MICRO 2 Study 2

| L7 Growth] How does simple diffusion move molecules across a membrane?

Molecules move from higher concentration to lower concentration without the cell using energy.

L7 Growth] What does it mean when diffusion reaches equilibrium?

There is no net movement in one direction because molecules are spread evenly, although they still move randomly.

| L7 Growth] How is facilitated diffusion different from simple diffusion?

Facilitated diffusion uses a membrane carrier or channel for a specific substance, but it still moves down its concentration gradient and does not require energy.

| L7 Growth] When would a cell need active transport instead of passive transport?

When it needs to move a substance against its concentration gradient or maintain a concentration difference; active transport requires energy.

[Deck 2 | L7 Growth] What makes group translocation unusual compared with other transport methods?

The substance is chemically changed while it is being transported into the cell, which can help trap it inside and prepare it for metabolism.

[Deck 2 | L7 Growth] How do phagocytosis and pinocytosis differ?

Phagocytosis engulfs large solid material or whole cells; pinocytosis takes in liquids and dissolved substances. These are forms of bulk transport used by eukaryotic cells, not typical bacteria.

[Deck 2 | L7 Growth] What happens to a bacterial cell placed in a hypotonic solution?

Water tends to enter the cell. The cell wall helps resist bursting, unlike many cells that lack a rigid wall.

[Deck 2 | L7 Growth] What is plasmolysis, and what causes it?

In a hypertonic environment, water leaves a walled cell and its cytoplasm or membrane pulls away from the cell wall.

[Deck 2 | L7 Growth] How can halophiles live in very salty environments?

They use adaptations that prevent excessive water loss and allow their proteins and cell systems to function at high salt concentrations.

[Deck 2 | L7 Growth] What is the difference between a halophile and an osmotolerant microbe?

A halophile requires or prefers high salt; an osmotolerant microbe can tolerate high osmotic pressure but does not necessarily require it.

[Deck 2 | L7 Growth] What is a capnophile?

A microbe that grows best when carbon dioxide levels are higher than those in ordinary air.

[Deck 2 | L7 Growth] Why can oxygen harm some anaerobic microbes?

Oxygen can generate toxic reactive oxygen compounds. Some anaerobes lack enough enzymes, such as superoxide dismutase or catalase, to detoxify them.

[Deck 2 | L7 Growth] How do microbes generally adapt their membranes to different growth temperatures?

They adjust membrane lipid composition so the membrane stays appropriately fluid at their usual temperature.

[Deck 2 | L7 Growth] How does a chemically defined medium differ from a complex medium?

A defined medium has a precisely known chemical composition; a complex medium contains ingredients such as extracts or digests whose exact chemical makeup is not fully known.

[Deck 2 | L7 Growth] What makes a differential medium useful?

It contains indicators or ingredients that make different microbes look different based on a biochemical reaction, helping distinguish them.

[Deck 2 | L7 Growth] What is the purpose of a reducing medium?

It lowers oxygen levels and helps support the growth of anaerobic microorganisms.

[Deck 2 | L7 Growth] Why might a clinical sample be placed in transport medium rather than ordinary growth medium?

Transport medium helps keep organisms alive during transit while limiting their multiplication, preserving the sample for testing.

[Deck 2 | L7 Growth] Why is agar useful for solid microbiological media?

It solidifies media, is generally not broken down by most microbes, and melts at a high temperature but solidifies as it cools.

[Deck 2 | L7 Growth] Why can a viable plate count underestimate the number of individual cells in a sample?

Cells may clump together, and a cluster may form just one colony; cells that cannot grow under the chosen conditions are also not counted.

[Deck 2 | L7 Growth] A population begins with 100 cells and doubles three times. How many cells would there be if no cells died?

100 × 2³ = 800 cells.

[Deck 2 | L8 Control] What does decimal reduction time (D-value) measure?

