Modelling Protein Synthesis
Jessie Maher
In this experiment, we produced a
simple model of a section of DNA, and
modelled the processes involved in
protein synthesis from the information
in DNA.
Introduction about DNA
• Dna molecule is a double stranded helix, made up of repeating subunits
called nucleotides.
•
-
Each nucleotide is made up of:
A cylic sugar
A phosphate group
A nitrogen base
•
-
The four bases are:
Adenine
Guanine
Cytosine
Thymine
• Alternate sugars and phosphates make the sides and the bases connect to
the sugars making a the rungs like on a ladder.
• Sequence of bases along DNA strand is the gene, gene contains information
needed to make a protein.
Introduction about Protein Synthesis
• Information about the number, type and sequence of amino acids that make up
polypeptides of protein molecule is found on the DNA strand ( code form ).
• Genetic code- sequence of the bases along DNA strand.
• Codon- 3 bases, the codon codes for one amino acid.
• The two processes that use information from the DNA for synthesis of protein:
- Transcription
- Translation
• RNA exists in the forms:
- Messenger RNA ( mRNA ) is made in the nucleus, copies a series of bases from
DNA and takes this message to a ribosome.
- Transfer RNA (tRNA) transfers amino acids to ribosome from the cytoplasm.
The Experiment
EQUIPMENT
• 42 tooth picks ( bonds between the chemicals )
• 18 milk bottles cut in half (36 halves) – ( sugar )
• 18 raspberries (36 halves) ( phosphate units )
• 25 jelly beans halved (5 each of 5 colours) ( bases )
- Purple: A
- Yellow: T
- Blue: C
- Green: G
• 4 different jelly snakes 6cm long ( amino acids )
• A4 white paper ( a cell )
• Coloured paper circle, 6cm diameter (a ribosome )
• Clean sharp knife
• Cutting board
• Gloves
• Scissors
• Marking pen
• Heinemann Biology textbook
DNA, positioned in the nucleus of a cell.
Protein Synthesis:
STEP 1- Transcription
• Transcription is the process where the information on the DNA is copied onto an
RNA molecule.
•Gene length of the DNA has unwinded.
• The gene contains the information about the protein that is being made.
• We are making RNA here, RNA has the base Uracil ( black jelly bean ) where
the thymine ( yellow jelly bean ) is in DNA.
• RNA polymerase moves along the strand linking complementary RNA
nucleotides to form a mRNA strand.
• The mRNA strands length is controlled by start codon ( codon AUG ) and the
stop codon ( either UAA, AUG or UGA ).
• The mRNA strand is modified, it contains only the base sequence that codes
for the protein, most genes contain introns ( non-coding regions ). The region
that codes for the protein are exons. The introns cut from the strand, and exons
join.
•The m-RNA now
moves into the
cytoplasm ( out of the
nucleus ).
STEP 2: ACTIVATION OF AMINO ACIDS
• Activation of amino acids- an enzyme attaches amino acids ( snake ) to its
specific triplet codons of t-RNA in the cytoplasm.
• The m-RNA is moving out of the nucleus into the cytoplasm.
STEP 3: TRANSLATION
• Translation is the process where the information now on the RNA molecule is
used to make a new polypeptide chain.
• mRNA strand binds to a ribosome at the end with the start codon. (Ribosome's
act as site for polypeptide synthesis )
•A tRNA carrying the amino acid methionine and anticodon (UAC) binds to
mRNA start codon within the ribosome.
• Another tRNA binds to the next codonits amino acid links with a polypeptide
bond to first amino acid.
Triplet codon
of tRNA
• First t-RNA is released from ribosome and the ribosome moves along the
m-RNA strand, two tRNAs at a time are temporarily bound within
ribosome and the amino acids link making polypeptide chain.
• Once one of the stop codons are reached the polypeptide chain is released
into cytoplasm, each protein has a certain shape made from the
twisting/folding of polypeptide chain or joining to another to make certain
protein.