Glycolysis Flashcards
(168 cards)
1
Q
Metabolism?
A
Process through which living systems acquire and utilize the free energy they need ro carry out their various functions
2
Q
How much energy is stored in glucose?
A
2870kJ/mol (lots of energy)
3
Q
How much energy is stored in palmitate(fatty acid chain)?
A
-9781kJ/mol(even more energy than glucose)
4
Q
Main energy currency in cells?
A
ATP
5
Q
How much energy is stored in ATP?
A
32.2 kJ/mol
6
Q
ATP reaction?
A
ATP + H2O —- ADP + Pi
delta G = -32.2 kJ/mol
7
Q
Why is ATP the main energy currency in cells and not glucose?
A
ATP levels are 1000 times higher than ADP levels in cells which drives the ATP reaction forward releasing energy. Glucose is not always abundant in cells.
8
Q
If you break ATP into ADP and Pi, how much energy will be released?
A
32.2. kJ/mol, this can be coupled to drive unfavorable reactions
9
Q
Catabolism?
A
Breaking down of complex molecules into simple ones
-Usually produces ATP
-Ex. Protein — AA
10
Q
Anabolism?
A
Conversion of simple molecules to complex molecules
-Usually requires an input of energy
11
Q
How is metabolism an integrated system?
A
Products of catabolism can be used for anabolism(sometimes wee need to break something down in order to build something else up)
12
Q
3 Steps of catabolism?
A
- Conversion of polymers and complex lipids to monomeric intermediates(ex. Polysaccharides to monosaccharides), energy released
- Conversion of monomeric sugars, amino acids & lipids to simpler organic compounds(ex. pyruvate, acetyl-CoA, CAC intermediates), release energy
- Degradation to inorganinc compounds (H2O, CO2, NH3), energy released
**Anabolism are steps three to one **but energy is inputed
13
Q
Glycolysis?
A
Breakdown of glucose
14
Q
Oxidative phosphorylation?
A
Use the consumption of O2 to phosphorylate ADP
15
Q
Central pahtways of energy metabolism ?
A
- Glycolysis
- Oxidative phosphorylation
16
Q
Futile Cycle?
A
A metabolic pathway where two opposing reactions occur simultaneously, resulting in a net loss of energy without producing a useful product
17
Q
Do cells want to do futile cycles?
A
NO, because it is a waste of energy
18
Q
Example of futile cycle?
A
If fatty acid degradation and synthesis ocurred simultaneously, no useful work would be done and more ATP would be consumed in the endergonic reactions of fatty acid synthesis than produced in the oxidation reactions
19
Q
2 ways to stop the futile cycle?
A
- Cells are organized in organelles, these separate enzymatic reactions through membranes
- Enzymes in an organelle are under regulation via covalent modifications or allosterically
- The delta G to go from FA to acetyl-CoA is -20 kJ/mol and to go from acetyl-CoA to FA it is +20kJ/mol(same energy used as released)
20
Q
A pathway must be exergonic to proceed?
A
A negative delta G is needed for a reaction to proceed spontaneously, otherwise it needs to be coupled to an exergonic reaction
21
Q
When does glycolysis occur?
A
In the absence of O2
22
Q
What is glycolysis?
A
-Splitting of glucose(6 carbon molecule) to two 3 carbon molecules(pyruvate)
23
Q
Where does glycolysis occur?
A
Every cell in the body
24
Q
Gluconeogenesis?
A
Occurs in the kidney and liver
These tissues can synthesize glucose from smaller molecules
25
When is gluconeogensis needed?
During fasting
26
T/F: Most tissues use glucose as their primary energy source?
True
27
T/F: Glycolysis is the first step of glucose oxidation?
True
28
Where does glycolysis occur in cells?
IN the cytosol
29
How many steps is glycolysis?
10
30
Phases of glycolysis?
1. Energy investment
2. Energy generation
31
Another name for glycolysis?
Fermentation
32
How is NAD+ regnerated after glycolysis?
1. Pyruvate is made at the end of glycolysis
2. Pyruvate is then immediately converted to lactate due to Lactate dehydrogenase(LDH)
3. This conversion reoxidizes NADH(removes its electrons) and creates NAD+
33
What is lactate?
