Theme 2 Module 3 Flashcards
genome
the set of chromosomes in a microrganism
Translation overview
cellular components are able to read genetic messages and translate the message into specific primary amino acid sequences
Role of tRNA
tRNA molecules are able to transfer amino acids, from a pool of cytoplasmically situated amino acids to a growing polypeptide strand in a ribosome
tRNA description
made up of a single RNA strand ranging between 70-90 nucleotides in length
hydrogen bonding between complementary base pairings
allows for the formation of four double-helical segments and three loops
clover leaf and can fold into a L
Anticodon Region
specific nucleotide triplet which forms complementary base-pairs with a specific mRNA codon for a specific amino acid
written in 3’ to 5’ and aligns with mRNA codon in 5’ to 3’
At the 3’ end of tRNA…
protruding amino acid attachment site made of a single stranded CCA nucleotide sequence
Terminal A (adenine) is point of attachment (activation)
Activation of tRNA molecule is carried out by…
aminoacyl tRNA synthestase
each aminoacyl tRNA synthetase is specific to the type of tRNA and corresponding amino acid
active site of enzyme recognizes the anticodon end of the tRNA and the region of the amino acid attachment site
20 existing aminoacyl synthetase for each amino acid
once bound to active site enzyme can catalyze covalent attachment of tRNA molecule
mRNA can code for…
64 possible codons
20 amino acids
but only 45 tRNA molecules so some can bind to more than one codon
AUG codon in mRNA codes for…t
the amino acid methionine which signals to protein translation machinery to begin
Wobble
when first base (5’ end) of codon will bind to (3’ end) of anticodon
greater flexibility for base pairing between third nucelotide of a codon and base for anticodon
flexibility–> wobble
Translation requires…
the assembly of ribosomes and associated molecular components along a transcribed mRNA strand
Prokaryotes-assembly + translation occurs in cytoplasm immediately after transcription
Eukaryotes-two seperate processed due to compartmentalization of DNA in nucleus and ribosomes
nucleus then cytosol
Initiation (Eukaryotes)
When translation initiation complex forms towards 5’ cap of mRNA and scans until AUG start is encountered
Initiation (Prokaryotes)
Since prokaryotes have no 5’ caps translation initiation complex assembled at one of more ribosome binding sites called Shine-Dalgarno sequences
Sequences tend to be located a few bases upstream of the translation start codon (AUG)
-Ability for translation to occur along multiple regions of a polycistronic mRNA (more than one protein) sequences allows prokaryotes to have specific open reading frames for more than one protein along a single mRNA strand
-this occurs becuase prokaryotes can have functionally related genes grouped together and they are transcribed a single unit from one promoter
In both prokaryotes and eukaryotes…
the large and small subunits of ribosome will assemble to form a functional ribosome only when they are attached to an mRNA molecule
includes two ribsomal subunits, the mRNA that requires translation, the charged tRNA methionine and initiation factors
Initiation (Eukaryotic) first step
initiation factors bind to 5’ cap of mRNA allows for recruitment of a small ribosomal subunit
other initiation factors will bind to tRNA charged with methionine
Partially assembled initiation complex will move along the mRNA in a 5’ to 3’ until an AUG is encountered
The large subunit of ribosome is then able to bind to the rest of the initiation complex using energy released from GTP hydrolysis and the next charged tRNA molecule can join the ribosome
Once ribosomal translation complex is assembled..
initiation factors are released
All polypeptides are synthesized from the amino end to the carboxyl end and methionine will be the first amino acid found at the amino end of a polypeptide
Methionine is located…
at peptidyl (P site) of ribosome
as ribosome scans mRNA subsequent charged tRNA enters and binds within aminoacyl (A site) of large ribosomal subunit
Sequence of mRNA coding for amino acids is read by the ribosome….
in successive, non-overlapping groups of three nucleotides
each incoming charged tRNA is delivered in association with a GTP-bound elongation factor
Once correct codon-anticodon pairing pairing GTP is hydrolyzed and aminoacyl end of tRNA is released
How can a peptidyl-transferase reaction to occur?
from the binding of a charged aminoacyl tRNA, this will involve the formation of a condensation reaction of a peptide bond in A site
Ribosome will continue to translocate along the mRNA molecule, enabled by…
binding of GTP bound elongation factors which cause the deacylated tRNA to move from the P site to E site and subsequent aminoacyl-tRNA enters A site and is released once it is deacylated tRNA in E site
Once ribosome reaches a stop codon..
GTP-bound release factors will bind to A site and catalyze hydrolysis of bond between the terminal amino acid in the polypeptide and the tRNA in the P site
Further GTP hydrolysis will enable dissociation of the translation complex
Basic machinery
Large and small subunits of the ribosome, an mRNA, a charged tRNA amino acids and initiation, elongation, and termination factors
Translation (Eukaryotes) overview
Initiation factors bind to the 5’ cap of the mRNA which recruits the small ribosomal subunit along with the methionine-charged transfer RNA
partially assembled initiation complex moves along mRNA in 5’ to 3’ direction until AUG is encountered
then the large subunit of the ribosome is able to bind to the rest of the initiation complex using the energy released from GTP hydrolysis and continues to scan the mRNA molecule
The charged tRNA molecules can then join the ribosome at the aminoacyl (A) site and induces a conformational change that allows for the formation of condensation reactions as peptide bonds between each amino acid added to polypeptide chain
with each peptide bond formed deacylated tRNA move from P site to E site
The subsequent aminoacyl-tRNA to enter A site allows for the release of deacylated tRNA
Process of translation terminated once ribosome reaches a stop codon with GTP bound release factors now able to bind to A site and catalyzing dissocation of translation complex
Fungus bread mold Neurospora Crassa by Beadle and Tatum established..
the relationship between genes and proteins referred to as one gene one enzyme
neurospora can grow well on minimal medium and so it must have some enzymes produced by a specific gene that convert simple substances needed
The synthesis of arginine can occur
through a metabolic pathway in a series of steps
eurospora cells that were
placed in Ornithine-only or citrulline-only
supplemented media, it was found that there was
also an inhibition in growth