Translation (RNA--> Protein) Flashcards
Transcription
converting DNA–> RNA
The moving of information that is encoding in the DNA –> RNA
Why is is called transcription
Language (monomers) between DNA and RNA is the same. They are both made out of nucleotides (they are poly nucleotides)
Translation
Language between RNA and Proteins are different. The monomers that the proteins are made of change. Proteins are made of amino acids whereas in RNA it is nucleotides
What does the genetic code do
It explains how nucleotide sequenced become amino acid sequences
How many nucleotides come together to form an amino acid?
3 nucleotides code for 1
amino acid
We call each of these nucleotides codons
How many possible RNA nucleotides are there?
4 Possible
How many nucleotide combinations are there
64 combinations forming aminos acids
How many amino acids are there
20
Why are there 64 codon combinations but only 20 amino acids. Why?
Redundancy in code.
Some amino acids are specified by more than one triplet. Many codons can code for the same amino acid
Amino acid code from RNA is universal for…
All present day organisms except for mitochondria who have their own transcription and translation mechanisms.
Is mRNA single or double stranded
Single
long strand of nucleotides
What is a reading frame
This considers where you start counting your nucleotides from
Each mRNA has three different reading frames
Deciding this depends on the starting codon.
Transfer RNA
tRNA
Messenger RNA
mRNA
Ribosonal RNA
rRNA
What is tRNA
A long strand of nucleotides.
Because complementary strands of nucleotides can hydrogen bond they are able to form secondary and tertiary structures.
tRNA forms a clover leaf shape. This has two important sections
What are the two important sections of the clover shaped secondary tRNA structure
Anti Codon -3 letter code that is complementary to the codon that is present in the mRNA. It recognisses the codons on the mRNA
3 prime end of the tRNA. This is where it attaches to the amino acid.
How many nucleotides normally form a tRNA
80
Further folding of the clover shape and Hydrogen bonding can cause what shape to form
L Shape
Final shape
Tertiary structure- always exists in this structure
Wobble (base) pairing
Looks at the redundancy in the code.
The nature of the nucleotides that creates tRNA is that the variations in the codons that create an amino acid tend to be in the last of the three codons
The idea of wobble pairing means that the tRNA can recognise flexibility
Why is there wobble pairing
Gives the cells conservation of resources and energy so it does not produce all 60 tRNAs
How are tRNAs manufactured inside the cell?
The enzyme- aminoacyl-tRNA synthetases
The enzyme bashing the amino acid and tRNA together
It brings them close together so there is a high energy bond that is formed.
It is an active process which means energy is expended in the process so one atp is consumed
Ribosome
A complex that is made of both proteins and rRNA.
What does mRNA do.
mRNA+tRNA+ Ribosomes
the mRNA brings the mRNA in close proximity with the tRNA and catalyses the whole process of forming a polynucleotide
Basically a Catalyst
What is the function of a ribosome
Peptidle transferase
produces a polypeptide
ribosomes create polypeptides
Bring together the mRNA and tRNA. As it builds the polypeptide chain it moves along the mRNA (like a little machine) one codon at a time.
What is the structure of a ribosome
The actual structure is unknown - Finer details
We know it is made up of one large subunit and one small
Each of the subunits are made of proteins as well as RNA
They are several million daltons in size (large subunit- can be seen under electron microscopes)
Quaternary structure
What are the three important sights in the ribosomes
The A site
The P site
The E site - the eject site
What is the function of the small subunit in a ribsome
Contains mRNA binding site and links to the tRNAs
What is the function of the large subunit in a ribosome
Catalyses the formation of the peptide bonds
How many steps are there for the translation of the mRNA molecule
Three step cycle that is repeated
What are the steps for translating mRNA
Starting point
- An mRNA molecule and small subunit are holding on to each other.
- A polypeptide chain is also holding on to the 3rd amino acid–> attached the the tRNA
- Peptide chain has formed between amino acids 2 and 3 in the polypeptide chains
Then…
- An incoming (new) tRNA comes into the ribosomes A site (this is tRNA 4)
- This tRNA carries the 4th amino acid.
