabolic pathways.
-Structure: Cellulose with its beta linkages yields a straight chain capable of interacting with other cellulose molecules to form strong fibrils.
-Signaling/Recognition: Glycosylated proteins can serve as distinguishing marks within the cell and at the cell surface. The ABO blood groups are defines by characteristic carbohydrate patterns. The influenza virus protein hemagglutinin will recognize species-specific carbohydrate signatures at the cell surface for effective infection.

30

What is the difference between an enantiomer and a diastereoisomer?

An enantiomer is a stereoisomer that is a perfect (non superimposable or nonidentical) mirror image. A chiral molecule has one perfect mirror image, but for larger carbohydrates that have the same chemical formula and have multiple chiral centers, variations in asymmetric carbon structures mean that additional stereoisomers exist. The stereoisomers that are not mirror images of each other are called diastereoisomers.

31

What are the chemical and structural differences between cellular and glycogen.

Both are glucose homopolymers. Glycogen is a branched polymer and contains alpha-1,4 linkages with beta-1,6 branch points about every 10 residues. Cellulose is a linear polymer that contains that contains beta-1,4 linkages. Because of the beta linkages, cellulose can assemble into very long straight chains which can form interchain hydrogen bonds to produce fibrils

32

Describe the role of carbohydrates in determining human blood types.

All blood groups have a basal oligosaccharide signature designated Type O because there is no active glycosyltransferase for additional modification. In type A, N-acetylgalactosamine is added to the Type O oligosaccharide by a specific glysocyltransferase. In Type B, galactose is added to the Type O oligosaccharide by another transferase. The presence of unique oligosaccharide signatures identifies blood cells as 'self'

33

What is the molecular basis of how erythropoietin protein relieves anemia?

Erythropoietin is a glycoprotein secreted by the kidney into the blood that stimulates the production of red blood cells. Glycosylation of erythropoietin enhances its stability in the blood, which leads to more stimulation of red blood cell production. For patients with anemias that are deficient in red blood cells, this extra stimulation of blood cell proliferation relieves anemia.

34

Explain the role of proteoglycans in cartilage.

Cartilage is composed, in part, of the proteoglycan aggrecan and the glycosaminoglycan hyaluronan. The glycosaminoglycan component of aggrecan cushions joints by releasing water on impact, and then rebinding water.

35

must be regenerated for glycolysis to proceed

NAD+

36

this molecule is an allosteric inhibitor of phosphofructokinase

ATP

37

an allosteric activator of glycolysis

AMP

38

how many moles of ATP does each mole of glucose produce in glycolysis

2

39

Why is glucose the most table hexose

the hydroxyl groups are all in the equatorial position

40

a potent allosteric activator of liver phosphofructokinase is _______, which is produced from fructose-6-phosphate by PFK2

fructose-2,6-biphosphate

41

increases the expression of most glycolytic enzymes and the glucose transporters GLUT1 and GLUT3

HIF-1

42

Which two 3-carbon molecules are generated by the cleavage of fructose-1,6-biphosphate?

glyceraldehyde-3-phosphate and dihydroxyacetone phosphate

43

What reaction is catalyzed by aldolase

reversible cleavage of F-1,6-BP to DHAP and GAP

44

What is the function of a thioester intermediate such as the one formed from GAP?

The thioester allows the two-step reaction to be coupled so the second reaction, the energetically unfavorable phosphorylation, can proceed

45

What type of enzyme catalyzes the intramolecular shift of a chemical group?

mutase

46

Fructose can enter glycolysis at two distinct points, depending on the tissue. How is fructose metabolized in adipose tissue?

Fructose is converted to fructose-6-phosphate

47

Lactose intolerance is caused by a deficiency of

lactase

48

How are glycolytic enzymes regulated?

-transcriptional control
-reversible phosphorylation
-allosteric control

49

During exercise, glycolysis is stimulated by a

feed-forward stimulation of pyruvate kinase

50

Which two isomeraization reactions occur in glycolysis? Why are these steps necessary?

Glucose 6-Phosphate is isomerize to Fructose 6-Phosphate, converting an aldiss to a ketose, which then allows phosphorylation at the number 1 carbon. Later in the pathway, dihydroxyacetone phosphate is converted to glyceraldehyde 3-phosphate, utilizing both of the molecules formed from fructose-1,6-biphosphate cleavage.

51

How is the conversion of phosphoenolpyruvate to pyruvate accompanied by ATP formation?

The enol phosphate possesses very high potential for phosphoryl transfer, which is due to the driving force of the tautomerization of the enol to the more stable ketone.

52

What are the two fermentation pathways for pyruvate and how do they contribute to sustaining glycolysis?

Lactic acid fermentation and ethanol fermentation. They mole for mole regenerate the NAD+ reduced by glyceraldehyde-3-phosphate dehydrogenase

53

Why is it more sensible for phosphofructokinase, rather han hexokinase, to be an important control step?

