Translation Flashcards
What are the basic requirements for translation
mRNA, charged tRNA, ribosomes, additional factor proteins, GTP
What are the three types of tRNA
mRNA, tRNA, rRNA
What does mRNA do
it has codon sequences that code for specific amino acids
carries gene information from DNA to ribosome
what does rRNA do
it is the major component with ribosomes
What does the small subunit and large subunit of a ribosome do
small subunit: attaches to mRNA
large subunit: binds the tRNA and catalyzes peptide bond formation
what does tRNA do
it carries the amino acid to the ribosome and pairs its anticodons with the codons on the mRNA
what are the two basic steps of translation?
tRNA charging, where the tRNA and its amino acid are correctly matched and catalyzed by an enzyme
A correct match between the tRNA codon and mRNA codon in the ribosome
what is the enzyme required to catalyze tRNA and its correct amino acid
aminoacyl-tRNA synthetase
What do aminoacyl-tRNA synthetase do
they use ATP to covalently bond a specific amino acid to a tRNA
What are the two primary functions of a ribosome
bring together mRNA and tRNA
form peptide bonds
what forms the peptide bonds in a ribosome
peptidyl transferase (enzyme)
What are the 3 sites on ribosomes?
A, P, E
What does the A( aminoacyl) site do
it holds tRNA with the next amino acid to be added
what does the P (Peptidyl) site do
it holds the tRNA with the growing polypeptide
what does the E-site do?
It is the exit site where tRNAs leave
what side of the poly peptide chain are the amino acids added?
the C terminus
What is the first part of the initiation complex assembly
- a mRNA, a small ribosomal, initiation facots, and the “initiator tRNA charged with Methionine assemble first at the P site
What is the second part of the initiation complex assembly
The complex scans the mRNA for the start codon (AUG)
What is the third part of the initiation complex assembly
A large ribosomal subunit binds to complete the complex and translation begins
how does termination occur in translation
- a stop codon in mRNA reaches the A site
- the A site accepts a protein “release factor”
- the “release factor” causes the addition of a water molecule instead of an amino acid
- this reaction releases the polypeptide and the translation assembly comes apart
How does a cell expend energy to from an initiation complex?
it expends energy obtained by hydrolysis of a GTP molecule to form the complex
Which direction is the polypeptide synthesized
it starts at the initial methionine at the N-terminus and towards the final C- Terminus Carboxyl end
How is energy used in elongation?
The codon recognition of the anticodon and codons requires hydrolysis of one GTP
What does GTP do in codon recognition?
it increases the accuracy and efficiency
How is GTP used in the last step of elongation
it is hydrolyzed to provide energy for the translocation step, where the tRNA in the p-site is released through the E site
When does termination begin
when the stop codon in the mRNA reaches the A site
What happens when the stop codon is reached at the A site
a release factor protein binds to the stop codon and this causes the addition of a water molecule instead of an amino acid to the polypeptide chain
The breakdown of the translation assembly requires what?
2 more GTP molecules
What are polyribosomes
they are formed when multiple ribosomes translate a single mRNA simultaneously
What do polyribosomes allow?
They allow a cell to make many copies of a polypeptide quickly
In what types of cells do polyribosomes occur in?
Prokaryotes and Eukaryotic Cells
What is coupled transcription and translation and where does it occur?
it is when transcription and translation occurs simultaneously
it occurs only within prokaryotes
How do proteins made by ribosomes on the rough ER get into the ER lumen
- the polypeptide synthesis begins in the ribosome
- an SRP binds to a signal peptide attached to the N-terminus of the polypeptide
- the SRP brings the ribosome to a receptor protein
- the SRP detaches and polypeptide synthesis resumes
- A signal Cleaving enzyme cuts off the signal peptide
- the completed polypeptide folds into its final conformation
what happens at each addition
- codon recognition
- peptide bond formation
- translocation