Pyruvate with an electron on it
34
Is the pyruvate to lactate reaction spontaneous?
Yes, it has delta G = -25.1 Kj/mol
35
Step 1 of glycolysis?
1. Glucose enters the cell and hexokinase catalyzes the phosphorylation of glucose(ATP dependent phosphorylation)
2. THis step produces phosphorlyated glucose G6P
3. This step requires an ATP molecule
36
Why does glucose need to be phosphorylated in step 1 of glycolysis?
-Traps the glucose in the cell and now it must go through glycolysis
37
Step 3 of glycolysis?
1. F6P is converted to FBP via the phosphofructokinase (PKF)
2. This step requires another ATP molecule
38
IF the cell has sufficient ATP what would happen to PFK?
PKF would be off since we don't need to generate anymore ATP thus the cell does not need to be doing glycolysis
39
Why is PFK the rate limiting step/enzyme?
- When PFK is working usually glycolysis is working
-If PFK is not working glycolysis is usually off
-Dictates the flow of the meatbolic pathway
40
T/F: PFK is allosterically regulated?
True
41
Steps 4 & 5 of glycolysis?
Step 4: Takes FBP and splits it inot two 3 carbon metabolites, GAP and DHAP
Step 5: DHAP become GAP, end up with 2 GAP molecules
42
Step 6 of glycolysis?
1. Catalyzed the GADPH, GAP is converted to BPG. BPG has delta G = -49.4 kJ/mol(more negative than ATP).
2. The BPG will then spontaneously hydrolyze
3. The GAP to BPG reaction is unfavorable but it is pulled by the hydrolysis of BPG.
43
Step 7 of glycolysis?
BPG generates 3PG and an ATP catalyzed by phosphoglycerate kinase
44
How is the ATP generated during step 7 of glycolysis?
Via substrate level phosphorylation. one molecule transfers its phosphate to another molecule
45
Why can BPG generate an ATP?
Because it deltaG is -49.4 kJ/mol and only 32.3 of that is needed to generate ATP
46
How are steps 6 and 7 coupled?
Step 6 has a deltaG of +6.3
Step 7 produces deltaG -17.2(after generation of ATP)
The remaining energy is used to drive reaction 6
47
Step 8 of glycolysis?
3PG is converted to 2PG
48
Step 9 of glycolysis?
Enolase enzyme takes 2PG and converts it to PEP which has an even more negative deltaG than BPG (deltaG = -61.9 kJ/mol)
49
Step 10 of glycolysis?
The negative deltaG of PEP is used to make another molecule of ATP and then PEP is converted to pyruvate which is just unphosphorylated PEP
50
How is ATP made during step 10 of glycolysis?
Substrate level phosphorlyation. Phosphate from PEP is transferred to ADP.
51
What enzyme catalyzes step 10 of glycolysis?
Pyruvate kinase
52
The three reactions pulling glycolysis forward?
1. Glucose --- G6P (catalyzed by hexokinase)
2. F6P -- FBP (catalyzed by phosphofructokinase)
3. PEP ---- Pyruvate(catalyzed by pyruvate kinase)
** These are the only 3 spontaneous reactions**
53
T/F: Most of the reactions function at or near equilibrium and are freely reversible in vivo?
True, but they are pulled forward due to the highly negative deltaG reactions
54
How is deltaG different in a test tube vs in a cell?
In a cell the deltaG is more accurate because it also depends on the concentration of the reactant in the environment to drive the reaction
Ex. Glucose has a highly negative deltaG but its not always found in high concentrations in the cell meaning that the reaction is less likely to occur
55
DeltaG of the three driving reactions of glycolysis?
1. Glucose-G6P (-33.5)
2. F6P-- FBP(-22.2)
3.PEP--Pyruvate(-16.7)
56
Is all glucose that we consume converted to energy?
No, some will be converted to heat or excreted as organic waste
57
T/F: Metabolism is a way to harvest energy stored within macronutrients?
True
58
PEP?
Metabolite with high phosphoryl potential meaning that the phosphate wants to be elsewhere which is why the phosphate is added to ADP to make ATP
59
If you are at rest and don't require energy/ATP what do your cells do?
