RESPIRATION Aerobic respiration - PowerPoint Presentation

Slide1

RESPIRATION

Aerobic respiration

 is the process of producing cellular energy involving oxygen. Cells break down food in the mitochondria in a long, multistep process that produces roughly 36 ATP. The first step in is

glycolysis

, the second is the citric acid cycle and the third is the electron transport system.

Anaerobic respiration

occurs when the amount of oxygen available is too low to support the process of aerobic

respiration

. There are two main types of

anaerobic respiration

, alcoholic

fermentation

and lactic acid

fermentation

.

Anaerobic respiration

is 

respiration

 using electron acceptors other than molecular oxygen (O

2

). In aerobic organisms undergoing 

respiration

, electrons are shuttled to an electron transport chain, and the final electron acceptor is oxygen.

It produces lactic acid, rather than carbon dioxide and water.

In aerobic organisms undergoing respiration, electrons are shuttled to an electron transport chain, and the final electron acceptor is oxygen. Molecular oxygen is a highly oxidizing agent and, therefore, is an excellent electron acceptor. In anaerobes other less-oxidizing substances such as

sulphate

(SO

4

2−

), nitrate (NO

3

−

),

sulphur

(S), or

fumarate

are used. These terminal electron acceptors have smaller reduction potentials than O

2

, meaning that less energy is released per oxidized molecule. Therefore, generally speaking, anaerobic respiration is less efficient than aerobic.

Anaerobic respiration takes place in the cytoplasm of cells. Indeed, most cells that use anaerobic respiration are bacteria or

archaea

, which don’t have specialized organelles

Both 

aerobic

 and 

anaerobic respiration

 involve chemical reactions which take place in the cell to produce energy, which is needed for active processes. 

Aerobic respiration

 takes place in the mitochondria and requires oxygen and glucose, and produces carbon dioxide, water, and energy.

Cellular respiration (both aerobic and anaerobic)

utilizes highly reduced chemical compounds such as NADH and FADH2 (for example produced during

glycolysis

and the citric acid cycle) to establish an electrochemical gradient (often a proton gradient) across a membrane, resulting in an electrical potential or ion concentration difference across the membrane. The reduced chemical compounds are oxidized by a series of respiratory

integra

membrane proteins with sequentially increasing reduction potentials with the final electron acceptor being oxygen (in aerobic respiration) or another chemical substance (in anaerobic respiration). A proton motive force drives protons down the gradient (across the membrane) through the proton channel of ATP

synthase

. The resulting current drives ATP synthesis from ADP and inorganic phosphate.

Fermentation,

in contrast, does not utilize an electrochemical gradient. Fermentation instead only uses substrate-level

phosphorylation

to produce ATP. The electron acceptor NAD+ is regenerated from NADH formed in oxidative steps of the fermentation pathway by the reduction of oxidized compounds. These oxidized compounds are often formed during the fermentation pathway itself, but may also be external. For example, in

homofermentative

lactic acid bacteria, NADH formed during the oxidation of glyceraldehyde-3-phosphateis oxidized back to NAD+ by the reduction of

pyruvate

to lactic acid at a later stage in the pathway. In yeast, acetaldehyde is reduced to ethanol to regenerate NAD+. The two processes thus generate ATP in very different ways, and the terms should not be treated as synonyms.

Along with photosynthesis and aerobic respiration, fermentation is a way of extracting energy from molecules, but it is the only one common to all bacteria and eukaryotes. It is therefore considered the oldest metabolic pathway, suitable for an environment that does not yet have oxygen. Yeast, a form of fungus, occurs in almost any environment capable of supporting microbes, from the skins of fruits to the guts of insects and mammals and the deep ocean, and they harvest sugar-rich materials to produce ethanol and carbon dioxide.

Types of Anaerobic Respiration

Lactic acid

fermentation

– In this type of anaerobic respiration, glucose is split into two molecules of lactic acid to produce two ATP.

