Exam 3 Summary Flashcards
1
Q
What occurs in the preparatory phase of glycolysis?
A
2 ATP are consumed, intermediates’ ΔG increases, hexose carbon chains are converted to glyceraldehyde 3-phosphate (G3P).
2
Q
What are the products of glycolysis?
A
4 ATP and 2 NADH, resulting in 2 pyruvate.
3
Q
What is ΔG’° in biochemical reactions?
A
Standard free energy change determined at standard conditions (pH 7.0, 1 mM Mg2+, 1 M other reactants).
4
Q
What does a negative ΔG’° indicate?
A
The reaction will spontaneously proceed in the forward direction.
5
Q
What does a kinase do?
A
Adds phosphate (usually from ATP).
6
Q
What is the role of isomerase in glycolysis?
A
Facilitates intramolecular rearrangement.
7
Q
Fill in the blank: Glycolysis is the process by which a molecule of glucose is degraded into _______.
A
two molecules of pyruvate.
8
Q
What is the primary fuel molecule used by cells for energy?
A
Glucose.
9
Q
What is the definition of a mutase?
A
Moves a group within the molecule (special isomerase).
10
Q
What does a dehydrogenase enzyme do?
A
Catalyzes oxidation, making NADH or FADH₂.
11
Q
What is the significance of NADPH in glucose metabolism?
A
Acts as a regulator.
12
Q
What is the function of a lyase enzyme?
A
Breaks bonds without water (no hydrolysis).
13
Q
What is the role of a carboxylase?
A
Adds CO₂ and needs biotin cofactor.
14
Q
What is the role of Glutamate in the active site during the reaction phase?
A
It serves first as a general base and then as a general acid.
15
Q
Why is the reaction involving PFK-1 considered the first committed step of glycolysis?
A
Because after this step, the product is committed to going only through glycolysis.
16
Q
What type of reaction does Aldolase catalyze?
A
A fully reversible reaction that converts a 6C compound into two different 3C compounds.
17
Q
Which compound is directly degraded in the payoff steps of glycolysis?
A
Glyceraldehyde 3-phosphate (G3P).
18
Q
What type of reaction occurs in Reaction 6 of the payoff phase?
A
An oxidation reaction that leads to the formation of a high-energy acyl phosphate.
19
Q
What is the significance of the acyl phosphate formed in Reaction 6?
A
It has a large negative ΔG’°, making it a high-energy intermediate capable of driving ATP synthesis.
20
Q
What enzyme transfers the high-energy acyl phosphoryl group to ADP in Reaction 7?
A
An enzyme named for the reverse direction of the reaction.
21
Q
What occurs in Reaction 8 of the glycolytic pathway?
A
A reversible shift of the phosphoryl group between C-3 and C-2 of glycerate.
22
Q
What is generated in Reaction 9 of the payoff phase?
A
Phosphoenolpyruvate (PEP), a second high-energy compound.
23
Q
What is the final product formed in Reaction 10 of glycolysis?
A
ATP and pyruvate.
24
Q
What is required for Pyruvate Kinase to function in glycolysis?
A
K+ and either Mg2+ or Mn2+.
25
What is the overall balance sheet of glycolysis?
Net of 2 ATP, 2 NADH, and 2 pyruvate.
26
Why is glycolysis considered an essentially irreversible process?
Due to the complete oxidation of glucose to CO2 and H2O with a standard free-energy change of -2,840 kJ/mol.
27
What are feeder pathways for glycolysis?
Carbohydrates that are catabolized through glycolysis, including monosaccharides like fructose, mannose, and galactose.
28
How is glucose released from glycogen during catabolism?
Glycogen phosphorylase catalyzes the attack by inorganic phosphate on the terminal glucosyl residue.
29
What is the role of UDP-glucose in glycolysis?
It acts as a coenzyme carrier of hexoses.
30
What happens to pyruvate under aerobic conditions?
It is oxidized to acetate (acetyl-CoA) for the citric acid cycle.
31
What is gluconeogenesis?
The conversion of pyruvate and related compounds to glucose when glucose levels are low.
32
Why must gluconeogenesis bypass certain reactions of glycolysis?
Because three reactions in glycolysis are especially irreversible at cellular conditions.
33
What is the first bypass step in gluconeogenesis?
The synthesis of phosphoenolpyruvate from pyruvate.
34
What is the role of pyruvate carboxylase in gluconeogenesis?
It requires acetyl-CoA as a positive effector.
35
What strategies are used to replenish cytosolic NADH during gluconeogenesis?
