Biochemistry: NAD+ Electron Acceptance

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Questions and Answers

What does the acceptance of two electrons at once imply for NAD+?

NAD+ can exist with just one electron.

NAD+ can accept any number of electrons simultaneously.

There will never be a form of NAD+ that has only one electron. (correct)

NAD+ can only function in the presence of three electrons.

How many hydrogen atoms does the substrate contain?

One hydrogen atom.

Three hydrogen atoms.

Four hydrogen atoms.

Two hydrogen atoms. (correct)

Which statement about the electron acceptance of NAD+ is accurate?

NAD+ does not interact with substrates.

NAD+ can only exist in its oxidized form.

NAD+ must accept two electrons at once. (correct)

NAD+ accepts only positive ions.

What relationship exists between the number of electrons accepted and the form of NAD+?

There cannot be a form of NAD+ with only one electron. Signup and view all the answers

What does the acceptance of hydrogen atoms by the substrate indicate?

The substrate has two hydrogen atoms available for reactions. Signup and view all the answers

What role does histidine play in the electron transfer process described?

It pulls electrons from serine. Signup and view all the answers

What molecule is produced from the oxidation of alcohol in this process?

Aldehyde Signup and view all the answers

Which ion is transferred to NAD+ in this process?

Hydride ion (H-) Signup and view all the answers

Which part of the process does serine participate in?

It acts as an electron donor to histidine. Signup and view all the answers

What is the subsequent effect of histidine pulling electrons from serine?

The alcohol is oxidized into an aldehyde. Signup and view all the answers

What is formed when a hydrogen atom is present in the reaction?

NAD+ Signup and view all the answers

What distinguishes NAD+ from NADP+?

The presence of a phosphate group Signup and view all the answers

In what type of biochemical reactions is NAD+ typically involved?

Catabolism reactions Signup and view all the answers

Why is there a difference between NAD+ and NADP+?

It is due to organizational purposes only Signup and view all the answers

What part of the NAD+ or NADP+ molecule changes with the addition of a phosphate group?

The terminal phosphate Signup and view all the answers

What makes the intermediate radical form of FAD unstable?

One electron state Signup and view all the answers

Why is the intermediate radical form of FAD never found free in solution?

It is harmful and unstable Signup and view all the answers

In which state is FAD considered harmful?

When it is in its one electron state Signup and view all the answers

Which statement accurately describes the behavior of FAD in its intermediate radical form?

It is unstable and harmful in one electron state Signup and view all the answers

What characteristic of the intermediate radical form of FAD impacts its stability?

Its one electron configuration Signup and view all the answers

What role do both FAD and FMN serve in biochemical reactions?

They serve as prosthetic groups. Signup and view all the answers

How do FAD and FMN differ in their role in reactions?

Some reactions specifically use FAD while others use FMN. Signup and view all the answers

Which of the following statements is true regarding FAD and FMN?

Both accept two electrons. Signup and view all the answers

What is the nature of the bond between FAD, FMN, and enzymes?

They are tightly bound as prosthetic groups. Signup and view all the answers

In terms of their electron accepting capabilities, what is true about FAD and FMN?

FAD and FMN can both accept two electrons. Signup and view all the answers

What role does the molecule play when bound to enzymes?

It acts as a prosthetic group. Signup and view all the answers

How does the molecule facilitate its function when associated with enzymes?

By stabilizing its radical form. Signup and view all the answers

What is a key function of the molecule when interacting with enzymes?

To stabilize its radical form. Signup and view all the answers

Why is the stabilization of the radical form important in biochemical processes?

It allows for efficient electron transfer. Signup and view all the answers

Which statement accurately describes the interaction between the molecule and enzymes?