The time at a specified condition needed to kill 90% of a microbial population, leaving one-tenth of the starting viable cells.

[Deck 2 | L8 Control] How does thermal death time differ from the D-value?

Thermal death time is the time needed to kill all microbes in a particular sample at a specified temperature; the D-value describes a 90% reduction.

[Deck 2 | L8 Control] Why does boiling water not reliably sterilize a sample?

Boiling kills many vegetative cells but may not destroy heat-resistant endospores.

[Deck 2 | L8 Control] What are two examples of dry-heat microbial control?

Incineration and a hot-air oven. Incineration burns contaminated material; a hot-air oven sterilizes suitable heat-resistant items.

[Deck 2 | L8 Control] Why is an autoclave more dependable than boiling for sterilization?

Pressurized steam reaches temperatures above the normal boiling point and can destroy endospores when used with an appropriate cycle.

[Deck 2 | L8 Control] What does a HEPA filter remove from air?

It captures very small airborne particles, including many microbes, and is used in applications such as clean-air systems and biological safety cabinets.

[Deck 2 | L8 Control] How do ionizing radiation and ultraviolet radiation differ?

Ionizing radiation penetrates more deeply and damages molecules including DNA; UV has limited penetration and mainly damages exposed nucleic acids.

[Deck 2 | L8 Control] Why do refrigeration and freezing usually slow microbial growth rather than sterilize food?

Low temperatures slow enzyme reactions and cell activity, but many microbes survive and may grow again when conditions improve.

[Deck 2 | L8 Control] How can high concentrations of salt or sugar preserve foods?

They reduce available water and create osmotic stress, which inhibits many microbes; some salt- or sugar-tolerant organisms can still survive.

[Deck 2 | L8 Control] What do phenolic compounds generally do to microbial cells?

They disrupt cell membranes and can denature proteins; some are used in disinfectants for surfaces.

[Deck 2 | L8 Control] What are common uses of chlorine compounds?

They are used to disinfect water and surfaces because they oxidize and damage important cell components.

[Deck 2 | L8 Control] How does hydrogen peroxide damage microbes?

It acts as an oxidizing agent that can damage proteins, membranes, and DNA; effectiveness depends on concentration and use conditions.

[Deck 2 | L8 Control] Why are aldehydes such as glutaraldehyde used for high-level disinfection?

They react with and cross-link proteins and nucleic acids, disabling many kinds of microbial structures and functions.

[Deck 2 | L8 Control] What are quaternary ammonium compounds, and what is one limitation?

They are cationic detergents that disrupt membranes and are used on some surfaces; they are not dependable against all endospores and certain resistant microbes.

[Deck 2 | L8 Control] How does chlorhexidine differ from a general surface disinfectant?

Chlorhexidine is a biguanide commonly used as an antiseptic on living tissue, especially skin, at suitable concentrations.

[Deck 2 | L8 Control] How do beta-lactam antibiotics such as penicillin interfere with bacterial growth?

They interfere with enzymes that cross-link peptidoglycan, weakening the cell wall as bacteria grow and divide.

[Deck 2 | L8 Control] How can a drug that blocks folic-acid synthesis harm bacteria?

Bacteria need folate to make certain molecules, including DNA building blocks; blocking the pathway limits growth. Human cells obtain folate from the diet rather than using the same complete pathway.

[Deck 2 | L8 Control] What is target modification as an antimicrobial-resistance mechanism?

The microbe changes the drug's binding site so the drug no longer binds well or works effectively.

[Deck 2 | L8 Control] How can reduced membrane permeability make a bacterium drug-resistant?

The drug enters the cell less effectively, so its internal concentration may stay too low to stop growth.

[Deck 2 | L8 Control] Why can unnecessary antibiotic use increase resistance in a microbial population?

The drug creates selection pressure: susceptible microbes are removed while resistant variants are more likely to survive and multiply.

[Deck 2 | L9 Genetics] What does it mean that the two DNA strands are complementary and antiparallel?