They convert G6P to glycogen for storage
60
What happens when you introduce O2 into yeast cells?
Glucose, G6P and F6P are at high concentrations and everything else is low. This is most likely because PFK which catalyzes F6P to FBP must be inhibited by O2. It is probably favourable that the yeast use oxidative phosphorylation instead
61
3 steps of glycolysis under the most control/rate-controlling reactions?
1. Glucose to G6P
2. F6P to FBP
3. PEP to pyruvate
62
How does G6P regulate hexokinase?
Hexokinase catalyzeds glucose conversion to G6P when G6P starts to accumulate in the cell it will itself inhibit hexokinase
63
Are enzymes ever 100% on/off?
No, they are constantly under regulation
64
Gluconeogenesis is just glycolysis backwards?
Yes
65
PFK structure?
1. Has two active sites where F6P binds and gets converted to FBP
2. Has an allosteric site the can enhance/inhibit what is happening at the active site usually by changing its conformation
66
How does ATP inhibit PFK?
If you have enough ATP you don't need to use glucose to generate more. ATP will bind to the enzymes allosteric site and stop PFK. All prior intermediate will accumulate into G6P and it will be converted to glycogen
67
How do AMP and ADP regulate PFK?
AMP and ADP are products of ATP hydrolysis thus they activate PFK. They will bind to it allosteric site and causing the conformation of the active sites to be active
68
How does citrate regulate PFK?
Citrate is found at the start of the citric acid cycle. If there is a build up of citrate in the cell this means the citric acid cycle is not turning. So PFK activity will be inhibited
69
PFK in low vs high ATP conditions?
Low ATP: PFK is easily activate by low concentrations of F6P susbtrate (hyperactive)
High ATP: PFK requires more F6P to be activated
70
How is F2, 6 BP generated?
They are generated by an isoforms of PFK called PFK-2
71
PFK-2?
Bifunctional and can convert F6P to F2, 6BP to activate PKF1
72
When is PFK2 used?
When there is a build of F6P because PFK1 cannot convert it fast enough. PFK2 will convert it to F2, 6BP to help hyperactivate PFK1 to convert more F6P and keep glycolysis going
73
How does F1, 6BP regulate pyruvate kinase?
Increase F1, 6BP in the cell bind PK and activates it. This creates a pull on glycolysis which prevents any inhibition of the produccts downstream of F1, 6BP(prevents inhibition on any steps between PFK and PK)
74
Feedfoward activation?
When F1, 6BP binds PK and activates it pulling glycolysis forward
75
What inhibits PK?
-ATP
-Acetly-CoA(not being used by citric acid cycle)
-Alanine
76
Why does alanine inhibit PK?
Alanine is an amino acid that is a key precursor to making more glucose. A build up of alanine signals to the cell that it wants to make glucose which inhibits glycolysis because we want to shift from consuming it to storing it.
77
T/F: Acetyl-CoA activates gluconeogenesis?
True because its not being used by the CAC
78
What reaction does pyruvate dehydrogenase catalyze?
Pyruvate + CoA + NAD+ --- Acetyl-CoA + CO2 + NADH
79
Where does the pruvate dehydroenase reaction occur?
In the mitochondria
80
How does pyruvate get into the mitochondrion?
Via pyruvate translocase(MPC)
Which is a pyruvate/H+ symport (both are transported into the mitochondria_
81
Why is a proton brought in with pyruvate?
Because pyruvate is negative and thus it must bring in a proton so as to not mess up the electrochemical gradient
82
Acetyl-CoA?
-2 carbon molecule
-Enters into the CAC and combines with oxaloacetate to generate citrate for the citric acid cycle
83
Pyruvate dehydrogenase complex?
Massive multi-enzyme complex
-9.5 megadaltons in eukaryotes
84
Main enzyme in the PDC that is regulated?
Pyruvate dehydrogenase
85
T/F: The PDC requires 5 different coenzymes for catalytic activity?
True
86
Pyruvate dehydrogenase reaction step 1?
1. Decarboxylation of pyruvate releases CO2
2. Pyruvate is put onto
TPP(product of step 1)
Catalyzed by pyruvate dehydrogenase
87
Step 2 of pyruvate dehydrogenase reaction?
