Lecture 12: Internal Structures of the Cell Wall: Nuclear Material and Ribosomes

What is cytoplasm?

The fluid-like substance inside the cell membrane that suspends cellular structures.

What is the composition of cytoplasm?

• 80% water

• proteins

• carbohydrates

• lipids

• inorganic ions

• dissolved gases

What are the major structures in the cytoplasm of prokaryotes?

• nucleoid

• ribosomes

• inclusion bodies

What cytoskeletal proteins are found in bacteria?

Homologs of tubulin and actin that regulate cell shape and size

What is the function of ribosomes?

Site of protein synthesis

How many ribosomes are in a prokaryotic cell?

About 10,000 to 20,000, making up 15-20% of cell mass.

What are the subunits of prokaryotic ribosomes?

• 30S (small)

• 50S (large)

• forming the complete 70S ribosome.

What is the composition of the 50S subunit?

• 31 proteins

• 5S rRNA,

• 23S rRNA.

What is the role of the 23S rRNA?

Involved in translocation and peptide bond formation

What is the composition of the 30S subunit?

16S rRNA and 21 ribosomal proteins.

What is the function of 16S rRNA?

Ensures translational accuracy and provides binding sites (A, P, and E sites).

What are the subunits of eukaryotic ribosomes?

40S (small) and 60S (large), forming the complete 80S ribosome.

What rRNAs are found in eukaryotic ribosomes?

5S, 18S, and 28S rRNA.

What is the function of the large ribosomal subunit?

Catalyzes peptide bond formation.

What Nobel Prize-winning discovery was made about ribosomes?

Their atomic structure and function, aiding antibiotic development.

What is an example of an antibiotic that targets ribosomes?

Azithromycin binds to the 50S subunit and inhibits protein synthesis.

Why does azithromycin not affect human cells?

Humans lack 50S ribosomal subunits.

What is the nucleoid?

The region in a bacterial cell containing the chromosome.

What is the function of the nucleoid?

Stores the bacterial chromosome and organizes genetic material for replication and gene expression.

What is the structure of the bacterial chromosome?

A single, continuous, circular double-stranded DNA molecule.

How is bacterial DNA compacted?

Through supercoiling stabilized by proteins.

Do prokaryotes have histones?

No, except for some Archaea.

What is the genome?

The complete copy of an organism's genetic information.

What is the origin of replication (oriC)?

The site where DNA replication begins, attached to the cell membrane.

What is "theta replication"?

The bidirectional replication of the bacterial chromosome.

How large can prokaryotic genomes be?

From ~0.5 Mbp in parasites to over 10 Mbp in symbionts.

Which bacterium has two chromosomes?

Vibrio cholerae, with one chromosome for virulence and metabolism, and another for essential genes.

What are plasmids?

Small, circular (or linear) DNA molecules that replicate independently of the chromosome.

How many genes do plasmids usually carry?

Typically less than 30.

What is the function of plasmids?

Carry genes that may provide advantages like antibiotic resistance and toxin production.

Are plasmids essential for bacterial survival?

No, but they can be beneficial in certain environments.

What is bacterial conjugation?

The transfer of genetic material between bacterial cells via plasmids.

What is a unique feature of Borrelia burgdorferi's genome?

It has a linear chromosome and at least 17 plasmids.

What disease does Borrelia burgdorferi cause?

Lyme disease.

How is Lyme disease transmitted?

By deer ticks.

What is the function of inclusion bodies?

Reserve deposits of nutrients in prokaryotic cells.

What is a key difference between prokaryotic and eukaryotic ribosomes?

Prokaryotic ribosomes are 70S, while eukaryotic ribosomes are 80S.

What are the forms of RNA found in bacterial ribosomes?

5S, 16S, and 23S rRNA, which contribute to ribosomal structure and function.