- The larger subunit on the ribosomes then moves (shifts slghtly) so that the 4th and 3rd amino acids are now in close proximity –> Forms a polypeptide bond between them.
- The 3rd tRNA is then pushed away and moves onto the E site where it is ejected ( it is now devoid of the amino acid it was carrying )
This process then repeats with a new incoming tRNA
The polypeptide chain grows from which end
The 5* end to the 3* end on the mRNA
Goes from the N terminus to the C terminus on the polypeptide chain
What is the start site crucial for
Getting the correct reading frame
If you don’t start with the correct reading frame the whole sequence of your amino acid changes
leads to protein garbage/mistranslated proteins
How do we set the correct reading frame
We have initiated tRNA
In all organisms the codon that starts the protein off starts with AUG–>codes for methionine–> Only one codon codes for methionine
This is the transcription start site
What is a charged tRNA
Any time a tRNA is attached to an amino acid we call it a charged tRNA
How does translation start
- The ribosome attaches onto the mRNA and looks for the AUG codon
- Whatever reading frame is provided by the UAG is used
- You now have the mRNA but it needs translating
- You don’t have the entire ribosome assembling at the very start. You have a small subunit attached with the initiator tRNA
- The methionine is attached to the initiator tRNA
What is the initiator tRNA
It has initiation factors that are bound to it.
These are proteins
They are charged
Charged methionine tRNA is attached to initiation factors (proteins)
this together is call initiator tRNA
It scans for fully formed mRNA
When is an mRNA fully formed
It has the RNA cap region and the polyA tail.
This is a fully formed stable mRNA molecule
What do the initiator tRNA and smaller subunit do
Goes along the cytoplasm and scans for the fully formed mRNA and when it comes across one it attached. Once its attached it starts scanning the genetic code that is present in the mRNA for the methionine codon which is within the mRNA.
Once it finds the aug the inititator tRNA loses the initiation factors ( the proteins that were bound to it) and instead the larger subunit for the ribosomes comes and attaches to it.
This fully formed ribosobes and now stable mRNA are now ready to start accepting the other tRNAs.
Then the polypeptides start forming.
When do the ribosome stop making polypeptides
The whole thing stops when the entire ribosome complex comes into contact with the stop codon.
We have three codons that code for the stop signal.
Once the ribosome hits the stop codon, instead of incorporating an amino acid a water molecule is incorporated.
When the water molecule is incorporated into the A site of the ribosome thats the signal for the mRNA to detach and the polpeptide to detach and the two ribosomal subunits to detach–> signifies the end of translation
What are the stop codons
UAA
UAG
UGA
almost universal
Release factors
Proteins that come into play once the water molecule enters the A site and all of this detachment is occurring. This detachment is aided by other proteins that are called release factors.
How long is this formed polypeptide active within a cell
It depends on the type of protein
e.g. if it is a structural protein that is part of the membranes in the cells/ hard tissue. The polypeptide survives for weeks/ months.
other more metabolic proteins have polypeptides that are only active for seconds/ minutes /hours
The stability of the protein within an organism depends on the function of the protein
How is the lifespan of a protein dictated / what is the lifespan of the protein dictated by
The rate of formation of the protein
The rate of degradation of the protein
The balance between protein formation and protein degradation dictates how much protein is available in a cell at any given point.
How does protein degradation occur
A dedicated machinery
called Proteasome
The proteasome is made of alot of proteases( proteins that are able to degrade other proteins)
What is the structure of a proteasome
Shaped like a barrel. The barrel is made up of all the proteases. At either end of these barrels you have cap proteins. These cap proteins form the structure but they also recognise which proteins is marked for degradation.
How do you mark proteins for degradation
There is a specific process for this.
Within a cell. If a ubiquitin molecule is added on to a protein. This means the protein is now marked for protein degradation. The ubiquitin added to an amino acid is recognised by the cap proteins that are present on the proteasome.
What is the process of protein degradation
The cap proteins recognise the ubiquitin on proteins and the protein is then taken into the ‘barrel’ and then comes out broken down into different peptides or amino acids.
What is ubiquitin
A small organic molecule
Not a protein
