Chapter 9: Cellular Respiration

Question 1

Cellular Respiration

Answer 1

both aerobic and anaerobic pathways which break down organic molecules in order to produce ATP
- Fuels are oxidized(every bond completely broken down) and O2 is consumed

Question 2

Redox Reactions

Answer 2

the transfer of one or more electrons from one reactant to another

• redox reactions move electrons closer to the electronegative atom releasing chemical energy(from electron potential energy)

Question 3

Terms in Redox Reactions

Answer 3

• Oxidation refers to when a substance has lost an electron
  • Reduction is when a substance gains an electron
• Reducing Agent: the electron donor
• Oxidizing agent: the electron recipient

Question 4

NAD+ and NADH

Answer 4

an electron carrier which cycles between its oxidized forms of NAD+ and its reduced form of NADH

- Electrons lose very little potential energy when transferred from glucose to NAD+

Question 5

How Electrons from NADH are released to Oxygen(acceptor molecule in CR)

Answer 5

-occurs in ETC where electrons are transfered from NADH to oxygen in an exergonic redox reaction
- Electrons cascade down the chain from one carrier molecule to the next giving up a small amount of energy each step
- Each ‘downhill’ carrier has a greater affinity for electrons its ‘uphill’ neighbor
- Therefore electrons fall down an energy gradient in the ETC until it reaches a more stable electronegative oxygen atom

Question 6

Glycolysis

Answer 6

• occurs in the cytoplasm and has two stages
• Breaks glucose into two 3 carbon molecules called pyruvates
• Substrate level phosphorylation produces 2 net ATP molecules
• 2 NAD+ is reduced to 2 NADH
• 2 O2 molecules are formed.

Question 7

Phases of Glycolysis

Answer 7

• Energy investment phase: where the cell spends ATP
  ○ Glucose and 2 ATP molecules enter, breaking glucose down into 2x 3-carbon sugars and 2 ADP+Pi
  • Energy payoff phase: ATP is produced by substrate level phosphorylation and NAD+ is reduced to NADH from the oxidation of glucose

Question 8

Intermediate Reaction Steps

Answer 8

1. In the presence of O2, pyruvate enters the mitochondria where the carboxyl group is fully oxidized and given off as Co2(removal of a carbon)
   2. The remaining 2-carbon fragments is oxidized with electrons being transferred to NAD+, storing energy as NADH
      3. Coenzyme A, is attached via its sulfur atom to the 2-carbon intermediate to form Acetyl CoA, which has high potential energy

Question 9

Citric Acid/Krebs Cycle

Answer 9

○ every single bond in the acetylcoA molecule is broken to extract energy

-further oxidizes acetylcoA in two turns to create 6 NADH, 2 FADH2

• 2 ATP are produced through substrate level phosphorylation

Question 10

Oxidative Phosphorylation

Answer 10

the production of ATP through ETC, Chemiosmosis and Oxidative Phosphorylation

• ETC accepts electrons from NADH or FADH2 generated passes these down the chain where they are combined with oxygen and hydrogen ions to form water
• creates proton motive force
• hydrogen ions move back into the matrix through ATP synthase
• movement through ATP synthase produces energy to synthesise ATP

Question 11

Chemiosmosis

Answer 11

an energy coupling mechanism using stored energy in the form of a H+ gradient to drive cellular work

Question 12

Process of ATP Synthase

Answer 12

1. Hydrogen ions flow down their concentration gradient through a channel called a stator
   
   2. The H+ enter binding sites within a rotor causing a conformation change so that the rotor spins within the membrane
   3. Each H+ creates 1 full turn before leaving the rotor and passing through a second channel into the mitochondrial matrix
   4. The spinning of the rotor causes an internal rod to spin which activates catalytic sites in the knob that produce ATP from ADP + Pi

Question 13

Proton Motive Force

Answer 13

the capacity of the proton electrochemical gradient to cause work

Question 14

ATP Production Amounts

Answer 14

• Glycolysis: +2 ATP
  
  • Krebs Cycle: +2 ATP
  • ETC: +32-34 ATP

Total: 36-38 ATP

Question 15

Reasons for being unable to get fixed ATP amounts

Answer 15

1. Phosphorylation and redox reactions are not directly coupled to each other therefore the ratio of the number of NADH molecules to the number of ATP molecules is not a whole number
   
   • 1 NADH results in 10 protons transported out of the inner mitochondrial membrane, and about 4 protons create an ATP
   • 1 FADH can only transport enough electrons for 1.5 ATP
   2. ATP yields vary on the type of shuttle used to transport electrons
      - The inner membrane is not permeable to NADH which must give up its electrons to either NAD+ or FAD
      - If given to NAD+ then 2.5 ATP can be produced
      - If given to FAD only about 1.5 ATP can be produced

The use of proton motive force generated by redox reactions can generate maximum ATP if working efficiently and all directed towards ATP synthesis

Question 16

Anaerobic Respiration

Answer 16

uses an ETC without o2 as the final electron acceptor

-uses either sulfate, sulfur or nitrate

Question 17

Fermentation

Answer 17

consists of glycolysis plus reactions that regenerate NAD+ by transferring electrons from NADH to Pyruvate or derivatives of pyruvate allowing the NAD+ to be reused to oxidize sugar, creating two ATP

Question 18

Types of Fermentation

Answer 18

Alcohol: where pyruvate is converted to acetaldehyde through the release of Co2 before reduced by NADH to ethanol regenerating the supply of NAD+

Latic Acid Fermentation: pyruvate is reduced directly by NADH to form lactate which regenerates NAD+ without the release of Co2

Question 19

Similarities between Fermentation and Aerobic Respiration

Answer 19

• both produce ATP by harvesting the chemical energy of food
  
  • both utilise glycolysis to oxidise glycose and other organic fuels into pyruvates, producing 2 ATP
  • NAD+ is the oxidizing agent accepting electrons in all glycolysis stages

Question 20

Differences between Fermentation and Aerobic Respiration

Answer 20

• The mechanisms for oxidizing NADH back to NAD+ required to sustain glycolysis
  • Yield of ATP:
  • Necessity of Oxygen:

Question 21

Ways Glycolysis can accept fuel

Answer 21

• In the digestive tract, starch is hydrolyzed
• Glycogen stored in the liver and muscle cells can be hydrolyzed
• Digestion of disaccharides
  • For protein to be used as fuel, they need to be digested into their constituent amino acids and must have their amino groups removed(deamination)
  • After fats are digested to glycrerol and fatty acids, glycerol can be converted to an intermediate of glycolysis and beta oxidazation breaks fatty acids down into 2-carbon fragments which can enter the citric acid cycle as Acetyl CoA

Question 22

How Cellular Respiration is Regulated

Answer 22

• Phosphofructokinase is the ‘pacemaker’ of cellular respiration as it catalyzes the first step that commits the substrate to the glycolytic pathway
  
  • Is an allosteric enzyme often inhibited by ATP; as ATP accumulates the inhibition of the enzyme slows down glycolysis
  • If ATP is being converted to ADP(and AMP) faster than ATP is being regenerated then it becomes active again