Chapter 8 - Glycolysis Flashcards
(134 cards)
1
Q
How could you determine which molecule contains the most energy?
A
Whichever is the most reduced
2
Q
Which 2 hormones regulate blood glucose concentration?
A
Insulin and glucagon
3
Q
How does glucose get into cells?
A
It is carried by transporters
4
Q
Glycolysis is the….
A
Oldest known and best studied pathway in living cells
5
Q
What is the key purpose of glycolysis?
A
The net formation of ATP
6
Q
Every intermediate in glycolysis serves as an….
A
Intermediate in another pathway in most cells
7
Q
What are the 2 mobile cofactors in pyruvate production?
A
ATP and NADPH
8
Q
Glycolysis pathway is a sequence of ____ enzymes that convert glucose to pyruvate
A
10
9
Q
What is the most common end product in glycolysis? (According to the book)
What could be the other end product
A
According to book - lactate
Other = pyruvate
10
Q
In the process of converting glucose to pyruvate, what high energy molecule is used?
A
NAD+
11
Q
When there is not enough NAD+…..
A
Glucose can no longer become pyruvate
12
Q
How does the body overcome the problem of a lack of NAD+?
A
Body has a way of converting NADH back to NAD+
13
Q
All the enzymes that catalyze glycolysis exist in the….
A
Cytosol
14
Q
Most mammalian cells use a ____ transport glucose protein called _____
A
Passive, GLUT
15
Q
GLUT has ___ isoforms
A
14
16
Q
What are isoforms?
A
Distinct proteins that have identical function but different kcat and km values
17
Q
What is the function of the liver?
A
Convert glucose to glycogen
18
Q
What is the function of the pancreas?
A
Secrets hormones that make the liver work - insulin, glucagon
19
Q
The GLUT 1 transporter is found in____ and _____
A
Red blood cells and is prominent in fetal tissues
20
Q
GLUT2 transporter is found in which 2 places?
A
Liver and pancreas
21
Q
The km for GLUT2 is relatively….
A
High
22
Q
The GLUT4 transporter is found in which 2 places?
A
Muscle and fat
23
Q
Is the GLUT4 transporter insulin sensitive?
A
YES
24
Q
GLUT1,2,4 - Which transporter uptakes glucose in response to extracellular glucose?
A
GLUT2
25
GLUT1,2,4 - Which transporter serves as the baseline glucose uptake for most cells?
GLUT1
26
The first step of glycolysis is catalyzed by…..
Hexokinase
27
What is the 1st step reaction (that hexokinase catalyzes)
Transfer of the phosphoryl group of ATP to glucose
Glucose + ATP —-> Glucose-6-P + ADP
28
What is the function of the hexokinase enzyme?
Protect the intermediates from hydrolysis. Conformational change among substrate (glucose) binding
29
Glucokinase is a _____ of hexokinase. It correlates with _____ transporter cells
Isozyme. Correlates with GLUT2 transporter cells
30
Most hexokinase enzymes have a similar affinity for….
Glucose
31
The km for glucokinase is very ….
High
32
Most hexokinase isozymes are product inhibited by….
Glucose-6-P
33
Which is the only transporter NOT inhibited by Glucose-6-P? WHY?
GLUT2 because it doesn’t have a transporter for removal
34
What is the 2nd step of glycolysis and what enzyme catalyzes it?
Isomerization of Glucose-6-P to Fructose-6-P.
Catalyzed by Glucose-6-P Isomerase
35
Explain what happens when Glucose-6-p is isomerized to fructose-6-P
Carbonyl moves from position 1 (aldehyde) to position 2 (ketone)
36
The isomerization of glucose-6-p to fructose-6-p is what kind of reaction?
An acid base reaction
37
Is the second step (isomerization) reversible?
YES
38
What is the 3rd step of glycolysis and what enzyme catalyzes it?
Phosphorylation of fructose-6-p to fructose-1,6-biphosphate
Catalyzed by PFK (Phosphofructokinase)
39
What is unique about the 3rd step of glycolysis?
