Exam Four Flashcards
1
Q
What step is the main control point for glycolysis?
A
step 3, phosphofructokinase
2
Q
What can pyruvate be converted to after glycolysis?
A
lactate, acetyl coA, and oxaloacetate
3
Q
What is the net reaction of glycolysis?
A
glucose + 2NAD+ + 2ADP + 2Pi –> 2 Pyruvate +2NADH + 2ATP + 4H+
4
Q
What is the enzyme that converts glucose to glucose-6-phosphate?
A
hexokinase
5
Q
How does hexokinase add a phosphate on the #6 carbon of glucose?
A
traps glucose inside the cell and lowers intracellular glucose concentration to allow further uptake
uses energy of ATP
6
Q
Why does hexokinase require ATP coupling?
A
Without ATP, the overall reaction would be nonspontaneous
7
Q
How does hexokinase “trap” glucose?
A
the addition of the negative charge by the phosphate group makes it difficult for glucose to escape the cell
8
Q
What is the enzyme that converts glucose-6-phosphate into fructose-6-phosphate?
A
phosphoglucose isomerase
9
Q
Why does glucose-6-phosphate need to be isomerized to fructose-6-phosphate?
A
this step makes the next steps easier/less energy required
10
Q
What is the enzyme that converts fructose-6-phosphate into fructose-1,6-biphosphate?
A
phosphofructokinase (PFK)
11
Q
What is/are the negative effector(s) of PFK?
A
PEP and ATP
12
Q
What is/are the positive effector(s) of PFK?
A
ADP
13
Q
What overall happens in the first 3 reaction of glycolysis?
A
sugar is activated via phosphorylation, 2 ATP requiring steps
14
Q
What is the enzyme that converts fructose-1,6-biphosphate into dihydroxyacetone phosphate (DHAP) and glyceraldehyde-3-phosphate (GAP)
A
aldolase
15
Q
What is the enzyme that converts DHAP to GAP?
A
triose phosphate isomerase
16
Q
Why is DHAP converted to GAP?
A
only GAP is the substrate for the next enzyme, so DHAP is useless
17
Q
How is the conversion of DHAP to GAP pulled forward?
A
GAP concentration is kept low
18
Q
What is the enzyme that converts GAP to 1,3-biphosphoglycerate with the help of NAD+ oxidation?
A
glyceraldehyde-3-phosphate dehydrogenase
19
Q
What are the 2 reactions that actually take place within the 6th reaction of glycolysis?
A
- oxidize GAP
- phosphorylate with Pi
20
Q
How is the GAPDH step pulled forward with a positive delta g?
A
this reaction is coupled with the following reaction in the pathway
21
Q
What is the enzyme that converts 1,3-BPG into 3-phosphoglycerate?
A
phosphoglycerate kinase
22
Q
What is special about the 7th reaction in glycolysis?
A
1st ATP production in glycolysis!
23
Q
What is the enzyme that converts 3-phosphoglycerate into 2-phosphoglycerate?
A
phosphoglycerate mutase
24
Q
What is the enzyme that converts 2-phosphoglycerate into phosphoenolpyruvate?
A
enolase
25
What is the enzyme that converts phosphoenolpyruvate into pyruvate?
pyruvate kinase
26
What is special about the last reaction in glycolysis?
it is irreversible and is the second ATP generating step
27
What are the four reactions in glycolysis with large negative delta Gs?
hexokinase (1), phosphofructokinase (3), phosphoglycerate kinase (7), and pyruvate kinase (10)
28
What are the reactions in glycolysis that use ATP?
hexokinase (1) and phosphofructokinase (3)
29
What are the reactions in glycolysis that make ATP?
phosphoglycerate kinase (7) and pyruvate kinase (10)
30
What is the reaction in glycolysis with a large positive delta G?
aldolase (4)
31
How does PFK 2 affect glycolysis?
When it is dephosphorylated, it stimulates PFK and the glycolysis pathway
32
What dephosphorylates PFK 2?
phosphoprotein phosphatase
33
What activates phosphoprotein phosphatase?
insulin
34
How does PFK 2 work when it is phosphorylated?
it works as phosphatase 2 which breaks down F 2,6 BP which inhibits glycolysis
35
When is insulin released?
