D1.2 Protein Synthesis

Transcription

The synthesis of pre-mRNA from DNA

Where does transcription occur?

The nucleus

What enzyme is used in transcription?

RNA Polymerase

Promoter Site

The start of the DNA sequence, where RNA polymerase binds to to begin transcription

Role of RNA Polymerase in transcription

RNA polymerase unwinds the DNA strand and moves along the template strand, adding RNA nucleotides to form RNA strand.

What is the template/antisense strand in DNA transcription?

The transcribed DNA strand

What is the coding/sense strand in DNA transcription?

Strand that is not transcribed

What is Gene expression

The process by which information carried by a gene has observable effects on an organism

What is translation

The synthesis of polypeptides from mRNA

Where does translation occur?

In the cytoplasm

What is a codon?

A sequence of 3 nucleotides that correspond to a certain amino acid

Role of mRNA in translation

Contains codons that correspond to an amino acid sequence that codes for a specific polypeptide.

Role of tRNA in translation

Translates the base sequence of mRNA into the amino acid sequence of a polypeptide. Anticodons on one end bind to the mRNA and allow the corresponding amino acid to bind to the other.

What are ribosomes?

Complex structures with large and small subunits for synthesizing polypeptides

Function of ribosome small structure

binding site for mRNA

Function of ribosome large structure

3 binding sites for tRNA: APE

A site of ribosomes

holds tRNA carrying next amino acid to be added to the chain

P site of ribosomes

holds tRNA carrying growing polypeptide

E site of ribosomes

empty/uncharged tRNA leaves ribosome

Degenerate

Different codons can code for the same amino acid

Gene mutation

A change to the base sequence of a gene

What causes sickle cell anemia?

A single base substitution on the beta-globin gene

Post-transcriptional modifications of mRNA

• Added methyl cap on the 5’ end and poly-A tails (chain of adenines) on the 3’ end

• Spliced out introns (useless sequences)

How does preproinsulin become insulin?

• Rough ER: Preproinsulin loses 24 amino acids → proinsulin

• Golgi Apparatus: cleaves and packages proinsulin → insulin