Chapter 8An Introduction to Metabolism

Metabolism

• Metabolism is the sum of all chemical reactions in your body.

• If a reactions breaks things down, it is catabolic

• If a reaction builds things up, it is anabolic

Energy

• Energy is the capacity to cause change.• Energy of motion is kinetic energy• Energy that is stored is potential energy• Potential energy that is released during a

chemical reaction is chemical energy

The Laws of Energy Transformation

• Thermodynamics is the study of energy transformations

• A closed system is a system that exchanges only energy with its surroundings, not matter. Putting a lid on the saucepan makes the saucepan a closed system.

• An open system is a system which continuously interacts with its environment or surroundings

• Organisms are open systems

The First Law of Thermodynamics

• According to the first law of thermodynamics, the energy of the universe is constant:

• – Energy can be transferred and transformed, but it cannot be created or destroyed

• The first law is also called the principle of conservation of energy

Energy is released or consumed

• In an exergonic reaction energy is released.

• When you break things down, you release energy

• All catabolic reactions are exergonic

• Cellular respiration is exergonic.

• These are spontaneous reactions

• Delta G (a measure of free energy) is negative

Energy is released or consumed

• In an endergonic reaction energy is absorbed.

• When you build things, you need energy

• All anabolic reactions are endergonic

• Photosynthesis is endergonic

• These are non-spontaneous reactions

• Delta G is positive

Making and breaking bonds

• Making bonds is called dehydration synthesis. You remove water to make a new bond.

• Breaking bonds is called hydrolysis. You add water to break a bond.

Introducing ATP

• ATP is adenosine triphosphate

• It is composed of a nitrogenous base called adenine, a ribose sugar, and a chain of 3 phosphate groups

• Energy is stored in the bonds between the phosphate groups.

• When a bond is broken between the Ps, it releases energy

Hydrolysis of ATP

• The bonds between the phosphate groups of ATP’s tail can be broken by hydrolysis

• Energy is released from ATP when the terminal phosphate bond is broken

• This release of energy comes from the chemical change to a state of lower free energy, not from the phosphate bonds themselves

The Regeneration of ATP

• ATP is a renewable resource that is regenerated by addition of a phosphate group to adenosine diphosphate (ADP)

• The energy to phosphorylate ADP comes from catabolic reactions in the cell

• The chemical potential energy temporarily stored in ATP drives most cellular work

Enzymes!

• Enzymes are proteins. They are catalysts that speed up chemical reactions by lowering the amount of energy needed for those reactions to start (activation energy)

Enzyme terms

• What an enzyme binds to and acts on is called the substrate.

• The place where the enzyme binds is the active site.

• Enzymes are specific and only fit to their own substrate like a key into a lock

• Enzymes are reusable and are used over and over

Factors affecting enzymes

• 1. Temperature

• 2. pH

• 3. Salinity

• Each enzyme has an optimal pH and temperature in which it can function

Factors affecting enzymes

• Some enzymes need helpers:

• Cofactors are INORGANIC and bind to the enzymes to make them work (zinc, iron, copper, minerals)- no carbon

• Coenzymes are ORGANIC and bind to the enzyme to make them work (vitamins)

Factors affecting enzymes

• Inhibitors block enzyme action

• Competitive inhibitors bind to the active site of the substrate so that the enzyme can’t get in

• Non-competitive inhibitors bind somewhere on the substrate, changing the shape of the active site, so enzymes no longer fit

Allosteric regulation

• Allosteric regulation may either inhibit or stimulate an enzyme’s activity

• Allosteric regulation occurs when a regulatory molecule binds to a protein at one site and affects the protein’s function at another site

Feedback Inhibition

• In feedback inhibition, the end product of a metabolic pathway shuts down the pathway

• This type of inhibition is done as a regulatory mechanism to meet the metabolic needs of the cell or organism. Mechanisms, such as cellular respiration, use feedback inhibition.

Specific Localization of Enzymes Within the

Cell• Structures within the

cell help bring order to metabolic pathways

• Some enzymes act as structural components of membranes

• In eukaryotic cells, some enzymes reside in specific organelles; for example, enzymes for cellular respiration are located in mitochondria

Mitochondria