Chapter 8: An Introduction To Metabolism

2.a.1 – All living systems require constant input of free energy (8.1-8.3).

4.b.1 – Interactions between molecules affect their structure and function (8.4 & 8.5).

The totality of an organism’s chemical processes

Concerned with managing the material and energy resources of the cell

Pathways that break down complex molecules into smaller ones, releasing energy

Example: Cellular respiration DOWNHILL!

Pathways that consume energy, building complex molecules from smaller ones

Example: Photosynthesis, condensation synthesis

UPHILL!

Energy cannot be created or destroyed

It can be converted from one form to another

The sum of the energy before the conversion is equal to the sum of the energy after the conversion

Some usable energy dissipates during transformations and is lost

During changes from one form of energy to another, some usable energy dissipates, usually as heat

The amount of usable energy therefore decreases

Ability to do work The ability to rearrange a collection of

matter Forms of energy:

› Kinetic› Potential› Activation

Kinetic: › Energy of action or motion› Ex: heat/thermal energy

Potential: › Stored energy or the capacity to do work› Ex: chemical energy

Energy needed to convert potential energy into kinetic energy

Potential Energy

Activation Energy

The portion of a system's energy that can perform work

Known as ΔG

ΔG = Δ H - T Δ SΔ = change (final-initial)ΔG = free energy of a systemΔH = total energy of a system

(enthalpy)T = temperature in oKΔS = entropy of a system

If the system has:› more free energy=less stable (greater

work capacity)› less free energy=more stable (less

work capacity)› As rxn moves towards equilibrium, ΔG

will decrease

These are the source of energy for living systems

They are based on free energy changes Two typesTwo types: exergonic and endergonic

Exergonic: › chemical reactions with a net

release of free energy› Ex: cellular respiration› - ΔG , energy out, spontaneous

Endergonic: › chemical reactions that absorb

free energy from the surroundings› Ex: Photosynthesis› + ΔG , energy in, non-spontaneous

- ΔG +ΔG

Couples an exergonic process to drive an endergonic one

ATP is used to couple the reactions together

Types:Types: mechanical, transport, chemical

AAdenosine TTripphosphate Made ofMade of::

1. Adenine (nitrogenous base)2. Ribose (pentose sugar)3. 3 phosphate groups*

*bonds can be broken to make ADP

Three phosphate groups and the energy they contain

Negative charges repel each other and makes the phosphates unstable› Tail is unstable = more free energy = more

instability Works by energizing other molecules by

transferring phosphate groups Hydrolysis of ATP = free energy is

released as heat (can be adv or not adv)

Energy released from ATP drives anabolic reactions

Energy from catabolic reactions “recharges” ATP

Very fast cycle

› 10 million made per second

Coupled RXN

Takes place in cytoplasm and mitochondria

Using special process called substrate-level phosphorylation› Energy from a high-

energy substrate is used to transfer a phosphate group to ADP to form ATP

Biological catalysts made of protein Speeds up rxn without being consumed Cause the speed/rate of a chemical rxn

to increase› By lowering activation energy

AB + CD AC + BD*AB and CD are “reactants”*AC and BD are “products”*Involves bond forming/breaking*Transition state: can be unstable

Unstable state

Energy is released as heat

Lower the activation energy for a chemical reaction to take place

Why do we need enzymes?› Cells can’t rely on heat to kick start rxns› Why? Denaturation, heat can’t decipher

between rxns› Enzymes are selective! Can only operate

on a given chemical rxn

Intro to

Enzy

mes movie

SubstrateSubstrate – – › the material the enzyme works on

Enzyme namesEnzyme names: : › Ex. Sucrase› “- ase” name of an enzyme› 1st part tells what the substrate is (i.e.

Sucrose)

Some older known enzymes don't fit this naming pattern

Examples: pepsin, trypsin

The area of an enzyme that binds to the substrate

Structure is designed to fit the molecular shape of the substrate

Therefore, each enzyme is substrate specific

Enzyme + Enzyme-Enzyme +

Subtrate Sub complex Product

Notice: Complex becomes product, but enzyme stays the same! Enzyme is NOT CONSUMED!

1. Lock and Key model2. Induced Fit model

Reminder:Reminder: Enzymes and substrates are usually held together by weak chemical interactions (H/ionic bonds)

Substrate (key) fits to the active site (lock) which provides a microenvironment for the specific reaction

Substrate “almost” fits into the active site, causing a strain on the chemical bonds, allowing the reaction

Usually specific to one substrate Each chemical reaction in a cell requires

its own enzyme Don’t change during rxn Always catalyze in direction towards

equilibrium

1) Active site is template for enzyme2) Enzymes may break/stretch bonds

needed to be broken/stretched3) Active site is microenvironment4) Active site directly participates in

chemical rxn

Environment Cofactors Coenzymes Inhibitors Allosteric Sites

Factors that change protein structure will affect an enzyme.

Examples:› pH shifts (6-8 optimal)› Temperature (up, inc activity)› Salt concentrations

Cofactors:Cofactors:› Non-proteinNon-protein helpers for catalytic

activity› Examples: Iron, Zinc, Copper

Coenzymes:Coenzymes:› Organic molecules that affect

catalytic activity› Examples: Vitamins, Minerals,

usually proteins

CompetitiveCompetitive › mimic the substrate and bind to the

active site (compete for active site)› Toxins/poisons – Ex: DDT› Can be used in medicine – painkillers,

antibiotics Noncompetitive

› bind to some other part of the enzyme› Causes active site to change shape

Inhibitor video

Identify forms of energy and energy transformations. Recognize the Laws of Thermodynamics. Recognize that organisms live at the expense of free

energy. Relate free-energy to metabolism. Identify exergonic and endergonic reactions. Identify the structure and hydrolysis of ATP. Recognize how ATP works and is coupled to metabolism. Recognize the ATP cycle Relate enzymes and activation energy. Recognize factors that affect enzymes specificity and

enzyme activity.. Recognize factors that control metabolism.