7.3 Translation Flashcards
What are ribosomes made of?
Proteins and ribosomal RNA
Why are ribosomes made of proteins?
For stability
Why are ribosomes made of ribosomal RNA?
For catalytic activity
What do ribosomes consist of?
A large and small subunit
What does the small ribosome subunit consist of?
An mRNA binding site
What does the large ribosomal subunit consist of?
Three tRNA binding sites
What are the three binding sites on the large subunit called?
Aminoacyl (A) site
Peptidyl (P) site
Exit (E) site
Where can ribosomes be found?
Freely floating in the cytosol or bound to the rough ER
What are the two sizes of ribosomes?
Prokaryotes = 70S
Eukaryotes = 80S
What is the structure of the tRNA molecule?
A cloverleaf structure with four regions
What are the four regions of the tRNA molecules?
The acceptor stem
The anticodon
The T arm
The D arm
What does the acceptor stem carries?
An amino acid
What does the anticodon associate with?
The mRNA codon
How does the anticodon associated with the mRNA codon?
Via complementary base pairing
What does the T arm associate with?
The ribosome
How does the T arm associate with the ribosome?
Via the E, P and A binding sites
What does the D arm associate with?
The tRNA activating enzyme
What is the tRNA activating enzyme responsible for?
Adding the amino acid to the acceptor stem
What does each tRNA molecule bind with?
A specific amino acid
Where does the tRNA molecule bind with specific amino acids?
In the cytoplasm
What catalyses the binding between tRNA molecule and amino acid?
A tRNA activating enzyme
What is each amino acid recognised by?
A specific enzyme
Why may the enzyme recognise multiple tRNA molecules?
Due to degeneracy
What is the two step process of an amino acid binding to the tRNA acceptor stem?
The enzyme binds ATP to the amino acid to form an amino acid AMP complex
The amino acid is then coupled to tRNA and the AMP is released and the tRNA molecule is charged
What is the function of the ATP in tRNA activation?
To create a high energy bond that is transferred to the tRNA molecule
What does the stored energy do in tRNA activation?
Provides the majority of the energy required for peptide bond formation during translation
What does the initiation stage of involve?
The assembly of the three components that carry out the process (mRNA, tRNA, ribosome)
In initiation, where does the small ribosomal subunit bind to?
The 5’- end of the mRNA
In initiation, up until what point does the small ribosomal subunit move along the mRNA?
Until it reaches the start codon
In initiation, what happens when the small ribosomal unit reaches the start codon?
The appropriated tRNA molecule bind to the codon via its anticodon
How does te tRNA molecule bind to the codon via its anticodon?
Complementary base pairing
In initiation, where does the large ribosomal subunit aligns itself to the tRNA molecule?
At the P site
In initiation, what does the large subunit do once it is at the P site?
Forms a complex with the small subunit
In elongation, what does the second tRNA molecule do?
Pairs with the next codon
In elongation, where does the second tRNA molecule pair with the next codon?
At the A site
In Elongation, what happens to the amino acid in the P site?
It is covalently attached to the amino acid in the A site
In elongation, via what type of bond and reaction is the amino acid in the P site attached to the amino acid in the A site?
A peptide bond and condensation reaction
In elongation, after the tRNA in the p site attaches to the A site, what happens to the tRNA in the P site?
It is now deacylated
What does deacylated mean?
No amino acid
In elongation, after the tRNA in the p site attaches to the A site, what happens to the tRNA in the A site?
It carries the peptide chain
What is the first thing that happens in translocation?
The ribosome moves along the mRNA strand by one codon position
In what directions does the ribosome move along the mRNA strand in?
A 5’- 3’ direction
In translocation, what happens to the deacylated tRNA?
It moves to the E site and is released
In translocation, what happens to the tRNA molecule which is carrying the peptide chain?
It moves to the P site
In translocation, now that the A site is unoccupied happens?
Another tRNA molecule attaches to the next codon in the unoccupied A site and the process is repeated
What does termination involve?
The disassembly of the components and the release of a polypeptide chain
When do elongation and termination stop repeating?
When the ribosome reaches a stop codon
What do the stop codons recruit?
