Chapter 10 - The Expression of Genetic Information: Transcription and Translation

Gene expression

Involves transcription and translation at the molecular level

Transcription

Produces an RNA copy of a gene (DNA à RNA).

Translation

Interprets the nucleotide sequence in mRNA to build a polypeptide with a specific amino acid sequence (RNA à protein).

Gene

An organized unit of nucleotide sequences transcribed into RNA, forming a functional product (protein or RNA).

Promoter

Functions as a recognition site during transcription.

Termination (Transcription)

RNA polymerase reaches a terminator, releases the transcript, and dissociates from DNA.

RNA Modifications in Eukaryotes

Pre-mRNA (immature precursor) is processed into mature mRNA.

5’ cap addition

A modified guanine is covalently attached to the 5’ end of pre-mRNA.

3’ poly A tail addition

Added to the 3’ end of pre-mRNA after transcription, increasing mRNA stability in the cytosol.

Introns

Intervening regions that are removed from pre-mRNA.

Exons

Expressed regions that are connected after intron removal.

Spliceosome

Removes introns precisely.

Alternative splicing

Allows complex eukaryotes to use the same gene to make different proteins.

Genetic code

Specifies the relationship between mRNA nucleotide sequence and polypeptide amino acid sequence.

Codons

Groups of 3 nucleotides that code for amino acids.

tRNAs

Translates the mRNA nucleotide sequence into the polypeptide amino acid sequence.

Anticodon

3-base sequence in tRNA complementary to an mRNA codon.

Aminoacyl-tRNA synthetases

Catalyzes the attachment of amino acids to tRNA molecules.

Ribosomes

The sites of translation.

Initiation (Translation)

mRNA, the first tRNA, and the ribosomal subunits assemble into a complex.

Elongation (Translation)

The ribosome moves in the 5’ to 3’ direction from the start codon towards the stop codon, synthesizing a polypeptide.

Termination (Translation)

The ribosome reaches a stop codon and the complex disassembles, releasing the polypeptide.