Glycolysis, glucose and pyruvate Flashcards
1
Q
What makes glucose a good fuel
A
- rich in potential energy (-2,840 Kj/mol)
- can be stored as polymer while keeping low cytosolic osmolarity
- readily available
2
Q
M3
Diff names for PPP
A
phosphogluconate pathway, hexose monophosphate shunt
3
Q
M3
What is NADPH used for?
A
Reductive biosynthesis
4
Q
M3
What cells undergo constitutive glycolysis
A
RBC’s, renal medula, brain, sperm
5
Q
M3
What is fermentation
A
general term for the anaerobic degradation of glucose or other organic nutrients to obtain energy, conserved as ATP.
6
Q
M3
What happens in the 2nd step of glycolysis?
A
Phosphohexose isomerase converts G-6-P to F-6-P.
7
Q
M3
What happens in step 4 of glycolysis?
A
F-1,6-B is converted to glyceraldehyde-3-phosphate and dihydroxyacetone-3-phosphate
Enzyme: aldolase
8
Q
M3
What molecule is converted to g-3-P in the 5th step of glycolysis?
A
Dihydroxyacetone phosphate
9
Q
M3
What is g-3-p converted to And what are its other by products and the enzyme involved
A
- Makes 1,3- Bisphophoglycerate
- enzyme: G-3-P dehydrogenase -
makes NADH and from NAD - phosphorylates molec. Using Pi
10
Q
M3
What is the first substrate level phosphorylation rxn in glycolysis
A
- 1,3- Bisphophoglycerate to 3-Bisphophoglycerate
- enzyme: phosphoglycerate kinase
- ADP–> ATP
11
Q
M3
What happens after the first substrate level phosphorylation rxn of glycolysis
A
- 3-phosphoglycerate is mutated to 2-phosphoglycerate -
- Enzyme: phosphoglycerate mutase
12
Q
M3
What does a mutase do?
A
Moves phosphate group
13
Q
M3
What does an isomerase do?
A
It rearranges the carbon structure
14
Q
M3
What happens after the phosphate group is moved in glycolysis?
A
- 2-phosphoglycerate is reacted to form phosphoenol pyruvate
- enzyme: enolase
- releases H2O
- OH group on carbon 3 is removed
15
Q
what are the 3 types of pathways
A
- Linear (product of rxns aresubstrates for subsequent rxns)
- Closed Loop (intermediates recycled)
- Spiral (same set of enzymes used repeatedly)
16
Q
what are 3 dietary sources of energy? list percentages and cal per gram
A
carbs = 40% 4 cal/g
Fat = 40 % 9 cal/g
Proteins = 20% 4 cal/g
17
Q
List 3 genral concepts of Digestion and Absorbtion
A
1) Food must be broken down into “absorbable”
components before any utilization is possible
2) Only monosaccharides are absorbed, thus complex
materials must be broken down to monosaccharides
3) Breakdown of complex carbohydrates or proteins
into monomer units involves hydrolysis; no other
reaction is required
18
Q
What kind of molecules provide enegy?
A
Oxidizable substrates
19
Q
complete oxidation of glucose to CO2 yields how much energy
A
686 kcal/mol
20
Q
reactions in calorimeter yield what
A
heat
21
Q
How is energy of digestibles harnessed
A
by tranducing it to ATP, which stores it as chemical energy
22
Q
one molecule of glucose reacts with how many O2’s?
A
6
23
Q
glucose and the other substrate make what? how many of these molecules are made per glucose?
A
CO2 and H2O
6 of each
24
Q
what 3 pathways does glycolysis lead to?
under what conditions?
what is their final product?