When well-fed/ high blood glucose levels
36
When is glucagon released?
When starving/low blood glucose levels
37
Why isn't hexokinase the major regulatory step?
you can enter glycolysis without hexokinase by converting glycogen to glucose-6-phosphate using glycogen phosphorylase and phosphoglucose mutase
38
How do other carbohydrates generate energy?
they have to turn into one of the intermediates in glycolysis to generate pyruvate
39
How is mannose converted to generate energy?
mannose ----> fructose-6-phosphate
40
How is galactose converted to generate energy?
Galactose-1-P ---> Glu-1-P ----> Glu-6-P
41
How is fructose (muscle and kidney) converted to generate energy?
----> fructose-6-phosphate
42
How is fructose (liver) converted to generate energy?
-----> fructose-1-phosphate
43
Why is Fru-1-P a trouble maker?
it can enter glycolysis without being checked by PFK because it immediately converts to GAP
44
What is the purpose of the pentose phosphate pathway (oxidation of glucose-6-phosphate)?
produce NADPH from NADP
45
What is the net reaction of the pentose phosphate pathway?
G-6-P + 2NADP+ + H2O ---> Ribose-5-Phosphate + 2NADPH + 2CO2 + 2H+
46
What does NADPH protect cells from?
free radicals
47
What is the degradation of glycogen to use glucose called?
glycogenolysis
48
What are the three enzymes important for glycogen breakdown?
glycogen phosphorylase, debranching enzyme, and phophoglucomutase
49
glycogen phosphorylase stops when it reaches to a point ________ glucose residues away from a branching point
four
50
What can you do with glu-1-phosphate?
1. convert into g-6-p for glycolysis
2. convert to free glucose to export
51
GLUT 1
most tissues
52
GLUT 2
liver, small intestine
53
GLUT 3
neurons
54
GLUT 4
muscle,fat - insulin activated
55
can G-6-P or G-1-P be transported in blood?
no
56
There is no glycogen formation or breakdown in the _______
brain
57
What is the first substrate for glycogen synthesis?
Glu-1-P
58
Primer protein that makes a minimum length (7) of glycogen before starting with glycogen synthase
glycogenin
59
How does phosphorylation affect glycogen synthesis?
it activates glycogen breakdown AND deactivates synthesis of glycogen
60
When is glycogen breakdown needed?
starving
61
What is the inhibitor of glycogen breakdown?
phosphoprotein phosphatase-1
62
What is the activator of glycogen synthesis?
glycogen synthase
63
What is on the active form of glycogen phosphorylase?
- P
64
What is on the inactive form of glycogen phosphorylase?
-OH
65
What is on the active form of glycogen synthase?
- OH
66
What is on the inactive form of glycogen synthase?
- P
67
What stimulates glycogen phosphorylase?
AMP
68
What inhibits glycogen phosphorylase?
ATP and G-6-P
69
What stimulate glycogen synthase?
G-6-P and ATP
70
What inhibits glycogen synthase?
AMP
71
What activates phosphatases?
insulin
72
What activates cAMP production and kinases
glucagon
73
How does phosphorylation change the conformation of protein?
a phosphate group adds 2 negative charges and allows for 2-3 more hydrogen bonds to form
74
Phosphorylation is tied to the concentration of _____ in the cell
ATP
75
the cAMP cascade is triggered by _______
glucagon and epinephrine
76
How do you stop the cAMP cascade?
Breaking cAMP/ decyclizing it
77
What is the enzyme that decomposes cAMP and therefore stops the cascade?
phosphodiesterase
78
What activates phosphodiesterase?
phosphorylation catalyzed by PKA
79
What competitively inhibits phosphodiesterase so cAMP effect is prolonged?
caffeine
80
What is the term for glycolysis under anaerobic conditions?
fermentation
81
What is the purpose of fermentation?
to produce NAD+
82
How many ATP per glucose are produced in yeast aerobically vs. anaerobically
32 ATP/glucose aerobically
2 ATP/glucose anaerobically
83
What is the purpose of lactate fermentation?
to produce NAD+, the lactate is not beneficial
84
What does pyruvate decarboxylase do?
convert pyruvate into acetaldehyde
85
Who has pyruvate decarboxylase in their bodies?
only yeast
86
What does pyruvate decarboxylase need as a decarboxylation cofactor?
