Protein Synthesis

From Gene to Protein• DNA acts as a template to

organise and produce proteins.• Proteins form the structure of the

body and the enzymes that run it.• A gene is a strip of DNA, which

codes for the formation of a protein.

• The gap between the DNA template in the nucleus and the actual formation of the protein is bridged by RNA.

From Gene to Protein• First, a copy of the DNA template is

made and carried out to the cytoplasm – tis is done via messenger RNA (mRNA).

• Then amino acids are collected from the cytoplasm and carried to the assembly point (ribosome) – this is done by transfer RNA (tRNA).

• The amino acids are clicked together in the right order using ribosomal RNA (rRNA) in the ribosomes.

RNA – Ribose Nucleic Acid

• RNA contains the sugar Ribose.• The base Thymine is replaced

with Uracil.• The strands are much shorter

than DNA.• RNA is single stranded.• There are 3 types:–mRNA– tRNA– rRNA

Messenger RNA (mRNA)

• This carries the genetic information from the DNA to the ribosomes.

• It is a long string, with nucleotides arranged in groups of 3 bases called codons.

• Each codon codes for a specific amino acids.

Transfer RNA (tRNA)• This is a clover-leaf shaped molecule.• It has a 3 base anticodon code,

(complementary to the codon on mRNA) at one end, and at the other end there is a particular amino acid.

• The function of tRNA is to pick up amino acids specific to the anticodon and carry them to the ribosomes.

• They are clicked into place in the correct order to make a protein.

Ribosomal RNA (rRNA)

• This makes up part of the structure of the ribosome, the site of protein synthesis in the cytoplasm.

• This is the most abundant RNA.• rRNA is made in the nucleolus.• Its function is to hold the mRNA and

tRNA together so that a peptide bond can form between the amino acids.

Ribosomes

• Consist of 2 subunits, made in the nucleolus.

• These leave the nucleus through the nuclear pores.

• The large and small subunits do not join until they are attached to a mRNA molecule.

• The ribosome consists of many proteins, enzymes and rRNA.

Protein Synthesis

• In the cell there are 2 codes: – The base codes on the DNA– The amino acid codes of a protein.

This involves 2 processes:TranscriptionTranslation

Transcription• A section of DNA unwinds and one side acts

as a template.• Using this a mirror image molecule known as

mRNA is formed.• It follows the strict base pairing rule.– C with G– A with T/U

• The process is controlled by enzymes.• Codes on the DNA act as punctuation

marking the start and end of the protein.

Transcription

• The mRNA moves out of the nucleus through the nuclear pore, and attaches itself to the large and small subunits of a ribosome.

Transcription

• http://www.youtube.com/watch?v=ztPkv7wc3yU&feature=related

• http://www.youtube.com/watch?v=ay6bd_r2JSw&feature=related

Transcription• Transcribe the following DNA sequence into

mRNA.

ATT CGT GCA AAA TCA GGT CGA TAC GGA

UAA GCA CGU UUU AGU CCA GCU AUG CCU

Translation• The mRNA molecule passes through a

slot between the large and small subunits of the ribosome.

• Here the mRNA is translated into protein.• The tRNA carries the appropriate amino

acids to the ribosome.• The anticodon on the tRNA matches the

mRNA, so the rRNA clicks the amino acid onto the growing polypeptide chain that will form a protein.

Translation

• As each new amino acid joins, the ribosome nudges the mRNA strand along 3 notches and the next tRNA falls into place.

• A strand of mRNA is read many times to produce many molecules of the same protein.

• http://www.youtube.com/watch?v=5bLEDd-PSTQ&feature=related

Summary

• http://www.youtube.com/watch?v=983lhh20rGY&feature=related