PROTE

IN S

YNTH

ESIS

BY :

SO

PH

I E G

OL L A

N

In this experiment we modelled the structure of DNA and the processes

involved in protein synthesis from the

information in the DNA

DNA STRUCTURE

DNA - a double stranded helix molecule which consists of subunits called nucleotides.

Each nucleotide contains a sugar, a phosphate, and a base.

There are four bases:

- adenosine

- thymine

- cytosine

- guanine

Alternate sugar and phosphates form the sides, and the bases are 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.

The complementary pairs are:

- Adenosine and thymine

- Cytosine and guanine

PROTEIN SYNTHESIS

The information about the number, type and sequence of amino acids, needed to make a protein molecule, is found as a code in DNA.

The code- a sequence of bases.

One gene sequence codes for one polypeptide (a single chain of many amino acids)

A set of 3 bases (a codon) codes for one amino acid of a polypeptide.

A protein is one or more polypeptides.

EQUIPMENT

42 toothpicks

18 milk bottles cut in half (36 halves) – sugar

18 raspeberry lollies cut in half- phosphate

25 jelly beans cut in half (5 of each 5 colours)- bases:

Adenosine- orange

Thymine- purple

Cytosine- pink

Guanine- green

Uracil- blue

4 jelly snake, aproxx. 6cm long, different colours

A4 white paper representing a cell

Colored paper circle, 6cm diameter- a ribosome

Clean sharp knife

Cutting board

Gloves

Scissors

Marking pen

Heinemann Biology textbook

TRANSCRIPTION

A gene length of DNA unwinds in the nucleus. This is the area containing the information about the protein to be made.

RNA polymerase enzyme moves along the exposed single DNA strand linking complementary RNA nucleotides together to form a mRNA strand.

RNA contains the base uracil where thymine is found in DNA. (uracil replaces thymine)

The ‘start’ codon and the ‘stop’ codon control the length of the mRNA strand

The mRNA strand is then modified so that it only consists of the base sequence that will code for the protein. It removes the non-coding regions, introns, while still in the nucleus by splicing the coding regions, exons, together.

The modified mRNA then moves from the nucleus into the cytoplasm

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.

mRNA passing out of the nuclear pores into the cytoplasm

triplet codons of tRNA with amino acids in the cytoplasm of the cell

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

the amino acid methionine at one end and anticodon (UAC) at the other, binds to the mRNA start codon within the ribosome.

A second tRNA binds to the next codon. Its amino acid links to the polypeptide bond of 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

Amino acid forming polypeptide bond (jelly snakes)

Ribosome

Triplet codon of tRNA

mRNA strand

DNA strand

A polypeptide chain forms (jelly snakes)

Snakes form the polypeptide chain

When a ‘stop’ codon is reached the polypeptide chain is released into the cytoplasm

Polypeptide chain

A polypeptide chain is only the primary structure of a protein. Each protein has a particular shape formed by the twisting or folding of its polypeptide chains

Proteins are vital components of a cell.