Molecular Biology Exam questions
and answers graded A+
Pyrimidine - ANS✅✅One carbon ring
Cytosine, Thymine, Uracil
Purine - ANS✅✅Two carbon rings
Adenine, Guanine
How are nucleotides joined together? - ANS✅✅Condensation to form phosphodiester bond
What is the function of mRNA? - ANS✅✅Carries genetic info out of nucleus
Transcript translated to protein
What is the function of tRNA? - ANS✅✅Carries aa to ribosome
Anticodon pairs with codon on mRNA strand
What is the function of rRNA? - ANS✅✅part of ribosome structure
most abundant RNA
coordinated coupling of tRNA to mRNA codons
Feedback inhibition - ANS✅✅Product of pathway is noncompetitive inhibitor
Binds to allosteric site to slow down rxn b/c too much product
Exonucleases - ANS✅✅Degrades nucleic acids by removing one terminal nt at a time
Cleaves phosphodiester bond at end of chain
5' --> 3' and 3' --> 5'
Endonucleases (Prok) - ANS✅✅Restriction enzymes
Cleaves phoshpodiester bonds w/i poly-nt chain
,Recognition site is palindromic sequence
Types I-V
ORI sites - ANS✅✅nt sequence where replication is initiated
Topoisomerase I - ANS✅✅Induces ss breaks
Remove DNA supercoils during TXN and DNA replication; for strand breakage during recombination;
for chr condensation; and to disentangle intertwined DNA during mitosis
topoisomerase II - ANS✅✅cuts both strands of one DNA double helix, passes another unbroken
DNA helix through it, and then reanneals the cut strands
Gyrase (topoisomerase II) - ANS✅✅Unwinds supercoiling caused by unwinding at the rep fork by
introducing DSBs
Helicase - ANS✅✅Breaks H-bonds of double helix at the replication fork
Primase - ANS✅✅DNApol α (DNA dep RNA pol)
adds short segments of complementary
RNA to ssDNA template (primers), serves as starting points for replication
single-strand DNA binding proteins (SSBPs) - ANS✅✅Binds ssDNA and prevents it from re-
annealing during TXN, replication, repair, and recombination
Okazaki fragments - ANS✅✅Short fragments of DNA synthesized by DNApol δ using the lagging
strand (3'->5') as a template
Ligase - ANS✅✅Closes gaps in DNA
Catalyzes phosphodiester bond between 3'OH and 5'P
What are the steps in DNA replication? - ANS✅✅1. Initiate
2. Elongate
3. Terminate
,Telomeres - ANS✅✅Repeat sequence (TTAGGG) at the ends of chr, protect chr from degradation
RNA polymerase - ANS✅✅DNA dependent RNApol
Transcribes DNA template to RNA (3'-->5'; anti-parallel)
Splicesomes - ANS✅✅Complex of snRNPs
Removes introns from pre-mRNA and splices exons together
Enhancers - ANS✅✅Short regions of DNA that bind proteins (TXN factors) that enhance TXN of a
gene
Poly-A tail - ANS✅✅Prevents mRNA from being degraded in cytoplasm
100-250 A's at 3' end
5' cap - ANS✅✅5'-5' pyrophosphate bridge to a methylated G added to 5' end of a mRNA
Protects against degradation and as a recognition signal for TLN apparatus
aminoacyl tRNA - ANS✅✅tRNAs that carry amino acids
Ribosomes - ANS✅✅Where TLN occurs
Prok: 30s and 50s
Euk: 40s and 60s
Catalyzes peptide bond between a.a.'s
What is the path of a tRNA in a ribosome? - ANS✅✅Acceptor > Peptidyl > Exit
How is translation initiated? - ANS✅✅small rRNA (40S) subunit binds mRNA and scans for start
codon (AUG)
Met-tRNA is brought to the P site
Large rRNA (60S) subunit binds
, How is translation terminated? - ANS✅✅Occurs when stop codon enters A site
Release factor recognizes stop codon, hydrolyzes ester bond with P site, releasing aa chain
Reverse transcriptase - ANS✅✅enzyme that transcribes RNA to cDNA (lacks introns)
RNA --> RNA:DNA --> cDNA (dsDNA)
Pleiotrophy - ANS✅✅a single gene controls the expression of many phenotypic traits
ie Sickle Cell Anemia
cDNA - ANS✅✅intron free complementary DNA
can be inserted into a plasmid
Vector - ANS✅✅helps carry DNA into cell
ie plasmids, virus
Open Reading Frame (ORF) - ANS✅✅sections of DNA that begin with start codons and end with
stop codons
DNA: 5' --> 3'
transcription: 3' --> 5' DNA --> RNA (promoter)
translation: 5' --> 3' mRNA
Spectrophotometer - ANS✅✅Measures amount of light absorbed
Quantitative measurement of [DNA/RNA]
At what wavelength does DNA and RNA absorb? - ANS✅✅260 nm
At what wavelength does protein absorb? - ANS✅✅280 nm
Organic isolation method - ANS✅✅1. Lyse
2. Add phenol/ chloroform > vortex/spin
3. Transfer aqueous layer (top) to new tube