Their bases pair specifically (A with T, G with C), and the two sugar-phosphate backbones run in opposite directions.

[Deck 2 | L9 Genetics] What is the origin of replication?

A DNA site where replication begins; in bacteria, replication usually proceeds in both directions from this site.

[Deck 2 | L9 Genetics] How do leading- and lagging-strand synthesis differ?

The leading strand is made continuously toward the replication fork; the lagging strand is made in short sections away from the fork.

[Deck 2 | L9 Genetics] What are Okazaki fragments?

Short DNA segments made on the lagging strand that are later joined together.

[Deck 2 | L9 Genetics] In which direction does DNA polymerase build a new DNA strand?

It adds nucleotides to the 3′ end, so the new strand is synthesized in the 5′-to-3′ direction.

[Deck 2 | L9 Genetics] What is the role of DNA gyrase in many bacteria?

It changes DNA supercoiling, helping compact the chromosome and relieve twisting problems during DNA processes.

[Deck 2 | L9 Genetics] What does RNA polymerase do during transcription?

It reads a DNA template and joins RNA nucleotides to make an RNA molecule.

[Deck 2 | L9 Genetics] What do start and stop codons signal during translation?

The start codon signals where protein translation begins; stop codons signal the end of translation.

[Deck 2 | L9 Genetics] What is the difference between a silent, missense, and nonsense mutation?

A silent mutation does not change the encoded amino acid; a missense mutation changes an amino acid; a nonsense mutation creates a premature stop codon.

[Deck 2 | L9 Genetics] Why can inserting or deleting one nucleotide cause a frameshift mutation?

Codons are read in groups of three. Adding or removing a number of bases that is not a multiple of three shifts the reading frame downstream.

[Deck 2 | L9 Genetics] How do spontaneous and induced mutations differ?

Spontaneous mutations arise without a specific external mutagen; induced mutations result from agents such as certain chemicals or radiation.

[Deck 2 | L9 Genetics] How does a bacterial operon help coordinate gene expression?

Several genes are controlled together, allowing the cell to turn related functions on or off as a group.

[Deck 2 | L9 Genetics] What jobs do beta-galactosidase and permease perform in the lac operon?

Beta-galactosidase breaks down lactose; permease helps lactose enter the bacterial cell.

[Deck 2 | L9 Genetics] In a repressible operon, how can an end product shut down its own production?

The end product acts as a corepressor by activating a repressor, which binds the operator and blocks transcription of the biosynthesis genes.

[Deck 2 | L9 Genetics] What is the difference between an F⁺ and an F⁻ bacterial cell?

An F⁺ cell carries the fertility factor and can act as a donor in conjugation; an F⁻ cell lacks the factor and can receive it.

[Deck 2 | L9 Genetics] How does an Hfr cell form, and why is it important?

An Hfr cell forms when the fertility factor integrates into the chromosome; conjugation can then transfer chromosomal genes to a recipient.

[Deck 2 | L9 Genetics] What makes generalized transduction different from specialized transduction?

Generalized transduction can transfer almost any bacterial gene because random host DNA may be packaged; specialized transduction transfers particular genes near a phage integration site.

[Deck 2 | L9 Genetics] What does it mean for a bacterial cell to be competent?

It is able to take up free DNA from its surroundings, which is required for natural transformation.

[Deck 2 | L9 Genetics] How can a transposon affect a bacterium when it moves into a new DNA location?

It may disrupt a gene, change gene expression, or carry traits such as antibiotic resistance to a new DNA location.

[Deck 2 | L9 Genetics] Why is horizontal gene transfer medically important?

It can spread traits such as antibiotic resistance or toxin production between bacteria, including bacteria that are not parent and offspring.

[Deck 2 | L10 Engineering] What does restriction fragment length polymorphism (RFLP) analysis compare?

