7. DNA, RNA and genes

Question 1

polynucleotide structure

Answer 1

phosphodiester bond has polarity- assymetric
directionality is 5’->3’
any polynucleotide has polarity

Question 2

DNA double helix

Answer 2

anti parallel chains

bases on inside, sugar and phosphate outside

Question 3

which forces hold DNA double helix

Answer 3

hydrogen bonding between bp

hydrophobic stacking forces

Question 4

DNA replication is…

Answer 4

semi conservative

Question 5

sequence of bases

Answer 5

genetic code

Question 6

phenotype

Answer 6

expressed information

Question 7

unit of DNA function

Answer 7

gene

Question 8

DNA-dependent DNA polymerase

Answer 8

• All four deoxynucleotide triphosphates are needed. (dAMP · dGMP · dTMP · dUMP · dCMP)
• DNA synthesis requires an RNA primer.

Question 9

why can DNA replication be a target for drugs

Answer 9

• Eukaryotic DNA replication does not require DNA gyrase (inhibitors can be used as anti- bacterial therapy)
• Eukaryotic DNA replication requires topoisomerase enzymes (inhibitors can be used for chemotherapy)
• Bacteria make folic acid.
• Synthesis of tetrahydrofolate essential for DNA replication (anti-cancer)

Question 10

RNA species in eukaryotic cells

Answer 10

– mRNA
– hnRNA
– tRNA
– rRNA
– 7S RNA
– snRNA

Question 11

which RNA species is most abundant in eukaryotic cells

Answer 11

rRNA

RNA in vivo is highly structured

Question 12

the precursor to mRNA

Answer 12

hnRNA

• contains non-coding intron sequences
• processed after transcription to yield mature mRNA
• introns within hnRNA are removed by splicing

Question 13

features an mRNA contains

Answer 13

– 5’ cap
– 5’ and 3' UTR 
– Ribosome Binding Site (RBS) or Kozak sequence
– Start/initiation codon
– Coding sequence/open reading frame (ORF)
– Termination/stop codon
– poly(A) addition consensus signal
– poly(A) tail

Question 14

5’ cap on eukaryotic mRNA

Answer 14

• Unusual 5’->5’ triphosphate linkage.
• Added post-transcriptionally.
• Important for translation.

Question 15

UTR=

Answer 15

untranslated region
• Eukaryotic mRNAs carry both 5’ and 3’ UTRs.
• UTRs carry important information affecting translation and mRNA stability.
UTR mutation causes human disease

Question 16

RBS (shine-dalgarno sequence)

Answer 16

– consensus: AGGAGG
– spacing with respect to AUG critical
– specific to bacterial mRNAs only

Question 17

Kozak sequence

Answer 17

– consensus: RccRccAUGG

– positions -3 and +4 critical

Question 18

3’ tail

Answer 18

• Tail added post-transcriptionally.
• Tail is a non-template-directed polymer of A residues known as a poly(A) tail.
• Tail addition requires consensus sequence.
– AAUAAA

Question 19

How is transcription termination achieved

Answer 19

cleavage of nascent hnRNA

Question 20

Function of Poly(A) tail

Answer 20

aids if efficient nucleocytoplasmic transport

regulates mRNA stability and translation