transcription and translation slides

What are the three main steps shared by replication, transcription, and translation

Initiation, Elongation, and Termination

What is the general goal of each process

Replication copies DNA, transcription makes RNA from DNA, and translation makes protein from RNA

What is RNA polymerase made of

Four core subunits: α, β, β′, and ω

What is the role of the sigma (σ) factor

It guides RNA polymerase to the promoter sequence on DNA

What happens after RNA polymerase binds to the promoter

It unwinds the DNA, forms the open complex, and begins RNA synthesis

What are the three stages of transcription

Initiation, Elongation, Termination

What happens during transcription elongation

RNA polymerase adds nucleotides to the 3′ end of the RNA strand, complementary to the DNA template

In transcription, the RNA sequence is identical to which DNA strand

The non-template (coding) strand, except U replaces T

What are the two types of transcription termination

Rho-dependent and Rho-independent termination

How does Rho-dependent termination work

Rho protein binds mRNA, catches RNA polymerase at a GC-rich pause site, and releases the transcript

How does Rho-independent termination work

A GC stem-loop followed by a U-rich region destabilizes the RNA-DNA hybrid, causing release

What are the three main types of RNA

mRNA, tRNA, and rRNA

What is the function of mRNA

It carries genetic information from DNA to the ribosome

What is the function of tRNA

It transfers specific amino acids to the ribosome during translation

What is the function of rRNA

It forms the structural and catalytic components of ribosomes

What enzyme attaches amino acids to tRNA

Aminoacyl-tRNA synthetase

How many codons exist in the genetic code

Sixty-four total (61 sense, 3 stop)

What does “degenerate” mean about the genetic code

Multiple codons can code for the same amino acid

What is translation

The process of synthesizing proteins from mRNA

What is the first amino acid in bacterial translation

N-formyl methionine (fMet)

What are the three sites on the ribosome

A site (Aminoacyl), P site (Peptidyl), E site (Exit)

What happens at each ribosomal site

A site receives new tRNA, P site holds growing chain, E site releases empty tRNA

What are the major steps of translation elongation

Codon-anticodon pairing, peptide bond formation, and translocation

What is the role of EF-Tu

It brings charged tRNAs to the A site using GTP

What is the role of EF-G

It uses GTP to move the ribosome one codon along the mRNA

How does translation end

Release factors bind the stop codon, freeing the peptide and disassembling the ribosome

Why can transcription and translation occur simultaneously in bacteria

Because there is no nucleus, ribosomes can bind mRNA as it is being synthesized

What happens to proteins after translation

They may be modified—fMet removed or small groups like phosphate, methyl, or adenyl added

What helps proteins fold correctly

Chaperones such as GroEL-GroES (Hsp60/Hsp10) and DnaK (Hsp70)

What happens to misfolded or unneeded proteins

They are degraded by proteases or proteasomes

What is a signal sequence

A short N-terminal amino-acid sequence that directs proteins for secretion

What is the Sec pathway

The SecYEG translocon that helps move proteins across the plasma membrane

What is the Type I secretion system

A one-step system that exports proteins directly outside the bacterial cell

How do bacterial cells constantly rebuild themselves

By degrading old proteins and reusing amino acids to make new ones

What determines a protein’s half-life in a cell

Its sequence, shape, and function

What do proteases do

They cut proteins at specific amino acid sequences for degradation

What do proteasomes do

They degrade proteins tagged for destruction, often by ubiquitin in eukaryotes