* Malate shuttling * Oxidation of lactate to pyruvate.
36
What is the second bypass step in gluconeogenesis?
The hydrolysis of fructose 1,6-bisphosphate to fructose 6-phosphate.
37
What is gluconeogenesis?
The synthesis of glucose from pyruvate using many steps of glycolysis
38
What is the first bypass step in gluconeogenesis?
Conversion of pyruvate to PEP
39
What is the second bypass step in gluconeogenesis?
Dephosphorylation of fructose 1,6-bisphosphate to fructose 6-phosphate
40
What enzyme catalyzes the second bypass in gluconeogenesis?
Fructose 1,6-bisphosphatase (FBPase-1)
41
How is FBPase-1 regulated?
Via phosphorylation by a kinase
42
What is the third bypass step in gluconeogenesis?
Conversion of glucose 6-phosphate to glucose
43
Which enzyme catalyzes the third bypass in gluconeogenesis?
Glucose 6-phosphatase
44
Where is glucose 6-phosphatase present?
Hepatocytes, renal cells, and epithelial cells of the small intestine
45
What is required for each molecule of glucose formed from pyruvate in gluconeogenesis?
6 high-energy phosphate groups: 4 from ATP and 2 from GTP
46
What is the net equation for gluconeogenesis?
2 pyruvate + 4 ATP + 2 GTP + 2 NADH + 2 H+ + 4 H2O → 2 glucose + 4 ADP + 2 GDP + 6 Pi + 2 NAD+
47
What is the primary function of glycolysis?
Conversion of glucose to ATP and NADH, yielding pyruvate
48
Which sugars can enter glycolysis after conversion?
Galactose, fructose, mannose
49
What are the possible fates of pyruvate?
* Enters citric acid cycle to become CO2 (aerobic)
* Ferments to lactic acid or ethanol (anaerobic)
50
What is the pentose phosphate pathway used for?
* Producing NADPH
* Making ribose 5-P for nucleotide biosynthesis
51
What are the end products of the pentose phosphate pathway?
* Ribose 5-P
* CO2
* NADPH
52
How does NADPH affect the pentose phosphate pathway?
High NADPH concentration inhibits glucose 6-P dehydrogenase, shifting use of glucose 6-P toward glycolysis
53
What is homeostasis?
Regulation of internal environment to maintain stable conditions
54
What can result from metabolic regulation failure?
Human diseases such as diabetes, hyperglycemia, hypoglycemia
55
What is the role of glucagon?
Signals low blood glucose, prompting liver to release glucose from glycogen or gluconeogenesis
56
What is the role of insulin?
Signals high blood glucose, prompting liver to absorb glucose for storage
57
What are the key enzymes in glycolysis and gluconeogenesis regulation?
* Hexokinase
* Phosphofructokinase-1 (PFK-1)
* Pyruvate kinase
58
What are isozymes?
Different proteins catalyzing the same reaction encoded by different genes
59
What is unique about hexokinase IV in the liver?
Has a lower affinity for glucose and is not inhibited by its product
60
What happens to glycolysis when blood glucose levels are low?
Glycolysis slows down and glucose is released into the blood via GLUT2
61
What is the feedback inhibition in the pentose phosphate pathway?
High NADPH concentration inhibits glucose 6-P dehydrogenase
62
What happens to glycolysis when glucose decreases?
Glycolysis slows down and glucose is released into blood via GLUT2
## Footnote
This indicates a regulatory mechanism sensitive to glucose levels.
63
How is hexokinase IV regulated?
Hexokinase IV is reversibly inhibited by a regulatory protein specific to hepatocytes
## Footnote
Fructose 6-phosphate (F6P) and glucose compete for binding to this regulatory protein.
64
What occurs at high concentrations of fructose 6-phosphate (F6P)?
The regulatory protein binds hexokinase IV and recruits it to the nucleus, preventing G6P production
## Footnote
This prevents the activity of hexokinase IV when its substrate is not present.
65
What is the role of phosphofructokinase-1 (PFK-1) in glycolysis?
PFK-1 is the 'committed' step to glycolysis and can be allosterically regulated
## Footnote
It has catalytic and allosteric sites.
66
What compounds activate and inhibit PFK-1?
Activated by ADP and fructose 1,6-bisphosphate; inhibited by ATP
## Footnote
High ATP levels indicate less need for glycolysis.
67
What does high AMP concentration do to PFK-1?
It activates PFK-1
## Footnote
This indicates a need for glycolysis when energy levels are low.