It is the slowest step - the rate limiting step. PFK is the most regulated enzyme in the pathway
40
Is the 3rd step of glycolysis reversible?
(Phosphorylation of fructose-6-p)
NO
41
Which step of glycolysis has a nearly identical mechanism to the 1st step?
3rd step.
42
PFK is regulated ______ by a large number of enzymes
Allosterically
43
What are the 2 major regulators of PFK?
Citrate
Fructose-2,6-biphosphate
44
Describe the citrate regulator of PFK
Negative modulator.
Pasteur effect - glucose utilization decreases in the presence of oxygen
45
Describe the fructose-2,6-biphosphate regulator of PFK
Positive modulator. Formed from fructose-6-p and catalyzed by PFK2
46
What is the 4th step of glycolysis and what enzyme catalyzes it?
Fructose 1,6P2 is split into 2 3 carbon intermediates - Dihydrxyacetone-P + Glyceraldehyde-P
Catalyzed by ALDOLASE
47
What is the 5th step of glycolysis and what enzyme catalyzes it?
Near equilibrium interconversion between Glyceraldehyde-P and Dehydroxyacetone-P
Catalyzed by Triose Phosphate Isomerase
48
The 5th step of glycolysis is similar in mechanism to the
2nd step - isomerization of glucose-6-p to fructose-6-p
49
In the 5th step of glycolysis, ALL dehydroxyacetone-p is converted to…
Glyceraldehyde-p
50
What is the 6th step of glycolysis and what enzyme catalyzes it?
Only oxidation reaction in glycolysis. Glyceraldehyde-P is converted to 1,3-bis-P-glycerate while NAD+ is reduced to NADH
Catalyzed by glyceraldehyde phosphate dehydrogenase
51
Which step of glycolysis was the first enzyme mechanism ever solved?
6th step :
Glyceraldehyde-P --> 1,3-bis-phosphoglycerate
regulated by glyceraldehyde phosphate dehydrogenase
52
Which enzyme catalyzes the ONLY oxidation reaction in glycolysis?
glyceraldehyde phosphate dehydrogenase (6th step)
Glyceraldehyde phosphate + NAD+ + Pi ---><--- 1,3-bis-phosphoglycerate +NADH
53
In the 6th step of glycolysis, which species is oxidized and which species is reduced?
NAD+ --><--NADH = reduction
Glyceraldehyde-P--><--1,3-bis-phospho glycerate = oxidation (1,3-bis gains an oxygen and a phosphate)
54
Which step is involved in a hydride transfer and what is a hydride transfer?
step 6. Hydrogen is transferred along with a pair of electrons to NAD+
55
Which step has an -SH group involved in the reaction and what could this do?
6th step. -SH can react with heavy metals and other electron deficient molecules, leading to enzyme inhibition
56
What is the first step of glycolysis in which ATP is produced?
7th step.
1,3bis---><---3-P-Glycerate
Phosphoglycerate kinase
57
What is the 8th reaction in glycolysis and what enzyme catalyzes it?
3-Phospho-Glycerate---><---- 2-phospho-glycerate
enzyme = phosphoglycerate mutase
58
the 9th step of glycolysis is a _____ reaction
dehydration
59
What is the 9th reaction of glycolysis and what enzyme catalyzes it?
2-Phospho-glycerate--><--PEP (P-enolpyruvate)
catalyzed by enolase
60
What can inhibit enolase in the 9th step?
fluoride
61
is fluoride a strong inhibitor of glycolysis? why or why not?
NO - it is a weak inhibitor of enolase because enolase inhibition is fairly weak and nonselective
62
What are the 2 ATP forming reactions of glycolysis?
7th step and 10th step
1,3-bis-phosphoglycerate----><---3-phosphoglycerate by phosphoglycerate kinase
PEP-----> pyruvate
pyruvate kinase
63
pyruvate kinase is regulated both ______ and by ____ modification
allosterically and by covalent modification
64
What is the KEY ALLOSTERIC REGULATOR of pyruvate kinase?
Fructose-1,6-biphosphate (product of PFK)
65
When PFK is more active, it ______ which in turn activates _____. What is this called?
