Translation Part 2 and Mutations/DNA Repair

messenger RNA (mRNA)

carries the genetic code that determine the order of amino acids in a polypeptide sequence

Transfer RNA (tRNA)

is responsible for transporting amino acids to the ribosome according to the mRNA sequence

small subunit

binds to the messenger RNA and decodes the genetic message

large subunit

can simultaneously bind to two tRNA molecules and mediates peptide bond formation

A site (aminoacyl site)- (initiation and elongation)

holds the tRNA that carries the next amino acid to be added to the chain

P and A

there are three sites for tRNA binding, codon-anticodon interactions between tRNA and mRNA occur only at what two sites?

P site (peptidyl site)- (elongation)

holds the tRNA that carries the growing polypeptide chain

A (aminoacyl) site

P (peptidyl) site

E (exit) site

What are the three sites for tRNA binding?

E site (elongation and termination)

is the exit site, where discharged tRNAs leave the ribosome

initiation- translation- in prokaryotes ONLY

small ribosomal subunit recognizes and binds to a sequence upstream (5’ end) of the start codon

initiation- translation- in eukaryotes ONLY

small ribosomal subunit recognizes and binds to the 5’ cap and a sequence upstream (5’ end) of the start codon

the small ribosomal subunit binds to mRNA at the 5’ end and locates the start codon

methionine-charged tRNA binds to the AUG start codon, completing the initiation complex

the large ribosomal subunit joins the initiation complex, with methionine-charged tRNA now occupying the P site

initiation (translation) steps

tRNA charging

aminoacyl- tRNA synthetase enzymes match up tRNAs with their specific amino acids

initiation factors

proteins that mediate binding between mRNA, tRNA, and the ribosomal subunits

ATP /GTP hydrolysis

assembling the initiation complex requires what?

n-terminus

e’ of mRNA corresponds to what of the peptide

codon recognition: the anticodon of an incoming tRNA binds to the codon at the A site

peptide bond formation met is linked to ser by peptidyl transferase activity of the large subunit

• (the bond between the amino acid (or polypeptide) and the tRNA in the P site is broken

• peptide bond is formed)

Elongation:the ribosome shifts down one codon, moving the uncharged tRNA to the E site, and the tRNA carrying the growing polypeptide chain to the P site, opening up the A site

• after peptide bond is formed, the ribosome moves to shift the tRNAs to the adjacent site

a new charged tRNA enters the A site and the polypeptide is transferred to its amino acid

the ribosome shifts down one codon, releasing the tRNA from the E site, moving the tRNA with the polypeptide to the P site, and opening up the A site.

Process repeats

elongation (translation) steps

wobble effect

the anticodon can sometimes pair with either C or U in the third position of the codon, which is known as what?

peptidyl transferase

helps connect amino acids to form a protein chain during the translation process

peptide formation

catalyzed by rRNA in the large ribosomal subunit

peptide bond

formed between the new amino acid and the existing amino acid (or the last amino acid of the polypeptide)

binding of the charged tRNA to A site

ensuring the correct charged tRNA is bound to the A site

movement of the tRNAs within the ribosome

Elongation factors (in translation) facilitate what?

a release factor binds to the complex when a stop codon enters the A site

• this release factor triggers the hydrolysis of the bond between the polypeptide and the tRNA in the P site

the release factor disconnects the polypeptide from the tRNA in the P site

the remaining components (mRNA and ribosomal subunits) separate

termination (translation) steps

hydrolysis of 2 GTP molecules

dissociation of the ribosomal subunits requires what?

ATP

protein synthesis utilizes a lot of what?

initiation

assembly of the complete initiation complex

elongation

binding of the charged tRNA to the A site

translocation of tRNA with growing peptide to the P site

termination

dissociation of the ribosomal subunits

P site

during translation initiation, the initial tRNA binds to what site in the ribosome?

several ribosomes

mRNA can be bound by

NO, only in prokaryotes

can co transcriptional translation (polyribosome) occur in both prokaryotes and eukaryotes?

Phosphorylation

Glycosylation

Proteolysis

post translational modifications:

phosphorylation

added phosphate groups alter the shape of the protein

glycosylation

adding sugars is important for targeting and recognition

proteolysis

cleaving the polypeptide allows the fragments to fold into different shapes

N-terminus

initial met (start codon) is cleaved off the

primary structure

secondary structure

tertiary structure

quaternary structure

protein structures

protein structure

defined as a polymer of amino acids joined by peptide bonds

protein structure

plays a critical role in the translation process

proteins

primary components of the molecular machinery involved in translation

3D structure of a protein

determines wide range of functions in cellular processes

mRNA

initiation factors

elongation factors

release factors

aminoacyl tRNA synthetases

tRNA

ribosome (ribosomal RNA+ ribosomal proteins)

what cellular components are required for translation

errors during DNA replication

spontaneous chemical changes in bases

caused by mutagens (ex. X-rays, carcinogens)- induced mutations

DNA mutations

errors during DNA replication

point mutations (base substitutions)

insertion or deletion of a single nucleotide (rare)

spontaneous chemical changes in bases

point mutations (base substitutions)

caused by mutagens (ex. X-rays, carcinogens)- induced mutations

point mutations (base substitutions)

insertion or deletion of a single nucleotide/large DNA fragments

During DNA replication, an incorrect nucleotide may be added to the growing chain

recognition of the mismatch causes the DNA polymerase to back up and excise the incorrect nucleotide

DNA polymerase adds the correct nucleotide and replication proceeds

Errors during DNA replication:

DNA repair steps

point mutation

single nucleotide change

methylated

in prokaryotes, DNA is ______after DNA replication

spontaneous mutation

point mutations caused by chemical changes in bases

chromosome alteration

mutations that change chromosome structure or number

chromosome alteration

they occur when a section of a chromosome breaks off and rejoins incorrectly, or does not rejoin at all