A release factor that signals for translation to stop
In termination what is released?
The polypeptide
In termination what does the ribosome disassemble back into?
It’s two independent subunits
What does initiation and elongation do until it reaches the stop codon?
Continues in a repeating cycle
In eukaryotes, what are the ribosomes separated from?
The genetic material
What separates the ribosomes from the genetic material?
The nucleus
After transcription, what must the mRNA transported from and how?
The nucleus via nuclear pores
After transcription, what must the mRNA be transported prior to?
Translation
What transports the mRNA from the nucleus after transcription?
The ribosome
What does the transport of the mRNA after transcription require?
Modification to the RNA construct
Why does transcription and translation need not to be separated in prokaryotes?
As they lack compartmentalised structures
When may ribosomes begin translating the mRNA molecule in prokaryotes?
While it is still being transcribed from the DNA template
Why is it possible for ribosomes to begin translating the mRNA molecule while it is still being transcribed from the DNA template?
Because both transcription and translation occur in a 5’ - 3’ direction
What is a polysome?
A group of two or more ribosomes translating an mRNA sequence simultaneously
How do polysomes appear?
As beads on a string
What are the beads?
Ribosomes
What is the string?
The mRNA strand
When may polysomes form in prokaryotes?
While the mRNA is still being transcribed from the DNA template
Ribosomes at which end of the polysome cluster will have a longer polypeptide chain?
The 3’ end
In eukaryotic cells, how are all proteins produced initially synthesised?
By ribosomes found freely circulating within the cytosol
When would the ribosome remain free and unattached?
If the protein is targeted for intracellular use within the cytosol
When would the ribosome become bound to the ER?
If the protein is targeted for secretion, membrane fixation or use in lysosomes
What determines protein destination?
The presence or absence of an initial signal sequence on a nascent polypeptide chain
What does SRP do?
Halts translation
What does the presence of the signal sequence that determines protein destination result in?
The recruitment of a SRP
Where does the SRP-ribosome complex dock?
At a receptor located on the ER membrane
What happens when the SRP ribosome complex docks on the ER membrane?
Translation is re-initiated and the polypeptide chain continues to grow
Once translation is re initiated, how does the polypeptide chain continue to grow?
Via a transport channel into the lumen of the ER
Once translation is re-initiated, where will the synthesised protein be transported and how?
To the Golgi complex or the lysosome via a vesicle
Once translation is re-initiated, where do the proteins targeted for membrane fixation get embedded?
Into the ER membrane
In protein destination, what happens once the polypeptide is completely synthesised within the ER?
The signal sequence is cleaved and the SRP is recycled
How many structures of protein are there?
Four
What is primary structure of protein?
The order/ sequence of amino acids which comprise the polypeptide chain
What forms the primary structure of protein?
Covalent peptide bonds between the amine and carboxyl groups of adjacent amino acids
What does primary structure control?
All subsequent levels of protein organisation
Why does the primary protein structure determine all levels of protein organisation?
It determines the nature of the interactions between R groups of different amino acids
What is secondary protein structure?
The way a polypeptide folds in a repeating arrangement to form alpha helices and beta sheets
What causes the folding in secondary protein structure?
Hydrogen bonding between the amine and carboxyl groups of non adjacent amino acids
How will sequences that do not form either an alpha helix or beta pleated sheet exist?
As a random coil
What does secondary structure provide the polypeptides chain with?
A level of mechanical stability
Why does secondary structure provide a level of mechanical stability?
Due to the presence of hydrogen bonds
What is tertiary protein structure?
The way the polypeptide chain coils and turns to deform a complex molecular shape
What causes tertiary structure?
Interactions between R groups
What is examples of interactions between R groups?
Hydrogen bonds, disulfirame bridges, ionic bonds and hydrophobic interactions
What is important for tertiary structure?
Relative amino acid positions
What is tertiary structure important for?
The function of the protein
What is quarternary structure?
Multiple polypeptides or prosthetic groups may interact to form a single, larger, biologically active protein
What is a prosthetic group?
An inorganic compound involved in protein structure or function
What is a conjugate protein?
A protein containing a prosthetic group
What may hold quaternary structures together?
A variety of bonds
