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BMS 610 Exam 3 > Chapter 14 - Glycolysis, Gluconeogenesis & Pentose Phosphate Pathway > Flashcards

Chapter 14 - Glycolysis, Gluconeogenesis & Pentose Phosphate Pathway Flashcards

1
Q

What defines a carbohydrate in biochemistry?

A

Organic molecules with aldehydes or ketones and multiple hydroxyl groups.

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2
Q

How are monosaccharides classified?

A

As simple sugars with one polyhydroxy aldehyde or ketone unit.

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3
Q

What is the main difference between monosaccharides and disaccharides?

A

Monosaccharides have a single unit, while disaccharides consist of two linked monosaccharide units.

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4
Q

What are glycosidic bonds?

A

Covalent bonds between monosaccharides in oligosaccharides and polysaccharides.

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5
Q

What characterizes a reducing sugar?

A

A sugar that can donate electrons in a redox reaction, often due to a free aldehyde group.

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6
Q

How do aldoses differ from ketoses?

A

Aldoses have a carbonyl group at the end of the chain; ketoses have it elsewhere.

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7
Q

What is an example of a common aldose?

A

Glucose.

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8
Q

What is a common example of a ketose?

A

Fructose.

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9
Q

Describe pyranoses and furanoses.

A

Pyranoses are six-membered rings; furanoses are five-membered rings in monosaccharides.

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10
Q

What process leads to the formation of hemiacetals and hemiketals?

A

Reaction of alcohol with aldehydes (hemiacetals) or ketones (hemiketals).

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11
Q

What is mutarotation in carbohydrates?

A

The interconversion between α and β anomers in solution.

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12
Q

What distinguishes D- and L-forms in monosaccharides?

A

The orientation of the hydroxyl group on the reference carbon farthest from the carbonyl group.

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13
Q

What are epimers?

A

Sugars that differ only in the configuration around one carbon atom.

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14
Q

What are anomers?

A

Isomers of a monosaccharide that differ at the hemiacetal or hemiketal carbon.

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15
Q

How do polysaccharides like starch and glycogen serve in biological systems?

A

As energy storage molecules; starch in plants, glycogen in animals.

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16
Q

What is the primary structural polysaccharide in plants?

A

Cellulose.

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17
Q

What is chitin, and where is it found?

A

A structural polysaccharide in fungal cell walls and arthropod exoskeletons.

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18
Q

What function do glycosaminoglycans serve?

A

They provide structural support and hydration in the extracellular matrix.

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19
Q

What is a proteoglycan?

A

A protein core with covalently attached glycosaminoglycan chains, important in the ECM.

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20
Q

How are glycolipids significant in cell membranes?

A

They help with cell recognition and communication.

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21
Q

What is an example of a hexose derivative?

A

Glucose-6-phosphate, used in cellular metabolism.

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22
Q

How does the Benedict’s test identify reducing sugars?

A

By forming a red precipitate when reducing sugars react with Cu²⁺.

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23
Q

What is the structure of starch?

A

Composed of amylose (linear) and amylopectin (branched) glucose polymers.

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24
Q

Describe the branching in glycogen.

A

Extensively branched with α(1→6) linkages every 8-12 residues.

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25
Q

How does cellulose differ structurally from starch?

A

It consists of β(1→4) linked glucose, forming straight, rigid chains.

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26
Q

What role do lectins play in glycobiology?

A

They bind specific carbohydrate moieties, facilitating cell recognition.

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27
Q

How does mass spectrometry help in carbohydrate analysis?

A

It determines the mass and structure of carbohydrate molecules.

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28
Q

What information does NMR spectroscopy provide in glycomics?

A

Details on the structure, conformation, and dynamics of carbohydrates.

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29
Q

What are glycoproteins and their function?

A

Proteins with attached carbohydrate chains, involved in immune response and cell signaling.

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30
Q

How do glycolipids participate in cell signaling?

A

Through oligosaccharide chains that interact with receptors in the cell membrane.

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31
Q

What is the glycocalyx?

A

A carbohydrate-rich layer on cell surfaces involved in cell recognition.

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32
Q

Describe the structure of amylose.

A

Amylose is a linear polymer of D-glucose with α(1→4) linkages.

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33
Q

What structural role does cellulose play in plants?

A

It provides rigidity and strength to plant cell walls.

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34
Q

What is a lactone, and how is it formed in carbohydrates?

A

A lactone is a cyclic ester formed from aldonic or uronic acids.

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35
Q

How do phosphorylated sugars function in cells?

