Microbiology

what are drawbacks in using a microscope to count cells

-debris in the sample may be mistaken for microbial cells -motile cells must be immobilized before counting -without specific stains, dead cells cannot be distinguished

Maintaining a constant cell population in a chemostat requires the monitoring and control of

-nutrient concentrations. the dilution rate of volume pumped in. -the population's waste products.

The cI (lambda repressor) protein

-represses the transcription of all other lambda-encoded genes. -competes with Cro to determine whether a lytic or lysogenic cycle will occur. -promotes lysogeny

Proteins to be exported are typically recognized by either

SecA or SRP

Which is true regarding release of the T4 bacteriophage?

T4 enzymes compromise the cell membrane and peptidoglycan, causing lysis of the host cell.

During penetration of an Escherichia coli cell by the T4 bacteriophage,

T4 lysozyme makes a pore in the cell wall, the tail sheath contracts, and the phage DNA is injected into the cell.

Turbidity of a liquid culture used as a proxy for cell number is most powerful when combined with a carefully constructed

growth curve relating to OD to cell number

The two types of structural symmetry in viruses are rod-shaped ________ and ________ (spherical) symmetry.

helical / icosahedral

Importing high concentrations of compatible solutes is a strategy cells use to counteract the effects of an environment containing a

high salt concentration

What is an effective way of growing an animal virus?

in a primary cell structure

If lambda phage were unable to express the Cro repressor protein, what would happen?

it would never enter the lytic pathway

Viral genomes can be

linear or circular. -double-stranded or single-stranded. -composed of RNA or DNA.

what are classified as a cardinal temperature

maximum, minimum, optimum

Animal viruses typically enter a cell by

membrane fusion or endocytosis.

microbes that naturally live within mammalian hosts are

mesophiles

Which type of microorganism would NOT be able to grow under anoxic conditions?

microaerophile

Proteins in psychrophilic cells generally have ________ than proteins found in cells that grow optimally at higher temperatures.

more α-helices and fewer β-sheets

which statement below provides an explanation of why a lagging strand exists during DNA replication

new nucleotides can be added only to a 3' (OH-) end.

The location on a bacterial chromosome where DNA replication begins is ________, and the binding of ________ opens up the double helix

oriC / DnaA

Why are serial dilutions often performed before aliquoting a sample of cells onto plates for counting colonies?

otherwise the colonies would be too numerous to count

Which type of secretion system is commonly used by pathogenic bacteria to inject toxic proteins directly into eukaryotic cells

type III secretion system

In gram-negative bacteria, which secretion systems depend on Sec or Tat to first move proteins across the inner membrane?

types II and V

The extracellular state of a virus is referred to as a

virion

The base pairing between ________ is especially strong because it contains an additional ________ bond, compared to ________.

C and G / hydrogen / A and T

What form of energy is used during both the initiation and the elongation of protein synthesis?

GTP

How is 16S rRNA involved in the translation of proteins?

It helps initiate translation by base pairing with the ribosome binding site (RBS) on the mRNA.

Why is the T4 genome resistant to restriction enzymes?

It modifies its DNA, using 5-hydroxymethlycytosine instead of cytosine.

If a mutation were to occur in lambda phage that made it unable to express integrase, what would happen?

It would be unable to recombine with the bacterial chromosome.

The most common first-position amino acid in bacterial proteins is

N-formylmethionine.

A nucleotide sequence that usually contains 5′-TATAAT-3′ is called the

Pribnow box or -10 region

Which enzyme is responsible for opening up the dsDNA in order for RNA polymerase to transcribe a gene?

RNA polymerase

which enzyme is NOT present in a replisome

RNA polymerase

Why is plating efficiency an important metric of consideration in quantitative measurements of virus?

Virions do not infect host cells with 100 percent efficiency.

To speed up the growth rate in a chemostat, the ________ should be increased. To increase the cell density as well, the ________ should be increased.

dilution rate/ limiting nutrient

Which growth phase has the largest increase in cell numbers per unit of time?

exponential phase

True or False: Acidophiles maintain a cytoplasmic pH below 5.5.

false

Heat-sensitive liquids are typically sterilized by

filtration

The sigma subunit of RNA polymerase functions to

form RNA polymerase-DNA complexes. locate, recognize, and bind to promoter regions

what is an operon

a gene cluster transcribed as a single mRNA

A virus was used to alter human cells. mRNA for a gene was inserted into the virus, and the virus infected the human cells and inserted the gene into the genome of the cell. What type of virus could do this?

a retrovirus

A plaque assay uses the ________ technique.

agar overlay

________ organisms have a particularly difficult time maintaining a proton motive force to synthesize ATP using ATPase.

alkaliphilic

A product purchased from a drug store guaranteed to kill or inhibit bacteria on skin is best described as a(n)

antiseptic

Which type of microorganism shows even growth throughout thioglycolate broth?

areotolerant anaerobe

in most prokaryotes, DNA replication proceeds ______________

bidirectionally

What is the function of the Tus protein (encoded by tus)?

binding the terminus (Ter site) and blocking progress of the replication fork

The targets of the T4 bacteriophage during attachment to Escherichia coli are

carbohydrates in the LPS layer of the outer membrane.

________ and peroxidase both detoxify H2O2.

catalase

The time required for a 10-fold reduction in the viability of a microbial population using a particular heating method is called the

decimal reduction time

The exact composition of ________ media is known. _______ media inhibit the growth of some microbes. ________ media are used to culture fastidious microbes, particularly pathogens.

defined / selective / enriched

________ is used to reduce microbes in food products to increase shelf life, and ________ is routinely used to sterilize a variety of food products, surgical supplies, and laboratory equipment.

pasteurization / ionizing radiation

unlike Eukarya, Archaea and Bacteria do not have a nucleus, so they can ______________

perform coupled transcription and translation

__________ are genetic elements that replicate separately from the chromosome

plasmids

RNA virus genomes may be either

plus sense or minus sense.

A viral capsid is composed of individual units of ________ called ________.

proteins / capsomeres

adenine and guanine are classified as _______________ whereas cytosine and thymine are classified as ___________.

purines and pyrimidines

The enzyme ________ is used by retroviruses to transfer information from RNA to DNA.

reverse transcriptase

In prokaryotes, MOST mRNAs have a short half-life, after which they are degraded by

ribonucleases

Lambda DNA is replicated by

rolling circle replication

If a heterotrophic bacterium were grown in a minimal glucose medium and transferred during exponential growth phase into the complex LB medium, the cell would have a relatively

short lag phase because of the availability of amino acids and other nutrients.

In Bacteria and Archaea, most proteins that are transported across membranes begin with a 15-20 residue amino acid sequence called a

signal sequence

In a disc diffusion assay, the zone of inhibition will be ________ for organisms more resistant to an antimicrobial agent.

smaller

For which of the following populations/samples would it be MOST inappropriate to use the spread-plate technique to quantify viable cells?

soil sample

In which growth phase is there no increase or decrease in cell number because some cells are dividing while others are dying?

stationary phase

During translation, a (3-nucleotide) codon in an mRNA transcript is recognized by a(n) ________ that carries with it the corresponding amino acid.

tRNA anticodon

What happens when a culture is incubated above the organism's maximum temperature for growth?

the cell membranes collapse, proteins denature, and the cell usually dies

The term ________ is used to reference concentrations of viruses.

titer

True or False: Protein chaperones are found in all domains of life, and their sequences are highly conserved among all organisms

true

True or False: Ribosomes are often the target of antibacterial drugs such as tetracycline

true