Energy-Releasing Pathways

It is the main energy carrier for cells.

It is consists of:

a. Adenosine – a substance made up of the

purine adenine plus a five-carbon sugar ribose

b. Triphosphate Group

It is released from food molecules ingested by

organisms in the process of respiration.

Adenosine Triphosphate (ATP)

The energy input from ATP

formation can come from sunlight,

small inorganic compound, or from the

breakdown of carbohydrates, lipids and

proteins.

Of the foods we eat, carbohydrates

are the main source of energy. A good

example is glucose. Our cells use

glucose first as long as it is available,

then lipids, and proteins as the last

resort.

A process where chemical energy is

released from various carbohydrates.

It has three pathways:

A. Aerobic Respiration

B. Anaerobic Electron Transport

C. Fermentation

CARBOHYDRATE METABOLSM

After Glycolysis,what’s next?

Glucose (carbohydrate)

Glycolysis ATP

no oxygen with oxygen

Fermentation Aerobic Respiration

‘Glyco’ means sugar.

‘Lysis’ means break.

This step doesn’t proceed without an energy

input from ATP

GLYCOLYSIS: The First Stage

It takes place in the cytoplasm

Glycolysis

In this process, Glucose is phosphorylated toglucose-6-phosphate.

Then, breaks into 2 three-carbon molecules of PGAL. ATP provides a

phosphate group to each PGAL and removes hydrogen atoms. NAD+

picks up the Hydrogen and becomes reduced to NADH; 2 molecules

are formed.

As a result, 4 ATP molecules and 2 NADH are generated from the PGAL

molecule and is converted to pyruvic acid.+

*aerobe- uses Oxygen as the final electron

acceptor in carbohydrate metabolism.

An Oxygen-dependent pathway which takes

place in the Mitochondrion

A. Aerobic Respiration

This pathway commonly yields 36 ATP

molecules for every glucose molecules

degraded.

H+ and electrons are transferred to NAD+

and FAD which in turn transfer them to an

electron transport system.

Occurs as a series of chemical reaction in

which Oxygen convert the chemical energy

stores in organic molecules to ATP and

reduced H2 acceptors. E.g. NADH

A. Aerobic Respiration

The pyruvic acid must be converted first to

Acetyl-CoA; a two-carbon molecule of Acetyl

Group.

During this transformation, the pyruvic acid

loses H2O and produces CO2 + NADH+ H+

(as NAD+ accept H2 ). Now, the 2 molecules

of Acetyl-CoA are ready to enter the Krebs

Cycle.

P.A + CoA + NAD+ Acetyl-CoA +CO 2 + NADH

+ H +

After Glycolysis…

Conversion of Pyruvic Acid to Acetyl-CoA

Also known as Citric Acid Cycle

The cycle was named after a British

biochemist named Sir Hans Adolf Krebs.

KREBS Cycle: The Second Stage

This occurs in the inner matrix of Mitochondria

Krebs Cycle

Krebs Cycle http://www.1lecture.com/Biochemistry/How%20the

%20Krebs%20Cycle%20Works/index.html

Step 1: Acetyl CoA combines with

Oxaloacetic acid to form citric acid

(regenerates CoA)

Step 2: Citric acid releases CO2 and a H atom

that combines with NAD+ to form NADH + H+

to form 5 carbon compound.

Step 3: 5 carbon compound releases CO2 and

a Hydrogen atom (combines with NAD+ to

form NADH + H+) to form a 4 carbon

compound. A molecule of ATP is formed.

Krebs Cycle

Krebs Cycle

Step 4: 4 Carbon compound releases a

hydrogen atom ( combines with FAD to Form

FADH2) and is converted to another 4 carbon

compound.

Step 5: The 4 carbon compound releases a

hydrogen atom and is (combines with NAD+

to form NADH + H+)converted back into

Oxaloacetic acid.

In this stage, one acid is formed to another;

Acetyl CoA (2-C) reacts with oxloacetic acid

(4-C). Citric Acid is eventually reduced to

other forms:

ketoglutaric acid (5-c)

succinic acid (4-c)

malic acid (4-c)

oxaloacetic acid (4-c)

Krebs Cycle

Which become regenerated to start

the cycle all over again because it takes two

preparatory reaction sequences of Krebs

Cycle to dismantle the 2 pyruvates.

The breakdown of the pyruvates add

only 2 ATP molecules (one for each) and

many electron carriers to the number that

can be used in the third stage, the Electron

Transport Phosphoryatio.

Krebs Cycle

ELECTRON TRANSPORT PHOSPHORYLATION: The Third Stage

The most impressive of all ATP-yielding mechanisms

This stage is carried out by enzymes embedded in

the inner membrane of the mitochondrion.

It involves two events:

1. The transfer of electrons and Hydrogen through

a membrane- bound transport system.

2. Actual formation of ATP

ELECTRON TRANSPORT PHOSPHORYLATION: The Third Stage

*anaerobes cannot ever use Oxygen as the

final electron acceptor thus, an inorganic

compound is the final acceptor.

In this pathway, NADH from Glycolysis transfers

electrons to a small transport system bound in

the plasma membrane and the NAD+ is thereby

regenerated.

The reaction do not add any more ATP.

B. Anaerobic Electron Transport

The breakdown of pyruvates without

Oxygen.

The net yield is 2 ATP. The remaining

reactions only serve to regenerate NAD+

It comes in 2 forms:

1. Alcoholic Fermentation

2. Lactic Acid Fermentation

C. Fermentation Pathways

1. Alcoholic Fermentation

During this process, pyruvates are broken

down to acetyldehyde. This accepts

electrons from NADH and thereby

becomes ethanol.

It occurs in some plants and some one-

celled organisms.

Fermentation Pathways

ALCOHOLIC FERMENTATION

Ex: Production of beer and wine

Fermentation pathways

2. Lactic Acid Fermentation

It takes place when there is a short supply

of Oxygen in cells.

Fermentation Pathways

Example:

Occurs in muscle cell when strenuous exercise

causes muscle cells to use up all the oxygen

available to them. They switch to anaerobic

respiration and lactic acid builds up in the cells,

changing the acidity of the cytoplasm.

Production of cheese and yogurt

Fermentation pathways