1. TPP is regenerated
2. Pyruvate combines with lipoamide to form acetyl-dihydrolipoamide
88
Step 3 of pyruvate dehydrogenase reaction?
1. Acetyl-dihydrolipoamide combines with CoA to form Acetly-CoA
89
Step 4 of the pyruvate dehydrogenase reaction?
1. The lipoamide from step 3 now has additonal electrons on it these are transferred to FAD to regenerate the lipoamide for step 3
90
Step 5 of pyruvate dehydrogenase reaction?
1. FAD is now reduced.
2. FAD then transfers its electrons to NAD+ to generate NADH (reduces NAD+)
3. This then reoxidizes FAD so that it can accept more electrons from lipoamide
91
Why is pyruvate dehydrogenase reaction irreversible?
Because step 1 is irreversible when we remove CO2 the pyruvate must now go through the reaction
92
Products of the pyruvate dehydrogenase reaction?
- Acetly-CoA(for CAC) and NADH(for oxidative phosphorylation)
93
What happens to the CO2 in pyruvate dehydrogenase reaction?
It diffuses out of the mitochondria
94
Mechanistic advantages of multi-enzyme complexes?
1. Minimized distances for substrates in between active sites
2. Metabolic intermediates are channeled between successive enzyme sites
3. Coordinated control of reactions
95
Why is Minimized distances for substrates in between active sites an advantage?
Increased rate of reaction without having to maintain large pools of intermediates
96
WHy is Metabolic intermediates are channeled between successive enzyme sites an advantage?
-Side reactions are minimized
-Protection for chemically labile intermediates
97
Why is coordinated control of reactions an advantage?
Shutting off one enzyme effectively shuts the system down
98
What enzyme catalyzes the production of Acetyl-CoA?
-E2: dihydrolipoyl transacetate
99
Coenzyme A?
Functions as a carrier of acetyl and other acyl groups
100
Acetyl CoA?
-Acetyl thioester
-High energy compound
-Has high acyl group transfer potential and can donate the acetyl group to several acceptors
101
Hydrolysis of Acetyl-CoA?
Produces -31.5 kJ/mol
102
Bond that contains all the energy in Acetyl CoA?
Thioester bond
103
How is PDC regualted by allostery?
The products of the the pyruvate dehydrogenase reaction, acetyl-CoA and NADH, inhibit pyruvate oxidation. They shuts down E1(pyruvate dehydrogenase) through product inhibition
104
Regulation of PDC by phosphorylation?
The phosphorylation of pyruvate dehydrogenase on three specific serine residues inactivates the enzyme. The phosphorylation is done by PDH kinase and the phosphate can be removed to active the enzyme by PDH phosphatase
105
When is PDH kinase active?
In conditions of high NADH, Acetyl-CoA and ATP when we don't need pyruvate oxidation
106
When is PDH kinase inhibited?
In conditions of high pyruvate and ADP
107
The citric acid cycle?
-A series of 8 enzymatic reactions that combine acetyl CoA(2 carbons) with oxaloacetate(4 carbons) to generate CO2, NADH and FADH2 and regenerates the starting product oxaloacetate
108
Other names for CAC?
-Krebs cycle
-Tricarboxylic acid cycle
109
T/F: The CAC is part of the aerobic metabolism ?
True, but it does not directly consume O2
110
Purpose of the CAC?
To generate electron carriers
-NAD+ and FAD
-And to produce intermediates for biosynthesis
111
Every turn of the CAC generates how many electron carriers ?
-3 NADH
-2 FADH
112
CAC is Amphibolic?
Amphibolic: both a site of anabolism and catabolism
113
Anabolism in the CAC?
CAC intermediates are the starting point of the anabolic pathways
Ex. Gluconeogenes, fatty acid synthesis, etc
114
Catabolism in CAC?
CAC intermediates are the end point of catabolic pathways. The aerobic catabolism of carbohydrates, amino acids and lipids merge into the CAC
115
Cataplerotic reactions?
These are reactions the promote anabolism and deplete the CAC intermediates by using them form anabolic reactions
116
Anaplerotic reactions?
These are catabolic reactions that replensih the CAC intermediates
Ex. PDH promotes catabolism
117
CAC is a reservoir?