A
pyruvate fermentation to ethanol and CO2 in yeast; under hypoxic or anaerobic conditions
pyruvate to LActate in anaerobic conditions (vigorously contracting muscle, erythrocytes, in other cells and some microoganisms)
to acetyl CoA, CO2 and NADH via PDH in aerobic conditions
25
what is the role of glycolysis in muscles
production of lactic acid under anaerobic conditions; regenerate NAD+ to drive glycolysis forward; lactate released into bloodstream and delivered to liver where it is converted to glucose
26
role of glycolysis in liver
major function to
maintain blood glucose levels;
excess glucose converted to
fatty acids -- adipose tissue,
or to glycogen
27
role of glycolysis in RBCs
since they lack
mitochondria, glycolysis is
essential for energy production;
lactate is end product
28
role of glycolysis in the brain
glucose is aerobically
catabolized to CO2 and H2O;
reducing equivalents in NADH
delivered to mitochondria
29
what are the 4 uses of glucose
1) a storage form (glycogen),
2) energy source (ultimate conversion to CO2)
3) source of metabolic intermediates and electrons
4) precursor of all other sugars found in mammals
30
what does glucose membrane transport depend on and where?
Transport of glucose may be hormone-dependent
| (insulin in muscle) or not (liver)
31
what cells use glucose exclusively or nearly exclusively?
brain cells and RBC's
32
how many grams of glucose does the brain need per day?
120 g
33
what are the dietary sources of glucose
- milk: lactose
- fruits: glucose, fructose, higher sugars
- table sugar: sucrose
- vegetables: starches
- roughage: cellulose, etc
34
why is maintanence of glucose levels important and how is it maintained?
1) Since the brain is heavily dependent on glucose under
normal conditions, maintenance of blood glucose levels is
very important
2) Nearly continual process utilizing both storage forms
(glycogen) and de novo synthesis (gluconeogenesis)
from non-carbohydrate sources (primarily amino acids)
35
what happens after glucose is split to glyceraldehyde
it is rearranged to pyruvate (and then lactate or ethanol)
36
how many ATP and NADH are generated per molecule of glucose?
2 ATP and 2 NAH
37
what is the fate of NADH in aerobic conditions?
it is reoxidized with Oxygen as teh final electron acceptor
38
what is the formula for glycolysis
Glucose+2ADP+2NAD++2Pi -\> 2pyruvate+2ATP+2NADH+2H++2H20
39
what cells carry out glycolysis
Essentially all cells carry out glycolysis
40
what aspect of glycolysis differs in the different cells
the rate of the reactions
41
what the 2 functions of glycolysis
1. generate ATP
2. make pyruvate for TCA cycle to reduce glucose to CO2 and H2O
42
NAME THE 2 PHASES
1) Preparatory phase: investment of 2 ATP to
utilize a single glucose molecule as fuel
2) Payoff phase: Yields 4 ATP and 2 NADH
per glucose molecule
43
what are the advantages of phosphorylation
1) Transport: cells have transport systems on
membranes for fuel molecules such as glucose;
phosphorylated glucose is no longer recognized
by glucose transport system; trapped in cell
2) Binding: To allow strong highly specific
interaction between enzymes and substrates;
phosphate provides large electrically charged
functional group
3) Synthesis of ATP: substrate level phosphorylation
- phosphate group is directly transferred
to ADP from substrate to make ATP
44
in the first reaction of glycolysis:
what are the , substrates/products, cofactors, delta G,
what is a result of the phosphorylation of glucose
* glucose is phosphorylated on C-6
* requires a Mg2+: ATP complex
* phosphorylation retains glucose in the cell
Enzyme: hexokinase
45
what is the 1st priming reaction of glycolysis
the first one
46
what is the shape of the intermediate in the 1st rxn of glycoslysis
trigonal bipyramid
47
what do different hexokinases phosphorylate
Phosphorylates hexoses such as glucose,
fructose, and mannose
48
what are the main forms of hexokinases?
what cells are they in?
which on is responsible for DM?
Two major forms: hexokinase (all cells, types
I, II, and III) & glucokinase (liver,pancreatic
β-cells;type IV; mutated in diabetes mellitus)
49
what is the Km of hexokinase I and why is it significant
what is the conc. of glucose in the blood normally
Km for hexokinase is 0.1 mM; ensures that its
activity is independent of blood glucose
concentration (4 - 5 mM)
50
what is the Km for glucokinase?
why is this significant?
