Chapter 7 – Cellular Respiration
Phases 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 Respiration
Chapter 7 – Cellular Respiration
Chapter 7 – Cellular Respiration
Mitochondria 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 Respiration
Glycolysis
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 Respiration
Chapter 7 – Cellular Respiration
Chapter 7 – Cellular Respiration
Chapter 7 – Cellular Respiration
Chapter 7 – Cellular Respiration
Chapter 7 – Cellular Respiration
Chapter 7 – Cellular Respiration
Transition 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 Respiration
Chapter 7 – Cellular Respiration
Krebs 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 Respiration
Chapter 7 – Cellular Respiration
Electron Transport System (ETS) – Arnold’s comparison with ETS in chloroplasts
Chapter 7 – Cellular Respiration
Electron 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 Respiration
Electrons enter ETS from NADH & FADH2
As the electrons are passed from carrier to carrier, H+ are pumped from the matrix
into 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 Respiration
Chapter 7 – Cellular Respiration
Chapter 7 – Cellular Respiration
Energy 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 Respiration
Chapter 7 – Cellular Respiration
How do we utilize other molecules in the cellular respiration pathway?
Chapter 7 – Cellular Respiration
Fermentation
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 Respiration
Chapter 7 – Cellular Respiration
PRACTICE 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?