MICRO EXAM 2 Study 1

[L7 Growth] What is microbial growth usually referring to?

An increase in the number of microbial cells, not necessarily an increase in the size of one cell.

[L7 Growth] What is binary fission?

A type of asexual reproduction in which one cell divides into two daughter cells.

[L7 Growth] What must happen before a bacterial cell divides by binary fission?

It grows, replicates its DNA, separates the chromosome copies, and forms a division septum.

[L7 Growth] What does generation time mean?

The time required for a microbial population to double under specific conditions.

[L7 Growth] What is the relationship between a short generation time and growth rate?

A shorter generation time means the population doubles more quickly.

[L7 Growth] What happens during the lag phase of a growth curve?

Cells adjust to the new environment and make needed molecules; cell number changes little.

[L7 Growth] Why can cells be metabolically active during the lag phase?

They are adapting, repairing, and preparing to divide even though the population is not increasing much.

[L7 Growth] What defines the log or exponential phase?

Cells divide at a relatively constant, rapid rate, so the population increases exponentially.

[L7 Growth] Why are cells in log phase often most susceptible to antibiotics that target cell-wall synthesis?

They are actively making new cell walls as they grow and divide.

[L7 Growth] What causes a population to enter stationary phase?

Nutrients become limited and waste accumulates, so new cells are produced at about the rate cells die.

[L7 Growth] What characterizes the death or decline phase?

Viable cell numbers decrease because cells die faster than new cells are produced.

[L7 Growth] What does a standard bacterial growth curve plot?

The number of viable cells against time.

[L7 Growth] What is a colony-forming unit (CFU)?

A viable cell or group of cells that can produce a visible colony on solid medium.

[L7 Growth] What is the purpose of a viable plate count?

To estimate the number of living, culturable microorganisms in a sample.

[L7 Growth] Why are plates with too many colonies difficult to count accurately?

Colonies overlap or merge, making individual colonies hard to distinguish.

[L7 Growth] What is turbidity used to estimate?

Microbial growth by measuring how cloudy a liquid culture has become; it can include live and dead cells.

[L7 Growth] How does direct microscopic counting differ from viable plate counting?

Microscopic counting can include dead cells; viable plate counting estimates cells able to grow into colonies.

[L7 Growth] What is a psychrophile?

A microorganism adapted to cold conditions, with a low optimum growth temperature.

[L7 Growth] What is a psychrotroph?

A microorganism that can grow in the cold, including refrigeration temperatures, but usually grows best at warmer temperatures.

[L7 Growth] What temperature group includes many human pathogens?

Mesophiles, which grow best at moderate temperatures, commonly near body temperature.

[L7 Growth] What is a thermophile?

A microorganism whose optimum growth temperature is high compared with that of mesophiles.

[L7 Growth] What is a hyperthermophile?

A microorganism that grows optimally at extremely high temperatures.

[L7 Growth] What are acidophiles and alkaliphiles adapted to?

Acidophiles grow best at low pH; alkaliphiles grow best at high pH.

[L7 Growth] What is an obligate aerobe?

An organism that requires oxygen for growth.

[L7 Growth] What is an obligate anaerobe?

An organism for which oxygen is harmful or lethal.

[L7 Growth] How does a facultative anaerobe behave with oxygen present?

It can grow with or without oxygen but usually grows better when oxygen is available.

[L7 Growth] What distinguishes a microaerophile from an obligate aerobe?

A microaerophile needs oxygen at a lower concentration than is found in normal air.

[L7 Growth] What does an aerotolerant anaerobe do with oxygen?

It does not use oxygen for respiration but tolerates its presence.

[L7 Growth] What happens to many cells in a hypertonic environment?

Water leaves the cell; in cells with walls, the membrane and cytoplasm may pull away from the wall in plasmolysis.

[L7 Growth] What is the difference between enriched and selective media?

Enriched media add nutrients for demanding microbes; selective media inhibit some organisms while allowing others to grow.

[L8 Control] What is sterilization?

The destruction or removal of all microbial life, including endospores.

[L8 Control] How does commercial sterilization differ from complete sterilization?

It aims to destroy dangerous organisms such as Clostridium botulinum endospores in food, not necessarily every organism.

[L8 Control] What is disinfection?

The destruction or removal of many or all pathogens on inanimate objects; endospores may remain.

[L8 Control] What is antisepsis?

Using antimicrobial chemicals on living tissue to reduce or remove microbes.

