Transcription & Translation – ‘Patterns of Life’ pg 121-133 PROTEIN SYNTHESIS Transcription & Translation – ‘Patterns of Life’ pg 121-133

Introduction DNA contains the code to make protein DNA is in the nucleus Protein is made in the ribosome The information must get from the nucleus to the ribosome - mRNA

Nuclear envelope Continuous with pores rough endoplasmic reticulum and ribosomes.

Key Pieces of Equipment DNA RNA – 3 types Messenger (mRNA) Transfer (tRNA) Ribosomal (rRNA) RNA polymerase (protein)

RNA vs DNA Single stranded Thyamine (T) is replaced by Uracil(U) A lot smaller No oxygen molecule

RNA Linear polymer Bases: Purines (adenine & guanine) Pyrimidines (cytosine & uracil) Most are single stranded, therefore does not form a double helix. Although can fold and twist into itself.

Messenger RNA Codon a sequence of three nucleotides that code for a single amino acid mRNA carries the code from the nucleus to the ribosome

Transfer RNA Transfer RNA (tRNA): decodes the information tRNA has an anti-codon which matches a specific codon of mRNA Each tRNA attaches to a specific amino acid that compliments its anti-codon There are 20 different tRNA types (one for each type of amino acid)

Ribosomal RNA Ribosomal RNA (rRNA): makes up approximately 50% of a ribosome. The assembly place of protein synthesis.

Ribosome 2 subunits – heavy and light

The Genetic Code 20 different amino acids used to produce proteins. The code for a specific amino acid is controlled by the 4 different nucleotides (T,C,A,G) in the DNA. This code goes in sequences of three (Triplets) A triplet codes for a single amino acid WHY?

These triplets produce codons in mRNA A codon codes for a specific amino acid Some combinations act as STOP (UAA, UGA, UAG) and START (AUG) signals. One codon is the start codon - AUG

Genetic Code cont.

Protein Synthesis-the process Two parts to protein synthesis: Translation of mRNA from DNA Occors in the nucleus Transcription of mRNA into a polypeptide chain Occurs at the ribosome

Transcription One section of DNA unwinds. One side acts as a template for the mRNA to be synthesised.

The RNA polymerase reads the DNA from 3’ end of the DNA. RNA polymerase then binds complementary bases to form the mRNA.

Codes on the DNA act as punctuation, indicating beginning and end of protein and transcription. Once termination sequence reached, transcription ceases. The mRNA is then completed and it travels out of the nucleus to the ribosome

Translation mRNA becomes bound to a ribosome. The mRNA’s strand is placed in the ‘P’ site (the first position on a ribosome)

Next to the ‘P’ site is the ‘A’ site. Both sites hold one tRNA molecule. Once the start codon is placed into the ‘P’ site, translation occurs.

Next a tRNA fits into the ‘P’ site based upon the codon on the mRNA lined up on the ‘P’ site. Another tRNA fits into the ‘A’ site also based on the codon on the mRNA at the ‘A’ site.

When both sites have a tRNA present, the amino acids on the tRNA bond together to form the first link of a protein chain.

Once the two amino acids have linked together: The tRNA in the P site is released The mRNA moves codon so the tRNA in the ‘A’ site is shifted into the ‘P’ site.

The ‘A’ site is now clear so a new tRNA molecule moves in corresponding to the mRNA This amino acid links to the protein chain. This process continues until a stop codon is read at the ‘A’ site.

Termination Once a stop codon is read at the ‘A’ site, the ribosome has finished synthesising the protein. A new tRNA molecule is not added to the protein chain. The two ribosome units separate. Protein chain released from ribosome.

Protein synthesis animation http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter15/animations.html#