BY A M Y T U R N E R

DEMONSTRATING PROTEIN SYNTHESIS

DNA

A gene on the DNA strand provides the information required to make the polypeptide

in the form of a designated sequence of bases.

DNA• Each nucleotide contains a sugar (milk bottle), a

phosphate (raspberry), and a base (yellow, purple, blue and green jellybean).

• There are four bases:• Adenine represented by purple jellybeans.• Thymine represented by yellow jellybeans• Cytosine represented by blue jellybeans• Guanine represented by green jellybeans. • Alternate sugar and phosphates form the sides with bases

connected to the sugars making “rungs” like a ladder. • The chemical structure of the bases allow them each to

pair up with only one other base eg: AT and CG

The start codon (AUG) and a stop codon control the length of the mRNA strand.

After the whole gene has been copied, the mRNA strand is modified so that it consists only of the base sequence that will code for

the protein.Each type of amino acid is attached to its

specific tRNA.

The start codon (AUG) end of the mRNA strand binds onto a ribosome. A tRNA

carrying the amino acid methionine and anticodon (UAC) binds to the mRNA start

codon within the ribosome.A second tRNA binds to the next codon. Its amino acid links with a polypeptide bond to

the first amino acid.

The first tRNA is released from the ribosome. The ribosome moves along the mRNA strand one codon at a time. Two tRNAs at a time are temporarily bound within the ribosome and

their amino acids linked together. A polypeptide chain forms.

When a stop codon is reached the polypeptide chain is released into the

cytoplasm. The chain folds on itself and may join other polypeptides to form a protein. Its

specific shape is vital for its particular function.

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