Translation

Question 0

Where is the genetic code found?

Answer 0

In mRNA

Question 1

What is translation.

Answer 1

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

Question 2

Properties of the genetic code?

Answer 2

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

Question 3

Why is the genetic code unambiguous ?

Answer 3

Because each codon specifies one single amino acid

Question 4

Why is the genetic code universal ?

Answer 4

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

Question 5

Why is the genetic code generate ( redundancy)?

Answer 5

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

Question 6

What is the wobble effect?

Answer 6

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

Question 7

Experiments that help decipher the genetic code?

Help to determine which codon code for which amino acid..

Answer 7

Marshall Nirenberg and Heinrich Matthael

Triple binding assay

Question 8

Structure of tRNA?

Answer 8

-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.

Question 9

Structure of ribosomes!

Answer 9

Made up of proteins and rRNA

• contains 1 DNA binding site and 3 binding sites for tRNA.
• —>tRNA binding sites ( A P E )

Question 10

Ribosomal tRNA binding sites. ( A P E )

Answer 10

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.

Question 11

What are the stages of transcription?

Answer 11

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

Question 12

What happens during the initiation stage of transcription?

Answer 12

-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.

Question 13

What are the initiation factors?

Answer 13

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.

Question 14

What is the kozak sequence?

Answer 14

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

Question 15

What is the Shine-Delgarno sequence?

Answer 15

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

Question 16

What are the steps during the Elongation stage of transcription ?

Answer 16

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.

Question 17

What determines the sequence of amino acid ?

Answer 17

The order of codons…

Question 18

What reactions form Peptide Bonds?

Answer 18

Dehydration reactions ( same thing as condensation reactions )

Question 19

What are the steps during the termination stage of transcription ?

Answer 19

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 )