TPP
87
What does alcohol dehydrogenase do?
convert acetaldehyde into ethanol
88
What is the purpose of using alcohol dehydrogenase to convert acetaldehyde into ethanol?
produce NAD+
89
What occurs if there is a shortage of NAD+?
ATP production in glycolysis is slowed down
90
What happens if there is too much NADH?
trouble getting glucose to brain because there is not enough pyruvate for gluconeogenesis
91
What is the goal of gluconeogenesis?
producing free glucose
92
Where does gluconeogenesis occur?
mainly in the liver, but also in the kidney and small intestine
93
Why is it necessary to produce free glucose?
to supply glucose to the brain and for transport in the blood stream
94
What are the precursors of gluconeogenesis?
pyruvate, oxaloacetate, and glucogenic amino acids
95
What 3 steps in glycolysis need to be replaced in gluconeogenesis?
10. pyruvate kinase
3. PFK
1. hexokinase
96
What replaces pyruvate kinase in gluconeogenesis?
pyruvate carboxylase and phosphoenolpyruvate carboxykinase
97
What replaces phosphofructokinase in gluconeogensis?
fructose biphosphatase
98
What replaces hexokinase in gluconeogenesis?
glucose-6-phosphatase
99
What does pyruvate carboxylase use as a carrier for CO2
biotin (cofactor adding carbon)
100
cofactor removing carbon
TPP
101
What regulates the futile cycle/prevents waste?
fructose-2,6-biphosphate
102
What is fructose-2,6-biphosphate?
positive allosteric effector for PFK and negative allosteric effector for FBPase
103
Why is the citric acid cycle both catabolic and anabolic?
it is catabolic because it is breaking compounds apart and it is anabolic because the reduced cofactors produced may be helpful in other anabolic pathways
104
What is the enzyme that converts pyruvate into acetyl CoA
pyruvate dehydrogenase
105
What is the overall reaction of pyruvate dehydrogenase?
pyruvate + CoA-SH + NAD+ ---> CO2 + Acetyl-CoA + NADH + H+
106
How many steps are done and how many enzymes are used in the conversion of pyruvate into acetyl-coa
5 steps by 3 enzymes
107
What does E1 do?
decarboxylate pyruvate using TPP
108
What does E2 do?
oxidize the substrate using lipoamide cofactor
109
What does E3 do?
oxidize lipoamide using FAD-S-S
110
How is Beri-Beri disease caused?
thiamine deficiency that leads to limitations of pyruvate conversion to acetyl CoA which leads to loss of neural function
111
What is the location of TPP?
bound to E1
112
What is the function of TPP?
decarboxylates pyruvate yielding a hydroxyethyl-TPP carbanion
113
What is the location of lipoic acid?
covalently linked to a Lys on E2
114
What is the function of lipoic acid?
accepts the hydroxyethyl carbanion from TPP as an acetyl group
115
What is the location for CoA?
substrate for E2
116
What is the function of CoA?
accepts the acetyl group from lipoamide
117
What is the location of FAD?
bound to E3
118
What is the function of FAD?
reduced by lipoamide
119
What is the location of NAD+?
Substrate for E3
120
What is the function of NAD+?
reduced by FADH2
121
What is step one in pyruvate to acetylcoa
decraboxylation of pyruvate
122
what is step two in pyruvate to acetylcoa
oxidation of carbon by lipoamide
123
what is step 3 in pyruvate to acetylcoa
formation of acetyl-coa
124
what is step 4 in pyruvate to acetylcoa
reoxidation of the lipoamide by FAD
125
what is step 5 in pyruvate to acetylcoa
reoxidation of FAD by NAD+ forming NADH
126
Why is the citric acid cycle considered to be part of aerobic metabolism even though O2 does not explicitly appear in any reaction?
