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Flashcards in Translation Deck (20):

What is translation.

Cytosolic mRNA is recognized by a ribosome .Ribosomes read the mRNA and make a protein.


Where is the genetic code found?



Properties of the genetic code?

-Degenerate( redondancy)
- non overlapping
- 61 of the 64 code for amino acids.
- 3 codons do not code for an amino acid. Called stop codons
-AUG : always start codon


Why is the genetic code unambiguous ?

Because each codon specifies one single amino acid


Why is the genetic code universal ?

Because the codes for amino acid is the same for all the species.
Example: AAA codes for lysine in all species including bacteria.


Why is the genetic code generate ( redundancy)?

More than one codon can codes for the same amino acid.


What is the wobble effect?

The last nucleotide of a codon can often be changed with not effect on amino acid. Allows flexibility .


Experiments that help decipher the genetic code?
Help to determine which codon code for which amino acid..

Marshall Nirenberg and Heinrich Matthael
Triple binding assay


Structure of tRNA?

-At the 3' end is the a.a binding site. Acceptor stem
-Anticodon loop: at the center of the middle loop
Anticodons binds to the complementary codon codon in mRNA.


Structure of ribosomes!

Made up of proteins and rRNA
- contains 1 DNA binding site and 3 binding sites for tRNA.
- --->tRNA binding sites ( A P E )


Ribosomal tRNA binding sites. ( A P E )

A- aminocyl site: holds the tRNA that just arrive
P- holds the tRNA with growing polypeptide chain.
E- exit site: holds the tRNA with no amino acid.


What are the stages of transcription?

-Initiations aided by Initiation factors( IF2, IF3, IF4)
-Elongation aided by elongation factors ( EF)
- Termination.


What happens during the initiation stage of transcription?

-IF3 binds to the small subunit of the ribosome and it apart from large subunit.
-Recruitment of " Initiator tRNA via IF2.( methionine 1st a.a)
- mRNA binds to the small subunit.
( in eukaryotes IF4 binds to 5' Cap and interaction b/t IF4 &IF3 bringing mRNA and small subunit together)
- ribosome start scanning for AUG ( upstream is located kozak sequence)
-bacteria mRNA bind via IF3 only.( shine Delgrado sequence help the ribosome)
-IF 3 leaves and the large subunit binds to the assemble complex.


What are the initiation factors?

IF2: help recruit the Initiator tRNA ( methionine )
IF3: binds to the small subunit and keep it apart from the large.
IF4: binds to the 5'Cap and helps mRNA attachment to small subunit.


What is the kozak sequence?

An upstream sequence that helps ribosomes locate the first UAG( start codon)


What is the Shine-Delgarno sequence?

A sequence in prokaryotes Before AUG that helps ribosome locate it.


What are the steps during the Elongation stage of transcription ?

Stage where the polypeptide is actually being made. Aided by Elongation factors ( EF)
- the ribosome reads the next 3 nucleotides and the complementary tRNA will bind to the A site.
-The methionine is removed for the 1st tRNA and is enzymatically added( enzyme rRNA) to the second tRNA in then A site. A peptide bond is formed.
-the uncharged tRNA in the P site moves to the E site briefly and then exits.
-mRNA is shifted by 3 nucleotides ( aid by EF)
- the tRNA Witt the 2 a.a now moves to the P site and the 3 rd codon is exposed in the a-site
The tRNA with the complementary anticodon comes into the A-site.


What determines the sequence of amino acid ?

The order of codons...


What reactions form Peptide Bonds?

Dehydration reactions ( same thing as condensation reactions )


What are the steps during the termination stage of transcription ?

The process stops
- when the ribosomes arrive to one of three stops codons , no tRNA has the corresponding anticodon ( no a.a can be added to the chain)
-This act as a signal to ribosome that it needs to end translation.
- protein release factors bind to the ribosomes and release both mRNA and polypeptide ( cut polypeptide from last tRNA )