Chapter 6Ong Yee Sing

2017

6.1 Adenosine triphosphate

Objectives

• Discuss the role of ATP in metabolism

• Describe the structure of ATP

• Describe how ATP provide energy

• Explain the reaction of a cell to the viability of ATP

• Saccharides are the main source of energy for cells.

• Fats are the main energy storage substances.

• Saccharides and fats have to be oxidized to release energy.

• Adenosine triphosphates (ATPs) are the direct energy carrier in the cells.

Energy substances

Function of ATP• The energy released

from the ATP molecule is utilized by the cell to carry out all kinds of activities. Examples:• Contraction of

muscles• Transmission of

nervous impulse• Active transport of

substances• Growth of cells and

cell division, etc.

ATP binding cassette (ABC) proteins

requires ATP to transport anthocyanininto the vacuole.

Structure of ATP• It is chiefly produced by the

mitochondria.

• The structural formula of ATP can be simplified as

A—P~P~P• A = adenosine (adenine + ribose)

• P = phosphate (one central phosphorus atom surrounded by four oxygen atoms)

• ~ = high energy phosphate bond

Hydrolysis of ATP

• A great amount of chemical energy in the ATP molecule is stored in the high energy phosphate bond.

• The hydrolysis of this bond releases energy.

• This reaction is said to be exogernic放能.

Energy released hydrolysis of ATP and ADP

ATPase, water

ATP ⇋ ADP + Pi + 3.3 x 104 J/mol

ATPase, water

ADP ⇋ AMP + Pi + 2.8 x 104 J/mol

Reaction progression

Energy

ATP

ADP + Pi

AMP + Pi + Pi

AMP is not a high energy molecule• In AMP, the phosphate is joined to the

adenosine with a phosphoester bond, not the phosphate bond, which links a phosphate group to another phosphate group.

• Energy released when the phosphoester bond is broken is not a large amount (9.6 x 103 J/mol).

• AMP aka oxyadenosinemonophosphate of RNA.

[ATP]/[ADP] ratio• The ratio of the content of AMP, ADP and

ATP in the cell can reflect the energy condition of the cell and the direction of metabolism in the cell.

• When the amount of ATP is high, this shows that the quantity of energy in the cell is sufficient • The cell will limit or restrict the oxidation of

substances. • The cell promotes the synthesis of

macromolecules such as glycogen and lipids to store the excess energy.

• When the amount of ATP and ADP decreases, this shows that the amount of energy in the cell is not sufficient.• The cell will promotes respiration so to

increase the production of energy. • Macromolecules will be oxidized to produce

more ATP.

• The ratio of [ATP]/[ADP] in the cytosol is typically 200:1 or more.

Quiz

• Based on the figure, what is the ATP/ADP ratio in this muscle cell?

ATP/ADP ratio

=ATP

ADP

=7mM

0.04mM

=175

1

• ATP releases energy is NOT a reversible reaction, but ADP can be recycled to reform ATP with energy added.

• Generally different enzymes are involved in hydrolysis and synthesis of ADP.

ADP is recyclable

Synthesis of ATP vs hydrolysis of ATP

Synthesis of ATP Hydrolysis of ATP

Equation of reaction ADP + Pi + energy ATP ATP ADP + Pi + energy

Type of reaction Synthesis / Anabolism Hydrolysis / Catabolism

Enzyme ATP synthase ATPase

Source of energyLight (photosynthesis)

Chemical (respiration)

High energy

phosphate bond

Energy conversion Storage Release

Function of energy Storage as ATP Utilized in cellular activities

Location of reaction Mitochondria, chloroplast Almost all parts in a cell

Conclusion

• Saccharides are the main source of energy for cells.

• Fats are the main energy storage substances.

• Adenosine triphosphates (ATPs) are the direct energy carrier in the cells.

• ATP can be hydrolysed into ADP, which in turns can be hydrolysed into AMP.

Quiz

• How many ATPs can be formed from 30 adenosine and 60 phosphate?

A. 10

B. 20

C. 30

D. 60