It compares the lengths of DNA fragments produced by cutting DNA with restriction enzymes; differences can help distinguish DNA samples.

[Deck 2 | L10 Engineering] Why must a restriction enzyme cut the donor DNA and vector at compatible sites in cloning?

Compatible ends allow the DNA insert to pair with the opened vector before ligase seals the backbone.

[Deck 2 | L10 Engineering] What is a multiple cloning site in a plasmid vector?

A short region containing several restriction-enzyme recognition sites where a DNA insert can be introduced.

[Deck 2 | L10 Engineering] How does an expression vector differ from a basic cloning vector?

An expression vector includes control elements, such as a suitable promoter, that allow the inserted gene to be transcribed and often translated into a protein.

[Deck 2 | L10 Engineering] What is the role of a promoter in an expression vector?

It provides a site where RNA polymerase and related factors can start transcription of the inserted gene.

[Deck 2 | L10 Engineering] Why is an antibiotic-resistance marker often included in a cloning vector?

It allows researchers to select cells that have taken up a vector by growing them under conditions where cells without the marker do not survive.

[Deck 2 | L10 Engineering] How does blue-white screening help identify some recombinant plasmids?

In a common system, an insert disrupts the lacZ marker: colonies with inserts appear white, while colonies with an intact marker appear blue on the appropriate indicator medium.

[Deck 2 | L10 Engineering] Why is a thermostable DNA polymerase useful in PCR?

It remains functional through repeated high-temperature denaturation steps, so fresh polymerase does not need to be added after every cycle.

[Deck 2 | L10 Engineering] What happens to the target-DNA amount during ideal PCR amplification?

It roughly doubles each cycle, so after n ideal cycles the amount is about the starting amount multiplied by 2ⁿ, until reagents or other limits slow amplification.

[Deck 2 | L10 Engineering] Why does the annealing temperature matter in PCR?

If it is too low, primers may bind nonspecifically; if it is too high, primers may not bind well enough, reducing yield.

[Deck 2 | L10 Engineering] What can a negative control reveal in a PCR experiment?

If the no-template control produces a band or signal, the reagents may be contaminated or the result may reflect an unintended amplification.

[Deck 2 | L10 Engineering] How can the number and position of bands in a DNA gel help interpret a sample?

Bands reveal fragments of different sizes; comparison with a DNA ladder estimates size, and extra or missing bands can indicate different DNA patterns or an experimental problem.

[Deck 2 | L10 Engineering] Why do Sanger sequencing reactions use dideoxynucleotides (ddNTPs)?

A ddNTP lacks the 3′-OH needed to add another nucleotide, so its incorporation stops DNA-chain extension at that base.

[Deck 2 | L10 Engineering] How can Sanger sequencing determine the order of DNA bases?

Fragments ending at different bases are separated by size, and the terminal base of each fragment is detected to reconstruct the sequence.

[Deck 2 | L10 Engineering] What is the difference between genomic DNA and complementary DNA (cDNA)?

Genomic DNA includes the organism's genomic sequences; cDNA is made from an RNA template using reverse transcriptase and represents the RNA sequences present in that sample.

[Deck 2 | L10 Engineering] What does nucleic-acid hybridization depend on?

Complementary nucleic-acid strands pairing through base matching under suitable temperature and salt conditions.

[Deck 2 | L10 Engineering] Why must a DNA probe be complementary to its target sequence?

Complementarity allows the labeled probe to bind specifically to the matching DNA or RNA sequence, helping detect that target.

[Deck 2 | L10 Engineering] Why might a gene from one organism need a suitable promoter to work in another organism?

The host must recognize the promoter and the gene's control signals; a promoter from the donor may not function correctly in the new host.

[Deck 2 | L10 Engineering] How can recombinant bacteria be used to produce a human protein?

Researchers insert the gene into an appropriate expression vector, introduce it into a suitable host, and provide conditions for the host to make the protein.