and answers graded A+
Pyrimidine - ANS✅✅One carbon ring
Cytosine, Thymine, Uracil
Purine - ANS✅✅Two carbon rings
Adenine, Guanine
How are nucleotides joined together? - ANS✅✅Condensation to form phosphodiester bond
What is the function of mRNA? - ANS✅✅Carries genetic info out of nucleus
Transcript translated to protein
What is the function of tRNA? - ANS✅✅Carries aa to ribosome
Anticodon pairs with codon on mRNA strand
What is the function of rRNA? - ANS✅✅part of ribosome structure
most abundant RNA
coordinated coupling of tRNA to mRNA codons
Feedback inhibition - ANS✅✅Product of pathway is noncompetitive inhibitor
Binds to allosteric site to slow down rxn b/c too much product
Exonucleases - ANS✅✅Degrades nucleic acids by removing one terminal nt at a time
Cleaves phosphodiester bond at end of chain
5' --> 3' and 3' --> 5'
Endonucleases (Prok) - ANS✅✅Restriction enzymes
Cleaves phoshpodiester bonds w/i poly-nt chain
,Recognition site is palindromic sequence
Types I-V
ORI sites - ANS✅✅nt sequence where replication is initiated
Topoisomerase I - ANS✅✅Induces ss breaks
Remove DNA supercoils during TXN and DNA replication; for strand breakage during recombination;
for chr condensation; and to disentangle intertwined DNA during mitosis
topoisomerase II - ANS✅✅cuts both strands of one DNA double helix, passes another unbroken
DNA helix through it, and then reanneals the cut strands
Gyrase (topoisomerase II) - ANS✅✅Unwinds supercoiling caused by unwinding at the rep fork by
introducing DSBs
Helicase - ANS✅✅Breaks H-bonds of double helix at the replication fork
Primase - ANS✅✅DNApol α (DNA dep RNA pol)
adds short segments of complementary
RNA to ssDNA template (primers), serves as starting points for replication
single-strand DNA binding proteins (SSBPs) - ANS✅✅Binds ssDNA and prevents it from re-
annealing during TXN, replication, repair, and recombination
Okazaki fragments - ANS✅✅Short fragments of DNA synthesized by DNApol δ using the lagging
strand (3'->5') as a template
Ligase - ANS✅✅Closes gaps in DNA
Catalyzes phosphodiester bond between 3'OH and 5'P
What are the steps in DNA replication? - ANS✅✅1. Initiate
2. Elongate
3. Terminate
,Telomeres - ANS✅✅Repeat sequence (TTAGGG) at the ends of chr, protect chr from degradation
RNA polymerase - ANS✅✅DNA dependent RNApol
Transcribes DNA template to RNA (3'-->5'; anti-parallel)
Splicesomes - ANS✅✅Complex of snRNPs
Removes introns from pre-mRNA and splices exons together
Enhancers - ANS✅✅Short regions of DNA that bind proteins (TXN factors) that enhance TXN of a
gene
Poly-A tail - ANS✅✅Prevents mRNA from being degraded in cytoplasm
100-250 A's at 3' end
5' cap - ANS✅✅5'-5' pyrophosphate bridge to a methylated G added to 5' end of a mRNA
Protects against degradation and as a recognition signal for TLN apparatus
aminoacyl tRNA - ANS✅✅tRNAs that carry amino acids
Ribosomes - ANS✅✅Where TLN occurs
Prok: 30s and 50s
Euk: 40s and 60s
Catalyzes peptide bond between a.a.'s
What is the path of a tRNA in a ribosome? - ANS✅✅Acceptor > Peptidyl > Exit
How is translation initiated? - ANS✅✅small rRNA (40S) subunit binds mRNA and scans for start
codon (AUG)
Met-tRNA is brought to the P site
Large rRNA (60S) subunit binds
, How is translation terminated? - ANS✅✅Occurs when stop codon enters A site
Release factor recognizes stop codon, hydrolyzes ester bond with P site, releasing aa chain
Reverse transcriptase - ANS✅✅enzyme that transcribes RNA to cDNA (lacks introns)
RNA --> RNA:DNA --> cDNA (dsDNA)
Pleiotrophy - ANS✅✅a single gene controls the expression of many phenotypic traits
ie Sickle Cell Anemia
cDNA - ANS✅✅intron free complementary DNA
can be inserted into a plasmid
Vector - ANS✅✅helps carry DNA into cell
ie plasmids, virus
Open Reading Frame (ORF) - ANS✅✅sections of DNA that begin with start codons and end with
stop codons
DNA: 5' --> 3'
transcription: 3' --> 5' DNA --> RNA (promoter)
translation: 5' --> 3' mRNA
Spectrophotometer - ANS✅✅Measures amount of light absorbed
Quantitative measurement of [DNA/RNA]
At what wavelength does DNA and RNA absorb? - ANS✅✅260 nm
At what wavelength does protein absorb? - ANS✅✅280 nm
Organic isolation method - ANS✅✅1. Lyse
2. Add phenol/ chloroform > vortex/spin
3. Transfer aqueous layer (top) to new tube