Km for glucokinase is 10 mM; only turns on
when cell is rich in glucose; ensures its
activity is dependent on blood glucose levels
Glucokinase functions when glucose levels are
high to sequester glucose in the liver.
51
which hexokinase is inhibited by G-6-P
```
Hexokinase (not glucokinase) is allosterically
inhibited by (product) glucose-6-P
```
52
why phosphoryl group is transfered by hexokinase and to what atom?
Hexokinase transfers the γ-phosphoryl grp of ATP to the oxygen
atom at C-6 of glucose, producing glucose 6-P and ADP
53
name the 2nd reaction of glycolysis
Enzyme:Phosphohexose isomerase
• Interconverts glucose 6-phosphate and fructose 6-phosphate.
Mg2+ cofactor
54
what enzymes have a dimer structure?
hexokinase, phosphohexose isomerase
55
what is the structure of the substrates of phosphohexose isomerase?
• Uses open chain structure as substrate
• Interconversion proceeds through a cis-enediol
intermediate; with the enzyme present the energy
barriers around enediol are lowered enough to speed
the interconversion.
56
Reaction 3 of glycolysis
enzyme, cofactors, delta G knot
* PFK-1
* Cofactors: ATP, Mg2+
* makes F-1,6- Bisphosphate from β-D-fructose-6-phosphate
* The second priming reaction, first committed step
57
what is the major control point in glycolysis?
PFK-1's rxn
58
what is the structure of PFK-1 and what are the two states it can exist in
what stabilizes these states?
• PFK is a homotetramer that can exist in two
states, R-state and T-state
• F-6-P stabilizes the R state, while ATP
stabilizes the T state and inhibits PFK
59
what are the effect of ATP, citrate and AMP on PFK-1
* ATP inhibits, AMP reverses inhibition
* Citrate is also an allosteric inhibitor
60
what effect does fructose 2,6 bisphosphate have on PFK1?
in what tissues?
• Fructose-2,6-bisphosphate is allosteric
activator in liver; prevents inhibition by ATP
61
what happens to PFk 1 in low energy or high energy status
* Low energy status: PFK increases activity
* High energy status: PFK decreases activity
62
what disease does PFK deficiency lead to?
what kind disease is it? what is the genetic component?
```
Tauri disease (glycogen
storage disease IV)- autosomal recessive disorder
```
63
what is the 4th rxn of glycolysis
enzyme, cofactors, substrate/products
what is notable about this rxn
* aldolase
* no cofactors noted
* F-1,6-BP to G-3-P (C4-C6) and Dihydroxyacetone phosphate (DHAP) (C1-C3)
64
what kind of cleavage happens in rxn 4 of glycolysis
Hexose cleaved to form two trioses; aldol cleavage
65
what kind of intermediate does aldolase's rxn proceed through?
Schiff-base intermediate
66
what is a precursor to triacylglycerols
DHAP (or DHA?)
67
5th reaction of glycolysis
Triose Phosphate Isomerase (TPI)
-Conversion of DHAP to G-3-P by TPI;
maintains steady state [G-3-P]; reversible
no cofactors
68
What kind of intermediates does teh second phase of glycolysis yield?
what are they?
• Second phase involves two very high
energy phosphate intermediates • .
– 1,3 BPG
– Phosphoenolpyruvate
69
Rxn 6 of glycolysis
enzyme, cofactors, substrates/products
Glyceraldehyde-3P-Dehydrogenase
G-3P + Pi --\> 1,3- bisphosphoglycerate
yields 1 NADH +H+
70
what molecule is in the active site of G-3-P
cystine
71
what part of the rxn by Glyceraldehyde-3P-Dehydrogenase is reversible
formation of first intermediate with high phosphoryl group
transfer potential 1,3-BPG
72
what intermediates does G3P dehydrogenase form
a thiohemiacetal and then a thioester with C1 of GAP
73
how many hydrogens are formed by G3P dehydrogenase?
