Chapter 6 - Respiration
CHAPTER 6 - RESPIRATION
O
2
Glucose
HEAT + ENERGY
CO
2
+
H
2
O

The only reason humans need to breathe oxygen is to accept electrons in the final stage of ATP synthesis in the mitochondria.

Outline
I. OVERVIEW
II. GLYCOLYSIS
Getting to glucose
Mechanisms by which ATP is synthesized
Glycolysis – steps in the process
Glycolysis - summary
III. THE AEROBIC PATHWAY
Mitochondrion structure
A preliminary step
The Krebs cycle
Oxidative phosphorylation
IV. ANAEROBIC PATHWAYS
V. OTHER TYPES OF RESPIRATION

Outline
OVERVIEW

I. OVERVIEW
All organisms harvest energy from stored chemicals (starch, sugars, lipids) in the same way
The metabolic pathways by which organisms liberate stored energy are referred to as cellular respiration

Respiration of glucose - equation
THE OVERALL EQUATION
FOR
RESPIRATION OF GLUCOSE
C
6
H
12
O
6
+ O
2
CO
2
+ H
2
O + ENERGY
Carbon Dioxide

Cellular Respiration

Cellular Respiration
Glucose → CO2 + H2O + energy (ATP)

Overview
This is the same equation for starting a fire using glucose as a fuel.
The difference is that the reaction in living systems is tightly controlled and energy normally lost as heat is captured for other uses.

Glucose is used as a source of energy for two kinds of respiration:
Aerobic
Anaerobic

Overview - aerobic respiration
Aerobic Respiration - requires oxygen as the terminal electron acceptor
1) Stages involved a) Krebs cycle b) Oxidative phosphorylation (synthesis of ATP)
2) Disposition of Energy a) Some energy is stored in ATP and in other compounds b) Other energy dissipates as heat

Overview - anaerobic respiration
Anaerobic Respiration: (without oxygen)
Fermentation: Metabolic pathways by which energy is liberated from pyruvic acid, the end product of glycolysis, in the absence of oxygen.

Outline
GLYCOLYSIS

Glycolysis is the breakdown of glucose to pyruvic acid (pyruvate).

molecules
GLUCOSE IS NOT ABUNDANT IN
CELLS
CELLS OBTAIN GLUCOSE BY
BREAKING DOWN GLUCOSE-
CONTAINING STORAGE MOLECULES,
OFTEN SUCROSE OR STARCH

Sucrose, Starch, Fructose, etc
Fig 6-2

molecules
COMMON GLUCOSE STORAGE COMPOUNDS
•
SUCROSE (TABLE SUGAR), FRUCTOSE (FRUIT SUGAR)
AND OTHER SUGARS
•
STARCH
•
POLYMERS OF FRUCTOSE

GLUCOSE IS RETREIVED FROM
SUCROSE BY BY HYDROLYSIS
Requires the enzyme “sucrase”

molecules
STARCH IS A BRANCHED POLYMER
MADE UP OF GLUCOSE MOLECULES
SEVERAL DIFFERENT
KINDS OF ENZYMES
ARE REQUIRED TO
BREAKDOWN
STARCH
• Amylases
• Starch phosphorylase
•
Debranching enzymes

molecules
Amylases hydrolyze alpha 1-4 glucose linkages
Starch phosphorylase cleaves glucose at the end of a chain end by adding a phosphate to it starch + H2PO4 → glucose 1-phosphate
Debranching enzymes hydrolize starch at branch points

Outline
GLYCOLYSIS
Mechanisms by which ATP is synthesized

Synthesis of ATP
ATP is synthesized during respiration by -
1. Substrate-level phosphorylation
2. ATP synthase complexes in mitochondrial and chloroplast membranes
( Oxidative Phosphorylation )

PHOSPHOENOLPYRUVIC
ACID
=Transfer of a phosphate directly from an organic molecule to ADP to make ATP

ATP synthase complex
Oxidative
Phosphorylation =
Coupling energy from an electron donor with an electrochemical gradient that spans a membrane to phosphorylate ADP
Fig 6-15

Outline
GLYCOLYSIS

This is glycolysis
Fig 6-2

Glycolysis occurs in the cytoplasm!!!!

