Test 3 Unit 3-Energy and Cellular Respiration Flashcards

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1
Q

What is the law of Thermodynamics and define all variables.

A
ΔG = ΔH - TΔS
ΔG: Free energy, spontaneous reactions
ΔH: Enthalpy, potential energy
ΔS: Entropy, disorder
T: Temperature
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2
Q

Explain how enthalpy (ΔH) works.

A

Transformations that absord energy (endothermic) result in the products having MORE potential energy. (+ΔH)
Transformations that release energy (exothermic) result in the products having LESS potential energy. (-ΔH)

*If you gain potential energy (+ΔH), reaction is NOT spontaneous.

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3
Q

Explain how enthropy (ΔS) works.

A

The measure of wheter a reaction gains disorder.
Gas > Liquid > Solid.
*Reactions that gain disorder (+ΔS) tend to be spontaneous.

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4
Q

Explain free energy (ΔG).

A
-ΔG = spontaneous (exergonic)
\+ΔG = NOT spontaneous (endergonic)
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5
Q

Explain how exergonic and endergonic reactions relate to catabolic and anabolic reactions.

A
  • Catabolic = energy released = exergonic = spontaneous

- Anabolic = energy required = endergonicc = not spontaneous

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6
Q

Why does ATP hydrolysis release free energy?

A

ATP hydrolysis releases free energy, so it is exergonic (spontaneous) because:

  1. decrease in potential energy
  2. increase in entropy
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7
Q

Why is there less potential energy in ADP than in ATP?

A

Because the loss of the terminal phosphate has decreased the electrical repulsion among the negatively charged oxygen atoms of the phosphate groups.

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8
Q

Explain how ATP hydrolysis can make other reactions spontaneous in the cell
.

A

Through energy coupling: an endergonic reaction occurs by being coupled to an exergonic reaction. the energy is provided by the exergonic breakdown of ATP.

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9
Q

Explain the concept of activation energy for enzymes

A

For chemical reactions to occur, bonds need to be broken and this requires a small input of energy called ACTIVATION ENERGY. Enzymes can accelerate reactions by lowering the activation energy.

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10
Q

Explain how enzymes reduce the amount of activation energy required to start a reaction

A

Enzymes reduce the activation energy by inducing the transition state. The binding of substrate(s) to an active site results in the substrate’s acquiring the transition state conformation. Enzymes can:

  1. Bring reacting molecules together (reacting molecules can assume the transition state only when they collide)
  2. Charge interactions: expose the reactant to altered charges that promote catalysis
  3. Change the shape of a substrate into a conformation that mimics the transition state.
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11
Q

What is a cofactor?

A

A nonprotein group that binds very precisely to the enzyme. Cofactors are often metals, such as iron, copper, zinc, or manganese. The cofactor binds to the enzyme and activates it.

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12
Q

Give an example of an enzymatic cofactor.

A

ATP, vitamins (nonprotein groups), Retinal, Ascorbic acid, or vitamin C, is used as a cofactor in hydroxylases.

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13
Q
How can 
1.substrate concentration
2.enzyme concentration 
3.pH 
4.temperature 
affect the rate of reaction?
A
  1. In the presence of excess substrate, the rate of catalysis is proportional to the amount of enzyme. At some point, it reaches a saturation level if the enzyme concentration is constant (↑ substrate = not so efficient!)
  2. As enzyme concentration increases, the rate of product formation increases. (↑ enzyme = very efficient!)
  3. An enzyme has an optimal pH at which it is most active
  4. An enzyme has an optimal temperature at which it is most active. Heat-sensitive enzymes can be activated/inhibited with temperature changes.
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14
Q

Explain how enzymes can be regulated through competitive and non competitive interactions

A
  • Competitive regulation: the competitive inhibiter molecule competes with the substrate for the active site and the substrate is unable to bind when the inhibitor is bound to active site.
  • Non-competitive (allosteric) regulation: Can be activation or inhibition
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15
Q

Explain how allosteric activation/inhibition works.

