Protein synthesis Flashcards
what portion of mRNA is translated
the coding region(CDS)
What specifies amino acids
the codons on the coding region of the mRNA
what decodes the message of the mRNA
anticodons on corresponding charged tRNA
what is translation.
this is a multi-staged process carried out by ribosomes. it is the conversion of mature mRNA to form amino acids and ultimately an elongated polypeptide chain. it occurs as a result of the mRNA binding to the translational machinery which is the ribosome.
what are features of protein synthesis
it is carried out by two population of ribosomes: some bound to the ER and some free in the cytoplasm
it is a fast process
it usually adds 20 amino acids per second and can synthesize a molecule of actin every 20
seconds
it occurs within the cleft between the ribosome units
what are ribosomes
these are ribonucleoprotein complexes comprising of ribosomes and DNA
what is the composition of eukaryotic ribosomes
there are two subunits of eukaryotic ribosomes; the 40s and 60s ribosomes which together form the 80s ribosomes.
the 60s ribosome which is the larger subunit is made up of three RNAs; 5s,5.8s and 28s (120, 60 & 4700) nucleotides and it is made of 49 proteins.
the 40s which is the smaller subunit is made of the 18s RNA(1800 nucleotides) and 33 proteins.
what is the composition of prokaryotic ribsosomes
the 70s ribosome which is the prokaryotic ribosome is made up of two subunits; 50s and 30s ribosome
the 50s subunit is made of two RNAs; the 23s and the 5s and has 31 proteins.
the 30s ribosomes is made up of 16s RNA and 21 proteins.
how many binding sites does a 80s ribosome have and what are they?
it has 3 binding sites and they are;
Exit
Peptidyl binding site
Aminoacyl tRNA binding site
what is the composition of a mRNA
A mRNA contains; a 5’ cap, 5’ UTR, coding region, 3’ UTR, and 3’ polyadenylation.
what are the 3 process of protein synthesis
initiation; assembly of ribosomes on the mRNA with the first initiator tRNA called the aminoacyl tRNA(met-tRNAi)
elongation; charged tRNA come to the ribosomes and the addition of amino acid one at a time to form a polypeptide chain.
termination; ribosome encounters a stop codon, protein synthesis stops and the polypeptide chain is released.
what are eukaryotic translation factors
Proteins directly involved in translation are called initiation or elongation factors and have a name that is systematic
- Initiation factors are call eIF + a number
- For eukaryotic initiation factor 1 , 2 etc
- Elongation factors are called eF + number
- for elongation factor 1, 2, etc
*Others associated with a ribosomal subunits
* L or S for large subunit or small subunit eg
L22
explain the process of initiation
transcription factors firstly bind to the cap and poly a-tail of the mRNA.
the 40s ribosome then binds to the ribosome and met-tRNA, GTP, and eIF2 bind to the p-site of the 40s ribosome to form a 40s pre-initiation complex.
`then scanning commences, this is a process where the ribosome tries to find the start codon on the mRNA molecule. it occurs as a result of the hydrolyses of ATP. once the start codon has been found, the codon of the met-tRNA binds to the start codon, and initiation pauses.
after initiation pauses, the 80s ribosomes is then formed as a result of the binding of the 60s ribosome to the 40s preinitiation complex, this is catalyzed by energy released from GTP. some initiation factors are then released and (2&3) and eIF5 hydrolyses GTP.
with the met-tRNA at the p-site, a charged tRNA binds to the A-site and peptidyl transferase catalyses the formation of a bond between the amino acids bound to the tRNA
what are the energy requirements for protein synthesis
charging of tRNAs with amino acids - 1 ATP
Initiation of polypeptide synthesis- GTP and nATP
elongation of polypeptide chain- 2 GTP per amino acid
termination of polypeptide synthesis and release of polypeptide.