2 hydrogens formed, one from C1 and the other from the phosphate
74
what carbon does NAD+ accept a hydride ion from?
why is this important?
from C1 and is reduced to NADH (NAD+
must be regenerated to sustain the forward reaction
75
rxn 7 of glycolysis
1,3 bisphosphoglycerate + ADP --\> 3- Phosphoglycerate + ATP
enzyme: phosphoglycerate kinase (PGK)
no cofactos noted
76
Deficiencies in Phosphoglycerate Kinase (PGK) lead to what
haemolytic anemia,
myopathy, central nervous system disorder, growth retardation
77
rxn 8 of glycolysis
Phosphoglycerate Mutase
interconverts 3-phosphoglycerate and 2-phosphoglycerate
Mg2+
78
Phosphoglycerate Mutase PGAM deficinecies lead to
muscle dysfunction with exercise
intolerance and muscle breakdown
79
Phosphoglycerate Mutase rxn involves
• involves formation of 2,3-bisphosphoglycerate via transient
phosphorylation of a histidine residue of the enzyme.
80
Rxn 9 of glycolysis
Enolase
converts 2-phosphoglycerate to phosphoenolpyruvate (PEP).
relases H20
no cofactors noted
81
Rxn 10 of glycolysis
Pyruvate Kinase
-transfers a phosphate from phosphoenolpyruvate to ADP,
producing pyruvate and ATP
no cofactors noted
82
what inhibits and what activates Pyruvate kinase
* Allosterically activated by AMP, F-1,6-biP (feed-forward activation)
* Allosterically inhibited by ATP and acetyl-CoA
83
interconversion of pyruvate is called.
what forms does it interconvert between
tautomerization
enol and keto forms
• Enolpyruvate is formed first that is rapidly converted to pyruvate
-PEP is the second compound with high phosphoryl group potential
-pyruvate kinase transfers this phosphate to ADP in rxn with
large negative G’o
84
lactic acid fermentation rxn
lactate dehydrogenase
pyruvate--\> L-lactate
G= -25 kj/mol
location: cytosol
regenarates NAD+ under anaeronic conditions
85
what is fermentation
processes that extract energy from
metabolic fuel without changing concentration of
NAD+ and NADH
86
Can NADH be transported to into the mitochondria?
not directly
87
in what cells is the cori cycle important?
where is lactate circulated back to?
* Lactate made in muscle under anaerobic conditions
* major product in erythrocytes
* Lactate is circulated back to liver to reform glucose
88
89
what is the first rxn in ethanol fermentation
pyruvate to acetaldehyde
pyruvate decarboxylase
cofactors: Mg, TPP
90
what is teh 2nd rxn in ethanol fermentation
acetaldehyde to ethanol
alcohol dehydrogenase
Cofactors: NADH +H+
yields: NAD+
91
what are teh GLUT transporters in hepatocytes
• GLUT 1, GLUT 2 - hepatocytes (plasma membrane)
92
what is the glucose transporter int he brain
• GLUT 3 - brain neurons (plasma membrane)
93
Where are GLUT 4 transporters found
• GLUT 4 - muscle, adipose tissue (in intracellular
vesicles and move to plasma membrane in response
to insulin signal from pancreatic β cells)
94
type 1 DM is lacking what cells
• Type 1 Diabetes Mellitus - have too few β cells
95
what happens to the blood glucose levels in type 1 DM and why?
what do muscle and fat tissue use when they cant access glucose? what energy molecules are formed as a result?
• Cells unable to take up glucose --- abnormally high
levels of glucose in blood (hyperglycemia)
• Muscle and fat tissue use fatty acids (triacylglycerol)
as principal fuel ---breakdown products are
converted to “ketone bodies” --- ketoacidosis
96
what happens to the rate of glucose uptake in tumor cells?
what changes happen as a result?
