Translation Flashcards
translation
process by which mRNA is decoded and a protein is produced
which direction is mRNA translated?
5’ to 3’, into a protein from the amino (N)-terminus to the (C)-terminus
what is the start codon for translation?
AUG (methionine)
degenerate
the genetic code is referred to this since more than one codon can code for the same amino acid, however it is unambiguous (each codon only specifies for one a.a)
how do mutations arise?
as a result of DNA damage or incorrect incorporation of bases
frameshift mutation
mutation that shifts the “reading” frame of the genetic message by inserting or deleting a nucleotide
point mutation
gene mutation in which a single base pair in DNA has been changed
silent mutation
alters a base but does not change the amino acid
missense mutation
a point mutation in which a codon that specifies an amino acid is mutated into a codon that specifies a different amino acid
nonsense mutation
changes a normal codon into a stop codon
insertion
a mutation involving the addition of one or more nucleotide pairs to a gene
deletion
a lose of one or more nucleotide bases
what are the steps of translation?
initiation, elongation, termination
tRNA in translation
- each tRNA molecule carries one type of amino acid
- the reaction requires ATP and once the a.a. is attached the tRNA is charged
- the tRNA for the start codon differs from tRNA that codes mot methionine within the protein
- charged tRNAs donate their a.a. to the protein chain while the anticodon is attached to the mRNA
- the tRNA is then released; the charged tRNA that codes for the next a.a attaches
initiation of translation
- involves formation of a complex b/w the methionyl-tRNA, initation factors, the mRNA and the small ribosomal subunit (40S)
- the large subunit (60S) binds to complete the ribosome which has 2 binding sites for tRNAs, the peptidyl (P) and aminoacyl (A) sites
elongation
peptidyltransferase catalyzes the formation of the peptide bond
peptidyltransferase
the ribosome makes the peptide bonds that stitch amino acids together
termination
- elongation continues until a stop codon is reached
- no tRNAs that match these codons so release factors bind to the ribosome, allowing the last peptide bond to form before releasing the new polypeptide
- requires a lot of energy expenditure
what are the stop codons?
UGA, UAG, UAA
posttranslational modifications
after the protein emerges from the ribosomes chaperone proteins help it to fold correctly
- a # of different modifications can then be made to the new protein
glycolysation
a common posttranslational modification, especially for secreted or integral membrane proteins; y-carboxylation occurs in some of the proteins involved in blood coagulation
protein targeting
the sorting and transportation of proteins from the site of synthesis on ribosomes to compartments in the cell where they are needed
- once proteins are released, those destined for the cytosol remain but where they are but those w/ “signal sequences” are targeted to the organelle in which they function (nuclear localization signals are an example)
polysomes
multiple ribosomes can attach to an mRNA, each producing the same proteins
what happens to proteins that will be secreted into membranes or organelles?
they are translated into the ER due to a SRP that causes the ribosome to dock onto the ER to complete protein synthesis
signal-recognition particle (SRP)
binds to the signal peptide and brings the signal peptide and its ribosome to the ER
proteins synthesized into the ER
proteins translated into the lumen of the ER are carried in the vesicles to the Golgi complex
- those proteins not destined to stay in the Golgi or go back to the ER heave in vesicles from the other side of the Golgi
- these vesicles either become lysosomes or fuse with the cell membrane to release secreted membrane proteins or imbed membrane-spanning proteins in the cell’s outer lipid bilayer
Huntington’s disease
a human genetic disease caused by a dominant allele; extra CAGs in the gene lead to neurodegenerative disorder and death
