Transcription and Translation

Basic Principles (definition)

• The process by which DNA directs protein synthesis is known as gene expression

• includes two stages, called transcription and translation

Transcription and Translation Structure

DNA

Nucleus | Transcription

mRNA

Cytoplasm | Translation

Protein

Transcription

• process whereby a DNA molecule serves as a template for the formation of mRNA

• is the synthesis of RNA under the direction of DNA

• produces messenger RNA (mRNA)

Translation

• process by which ribosomes use the sequence of codons in mRNA to produce a polypeptide with a particular sequence of amino acids

• is the actual synthesis of a polypeptide, which occurs under the direction of mRNA

• occurs on ribosomes

Prokaryotes

transcription and Translation occur together

Eukaryotes

RNA transcription are modified before coming true mRNA

Ribosomes

• measures 20 ×30nm

• are particles made of ribosomal RNA and protein

• composed one large subunit and one small subunit

• subunits are made up of proteins and ribosomal RNA (rRNA)

Ribosomes location

• located in the cytoplasm, singly or in groups called polyribosomes

• ribosomes are also attached to the endoplasmic reticulum

Ribosomes Function

• sites of protein synthesis in the cell

• ribosomes receive mRNA from the nucleus

• sequence of codons in mRNA indicates sequence of amino acid residues in a polypeptide

Genes

• are the units of inheritance

• are made up of nucleic acids

A Gene

is a functional region of DNA that specifies a certain inheritable characteristics or trait

The Region of DNA

stores the information that specifies the sequence of amino acid residues that form a specific polypeptide or protein

Genetic infomation

is encoded as a sequence of nonoverlapping base triplets or codons

Codon

• a triplet of bases that specifies an amino acid

• a sequence of 3 nucleotides in mRNA that code for a single amino acid

How many bases correspond to an amino acid?

3

A codon in messenger RNA

is either translated into an amino acid or serves a translational stop signal

During transcription

The gene determines the sequence of bases along the length of an mRNA molecule