MCB3020 Cumulative Final (exam2)

How many generations does it take for a single bacterial cell to become 256?

8

A mutation that changes the amino acid sequence of the resulting protein by substitution is called a

missense mutation

Why would it be beneficial for cells to wait until a critical population density is reached before expressing certain genes?

Without a certain density, it would be highly unlikely that the molecules produced by a cell in the group could find and bind to other cells of the population effectively.

Which of the following methods of genetic recombination is common to both eukaryotic and bacterial cells?

vertical gene transfer

T/F During replication, the point where separation of the DNA double helix occurs is called the replication fork.

True

Cells may enter stationary phase because of

• the accumulation of toxic waste products

• a lack of available oxygen

• the depletion of an essential nutrient

• All of the choices are correct.

T/F During the lag phase of microbial growth, the cells are metabolically inactive

False

T/F High concentrations of sugar or salt are used to control food spoilage because most microorganisms only grow well in habitats with high water activity.

True

Which microbial control method best describes how an autoclave sterilizes material?

by heat

The total number of viable microorganisms remains constant in stationary phase because

either there is a balance between cell division and cell death or there is a cessation of cell division even though the cells may remain metabolically active

The site on the DNA to which a repressor protein binds is the

operator

The destruction or removal of all viable organisms is called

sterilization

Which will require a longer time to kill?

a larger population of microorganisms

The length of the lag phase of growth can vary depending on

• the nature of the growth medium

• the condition of the microorganisms

• All of the choices are correct.

• the temperature

Mutations that result in the death of an organism when expressed are called

lethal mutations

T/F Genes for antibiotic resistance can be found in antibiotic-producing bacteria as well as in non-antibiotic-producing bacteria.

true

Which of the following inhibits bacterial growth but does not kill bacteria?

bacteriostatic agent

Which microbial control method best describes the process of pasteurization?

heat

Select all the differences between cellular DNA and cellular RNA to test your understanding of these nucleic acids.

• DNA is double-stranded, RNA is single-stranded

• DNA nucleotides contain deoxyribose whereas RNA nucleotides contain ribose

DNA in cells can encode thousands of different proteins. Why do cells require mechanisms to regulate expression of the genes that code for these proteins?

Not all proteins are needed at all times, or in equal amounts. Regulating their expression saves energy and time.

T/F DNA replication results in two identical daughter molecules each consisting of one old (original) strand and one newly synthesized strand.

True

vertical gene transfer examples

• from parent to offspring

• crossing over between sister chromosomes during meiosis

• fusion of gametes

horizontal gene transfer

• transduction

• genes from one independent, mature organism, transferred to another mature organism

• transformation

• conjugation

Examine the graph. Lines A, B, and C represent different microbes' survival in the presence of "XYZ" antimicrobial compound. How long should you treat surgical plastics to ensure the diverse population of microbes are sterilized?

4 hours

Which of the following is an example of gene regulation at the posttranslational level?

alteration of protein structure

Which of these techniques sterilizes on the basis of the size of the microbes to be removed?

filtration

cidal

kills the microbe

static

keeps the microbe from dividing

T/F Bacterial isolates from post-surgical infections of several patients on the same hospital floor demonstrate an increase in resistance to similar antibiotics. The pattern of antibiotic resistance in these cases is most likely due to vertical gene transfer among bacteria that carry resistance genes to bacteria that lack those genes.

false

Organisms that grow near deep-sea volcanic vents are likely to be

thermophilic

Transposons can cause mutations by

"jumping" into a gene and disrupting its function

Sterilization involves _________blank all viable microorganisms

killing OR removing

Bacterial replicons differ from eukaryotic and archaeal replicons in that

bacteria have no histones and a single origin of replication, whereas eukaryotes and archaea have multiple origins of replication, and their DNA is associated with histones

Choose the best description of how filtration works to control microbes

A filter is a solid material containing small holes that only allows liquids to pass but restricts larger substances from passing to a sterile environment.

T/F The bacterial initiator tRNA is  ƒMet−tRNAiMetƒMet-tRNAiMet whereas the eukaryotic initiator tRNA lacks the formyl group on the amino moeity; Met−tRNAiMetMet-tRNAiMet ^t. Archaea, which, like bacteria, lack a nucleus, utilize the same initiator tRNA as bacteria,  ƒMet−tRNAiMetƒMet-tRNAiMet in the initiation of translation

False

T/F Microorganisms show differential sensitivity to antimicrobial agents.

true

A _________blank mutation is one that causes premature termination of the synthesis of the protein product

nonsense

silent mutation

A mutation that changes a codon into a different codon, but both codons specify the same amino acid; this causes no change in the resulting polypeptide

frameshift mutation

A mutation resulting from an insertion or deletion of bases that causes a change in the reading frame of the mRNA

Which of the following is a reason for the occurrence of a lag phase in a bacterial growth curve?

• The organisms may have been injured and require time to recover.

• The medium may be different from the previous growth medium so that the cells must synthesize new enzymes to use different nutrients.

• The cells may be old and depleted of ATP, essential cofactors, and ribosomes that must be synthesized before growth can begin.

• All of these are potential reasons.

Horizontal gene transfer can occur via

conjugation

Assess the diagrams and drag the picture labels to place each stage of eukaryotic translation initiation into the correct order.

1) Activation of mRNA by elongation initiation factors

2) Formation of the 43s complex

3) 43s complex binds to 5’ mRNA leader sequence

4) 43s complex scans the mRNA and halts at the start codon

5) 60s subunit attaches to 43s-mRNA complex to form complete 80s ribosome

If a frameshift mutation causes a stop codon to be inserted into the DNA sequence

the resulting protein will be too short and nonfunctional

Which of the following was the major contribution made by Avery, MacLeod, and McCarty that strengthened the argument that the transforming agent in Griffith's experiment was DNA?

Transformation of nonvirulent cells with a DNA extract was blocked only if DNase was added.

Organisms that do not require oxygen for growth but grow better in its presence are called

facultative anaerobes

Which of the following influence(s) the efficiency of an antimicrobial agent?

• Duration of exposure

• Concentration of the agent

• All of the choices are correct.

• Temperature

Gamma radiation

is used to sterilize some food products

The limitation on microbial growth rate at high nutrient levels is/are

the saturation of the transport proteins for nutrient uptake

Most bacterial and archaeal cells divide by

binary fission

The reduction of the microbial population to levels that are considered safe by public health standards is called

sanitization

Organisms that are not drastically affected by increased pressure are called

barotolerant

The genetic code is translated in groups of _________ bases.

3

During replication, which enzyme unwinds the two strands of the DNA molecule from one another?

helicases

The process by which the base sequence of an RNA molecule is used to direct the synthesis of a protein is called

translation

Archaea and eukaryotes can regulate cellular processes posttranslationally by using

feedback inhibition and covalent modifications

Transposable elements are important factors in the evolution of bacteria because they

can transfer antibiotic resistance from one bacterial cell to another

In eukaryotes, the initiator tRNA for translation is

Met−tRNAiMetMet-tRNAiMet , which is also used by archaea

It is easier to transform bacteria with plasmid DNA since plasmids

can independently replicate within the host and are not as easily degraded as are linear fragments