Microbiology: Chapter 3

Question 1

What is the nucleoid region in prokaryotic cells?

Answer 1

Part of a prokaryotic cell (like bacteria and archaea) where its genetic material (DNA) is located.
DNA is arranged in a cluster, not membrane-bound, and supercoiled around histone-like proteins.
Transcription and Replication occurs here.

Question 2

Where does transcription occur in bacterial cells?

Answer 2

In the nucleoid region; DNA is used to make an RNA template.

Question 3

What is found inside the cytoplasm/cytosol of bacterial cells?

Answer 3

Polyribosomes, metabolites, enzymes, cytoskeletal fibers (provide structure and assist in division), and sometimes flagella.
RNA is also present here.

Question 4

Describe bacterial DNA.

Answer 4

One single circular chromosome, double-stranded, not membrane bound, in a cluster, supercoiled around histone-like proteins, about 3000–3200 genes.

Question 5

How does bacterial DNA compare to human DNA?

Answer 5

Humans have ~23,000 genes in 46 chromosomes (23 pairs), wrapped tightly around histone proteins with grooves and channels.
Bacteria have one circular chromosome and histone-like proteins; no nuclear membrane is needed.

Question 6

What does supercoiling bacterial DNA accomplish?

Answer 6

Supercoiling compacts DNA to fit in nucleoid region and stores energy for unwinding.

Question 7

How do bacteria selectively use DNA for transcription?

Answer 7

Only specific sections of the supercoiled chromosome are opened as needed. DNA gyrase relaxes supercoiling, and topoisomerase 1 re-supercoils sections after use.

Question 8

What processes occur at the nucleoid-cytoplasm interface in bacteria?

Answer 8

DNA replication, transcription, and translation can occur simultaneously here.
Polyribosomes attach to RNA as it’s transcribed.

Question 9

Why are antibiotics effective against bacteria?

Answer 9

Because bacteria lack internal membranes, antibiotics only need to cross the cell wall and membrane.

Question 10

What is the difference between transcription and translation?

Answer 10

Transcription: DNA → RNA (in nucleoid)
Translation: RNA → protein (ribosomes at nucleoid-cytoplasm interface)

Question 11

How do ribosomes function in translation? Explain the 3 Sites.

Answer 11

Ribosomes have 2 subunits (large and small). The small subunit binds mRNA, then the large subunit joins.
There are 3 sites:
A site: entry of aminoacyl-tRNA
P site: holds tRNA with growing peptide chain, peptide bond forms
E site: empty tRNA exits
At stop codon, release factor releases polypeptide and ribosomal subunits dissociate.

Question 12

What happens at stop codon?

Answer 12

At stop codon, release factor releases polypeptide and ribosomal subunits dissociate.

Question 13

What are polyribosomes?

Answer 13

Multiple ribosomes attached to a single RNA molecule, translating simultaneously.

Question 14

What are plasmids? How are they acquired? What are they used for?

Answer 14

Extra-chromosomal DNA, optional in cells, often carries 3–5 genes.
Can be acquired by scavenging free DNA or via conjugation.
Used for protein production, defense, survival.

Question 15

How does conjugation work in bacteria?

Answer 15

Genetic material passed from one bacterium to another from direct contact (cell-to-cell contact)
Donor cell with plasmid forms a sex pilus to transfer a copy to the recipient. Plasmid replication is semi-conservative. Sex pilus disintegrates after transfer.

Question 16

What is semi-conservative DNA replication?

Answer 16

Each new DNA molecule has one original strand and one newly synthesized strand, minimizing errors.

Question 17

What happens to plasmids when cells are stressed?

Answer 17

Cells may discard plasmids to conserve energy or resources.

Question 18

What are inclusion bodies and types of them?

Answer 18

Non-membrane-bound internal structures used for storage or waste. Store carbon and energy.
Types: Gas vesicles, Thylakoids, Carboxysomes, Magnetosomes.

Question 19

What are gas vesicles?

Answer 19

Protein-bound gas pockets that prevent water entry, allowing cells to float for photosynthesis (e.g., cyanobacteria).

Question 20

What are thylakoids?

Answer 20

Sites of photosynthesis in photoautotrophic cells.

Question 21

What are carboxysomes?

Answer 21

Protein-bound structures filled with CO₂ and enzymes like RuBisCo for CO₂ fixation.

Question 22

What are magnetosomes?

Answer 22

Membrane-bound iron-containing crystals (Fe3O4 or Fe3F4) that align cells with Earth’s magnetic field for navigation in aquatic environments.

Question 23

What are storage granules and what ARE the different kinds of storage granules? (4 types and know whats stored IN THOSE granules)

Answer 23

Non-membrane-bound substances densely packed with excess materials.
Carbon (glycogen, glucose polymers, Poly-β-hydroxybutyrate, Poly-β-valerate)
Phosphate granules (polyphosphate for ATP, nucleic acids, phospholipids)
Sulfur granules (energy source in sulfur-rich environments)
Acid calcisomes (store calcium and phosphorus)

Question 24

What “excess materials” do storage granules contain?

Answer 24

Carbon (glycogen, glucose polymers, Poly-β-hydroxybutyrate, Poly-β-valerate)
Phosphate granules (polyphosphate for ATP, nucleic acids, phospholipids)
Sulfur granules (energy source in sulfur-rich environments)
Acid calcisomes (store calcium and phosphorus)

Question 25

What do phosphate granules store and what are they used for?

Answer 25

Phosphate granules store inorganic phosphate (polyphosphate chains). The stored phosphate can be used for: ATP synthesis (energy production) Nucleic acid synthesis (DNA/RNA) Phospholipid production (cell membranes) They help regulate energy and metabolic balance, especially when external phosphate is scarce.

Question 26

What carbon storage compounds can be found in bacterial storage granules?

Answer 26

glycogen, glucose polymers, Poly-β-hydroxybutyrate, Poly-β-valerate

Question 27

What do sulfur granules store and what is their purpose?

Answer 27

Sulfur granules store elemental sulfur in organisms living in sulfur-rich environments (like coastlines, lakes, rivers). They serve as an energy source when external sulfur becomes unavailable.

Question 28

What are acid calcisomes and what do they store?

Answer 28

Acid calcisomes are storage granules that contain calcium and phosphorus. They help maintain ion balance and store phosphorus for future metabolic use.

Question 29

What are Poly-β-hydroxybutyrate and Poly-β-valerate used for?

Answer 29

Biodegradable plastics and self-dissolving sutures. Poly-β-hydroxybutyrate: strong but brittle. Poly-β-valerate: flexible, less strong.

Question 30

What is unique about Mycoplasma?

Answer 30

Does not have as big of a genome as most bacteria.

Question 30

What is unique about transcription and translation in bacteria and archaea?

Answer 30

Bacteria and archaea can carry out transcription and translation simultaneously. As RNA is being transcribed from DNA in the nucleoid region, ribosomes attach to the mRNA and begin translating it into protein at the same time, often forming polyribosomes.

Question 31

What happens during transcription?

Answer 31

DNA is used to make an RNA template.

Question 32

Where does Translation occur in prokaryotes?

Answer 32

Cytoplasm or nuceloid-cytoplasm interface

Question 33

Can cells with magnetesomes move freely or actively? Why?

Answer 33

No, because they typically lack a flagella.