Chapter 27: Bacteria and Archaea(2)

Question 1

Do prokaryotic cells have a nucleus? if not what?

Answer 1

Prokaryotes lack a membrane-bounded nucleus; their chromosome is located in
the nucleoid, a region of cytoplasm that is not enclosed by a membrane.

Question 2

What are plasmids?

Answer 2

In addition to its single chromosome, a typical prokaryotic cell may also have much smaller rings of independently replicating DNA molecules called plasmids.

Question 3

What are the differences in DNA replication, transcription, and translation in prokaryotes? How do they allow antibiotics to inhibit bacterial growth?

Answer 3

Prokaryotic ribosomes are slightly smaller than eukaryotic ribosomes and differ
in their protein and RNA content.

These differences allow certain antibiotics, to bind to ribosomes and block protein synthesis in prokaryotes but not in eukaryotes. As a result, people can use these antibiotics to kill or inhibit the growth of bacteria.

Question 4

Prokaryotes reproduce quickly by__________.

Answer 4

Prokaryotes reproduce quickly by binary fission.

Question 5

What are the key features of prokaryotic biology?

Answer 5

They
– are small
– reproduce by binary fission
– have short generation times

Question 6

Describe two adaptations that enable prokaryotes to survive in environments too harsh for other organisms.

Answer 6

• Protective cell wall and capsule
• Endospore

Question 7

What are the 3 factors that allow prokaryotes to show great genetic variation?

Answer 7

Three factors contribute to this genetic diversity:

– Rapid reproduction
– Mutation
– Genetic recombination

Question 8

How do rapid reproduction and mutation rates aid the diversity of prokaryotes?

Answer 8

Mutation rates during binary fission are low, but because of rapid reproduction, mutations can accumulate rapidly in a population

– The high diversity that results from mutations and rapid reproduction allows for rapid evolution

Question 9

Define genetic recombination.

Answer 9

Genetic recombination – combining DNA from two sources, contributes to diversity.

Question 10

How can prokaryotic DNA be brought from different sources?

Answer 10

Prokaryotic DNA from different individuals can be brought together by

– transformation,
– transduction, and
– conjugation

Question 11

Differentiate between horizontal and vertical gene transfer.

Answer 11

When individuals are members of different species, this movement of genes from one organism to another is called horizontal gene transfer (in contrast to vertical gene transfer, the movement of genes from parent to offspring).

Question 12

What is transformation?

Answer 12

A prokaryotic cell can take up and incorporate foreign DNA from the surrounding environment

– May lead to genotypic and possibly phenotypic change in prokaryotic cell

Question 13

What is transduction?

Answer 13

In transduction, phages (from “bacteriophages,” the viruses that infect bacteria) carry prokaryotic genes from one host cell to another.

Question 14

What is conjugation?

Answer 14

In a process called conjugation, DNA is transferred between two prokaryotic cells (usually of the same species) that are temporarily joined.

Question 15

What is the F-factor?

Answer 15

The ability to form pili and donate DNA during conjugation results from the presence of a particular piece of DNA called the F factor.

The F factor can exist either as a plasmid or as a segment of DNA within the bacterial chromosome

Question 16

The F factor in its plasmid form is called the _______.

Answer 16

The F factor in its plasmid form is called the F plasmid.

Question 17

Explain F-factor as a plasmid.

Answer 17

Cells containing the F plasmid, designated F+ cells, function as DNA donors during conjugation. Cells lacking the F factor, designated F-, function as DNA recipients during conjugation.

The F+ condition is transferrable in the sense that an F+ cell converts an F- cell to F+ if a copy of the entire F plasmid is transferred

Question 18

Explain the conjugation and transfer of an F plasmid.

Answer 18

1. A cell carrying an F plasmid (an F+ cell) forms a mating bridge with an F– cell. One
   strand of the plasmid’s DNA breaks at the point marked by the arrowhead.
2. Using the unbroken strand as a template, the cell synthesizes a new strand
   (light blue). Meanwhile, the broken strand peels off (red arrow), and one end enters the F–cell. There synthesis of its complementary strand begins.
3. DNA replication continues in both the donor and recipient cells, as the transferred plasmid strand moves farther into the recipient cell.
4. Once DNA transfer and synthesis are completed, the plasmid in the recipient cell circularizes. The recipient cell is now a
   recombinant F+ cell.

Question 19

What is the name for an F- factor built into a chromosome?

Answer 19

A cell with the F factor built into its chromosome is called an Hfr cell (for high frequency of recombination)

Question 20

Explain how the f-factor functions as a chromosome.

Answer 20

During conjugation, an Hfr cell donates chromosomal DNA to an F- cell. The exchange of DNA segments between the two chromosomes creates a new bacterium with genes from two different cells. This creates a new genetic variant that can undergo evolution.