CAC is a resevoir of metabolic intermediates that can be taken out when a cell needs it to make more complex molecules. If you take one intermediate out every metabolite after will decrease in concentration (cateplerosis)
118
Is the CAC anerobic or aerobic?
Anaerobic but it supprots aerobic metabolism
119
Does CAC harvet energy?
Yes it stores energy in electron carrier
And makes GTP via substrate level phosphorylation
120
All of the products of one turn of the CAC?
-3 NADH
- 1 FADH2
- 1GTP
-1 CoA
-2 CO2
121
How many products of the CAC do you get from one molecule of glucose?
-6 NADH
- 2 FADH2
- 2 GTP
-2 CoA
-4 CO2
122
First reaction of the CAC?
Oxaloacetate combines with acetyl-CoA to make citrate(6 carbon) this is catalyzed by citrate synthase
123
Last reaction of CAC?
Malate dehydrogenase makes oxaloactate
124
How is GTP generated in the CAC?
Succinyl-CoA similar to acetyl-CoA has a high energy thioester bond that can generate GTP directly
125
What drives the CAC?
The majority of the CAC is made up of reversible reactions but there are three reactions with highly negative deltaG's that drive the CAC forward
126
How many ATP molecules can be generated from NADH and FADH2?
NADH generates 2.5 ATP molecules
FADH2 generates 1.5 ATP molecules
127
How many ATP molecules can be generated per turn of the CAC?
3 NADH = 7.5 ATP molecules
1 FADH2 = 1.5 ATP
Total of 10 ATPs can be made per cycle (also count GTP as ATP)
128
For every glucose molecule how many ATPs can be made in the CAC?
20 ATPs
129
T/F: The enzymes in the CAC under the most control are those that catalyze the highly negative deltaG reactions?
True
130
How is the CAC regulated by the redox state of the cell?
If NADH builds up in the mitochondria it will inactivate the CAC. The respiratory chain oxidizes NADH to NAD+ reactivating the CAC
131
How does the energy state of the cell regulate the CAC?
If there is high levels of ATP the CAC will be inhibited because we don't need more energy
132
How is CAC regulated by availability of energy rich compounds?
High levels of acetyl-CoA and succinyl-CoA inhibit the CAC enzymes
133
How many ATPs are produced by glycolysis?
Net 2 ATPs
Plus glycolysis produced 2 NADH molecules which is equivalent to 5 ATP
So glycolysis in total makes ATP molecules
134
How many ATP molecules does pyruvate dehydrogenase make?
It makes 1 NADH so 2.5 ATP molecules from 1 pyruvate
135
Total amount of ATP generated via glycolysis, PDC and CAC from one molecule of glucose?
1. Glycolysis = 7
2. PDC = 5
3. CAC = 20
Total = 32 ATP per glucose moelcule
136
2 membranes of the mitochondrion?
Inner membrane: highly invaginated and forms cristae where the respiratory chain is embedded
Outer
137
What is between the inner/outer membranes of the mitochondria and what in within the inner membrane?
Inner/outer: Intermembrane space
Inner" matrix
138
How many complexes make up the oxidative phosphorylation?
4
139
How does the oxidative phosphorylation work?
1. Electrons are passed through the complexes causing conformational changes to occur in the complexes
2. These conformational changes lead to H+ being pumped from the matrix into the intermembrane space
3. This only occurs in complexex I, III and IV
140
Does complex II pump protons?
No, it is succinate dehydrogenase enzyme for the CAC and converts FADH2 to FAD
141
How many protons does complex I, III and IV pump into the intermembrane space?
Complex I: 4 H+
Complex III: 4 H+
COmplex IV: 2H+
142
How many protons does one NADH vs FADH2 molecule pump across the intermitochondrial membrane ?
1 NADH molecule pumps 10 H+ across
1 FADH2 only pump 6H+ since it bypasses complex I
143
How many electrons are in each NADH molecule?
2
144
How is H2O made?
For every O atom consumbed by H2O 2 electrons have to pass through the respiratory chain and 10H+ must be pumped through ATP synthase
145
Why are protons pumped into the intermembrane space?
