Biochem Ch. 13.4: Redox Reactions

Mechanical work can be driven by ___, as well as cellular processes.

electrons

What are three examples of cellular transducers

Mitochondria, flagellum, transport system

Chemical, mechanical, osmotic

What is pumped out as e- pass through the ETC?

Protons

What enzyme makes the majority of our ATP?

ATP synthase

__ organic compounds serve as fuels from which electrons can be stripped off during oxidation

Reduced

What’s the most oxidized compound?

CO₂

Oxidation and reduction def

• Oxidation = loss of e-, gain of O, loss of H

• Reduction= Gain of e-, loss of O, gain of H

The thing being oxidized is the ___ agent and the thing being reduced is the __ agent

Reducing agent, oxidizing agent

Ferrous iron=… Ferric iron =…

Fe_⁺², Fe⁺³

Half reactions are always written as…

REDUCTIONS

What is the Nernst equation?

Remember we use pH=7 for standard calculations

The half-rxn with a __ reduction potential will proceed as…

MORE +

Electrons move towards the ___ reduction potential

more positive

How were std red potentials determined?

By reference to the standard hydrogen electrode. Everything 1M BUT pH=7, std T and P

Equation relating reduction potential and free energy

How to find the change in reduction potential when given two reduction potentials

Acceptor-donor

For a - change in G, we need a __ change in reduction potential

Positive- indicated spontaneous rxn under std conditions

How to find the actual reduction potential in a given system

NAD and NADP are…

Nicotinamide (“pyridine”) nucleotides

FMN and FAD are…

Flavin nucleotides

NAD is used … and NADP is used…

For breaking things down, for building things up

NAD and NADP are redox ___

Cofactors

NAD and NADP move e- around in the form of a __

Hydride (two e-)

NAD and NADP are derived from…

The vitamin niacin

Usually, a hydride form an __ is transferred to NAD+ to give __

alcohol, NADH

On what part of NAD or NADP does the hydride come on and off?

Nicotinamide ring

In NADP, there is a phosphate group on…

the 2’ C

Draw NAD

Why do we need NAD and NADP?

• Used for different things

• Enzymes specifically recognize one or the other

• Can keep them at different ratios in different areas of the cell

Both NAD and NADP act as… meaning they are __ bound

Substrates, loosely

NAD is usually found in the …

Mitochondria

NADP is mainly found in the…

Cytosol

NADH/NAD ratio is kept

LOW

NADPH/NADP ratio is kept

HIGH

NAD+ reduction involves 2 __ and 2 __

Protons and electrons though only one H is put onto the NAD

Reduction of NAD is ___, based on the ___. It can be put on as…

Stereospecific, enzyme. Pro-R or Pro-S

NADH absorbs at ___ nm

340 nm

Formation of NADH can be monitored by what method

UV-Spectrophotometry

What kind of enzyme typically uses NAD as a cofactor?

Dehydrogenases

Write out the two mechanisms by which NAD is either oxidized or reduced

Why do we produce lactate in our muscle cells when we exercise?

• We run out of oxygen locally, and we can’t do aerobic respiration, we only can do glycolysis. But now we aren’t regenerating NAD, and that’s bad

• We turn pyruvate into lactate by adding two electrons

• Rxn is catalyzed by lactate dehydrogenase (converts the carbonyl of pyruvate to an alcohol group

• That’s why we do anaerobic respiration to do something with this lactate we produce and we get lactic acid buildup

What rxn does alcohol dehydrogenase catalyze

Ethanol to acetaldehyde with the reduction of NAD+ to NADH and vice versa

How can we measure the rate of the ethanol to acetaldehyde rxn

Absorbance at 340 nm to measure NADH production per unit og time

The reduction of acetaldehyde to ethanol is very __ under std conditions

Favorable!

So if reduction of acetaldehyde is very favorable, why aren’t we always drunk?

• Acetaldehyde is rapidly removed from the body as CO_2, so it skews equilibrium

• Ratio of NADH to NAD+ is very LOW in the liver, so it changes the free energy change of the rxn

What is the 6th step in glycolysis and what cofactor does it use? What enzyme does it use?

• Conversion of glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate (adds a phosphate onto the carbonyl C)

• Uses NAD+ and reduces it to NADH

• Glyceraldehyde 3-phosphate dehydrogenase (GAPDH)

The active site of GAPDH comes loaded with…

NAD+

What important AA reside is in the active site of GAPDH?

A cysteine, but it is ionized bc the surrounding environment dropped its pKa. It’s now a good nucleophile. It becomes covalently attached to GAPDH

Mech of GAPDH

1. Cys attacks carbonyl of GAPDH and becomes covalently linked

2. - tetrahedral int reforms a carbonyl (oxidation) and a hydrogen is pushed onto NAD+, forming NADH

3. NADH leaves active site and is replaced by another molecule of NAD+.

4. A free phosphate attacks the carbonyl of the covalent int, which generated 1,1-bisphosphoglycerate and the Cys residue

What is the disease pellagra caused by?

Niacin deficiency

Can we make niacin?

We need to take it in by our diet

What happens with pellagra?

• Level of NADH is reduced bc we don’t have niacin to make the nicotinamide ring

• All dehydrogenases are inhibited

Corn has very low__

Niacin, makes it easier to get pellagra

Now, certain foods are fortified with __ to reduce prevalence of pellagra

Niacin

Flavin cofactors allow __ e- transfers

Single (can do e- transfer stepwise)

Flavin cofactors are__ bound to proteins, unlike NAD and NADP

Tightly, sometimes covalently

Flavoproteins can __ flavin reduction potential

tune

FAD can be reduced to form…

Alkenes from alkanes

Flavins are derived from what vitamin

Vitamin B2

A flow of e-s occurs when two half cells have different __ for e-s. The difference in e- __ results in an __

Affinity. Difference in e- affinity results in an electromotive force (emf)

What are the 4 ways that e- can be transferred from a donor to an acceptor

1. Directly as e-

2. As protons

3. As hydrides

4. Direct combination with oxygen

T or F: the oxidation of glucose occurs all in one step

False! Happens step-wise to control the release of energy

Coenzymes function __and therefore are always __

Catalytically, recycled

Since FAD and FMN are bound so tightly to their corresponding flavoprotein, they are actually considered __ __

prosthetic groups