UWEC Microbiology Exam 3

Ch. 8, 12, 13, 14

How do eukaryotes promote genetic diversity?

Sexual reproduction

How do prokaryotes promote genetic diversity?

Horizontal gene transfer and reproduction by binary fission

Mutation

any change in a nucleotide or nucleotide sequence

Wild-type

the phenotype of the typical form of a species as it occurs in nature

Genotype

an organism's complete set of genetic instructions

Phenotype

set of observable traits or physical characteristics of an organism

Silent mutation

a DNA change that alters a codon but does not change the resulting amino acid sequence

auxotroph

an organism that cannot synthesize a specific organic compound essential for its growth

Prototroph

a microorganism or cell that can synthesize all of its required growth factors, amino acids, and metabolites internally from basic inorganic materials

spontaneous mutation

mutations that occur naturally in the absence of mutagens

induced mutation

a permanent change in a DNA sequence caused by external environmental agents

frameshift mutation

a genetic change caused by the insertion or deletion of nucleotide bases in numbers that are not a multiple of three

transposable element

“jumping genes”, DNA sequences that move or copy themselves to new positions within a genome

point mutation

a genetic alteration where a single nucleotide base is substituted, inserted, or deleted in a DNA or RNA sequence

reading frame

a way of dividing a sequence of nucleotides (DNA or RNA) into a set of consecutive, non-overlapping triplets (called codons) that direct the synthesis of proteins

homologous recombination

a biological process where nucleotide sequences are exchanged between two similar or identical DNA molecules

How do spontaneous mutations occur? What types of mutations occur spontaneously?

Spontaneous mutations occur naturally without external agents, driven primarily by errors during DNA replication, spontaneous chemical damage, or the movement of mobile genetic elements

What are the three types of mutations that can occur as a result of a point mutation that results in a base substitution?

silent mutations, missense mutations, and nonsense mutations

What are the potential consequences of mutations on the functioning of the gene product and the survival of the cell/organism?

Neutral (silent mutations), beneficial (antibiotic resistance mutations), detrimental (mutations causing sickle cell or cystic fibrosis)

process by which a base substitution error during DNA replication can become a permanent mutation.

when a mispaired nucleotide escapes DNA polymerase proofreading and post-replication mismatch repair, and the cell subsequently undergoes another round of DNA replication

silent mutations

a change in a DNA base pair that does not alter the amino acid sequence of a protein

missense mutations

a point mutation where a single DNA base change causes a different amino acid to be inserted into a protein

nonsense mutations

a genetic change that turns an amino acid-coding codon into a premature stop codon

What is the effect of adding or subtracting 1 or 2 nucleotides during DNA replication? What effect does this type of mutation have on the gene product?

Adding or subtracting 1 or 2 nucleotides causes a frameshift mutation. Because the genetic code is read in non-overlapping triplets (codons), shifting the reading frame by 1 or 2 bases alters every downstream codon, resulting in a completely different, often truncated or non-functional gene product.

What is the effect of adding or subtracting 3 contiguous nucleotides during DNA replication? Of adding or subtracting 3 non-contiguous nucleotides?

fundamentally changes the genetic code

Transduction

transfer of bacterial DNA using bacteriophage

Natural vs. Artificial competence

Generalized vs. Specialized transduction

Generalized: any gene can be transferred
Specialized: only specific genes can be transferred

Conjugation

transfer of DNA from one bacterial cell to another + requires direct contact

What type(s) of mutation(s) are caused by transposable elements? What are the effects of these mutations on the gene product?

Why can mutations caused by transposons be classified as either spontaneous or induced?

Base analogs (AZT)

Chemical modification of bases

Intercalating agents (ethidium bromide)

Transposons

UV radiation

X-rays

Proofreading by DNA polymerase

Mismatch repair

Dark repair (What type of mutation is repaired by dark repair? What human disease is a result in defects in dark repair?)

Light repair (photoreactivation) (What enzyme is associated with light repair and how does it become activated and how does it function? What types of organisms can perform light repair?)

What is the difference between horizontal and vertical transmission of genes in bacteria?

What are the mechanisms by which horizontal transmission can occur?

Describe the mechanism by which DNA mediated transformation occurs.

What are the requirements for DNA mediated transformation?

