Metabolism & Energy Metabolism – sum of an organism’s chemical

reactions Two Main Types of Metabolic Pathways:

Catabolic Pathways: breaking down molecules to release energy (downhill)

Ex. Cellular Respiration Anabolic Pathways: uses energy to build

complex molecules from simple molecules (uphill)

Ex. Photosynthesis Energy released from catabolic pathways, drive

anabolic pathways.

Energy Energy – the ability to do work

Ability to rearrange a collection of matter Various Types – kinetic, potential, light,

chemical, etc. 1st Law of Thermodynamics: energy can be

transformed and transferred, but it cannot be created or destroyed Aka – energy of the universe is constant

2nd Law of Thermodynamics: every energy transfer/transformation makes the world more disordered (more entropy)

Energy Continued – 2nd Law of Thermodynamics As living things perform chemical reactions that do work

some forms of energy are converted to heat Heat can only do work if there is a temperature

difference (heat will flow from a warmer to cooler area) Temperature is uniform in cells, so no work can be

performed by the heat that is released during chemical reactions Ex. Rooms with lots of people get warm

This leads to entropy (more disorder or randomness) The more randomly arranged a collection of matter is, the greater

its entropy Gases have more entropy than liquids and liquids have more

entropy than solids

Gibbs Free Energy

ΔG = ΔH – T ΔS Where….

ΔG = total available energy ΔH = change in enthalpy

Enthalpy = total energy in a system T = temperature in Kelvin ΔS = change in entropy

Entropy = measure of the disorder in a system

Spontaneous Reactions

Increase the entropy (disorder) of the universe

Occur without an input of energy Exergonic Are reactions that can occur on their

own Examples:

Water flowing downhill Cellular Respiration

Chemical Reactions & Energy

Exergonic Reactions: 1) Net release of free energy2) Occur spontaneously3) ΔG < 0

Endergonic Reactions:1) Absorbs free energy

2) Non-spontaneous3) ΔG > 0

Cellular Respiration vs. Photosynthesis

Cellular Respiration ΔG = -686 kilocalorie or -686 Calories

Photosynthesis ΔG = 686 kilocalorie or 686 Calories

Prove these numbers with Gibbs Free Energy

ATP: The Energy Molecule

ATP is the fuel that powers work in cells b/c it links exergonic reactions to endergonic reactions

ATP helps cells do….1) Chemical Work: dehydration synthesis

or hydrolysis2) Mechanical Work: muscle contraction3) Transport Work: active transport

Energy: ATP Structure

Made up of…1) Adenine 2) Ribose3) Three phosphate groups

Have like charges so they repel each other Bonds b/w phosphates are unstable Energy of repulsion is stored in the bonds

that hold the phosphates together

ATP Structure

ATP & Cellular Reactions ATP is constantly broken down and re-made Making ATP (from ADP & P) endergonic

+7.3 kilocalories Breaking ATP down exergonic

-7.3 kilocalories ATP is like a rotating door through which

energy is passed as it moves from catabolic to anabolic pathways.

The energy temporarily stored in ATP drives almost all cellular work!!!

ATP Cycle

More About ATP…..

Transferring a P from ATP (forming ADP) to another molecule transfers energy

The molecule receiving the P, and hence energy, is PHOSPHORYLATED

Nearly all endergonic reactions require less energy that provided by the cleavage of ATP

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

Living Systems & 2nd Law of Thermodynamics

Living systems do not violate the 2nd law of thermodynamics Which states that entropy increases over

time

Order is maintained by coupling cellular processes that increase entropy (exergonic) with those that decrease entropy (endergonic) ATP Cycle

Living Systems & 2nd Law of Thermodynamics

Energetically favorable reactions, such as ATP ADP + P, are exergonic

The energy released from this reaction can be used to maintain or increase order in a system by being couple with reactions that have a positive free energy change (endergonic)

How is Free Energy Used by Living Organisms?

Chemical Reactions Dehydration synthesis – makes polymers Hydrolysis – breaks down polymers

Body temperature regulation Endothermy: using thermal energy made

by chemical reactions to maintain the homeostasis of body temperature

Ectothermy: use external thermal energy to regulate and maintain body temperature

How is Free Energy Used by Living Organisms?

Reproduction/Raising Offspring Seasonal reproduction in plants

Excess Acquired Free Energy vs Free Energy Used Results in energy storage or growth

Insufficient Required Free Energy vs Free Energy Used Loss of mass, and, eventually, death

Enzymes Definition: Proteins that speed up the rate of a chemical

reaction Have a 3-D shape conferred by their primary,

secondary, tertiary, and quaternary structure -- let’s review those!

Can build (dehydration synthesis) or break down (hydrolysis)

Enzyme, Substrate & Active Site – What’s the Relationship? Enzyme – catalyst Substrate – molecule(s) the enzyme is working

on Active Site – area where the enzyme and

substrate fit together Shape is essential to function!

Enzymes & Energy

EA (Activation Energy) Energy required to break bonds in the reactants Enzymes act to lower the activation energy

Enzymes & Activation Energy

How Do Enzymes Lower Activation Energy?

Active sites hold onto and put stress on the substrate (molecule the enzyme if working on)

Bonds are broken Less energy is needed to achieve the

transition state

Enzymes & Activation Energy

If there was no barrier of activation energy proteins, DNA & other molecules would spontaneously decompose

Enzymes can only lower activation energy; they CANNOT cause a rx’n to occur that would not occur spontaneously

Enzyme Characteristics

Specific Binds to a substrate based on shape recognition

Substrate binds to the active site by induced fit active site is slightly flexible, but clasps tightly when the enzyme and substrate meet.

Reusable can be used over & over

The Catalytic Cycle of Enzymes

Substrate isconverted into

products

Products leave; Active Site is open

Enzyme and substrate meet;

Held togetherby weak bonds

Enzyme Action

What Factors Affect Enzyme Activity?

1) Temperature Above optimal temp – enzyme denature

(lose their shape) – Explain why.

What Factors Affect Enzyme Activity? 2) pH

Every enzyme has an optimal pH Pepsin is found in the stomach (acidic) while

trypsin is found in the small intestine (slightly basic)

What Factors Affect Enzyme Activity?

3) Substrate Concentration At some point, every enzyme is

saturated with substrate and the reaction cannot proceed any faster

What Factors Affect Enzyme Activity?

4) Cofactors: helper(s) to the enzyme; may bind to the active site OR bind loosely & reversibly along with the substrate

What Factors Affect Enzyme Activity?

Another cofactor example

What Factors Affect Enzyme Activity? 5) Enzyme Inhibitors: inhibits the substrate from binding to the active site…

A. Competitive Inhibitors – resemble substrate structure and compete for a place in the active site

B. Noncompetitive Inhibitors – Binds to a part of the enzyme away

from the active site changes enzyme shape

Competitive vs. Noncompetitive Inhibitors

Enzymes & Allosteric Regulation Allosteric Regulation: an enzyme can

change b/w 2 conformational shapes due to activators or inhibitors

Feedback Inhibition & Cooperativity

Feedback Inhibition: Metabolic pathway is turned on and off by its product; the end product acts to inhibit the enzyme that catalyzes the reaction

Cooperativity: A mechanism where one substrate may prime an enzyme to accept additional substrate molecules more easily

Denatured?

What does it mean if an enzyme has been denatured?

How does an enzyme become denatured?

Denaturation

Explain how changes in the following affect an enzymes function: temperature, pH, salt concentration