[Deck 2 | L10 Engineering] Why is a cloning experiment usually checked rather than assuming every colony has the correct insert?

A colony may contain an empty vector, the wrong insert, or an insert in the wrong orientation, so screening or DNA analysis is needed to confirm it.

[Deck 2 | L11 Classification] What kinds of evidence can be combined to classify a microorganism?

Cell and colony appearance, physiology and biochemical reactions, antigen patterns, and genetic or molecular sequences can all contribute.

[Deck 2 | L11 Classification] Why is colony appearance useful but not sufficient by itself for bacterial identification?

Different bacteria can form similar-looking colonies, and one species can look different under different growth conditions.

[Deck 2 | L11 Classification] What is serological classification based on?

Antigen-antibody reactions that reveal whether microbes share particular surface or other antigens.

[Deck 2 | L11 Classification] What can a biochemical test reveal about a bacterial isolate?

It can show whether the isolate performs a particular metabolic reaction, such as using a substrate or producing a specific enzyme.

[Deck 2 | L11 Classification] Why can phenotype-based classification sometimes disagree with evolutionary relationships?

Unrelated organisms can evolve similar traits, and environmental conditions can change the traits that are observed.

[Deck 2 | L11 Classification] What makes 16S rRNA useful for comparing bacteria and archaea?

The gene is present broadly and contains conserved regions for alignment plus variable regions that help distinguish lineages.

[Deck 2 | L11 Classification] Why are conserved and variable sequence regions both useful in molecular classification?

Conserved regions make it possible to compare related sequences, while variable regions provide differences that help separate groups.

[Deck 2 | L11 Classification] Why can whole-genome comparisons provide more information than one gene alone?

They compare much more genetic material, which can resolve relationships that a single marker gene may not distinguish.

[Deck 2 | L11 Classification] What is a microbial strain?

A particular genetic or biological variant within a species; different strains of one species may differ in traits such as virulence or drug resistance.

[Deck 2 | L11 Classification] What is an isolate in microbiology?

A microorganism or population separated from a sample and grown or maintained for study.

[Deck 2 | L11 Classification] What is a serotype?

A variant within a species distinguished by its specific antigen pattern.

[Deck 2 | L11 Classification] What is a biovar?

A variant of a microbial species distinguished by biochemical or physiological characteristics.

[Deck 2 | L11 Classification] Why is classification broader than identifying an unknown isolate?

Identification determines what a particular sample most likely is; classification organizes organisms into groups and reflects their similarities and relationships.

[Deck 2 | L11 Classification] Why can similar cell shapes be weak evidence of close evolutionary relatedness?

Simple shapes such as rods or spheres have evolved in many lineages, so appearance alone may not reveal ancestry.

[Deck 2 | L11 Classification] How can genetic evidence cause a microorganism to be reclassified?

Sequence or genome data may show that it is more closely related to a different group than its older, appearance-based classification suggested.

[Deck 2 | L11 Classification] How do bacteria and archaea compare in the three-domain system?

They are both prokaryotic cells, but they are placed in separate domains because their molecular and biochemical features differ substantially.

[Deck 2 | L11 Classification] Why should a phylogenetic tree be read as a hypothesis based on evidence rather than a picture of appearance?

Its branches represent inferred evolutionary relationships, usually based on molecular or other shared data, not how similar organisms look.

[Deck 2 | L11 Classification] What does a taxonomic name tell you that a strain designation may not?

The species name identifies the broader named organism group; a strain designation identifies a particular variant within that species.

[Deck 2 | L11 Classification] Why is identifying bacterial pathogens often based on several tests rather than one test?

Combining independent results reduces misidentification because many individual traits are shared by multiple organisms.

[Deck 2 | L11 Classification] What is the purpose of Bergey's Manual of Systematics of Archaea and Bacteria?

It is a reference resource for systematics and classification of prokaryotes, using evidence about their characteristics and relationships.