68
What is the effect of high citrate concentration on gluconeogenesis?
It favors gluconeogenesis
## Footnote
High citrate indicates that energy needs are being met via the citric acid cycle.
69
What is F2,6BP and its role in glycolysis?
F2,6BP is a potent allosteric activator of PFK-1
## Footnote
It increases PFK-1 affinity for substrate and inhibits FBPase-1.
70
What is the effect of F2,6BP on gluconeogenesis?
F2,6BP inhibits FBPase-1
## Footnote
This means it inhibits gluconeogenesis in the liver.
71
What are the three isozymes of pyruvate kinase and their regulation?
All are inhibited by high ATP, acetyl-CoA, and long-chain fatty acids; activated by F1,6BP
## Footnote
These signals indicate energy availability and the need for glycolysis.
72
What is the effect of glucagon on liver pyruvate kinase?
Glucagon activates cAMP-dependent protein kinase A (PKA), which phosphorylates and inactivates the liver L isozyme
## Footnote
This process slows glucose use for fuel in the liver.
73
What does high acetyl-CoA concentration indicate for pyruvate regulation?
It indicates energy needs are being met through oxidative phosphorylation, favoring gluconeogenesis
## Footnote
This inhibits pyruvate dehydrogenase and activates pyruvate carboxylase.
74
What is glycogenolysis?
The breakdown of cellular glycogen to glucose 1-phosphate
## Footnote
This process releases monomers from glycogen granules.
75
How is glycogen breakdown catalyzed?
By glycogen phosphorylase
## Footnote
This enzyme works primarily in the liver and to a lesser extent in muscle.
76
What is the role of phosphoglucomutase in glycogen metabolism?
It catalyzes the reversible conversion of glucose 1-phosphate to glucose 6-phosphate
## Footnote
This is crucial for integrating glycogen breakdown into glycolysis.
77
How is glucose-6-phosphate transported out of the liver cell?
It is transported into the Endoplasmic Reticulum via the G6-P transporter
## Footnote
Glucose 6-phosphatase dephosphorylates G6-P before it enters the bloodstream.
78
What is glycogenesis?
The synthesis of glycogen
## Footnote
This process involves the conversion of glucose to glycogen for energy storage.
79
What sugar nucleotide is required for glycogen synthesis?
UDP-Glucose
## Footnote
It donates glucose for the formation of glycogen.
80
What is the role of glycogenin in glycogen synthesis?
Glycogenin acts as a primer for the synthesis of glycogen
## Footnote
It initiates the assembly of new glycogen chains.
81
What enzyme catalyzes the branching of glycogen?
Amylo-(1,4 to 1,6)-transglycosylase
## Footnote
This enzyme creates α1-6 linkages to form branches in glycogen.
82
What is metabolic regulation's role in glucose and glycogen homeostasis?
It ensures the maintenance of energy balance in the body
## Footnote
Homeostasis is crucial for cellular function and overall health.
83
What type of linkage is formed between glucose residues in glycogen?
α1-6 linkage
## Footnote
This linkage occurs with the first glucose residue in the chain.
84
What is metabolic regulation?
Homeostasis
## Footnote
Achieving homeostasis involves regulating various metabolic pathways.
85
What is reciprocal regulation in metabolism?
Reciprocal regulation of glycolysis and gluconeogenesis
## Footnote
This process helps maintain glucose levels in the body.
86
What catalyzes the phosphorylation of glycogen phosphorylase b?
Phosphorylase b kinase
## Footnote
This enzyme is activated by protein kinase A (PKA).
87
What initiates an enzyme cascade in glycogen breakdown?
Elevated [cAMP] in response to epinephrine or glucagon
## Footnote
This increase leads to the activation of various enzymes involved in glycogen catabolism.
88
What is the role of glucose-6-phosphatase?
Expressed only in hepatocytes
## Footnote
This enzyme is crucial for the final step of gluconeogenesis.
89
What happens at low [glucose] levels in the liver?
Phosphorylase a is present, promoting glycogen catabolism
## Footnote
This process releases glucose into the blood.
90
What effect does high [glucose] have on phosphorylase a?
Glucose binds to the allosteric site, inducing a conformational change
## Footnote
This change exposes the Ser-P residue.
91
What is the function of insulin in glycogen metabolism?
Promotes protein phosphatase 1 (PP1), which dephosphorylates phosphorylase a to convert it to phosphorylase b
## Footnote
Phosphorylase b does not digest glycogen.
92
What is the default state of glycogen synthase?
Glycogen synthase a makes glycogen
## Footnote
This active form can be inactivated by phosphorylation.