[L8 Control] What is sanitization?

Reducing microbial numbers to public-health standards, such as on eating utensils.

[L8 Control] What is degerming?

Removing microbes from a limited area, often by mechanical cleaning such as wiping skin with alcohol.

[L8 Control] What is asepsis?

The absence of significant microbial contamination.

[L8 Control] What is the difference between bactericidal and bacteriostatic treatment?

Bactericidal treatment kills bacteria; bacteriostatic treatment stops or slows their growth.

[L8 Control] Why are bacterial endospores difficult to destroy?

They are dormant structures with protective layers and unusually high resistance to heat, chemicals, and drying.

[L8 Control] How does an autoclave kill microbes?

It uses steam under pressure; a common cycle is about 121°C at 15 psi for around 15 minutes, depending on the load.

[L8 Control] Why is moist heat generally more effective than dry heat at the same temperature?

Moist heat transfers energy efficiently and denatures proteins effectively.

[L8 Control] What is the purpose of pasteurization?

To reduce spoilage organisms and pathogens in foods and drinks without sterilizing them.

[L8 Control] What does high-temperature short-time (HTST) pasteurization commonly use for milk?

About 72°C for 15 seconds.

[L8 Control] What is filtration useful for when heat would damage a material?

Removing microbes from heat-sensitive liquids or air by passing them through a filter.

[L8 Control] How does ionizing radiation damage microbial cells?

It creates ions and reactive molecules that damage DNA and other cell components.

[L8 Control] How does ultraviolet radiation harm microorganisms?

It damages DNA, including by causing abnormal bonds between adjacent pyrimidines.

[L8 Control] What is the main limitation of ultraviolet radiation for sterilizing objects?

It has poor penetrating power, so shaded areas or material beneath surfaces may not be treated.

[L8 Control] What is phenol coefficient testing designed to compare?

The effectiveness of a disinfectant relative to phenol under specified test conditions.

[L8 Control] What do alcohols such as ethanol do to microbes?

They denature proteins and disrupt lipid membranes; they are not reliable endospore killers.

[L8 Control] Why is 70% alcohol often more effective than nearly pure alcohol for disinfection?

Water slows evaporation and helps the alcohol penetrate and denature proteins.

[L8 Control] What is a common use of halogens such as chlorine?

Disinfecting water and surfaces; chlorine can oxidize cellular components.

[L8 Control] What does selective toxicity mean in antimicrobial therapy?

The drug harms the microbe more than the host by targeting a microbial feature or process.

[L8 Control] Why do antibiotics that target peptidoglycan usually affect bacteria more than human cells?

Human cells do not have peptidoglycan cell walls.

[L8 Control] How do drugs that inhibit bacterial ribosomes work?

They interfere with protein synthesis at bacterial ribosomes, which differ from eukaryotic cytoplasmic ribosomes.

[L8 Control] What is a narrow-spectrum antimicrobial?

A drug effective against a limited group of microorganisms.

[L8 Control] What is a broad-spectrum antimicrobial?

A drug effective against a wide range of microorganisms.

[L8 Control] What is the minimum inhibitory concentration (MIC)?

The lowest concentration of a drug that visibly inhibits microbial growth under test conditions.

[L8 Control] What is antimicrobial resistance?

The ability of a microbe to survive or grow despite a drug that would normally inhibit or kill it.

[L8 Control] How can a bacterium resist an antibiotic by drug inactivation?

It produces an enzyme that chemically destroys or modifies the drug, such as a beta-lactamase.

[L8 Control] How can efflux pumps contribute to resistance?

They transport an antimicrobial out of the cell, lowering its intracellular concentration.

[L9 Genetics] What is genetics?

The study of heredity, gene expression, and how genetic information changes.

[L9 Genetics] What is a genome?

The complete set of genetic material in a cell or organism.

[L9 Genetics] How is a typical bacterial chromosome organized?

As one main circular, double-stranded DNA molecule located in the nucleoid region.

[L9 Genetics] What is a plasmid?

A small, usually circular DNA molecule separate from the bacterial chromosome that can replicate independently.

[L9 Genetics] Why can plasmids be important even if they are not essential for basic survival?

They may carry useful genes, such as genes for antibiotic resistance, toxins, or specialized metabolism.

[L9 Genetics] What is a gene?

A DNA sequence that contains information to produce a functional product, usually a protein or RNA.

[L9 Genetics] How do genotype and phenotype differ?

