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Transcript
Ch. 6: Cellular Respiration
Harvesting Chemical Energy
Cellular Respiration: An Overview
A cellular process that breaks down nutrient
molecules with the production of ATP

Consumes oxygen and produces carbon dioxide (CO2)
◦ Cellular respiration is an aerobic process.

Usually involves the complete breakdown of glucose to
CO2 and H2O

Occurs in 3 steps
Overview

Cellular respiration is an exergonic
◦ produces up to 32 ATP molecules from each
glucose molecule
◦ captures only about 34% of the energy
originally stored in glucose

Other foods (organic molecules) can also
be used as a source of energy.
Figure 6.2
O2
Breathing
CO2
Lungs
CO2
Bloodstream
O2
Muscle cells carrying out
Cellular Respiration
Glucose  O2
CO2  H2O  ATP
Cellular Respiration: An Overview
Cellular Respiration: An Overview

Terms to Know…
◦ Oxidation = the loss of electrons
 Compound becomes more positive
◦ Reduction = the gain of electrons
 Compound becomes more negative
◦ Electrons and protons (H+) travel TOGETHER
Oxidation
C6H12O6
+
6O2
6CO2
+
6H2O
+ energy
glucose
Reduction


Electrons are removed from substrates
and received by oxygen, which
combines with H+ to become water.
Glucose is oxidized and O2 is reduced
Important enzymes
NAD+
◦ A coenzyme of oxidation-reduction.
◦ Each NAD+ molecule is used over and over again
◦ Reduced into NADH
 Accepts 2 electrons plus a hydrogen ion (H+)

FAD
◦ Also a coenzyme of oxidation-reduction
◦ Sometimes used instead of NAD+
◦ Reduced into FADH2
 Accepts two electrons and two hydrogen ions (H+)
Cellular Respiration

Respiration is a cumulative function of 3
metabolic stages
◦ Glycolysis
 Only reactions that takes place outside of mitochondria
and doesn’t require O2
 Think back to the Endosymbiatic theory!!!!
◦ Citric acid cycle (Krebs Cycle)
 Matrix of the mitochondria
◦ Oxidative Phosphorylation
 Electron transport chain (ETC)
 Occurs in the mitochondrial membrane because of the
enzymes (proteins)
Cellular Respiration
Glucose
Glycolysis
Oxygen Absent
ATP
Oxygen Present
Anaerobic Respiration
Aerobic Respiration
(Fermentation)
(Krebs Cycle & ETC)
ATP
Glycolysis: “glucose-splitting”

Big Picture:
◦ Glucose (6-C) is broken down into 2
molecules of pyruvate (3-C)

Occurs in the cytoplasm
◦ Occurs without oxygen..again think evolution!
Oxidation results in NADH and 2 ATP
 Made up of 2 phases:

◦ Energy investment phase
◦ Energy yielding (payoff) phase
Glycolysis: Energy Investment Phase
Glucose is converted
into 2 G3P
(Glyceraldehyde-3phosphate)
 Requires 2 ATP

ENERGY
IN
Glycolysis: Energy-Yielding Phase
◦ 2 G3P are converted
into 2 Pyruvate (3C)
molecules.
◦ Dehydrogenase enzymes
remove H+ from
intermediate
compounds and attach
them to 2 NAD to
produce 2NADH
Substrate-Level Phosphorylation

An enzyme transfers a phosphate group
directly from an organic molecule to ADP
to form ATP

The ATP produced in Glycolysis & the
Krebs Cycle is produced by this method.
enzyme
ADP
BPG
ATP
3PG
Net Gain in Glycolysis

2 ATP
- 2 ATP (Energy investment phase)
+ 4 ATP (Energy yielding phase)
+ 2 ATP

2 NADH
◦ Electron carriers
◦ Will be used to make ATP later 
Choices, Choices! 

If oxygen is absent, anaerobic respiration
occurs
◦ Fermentation
 Yeast & some bacteria  alcoholic fermentation
 Animal muscle lactic acid fermentation

If oxygen is present, aerobic respiration
occurs
◦ Krebs Cycle and Electron Transport Chain
Cellular Respiration
Glucose
Glycolysis
Oxygen Absent
Anaerobic Respiration
ATP
Oxygen Present
Aerobic Respiration
(Fermentation)
ATP
Fermentation


Fermentation is an anaerobic process that
reduces pyruvate to either lactate or alcohol
and CO2
2 major types:
◦ Alcoholic and lactic acid fermentation

