Chapter 7 – Cellular Respirationcitruscollege.edu/lc/archive/biology/Documents/KondoNotes/lewis_ch... · Chapter 7 – Cellular Respiration ... 4. Electron transport system

Chapter 7 – Cellular RespirationPhases of aerobic cellular respiration

1. Glycolysis

2. Transition or Acetyl-CoA reaction

3. Krebs cycle

4. Electron transport system

These phases are nothing more than metabolic reactions involving the conversion of glucose & other molecules into carbon dioxide & water

The resulting energy released from this conversion will be used to produce ATP

Chapter 7 – Cellular Respiration



Chapter 7 – Cellular RespirationMitochondria structure

Similar in arrangement to the chloroplast

1. It is a double membrane organelle

2. The intermembrane space is bounded by the outer membrane & the inner membrane

3. The inner membrane encloses a central space called the matrix. The transition reaction & Krebs cycle occur within matrix

4.The inner membrane is folded into cristae. The electron transport system is located in the inner membrane or cristae.

Chapter 7 – Cellular RespirationGlycolysis

Aerobic cell respiration begins with glycolysis

1. Glycolysis occurs in the cytoplasm

2. Reactants = glucose, 2 NAD+, 2 ATP, 4 ADP, 4 Pi

3. Products = 2 pyruvates, 2 NADH, 4 ATP (Net 2 ATP), 2 H2O

NAD+ = nicotinamide adenine dinucleotide – a co-enzyme necessary for the reaction to go forward, H+ donator in the electron transport chain

During glycolysis NAD+ is reduced to NADH.

Since it’s being reduced, are other molecules being oxidized?

What kind of a reaction is the conversion of glucose (C6H12O6) into carbon dioxide

(CO2) & water (H2O) ? Anabolic or catabolic?

Does this reaction require an input of energy to get it going?







Chapter 7 – Cellular RespirationTransition or Acetyl-CoA reaction

1. Occurs in the matrix

2. Reactants = 2 pyruvates, 2 co-enzyme A (CoA), 2 NAD+

3. Products = 2 acetyl CoA, 2 NADH + H+, 2 CO2


Chapter 7 – Cellular RespirationKrebs Cycle

1. Occurs in the matrix

2. Reactants = 2 acetyl CoA, 2 ADP, 2 Pi, 6 NAD+, 2 FAD

3. Products = 2 ATP, 6 NADH, 2 FADH2, 4 CO2

4. For every acetyl-CoA that enters the Krebs cycle, the cycle turns once. For every glucose molecule that starts cell respiration, 2 pyruvates are formed, forming 2 acetyl CoAs, thus turning the Krebs cycle twice

FAD – flavin adenine dinucleotide – co-enzyme necessary for the reaction as well as an electron donor in the electron transport chain

During Krebs cycle both NAD+ & FAD are reduced to NADH & FADH2 respectively

If both of these molecules are being reduced, are other molecules being oxidized?


Chapter 7 – Cellular RespirationElectron Transport System (ETS) – Arnold’s comparison with ETS in chloroplasts

Chapter 7 – Cellular RespirationElectron transport System

1. Occurs in within the inner membrane

2. Reactants = 6 NADH, 2 FADH2, 6 O2, ADP + Pi

3. Products = approximately 36 – 38 ATPs, 4 H2O, ATP

Chapter 7 – Cellular RespirationElectrons enter ETS from NADH & FADH2

As the electrons are passed from carrier to carrier, H+ are pumped from the matrixinto the intermembrane space, creating a huge concentration gradient for the H+ to flow down

The H + flow back into the matrix through ATP synthase, thus creating ATP from ADP & Pi

The electrons “jump off” the last carrier & combine with O2 to form H2O

This process of producing ATP in the presence of O2 is called oxidative phosphorylation & the overall process of utilizing a concentration gradient to produce ATP is called chemiosmosis or chemiosmotic phosphorylation

The direct transfer of a Pi from one molecule to ADP (glycolysis & Krebs) – substrate level phosphorylation



Chapter 7 – Cellular RespirationEnergy yield from glucose metabolism

ATP produced via substrate level phosphorylation

Glycolysis – 2 ATP

Krebs Cycle – 2 ATP

ATP produced via chemiosmosis

2 NADH from glycolysis – 4 ATP

2 NADH from transition step – 6 ATP

6 NADH from Krebs Cycle – 18 ATP

2 FADH2 from Krebs Cycle – 4 ATP

TOTAL

36 ATP

Efficiency 36 ATP = 263 kcal 1 glucose = 686 kcal

39% of the energy in glucose is converted to ATP, the rest is lost as HEAT


Chapter 7 – Cellular RespirationHow do we utilize other molecules in the cellular respiration pathway?

Chapter 7 – Cellular RespirationFermentation

Ability to produce ATP when oxygen is NOT available

Phases

1. Glycolysis

2. Reduction of pyruvate to lactic acid or alcohol

Reduction step

1. Pyruvate is reduced to lactic acid or alcohol via the oxidation of NADH back to NAD+

2. Once NAD + is regenerated it can go back to the glycolytic pathway & be reduced again, thus enabling glycolysis to keep on running

Details

1. Only produces 2 ATPs per glucose

2. Lactic acid buildup will eventually change the pH in the muscle, leading to ….

Efficiency = 14.6 kcal / 686 kcal = 2.1%


Chapter 7 – Cellular RespirationPRACTICE QUESTIONS

1. What are the 4 steps of aerobic cellular respiration & where do they specifically occur in the cell or mitochondria?

2. Describe the structure of a mitochondria

3. What goes in & comes out of glycolysis, the transition reaction, & Krebs?

4. What is NADH?

5. How many times does Krebs cycle turn with every glucose metabolized?

6. Describe how ATP is synthesized in the ETS?

7. How does this compare with ATP synthesized in glycolysis?

8. What are the 2 possible products of fermentation?

9. What do your muscles start to hurt when they are going through fermentation?