351 Bio - Exam 3 (Lectures 19-25)

Nutrients

Supply of monomers (or precursors of) required by cells for growth

Macronutrients

Nutrients required in large amounts

Micronutrients

Nutrients required in trace amounts

What are the 8 main Macronutrients

Carbon, Nitrogen, Phosphorus, Sulfur, Potassium, Magnesium, Calcium, Sodium

What macronutrient is required by ALL cells and is a Major element in ALL classes of macromolecules

Carbon

The typical bacterial cell is made of 50% of what macromolecule

Carbon

Heterotrophs uses

organic carbon

Autotrophs uses

carbon dioxide (CO2)

What is a key element in proteins, nucleic acids, and many more cell constituents

Nitrogen

The typical bacterial cell is made of 13% of what macromolecule

Nitrogen

What is the function of Phosphorus (P) in cells?

It’s needed for the synthesis of nucleic acids and phospholipids.

What is the role of Sulfur (S) in cells?

It’s a component of sulfur-containing amino acids (cysteine and methionine), vitamins (thiamine, biotin, lipoic acid), and coenzyme A.

Which amino acids contain Sulfur (S)?

Cysteine and methionine.

Which element is required by enzymes for activity?

Potassium (K)

What is the function of Magnesium (Mg) in microbial cells?

It stabilizes ribosomes, membranes, and nucleic acids, and is required by many enzymes.

Which element helps stabilize ribosomes, membranes, and nucleic acids?

Magnesium (Mg)

What is the function of Calcium (Ca) in microbes?

It helps stabilize cell walls and contributes to the heat stability of endospores.

Which element plays a key role in the heat stability of endospores?

Calcium (Ca)

What is the role of Sodium (Na) in microbes?

It’s required by some microbes, especially marine microbes.

What is the function of Iron (Fe) in cells?

It’s a key component of cytochromes and FeS proteins involved in electron transport.

Growth factors

Organic compounds required in small amounts by certain organisms

What are some examples of growth factors

Vitamins, amino acids, purines, and pyrimidines.

Which type of compound is the most commonly required growth factor?

Vitamins

What is the main function of vitamins in cells?

Most function as coenzymes.

What is a culture media?

Nutrient solutions used to grow microbes in the laboratory.

What is defined media?

Media where the precise chemical composition is known.

What is complex media?

Media composed of digests of chemically undefined substances, such as yeast or meat extracts.

What is enriched media used for?

It contains complex media plus extra nutrients to support nutritionally demanding organisms.

What is selective media?

Media that contains compounds that inhibit the growth of some microbes but not others.

What is differential media?

Media that contains an indicator (usually a dye) to detect specific chemical reactions during growth.

What is a pure culture?

A culture containing only a single kind of microbe.

What are contaminants in a culture?

Unwanted organisms that are not part of the intended culture.

In what types of media(s) can cells be grown?

Cells can be grown in liquid or solid culture media.

How are solid media prepared?

By adding a gelling agent such as agar or gelatin.

What do cells form when grown on solid media?

Isolated masses called colonies.

What is metabolism?

The sum total of all chemical reactions that occur in a cell.

What are catabolic reactions (catabolism)?

Energy-releasing metabolic reactions.

What are anabolic reactions (anabolism)?

Energy-consuming metabolic reactions, usually involved in biosynthesis.

What are chemoorganotrophs?

Microorganisms that obtain energy from organic compounds.

What are chemolithotrophs?

Microorganisms that obtain energy from inorganic compounds.

What are phototrophs?

Microorganisms that obtain energy from light.

What does the suffix “-troph” mean?

To eat

Energy

units of kilojoules (kJ), a unit for heat energy, some energy is lost as heat

What is free energy (G)?

The energy released that is available to do work.

What does ΔG⁰′ represent?

The change in free energy during a reaction under standard conditions.

What does it mean when a reaction has a negative ΔG⁰′?

It releases free energy (exergonic reaction).

What does it mean when a reaction has a positive ΔG⁰′?

It requires energy (endergonic reaction).

What is free energy of formation (Gf⁰)?

The energy released or required during the formation of a molecule from its elements.

What is the formula to calculate the change in free energy (ΔG⁰′) for a reaction?

ΔG⁰′ = Gf⁰[C + D] – Gf⁰[A + B].

For the reaction A + B → C + D, what does ΔG⁰′ tell us?

Whether the reaction releases or requires energy under standard conditions.

Why is ΔG⁰′ not always a good estimate of actual free-energy changes?

Because it only applies under standard conditions, not the real conditions found in cells.

What does ΔG represent?

The actual free-energy change that occurs under real (nonstandard) conditions.

What is the formula for calculating actual free-energy change (ΔG)?

ΔG = ΔG⁰′ + RT ln K

What information do free-energy calculations not provide?

They do not indicate the rate of a reaction.

