Genetic Material pt2 Flashcards
What is transcription?
Transcription is the process of copying DNA segments into RNA.
Where does transcription occur in prokaryotes?
In the cytoplasm, through initiation, elongation, and termination phases.
How is transcription initiated in prokaryotes?
RNA polymerase recognizes a promoter site (-10 Pribnow box, -35 sequence), unwinds DNA, and starts RNA synthesis.
How does RNA elongation occur?
RNA polymerase synthesizes RNA in the 5’-3’ direction using the DNA antisense strand as a template.
What happens during termination in prokaryotic transcription?
Transcription stops at a termination sequence, releasing the RNA transcript.
Key differences between prokaryotic and eukaryotic transcription?
-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.
What is translation?
The process of synthesizing proteins from mRNA.
Where does translation occur in prokaryotes?
In the cytoplasm, often coupled with transcription.
How is initiation different in prokaryotic and eukaryotic translation?
-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.
What are the ribosomal sites in elongation?
-A (aminoacyl) site: Binds incoming aminoacyl-tRNA.
-P (peptidyl) site: Holds tRNA with the growing polypeptide chain.
-E (exit) site: Releases used tRNA.
How does elongation proceed?
RNAs cycle through A, P, and E sites; peptide bonds form between amino acids; ribosome translocases codon by codon.
What catalyzes peptide bond formation?
Peptidyl transferase, an RNA-based ribozyme in the 50S ribosomal subunit.
How does termination occur in translation?
A stop (nonsense) codon (UAA, UAG, or UGA) is recognized by release factors, releasing the polypeptide, and ribosomal subunits dissociate.
Differences in transcription and translation between prokaryotes and eukaryotes?
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.
How do bacteria reproduce?
Bacteria divide by binary fission, producing identical daughter cells through vertical transmission of genetic information.
What is horizontal transmission in bacteria?
The transfer of genetic information between bacteria through methods such as conjugation, transduction, and transformation.
What is bacterial conjugation?
The transfer of DNA from a living donor bacterium to a living recipient bacterium through cell-to-cell contact.
Who proposed the concept of bacterial conjugation?
Lederberg and Tatum, who discovered the transfer of the F-factor between E. coli cells.
What are the steps involved in bacterial conjugation?
-Mating pair formation
-Conjugal DNA synthesis
-DNA transfer
-Maturation
-Donor Bacterium(F+) contains a speclized structre called a pilus that extends from its surface attaching to the Recpient Bacterium(F-) bringing the two cells together and forming a conjugation bridge allwoing the transfer of plasmid from the F+ to the F-. The plasmid can then integrate with with host cell DNA of exist independently
-At the end of conjugation the F- becomes a F+
What is the mechanism of bacterial conjugation?
-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.
What is bacterial transduction?
The transfer of genetic material from one bacterium to another through a bacteriophage.
What happens in generalized transduction?
-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.
What happens in specialized transduction?
-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.
What is bacterial transformation?
The process of DNA uptake by bacteria from their environment, first observed in Streptococcus pneumoniae by Griffith.
