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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 - PowerPoint PPT Presentation
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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
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