Modelling Protein Synthesis

1. Modelling Protein Synthesis Jessie Maher

2. 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.

3. 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.

4. 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.

5. 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

6. DNA, positioned in the nucleus of a cell.

7. 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.

8. 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.

9. 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 ).

10. 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.

11. 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 codon- its amino acid links with a polypeptide bond to first amino acid. Triplet codon of tRNA

12. 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.

13. 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.