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Intro Bio II Exam 1 > Cellular Respiration > Flashcards

Cellular Respiration Flashcards

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1
Q

Cellular respiration formula

A

Sugar + 6 O2 —> 6 CO2 + 6 water + energy (ATP)

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2
Q

How do plants store energy?

A

In the form of glucose

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3
Q

Laws of Thermodynamics

A

1 - conservation of energy; 2 - entropy

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4
Q

Catabolic pathways

A

Breakdown molecules to release energy or liberate high energy electrons

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5
Q

Anabolic pathways

A

Build things needed in the cell and require energy input (making bonds requires energy)

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6
Q

Metabolism and body temperature

A

All of the reactions that make up our metabolism help us maintain our body temperature by releasing small packets of heat

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7
Q

Enthalpy/entropy in the cell

A

Since we are most concerned with usable energy, we often disregard enthalpy. The cell is a low entropy environment.

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8
Q

Gradients as a form of energy

A

Concentration gradients are a form of potential energy

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9
Q

How is work done in a cell?

A

By using potential energy in the form of gradients and energy sources like ATP.

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10
Q

Examples of processes that require energy in the cell

A

Pumping ions, translating proteins, transporting glucose across the membrane, transcription

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11
Q

Do reactions in the cell proceed spontaneously?

A

Overall, reactions in the cell proceed spontaneously under normal conditions. Typical biochemical reactions are exergonic. Endergonic reactions will not happen without an input of energy.

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12
Q

How do enzymes affect the energy of a reaction?

A

Enzymes lower the activation energy of a reaction which is altering the kinetics of the reaction (NOT the thermodynamics)

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13
Q

Types of enzymes

A

Kinase, isomerase, mutase, dehydrogenase, and others

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14
Q

Kinase

A

Catalyze the transfer of a phosphate group from ATP to another molecule or the reverse

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15
Q

Isomerase

A

Catalyze the interconversion of isomers and selects the correct isomer using Le Chatelier’s principle

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16
Q

Mutase

A

Catalyze the intramolecular transfer of a phosphate group. A phosphate group moves from one part of the molecule to another. This is different than a kinase which must involve ATP.

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17
Q

Dehydrogenase

A

Catalyze an oxidation-reduction reaction.

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18
Q

Purpose of catabolism in the cell

A

Breakdown via oxidation the macromolecules consumed from food to release energy. The oxidation of a molecule releases high energy electrons that can be used to make ATP.

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19
Q

Electron acceptors/carriers

A

(Oxidized version)NAD+, FAD (this molecules indicate a re-dox reaction)
(Reduced version) NADH, FADH2

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20
Q

How can you tell between two molecules which is more oxidized?

A

Count oxygen atoms connected to carbons (especially if there is a central carbon)

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21
Q

Why does a fat molecule yield more energy per carbon than a carbohydrate?

A

Fat molecules are more reduced than a carbohydrate (more C-H bonds and fewer C-O bonds) so it has the potential to be oxidized than a carbohydrate

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22
Q

Components of NAD+/NADH

A

Nicotinamide mononucleotide (NMN) and adenosine monophosphate (AMP)

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23
Q

Advantage of a stepwise pathway in cellular respiration instead of “direct burning of sugar”

A

Each reaction can proceed because activation energies are overcome by body temperature. This stepwise pathway allows for energy storage as opposed to all of the energy of these reactions being released at once as heat.

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24
Q

What is the most common energy source in the cell?

A

ATP

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25
Q

Why is the high energy bond in ATP not broken all the time?

A

ATP is stable and won’t hydrolyze easily; ATP hydrolysis has a high activation energy

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26
Q

Where does glycolysis occur in the cell?

A

Cytosol

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27
Q

Where does pyruvate oxidation occur?

A

Mitochondrial matrix

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28
Q

where does the citric acid cycle occur?

A

Mitochondrial matrix

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29
Q

What are the benefits of compartmentalizing the citric acid cycle, pyruvate oxidation, and electron transport chain?

A

1) more efficient to have all materials in one place
2) some byproducts of these reactions are toxic free radicals which would damage important cell parts like DNA if these reactions were not done in a compartment

30
Q

Where does the electron transport chain occur?

A

Inner mitochondrial membrane

31
Q

Steps in the aerobic metabolism of glucose

A
  1. Glycolysis (glucose —> pyruvate)
  2. Pyruvate oxidation (pyruvate —> acetyl CoA)
  3. Citric Acid Cycle
  4. Electron Transport
32
Q

In which step of metabolism is most of the ATP produced?