This is done to store energy. The disequilibrium of H+ in the intermembrane space compared to the matrix is a potential source of energy that creates an electrochemical gradient of about 150 to 200 mV
146
NADH to H2O reaction?
NADH + H+ + 1/2O2 -- NAD+ H2O
deltaG = -220 kJ/mol
147
What does it mean that NADH has a low standard reduction potential?
This means that it wants to give it electrons away
148
What does it mean that O2 has high standard reduction potential?
It is a very good electron acceptor, readily accepts them from NADH
149
T/F: electrons flow from low to high reduction potentials?
True
150
T/F: from NADH to O2 we are able to make many molecules of ATP?
True, since the reaction from NADH to O2 released 220 kJ/mol of energy and ATP production only requires 32.2 kj/mol
151
Chemi-osmotic coupling?
The idea that the electrochemical gradient created by protons is used to drive ATP production
152
Respiratory chain can function in the absence of phosphate, evidence for chemi-osmotic coupling?
Don't need to make a molecule like BPG that has a phosphate, the chain can cosume O2 even if you don't have a high energy intermediate with a phosphate
153
The # of moles of ATP generated through NADH oxidation was not an integer, evidence for chemi-osmotic coupling?
If there was a high energy intermediate that delivered ATP the amount of ATP molecules for every O2 you consume should be an integer
154
An intact IMM is required for OXPHOS(generation of ATP), evidence for chemi-osmotic coupling?
Protons must be pumped across the IMM if disrupted you cannot make ATP
155
Key electron transport proteins span the IMM, evidence for chemi-osmotic coupling?
Localized where they can make a membrane potential
156
Uncouplers such as 2.4-Dinitrophenol(DNP) inhibit ATP synthesis, evidence for chemi-osmotic coupling?
Uncouplers allow protons to bypass the IM and go back to the matrix you don't make the membrane potential or any ATP
157
Generting an artifical proton gradient permits ATP synthesis without electron transport, evidence for chemi-osmotic coupling?
Yes
158
Why is cellular respiration and breakdown of glycolysis so many steps and redox reactions?
Because it allows for controlled and efficient energy extraction. If you did it all in one step it would release too much energy at once and not a lot of it would be harnessed and it could damage the cells(combustion)
159
C-ring in mammals ATP synthase?
C-ring in mammals has 8 subunits
-This neans for every 360 degree turn 8 H+ will go through
-This also means 3 ATP are created per 360 degree turn
160
How does the ATP synthase work?
1. Protons go through the ATP synthase channel
2. The protons push the FOC subunit ring embedded in the intermitochondrial membrane which causes the C-ring to turn
3. One proton per C-ring subunit is needed
161
Are 32 ATP molecules always generated by a molecule of glucose?
NO, this is the mximal amount of ATP that can be generated it is not necessarily always generated
162
P/O ratio?
The amount of ATP molecules generated for every O atom consumed
163
What complex oxidizes NADH vs FADH2?
NADH is oxidized by complex I
FADH2 is oxidized by complexII
164
How many H+ molecules are needed to generate a molecule of ATP?
In the C-ring complex we saw that 8H+ were transported which produced 3 ATP molecules
8/3 = 2.7
This means that 2.7 H+ molecules are needed to generate one molecule of ATP
165
Why is the real number of H+ molecules to generate ATP 3.7?
To make ATP we need ADP and Pi.
Pi must be transported into the matrix, however it is negatively charged, so it requires an H+ to be transported this is where the extra H+ comes from
166
Why does NADH produce 2.5 ATP molecules?
NADH pumps a total of 10H+ molecules across the intermitochondrial membrane. (4 from complex I, 4 from complex II and 2 from complex IV)
10/3.7 = 2.7 ATP however we round down to 2.5 ATP
167
Why does FADH2 produce 1.5 ATP molecules?
FADH2 pumps a total of 6H+ across the intermitochondrial membrane(skips complex I, 4 Complex II and 2 from complex IV)
6/3.7 = 1.62 however we round down to 1.5 ATP
168
How is NADH from glycolysis shuttled into the mitochondria?
1. NADH is used to reduce oxaloacetate to malate
2. The malate aspartate shuttle then transports malate into the mitochondria
3. Malate dehydrogenase then generates NADH in the mitochondria
