Energy and Metabolism 1

Energy and Metabolism Chapter 6

Topics you are not responsible for:How biochemical pathways evolve

Read on your own about:Laws of thermodynamics

End of Chapter questions: all

Do all mQuiz questions

Energy and Metabolism 2

How does the body “deal with” alcohol?

Too much of a bad thing Too much of a good thing

NADH -- e- source for ATP production-- too much causes metabolic

disordersADH deficiency in Asian races

Disulfiram (antabuse) – ADH inhibitor

Energy and Metabolism 3

How much “useable” energy exists in the molecules of a cell?

G = H - TS

G = usable energy (Gibbs free energy)

Which equals …

H = energy content in the molecular bonds (enthalpy)?

… Less …

S = disorder (entropy)

x Temperature (Kelvin scale)

Energy and Metabolism 4

What happens to the energy of a molecule during a chemical reaction?

How does the energy content in the molecular bonds (enthalpy) change?

ΔH

How does the energy of disorder (entropy) change?

ΔS (x Temperature)

How does the total usable (‘Free’) energy (G) of the system change during the reaction?

ΔG = ΔH – ΔST = -7 Kcal/mol

“Catabolic” reaction “Exergonic” -- energy is released

Energy and Metabolism 5

Catabolic (exergonic) reactions occur spontaneously… but often slowly. Why?

What is activation energy?

Energy and Metabolism 6

What happens if the reaction is reversed?

Will ΔG (usable energy of the system) be increase or decrease?

What happens to useable energy of the system?

ΔG = ΔH – ΔST = +7 Kcal/mol

Example of an Anabolic reaction (endergonic) -- energy must be added to the system

Energy and Metabolism 7

How does an enzyme affect reaction energetics?

How does it do so?

“Catalytic site”

Substrate orientation

Enzyme movements

Bond destabilization

Catalysis

Funke T et al. PNAS 2006;103:13010-13015

EPSP synthase binding to SP3

Energy and Metabolism 8

Enzyme reactions are reversible

In a closed system. . . . . . will reach “equilibrium”

-- what does this mean?

Sucrase Equilibrium Constant = 1.4x105 (140,000)= [products] = ____[G] x [F]___ [reactants] [sucrose] x [H20] If > 1, Rx is exergonic

Why aren’t [ ]s the same at equilibrium? -- affinities for catalytic site

What is EC of reverse sucrase reaction?

Energy and Metabolism 9

In enzymatic reactions, energy can pass to or from ATP

Glutamine synthase reaction Glutamate + NH3 + ATP Glutamine + ADP + Pi

if: Substrate +ATP Product + ADP +Pi = endergonic / anabolic reaction

if: Substrate +ADP+Pi Product + ATP = exogonic / catabolic reaction

Understand this

Energy and Metabolism 10

What is a metabolic pathway?

-- sequential series of enzymatic reactions-- e.g., Glycolysis, Krebs cycle, etc. Enzyme 1

Enzyme 2

Enzyme 3

Cellular “metabolism” = sum of all enzymatic activities

Energy and Metabolism 11

If all enzymes are reversible, then why do molecules pass one way through metabolic pathways?

What controls flow direction?

1) Reactant vs Product affinities

2) Reactant vs Product concentrations

2) Product removal

Fig 6.13 in text is special case

Energy and Metabolism 12

What controls the rate of enzyme activity?

Various physical factors?pH

Temperature

Reactant & substrate concentrations

Activators and Inhibitors

Models

Energy and Metabolism 13

Control of enzyme activity, con’t.

Inhibitors

competitive

vs

non-competitive

InhibitorsInhibitors

Non-competitive = “allosteric regulation”

What is feedback inhibition?

Common regulatory mechanism

Response to decreased demand for products

Energy and Metabolism 15

In oxidation/reduction reactions, what serve as electron carrier?

Substrate + NAD Product + NADH = substrate oxidation

Substrate + NADH Product + NAD = substrate reduction

Understand this

NADH, FADH, NADPH examples of “coenzymes”

Lactate dehydrogenase Rx