Lesson # 15

Gene expression

Protein synthesis

• When a gene is expressed it means

that a protein is formed.

• In order for the protein to form

two steps need to take place:

1. DNA transcription

2. RNA translation

• Proteins are large biomolecules

important in giving structure and

taking part in metabolic processes.

• Proteins are made up of smaller

units called amino acids.

1. DNA Transcription

• The DNA code of a specific gene (locus) is re-written or transcribed into a

new molecule called messenger RNA (mRNA).

• RNA is a molecule made up of a single strand of nucleotides.

• The nucleotides found in RNA are

• Adenine (A)-- Uracil (U).

• Guanine (G) -- Cytosine (C)

• Thymine (T) is not found in RNA.

5’

5’

5’

3’

3’

3’

DNA Replication

• The section of DNA that needs to be transcribed un coils and strands separate.

• The strand 3’5’ serves as a template for the formation of the mRNA transcript.

• The mRNA transcript will exit the nucleus.

• When it reaches a ribosome it will be translated.

mRNA Translation

• The code is written in triplets.

• Every 3 nucleotides translates for a specific amino acid.

• Triplets are also called codons.

• The ribosome reads the codons and bonds the corresponding amino acid.

• In the end, there will be a chain of amino acids forming the new protein.