Phosphofructokinase catalyzes the first committed step in the glycolytic pathway. At this point, the molecule is committed to entering the glycolytic path. In contrast, production of glucose 6-phosphate is the first step in many different paths. Thus, glycolytic control would not be maintained by tight regulation of hexokinase

54

Describe the regulation of PFK in the liver.

PFK is still inhibited by ATP as in the muscle cells, but the ATP levels do not fluctuate as dramatically in the liver. PFT is inhibited by citrate, which indicates an abundance of precursors for the citric acid cycle. Thus, there is no need to further metabolize glucose for this purpose. Fructose-2,6-biphosphate (F2, 6BP) is an activator of PFK in a feedforward stimulation mechanism to ensure glycolysis is accelerated with glucose is abundant. As the concentration of Fructose-6-Phosphate (F-6P) increases as the result of high blood glucose, it is converted to F2, 6BP. F2, 6BP increases PFK's affinity for F-6P and diminishes any inhibitory effect of ATP.

55

the major tissue in which gluconeogenisis takes place

liver

56

where does conversion of glucose-6-phosphate to glucose take place

endoplasmic reticulum

57

the reaction that uses GTP and not ATP as its high-phosphoryl-transfer potential donor

PEPCK (phosphoenolpyruvate carboxykinase) or oxaloacetate to PEP

58

an intermediate that is decarboxylated and phosphorylated to produce phosphoenolpyruvate

oxaloacetate

59

this essential cofactor is required for the carboxylation of pyruvate in humans

biotin

60

the enzyme that carboxylates pyruvate to oxaloacetate

pyruvate carboxylase

61

the cellular compartment where the first step is gluconeogenisis occurs

mitochondria

62

transport of oxaloacetate produced by PEPCK utilizes the mitochondrial and cytosolic enzyme _____

malate dehydrogenase

63

What do high levels of ATP and citrate do?

-indicate a high-energy-well-fed state
-promote gluconeogenesis
-inhibit glycolysis

64

the bifunctional enzyme

phosphofructokinase II

65

How does eating a meal influence the level of insulin released by the pancreas?

creates a high blood sugar which increases the level of insulin

66

acts as a glucose buffer for the rest of the body

liver

67

How does the liver behave (in regards to glucose) under low-energy conditions?

Does not utilize glucose, and it's a producer of glucose

68

the primary raw materials for gluconeogenesis

lactate and amino acids

69

Explain how fructose 2,6-biphosphate (F-2, 6-BP) levels are regulated in the cell, and the relationship between F-2, 6-BP levels and the blood glucose levels.

The levels in the cell of F-2, 6BP are regulated by the bifunctional enzyme, phosphofructokinase2/ fructose 2,6-biphosphatase. When glucose levels in the blood are low, the phosphatase function of the enzyme is activated and the kinase function is inhibited, lowering F-2,6-BP levels. This inhibits the glycolytic pathway. Conversely, when blood glucose levels are high, the phosphatase function is inhibited and the kinase function is activated, raising cellular F-2, 6-BP levels. This activates the glycolytic pathway.

70

What is the role biotin has in pyruvate carboxylase catalytic mechanism?

Biotin is the activated carbon 1 carrier. The flexible arm of biotin allows the CO2 to move from one active site of the enzyme to the second set of active site amino acid, where pyruvate is carboxylated

71

How are gluconeogenesis and glycolysis coordinated by nucleotides?

ATP inhibits glycolysis at PFK, while ADP inhibits the flow of carbon from pyruvate to glucose at pyruvate carboxylase and phosphoenol pyruvate carboxykinase. When ADP levels are high, adenylate kinase converts ADP to AMP and ATP. The increase in AMP (only in a low-energy state) results in the inhibition of gluconeogenesis and activates glycolysis in the liver.

72

Which metabolic steps differ from glycolysis in gluconeogenesis?

There are 3 irreversible steps in glycolysis which require 4 different steps in gluconeogenesis:
1. Pyruvate conversion to phosphoenolpyruvate via an oxaloacetate intermediate.
2. F-1,6-BP hydrolysis
3. The hydrolysis of glucose 6-phosphate

73

Describe the molecular basis of insulin resistance through PEPCK activity.

The presence of insulin in the blood indicates high glucose levels in the blood and should signal inhibition of gluconeogenesis. Insulin triggers the suppression of PEPCK gene transcription. In insulin resistance, PEPCK is not suppressed and gluconeogenesis remains active resulting in the liver delivering glucose into the bloodstream raising blood glucose levels.

74

What is a substrate cycle and how can it affect the relative flux of metabolic pathways?

Substrate cycles are pairs of irreversible reactions that produce and consume each others substrates/products. When substrate cycles are not equally paired with one another (one enzyme is faster than the enzyme in the other direction), they can magnify the effect of allosteric regulation of the enzymes.

75

How does a cell extract energy and reducing power from its environment

Catabolism/catabolic reactions

76

How does a cell synthesize the building blocks of its macromolecules and then the macromolecules themselves

Anabolism/anabolic reactions

77

What does the acidic environment of the stomach do?

denature proteins

78

digest proteins into amino acids and peptides

proteases and peptidases

79

digest dietary carbohydrates

alpha-amylase

80

digestive proteases and peptidases are first synthesized as these inactive precursor forms

proenzymes or zymogens

81

cleaves trypsinogen to form active trypsin

enteropeptidase

82

Why are inactive precursors important in digestive activity?