When PFK is more active it PRODUCES MORE PRODUCTS which in turn activates PYRIVATE KINASE. This is called FEED-FORWARD ACTIVATION
66
What enzymes phosphorylates and inactivates pyruvate kinase?
protein kinase A
67
What would cause an activation of protein kinase A?
hormonal regulation
68
In what organ is pyruvate kinase a SUBSTRATE for phosphorylation?
the liver
69
What enzyme catalyzes DEphosphorylation and returns pyruvate kinase back to its active form?
protein phosphatase
70
When would we WANT protein kinase A to attach a phosphate to pyruvate kinase?
when we don't want glycolysis to be that active anymore
71
Summary: What are the 2 COVALENT regulators of pyruvate kinase?
phosphorylates/deactivates pyruvate kinase = protein kinase A
dephosphorylates/activates = protein phosphatase
72
What is the key ALLOSTERIC regulator of pyruvate kinase?
fructose-1,6-biphosphate (product of PFK). It ACTIVATES pyruvate kinase by binding
73
What is the overall reaction of glycolysis?
Glucose + 2ADP + 2Pi + 2NAD+ ---> 2pyruvate + 2ATP + 2NADH
74
Which 2 molecules represent the connected ends of the glycolysis pathway?
glucose and pyruvate
75
The other molecules in the equation (besides glucose and pyruvate) are called...
mobile cofactors
76
what are the 2 categories of mobile cofactors in the glycolysis pathway?
phosphorylation cofactors and redox cofactors
77
What are the phosphorylation cofactors?
ATP, ADP, Pi
78
What are the redox cofactors?
NAD+, NADH
79
NADH--->NAD+
Oxidation or reduction?
NADH is oxidized to NAD+
80
How are the phosphorylation cofactors regenerated?
by all reactions in the cell that utilize energy in the form of ATP
81
What reaction MUST happen for glycolysis to continually operate?
NADH must be reoxidized to NAD+
82
How can the oxidation of NADH to NAD+ be accomplished? (2 ways)
the conversion of pyruvate to ethanol OR by the formation of lactate
83
The formation of lactate from pyruvate is catalyzed by the near equilibrium enzyme....
lactate dehydrogenase
84
Do any reactions follow the formation of lactate?
no- formation of lactate is a dead end in glucose metabolism
85
Write the reaction for the formation of lactate from pyruvate
pyruvate + NADH ---><--- lactate +NAD+
catalyzed by lactate dehydrogenase
86
There are many different ____ forms of the enzyme lactate dehydrogenase
izozyme
87
Several izozymes of lactate dehydrogenase form for different proteins in the ___,___,and____
liver,muscles, and heart
88
What can different izozoymes of lactate dehydrogenase be used for in a clinical setting?
to detect selective damage to heart cells. when they rupture, they will release lactate dehydrogenase into the bloodstream which can be differentiated from the other izozyme forms by electrophoresis
89
Some organisms, such as ____, can convert glucose to ____ instead of lactate
some organisms, such as YEAST can convert glucose to ETHANOL instead of lactate
90
What is the process called when organisms - such as yeast - convert glucose into ethanol?
fermentation
91
fermentation is a form of ____
glycolsysis
92
Fermentation has ____ steps. What are they?
2 steps:
1: Pyruvate---> Acetaldehyde + CO2
2: Acetaldehyde + NADH <----> Ethanol + NAD+
93
Why does the process of fermentation generate NAD+?
For glyceraldehyde phosphate dehydrogenase to continue glycolysis
94
One function of glycolysis is to.....
provide energy as ATP for other pathways
95
What is the NET gain of ATP in glycolysis?
2
96
Is the overall change in deltaGdegree in glycolysis positive or negative? What does this mean
negative - meaning that the process of glycolysis is thermodynamically allowed
97
In red blood cells, what is the ONLY means of ATP production?
