Genetic Material pt2

Question 1

What is transcription?

Answer 1

Transcription is the process of copying DNA segments into RNA.

Question 2

Where does transcription occur in prokaryotes?

Answer 2

In the cytoplasm, through initiation, elongation, and termination phases.

Question 3

How is transcription initiated in prokaryotes?

Answer 3

RNA polymerase recognizes a promoter site (-10 Pribnow box, -35 sequence), unwinds DNA, and starts RNA synthesis.

Question 4

How does RNA elongation occur?

Answer 4

RNA polymerase synthesizes RNA in the 5’-3’ direction using the DNA antisense strand as a template.

Question 5

What happens during termination in prokaryotic transcription?

Answer 5

Transcription stops at a termination sequence, releasing the RNA transcript.

Question 6

Key differences between prokaryotic and eukaryotic transcription?

Answer 6

-Prokaryotes: Continuous process, occurs in the cytoplasm, only one type of RNA polymerase is used, no post-transcriptional modifications.
-Eukaryotes: Separate process, uses three types of RNA polymerase enzymes, occurs in the nucleus, includes 5’ RNA cap and 3’ poly-A tail.

Question 7

What is translation?

Answer 7

The process of synthesizing proteins from mRNA.

Question 8

Where does translation occur in prokaryotes?

Answer 8

In the cytoplasm, often coupled with transcription.

Question 9

How is initiation different in prokaryotic and eukaryotic translation?

Answer 9

-Prokaryotes: Use N-formyl-methionine(fMet-tRNA) and Shine-Dalgarno (also known as the ribosomal binding site AGGAGG)) sequence to anchor mRNA.
-Eukaryotes: Use Met-tRNAi and 5’ mRNA cap to locate the start codon.

Question 10

What are the ribosomal sites in elongation?

Answer 10

-A (aminoacyl) site: Binds incoming aminoacyl-tRNA.
-P (peptidyl) site: Holds tRNA with the growing polypeptide chain.
-E (exit) site: Releases used tRNA.

Question 11

How does elongation proceed?

Answer 11

RNAs cycle through A, P, and E sites; peptide bonds form between amino acids; ribosome translocases codon by codon.

Question 12

What catalyzes peptide bond formation?

Answer 12

Peptidyl transferase, an RNA-based ribozyme in the 50S ribosomal subunit.

Question 13

How does termination occur in translation?

Answer 13

A stop (nonsense) codon (UAA, UAG, or UGA) is recognized by release factors, releasing the polypeptide, and ribosomal subunits dissociate.

Question 14

Differences in transcription and translation between prokaryotes and eukaryotes?

Answer 14

Prokaryotes:
-Transcription and translation occur simultaneously in the cytoplasm.
-Only one type of RNA polymerase is used
-Eukaryotes: Transcription occurs in the nucleus, and translation in the cytoplasm; RNA processing is required.

Question 15

How do bacteria reproduce?

Answer 15

Bacteria divide by binary fission, producing identical daughter cells through vertical transmission of genetic information.

Question 16

What is horizontal transmission in bacteria?

Answer 16

The transfer of genetic information between bacteria through methods such as conjugation, transduction, and transformation.

Question 17

What is bacterial conjugation?

Answer 17

The transfer of DNA from a living donor bacterium to a living recipient bacterium through cell-to-cell contact.

Question 18

Who proposed the concept of bacterial conjugation?

Answer 18

Lederberg and Tatum, who discovered the transfer of the F-factor between E. coli cells.

Question 19

What are the steps involved in bacterial conjugation?

Answer 19

-Mating pair formation
-Conjugal DNA synthesis
-DNA transfer
-Maturation

Question 20

What is the mechanism of bacterial conjugation?

Answer 20

-Pilus formation: Donor (F+) cell forms a sex pilus to contact an F- recipient cell.
-Physical contact: The pilus forms a conjugation tube enabling cell-to-cell contact.
-F-plasmid transfer: One strand of the F-plasmid enters the recipient cell.
-Complementary strand synthesis: Both donor and recipient synthesize a complementary strand, and the recipient becomes a donor.

Question 21

What is bacterial transduction?

Answer 21

The transfer of genetic material from one bacterium to another through a bacteriophage.

Question 22

What happens in generalized transduction?

Answer 22

-A bacteriophage infects a donor cell, initiating the lytic cycle.
-Viral enzymes hydrolyze host DNA into fragments.
-Bacterial DNA fragments are integrated into the viral genome and transferred to the next host during infection.

Question 23

What happens in specialized transduction?

Answer 23

-A temperate bacteriophage integrates its genome into the host DNA during the lysogenic cycle.
-Upon external stimulus, the lytic cycle begins, and the phage may carry specific bacterial genes.
-These restricted genes are transferred to a recipient bacterium.

Question 24

What is bacterial transformation?

Answer 24

The process of DNA uptake by bacteria from their environment, first observed in Streptococcus pneumoniae by Griffith.

Question 25

What are competent cells?

Answer 25

Cells capable of taking up DNA from their environment. Artificial competence can be induced with chemicals or electroporation.

Question 26

How is bacterial competence achieved artificially?

Answer 26

-Chemicals: Bacteria are chilled with calcium phosphate, incubated with DNA, and given heat shock to facilitate DNA entry.
-Electroporation: Electrical pulses make bacterial cells permeable, allowing DNA to enter.

Question 27

How are transformed cells identified?

Answer 27

-Transformed cells are grown on agar with antibiotics. Only cells with the antibiotic resistance gene survive and grow, indicating successful transformation.