C

6

H

12

O

6

(glucose)+ 2 ADP + 2 phosphate → 2 lactic acid + 2 ATP

Alcoholic fermentation

– In this type of anaerobic respiration, glucose is split into ethanol, or ethyl alcohol. This process also produces two ATP per sugar molecule

C

6

H

12

O

6

(glucose) + 2 ADP + 2 phosphate → 2 C

2

H

5

OH (ethanol) + 2 CO

2

+ 2 ATP

Other types of fermentation

– Other types of fermentation are performed by some bacteria and

archaea

. These include

proprionic

acid fermentation, butyric acid fermentation,

solvent

fermentation, mixed acid fermentation,

butanediol

fermentation,

Stickland

fermentation,

acetogenesis

, and

methanogenesis

.

Examples of Anaerobic Respiration

Sore Muscles and Lactic Acid

During intense exercise, our muscles use oxygen to produce ATP faster than we can supply

it.When

this happens,

muscle

cells can perform

glycolysis

faster than they can supply oxygen to the mitochondrial electron transport

chain.The

result is that lactic acid fermentation occurs within our cells – and after prolonged exercise, the built-up lactic acid can make our muscles sore!

Yeasts and Alcoholic Drinks

Alcoholic drinks such as wine and whiskey are typically produced by bottling yeasts – which perform alcoholic fermentation – with a

solution

of sugar and other flavoring

compounds.Yeasts

can use complex carbohydrates including those found in potatoes, grapes, corn, and many other grains, as sources of

sugar.Putting

the yeast and its fuel source in an airtight bottle ensures that there will not be enough oxygen around to interfere with the anaerobic respiration that produces the

alcohol!Alcohol

is actually toxic to the yeasts that produce it – when alcohol concentrations become high enough, the yeast will begin to die.

Swiss Cheese and

Propionic

Acid

Propionic

acid fermentation gives Swiss cheese its distinctive flavor. The holes in Swiss cheese are actually made by bubbles of carbon dioxide gas released as a waste product of a bacteria that uses

propionic

acid fermentation.

Vinegar and

Acetogenesis

Bacteria that perform

acetogenesis

are responsible for the making of vinegar, which consists mainly of acetic acid. Vinegar actually requires two fermentation processes, because the bacteria that make acetic acid require alcohol as fuel!

Glycolysis

is the process by which glucose is broken down

anaerobically

into incompletely oxidized compounds like

pyruvate

, a process which is usually coupled to the synthesis of 2 ATP and 2 NADH for every one glucose molecule processed.

ED pathway

occurs only in prokaryotes and it uses 6-phosphogluconate

dehydratase

and 2-keto-3-deoxyphosphogluconate

aldolase

to create

pyruvate

from glucose. ED pathway

produces only one ATP per glucose—half as much as the EMP

pathway

. ...

The

pentose phosphate pathway

(PPP; also

called

the

phosphogluconate

pathway

and the

hexose

monophosphate

shunt

) is a process that breaks down glucose-6-

phosphate

into NADPH and

pentoses

(5-carbon sugars) for use in downstream biological processes. ... During this process two molecules of

NADP

+

are

reduced to NADPH. The pathway is especially important in red blood cells (erythrocytes).

There are two distinct phases in the pathway. The first is the oxidative phase, in which NADPH is generated, and the second is the non-oxidative synthesis of 5-carbon sugars. For most organisms, the pentose phosphate pathway takes place in the

cytosol

; in plants, most steps take place in plastid.

Similar to

glycolysis

, the pentose phosphate pathway appears to have a very ancient evolutionary origin. The reactions of this pathway are mostly enzyme-catalyzed in modern cells, however, they also occur non-

enzymatically

under conditions that replicate those of the

Archean

ocean, and are catalyzed by metal ions, particularly ferrous ions (Fe(II)). This suggests that the origins of the pathway could date back to the

prebiotic

world.