3.1 Metabolism and Energy

Metabolism

All of the chemical reactions in a cell

To transform matter and energy

Step-by-step sequences metabolic pathways

Anabolic reactions

Build large molecules

Catabolic reactions

Break large molecules into smaller products

Metabolic Pathways

Energy

All organisms continuously capture, store and use energy

Cellular respiration releases energy from carbohydrates and other energy-rich molecules

Functions:

Survive

Grow

Reproduce

Carry out daily activities

Hummingbird heart rate:

Over 1000 beats per min

Energy

Capacity to do work

1. Kinetic energy:

Energy of motion

2. Potential energy:

Stored energy

Can transform from one form to another

Bond Energy

Measure the stability of a covalent bond

Forming bonds – energy is released

Breaking bonds – energy is used

Energy needed to break a bond is the same amount as the energy released when the bond was formed

Energy used Energy released

Net Energy released

Free atoms

have more

chemical

(potential)

energy than

any compound

Example: Cellular Respiration

Enthalpy Change (∆H)

change in the total energy of a system

difference in the energy needed to break the bonds

and the energy released when new bonds are form

Potential Energy Diagram

Endothermic Reaction

∆H is positive

Energy is absorbed

Exothermic Reaction

∆H is negative

Energy is released

Thermodynamics

Study of energy changes in a system

A system:

Can be a whole organism or a set of reactants and products

Biological systems are open systems (can exchange matter and energy with the surroundings)

First Law of Thermodynamics

Total amount of energy in the university is constant

Energy cannot be created or destroyed

Energy can be transformed from one types into another and transferred from one object to another

Example: Cellular Respiration

∆H is negative

Energy is released

Photosynthesis

Reversed reaction

Energy is absorbed

Transition State

Reactants

Products

Entropy

A measure of disorder

Continuously increases as energy available to do work is progressively transformed into unusable heat (ie. energy available is decreasing)

In chemical reactions, entropy increases when:

1. Solid reactants become liquids

2. Liquid reactants become gaseous

3. Complex molecules react to form simpler molecules

4. Solutes move with their concentration gradients

Second Law of Thermodynamics

During any process, the universe tends towards disorder

Only applies to closed system

Living organisms remain organized because they use inputs of matter and energy to reduce entropy and thus stay alive

Gibb’s Free Energy (G)

Energy available to do work in any system

(to break bonds and then form bonds)

G = H – TS

In biological reactions,

constant temperature, pressure and volume:

ΔG = ΔH – TΔS

(used to predict whether a chemical reaction is spontaneous or not)

G: Free energy

H: enthalpy

T: temperature

S: entropy

Exergonic Reaction

∆H<0 and ∆ S>0

→ ∆ G<0

→ spontaneous reaction

* Free energy is released in the form of heat

∆H>0 and ∆ S<0

→ ∆ G>0

→ not spontaneous reaction

* Energy must be supplied

Endogonic Reaction

Activation Energy

Most spontaneous reactions still require an initial input of energy

Biological catalyst (enzyme) reduces the amount of activation energy

Activation

energy

Thermodynamics and Metabolism

When a molecule is broken down (catabolic reaction):

Energy is released (∆H <0)

Entropy increases (∆ S >0)

Exergonic (spontaneous) reaction

When a molecule is built (anabolic reaction):

Endergonic (non-spontaneous) reaction

Coupled with catabolic reactions to get power

Through the energy molecule: ATP (adenosine triphosphate)

Thermodynamics and Metabolism

Catabolic reactions release energy

Energy captured in ATP

ATP used to power anabolic and endergonic reactions

Bonds between the negative

phosphate groups contain a

large amount of energy

Hydrolysis breaks these bonds

and releases the stored energy

to do work in the cell

Energy Dynamics of

ATP

The hydrolysis of ATP to ADP and Pi is

a highly exergonic reaction.

Repulsion between negative charges

on the neighbouring phosphate

groups makes the bonds between the

first and second and between the

second and third phosphate groups

unstable.

When these bonds are broken,

energy is released.

inorganic

Coupled Reactions

Use of ATP as a cycle

Most cells only have a few seconds’ supply of ATP at any given moment

Continuously produced