NADH and FADH2 produce lots of ATP when reoxidized by the electron transport chain
127
What is the enzyme that converts oxaloacetate and acetyl-coa into citrate?
citrate synthase
128
What is the enzyme that converts citrate into isocitrate?
aconitase
129
What is the enzyme that converts isocitrate and NAD+ into alpha-ketoglutarate, NADH, and CO2
isocitrate dehydrogenase
130
What is the enzyme that converts alpha-ketoglutarate, NAD+, and CoASH into Succinyl-CoA, NADH, and CO2?
alpha-ketoglutarate dehydrogenase
131
What is the enzyme that converts Succinyl-CoA, GDP, and Pi into Succinate, GTP, and CoASH?
succinyl-coA synthetase
132
What is the enzyme that converts Succinate and Q into fumarate and QH2?
succinate dehydrogenase
133
What is the enzyme that converts Fumarate and water into malate?
fumarase
134
What is the enzyme that converts malate and NAD+ into NADH and oxaloacetate?
malate dehydrogenase
135
The following is a list of possible products of glycolysis. Assuming ONE molecule of glucose is used in glycolysis, fill the blanks with the correct coefficients.
pyruvate
ATP (net amount)
NAH+
NADH
2, 2, 0, 2
136
Which 2 of the glycolysis intermediates contain a high-energy bond and are used to produce ATP by substrate-level phosphorylation in glycolysis?
phosphoenolpyruvate and 3-phosphoglycerate
137
Fructose-2,6-biphosphate is a compound that prevents futile cycle, because it is an activator of _______ and an inhibitor of ______. What are the correct enzymes for the blanks?
phosphofructokinase, fructose-1,6-biphosphatase
138
The phosphofructokinase (PFK) reaction is a major control point in glycolysis. It is the slowest reaction in glycolysis and is regulated by several molecules, but not by naturally changing concentrations of reactants and products. The molecules mentioned below allosterically regulate PFK activity. Indicate whether each condition described increases or reduces PFK activity (specifically in mammalian liver)
activation of PFK2, decreasing blood glucose concentration, increased pep concentration, increased levels of fructose 2,6 biphosphate, increased levels of ADP
activation of PFK2: increase PFK activity
decreasing blood glucose concentration: decrease PFK activity
Increased PEP concentration: decrease PFK activity
Increased levels of fructose 2,6 biphosphate: increase PFK activity
increased levels of ADP: increase PFK activity
139
In animal cells, the pyruvate produced in glycolysis is converted lactate under anaerobic condition. What is the name of enzyme that catalyzes the reaction above?
lactate dehydrogenase
140
What type of chemical change is made to the pyruvate in this reaction
pyruvate is reduced
141
what is the important product of this reaction other than lactate?
NAD+
142
What are the unique enzymes in gluconeogenesis that are used to reverse the irreversible steps in glycolysis?
pyruvate carboxylase, fructose biphosphatase, glucose-6-phosphatase, PEP carboxykinase
143
Which steps in gluconeogenesis consume or produce ATP?
pyruvate carboxylase, PEP carboxykinase, phosphoglycerate kinase
144
aspartate can be converted by transamination reaction into oxaloacetate (OAA). OAA can then be converted to glucose through gluconeogenic pathway. What is the energy yield or cost (in ATP-equivalent) of converting two molecules of OAA to 1 molecule of glucose?
4 ATP (equivalent) consumed
145
Glycogen synthesis requires formation of UDP-glucose. The process of UDP-glucose formation is thermodynamically driven by ______?
the hydrolysis of PPi
146
Muscle cells are not able to supply glucose for other tissues because they do not contain which of the following enzymes?
glucose-6-phosphatase
147
Glycogen phosphorylase catalyzes a _________ reaction that breaks __________ in glycogen. In the fasting state, the hormone glucagon _______ this enzyme, resulting in ________ blood glucose levels.
phosphorolysis, alpha 1,4 linkage, stimulates, increasing
148
The pentose phosphate pathway leads to production of _______? (select a pair of correct answers)
1. NADPH for anabolic metabolism
2. NADH for anabolic metabolism
3. NAD+ for glycolysis
4. Ribose-1-P for glycogen synthesis
5. Ribose-5-P for nucleotide production
1 and 5
149
What enzyme catalyzes the step between pyruvate to acetyl CoA and what is its cellular location?
pyruvate dehydrogenase in mitochondria
150
Which of the enzymes in the citric acid cycle is regulated by the cellular level of NADH?
isocitrate dehydrogenase
