Introduction to Metabolism

Objectives

1. Understand metabolism is the transfer of energy between forms.

2. Free energy dictates energy transfer.

3. ATP is the vehicle of energy transfer

4. Enzymes are responsible for speading up reactions

5. Enzyme regulation controls metabolism

Metabolism Basics1. Chemical processes that manage the

energy and materials of the cell (system)

2. Two types

-Anabolic (build/use energy)

-Catabolic (break apart/release energy)

3. Energy is the capacity to do work (metabolic work)

- Potential energy

- Kinetic energy

4. Chemical Energy – energy stored in chemical bonds

Chemical energy transfer obeys the laws of thermodynamics

Law 1. Energy can never be created or distroyed only tranfered

Law 2. For a process to be spontaneous the energy tranfer must increase entropy or dissorder.

“Organisms are islands of low entropy in an increasingly random universe.”

Gibbs Free Energy – Portion of system’s energy available to do work p. 146

*Gibbs = less then 0

The rxn is spontaneous and will occur without help or energy

*Why is it important for metabolic pathways to be spontaneous?

Spontaneous Change

Chemical Reactions are either

1. Exergonic reactions release Gibbs Free Energy that is/was stored in chemical bonds

2. Endergonic Uses energy and puts the energy in the new chemical bonds that are formed (ex. Glucose)

*Chemical rxns in a test tube will all reach an equilibrium

G = 0

-Any biological system at equalibrium is a dead system

-Movement of materials into and out of a biological system keeps the system from reaching an equilibrium.

-Most metabolic pathways have mechanisms that are multistep where each step shows a gradual decrease in Gibbs free energy

** Gas in a car example

“ATP is the energy token of life”

“Please clarify!!”

Cellular Work

1. There are three types of work that needs to get done in the cell

1. Chemical work or endergonic rxns

2. Transport work of pumps

3. Mechanical work of cilia or chromosomes in reproduction

2. How does the work get done? ATP

3. How does ATP allow cellular work to get done?

- The release of the third Phophate is exergonic

- mostly due to the negativity of the phophate groups

- Use of Phosphorylated intermediates

- ADP is recycled using energy from other molecules like Glucose

Biological Systems

-Rely on Exergonic reactions

-Exergonic reactions can occur fast or slow (rust)

-Catalysts speed up reactions

-Enzymes are biological Catalysts

-Reactants need energy to reach a transition state, which is unstable and will move towards the products.

-Enzymes lower the energy needed for reactants to reach the transition state.

Enzymes

1. React with a specific substrate

2. Have an active site

3. Substrate bonds to the active site through an induced fit way

4. Substrate bonds through weak intermolecular forces like Hydrogen bonds

Active sites do:

1. Orientation of substrate

2. Stabilize transition state

3. Favorable environment

4. Temporarily react with substrate

Enzyme activity is affected by

-pH and Temp

Cofactors 1. Cofactors or Coenzymes are bound to

the enzymes and are needed for the enzyme to do its job.

2. Vitamins play a big role in making coenzymes

Inhibitors1. Competitive – act directly with the active

site

2. Noncompetitive – act somewhere else but change the shape of the active site so substrate won’t fit

“Cells aren’t a bag of chemicals with thousands of different kinds of enzymes and substrates in a random mix.”

Allosteric Regulation

1. Activation

2. Inhibition

3. Feedback Inhibition