(1) Chapters 5, 6, 7 Textbook questions

What is the active site of an enzyme?

The region where the substrate binds and the reaction occurs.

What happens when an enzyme binds its substrate?

The substrate is transformed into product.

Where does a competitive inhibitor bind?

The enzyme's active site.

What effect does a competitive inhibitor have?

Prevents the substrate from binding.

Where does a noncompetitive inhibitor bind?

An allosteric site (not the active site).

What effect does a noncompetitive inhibitor have?

Changes the enzyme's shape so the active site no longer functions properly.

What is feedback inhibition?

The end product of a pathway inhibits an earlier enzyme to stop further production.

How does increasing substrate concentration affect enzyme activity?

Reaction rate increases until enzymes become saturated, then levels off.

How does increasing temperature affect enzyme activity?

Rate increases until the optimum temperature, then rapidly decreases due to enzyme denaturation.

What is oxidation?

Loss of electrons.

What is reduction?

Gain of electrons.

What is the final electron acceptor in aerobic respiration?

Oxygen (O₂).

What is the final electron acceptor in anaerobic respiration?

An inorganic molecule other than oxygen.

What is the major difference between respiration and fermentation?

Respiration uses an electron transport chain; fermentation does not.

What type of reactions are glycolysis and photophosphorylation?

Oxidation reactions.

Which molecule is reduced when acetaldehyde + NADH → ethanol + NAD⁺?

Acetaldehyde.

Which molecule contains the most energy for a cell?

Glucose.

Which E. coli culture produces the most lactic acid?

Anaerobic culture (without oxygen).

Which E. coli culture produces the most ATP?

Aerobic culture (with oxygen).

Which culture uses the most glucose?

Anaerobic culture because fermentation is less efficient.

What is binary fission?

Cell elongation, chromosome replication, DNA separation, membrane invagination, cell wall formation, and division into two daughter cells.

What does CHONPS stand for?

Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorus, Sulfur.

Why is carbon important?

Backbone of organic molecules.

Why is hydrogen important?

Source of electrons and component of organic molecules.

Why is oxygen important?

Component of organic molecules and electron acceptor in aerobes.

Why is nitrogen important?

Required for amino acids and proteins.

Why is phosphorus important?

Component of phospholipids, nucleic acids, and ATP.

Why is sulfur important?

Component of certain amino acids.

What does catalase do?

Breaks hydrogen peroxide into water and oxygen.

What does peroxidase do?

Breaks down hydrogen peroxide.

What does superoxide dismutase (SOD) do?

Converts superoxide radicals into oxygen and hydrogen peroxide.

What are direct methods of measuring microbial growth?

Direct microscopic count, plate count, filtration, and most probable number (MPN).

What are indirect methods of measuring microbial growth?

Turbidity, metabolic activity, and dry weight.

Why do refrigeration and freezing preserve food?

Low temperatures slow or stop microbial growth.

How many S. aureus cells are present after 7 hours if 6 cells divide every hour?

768 cells.

Why are nitrogen and phosphorus added after oil spills?

To provide nutrients needed for proteins, phospholipids, nucleic acids, and ATP.

Describe a planet inhabited by psychrophiles, obligate halophiles, and obligate aerobes.

Cold, salty, and oxygen-rich.

What temperature is most likely to kill a mesophile?

60°C.

Which is NOT a characteristic of biofilms?

Iron deficiency.

Which medium would NOT be used to culture aerobes?

Reducing media.

Which organism has peroxidase and SOD but lacks catalase?

Aerotolerant anaerobe.

How does gamma radiation kill microorganisms?

Direct DNA damage and formation of free radicals.

How does ultraviolet (UV) radiation kill microorganisms?

Formation of thymine dimers in DNA.

What is the difference between bactericidal and bacteriostatic agents?

Bactericidal agents kill bacteria; bacteriostatic agents stop bacterial growth.

Why doesn't viable cell count immediately drop after adding a bactericidal agent?

Cells do not all die instantly.

How are autoclaving, hot air, and pasteurization examples of equivalent treatments?

Higher temperature and moisture reduce the time needed to kill microorganisms.

How do salt and sugar preserve food?

They create a hypertonic environment that removes water from cells.

Why are salt and sugar considered physical methods of microbial control?

They alter osmotic pressure rather than directly damaging cells.

Give an example of a food preserved with sugar.

Jelly or jam.

Give an example of a food preserved with salt.

Meat.

Why can molds grow in jelly?

Molds tolerate high osmotic pressure better than bacteria.

Which disinfectant is preferable: A (1:2) or B (1:10,000)?

Disinfectant B because it remains effective even when greatly diluted.

Why did burn patients acquire Pseudomonas infections despite cleaning with quats?

Quats are less effective against Gram-negative bacteria, and Pseudomonas can survive and even grow in quats.

Which bacteria have porins, resist triclosan, and survive in quats?

Pseudomonas and Burkholderia.

Which method does NOT kill endospores?

Pasteurization.

Which sterilizes plastic Petri dishes and mattresses best?

Ethylene oxide.

Which cannot sterilize heat-sensitive solutions in plastic containers?

Autoclaving.

Which chemical is commonly used to control microbial growth in foods?

Organic acids.

Which disinfectant was most effective in the use-dilution test?

Disinfectant A.

Which disinfectants were bactericidal?

A, C, and D.

Which is NOT a characteristic of quaternary ammonium compounds?

Sporicidal.

Which method is most likely to be bactericidal?

Ionizing radiation.

Competitive inhibitor vs. noncompetitive inhibitor

Competitive binds the active site; noncompetitive binds an allosteric site and changes enzyme shape.

Aerobic respiration vs. anaerobic respiration

Aerobic uses oxygen as the final electron acceptor; anaerobic uses another inorganic molecule.

Respiration vs. fermentation

Respiration uses an electron transport chain; fermentation does not.

Catalase reaction

H₂O₂ → H₂O + O₂.

Superoxide dismutase reaction

Superoxide → O₂ + H₂O₂.

Three enzymes that detoxify oxygen radicals

Catalase, peroxidase, superoxide dismutase.

Four direct methods of microbial growth measurement

Direct microscopic count, plate count, filtration, most probable number.

Three indirect methods of microbial growth measurement

Turbidity, metabolic activity, dry weight.

Three key radiation facts

Gamma radiation causes DNA breaks; UV causes thymine dimers; ionizing radiation is bactericidal.

Three common food preservation methods

Salt, sugar, refrigeration.