RNA, Transcription, and Translation

How we get from DNA to proteins

RNA (Ribonucleic Acid) RNA is very similar to DNA, but with three

main differences: The backbone of RNA uses a ribose sugar molecule

in place of the deoxyribose sugar molecule that DNA uses

RNA is typically single stranded RNA uses the nucleotide uracil in place of thymine

RNA There are three main types

of RNA messenger RNA (mRNA) –

this carries messages contained in the DNA outside the nucleus to the ribosomes

ribosomal RNA (rRNA) – along with specific proteins it makes up the ribosomes, which make proteins

transfer RNA (tRNA) – carries amino acids to the ribosome and transfers them to the protein that is being built

Transcription Transcription is the process which copies a

piece of a strand of DNA into a complimentary piece of RNA to make messenger RNA

Just like in replication transcription requires enzymes for the process to occur

The main enzyme used is RNA polymerase. RNA polymerase separates the two strands of

DNA, uses one strand as a template to assemble nucleotides into a piece of RNA

This is very similar to replication, but instead of matching an A with a T, RNA uses a U (uracil) to match up with A

Transcription So, what would the RNA transcribed from this

piece of DNA say?

G G A T C C C G A A T G T C

5’

3’

Transcription

How do you think RNA polymerase knows which piece of DNA to copy?

Transcription Your DNA contains specific sequences of DNA

know as promoters Promoters are signals in the DNA that indicate

to enzymes where to bind and begin making RNA

Similar signals tell the RNA polymerase that the RNA is complete and transcription stops.

You might think that transcription is now complete, but there is still some editing that needs to be done

RNA Editing After transcription we are

left with pre-mRNA because it still needs to be cut.

Your cells take that large strand of RNA and cut out pieces called introns

The pieces that are left, exons, are spliced back together to make the final copy of mRNA

Then a cap and tail are added.

Translation Translation occurs when ribosomes use mRNA as instructions to attach amino acids together to make a protein. The mRNA strand exits the nucleus and enters

the endoplasmic reticulum where it can locate and bind to a ribosome

Every three nucleotides in the mRNA codes for an amino acid, which is brought to the ribosome by tRNA

Every three nucleotides are called a codon

Translation Scientists

have figured out how to read this code.

We use an amino acid codon wheel to easily figure out what each codon means.

AUG means start as well as methionine

Translation After the mRNA binds to the ribosome

it moves into different sites. The first site matches the anti-codon

on the tRNA with the codon on the mRNA

Each tRNA molecule has threenucleotides at the bottom of it called

theanti-codon which will form a compliment to some codon along the mRNA. Attached to the top of the tRNA molecule is the amino acid matching the mRNA codon

Translation When the tRNA comes into the first binding

site it binds and recognizes the codon on the mRNA in that site

Then the ribosome moves along the mRNA attaching the amino acid to the previous one creating a polypeptide chain and the now empty tRNA is released

This continues elongating the polypeptide chain until the ribosome reaches a stop codon

An enzyme binds to the mRNA in place of tRNA and tells the two parts of the ribosome to break apart releasing the mRNA and the polypeptide chain

http://www.youtube.com/watch?v=5bLEDd-PSTQ

Protein Synthesis After the polypeptide chain is released it must fold up

to become a protein The interactions create different bonds between amino

acids that give a protein it’s specific shape A protein’s shape is very important because that

determine it’s function If a protein does not fold up properly it will not be able

to do its job

Transcription and Translation