A

They trap sugars inside cells due to lack of transporters for phosphorylated forms.

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36
Q

What is chondroitin sulfate?

A

A glycosaminoglycan in cartilage providing structure and resistance to compression.

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37
Q

How does keratan sulfate function in the extracellular matrix?

A

It contributes to tissue hydration and resilience.

38
Q

What is the main difference between heparan sulfate and heparin?

A

Heparin is more highly sulfated and used primarily for anticoagulation.

39
Q

What are the roles of selectins in cell interactions?

A

They mediate cell adhesion, especially in immune responses.

40
Q

What is the role of integrins in glycobiology?

A

Integrins help cells anchor to the extracellular matrix and facilitate signaling.

41
Q

How does glycosylation affect protein function?

A

It can impact protein folding, stability, and recognition by other molecules.

42
Q

What is the difference between O-linked and N-linked glycosylation?

A

O-linked attaches to serine/threonine residues; N-linked attaches to asparagine residues.

43
Q

How does the structure of hyaluronic acid benefit the extracellular matrix?

A

Its large size and negative charge enable it to retain water and provide cushioning.

44
Q

What is the “sugar code” in glycobiology?

A

The information encoded by specific oligosaccharide structures on cell surfaces.

45
Q

How do enzymes recognize stereoisomers of sugars?

A

Enzymes are stereospecific, often recognizing only one isomer, such as D-glucose.

46
Q

What structural feature differentiates α and β anomers?

A

The orientation of the hydroxyl group on the anomeric carbon.

47
Q

How does tautomerization affect ketoses?

A

It allows ketoses to rearrange and act as reducing sugars under certain conditions.

48
Q

What is a glycosphingolipid?

A

A glycolipid with a sphingosine backbone, important in neural tissue.

49
Q

What are the primary bonds in peptidoglycan structure?

A

β(1→4) linkages between N-acetylglucosamine and N-acetylmuramic acid.

50
Q

What is an aggrecan, and where is it found?

A

A large proteoglycan in cartilage that binds to hyaluronan, providing compressive strength.

51
Q

How do hydrogen bonds influence polysaccharide structures?

A

They stabilize folding and contribute to rigidity in structural polysaccharides like cellulose.

52
Q

How are oligosaccharides typically analyzed?

A

Using methods like mass spectrometry and NMR to determine sequence and structure.

53
Q

What is the role of the conserved RGD sequence in integrins?

A

It facilitates binding with ECM components, like fibronectin and collagen.

54
Q

What happens during the formation of an acetal or ketal in carbohydrates?

A

A second alcohol group adds to a hemiacetal or hemiketal, forming a stable linkage.

55
Q

What structural role do glycosaminoglycans play in the ECM?

A

They form a gel-like matrix that supports cells and allows nutrient diffusion.

56
Q

What reaction does phosphohexose isomerase catalyze in glycolysis?

A

Converts glucose-6-phosphate to fructose-6-phosphate.

57
Q

Describe the role of aldolase in glycolysis.

A

It cleaves fructose-1,6-bisphosphate into glyceraldehyde-3-phosphate and dihydroxyacetone phosphate.

58
Q

What is the role of triose phosphate isomerase in glycolysis?

A

Converts dihydroxyacetone phosphate to glyceraldehyde-3-phosphate.

59
Q

What is the energy yield from glycolysis per molecule of glucose?

A

2 ATP (net) and 2 NADH.

60
Q

How does glucokinase differ from hexokinase?

A

Glucokinase is specific to the liver, has a higher Km for glucose, and is not inhibited by glucose-6-phosphate.

61
Q

Which enzymes bypass the irreversible steps of glycolysis in gluconeogenesis?

A

Pyruvate carboxylase, phosphoenolpyruvate carboxykinase, fructose-1,6-bisphosphatase, and glucose-6-phosphatase.

62
Q

Why is gluconeogenesis considered energetically expensive?

A

It requires 6 high-energy molecules (4 ATP and 2 GTP) per glucose synthesized.

63
Q

How is pyruvate converted to phosphoenolpyruvate (PEP) in gluconeogenesis?

A

Through pyruvate carboxylase converting pyruvate to oxaloacetate, then phosphoenolpyruvate carboxykinase converting oxaloacetate to PEP.

64
Q

What are the key roles of NADPH produced in the pentose phosphate pathway?

A

NADPH is crucial for biosynthesis of fatty acids and cholesterol and for reducing oxidative stress.

65
Q

What reaction does lactonase catalyze in the pentose phosphate pathway?