A

Electron transport chain

33
Q

Why is glucose immediately phosphorylated in the cell?

A

To prevent glucose from the leaving the cell, glucose is phosphorylated by hexokinase immediately to become G6P.

34
Q

Which two sugars does hexokinase recognize?

A

Glucose and fructose

35
Q

What is a committed step and which step in glycolysis is the first?

A

A committed step is a highly regulated step that is the “point of no return” in a process. In glycolysis, this is step 3 - F6P —> FBP using PFK as the catalyst

36
Q

What is a cofactor for every reaction that uses ATP?

A

Divalent cation like Mg2+

37
Q

Glycolysis steps 1 - 3: Phosphorylate glucose and create a symmetric molecule.

A
  1. hexokinase catalyzes the phosphorylation of glucose to glucose-6-phosphate
    - the phosphate group is taken from ATP (so ATP is used) and added to the 6’ carbon of glucose
  2. Isomerization - glucose-6-phosphate (G6P) is turned into fructose-6-phosphate (F6P) by phosphoglucose isomerase (PGI). Both isomers have the same energy so this reaction is reversible, but the reaction continues to make products because F6P is immediately used up in the next reaction.
  3. First committed step, highly regulated, irreversible - F6P is converted to FBP by phosphofructokinase (PFK). This step requires ATP. The phosphate group from ATP is added to F6P to create a biphosphate which is symmetrical.
38
Q

Glycolysis steps 4 - 5: Cleave and get two molecules of G3P.

A
  1. With FBP in its straight chain form it is cleaved into two 3-carbon isomers by aldolase - Dihydroxyacetone phosphate (DHAP) and glyceraldehyde-3-phosphate (GAP). We want both to be GAP.
  2. Turn DHAP into GAP using a isomerase.
39
Q

Glycolysis step 6: Convert G3P to high energy 1,3-BPG.

A

This step and subsequent steps happen for both molecules of GAP produced from FBP.
6. GAP is phosphorylated and oxidized by glyceraldehyde-3-phosphate dehydrogenase (GAPDH). NAD+, an electron carrier, becomes reduced to NADH. The result is 1,3-biphosphoglycerate (1,3-BPG).
This step is endergonic because it adds a free-floating phosphate to GAP, but this step still occurs because the Step 7 is very exergonic. Steps 6 & 7 are coupled.

40
Q

Glycolysis steps 7 - 10: Harvest energy from BPG and end with pyruvate.

A
  1. This is a substrate level phosphorylation step. 1,3-BPG is converted to lower energy 3-phosphoglycerate (3PG) by phosphoglycerate kinase (PGK) in a process that releases ATP. PGK takes the phosphate from 1,3-BPG and transfers it to ADP.
  2. Phosphoglycerate mutase adds a phosphate group to the 2’ carbon of 3PG forming 2,3-BPG-enzyme complex, then removes the phosphate group on the 3’ carbon to form 2-PG.
  3. 2-phosphoglycerate (2-PG) is converted to high energy phosphoenolpyruvate (PEP) by enolase.
  4. PEP transfers its phosphate to ADP with the help of pyruvate kinase (PK) and thus releasing more ATP.
41
Q

Which steps in a biochemical pathway are highly regulated and why?

A

“Big steps” that are highly exergonic are highly regulated because they’re essentially irreversible. For example, PFK (enzyme is glycolysis step 3) responds to many cellular signals before catalyzing step 3.

42
Q

What is the free energy change for every step in glycolysis (assuming 6&7 are coupled)?

A

Negative or 0 - spontaneous under cellular conditions (but not standard conditions)

43
Q

The presence of a dehydrogenase indicates what about a reaction?

A

This is a redox reaction.

44
Q

How is pyruvate converted to acetyl CoA?

A

Pyruvate dehydrogenase complex removes CO2 from pyruvate and attaches coenzyme A. In the process NAD+ is reduced to NADH. Breaking the C-C bond to release CO2 is highly exergonic. Since there are two pyruvate produced from one glucose, this process overall produces 2 CO2, 2 Acetyl CoA, and 2 NADH.

45
Q

Where is pyruvate made and where is it oxidized?

A

Pyruvate is the product of glycolysis in the cytosol. It travels through the mitochondrial membranes to the mitochondrial matrix where it is oxidized.

46
Q

In the citric acid cycle, oxaloacetate (4 carbons) becomes citrate (6 carbons) with the addition of what group and by what mechanism?

A

An acetyl group is added to oxaloacetate and CoA is a good leaving group.