-tumor cells:
glucose uptake and
glycolysis proceed
10x faster than in
normal cells
-hypoxic conditions
-change to dependence
in glycolysis
for ATP generation
-tolerance to low pH
97
how to tumor cells adapt to use glycolysis primarily
- tolerance to low pH
- inc. expression of
1) glycolytic enzymes
2) glucose transporters
GLUT1,3
98
tetrameric enzymes of glycolysis
G-3-P Dehydrogenase, triose phosphate isomerase (PFK-1 is homotetramer)
99
what type of reaction happens in rxn 6 of glycolysis
coupled oxidation and phosphorylation
100
what is the delta G of the rxn catalyzed by G3P dehydrogenase
6.3 kj/mol
101
which glycolysis rxn are noted to be at or near equilibrium
rxn 6
102
what is used to push rxn 6 of glycolysis
• C1 phosphoryl group has high group transfer potential,used to phosphorylate ADP to ATP in next step of glycolysis
103
what donates the phosphate in rxn 6 of glycolysis
inorganic phosphate (Pi)
104
what happens to the NADH formed in rxn 6 of glycolysis
• NADH generated in this reaction is reoxidized by respiratory electron transport chain (which generates more ATP)
105
what is the delta G of the rxn catalyzed by phosphoglycerate kinase (PGK)
-18.5 kj/mol
106
what is dephosphorylated by phosphoglycerate kinase
1,3-bisphosphoglycerate
107
In what rxn is substrate level phosphorylation done
1,3 bisphosphoglycerate + ADP --\> 3- Phosphoglycerate + ATP ; enzyme: phosphoglycerate kinase (PGK)
108
what part of the substrate donate the phosphoryl group for the 1st substrate level phosphorylation
the carboxyl group of 1,3-phosphoglycerate (PGA)
109
how many ATP's per molecule of glucose is made during substrate level phosphorylation rxns
2
110
what rxns of glycolysis lack cofactors (noted in the syllabus)
phosphoglycerate kinase rxn, enolase rxn, pyruvate kinase rxn, triose phosphate isomerase rxn, aldolase rxn
111
what rxns of glycolysis require ATP
hexokinase rxn, PFK-1 rxn
112
what rxns of glycolysis have Mg2+ as cofactors
phosphoglycerate mutase rxn, PFK-1 rxn, hexokinase rxn
113
what is the delta G of phosphoclycerate mutase rxn
4.4 kj/mol
114
where is the phosphoryl group move in phosphoglycerate mutase rxn. Is this reversible?
C3 to C2; it is reversible
115
delta G of Enolase rxn
7.5
116
what kind of rxn is catalyszed by enolase? what is released by enolase rxn? Is it reversible?
dehydration; H20 ; revesible rxn
117
compare the energy content of 2-Phosphoglycerate and phosphoenolpyruvate
simlar energy content
118
what is the purpose of enolase
rearrages 2- phosphoglycerate to PEP to a form from which more energy can be released via hydrolysis
119
what does release of H2O from 2-phosphoglycerate do
converts the phosphate group to a very high potential energy (energy gain)
120
delta G of pyruvate kinase rxn
-31.4 kj/mol; Large, negative ΔG; essentially irreversible
121
what is the 2nd substrate level phosphorylation rxn
PEP + ADP --\> Pyruvate + ATP ; Pyruvate kinase (no cofactors)
122
what kind of molecules does triose phosphate isomerase convert
ketose to aldose isomerization
123
delta G of tiose phosphate isomerase (TPI)
7.5; reversible
124
what is the most efficient enzyme known? Why?
triose phosphate isomeraze; Kcat/Km is near diffusion limit
125
delta G knot for aldolase
23.8 kj/mol; Near-equilibrium rxn; reversible
126
what carbon is first G3P made from and what carbons is dihydroxyacetone phosphate made from?
C4-C6; C1-C3
127
what is the 2nd priming rxn of glycolysis
PFK-1 rxn
128
delat G of PFK-1
• large -ΔG (-14.2) means PFK is highly regulated; irreversible
129
what kind of rxn in 2nd step of glycolysis
aldose to ketose isomerization
130
delta G knot for phosphohexose isomerase
• 1.7 KJ/mol; Near-equilibrium rxn (reversible); direction depends on levels of substrate and product
131
delta g knot for hexokinase
-16.7; large negative ΔG’o makes this reaction irreversible
132
what enxyme requires ATP:Mg2+ complex
hexokinase rxn