NAD+ acts as a hydrogen acceptor during
glycolysis
◦ If the supply of NAD+ runs out, then glycolysis
would have to stop.
◦ Fermentation occurs as simply a means of
recycling the NAD+, so that glycolysis can occur
again.
Alcoholic Fermentation


Occurs in some BACTERIA and
YEAST
2 step process:
◦ Carbon dioxide is released from
pyruvate (3-C), forming
acetaldehyde (2-C)
◦ Acetaldehyde is reduced by
NADH forming ethanol
◦ NAD+ is regenerated

Used to produce beer and wine
Lactic Acid Fermentation


Occurs in ANIMALS
1 step process:
◦ Pyruvate is reduced by NADH
forming lactic acid



NAD+ is regenerated
Occurs in muscle cells, causing
muscle pain and fatigue
Used to make yogurt and cheese
Cellular Respiration
Glucose
Glycolysis
Oxygen Absent
Anaerobic Respiration
ATP
Oxygen Present
Aerobic Respiration
(Fermentation)
ATP
Aerobic Respiration

After glycolysis, most of the energy from glucose remains
“locked” in 2 molecules of pyruvate

If oxygen is present, the pyruvate enters the
mitochondrial matrix to complete the Krebs Cycle
Preparatory Phase:
 Pyruvate (3-C) is converted to Acetyl CoA (2-C)
◦ CO2 is released as a waste product
◦ NADH is produced
The Krebs Cycle

Yield per pyruvate molecule (two turns):
◦ 3 NADH
◦ 1 FADH2
◦ 1 ATP
 (produced via substrate level phosphorylation)
◦ 2 CO2

CO2 released as a waste product
◦ We exhale this
Figure 6.9A
Acetyl CoA
CoA
CoA
2 CO2
Citric Acid Cycle
3 NAD
FADH2
3 NADH
FAD
3 H
ATP
ADP
P
Electron Transport Chain (ETC)

Collection of cytochrome molecules
embedded in the cristae membrane
◦ 4 reactions plus ATP synthase
Occurs in inner membrane of
mitochondrion
 Proton pump that produces a proton
gradient that will be used to create ATP

ETC
Electrons from NADH and FADH2 from
glycolysis and the Krebs Cycle lose electrons,
proton gradient
 The energy in each NADH molecule moves
enough protons (H+) into the mitochondrial
matrix to create 3 ATP

◦ 1 FADH2  2 ATP
ETC
The electrons from NADH and FADH2 are passed
from one electron acceptor molecule to another.
 Each electron acceptor is more electronegative than
the last.
 Oxygen is the final electron acceptor, producing
water

e-
oxygen
Steps of the ETC
I- NADH reductase oxidizes NADH to
NAD+ resulting in high energy electron
 II- high energy electron transfers through
coenzyme Q to cytochrome reductase
 III- travels through the cytochrome c
 IV- travels into cytochrome oxidase
where it is now low energy and binds to
oxygen to form water

Chemiosmosis

the energy the electrons
lose along the way moves
H+ out of the matrix and
into the intermembrane
space of the mitochondria

As H+ ions diffuse through
the membrane, ATP
synthase uses the energy
to join ADP and a
phosphate group  ATP
Oxidative Phosphorylation: ETC & Chemiosmosis
Figure 6.12
CYTOPLASM
Electron shuttles
across membrane
2 NADH
Mitochondrion
2 NADH
or
2 FADH2
6 NADH
2 NADH
Glycolysis
2
Pyruvate
Glucose
Pyruvate
Oxidation
2 Acetyl
CoA
Citric Acid
Cycle
2 FADH2
Oxidative
Phosphorylation
(electron transport
and chemiosmosis)
Maximum
per glucose:
2
ATP
by substrate-level
phosphorylation
2
ATP
by substrate-level
phosphorylation
 about
28-34 ATP
by oxidative
phosphorylation
About
32-38ATP
Process
ATP Produced
Directly by
Substrate-level
Phosphorylation
Reduced
Coenzyme
ATP Produced by
Oxidative
Phosphorylation
Total
Glycolysis
Net 2 ATP
2 NADH
4 to 6 ATP
6-8
Oxidation of
Pyruvate
-------
2 NADH
6 ATP
6
Krebs cycle
2 ATP
6 NADH
2 FADH2
18 ATP 4 ATP
24
Total: 36-38
This number is okay for prokaryotes but with eukaryotes this number is
more like 30 ATP