(2) Chapters 5, 6, 7 Textbook Questions

What happens when a substrate binds to an enzyme?

The substrate is converted into product.

What determines where a competitive inhibitor binds?

It has a similar shape to the substrate and fits into the active site.

Why can't a competitive inhibitor and substrate bind at the same time?

They compete for the same active site.

Can increasing substrate concentration overcome competitive inhibition?

Yes, in many cases.

Can increasing substrate concentration overcome noncompetitive inhibition?

No, because the enzyme's shape has changed.

What is an allosteric site?

A site other than the active site where regulators or inhibitors bind.

What happens to enzymes at temperatures above their optimum?

They denature and lose function.

What causes the reaction rate to level off as substrate concentration increases?

All enzyme active sites become occupied (enzyme saturation).

What is the purpose of oxidation in metabolism?

To release energy from molecules.

What is the purpose of reduction in metabolism?

To gain electrons and store energy.

Which process produces more ATP: respiration or fermentation?

Respiration.

Why does fermentation produce less ATP?

It does not use an electron transport chain.

What is the electron transport chain used for?

Generating ATP through oxidative phosphorylation.

What is the purpose of glycolysis?

To break down glucose into pyruvate while producing ATP and NADH.

What molecule carries high-energy electrons during metabolism?

NADH.

What molecule accepts electrons to become NADH?

NAD⁺.

What is the relationship between oxidation and reduction?

Oxidation and reduction always occur together.

During binary fission, what happens first?

The chromosome replicates.

What happens after DNA replication during binary fission?

The DNA is separated as the cell elongates.

What forms between the two daughter cells during binary fission?

A new cell wall (septum).

What is a generation time?

The time required for one cell division.

Formula for bacterial population growth?

Initial cells × 2ⁿ.

How many generations occur in 7 hours if generation time is 1 hour?

7 generations.

Why is carbon considered the backbone of life?

It forms the framework of organic molecules.

What cell structures require phosphorus?

ATP, DNA, RNA, and phospholipids.

Which macronutrient is found in amino acids containing sulfur?

Sulfur.

Why do aerobic organisms need catalase or peroxidase?

To detoxify hydrogen peroxide.

What toxic compound does superoxide dismutase remove?

Superoxide radicals.

What toxic compound does catalase remove?

Hydrogen peroxide.

What is the purpose of filtration in microbial counts?

To physically trap microorganisms for counting.

What does turbidity measure?

Cloudiness caused by microbial growth.

Why is dry weight considered an indirect measurement?

It estimates biomass instead of counting cells.

Why does refrigeration slow microbial growth?

Low temperature slows enzyme activity.

Why does freezing preserve food?

Most microbes become dormant.

Why can petroleum supply carbon but not enough nitrogen?

Petroleum lacks sufficient nitrogen-containing nutrients.

Why is ATP production impossible without phosphorus?

ATP molecules contain phosphate groups.

What kind of environment do psychrophiles prefer?

Cold temperatures.

What kind of environment do halophiles require?

High salt concentrations.

What does an obligate aerobe require?

Oxygen.

What temperature range do mesophiles prefer?

Moderate temperatures (around 20–45°C).

Why is reducing media used?

To remove oxygen for anaerobic growth.

What is selective media?

Media that favors growth of certain microbes while inhibiting others.

What is differential media?

Media that distinguishes organisms based on biochemical reactions.

What is enrichment media?

Media that enhances growth of a desired organism.

What is complex media?

Media containing nutrients of unknown exact composition.

What causes free radicals during gamma radiation?

Ionization of water molecules.

Why are free radicals harmful?

They damage DNA and other cellular components.

What DNA damage is caused by UV light?

Thymine dimers.

What is sterilization?

The destruction of all microorganisms, including endospores.

What is disinfection?

Destruction of most pathogenic microorganisms but not necessarily spores.

What is pasteurization?

Heat treatment that reduces microbial numbers without sterilizing.

What is autoclaving?

Sterilization using steam under pressure.

Why is moist heat more effective than dry heat?

Moisture transfers heat more efficiently.

How does high osmotic pressure inhibit microbes?

It causes water to leave the cell (plasmolysis).

Why are molds more likely than bacteria to grow in sugary foods?

Molds tolerate high osmotic pressure.

What is a use-dilution test?

A test that measures disinfectant effectiveness at different dilutions.

What does a higher use-dilution value indicate?

A more effective disinfectant.

Why are quaternary ammonium compounds less effective against Gram-negative bacteria?

The outer membrane reduces disinfectant penetration.

Which organisms may survive and grow in quaternary ammonium compounds?

Pseudomonas species.

Which sterilization method is used for heat-sensitive equipment?

Ethylene oxide gas.

Why can't autoclaving be used on many plastics?

High heat damages them.

Which preservation chemicals are commonly added to foods?

Organic acids.

Which microbial control method physically removes microbes rather than killing them?

Membrane filtration.

Does lyophilization kill microorganisms?

No; it preserves them.

Does deep-freezing kill microorganisms?

Usually no; it inhibits growth.

Which radiation is bactericidal?

Ionizing radiation.

What does bactericidal mean?

Kills bacteria.

What does bacteriostatic mean?

Stops bacterial growth without killing bacteria.