A
  1. Activation:
    Enzyme binds to allosteric activator and converts it to a HIGH-affinity state = the substrate can bind.
  2. Inhibition:
    Enzyme binds to allosteric inhibitor and converts it to a LOW-affinity state = the substrate is released.
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16
Q

What is the difference in efficiency of aerobic and anaerobic pathways?

A
  • Aerobic respiration: 1 glucose = 36-38 ATPS (MOST EFFICIENT!)
  • Anaerobic respiration: 1 glucose = 2-36 ATPS
  • Fermentation: 1 glucose = 2 ATPS
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17
Q

Why is anaerobic respiration and fermentation less efficient than aerobic?

A

Because it uses non-O2 compounds as electron acceptors which are less efficient because they are less electronegative than O2, so they have less affinity for electrons.
Fermentation is a back-up that uses organic compounds as electron acceptors.

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18
Q

Where and why in cellular respiration does fermentation occur?

A

Why? If oxygen is absent or in short supply

Where? In the cytosol. Pyruvate remains in the cytosol and is reduced using the NADH generated by glycolysis.

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19
Q

What are the 2 types of fermentation?

A
  1. Alcohol (in microorganisms such as yeasts, which are single-celled fungi)
  2. Lactate (in many bacteria and some plant and animal tissues)
20
Q

Explain oxidation and reduction.

A

-Oxidation is the loss of electrons by a molecule, atom, or ion. (oxidized)
-Reduction is the gain of electrons by a molecule, atom, or ion (reduced)
The reducing agent (oxidized) gives its electron to the oxidizing agent (reduced).

21
Q

Give examples of oxidation and reduction.

A

Glucose is oxidized to CO2 (CO2 is oxidized form).
O2 is reduced into H2O. (H2O is reduced form)
NAD+ is oxidized form
NADH is reduced form
FAD is oxidized form
FADH2 is reduced form

22
Q

Explain how redox processes lead to ATP production

A
  • Glycolysis: oxidation of glucose, converted into 2 pyruvate
  • Pyruvate oxidation: Oxidation of pyruvate forms Acetyl-CoA, which is oxidized to CO2. ATP and NADH is synthesized.
  • Oxidative phosphorylation: NADH oxidized and electrons are passed along ETC to create a proton gradient that is used to synthesize ATP

C6H12O6 + 6O2 → 6CO2 + 6H2O +ATP (glucose is oxidized, O2 is reduced)

23
Q

Illustrate how NAD+ and NADH serve as a transport for electrons in cellular respiration

A

1) In the energy releasing phase of Glycolysis, NAD+ accepts some electrons and 1 proton is reduced to NADH.
2) In Pyruvate Oxidation, the conversion of pyruvate to acetly-CoA leads to the transfer of 2 electrons and 1 proton to NAD+ which forms NADH.
3) In CAC, NAD+ is reduced 3 times to NADH
4) In Oxidative Phosphorylation, the potential energy resides in NADH that will be oxidized to NAD+ and the electrons released will start the ETC (proton-motive-force)

24
Q

What are the major pathways of cellular respiration?

A

Glycolysis, Pyruvate oxidation, Citric acid cycle, Oxidative phosphorylation (ETC + chemiosmosis).

25
Q

Which molecules do the transition/link between the 3-4 major pathways of cellular respiration?

A

Glycolysis –> PYRUVATE–> Pyruvate oxidation–> ACETYL-COA–>Citric acid cycle–>NADH and FADH2–> Oxidative phosphorylation (ETC + chemiosmosis).

26
Q

Explain the difference between the energy requiring phase and the energy releasing phase of glycolysis

A

Energy requiring phase uses 2 ATPs to transform glucose into 2 molecules of G3P
Energy releasing phase releases 4 ATPs and 2 NADH and transforms 2 G3P into 2 Pyruvate molecules.
Each reaction in glycolysis is catalyzed by its own enzyme (one of them being phosphofructokinase).

27
Q

What is substrate level phosphorylation?

A

ATP is generated by substrate-level phosphorylation, which is mediated by a specific enzyme called pyruvate kinase, is a mode of ATP synthesis. A phosphate group is transferred from a high-energy donor (PEP) directly to ADP, forming ATP.

28
Q

What is chemiosmosis?