Uses 1 ATP
Fig 6-4

Uses 2nd ATP

We will follow what happens to glyceraldehyde
3-phosphate only. Note-all products are from this point on are doubled

Generates 2 NADH
2 molecules

Generates 2 ATP

2 molecules

2 molecules

Generates 2 ATP

Total yield of energy-transport molecules from glycolysis
Fig 6-17

Outline
AEROBIC
RESPIRATION

Pyruvic acid is imported into mitochondria

The Krebs cycle occurs in the matrix of the mitochondria

Outline
AEROBIC
RESPIRATION
Oxidative decarboxylation of pyruvate

Pyruvate is transported into the mitochondria
Fig 6-7

Fig 6-17

Outline
AEROBIC
RESPIRATION

Fig 6-2

Krebs cycle = TCA cycle
The Krebs cycle is also called the
TCA cycle (tricarbocylic acid cycle) because citric acid has three carboxyl groups) or
The citric acid cycle

Krebs cycles X 2
The chemical reaction repeatedly recycles, taking in two carbons and producing two
CO
2 molecules

Two carbons enter
Fig 6-8

Two CO2 molecules are produced
(4/molecule of glucose)
Fig 6-8

Three molecules of
NADH are produced
(6/molecule of glucose)
Fig 6-8

One molecule of
ATP is produced
(2/molecule of glucose)
Fig 6-8

One molecules of
FADH
2 is produced
(2/molecule of glucose)
Fig 6-8

Fig 6-17

Outline
AEROBIC
RESPIRATION

Fig 6-2

NADH and ubiquinol from the Krebs cycle start a series of oxidation reduction reactions that move electrons through a series of carriers.
The electron carriers together are called an
“electron transport chain”

Fig 6-10
See next slide for oxidationreduction of
CoQ

Fig 6-13

Fig 6-10
See next slide for cytochrome structure

Fig 6-11

Energy from the flow of electrons maintains a proton gradient across the inner mitochondrial membrane
This proton gradient drives the synthesis of ATP.
This process is called
“oxidative phosphorylation”

H+
H+
H+
H+

ATP synthesis

Fig 6-17

Outline
ANAROBIC
RESPIRATION

Anaerobic respiration
Glycolysis works in an oxygen free environment and can occur in either anaerobic or aerobic respiration
The Krebs cycle and electron transport are inhibited by a lack of oxygen

Not Inhibited
Fig 6-2
Inhibited

If NADH from glycolysis builds up (because it’s not being used in oxidative
phosphorylation), NAD+ will become depleted
NAD+ is required to oxidize glyceraldehyde-3 phosphate
Therefore, glycolysis will stop

Excess NADH can be removed by conversion of pyruvic acid to acetaldehyde
Fig 6-18

Lactic acid
In some animals (you), in some fungi and bacteria, pyruvic acid is reduced to lactic acid instead of alcohol

Anaerobic respiration
Glycolysis
Krebs cycle
Pyruvic acid
Alcohol or lactic acid
Electron transport 36ATP 2ATP

Outline
OTHER TYPES
OF
RESPIRATION
Lipids, proteins, etc

Fig 6-19

Respiration of lipids
Lipids are important storage compounds.
They can be metabolized to yield acetyl Co-A for aerobic respiration

Outline
OTHER TYPES
OF
RESPIRATION
Cyanide resistant respiration

Cyanide-resistant electron transport
Fig 6-10
Cyanide

Aerobic respiration is inhibited when the terminal electron carrier combines with cyanide, azide or certain other negatively charged ions
This poisons the enzyme and stops electron transport

Some plants, fungi and bacteria
This pathway produces heat rather than ATPs but is aerobic (i.e., oxygen is the terminal electron acceptor)

Energy is captured from light by
Philodendron leaves and used for life processes and growth
When it flowers, the
Philodendron flower heats to as high as 46 C (115 F). The heat protects the flowers from freezing at night and disperses compound that attract polinators
Light energy —> Heat

END
End