You don't want active proteases in your cells degrading all your proteins

83

primary source of carbs

starch

84

initiates digestion by cleaving alpha-1,4 bonds but NOT alpha-1,6 bonds

alpha-amylase

85

secreted by the pancreas and convert the triacylglycerols into 2 fatty acids and monoacylglycerol

lipases

86

in the intestine, triacylglycerols are reformed from free fatty acids and monoacylglycerol and packaged into lipoprotein particles called

chylomicrons

87

why do chylomicrons enter the blood

so that the triaglycerols can be absorbed by tissues

88

activated carrier of phosphoryl groups

atp

89

what carries activated electrons derived from the oxidation of fuels

NAD+ and FAD

90

carry acyl groups

Coenzyme A and LIpoamide

91

what controls the amount of enzymes

transcription

92

what control the activity of enzymes

catalytic activity is regulated allosterically or by covalent modification. The energy status of the cells (relative amounts of ATP/ADP/AMP/Pi) is often an important regulator of enzyme activity.

93

what controls the accessibility of substrates

Opposing reactions, such as fatty acid synthesis and degradation may occur in different cellular components. Regulating the flux of substrates between compartments is used to regulate metabolism

94

have the same molecular formula but different structures

isomers

95

isomers that differ in the order of attachment of atoms

constitutional isomers

96

isomers in which atoms are connected in the same order but differ in the spatial arrangement

stereoisomers

97

non superimposable miroir images

enantiomers

98

isomers that are not mirror images

diastereoisomers

99

diastereoisomers that differ at one of several symmetric carbon atoms

epimers

100

diastereoisomers that differ at new asymmetric carbon atoms formed on ring closure

anomers

101

catalyse the formation of glycosidic bonds

glycosyltransferases

102

how are the monosaccharide substrates for glycosyltransferases activated

attachment to uridine diphosphate (UDP)

103

How are glycoproteins structured

carbs are attached to the nitrogen atom in the side chain of asparagine (N-linkage) or the oxygen atom of the side chain of serine or threonine (O-linkage)

104

what is cartilage composed of

the proteoglycan aggrecan and the glycosaminoglycan hyaluronan

105

what does the glycosaminoglycan component of aggrecan do

cushions joints by releasing water on impact and then rebinding water

106

one of the most abundant carbs in the world, also a glycosaminoglycan found in the exoskeleton of insects

chitin

107

conversion of one molecule of glucose to 2 molecules of pyruvate with the generation of 2 molecules of ATP

glycolysis

108

2 stages of glycolysis

1) Traps glucose in the cell and modifies it so that it can be cleaved into a pair of phosphorylated 3-carbon compounds
2) Oxidizes the 3-carbon compounds to pyruvate while generating 2 molecules of ATP

109

The 2 steps in the formation of glyceraldehyde 1,3-biphosphate

1) the highly exergonic oxidation of C1 in GAP to an acid
2) the highly endergonic formation glyceraldehyde 1,3 diphosphate from the acid

110

How are the 2 reactions in the formation of glyceraldehyde 1,3 diphosphate linked

by the formation of an energy-rich thioester in the active site of glyceraldehyde 3-phosphate dehydrogenase

111

ATP-generating pathways in which electrons are removed from one organic compound and pass to another organic compound (anaerobic)

Fermentation

112

The formation of ethanol from pyruvate in ethanol fermentation regenerates this

NAD+

113

oxidized by alcohol dehydrogenase, regenerating NAD+

NADH generated by glyceraldehyde 3-phosphate dehydrogenase in ethanol fermentation

114

can be oxidized by converting pyruvate to lactate in a reaction catalyzed by lactate dehydrogenase

NADH

115

the conversion of glucose into 2 molecules of lactate

lactic acid fermentation

116

In the liver, this activates PFK

F26BP

117

primary enzyme for glucose phosphorylation in the liver

glucokinase (isoenzyme)

118

when does glucokinase phosphorylate glucose

when blood glucose is high (has a low affinity for glucose)

119

why does glucose phosphorylation by glucokinase matter?a

This ensured that hexokinase in muscle and brain cells get first dibs on glucose when it is limiting. It also ensures no glucose is wasted when glucose is abundant.

120

inhibits pyruvate kinase in the muscle

ATP and alanine

121

synthesized by pyruvate by a single step

alanine

122

activates pyruvate kinase in the muscle

F16BP (a product upstream in glycolysis)

123

How is pyruvate kinase regulated int he liver?

Low blood glucose yields PK phosphorylation. High Blood glucose yields PK dephospho rylation.

124

secreted by the pancreas in response to an increase in blood glucose levels and stimulates glucose uptake by tissues

insulin

125

conversion of pyruvate into PEP begins with formation of

oxaloacetate

126

what vital does pyruvate carboxylase require as a cofactor

biotin