Introductory Questions #61) Explain how potential energy is different from kinetic

energy. What are some ways we can measure energy?

2) Define each variable in the equation: ∆G = ∆H – T ∆S

3) How much energy expenditure will Trent Samaha have to exert to ask Ema Armstrong to Homecoming? (Ema please go outside to answer the question…NOW!)♥

3.5)What is the difference between an exergonic reaction and an endergonic reaction?

4) How is ATP associated with coupled reactions? What purpose does it serve?

5) How is an electron carried from one molecule to the next? Name a molecule that can carry an electron.

Chapter 8

An Introduction to Energy & Metabolism(Pages 141-159)

Topics:•Thermodynamic Laws

•Catabolism & Anabolism (metabolism)

•Exergonic vs. Endergonic Reactions

•Free Energy

•ATP Cycle & Energy Coupling

•Enzyme (structure & function)

Main Topics to Cover-Ch. 8

• Potential vs. Kinetic Energy• First Two Laws of Thermodynamics• Entropy, Enthalpy, and Free Energy• Endergonic vs. Exergonic Reactions• Anabolism & Catabolism = Metabolism• Energy Coupling: Oxidation/Reduction• ATP; Structure & Function• Enzymes Structure & Function (Lab #6)

-allosteric, feedback mechanisms, inhibitory sit.

• Energy is defined as the capacity to do work

• All organisms require energy to stay alive

• Energy makes change possible

Energy is the capacity to perform work

• Living cells are compartmentalized by membranes

• Membranes are sites where chemical reactions can occur in an orderly manner

• Living cells process energy by means of enzyme-controlled chemical reactions

ENERGY AND THE CELL

• Kinetic energy is energy that is actually doing work

• Potential energy is stored energy

Figure 5.1A

Figure 5.1B

Thermodynamics

• Energy (E)~ capacity to do work; Kinetic energy~ energy of motion; Potential energy~ stored energy

• Thermodynamics~ study of E transformations• 1st Law: conservation of energy; E transferred/transformed, not

created/destroyed

• 2nd Law: transformations increase entropy (disorder, randomness)

• Combo: quantity of E is constant, quality is not

• First law of thermodynamics

• Energy can be changed from one form to another– However, energy cannot be created or

destroyed

Two laws govern energy conversion

Figure 5.2A

• Second law of thermodynamics

• Energy changes are not 100% efficient– Energy conversions increase disorder, or

entropy – Some energy is always lost as heat

Figure 5.2B

Metabolism/Bioenergetics

• Metabolism: The totality of an organism’s chemical processes; managing the material and energy resources of the cell

• Catabolic pathways: degradative process such as cellular respiration; releases energy

• Anabolic pathways: building process such as protein synthesis; photosynthesis; consumes energy

Equation Used to Determine Free Energy of a System

G = H - T S G: Quantity of Free Energy H: Enthalpy = System’s Total Energy

(chemical Bond energy) T: Temperature (absolute temp. in Kelvin units) S: Entropy = Disorder of the system

Spontaneous Reaction = G will be negative (energy is released ie. Exergonic.)

Non spontaneous Reaction (Endergonic) G will be positive.

What happens when G is ZERO ???

Free Energy• Free energy: portion of system’s E that can perform work

(at a constant T)• Exergonic reaction: net release of free E to surroundings• Endergonic reaction: absorbs free E from surroundings

ATP & Energy Coupling

See Pgs.

• ATP is thought as the energy “currency” of a cell• In cellular respiration, some energy is stored in

ATP molecules• ATP powers nearly all forms of cellular work• ATP molecules are the key to energy coupling

ATP shuttles chemical energy within the cell

General Facts about ATP

• Human use about 99 lbs of ATP each day @rest

• Every second 10 million ATP’s are made from ADP

• Bacteria has about a one-second supply of ATP

Energy Coupling & ATP

• Energy coupling: use of exergonic process to drive an endergonic one (ATP)

• Adenosine triphosphate (nucleotide w/3 PO4’s)

• ATP tail: high negative charge

• ATP hydrolysis: release of free Energy

• Phosphorylation: binding of the released phosphate to another molecule

Introductory Video for Chapter 8 “Metabolism”

1) Name the American Olympiad profiled in this video. What condition did she have?

2) What are the two major reasons why cells use energy?3) What unique metabolic process does Dr. Margo Haygood

discuss in the video? Name the enzyme used for this process.

4) Which two laws of thermodynamics are summarized by Dr. Saltman & Dr. Haygood?

5) Briefly explain how enzymes are able to speed up reactions based on the information from the video. Describe the mechanisms that regulate enzyme activity.

The Hydrolysis of ATP

• When the bond joining a phosphate group to the rest of an ATP molecule is broken by hydrolysis, the reaction supplies energy for cellular work. G = -32 KJ/mol (-7.6 Kcal/mol)

Figure 5.4A

Phosphategroups

Adenine

Ribose

Adenosine triphosphate

Hydrolysis

Adenosine diphosphate(ADP)

Energy

• The ATP cycle

Figure 5.4C

Energy from exergonic reactions

Deh

yd

rati

on

syn

thes

is

Hyd

roly

sis

Energy for endergonic reactions

Example of Energy Coupling w/ATP

• Forming the Disaccharide Sucrose involves:

glucose + fructose → sucrose (G = +27 KJ/mol)

ENDERGONIC Reaction

Couple w/hydrolysis of ATP (G = - 32KJ/mol)

Occurs in a couple of reaction steps:

