Chapter 8 An Introduction To Metabolism

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Chapter 8 An Introduction To
Metabolism
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Metabolism

• The totality of an organisms chemical processes.
• Concerned with managing the material and energy
  resources of the cell.

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Catabolic Pathways

• Pathways that break down complex molecules into
  smaller ones, releasing energy.
• Example Respiration

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Anabolic Pathways

• Pathways that consume energy, building complex
  molecules from smaller ones.
• Example Photosynthesis

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Energy

• Ability to do work.
• The ability to rearrange a collection of matter.
• Forms of energy
• Kinetic
• Potential
• Activation

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Kinetic Energy

• Energy of action or motion.

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Potential Energy

• Stored energy or the capacity to do work.

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Activation Energy

• Energy needed to convert potential energy into
  kinetic energy.

Activation Energy
Potential Energy
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Energy Transformation

• Governed by the Laws of Thermodynamics.

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1st Law of Thermodynamics

• Energy can be transferred and transformed, but it
  cannot be created or destroyed.
• Also known as the law of Conservation of Energy

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2nd Law of Thermodynamics

• Each energy transfer or transformation increases
  the entropy of the universe.

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Entropy

• Measure of disorder.

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Summary

• The quantity of energy in the universe is
  constant, but its quality is not.

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Question?

• How does Life go against Entropy?
• By using energy from the environment or external
  sources (e.g. food, light).

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Free Energy

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

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Free Energy

• G H - TS
• G free energy of a system
• H total energy of a system
• T temperature in oK
• S entropy of a system

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Free Energy of a System

• If the system has
• more free energy
• it is less stable
• It has greater work capacity

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Spontaneous Process

• If the system is unstable, it has a greater
  tendency to change spontaneously to a more stable
  state.
• This change provides free energy for work.

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Free Energy Changes
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Chemical Reactions

• Are the source of energy for living systems.
• Are based on free energy changes.

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Reaction Types

• Exergonic chemical reactions with a net release
  of free energy.
• Endergonic chemical reactions that absorb free
  energy from the surroundings.

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Exergonic/Endergonic
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Biological Examples

• Exergonic - respiration
• Endergonic - photosynthesis

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Cell - Types of Work

• Mechanical - muscle contractions
• Transport - pumping across membranes
• Chemical - making polymers

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Cell Energy

• Couples an exergonic process to drive an
  endergonic one.
• ATP is used to couple the reactions together.

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ATP

• Adenosine Triphosphate
• Made of
• - Adenine (nitrogenous base)
• - Ribose (pentose sugar)
• - 3 phosphate groups

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Adenine
Phosphates
Ribose
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Key to ATP

• Is in the three phosphate groups.
• Negative charges repel each other and makes the
  phosphates unstable.

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ATP

• Works by energizing other molecules by
  transferring phosphate groups.

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ATP vs Food

• ATP
• Renewable energy resource.
• Unstable bonds
• Food
• Long term energy storage
• Stable bonds

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ATP Cycles

• Energy released from ATP drives anabolic
  reactions.
• Energy from catabolic reactions recharges ATP.

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ATP Cycle
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ATP in Cells

• A cell's ATP content is recycled every minute.
• Humans use close to their body weight in ATP
  daily.
• No ATP production equals quick death.

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Enzymes

• Biological catalysts made of protein.
• Cause the rate of a chemical reaction to increase.

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Enzymes

• Lower the activation energy for a chemical
  reaction to take place.

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Enzyme Terms

• Substrate - the material the enzyme works on.
• Enzyme names Ex. Sucrase
• - ase name of an enzyme
• 1st part tells what the substrate is. (Sucrose)

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Enzyme Name

• Some older known enzymes don't fit this naming
  pattern.
• Examples pepsin, trypsin

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Active Site

• 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.

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Homework

• Read chapter 8, 41
• Exam 2 this week, no broadcast on Thursday
• Chapter 8 Fri. 10/10
• Chapter 41 Mon. 10/20

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Models of How Enzymes Work

• 1. Lock and Key model
• 2. Induced Fit model

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Lock and Key Model

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

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Induced Fit Model

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

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Substrate
Active Site
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Enzymes

• Usually specific to one substrate.
• Each chemical reaction in a cell requires its own
  enzyme.

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Factors that Affect Enzymes

• Environment
• Cofactors
• Coenzymes
• Inhibitors
• Allosteric Sites

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Environment

• Factors that change protein structure will affect
  an enzyme.
• Examples
• pH shifts
• temperature
• salt concentrations

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• Cofactors non-organic helpers required for the
  proper function of enzymes.
• Nonprotein ions or molecules
• Ex. Fe, Zn, Cu
• NADH
• Coenzyme Q

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• Coenzymes organic helpers to enzymes. Ex.
  vitamins

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Enzyme Inhibitors

• Competitive - mimic the substrate and bind to the
  active site.
• Noncompetitive - bind to some other part of the
  enzyme.

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Allosteric Regulation

• The control of an enzyme complex by the binding
  of a regulatory molecule.
• Regulatory molecule may stimulate or inhibit the
  enzyme complex.

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Allosteric Regulation
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Control of Metabolism

• Is necessary if life is to function.
• Controlled by switching enzyme activity "off" or
  "on or separating the enzymes in time or space.

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Types of Control

• Feedback Inhibition
• Structural Order

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Feedback Inhibition

• When a metabolic pathway is switched off by its
  end-product.
• End-product usually inhibits an enzyme earlier in
  the pathway.

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Structural Order

• Separation of enzymes and metabolic pathways in
  time or space by the cell's organization.
• Example enzymes of respiration

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Summary

• Recognize that Life must follow the Laws of
  Thermodynamics.
• The role of ATP in cell energy.
• How enzymes work.