What is activation energy?

The energy required to bring all molecules in a chemical reaction into the reactive state.

Why is catalysis important in biochemical reactions?

It lowers the activation energy barrier, allowing reactions to occur faster.

What is a catalyst?

A substance that lowers the activation energy of a reaction and increases the reaction rate without affecting the reaction’s energetics or equilibrium.

How does a catalyst affect activation energy?

It lowers the activation energy needed for a reaction to occur.

How does a catalyst affect the equilibrium of a reaction?

It does not change the equilibrium point or overall energetics—only the rate.

What are enzymes?

Biological catalysts, usually proteins (though some are RNA), that speed up biochemical reactions.

Are all enzymes proteins?

Most are proteins, but some are catalytic RNAs (ribozymes).

How specific are enzymes?

Enzymes are highly specific to their substrates

How does the size of an enzyme compare to its substrate?

Enzymes are generally larger than their substrates.

What types of weak bonds do enzymes typically rely on?

Hydrogen bonds, van der Waals forces, and hydrophobic interactions.

What is the active site of an enzyme?

The region on the enzyme where the substrate binds.

What do many enzymes contain that help in catalysis but are not substrates?

Small nonprotein molecules such as prosthetic groups or coenzymes.

What are prosthetic groups?

Nonprotein molecules that bind tightly, often covalently and permanently, to enzymes.

Give an example of a prosthetic group.

The heme group in cytochromes.

What are coenzymes?

Small, loosely bound nonprotein molecules that assist enzymes during catalysis.

How are coenzymes different from prosthetic groups?

Coenzymes bind loosely and reversibly, while prosthetic groups bind tightly and often permanently.

What are most coenzymes derived from?

Vitamins

Give an example of a common coenzyme.

NAD⁺/NADH.

What is the role of energy from oxidation–reduction (redox) reactions in cells?

It is used to synthesize energy-rich compounds, such as ATP.

How do redox reactions occur?

In pairs, as two half-reactions: one oxidation and one reduction.

What is an electron donor?

The substance that is oxidized in a redox reaction; also called the energy source.

What is an electron acceptor?

The substance that is reduced in a redox reaction.

In a redox reaction, what happens to the electron donor and acceptor?

The donor loses electrons (oxidized), and the acceptor gains electrons (reduced).

What is reduction potential (E0′)?

The tendency of a substance to donate electrons, expressed in volts (V).

Can substances act as electron donors or acceptors in different situations?

Yes, depending on the redox couple they are involved in.

In a redox reaction, which substance donates electrons?

The reduced substance of a redox couple with a more negative E0′.

Which substance accepts electrons in a redox reaction?

The oxidized substance of a redox couple with a more positive E0′.

What does the redox tower represent?

The range of possible reduction potentials for various substances.

In the redox tower, which substance donates electrons?

The reduced substance at the top of the tower.

In the redox tower, which substance accepts electrons?

The oxidized substance at the bottom of the tower.

How is the amount of energy released related to the electron “drop” in the redox tower?

The farther the electrons drop, the greater the energy released; ΔE0′ is proportional to ΔG0′.

What role do electron carriers play in redox reactions?

They act as intermediates, transferring electrons between reactions.

Into what two classes are electron carriers divided?

Prosthetic groups (attached to enzymes) and coenzymes (diffusible).

Give examples of common electron carriers.

NAD⁺ and NADP⁺

Can electrons exist alone in solution?

No, electrons do not exist freely in solution.

What is the redox role of NAD⁺ and NADH?

NAD⁺ is reduced to NADH by accepting electrons; NADH can then donate electrons in other reactions.

What is meant by reducing power in cells?

The ability of molecules like NAD⁺/NADH to transfer electrons and protons to facilitate redox reactions.

Do NAD⁺/NADH get consumed in redox reactions?

No, they are recycled and can be used repeatedly.

Are NAD⁺/NADH used in many types of reactions?

Yes, they are common electron carriers in diverse reactions.

What is the primary difference between NAD⁺/NADH and NADP⁺/NADPH?

NADP⁺/NADPH is more commonly used in anabolic (biosynthesis) pathways.

What does NAD⁺/NADH cycling refer to?

The continuous oxidation and reduction of NAD⁺ to NADH and back, enabling ongoing electron transfer.

Where is chemical energy released in redox reactions primarily stored?

In certain phosphorylated compounds, such as ATP.

Besides phosphorylated compounds, where else is chemical energy stored in cells?

In coenzyme A (CoA).

What is the main purpose of energy-rich compounds?

To store and transfer energy for cellular processes.

How is long-term energy stored in cells?

As insoluble polymers that can be oxidized to generate ATP.

Name examples of long-term energy storage compounds in prokaryotes.

Glycogen, poly-β-hydroxybutyrate (PHB), other polyhydroxyalkanoates (PHA), and elemental sulfur.