A

The ability of cells to use the proton-motive force to do work. The protons move through the ATP synthase and make it spin and results in ATP synthesis.

29
Q

What is the difference between substrate level phosphorylation and chemiosmosis?

A

Chemiosmosis uses the enzyme ATP synthase and a proton-motive force whereas SLP uses the enzyme pyruvate-kinase and a high-energy donor.

30
Q

Why is O2 the best electron acceptor?

A

By being highly electronegative, O2 has greater affinity for electrons than any other electron acceptor.

31
Q

Where are the carbon atoms of a glucose molecule released in cellular respiration?

A

-2 CO2 in pyruvate oxidation
-4 CO2 in citric acid cycle
total of 6 carbons (CO2)

32
Q

How and where can different monosaccharides, amino acids and fatty acids enter cellular respiration to be converted to energy?

A
  • Glycerol can be converted to G3P and be phosphorylated and enter glycolysis
  • Carbohydrates are broken down and can enter glycolysis (like fructose)
  • Fatty acids can undergo fatty acid oxidation (split onto 2-carbon segments) and transform into Acetyl-CoA and therefore enter the CAC
  • Proteins are hydrolyzed to amino acids and NH2 is removed and the remainder of the molecule enters as pyruvate or acetyl-coA.
33
Q

Give an example of an amino acid that can enter cellular respiration to be converted to energy?

A

Alanine is converted into pyruvate, which can undergo pyruvate oxidation, CAC and oxidative phosphorylation.

34
Q

How many ATP/NADH are released in Glycolysis?

A

2 ATPs by substrate-level phosphorylation.

2 NADH.

35
Q

How many ATP/NADH are released in Pyruvate oxidation?

A

2 NADH.

36
Q

How many ATP/NADH/FADH2 are released in Citric acid cycle?

A

2 ATPs by substrate-level phosphorylation.
6 NADH.
2 FADH2.

37
Q

How many ATP/NADH/FADH2 are released in Oxidative phosphorylation?

A

None. the NADH and FADH released is used to create a proton gradient that will induce ATP synthesis where 10p+/NADH and 6p+/FADH2.

38
Q

How is the free energy released in the ETC used to synthesize ATP?

A

In the electron transport chain, electrons are passed from one molecule to another through 4 complexes, and energy released in these electron transfers is used to form an electrochemical gradient (proton gradient in the intermembrane space). In chemiosmosis, the energy stored in the gradient is used by ATP synthase to make ATP.

39
Q

How is cellular respiration regulated?

A

The rate of ATP generation matches the requirements of the cell for chemical energy.
It is mainly regulated by the allosteric enzyme phosphofructokinase, which catalyses the conversion of fructose 6-phosphate to fructose 1,6-bisphosphate.

40
Q

What are phosphofructokinase’s inhibitor/activator?

A

Activator: ADP
Inhibitor: ATP

41
Q

How does phosphofructokinase regulate cellular respiration in ATP excess?

A

When there is excess ATP, it binds to phosphofructokinase and inhibits its activity. This slows or stops the reactions after glycolysis.

42
Q

How does phosphofructokinase regulate cellular respiration when there is no enough ATP?

A

When there is no enough ATP, ADP accumulates and binds to phosphofructokinase. It activates the enzyme to produce ATP.

43
Q

Briefly explain how the ETC works and how NADH and FADH2 are related to it.

A

It extracts the potential energy in NADH and FADH2. Electrons move spontaneously down a potential energy gradient from 1 complex to the next (4 complexes total). The release of energy is used to pump protons into the intermembrane space. There is also smaller electron carriers, ubiquinone and cytosol c, that act as shuttles between major complexes. The transport is done by prosthetic groups (cofactors).

44
Q

Describe the # protons pumped by each complex for NADH and FADH2.

A
NADH:
1 pumps 4 p+
2 pumps 0 p+
3 pumps 4 p+
4 pumps 2 p+
FAHD2:
1 pumps 0 p+
2 pumps 0 p+
3 pumps 4 p+
4 pumps 2 p+
45
Q

Describe the electron flow during ETC.

A

Electron flow is spontaneous from high to low potential energy (down free energy gradient)