RNA and the Genetic Code

Question 1

Degenerate Code:

Answer 1

Allows for multiple codons to encode for the same

amino acid

Question 2

Point Mutations: Silent

Answer 2

Mutations with no effect on protein synthesis.

Usually found in the 3rd base of a codon

Question 3

Point mutations: Nonsense

Answer 3

Mutations that produce a

premature STOP codon

Question 4

Point Mutation: missense

Answer 4

Missense: Mutations that produce a codon that codes

for a DIFFERENT amino acid.

Question 5

Frameshift

Mutations:

Answer 5

Result from a nucleotide addition or deletion, and

change the reading frame of subsequent codons

Question 6

Name the three types of RNA and state their functions

Answer 6

Messenger RNA (mRNA): Transcribed from DNA in the 
nucleus, it travels into the cytoplasm for translation. 
Transfer RNA (tRNA): Brings in amino acids and 
recognizes the codon on the mRNA using its anticodon. 
Ribosomal RNA (rRNA): Makes up the ribosome and is 
enzymatically active.

Question 7

tRNA

Answer 7

Translates the codon into the correct amino acid.

Question 8

Ribosomes:

Answer 8

Factories where translation (protein synthesis) occurs.
Eukaryotes: 80s ribosomes
Prokaryotes: 70s ribosomes

Question 9

Initiation: Prokaryotes

Answer 9

Prokaryotes: When the 30S ribosome attaches to the
Shine-Delgarno Sequence and scans for a start codon; it
lays down N-formylmethionine in the P site of the
ribosome.

Question 10

Initiation: Eukaryotes

Answer 10

Eukaryotes: When the 40S ribosome attaches to the 5’
cap and scans for a start codon; it lays down methionine
in the P site of the ribosome.

Question 11

Elongation:

Answer 11

The addition of a new aminoacyl-tRNA into the A site of
the ribosome and transfer of the growing polypeptide
chain form the tRNA in the P site to the tRNA in the A
site. The now uncharged tRNA pauses in the E site before
exiting the ribosome. The A site tRNA moves to the P site

Question 12

Termination:

Answer 12

Occurs when the codon in the A site is a stop codon;
release factor places a water molecule on the
polypeptide chain and thus releases the protein.

Question 13

Posttranslational

Modifications

Answer 13

Folding by chaperones. Formation of quaternary
structure. Cleavage of proteins or signal sequences.
Covalent addition of other biomolecules
(phosphorylation, carboxylation, glycosylation,
prenylation).

Question 14

DNA Ligase

Answer 14

Fuse the DNA strands together to create one strand.

Question 15

Helicase:

Answer 15

Unwinds the DNA double helix

Question 16

RNA Polymerase II:

Answer 16

Binds to the TATA box within the promoter region of the
gene (25 base pairs upstream from first transcribed
base).

Question 17

hnRNA

Answer 17

Collective term for the unprocessed mRNA in nucleus

Question 18

Posttranscriptional

Modification

Answer 18

The process in eukaryotic cells where primary transcript

RNA is converted into mature RNA. Introns cut out

Question 19

Posttranscriptional Modifications: Exons

Answer 19

Exons: Exit the nucleus and form mRNA

Question 20

Posttranscriptional Modification: Introns

Answer 20

introns: Spliced out so they stay in nucleus. Introns also

enable alternative splicing

Question 21

Posttranscriptional Modification

Answer 21

Alternative splicing: Usually introns are cut away and
exons remain, but alternative splicing might change
that. A certain exon may be cut out, or an intron may
stay. This allows for the RNA segment to code for more
than one gene.

Question 22

What is the purpose of the 5’ cap and poly A tail?

Answer 22

5’ Cap and Poly-A tail are added to the mRNA. The cap

and tail stabilize mRNA for translation.

Question 23

Operons:

Answer 23

Inducible or repressible clusters of genes transcribed

as a single mRNA.

Question 24

Inducible Systems:

Answer 24

Under normal conditions, they are bonded to a
repressor. They are turned on when an inducer pulls
the repressor off. Example: Lac operon.

Question 25

Repressible Systems definition and example

Answer 25

Transcribed under normal conditions; they can be
turned off by a corepressor coupling with the
repressor and the binding of this complex to the
operator site. Example: Trp operon

Question 26

Transcription

Factors

Answer 26

Search for promoter and enhancer regions in the DNA,

then bind to the DNA and recruit RNA polymerase

Question 27

Promotors:

Answer 27

Are within 25 base pairs of the transcription start site.

Question 28

Enhancers

Answer 28

Are more than 25 base pairs away from the

transcription start site.