The molecule binds to enzymes and stabilizes its radical form. Signup and view all the answers

Study Notes

Biochemistry Study Notes

Sheet number: 30
Year: 2024
Authors: Tala Alkaiam; Saleen Abu Mushref; Nafez Abu Tarboush
Topic: Activation-Transfer Coenzyme
- 4-PLP: Inactive form is Pyridoxine (B6). Active form is Pyridoxal phosphate (PLP). Vitamin B6 oxidized into aldehyde, then phosphate is added.
- Function: Involved in the metabolism of amino acids via transamination reactions. Transaminases are crucial enzymes for amino acid synthesis and breakdown.
- Mechanism: Reactive aldehyde forms covalent bonds with amino groups. Ring nitrogen withdraws electrons from the bound amino acid.
Topic: Oxidation-Reduction Coenzymes
- Characteristics: Large number of coenzymes that don't form covalent bonds with substrates. Bind to the enzyme itself.
- Common examples: NAD+ (B3, Niacin); FAD (B2, Riboflavin); others work with metals to transfer single electrons to O2 (Vitamins E & C).
Topic: A- NAD+
- Structure & Function: Derived from Niacin (B3). Its functional group (C opposite to N) accepts a hydride ion (H-) from the substrate. This means it accepts two electrons at once.
- Mechanism: The substrate has two hydrogen atoms. Dissociates into H+ which dissolves and a keto group (C=O) is formed. ADP part of the molecule binds tightly. Different from NADP+ (structural difference in substance attached to Adenine's ribose).
Topic: B- FAD
- Structure & Function: Derived from Riboflavin (B2). Flavoproteins are conjugated proteins containing Flavin derivatives (FAD & FMN), involved in oxidation-reduction reactions. FAD and FMN are tightly bound prosthetic groups to enzymes.
- Mechanism: Accepts two electrons sequentially unlike NAD+. In first step, accepts one electron to form a radical, then second electron to become fully reduced as FADH2.
Topic: Alcohol Dehydrogenase (ADH)
- Function: Removes hydrogen from alcohol to oxidize it to an aldehyde.
- Mechanism (crucial steps): Histidine pulls electrons from serine, which pulls electrons from alcohol. Electrons are transferred (as a hydride ion, H-) to NAD+. Zinc stabilizes the oxyanion, ensuring reaction efficiency.
Topic: Metalloenzymes:
- Role of metal ions: Usually incorporated during synthesis, affects structure and/or catalytic mechanism.
- Example: Liver alcohol dehydrogenase (dimer); 2 Zn2+ in each monomer, one for structural support and catalytic role. Carbonic anhydrase; Zinc atom is bound to four or more groups.
Topic: Enzyme Kinetics
- General behavior: Enzymes can follow zero-order or first-order kinetics. Reactions increase with substrate concentration until all active sites are saturated. Limiting factor is active sites.
- Characteristics/details: Initially (lower substrate concentrations); reaction follows first-order kinetics, rate increases with substrate. At higher concentrations; rate plateaus (zero-order kinetics). Vmax (maximal velocity) is reached when all active sites are occupied.
Topic: Reaction Rate Law.
- Definition: Proportional to the concentration of reactants.
- Mathematical relationship: Rate = -Δ[A]/Δt, or k[A] in simpler cases.
- Rate constants (k): Measure of how quickly a reaction proceeds; influenced by activation energy (Ea)
Topic: Water-Soluble Vitamins (listed by name and coenzyme)
- Details: Each vitamin is shown in a table with coenzyme or active form/primary biofunction.
Topic: Catalytic Metals
- Role: Metals function in enzymes either as tightly bound components (metalloenzymes) or loosely bound components (metal-activated enzymes).
- Mechanism: Act as electrophiles, attracting electrons. Specific examples include Mg2+, Mn2+, Ca2+, and K+. Example: Phosphofructokinase (Mg2+ required).

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Description

This quiz explores the role of NAD+ in biochemical reactions, particularly focusing on its ability to accept electrons and the implications for substrates. Test your understanding of electron acceptance, hydrogen atoms, and the relationship between electron transfer and NAD+ forms.