Reaction#1: Glucose + ATP → glucose-P + ADP

**glucose has been phosphorylated

**ATP has been hydolyzed

Reaction #2: Glucose-P + fructose → Sucrose + Pi

(Pi is a low energy inorganic phosphate)

• How ATP powers cellular work

Figure 5.4B

Reactants

Po

ten

tia

l en

erg

y o

f m

ole

cule

s

Products

Protein

Work

Three Functions of ATP

Enzymes: Structure & Function

See Pgs. 150-157

Lab #3- Enzyme Catalysis w/Catalase

Three Parts to the lab:• Establish Baseline Amount of H2O2

• Uncatalyzed Decomposition of H2O2

• Time Trials w/Catalase to determine Rxn rate

• Procedure:– 10 ml H2O2 in a beaker– 1.0 ml (H2O or Catalase)– 10 ml 1 M H2SO4– Mix well– Take a 5 ml sample and titrate in KMnO4– Read Initial and final measurements on buret– Record Data

• For a chemical reaction to begin, reactants must absorb some energy– This energy is called the energy of activation

(EA) – This represents the energy barrier that prevents

molecules from breaking down spontaneously

Enzymes speed up the cell’s chemical reactions by lowering energy barriers

Enzymes

• Catalytic proteins: change the rate of reactions w/o being consumed

• Free E of activation (activation E): the E required to break bonds

• Substrate: enzyme reactant• Active site: pocket or groove

on enzyme that binds to substrate

• Induced fit model

• A protein catalyst called an enzyme can decrease the energy barrier

EA barrier

Reactants

1 Products 2

En

zym

eFigure 5.5A

• Enzymes are selective– This selectivity determines which chemical

reactions occur in a cell

A Specific Enzyme Catalyzes each Cellular Reaction

How an Enzyme Works-Sucrase

How Enzymes Work

• http://www.ekcsk12.org/science/aplabreview/lab02.htm

**Description of Enzyme Lab

• Lab Simulation:http://bioweb.wku.edu/courses/Biol114/enzyme/enzyme1.asp

Effects on Enzyme Activity• Temperature• pH• Cofactors: inorganic, nonprotein

helpers; ex.: zinc, iron, copper

• Coenzymes:organic helpers

ex. vitamins

Enzyme Inhibitors

• Irreversible (covalent); reversible (weak bonds)• Competitive: competes for active site (reversible); mimics

the substrate• Noncompetitive: bind to another part of enzyme (allosteric

site) altering its conformation (shape); poisons, antibiotics

• Inhibitors interfere with enzymes– A competitive

inhibitor takes the place of a substrate in the active site

– A noncompetitive inhibitor alters an enzyme’s function by changing its shape

Enzyme inhibitors block enzyme action

Substrate

Enzyme

Active site

NORMAL BINDING OF SUBSTRATE

Competitiveinhibitor

Noncompetitiveinhibitor

ENZYME INHIBITION

Figure 5.8

Competitive & Noncompetitive Inhibitors

• Enzyme activity is influenced by – temperature – salt concentration – pH

• Some enzymes require non-protein cofactors such as: Fe, Zn, Cu, etc.

The Cellular environment affects enzyme activity

• Certain pesticides are toxic to insects because they inhibit key enzymes in the nervous system

• Many antibiotics inhibit enzymes that are essential to the survival of disease-causing bacteria– Penicillin inhibits an enzyme that bacteria use in

making cell walls

Some Pesticides and Antibiotics inhibit Enzymes

Allosteric Enzymes-How they Work

Feedback Inhibition

Introductory Questions #6

1) Explain how potential energy is different from kinetic energy. What are some ways we can measure energy?

2) Define each variable in the equation: ∆G = ∆H – T ∆S

3) What is the difference between an exergonic reaction and an endergonic reaction?

4) How is ATP associated with coupled reactions? What purpose does it serve?

5) How is an electron carried from one molecule to the next? Name a molecule that can carry an electron.

Introductory Questions #7

1) Name three ways that enzyme activity can be measured as mentioned in your lab guidesheet.

2) Explain how the reactivity of pepsin is different from trypsin. (see pg. 154)

3) Give an two examples of a cofactor and two examples of a conenzyme. How are they different?

4) How is a competitive inhibitor different from a non-competitive inhibitor?

5) What is an allosteric enzyme?

Energy Transfer in Redox Reactions

See Pgs. 161-162

Redox-Defining Terms• Oxidation = Electrons are lost• Reduction = Electrons are gained• These two reactions are complementary and

occur simultaneously (they must go together)• Electrons cannot exist in a free state, they must

be associated with a molecule• This process allows electrons to be transferred

from one molecule to another• Often occur in a series• Essential for cellular respiration & Photosynthesis

Electrons are transferred by a carrier molecule by the hydrogen

atom• Common electron carrier: NAD+

• NAD+ is Nicotinamide adenine dinucleotide

• When NAD+ is reduced it gains an electron and becomes reduced.

• The electron losses some of its free energy during the transfer

• Expressed as: X-H2 + NAD+ X+ NADH + H+

(oxidized) (reduced)

Other Electron Carriers (hydrogen acceptors)

• NADP+ (see in photosynthesis)

• FAD + (see in the Kreb cycle for cellular respiration)

• Cytochromes – embedded in membranes

**Remember that:

Reduced state more free energy vs. Oxidized state which has less free energy

• Fireflies use light, instead of chemical signals, to send signals to potential mates

• Females can also use light flashes to attract males of other firefly species — as meals, not mates

Cool “Fires” Attract Mates and Meals

• The light comes from a set of chemical reactions, the luciferin-luciferase system

• Fireflies make light energy from chemical energy

• Life is dependent on energy conversions