Chapter 8: Metabolism and Energy

Metabolism

Total system of all chemical reactions in a living being

Metabolic Pathway

A specific molecule goes through step-by-step changes to make a final product

What allows for metabolic pathways to be completed?

Enzymes that catalyze at each step

Catabolic Pathways

Complex molecules are broken down into simple compounds, releasing energy in the process

Anabolic Pathways

Simple compounds are built into complex molecules, consuming energy in the process

Which type of reaction is consider downhill and up? Uphill?

Catabolic Pathways → downhill

Anabolic Pathways → uphill

T or F: Anabolic Pathways are used to power Catabolic Pathways

F, Catabolic Pathways (downhill) reactions release energy which is used to power the Anabolic Pathways (uphill)

Energy

Capacity of a system to cause change in its surroundings, and can exist in various forms

Work

The process of moving matter against opposing forces

What powers work?

Energy

Bioenergetics

The study of how energy flows through and is used by living beings

Kinetic Energy

Energy of motion

Thermal Energy

Kinetic energy at the atomic level

Heat

Released when transferred from one object to another

Potential Energy

Energy of location and structure

Chemical Energy

Potential energy stored in chemical bonds

How is Chemical Energy released?

Through chemical reactions

Thermodynamics

The study of how a system transforms and exchanges energy with surroundings

What are the 2 different types of systems in terms of energy?

Isolated and Closed Systems

Isolated System

No energy or matter exchange with the surroundings

Open System

Energy transformation and exchange between the system and surroundings

First Law of Thermodynamics

Energy can be transferred or transformed, but never created or destroyed

What is another name for the First Law of Thermodynamics

Principle of Conservation of Energy

Second Law of Thermodynamics

During energy transfer or transformation, some energy is converted to thermal energy and lost as heat

T or F: Heat cannot be used to do work

T

Entropy

Measure of how disordered a system is

• How much energy in the system cannot be used to do work

How is Entropy increased?

Every transfer and transformation of energy

Spontaneous vs. Nonspontaneous Processes

Spontaneous → Processes that increase the entropy of the universe (no energy)

Nonspontaneous → Processes that can decrease entropy (need energy)

Increasing Order vs. Increasing Disorder

Increasing Order → Forming complex, organized structures

Increasing Disorder → Breaking down organized matter and releasing heat

Free Energy (G)

The measure of how much energy in a system can do work

What is the equation for Free Energy (G)?

ΔG = G _{final state} - G _{initial state}

What does negative ΔG for a chemical reaction imply?

• No energy input

• Spontaneous

• System loses free energy becoming more stable

T or F: There is a direct relationship between Free Energy and stability

F, It’s an inverse relationship (more G = more unstable)

What does positive ΔG for a chemical reaction imply?

• Energy needed

• Nonspontaneous

T or F: Systems tend to move towards lower G (energy stability)

T

Equilibrium

The state of maximum stability, where forward and reverse reactions occur at same rate

How do systems move in terms of Equilibrium?

Spontaneously moves towards Equilibrium but never away from it

Which type of system reaches Equilibrium with no change in Free Energy?

Isolated Systems

What keeps Open Systems from reaching Equilibrium? How?

Metabolic pathways which provide energy

Exergonic Reaction (in terms of free energy)

• Free Energy is released to surroundings

• Negative ΔG

Endergonic Reaction (in terms of free energy)

• Free Energy is taken in from surroundings

• Positive ΔG

• Products store less G than reactants

Compare the Spontaneity of Endergonic and Exergonic Reactions

Endergonic Reaction → nonspontaneous

Exergonic Reaction → spontaneous

Which chemical reaction type is energetically favorable for reactants and why?

Exergonic → allows a system to move towards a state of lower G (higher stability)

What is the relationship between Free Energy and work that can be done?

The greater the decrease in free energy, the greater the amount of work that can be done through that chemical reaction

Which chemical reaction type is energetically unfavorable for reactants and why?

Endergonic → allows a system to move towards a state of higher G (lesser stability)

What are the 3 types of Work cells perform?

1. Chemical Work

2. Transport Work

3. Mechanical Work

Chemical Work

Pushes endergonic chemical reactions forward

Transport Work

Pushes substances against their concentration gradient, across membranes

Mechanical Work

Movement of internal structures

What is ATP composed of?

1. Ribose (sugar)

2. Adenine (nitrogenous base)

3. 3 Phosphate groups

When is the energy in ATP released?

When the terminal phosphate bond is broken by hydrolysis

What is the role of Potential Energy in ATP (using repulsion)?

• Potential Energy is stored in the phosphate groups

  • The repulsion between negative charges of phosphate groups wants each to push away but are held in place

Phosphorylation

ATP transfers a phosphate group to another molecule

Phosphorylated Intermediate

A temporary molecule that has a phosphate group attached to it during a chemical reaction

How do Phosphorylated Intermediates compare to their original form?

Higher free energy (less stable, more reactive) than their original form

What is ATP coupling and it’s steps?

• Exergonic Breakdown: Breaking ATP into ADP and Phosphate releases free energy

• Endergonic Driving: Cells use released energy to power reactions that require an energy input

• Then a Phosphate is added to ADP

Catalyst

Chemical agents used to speed up reactions without being consumed in the process

Enzyme

Usually protein based catalysts that speed up specific reactions

What must happen for molecules to facilitate bond breakage and start a reaction?

Molecules will absorb energy and contort into unstable states

Activation Energy (E_A)

The amount of energy a reactant molecule needs to absorb into order to break its bonds

Where does Activation Energy come from?

Thermal energy (heat) from the surrounding environment

Transition State (in terms of Activation Energy)

When a molecule is at it’s highest-energy, most unstable moment in a chemical reaction

What are the steps of a chemical reaction going through the Activation Energy barrier?

1. Start with a molecule 

2. Molecule absorbs energy

3. Molecule then twists and destabilizes 

a. Transition state

4. Reaction happens