In what types of bacteria can DNA mediated transformation occur?

What are the two types of transduction and what is used to transfer DNA during transduction?

What types of genes can be transferred during both types of transduction?

Be able to describe the mechanism by which generalized transduction occurs.

What is conjugation and what are the requirements for conjugation to take place?

Transfer of DNA from one bacterial cell to another; requires direct contact

In what types of bacteria can conjugation take place?

Gram positive and gram negative bacteria

In what types of bacteria can conjugation using the F pilus occur?

In Gram negative bacteria, a donor cell (F+) transfers DNA to a recipient cell (F-)

Describe the mechanism by which conjugation occurs between an F+ cell and an F- cell.

1. the F pilus contacts the recipient F- cell

2. the pilus retracts and pulls the donor and recipient cells together

3. A single strand of the F plasmid is transferred to the recipient cell; it’s complement is synthesized as it enters that cell. The strand transferred by the donor is replaced, using the remaining strand as a template for DNA synthesis

4. End of transfer process: both the donor and recipient cells are F+ and synthesize the F pilus

What is the difference between an F+ cell and an Hfr cell?

What is the difference between the types of genes that can be transferred by F+ cells and Hfr cells?

characteristics of plasmids and explain the functioning of the features of plasmids.

• circular + double stranded DNA

• replicate independently of chromosomal DNA

• carry a few to several hundred genes

• transferred through conjugation —> transformation in the lab

What types of genes can be carried on plasmids?

non-essential

How are plasmids transferred from cell to cell?

conjugation

What types of genes are found on R plasmids?

genes that make organism resistant to antibiotics

Features and the functions of the features of a transposon (transposable element)

• jumping genes

• transposase gene: allows transposon to insert somewhere else

• inverted repeat sequence: read the same forward and backward, surrounds transposase gene

How can transposons move both within a cell and between cells?

Importance of gene transfer in bacteria both from a bacterial perspective and a human perspective.

Bacterial: genetic variation, adaptation to changing environments
Human: spread of antibiotic resistance genes, transfer of virulence factors

how the CRISPR system functions

What is the function of the CRISPR system in bacteria?

bacterial immune system against bacteriophage

How can CRISPR potentially be used to treat diseases in humans?

What are the general characteristics of fungi

• chemoorganoheterotrophs

• aerobic or facultative anaerobes

• eukaryotes

• reproduce sexually and asexually

• spores

• cell walls contain glycans, mannans, and chitin

• cell membrane contains ergosterol

What are the two morphologies of fungi

single cell yeast, filamentous molds

How do yeast reproduce

budding (blastospores)

Mycology

Hypha

single mold filament

Mycelium

mass of hyphae

Thallus

mold colony

Blastospore

Septa

Septate

Aseptate

Mycosis

Dimorphic fungus

can grow as yeast or mold depending on environemental conditions

Difference between vegetative and reproductive mycelium

Thermal dimorph

determine morphology based on temperature

Room temp: grow as mold

Body temp : grow as yeast

At what temperature do thermal dimorphs grow as a mold

At what temperature do thermal dimorphs grow as a yeast?

37C - body temperature

Why are thermal dimorphs clinically significant?

Under what conditions does Candida albicans grow as a yeast?

Room temperature

Under what conditions does it grow filamentously?

37C - body temperature

What are the general types of mycoses?

Superficial, cutaneous, subcutaneous, systemic

Examples of fungal toxins

Ergotamine, aflatoxins

What is a dermatophyte

fungi that require keratin for growth

What types of infections do dermatophytes cause?

hair, skin, nail infections

What enzyme produced by dermatophytes facilitates their ability to cause hair, skin and nail infections

Keratinase

Virion

A virus particle

Nucleocapsid

Capsid and nucleic acid together

capsid

Protein coat composed of subunits called capsomeres

capsomere

capsid subunit

temperate bacteriophage

bacteria that can undergo lysogeny

prophage

Integrated DNA in a bacteriophage

lysogen

Bacterial cell thats chromosome includes integrated bacteriophage DNA

lysogeny

State of latency in which a bacteriophage has established a latent state inside a bacterial cell

provirus

proto-oncogene

genes that encode proteins that function in the regulation of cell growth or differentiation