PROTEIN SYNTHESIS
In this experiment we modeled the structure of DNA
and the processes involved in protein synthesis
DNA Structure
DNA is a double stranded helix molecule made of subunits called
nucleotides.
Each nucleotide contains a sugar (deoxyribose), a phosphate, and a base.
There are four bases (adenosine, thymine, cytosine and guanine).
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, thus they form complementary pairs.
Protein Synthesis
Information about the number, type and sequence of amino acids necessary to
make a protein molecule, is found as a code in the DNA. This code is in the
sequence of bases. One gene sequence codes for one polypeptide. A set of 3
bases (a codon) codes for one amino acid of a polypeptide. A protein is made of
one or a small number of polypeptides.
Equipment
• 42 tooth picks representing the
bonds between the chemicals
• 18 milk bottle lollies cut in half
(36 halves) representing sugar
• 18 raspberry lollies (36 halves)
representing phosphate units
• 25 jelly beans halved (5 each
of 5 colours) representing
bases
• 4 different jelly snakes 6cm
long representing amino acids •
• A4 white paper representing a •
cell
•
• Coloured paper circle, 6cm
•
diameter, representing a
•
ribosome
•
Clean sharp knife
Cutting board
Gloves
Scissors
Marking pen
Heinemann Biology textbook
Transcription
A gene length of DNA unwinds in the nucleus.
RNA polymerase enzyme moves along the exposed single DNA
strand linking complementary RNA nucleotides together to form
a messenger RNA strand. RNA contains the base uracil where
thymine is found in DNA.
The start codon (AUG) and a stop codon control the length of the
mRNA strand.
The mRNA strand is then modified to remove non-coding regions
called introns. Protein coding regions, exons, are spliced together.
In the cytoplasm, an enzyme attaches amino acids to tRNA
molecules. Each type of amino acid is attached to its
specific tRNA.
The modified mRNA moves out of the
nucleus into the cytoplasm.
Translation
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.