Microbial Cell Structure and Function

Flashcards about microbial cell structure and function.

What are endospores?

Highly differentiated cells produced by certain bacteria species, extremely resistant to heat, harsh chemicals, and radiation.

What is the main function of endospores?

Survival structures that enable the organism to endure unfavorable growth conditions.

Describe the endospore life cycle.

Vegetative cell -> endospore -> vegetative cell.

Where are endospore-forming bacteria commonly found?

Soil (e.g., Bacillus sp.)

What are SASPs and their function?

Small acid-soluble proteins that bind tightly to DNA, protect it from UV radiation, and function as a carbon and energy source during germination.

What is the role of dipicolinic acid (DPA) in endospores?

Binds free water within the endospore, helping to dehydrate it, and stabilizes DNA against heat denaturation.

What is the function of cell inclusions in prokaryotic cells?

Energy reserves and reservoirs of structural building blocks.

Give examples of different types of cell inclusions.

Poly-β-hydroxybutyric acid (PHB), Polyphosphate and Sulfur, Cyanophycin granules, Carboxysomes, Magnetosomes

What is the function of gas vesicles in prokaryotes?

Confer buoyancy, allowing cells to position themselves in a water column in response to environmental conditions.

What two proteins are gas vesicle membranes composed of?

GvpA (forms the vesicle shell) and GvpC (strengthens the shell).

What are the two classes of protein export in bacteria?

Sec-dependent and Sec-independent

What are the two major pathways that exist to secrete proteins across the cytoplasmic membrane in bacteria?

Sec-pathway and Tat-pathway

Describe the function of the Sec-pathway.

Catalyzes the transmembrane translocation of proteins in their unfolded conformation.

Describe the function of the Tat-pathway.

Catalyzes the translocation of secretory proteins in their folded state.

What is the role of signal peptides?

Amino-terminal extension of the secretory protein necessary for correct targeting to the translocation pathway.

What is the role of TTSS (Type III Secretion System)?

Many pathogenic bacteria excrete protein toxins or other harmful proteins into the host during infection.

What is the functional unit of genetic information?

The gene

Where are genes physically located?

Chromosomes or other large molecules known collectively as genetic elements

What is the genome?

The total complement of genes in a cell

How is prokaryotic DNA organized?

Single, circular DNA molecule localized within the nucleoid.

What is supercoiling and why is it important?

Occurs in a circular DNA duplex and is how DNA is packed into a small space.

What enzyme inserts negative supercoils into DNA?

DNA gyrase

What are operons?

A single mRNA carrying multiple coding sequences

What are plasmids?

Circular double-stranded DNA molecules that replicate independently of the host chromosome.

What types of genes do Plasmids carry?

Nonessential (but often very helpful) genes

Give examples of phenotypes conferred by plasmids in prokaryotes.

Antibiotic resistance, virulence factors (toxins, enzymes), metabolic functions (degradation of compounds), conjugation

What are the three different types of Plasmids?

Resistance Plasmids(R factors), Plasmids Encoding Virulence and Conjugative plasmid

What are transposons and insertion sequences?

Stretches of DNA that can move from one site to another.

What is the function of transposase?

Enzyme necessary for transposition.

Describe the process of replication of circular DNA.

Bidirectional replication from an origin, forming a theta structure.

What is vertical gene transfer?

Transfer of genes from one generation to the next, occurs during binary fission from mother cell to daughter cells

What is horizontal gene transfer?

Transfer of genes between cells of the same generation

What are the three mechanisms of horizontal gene transfer?

Transformation, transduction, and conjugation.

What is transformation?

A genetic transfer process by which free DNA is incorporated into a recipient cell and brings about genetic change.

What is a competent cell?

A cell that is able to take up DNA and be transformed.

What is transduction?

A bacterial virus (bacteriophage) transfers DNA from one cell to another.

What are the two types of transduction?

Generalized transduction and specialized transduction.

What is conjugation?

A mechanism of genetic transfer that involves cell-to-cell contact.

What is the function of the tra region on the F plasmid?

Contains genes that encode transfer functions for conjugation.

What DNA replication mechanism is utilized during congugation?

Rolling circle replication

What is CRISPR/Cas9?

Adaptive immune system in bacteria which detects and recognizes foreign DNA and cleaves it

What is the function of Cas (CRISPR-associated) endonuclease?

Can target and cleave invading DNA in a sequence-specific manner.