Microbiology Exam 2 South Dakota State University

What is an enzyme?

A protein that acts as a biological catalyst, speeding up chemical reactions in cells.

What is a substrate?

The molecule that an enzyme binds to and acts upon during a reaction.

What is the active site?

The region on an enzyme where the substrate binds and the reaction occurs.

What happens to enzymes during a reaction?

They are not permanently changed and can be reused.

What determines enzyme specificity?

The shape and chemical properties of the active site.

What model describes how enzymes bind substrates?

The lock-and-key model.

What is activation energy?

The energy required to start a chemical reaction.

How do enzymes speed up reactions?

By lowering the activation energy required for the reaction.

Do enzymes change the equilibrium of a reaction?

No, they only speed up how quickly equilibrium is reached.

What is an apoenzyme?

The protein portion of an enzyme.

What is a cofactor?

A non-protein molecule required for some enzymes to function.

What is a coenzyme?

An organic cofactor often derived from vitamins.

examples of coenzymes.

NAD⁺, NADP⁺, FAD, FMN.

What is a holoenzyme?

An apoenzyme combined with its cofactor.

What are the four levels of protein structure?

Primary, secondary, tertiary, and quaternary.

At which protein structure level is the active site formed?

Tertiary structure.

What is protein denaturation?

Loss of protein structure due to factors like heat, pH changes, or chemicals.

What happens to enzyme activity at very high temperatures?

The enzyme denatures and activity decreases.

What happens to enzyme activity at very low temperatures?

Activity slows because molecular collisions decrease.

What is optimal temperature?

The temperature at which an enzyme works best.

How does pH affect enzyme activity?

Each enzyme has an optimal pH; activity decreases outside that range.

What happens when substrate concentration increases?

Reaction rate increases until enzymes become saturated.

What happens when enzyme concentration increases (with excess substrate)?

Reaction rate increases.

What is a competitive inhibitor?

A molecule that competes with the substrate for the enzyme’s active site.

What is a noncompetitive inhibitor?

A molecule that binds to a different site on the enzyme and changes its shape.

What is an allosteric site?

A regulatory site on an enzyme where molecules bind to alter enzyme activity.

What is feedback inhibition?

When the end product of a pathway inhibits an earlier enzyme in the pathway.

What are endoenzymes?

Enzymes that function inside the cell.

What are exoenzymes?

Enzymes secreted outside the cell to break down large molecules.

What are constitutive enzymes?

Enzymes that are always produced because they are needed for basic metabolism.

What are inducible enzymes?

Enzymes produced only when their substrate is present.

What is a metabolic pathway?

A series of enzyme-controlled reactions converting a starting compound into a final product.

What are prions?

Misfolded proteins that cause other proteins to misfold and lead to disease.

What are exotoxins?

Toxic proteins secreted by microorganisms.

What does botulinum toxin do?

Blocks release of acetylcholine at neuromuscular junctions, causing paralysis.

What are the main components of the cytoplasmic membrane?

Phospholipids and proteins.

What model describes the structure of the cell membrane?

The fluid mosaic model.

In a phospholipid bilayer, where are the hydrophilic heads located?

Facing outward toward water.

In a phospholipid bilayer, where are the hydrophobic tails located?

Facing inward away from water.

What is the main function of the cytoplasmic membrane?

Acts as a selective barrier controlling movement into and out of the cell.

Which molecules can easily diffuse across the membrane?

Small nonpolar molecules like O₂, CO₂, and N₂.

What type of molecules cannot easily cross the membrane without help?

Sugars, ions, amino acids, ATP, and large molecules.

What is simple diffusion?

Movement of molecules from high concentration to low concentration without energy.

What is facilitated diffusion?

Passive movement across a membrane using transport proteins.

What is osmosis?

Movement of water across a semipermeable membrane.

What is active transport?

Movement of molecules against the concentration gradient using energy.

What two energy sources can power active transport in bacteria?

ATP and proton motive force (PMF).

What is group translocation?

A transport process where a molecule is chemically modified during transport.

What is pinocytosis?

A type of endocytosis where cells take in liquid.

What is phagocytosis?

A type of endocytosis where cells engulf solid particles.

What structures digest materials brought into the cell during phagocytosis?

Lysosomes.

Where is the electron transport chain located in prokaryotes?

In the cell membrane.

What is the proton motive force (PMF)?

Energy generated by proton movement across a membrane used to produce ATP.

What is the function of ribosomes?

Protein synthesis (translation).

What size ribosomes do prokaryotes have?

70S ribosomes.

What two subunits make up prokaryotic ribosomes?

30S and 50S.

What size ribosomes do eukaryotes have?

80S ribosomes.

Why are ribosomes important in medicine?

Many antibiotics target bacterial ribosomes.

What is the nucleoid?

The region in a prokaryotic cell where the chromosome is located.

What type of chromosome do most bacteria have?

A single circular chromosome.

What are plasmids?

Small circular DNA molecules separate from the chromosome.

What advantages can plasmids give bacteria?

Antibiotic resistance or new metabolic abilities.

What are endospores?

Highly resistant dormant structures formed by some bacteria.

Why do bacteria form endospores?

To survive harsh environmental conditions.

Which bacteria commonly produce endospores?

Bacillus and Clostridium species.

What molecule helps make endospores heat resistant?

Calcium dipicolinate.

What triggers sporulation?

Nutrient depletion or harsh conditions.

What happens during germination?

An endospore returns to an active vegetative cell.