Gene Expression

Transcription

Takes place in nucleus (eukaryotic)

Part of DNA that serves as a template for mRNA formation

Translation

Cytoplasm (eukaryotic)

Sequence of mRNA bases determines the sequence of amino acids in a polypeptide

tRNA's bring amino acids to ribosome

How is mRNA formed?

transcription

Function of mRNA

Carry genetic information from DNA to the ribosomes for protein synthesis

Primary RNA

Dirent product of transcription in eukaryotic cells

Contains both intron and exon segments of DNA

Introns

Intra-gene segments which get removed

Exons

Remain in mRNA

What is 5' cap?

Guanine nucleotide connected to the first nucleotide of the primary RNA transcription

Helps during translation and also transports the mRNA into the cytoplasm

What is 3'polyA tail?

Large string of adenine nucleotides added to the last nucleotide of the transcript

Helps with transport of mRNA out of nucleus, with increasing stability of mRNA and with translation

Stop Codons

Signal termination of translation

3 of them

tRNA

Transports amino acides to ribosomes

Amino acid on one end, anticodon on other end

Ribosomal Subunits

Small and large

Subunits join together just before translation occurs

Has binding sites for mRNA and 3 tRNA's

Translation: Initiation

Brings all translation components together at the start of codon (AVG)

Initiator tRNA attaches to the start codon

Translation: Recognition & Elongation

Polypeptide increases in length

Translation: Termination

Occurs at a stop codon

Where is gene expression controlled?

cell

Operon

Cluster of genes usually coding for proteins related to a certain metabolic pathway

Promoter

Sequence of DNA where transcription begins

Operator

Sequence of DNA where a repressor protein binds

Promoters: Prokaryotic vs. Eukaryotic

Prokaryotes: single promoter can serve several genes

Eukaryotes: each gene has its own promoter

General Steps for Gene Expression

1. DNA Template Strand

2. Transcription

3. mRNA

4. Translation (codons to amino acids)

5. Protein

Transcription: Initiation

RNA polymerase goes down 3’ to 5’ DNA template to creates a complimentary strand (using U)

Transcription: Elongation

RNA Polymerase continues to go downstream

Transcription: Termination