GLYCOLYSIS
98
On the thermodynamic graph of glycolysis, what 3 enzymes account for the 3 downwards sloping areas? why???
hexokinase
PFK
pyruvate kinase
This is so because they're metabolically irreversible
99
What do the shallow slopes on the thermodynamic graph account for?
near equilibrium reactions
100
At high altitudes, 2,3-bis-phospho-glycerate _______ the affinity of oxygen for hemoglobin
DECREASES
101
The formation pf 2,3-bis-phospho-glycerate is an example of a....
shunt pathway
102
How is 2,3-bis-phospho-glycerate formed?
mutase enzyme catalyzes the reaction of 1,3-bis-phosphog-glycerate (from the glycolysis pathway)
103
What does a phosphatase enzyme do?
takes a phosphate off a molecule
104
Since Arsenate is similar electronically to ____, it can substitute for in the reaction with the enzyme ________
phosphate, glyceraldehyde-phosphate dehydrogenase
105
When arsenate substitutes for phosphate in the glyceraldehyde-phosphate dehydrogenase reaction, what molecule is formed?
1-arseno-3-phospho-glycerate
106
After 1-arseno-3-phospho-glycerate is produced, what happens?
it is RAPIDLY and nonenzymatically hydrolyzed to 3-phosphoglycerate
107
In the liver, fructose is transported across the membrane via_____, where it is converted to _____
GLUT2, fructose-1-phosphate
108
What is the purpose of phosphofructokinase?
rate limiting step for glucose metabolism
109
What does fructose-1-phosphate do?
BYPASSES Phosphofructokinase metabolism, leading to rapid and uncontrolled entry of fructose into pathway
110
Besides fructose, what other molecules can enter glycolysis?
galactose (derived from lactose)
Glycogen (polymer)
111
What are some alternative endpoints of glycolysis?
-ethanol formation (by yeast and other microorganisms)
-mammals - pyruvate to alanine
-nearly ALL CELLS have a pathway for the complete oxidation of pyruvate
112
What are the substrates and products of aldolase?
substrate: Frustose-1,6-biphosphate
products: dihydroxyacetone-phosphate and glyceraldehyde-phosphate
113
What is the product of pyruvate kinase?
pyruvate
114
In the last step of glycolysis, what high energy molecule is used to generate ATP?
(ex of Substrate level phosphorylation)
PEP
115
During the process of glycolysis (converting glucose into 2 lactate molecules), how many NADH molecules are produced?
NONE - ALL NADH is converted back to NAD+
116
more oxidized = ____ energy
less
117
most reduced = ____ energy
most
118
Why is it crucial to convert pyruvate to lactate in anaerobic conditions?
allows glucose to be continually broken down to make ATP due to the recycling of NADH to NAD+
119
How many molecular oxygen is consumed during glycolysis of one glucose molecule?
ZERO
120
Why is arsenate considered a poison when glycolysis is concerned?
it generates a shunt to bypass ATP production
121
How many ATP are generated in the presence of arsenic?
ZERO
122
What is the function of 2,3-biphopshoglycerate
releases more o2 from hemoglobin
123
1,3-bis-phosphoglycerate contains a lot of _____ and thus can be used for _______
energy, substrate level phosphorylation
124
what does insulin do?
helps glucose ENTER cells so that is can be used for energy
125
When blood insulin concentration is high, what does the GLUT4 transporter do?
provides an increased uptake of glucose
126
the km for GLUT1,4 is relatively____
low
127
the km for which glucose transporter is relatively high?
GLUT2
128
Which of the GLUT transporters is near equilibrium?
GLUT2
129
Does a high km or low km mean the reaction is near equilibrium?
high km
130
Why is it crucial to convert pyruvate to lactate in anaerobic conditions?
it allows glucose to be continuously broken down to make ATP due to the recycling of NADH to NAD+
131
Which 2 enzymes catalyze substrate level phosphorylation?
phosphoglycerokinase and pyruvate kinase
132
What molecule is made from an intermediate molecule in glycolysis and controls how hemoglobin binds to oxygen?
2,3-bis-phosphoglycerate
133
What molecule increases PFK activity?
fructose2,3 biphosphate
134
How many electrons can NAD+ absorb and carry?
2