93
What inhibits glycogen synthase activity?
Phosphorylation by casein kinase II (CKII) and GSK3
## Footnote
This results in the conversion to glycogen synthase b (inactive).
94
What role does insulin play in glycogen synthesis in the liver?
Inhibits GSK3, allowing glycogen synthesis to continue
## Footnote
Insulin activates PP1, promoting conversion of glycogen synthase b to a.
95
What is the first step in the citric acid cycle?
Pyruvate is oxidized to acetyl-CoA and CO2
## Footnote
This reaction is catalyzed by the pyruvate dehydrogenase complex.
96
How many coenzymes does the pyruvate dehydrogenase complex require?
5 coenzymes
## Footnote
These include TPP, CoA, lipoate, NAD, and FAD.
97
What is substrate channeling in the pyruvate dehydrogenase complex?
Maintaining substrates on the surface of the complex
## Footnote
This enhances the efficiency of the enzymatic reactions.
98
What is the function of coenzyme A (CoA)?
Acts as an acyl carrier with a reactive thiol group
## Footnote
The -SH group forms a thioester with acetate in acetyl-CoA.
99
What are the three core enzymes of the pyruvate dehydrogenase complex?
E1: Pyruvate dehydrogenase, E2: Dihydrolipoyl transacetylase, E3: Dihydrolipoyl dehydrogenase
## Footnote
This complex has a very large molecular weight.
100
What is the significance of the citric acid cycle?
It is amphibolic, serving both catabolic and anabolic functions
## Footnote
It generates energy, materials for synthesis, and waste.
101
What is the outcome of the first step in the citric acid cycle?
Two carbons enter as acetyl-CoA and two carbons leave as CO2
## Footnote
This process helps regulate the cycle's activity.
102
What happens to oxaloacetate in the citric acid cycle?
It is present in very low concentrations, allowing for regulation
## Footnote
The formation of new oxaloacetate molecules is controlled.
103
What is the first step of the citric acid cycle?
Acetyl-CoA is fused to oxaloacetate
## Footnote
This step initiates the cycle and is crucial for the regulation of the entire process.
104
How does the concentration of oxaloacetate affect the citric acid cycle?
OAA is present in very low concentration, allowing control of the cycle by regulating the formation of newly synthesized oxaloacetate molecules.
105
What regulates the formation of acetyl-CoA by the pyruvate dehydrogenase complex (PDC)?
It is inactivated by a kinase that is under allosteric control by ATP (activated), and activated by a phosphatase.
106
How many oxidation reactions are in the citric acid cycle?
Four of the eight steps are oxidation reactions.
107
What are the energy payoffs per cycle of the citric acid cycle?
* 1 ATP (or GTP)
* 3 NADH
* 1 FADH2
108
What is the net ATP produced from one glucose molecule through glycolysis, pyruvate oxidation, and the citric acid cycle?
Approximately net +32 ATP per glucose.
109
Fill in the blank: The citric acid cycle is also known as the _______.
Krebs cycle.
110
What is the role of anaplerotic reactions in the citric acid cycle?
Anaplerotic reactions replenish intermediates when they are shunted to other pathways.
111
What activates pyruvate carboxylase?
Activated by acetyl-CoA (positive allosteric modulator).
112
True or False: Excess F1,6BP means less TCA cycles are needed for glucose oxidation.
False.
113
What ensures production of intermediates in the citric acid cycle at stable rates?
Regulation of the citric acid cycle.
114
What are the cofactors involved in the citric acid cycle?
* NAD+
* CoA
* GDP
* FAD
115
What is the ΔG'° for the highly regulated step involving KDH?
-33.5 kJ/mol.
116
What does the term 'amphibolic' refer to in the context of the citric acid cycle?
It refers to the cycle's role in both catabolic and anabolic processes.
117
Which enzyme is the 'committed' step to glycolysis?
PFK-1.
118
What is the impact of high ATP levels on glycolysis?
High [ATP] means less need for glycolysis.
119
What is the relationship between glycolysis and gluconeogenesis in terms of regulation?
Reciprocal regulation; when one goes up, the other goes down.
120
What is the role of complex signal cascades in metabolism?
They facilitate the regulation of metabolic pathways.
121
What are the inputs and outputs of pyruvate oxidation?
Inputs: pyruvate; Outputs: acetyl-CoA, NADH, CO2.
122
What is the significance of the high-energy thioester bond in acetyl-CoA?
It primes acetyl-CoA for entry into the TCA cycle.
