7. Cellular Respiration Flashcards
What type of reaction is cellular respiration, and what is its final goal?
- series of catabolic reactions
- converts energy stored in molecules like carbohydrates + lipids to produce ATP
What is anaerobic vs aerobic respiration?
anaerobic: can occur without oxygen
aerobic: requires oxygen
- reactants: glucose + oxygen
- products: CO2 + water + energy
What is phosphorylation?
When we add phosphate groups
In the context of ATP, this means adding a phosphate group to ADP to create ATP
What are the two types of phosphorylation? What produces most of the ATP in cellular respiration?
- substrate level
- organic molecule transfers a phosphate group directly to ADP to make ATP - oxidative
- chemical energy is transported to electron carriers, which are transported in the electron transport chain to a final electron acceptor. in this process, the released energy is harnessed to produce ATP
oxidative phosphorylation produces most of the ATP in cellular respiration
What is the final electron acceptor in aerobic respiration?
oxygen
O2 -> H2O
What is oxidation vs reduction?
Oxidation is loss of electrons
Reduction is gain of electrons
The molecule that loses its electrons is oxidized, and the molecule that gains electrons is reduced
OIL RIG
What are the oxidized and reduced forms of the electron carriers:
- NAD
- FAD
oxidized form:
- NAD+
- FAD
reduced form:
- NADH
- FADH2
Note that:
- oxidation -> less C-H bonds
- reduction -> increase in C-H bonds
How do electron carriers act as shuttles?
Electron carriers like NAD+, FAD first accept electrons from the breakdown of fuel molecules.
Then in their reduced forms, NADH and FADH2, they an donate these electrons (and energy) to the electron transport chain
In this way they act as shuttles for transferring electrons
Note: the oxidation/reduction reactions are always coupled with another non-electron carrier molecule, which experiences the opposite reaction
Consider the simplified cellular respiration reaction as a redox reaction:
C6H12O6 + 6O2 => 6CO2 + 6H2O + energy
What molecule is oxidized and what is reduced?
Glucose is oxidized
- Before: C shared electrons equally with its C-C and C-H bonds
- After: O is more electronegative in CO2, and so C is oxidized (loses its electrons to O)
Oxygen is reduced
- Before: O in O2 has equal sharing of electrons
- After: O in H2O is more electronegative, and electrons are more likely to be found near it (reduced)
What are the 4 stages of cellular respiration?
- glycolysis
- pyruvate oxidation
- citric acid cycle
- oxidative phosphorylation
What stage is glycolysis?
- What are the inputs and outputs?
- where does it take place?
first stage of cellular respiration
- inputs: glucose
- outputs: atp, 2 pyruvate
it takes place in the cytoplasm
What stage is glycolysis?
- What are the inputs and outputs?
- where does it take place?
first stage of cellular respiration
- inputs: glucose
- outputs: small amount of ATP, 2 pyruvates
(and reduced electron carriers)
goes from 6-carbon glucose to 2 3-carbon pyruvates
it takes place in the cytoplasm
What stage is pyruvate oxidation?
- What are the inputs and outputs?
- where does it take place?
stage 2
- inputs: pyruvate
- outputs: acetyl-CoA + CO2 (and reduced electron carriers)
takes place in the mitochondria
What stage is the citric acid cycle (aka. krebs cycle)?
- What are the inputs and outputs?
- where does it take place?
stage 3
- inputs: acetyl-CoA
- outputs: CO2, small amount of ATP (and reduced electron carriers)
takes place in the mitochondria
What stage is oxidation phosphorylation?
stage 4
- reduced electron carriers generated in stages 1, 2, 3 donate their high energy electrons to the electron transport chain
- A large amount of ATP is released
T/F: Glycolysis requires oxygen
False; considered a universal catabolic pathway
What are the three stages of glycolysis?
- Preparatory phase: Consumes 2 ATP and combines with glucose to destabilize it, also traps the phosphorylated glucose in the cell (no longer glucose, and cannot traverse through the cell membrane by specific membrane transporters)
- Cleveage phase: Splits the molecule into two (each with 3 carbons)
- Payoff phase: Uses 2 ATP molecules, reducing the electron carriers (NAD+ to NADH), producing two pyruvates, and also producing 4 ATP molecules (net gain of 2 ATP)
Why do we add two phosphates to glucose in the first step of glycolysis?
- Prevents the (now phosphorylated) glucose from leaving the cell
- Destabilizes the molecule
What is the overall chemical equation for glycolysis?
Glucose + 2NAD+ + 2ADP + 2P
->
2Pyruvate + 2ATP + 2NADH + 2H + 2H2O
Wt the end of glycolysis, what molecules contain some of the chemical energy held in the original glucose molecule?
pyruvate, ATP, NADH
With respect to mitochondria:
What is the space between the outer membrane + inner membrane called?
What is the space inside the inner membrane called?
Intermembrane space: between the two membranes
Mitochondrial matrix: space inside the inner membrane
Where does pyruvate oxidation take place in the mitochondria?
Inside the mitochondrial matrix
Describe the order of events in the oxidation reaction from:
Pyruvate -> CO2 + Acetyl-CoA
- Pyruvate travels to the mitochondria matrix
- Part of the pyruvate molecule oxidizes and splits off to become CO2 (the most oxidized + least energetic form of carbon)
- In the process of 2, electrons lost are donated to NAD+ to reduce it to NADH
- The remaining acetyl group of the pyruvate molecule is transferred to CoA (coenzyme A) which carriers it to the next set of reactions
These reactions are catalyzed by a group of enzymes called the pyruvate dehydrogenase complex
What are the products of one molecule of pyruvate?