Oxaloacetate + acetyl CoA —> citrate + CoA

47
Q

For one acetyl group/one turn of the citric acid cycle, how many of NADH, FADH2, ATP, and CO2 are produced?

A

3 NADH
1 FADH2
2 CO2
1 ATP

48
Q

How many ATP are NADH and FADH2 “worth”?

A
  1. 5 ATP = 1 NADH

1. 5 ATP = FADH2

49
Q

At the end of the citric acid cycle, where is all of the bond energy from the original glucose molecule stored?

A

In the electron carriers, NADH and FADH2.

50
Q

At the end of the citric acid cycle, where are all of the carbons from the original glucose molecule?

A

Oxidized to CO2

51
Q

How does the energy in NADH and FADH2 translate to ATP?

A

Electrons from NADH and FADH2 are passed through proteins in the inner mitochondrial membrane which pump H+ out of the matrix creating a proton gradient. This gradient is a source of potential energy which the enzyme ATP synthase uses to do the work of ADP + Pi —> ATP

52
Q

Electrons are passed from ___ energy carriers to —— energy carriers. High energy carriers have a ___ affinity for electrons and low energy carriers have a ___ affinity for electrons.

A

High —> low energy

Low —> high affinity

53
Q

What is the final acceptor of electrons in the ETS and how is it transformed?

A

oxygen accepts electrons last and becomes water

54
Q

How do NADH & FADH2 move their electrons through the ETS?

A

NADH —> 1 —> Q —> 3 —> 4 resulting in 3 protons pumped out of the matrix

FADH2 —> 2 —> Q —> 3 —> 4 resulting in 2 protons pumped out of the matrix which is why 1 FADH2 translates to only 1.5 ATP

55
Q

What are the major proteins involved in ETS?

A

Complex I, III, and IV are proton pumps
Complex II accepts electrons from FADH2 while complex I accepts electrons from NADH. Complex II is NOT a proton pump.

Proteins Q and Cytochrome C are electron chaperones. Q mediates transfer of electrons from I —> III and CC mediates transfer of electrons from III —> IV

56
Q

What happens if the ETS is inhibited? (No oxygen, for example)

A

ETS does not proceed, TCA does not proceed, Glycolysis —> anaerobic

57
Q

Why do protons tend to stay in the inner membrane space instead of leaving the mitochondria?

A

The matrix has an overall negative charge so they “hover” close by in the inner membrane space.

58
Q

ATP synthase requires a _____ in order to get over the entropic barrier and create ATP.

A

Proton gradient

59
Q

Where does NADH exist within the cell?

A

Cytoplasm - from glycolysis

Mitochondrial matrix - from TCA

60
Q

If the cell lacks oxygen, which step follows glycolysis?

A

Fermentation - pyruvate is converted into lactic acid in mammals, alcohol in yeast

61
Q

Where does lactic acid go once formed from anaerobic respiration?

A

Blood —> liver which can make glucose from lactic acid

62
Q

What is the purpose of fermentation?

A

Avoid the build up of NADH in the cytoplasm by regenerating NAD+

63
Q

Where is FADH2 found in the cell and why?

A

Only in the mitochondrial matrix inside a protein where the redox reaction occurs because FADH2 is nonpolar/insoluble in aqueous conditions

64
Q

ATP outputs from each block of cellular respiration

A

Glycolysis - 2 ATP
TCA - 2 ATP
ETS - 28 ATP

65
Q

NADH, FADH2 outputs from each block of cellular respiration

A

Glycolysis - 2 NADH
Pyruvate Oxidation - 2 NADH
TCA - 6 NADH, 2 FADH2

66
Q

How do proteins yield energy?

A

Protein —> amino acid —> substrates used in TCA, NH3 converted into urea and expelled

67
Q

How does glycogen yield energy?

A

Glycogen is a glucose polymer so it is chopped up, converted to G6P so it is trapped in the cell, then continues on through glycolysis, etc.

68
Q

How does fat yield energy?

A

Fat (triglycerides) = glycerol + 3 fatty acid tails

Glycerol —> glycolysis
Fatty acids —> (chopped up to become) acetyl CoA

69
Q

Where is glycogen stored?

A

Liver, muscle, kidney

70
Q

How much ATP will a cell make?

A

Only as much as it needs - there are no big stores of ATP

71
Q

How does ATP act as a signal?

A

ATP is an allosteric inhibitor of PFK - negative feedback

72
Q

Examples of negative feedback signals in cellular respiration

A
  • High [citrate] inhibits PFK

- High [ATP] inhibits PFK

Intro Bio II Exam 1 (5 decks)

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