4.4 aerobic respiration

How Cells Harvest Chemical Energy

Introduction to Cell Metabolism

Glycolysis

Aerobic Cell Respiration

Anaerobic Cell Respiration

Breathing and Cell Respiration are related

O2 CO2 BREATHING

Lungs

Muscle cells
CO2 Bloodstream O carrying out
2

CELLULAR
RESPIRATION
Sugar + O2 → ATP + CO2 + H2O

Cellular Respiration uses oxygen and glucose to produce
Carbon dioxide, water, and ATP.

Glucose Oxygen gas Carbon Water Energy
dioxide

How efficient is cell respiration?

Energy released Energy released Gasoline energy
from glucose from glucose converted to
(as heat and light) banked in ATP movement
100%

About
40% 25%
Burning glucose “Burning” glucose Burning gasoline
in an experiment in cellular respiration in an auto engine

Reduction and Oxidation

OILRIG

Oxidation is losing electrons

Reduction is gaining electrons

Loss of hydrogen atoms

Energy
Glucose
Gain of hydrogen atoms

Glucose gives off energy as is is oxidized

OILRIG
Gain or loss of electrons is often in the form of
hydrogen. The hydrogen is then passed to a coenzyme such
as NAD+


What are some common co-enzymes?
NAD+ and FAD
NAD+ + 2 H ⇒ NADH + H+

FAD + 2H ⇒ FADH2

Remember that H =2 electrons and 2H+


These co-enzymes are very important for cell
respiration because they transfer high-energy
electrons to electron transport systems (ETS).


As the electrons move from carrier to carrier,
energy is released in small quantities.

Electron transport system
(ETS)

Generation of ATP

There are two ways to generate ATP

Chemiosmosis

Substrate-Level Phosphorylation

Generation of ATP

Chemiosmosis

Cells use the energy
released by “falling”
electrons in the ETS to
pump H+ ions across a
membrane

Uses the enzyme ATP
synthase.

Generation of ATP

Chemiosmosis

Generation of ATP

Substrate Level Phosphorylation

Enzyme

ATP can also be
Adenosine
made by transferring
phosphate groups
from organic substrate
molecules to ADP
Adenosine

product
Figure 6.7B

General Outline

Glucose

Glycolysis

Oxygen No Oxygen
Pyruvic Acid
Aerobic Anaerobic

Transition Reaction Fermentation
Krebs Cycle
ETS

36 ATP

Glycolysis

Where? The cytosol

What? Breaks down glucose to pyruvic acid

Steps 1 – 3 A fuel Glucose
molecule is energized, Step
using ATP.
Glycolysis
1
Glucose-6-phosphate
2

Fructose-6-phosphate

Energy In: 2 ATP
3

Fructose-1,6-diphosphate
Step 4 A six-carbon 4
intermediate splits into
two three-carbon Glyceraldehyde-3-phosphate
intermediates. (G3P)

5
Step 5 A redox
reaction generates
NADH. 1,3-Diphosphoglyceric acid
(2 molecules)
6

Steps 6 – 9 ATP 3-Phosphoglyceric acid
Energy Out: 4 ATP and pyruvic acid
are produced.
7 (2 molecules)

2-Phosphoglyceric acid
8 (2 molecules)

2-Phosphoglyceric acid
(2 molecules)

NET 2 ATP 9
Pyruvic acid
(2 molecules
per glucose molecule)

General Outline of Aerobic Respiration

Glycolysis

Transition Reaction

Krebs Cycle

Electron Transport System

Transition Reaction

Each pyruvic acid molecule is broken down to form
CO2 and a two-carbon acetyl group, which enters the
Krebs cycle

Pyruvic Acid Acetyl CoA

Krebs Cycle

Where? In the Mitochondria

What? Uses Acetyl Co-A to generate ATP, NADH,
FADH2, and CO2.

General Outline of Aerobic Respiration

Glycolysis

Krebs Cycle



Protein
complex
Intermembrane
Electron
space
carrier

Inner
mitochondrial
membrane
Electron
flow
Mitochondrial
matrix

ELECTRON TRANSPORT CHAIN ATP
Figure 6.12 SYNTHASE


For each glucose molecule that enters cellular
respiration, chemiosmosis produces up to 38 ATP
molecules

Overview of Aerobic Respiration

Fermentation
Requires NADH generated by glycolysis.

Where do you suppose these reactions take place?

Yeast produce carbon dioxide and ethanol

Muscle cells produce lactic acid

Only a few ATP are produced per glucose

4.4 aerobic respiration

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