Theme 2 Module 3

Question 1

genome

Answer 1

the set of chromosomes in a microrganism

Question 2

Translation overview

Answer 2

cellular components are able to read genetic messages and translate the message into specific primary amino acid sequences

Question 3

Role of tRNA

Answer 3

tRNA molecules are able to transfer amino acids, from a pool of cytoplasmically situated amino acids to a growing polypeptide strand in a ribosome

Question 4

tRNA description

Answer 4

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

Question 5

Anticodon Region

Answer 5

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’

Question 6

At the 3’ end of tRNA…

Answer 6

protruding amino acid attachment site made of a single stranded CCA nucleotide sequence
Terminal A (adenine) is point of attachment (activation)

Question 7

Activation of tRNA molecule is carried out by…

Answer 7

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

Question 8

mRNA can code for…

Answer 8

64 possible codons
20 amino acids
but only 45 tRNA molecules so some can bind to more than one codon

Question 9

AUG codon in mRNA codes for…t

Answer 9

the amino acid methionine which signals to protein translation machinery to begin

Question 10

Wobble

Answer 10

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

Question 11

Translation requires…

Answer 11

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

Question 12

Initiation (Eukaryotes)

Answer 12

When translation initiation complex forms towards 5’ cap of mRNA and scans until AUG start is encountered

Question 13

Initiation (Prokaryotes)

Answer 13

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

Question 14

In both prokaryotes and eukaryotes…

Answer 14

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

Question 15

Initiation (Eukaryotic) first step

Answer 15

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

Question 16

Once ribosomal translation complex is assembled..

Answer 16

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

Question 17

Methionine is located…

Answer 17

at peptidyl (P site) of ribosome
as ribosome scans mRNA subsequent charged tRNA enters and binds within aminoacyl (A site) of large ribosomal subunit

Question 18

Sequence of mRNA coding for amino acids is read by the ribosome….

Answer 18

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

Question 19

How can a peptidyl-transferase reaction to occur?

Answer 19

from the binding of a charged aminoacyl tRNA, this will involve the formation of a condensation reaction of a peptide bond in A site

Question 20

Ribosome will continue to translocate along the mRNA molecule, enabled by…

Answer 20

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

Question 21

Once ribosome reaches a stop codon..

Answer 21

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

Question 22

Basic machinery

Answer 22

Large and small subunits of the ribosome, an mRNA, a charged tRNA amino acids and initiation, elongation, and termination factors

Question 23

Translation (Eukaryotes) overview

Answer 23

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

Question 24

Fungus bread mold Neurospora Crassa by Beadle and Tatum established..

Answer 24

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