Modelling Protein Synthesis Aim: To model the structure of DNA and the processes involved in the process of photosynthesis. Caitlan Deeth

Equipment 42 toothpicks Clean cutting board 18 milk bottles cut into 36 halves, representing sugar Gloves Scissors 18 raspberry lollies cut in half, to represent phosphate Marking pen A4 white paper 25 jelly beans of 5 colours, representing: Small coloured paper circle Heinemann Biology Textbook Orange- Adenine Pink- Cytosine Green- Guanine Purple- Thymine Blue- Uracil 4 different coloured jelly snakes, cut 6cm long Clean, sharp knife

The Structure of dna A double-stranded helical molecule The molecule resembles a ladder, with bases forming the rungs and alternating sugars and phosphate, the sides It is made up of nucleotides, a series of subunits, each containing: The bases form complimentary pairs, Adenine bonding with Thymine and Guanine with Cytosine. A sugar (called deoxyribose) A phosphate A base Adenine (A) , Guanine (G), Thymine (G) & Cytosine (C) are the names given to the 4 types of bases

The DNA strand contains information on the type, number and sequence of amino acids that make up the polypeptides of a protein chain. It is found in code as a sequence of bases, with a set of three bases (called a codon), coding for one polypeptide.

Within the nucleus, the double DNA strand will unwind. Transcription Within the nucleus, the double DNA strand will unwind.

The enzyme RNA polymerase links complimentary RNA nucleotides together, moving along the exposed DNA strand, to form an mRNA strand, or Messenger RNA. Where Thymine is located on the DNA strand, it is replaced with Uracil along the RNA.

A ‘start’ (AUG) and ‘stop’ codon determines the length of the mRNA strand. Once the whole gene is copied the strand is modified so that non-coding regions for that protein (called introns) are cut out, and the coding regions, or exons, are joined together.

Activation of amino acids 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 from the nucleus into the cytoplasm.

translation The mRNA strand binds on to a ribosome at the end, with the start codon AUG. A tRNA molecule carrying the amino acid methionine as well as the anticodon UAC binds to the start codon. A second tRNA then binds to the next codon, with its amino acid linking with a peptide bond to the first amino acid.

The first tRNA is released from the ribosome, which moves along the mRNA strand one codon at a time. Two tRNA’s are temporarily bound within the ribosome at a time, and their amino acids linked together.

This forms a polypeptide chain.

When a ‘stop’ codon is reached the polypeptide chain is released into the cytoplasm. The protein’s specific function is determined by its shape. The chain twists and folds in on itself to give it a specific conformation or shape.