- One CO2
- One NADH
- One acetyl-CoA
What are the inputs and products of the citric acid cycle?
Inputs: acetyl-CoA
Products: CO2, ATP, reduced electron carriers
energy in the process of making CO2 is:
- transferred to ATP by substrate-level phosphorylation
- transferred to reduced electron carriers, NADH and FADH2
Using the number of carbons, explain the reactants + products of the following reactions in the citric acid cycle:
- acetyl + oxaloacetate -> citric acid
[… oxidization stuff happens …] - succinyl-CoA -> Succinate
[ … oxidation stuff happens …]
back to oxcaloacetate!
1
acetyl (2C) + oxaloacetate (4C) combines to form citric acid (6C)
[…in between…]
oxidation reactions form 2CO2 and 2NADH
2
Both are now 4C
Substrate-level phosphorylation occurs to for GDP -> GTP, which then donates its phosphate to form one ATP
[…in between…again…]
one FADH2 and one NADH is formed from oxidation
Total: 4 redox reactions
T/F Some bacteria run the citric acid cycle in reverse
T
Running the cycle in reverse requires energy (supplied by sunlight or chemical reactions)
- Builds organic molecules (using intermediates produced by the cycle)
What is the Electron Transfer Chain (ETC)?
- The mitochondrial inner membrane
- Made up of four large protein complexes
- Transfers electrons and pumps protons to create a proton gradient (many protons outside, few protons inside)
What is the final electron acceptor?
oxygen
What happens after oxygen accepts the electron?
It is reduced to H2O
Which complexes do NADH and FADH2 drop off their (2) electrons?
NADH: Complex I
FADH2: Complex II
Which complexes are responsible for pumping the protons out of the matrix?
Complexes I, III, and IV
What is the role of the ATP synthase? What are its components?
The ATP synthase uses the proton gradient maintained by the electron transport chain to turn like a turbine, its rotational energy converted into the energy bonds of ATP
Formed by components F0 and F1:
- F0: a channel that rotates as protons pass through it
- F1: located sticking out of the matrix side of the membrane, uses this rotational energy to catalyze the synthesis of ATP
What is the role of CoQ in the electron transport chain?
An electron carrier that transports electrons from Complexes I and II to Complex III
What is the role of Cytochrome c in the electron transport chain?
Transports electrons from Complex III to Complex IV
How many molecules of ATP are produced in the complete oxidation of glucose?
32 (though this might vary)
What is the approximate yield ratio for ATP per NADH and FADH2
2.5 ATP/NADH
1.5 ATP/FADH2
Under anaerobic conditions, how is ATP synthesized in animal cells?
After the pyruvate is produced from glycolysis, it is used in lactic acid formation
- Regenerates NAD+
- Produces two ATP
What is the equation for lactic acid fermentation?
glucose + 2ADP + 2P
->
2 lactic acid + 2 ATP + 2H2O
Under anaerobic conditions, how is ATP synthesized in plant/fungi cells?
After the pyruvate is produced from glycolysis, it is used in ethanol formation
- Regenerates NAD+
- Produces two ATP
What is the equation for ethanol fermentation?
glucose + 2ADP + 2P
->
2 ethanol + 2CO2 + 2ATP + 2H2O
How is NADH oxidized in aerobic vs anaerobic conditions, and why is this important?
aerobic conditions:
- oxidized when NAD+ donates its electrons to the electron transport chain
anaerobic conditions:
- oxidized when pyruvate or its derivative is reduced
NAD+ is required for glycolysis so this oxidation is necessary
What is excess glucose stored as in animals?
glycogen
- large, branched chain of glucose molecules attache to a central protein
What is excess glucose stored as in plants?
starch
- large, branched chain of glucose molecules
Where is glycogen stored, and how is it used?
- stored in muscle: used by muscle for ATP
- stored in liver: glycogen storehouse for the whole body
To break it down:
- glucose molecules at the end are cleaved off, and through some conversions, becomes an intermediary product in glycolysis (glucose 6-phosphate)
Note: one glucose molecule cleaved off in this way produces 3 ATP by glycolysis (vs. 2), since we bypass the first step of consuming 1 ATP
How do other sugars get processed in cellular respiration?
- they get converted into intermediates found in glycolysis, and the rest is the same
How are lipids broken down to generate ATP?
- first they are broken down into the fatty acid chains
- then sequentially remove 2 C from the ends (called beta-oxidation)
- this process produces NADH and FADH2 molecules that provide electrons for ETC (which then produces ATP)
- the final product of beta-oxidation is acetyl-CoA, which also feeds into the citric acid cycle
key term: beta-oxidation
How are proteins converted into ATP?
- first broken down into amino acids
- then these enter various points in glycolysis, pyruvate oxidation, and the citric acid cycle
How is ATP production regulated?
- can determine ATP levels by looking at high NAD+ levels (needs ATP) vs high NADH levels (inhibits ATP production)
- or high citrate (not consumed, needs to slow)
- enzymes control key steps of the pathway
- etc. reaction 3 of glycolysis requires the consumption of ATP. We can control this to make sure that the step does not happen