A

Converts 6-phosphoglucono-δ-lactone to 6-phosphogluconate.

66
Q

What is the function of 6-phosphogluconate dehydrogenase in the pentose phosphate pathway?

A

Catalyzes the oxidative decarboxylation of 6-phosphogluconate to ribulose-5-phosphate, generating NADPH.

67
Q

What does transaldolase do in the non-oxidative phase of the pentose phosphate pathway?

A

Transfers a three-carbon unit to form fructose-6-phosphate and erythrose-4-phosphate.

68
Q

Which phase of the pentose phosphate pathway is responsible for producing ribose-5-phosphate?

A

The oxidative phase.

69
Q

What is the role of xylulose-5-phosphate in carbohydrate metabolism?

A

It activates phosphoprotein phosphatase 2A, increasing fructose 2,6-bisphosphate levels and promoting glycolysis.

70
Q

Why is fructose metabolism particularly active in the liver?

A

The liver has fructokinase, which converts fructose directly to fructose-1-phosphate, bypassing hexokinase.

71
Q

What effect does high ATP concentration have on phosphofructokinase-1 (PFK-1)?

A

High ATP levels inhibit PFK-1, slowing glycolysis when cellular energy is sufficient.

72
Q

How does AMP regulate fructose-1,6-bisphosphatase (FBPase-1) in gluconeogenesis?

A

High AMP inhibits FBPase-1, slowing gluconeogenesis under low-energy conditions.

73
Q

Describe how insulin affects fructose 2,6-bisphosphate levels.

A

Insulin increases fructose 2,6-bisphosphate levels, promoting glycolysis and inhibiting gluconeogenesis.

74
Q

What is the role of pyruvate decarboxylase in ethanol fermentation?

A

Catalyzes the decarboxylation of pyruvate to acetaldehyde, the first step in ethanol fermentation.

75
Q

What happens to lactate produced in muscles during anaerobic respiration?

A

It is transported to the liver, where it can be converted back to glucose in gluconeogenesis.

76
Q

Why is glycerol an important gluconeogenic substrate?

A

It can be converted to dihydroxyacetone phosphate and enter gluconeogenesis.

77
Q

How does pyruvate carboxylase contribute to gluconeogenesis?

A

It converts pyruvate to oxaloacetate in the mitochondria, a crucial step in bypassing pyruvate kinase.

78
Q

What cofactor is essential for pyruvate carboxylase activity?

A

Biotin, which carries CO₂ for carboxylation of pyruvate.

79
Q

Explain the biochemical basis of lactose intolerance.

A

Due to the absence of lactase, lactose cannot be broken down, leading to gastrointestinal symptoms.

80
Q

How does phosphoenolpyruvate carboxykinase (PEPCK) regulate gluconeogenesis?

A

It converts oxaloacetate to PEP, a rate-limiting step in gluconeogenesis.

81
Q

What is the consequence of glucose-6-phosphatase deficiency?

A

Impaired glucose release from the liver, causing glycogen storage diseases.

82
Q

What is the impact of G6PD deficiency on red blood cells?

A

Reduced NADPH production compromises the cell’s ability to neutralize oxidative stress, leading to hemolysis.

83
Q

How does alcohol consumption affect gluconeogenesis?

A

It produces excess NADH, which inhibits gluconeogenesis, potentially causing hypoglycemia.

84
Q

What is the function of sedoheptulose-7-phosphate in the pentose phosphate pathway?

A

It is an intermediate formed by transketolase reactions in the non-oxidative phase.

85
Q

Why is glycolysis considered a “substrate-level phosphorylation” process?

A

ATP is produced directly through enzyme-catalyzed reactions without the need for an electron transport chain.

86
Q

Describe the role of thiamine pyrophosphate (TPP) in fermentation.

A

TPP stabilizes the carbanion intermediate in pyruvate decarboxylase reaction during ethanol fermentation.

87
Q

Why is gluconeogenesis critical during fasting?

A

It supplies glucose to organs that depend on it, like the brain and red blood cells.

88
Q

How does glucose-6-phosphate serve as a metabolic branch point?

A

It can enter glycolysis, gluconeogenesis, or the pentose phosphate pathway based on cellular needs.

89
Q

What role does lactate dehydrogenase play in glycolysis under anaerobic conditions?

A

It reduces pyruvate to lactate, regenerating NAD+ for glycolysis.

90
Q

Why is acetyl-CoA an allosteric activator of pyruvate carboxylase?

A

It signals high energy availability, promoting gluconeogenesis.

BMS 610 Exam 3 (4 decks)

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