Genotype is the genetic makeup; phenotype is the observable traits produced through gene expression and environment.

[L9 Genetics] What enzyme unwinds and separates DNA strands during replication?

Helicase separates the strands by disrupting the hydrogen bonds between bases.

[L9 Genetics] What does DNA polymerase do during replication?

It adds complementary DNA nucleotides to build a new strand, extending from a primer.

[L9 Genetics] Why is DNA replication described as semiconservative?

Each new DNA double helix contains one original strand and one newly made strand.

[L9 Genetics] What is the purpose of a primer in DNA replication?

It provides a starting point with a free 3′ end for DNA polymerase to extend.

[L9 Genetics] What is the central flow of genetic information in a typical cell?

DNA is transcribed into RNA, and RNA can be translated into protein.

[L9 Genetics] What is transcription?

Making an RNA copy from a DNA template using RNA polymerase.

[L9 Genetics] What is translation?

Using the codons in mRNA to assemble amino acids into a protein at a ribosome.

[L9 Genetics] What is the job of mRNA?

It carries the coding instructions from DNA to the ribosome.

[L9 Genetics] What is the job of tRNA during translation?

It carries a specific amino acid and uses its anticodon to pair with an mRNA codon.

[L9 Genetics] What is the role of rRNA?

It forms a major structural and functional part of ribosomes and helps catalyze protein synthesis.

[L9 Genetics] Which RNA base is used instead of thymine?

Uracil (U).

[L9 Genetics] What is a codon?

A sequence of three nucleotides in mRNA that specifies an amino acid or a stop signal.

[L9 Genetics] What is a mutation?

A change in the nucleotide sequence of genetic material.

[L9 Genetics] How can a point mutation affect a protein?

It may change one amino acid, create a stop codon, or have no effect on the amino acid sequence.

[L9 Genetics] What is a frameshift mutation?

An insertion or deletion of nucleotides not in multiples of three that shifts how codons are read.

[L9 Genetics] What is an operon?

A group of genes controlled together under shared regulatory elements, common in bacteria.

[L9 Genetics] When is the lac operon generally turned on?

When lactose is present, lactose-derived inducer inactivates the repressor so the genes for lactose use can be transcribed.

[L9 Genetics] What normally happens to the lac operon when lactose is absent?

The repressor binds the operator and blocks transcription of the structural genes.

[L9 Genetics] How does a repressible operon such as the arginine operon behave?

It is generally on until enough end product accumulates and activates a repressor that shuts transcription off.

[L9 Genetics] What is conjugation?

Direct transfer of DNA between bacterial cells in contact, often involving a pilus and a conjugative plasmid.

[L9 Genetics] What is transformation?

A cell takes up free DNA from its surroundings and may incorporate it into its own genetic material.

[L9 Genetics] What is transduction?

A bacteriophage transfers bacterial DNA from one cell to another.

[L9 Genetics] What are transposons?

Mobile DNA segments that can move between locations in a chromosome or between chromosomes and plasmids.

[L10 Engineering] How do bioengineering and biotechnology differ?

Bioengineering deliberately modifies an organism's genome; biotechnology uses organisms or their pathways to make useful products.

[L10 Engineering] What does DNA denaturation mean in genetic techniques?

Heat or chemicals disrupt base-pair hydrogen bonding so the two DNA strands separate.

[L10 Engineering] What happens when denatured DNA is slowly cooled under suitable conditions?

Complementary strands can anneal and hydrogen-bond again.

[L10 Engineering] What is a restriction endonuclease?

An enzyme that recognizes a particular DNA sequence and cuts the DNA at or near that site.

[L10 Engineering] What is a palindromic DNA recognition sequence?

A sequence whose 5′-to-3′ reading on one strand matches the 5′-to-3′ reading on the complementary strand.

[L10 Engineering] What are sticky ends?

Short single-stranded overhangs produced by staggered DNA cuts that can base-pair with matching ends.

[L10 Engineering] What are blunt ends?

DNA ends cut straight across without single-stranded overhangs.

[L10 Engineering] What is the function of DNA ligase in recombinant DNA work?

It joins DNA fragments by sealing the sugar-phosphate backbone.

[L10 Engineering] What is recombinant DNA?

DNA made by combining genetic material from different sources.

[L10 Engineering] What is a cloning vector?

A DNA carrier, such as a plasmid, used to deliver and replicate inserted DNA in a host cell.