Molecular Biology (MB) Exam Prep 2025–
2026 | 300+ Practice Questions & Study Notes
| DNA, RNA, PCR, Blotting, Hybridization &
Genetics
Pyrimidine
One carbon ring
Cytosine, Thymine, Uracil
Purine
Two carbon rings
Adenine, Guanine
How are nucleotides joined together?
Condensation to form phosphodiester bond
What is the function of mRNA?
Carries genetic info out of nucleus
Transcript translated to protein
What is the function of tRNA?
Carries aa to ribosome
Anticodon pairs with codon on mRNA strand
What is the function of rRNA?
part of ribosome structure
most abundant RNA
coordinated coupling of tRNA to mRNA codons
Feedback inhibition
Product of pathway is noncompetitive inhibitor
Binds to allosteric site to slow down rxn b/c too much product
Exonucleases
,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)
Restriction enzymes
Cleaves phoshpodiester bonds w/i poly-nt chain
Recognition site is palindromic sequence
Types I-V
ORI sites
nt sequence where replication is initiated
Topoisomerase I
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
cuts both strands of one DNA double helix, passes another unbroken DNA helix through it, and
then reanneals the cut strands
Gyrase (topoisomerase II)
Unwinds supercoiling caused by unwinding at the rep fork by introducing DSBs
Helicase
Breaks H-bonds of double helix at the replication fork
Primase
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)
Binds ssDNA and prevents it from re-annealing during TXN, replication, repair, and
recombination
Okazaki fragments
Short fragments of DNA synthesized by DNApol δ using the lagging strand (3'->5') as a template
,Ligase
Closes gaps in DNA
Catalyzes phosphodiester bond between 3'OH and 5'P
What are the steps in DNA replication?
1. Initiate
2. Elongate
3. Terminate
Telomeres
Repeat sequence (TTAGGG) at the ends of chr, protect chr from degradation
RNA polymerase
DNA dependent RNApol
Transcribes DNA template to RNA (3'-->5'; anti-parallel)
Splicesomes
Complex of snRNPs
Removes introns from pre-mRNA and splices exons together
Enhancers
Short regions of DNA that bind proteins (TXN factors) that enhance TXN of a gene
Poly-A tail
Prevents mRNA from being degraded in cytoplasm
100-250 A's at 3' end
5' cap
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
tRNAs that carry amino acids
Ribosomes
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?
Acceptor > Peptidyl > Exit
How is translation initiated?
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?
Occurs when stop codon enters A site
Release factor recognizes stop codon, hydrolyzes ester bond with P site, releasing aa chain
Reverse transcriptase
enzyme that transcribes RNA to cDNA (lacks introns)
RNA --> RNA:DNA --> cDNA (dsDNA)
Pleiotrophy
a single gene controls the expression of many phenotypic traits
ie Sickle Cell Anemia
cDNA
intron free complementary DNA
can be inserted into a plasmid
Vector
helps carry DNA into cell
ie plasmids, virus
Open Reading Frame (ORF)
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
2026 | 300+ Practice Questions & Study Notes
| DNA, RNA, PCR, Blotting, Hybridization &
Genetics
Pyrimidine
One carbon ring
Cytosine, Thymine, Uracil
Purine
Two carbon rings
Adenine, Guanine
How are nucleotides joined together?
Condensation to form phosphodiester bond
What is the function of mRNA?
Carries genetic info out of nucleus
Transcript translated to protein
What is the function of tRNA?
Carries aa to ribosome
Anticodon pairs with codon on mRNA strand
What is the function of rRNA?
part of ribosome structure
most abundant RNA
coordinated coupling of tRNA to mRNA codons
Feedback inhibition
Product of pathway is noncompetitive inhibitor
Binds to allosteric site to slow down rxn b/c too much product
Exonucleases
,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)
Restriction enzymes
Cleaves phoshpodiester bonds w/i poly-nt chain
Recognition site is palindromic sequence
Types I-V
ORI sites
nt sequence where replication is initiated
Topoisomerase I
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
cuts both strands of one DNA double helix, passes another unbroken DNA helix through it, and
then reanneals the cut strands
Gyrase (topoisomerase II)
Unwinds supercoiling caused by unwinding at the rep fork by introducing DSBs
Helicase
Breaks H-bonds of double helix at the replication fork
Primase
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)
Binds ssDNA and prevents it from re-annealing during TXN, replication, repair, and
recombination
Okazaki fragments
Short fragments of DNA synthesized by DNApol δ using the lagging strand (3'->5') as a template
,Ligase
Closes gaps in DNA
Catalyzes phosphodiester bond between 3'OH and 5'P
What are the steps in DNA replication?
1. Initiate
2. Elongate
3. Terminate
Telomeres
Repeat sequence (TTAGGG) at the ends of chr, protect chr from degradation
RNA polymerase
DNA dependent RNApol
Transcribes DNA template to RNA (3'-->5'; anti-parallel)
Splicesomes
Complex of snRNPs
Removes introns from pre-mRNA and splices exons together
Enhancers
Short regions of DNA that bind proteins (TXN factors) that enhance TXN of a gene
Poly-A tail
Prevents mRNA from being degraded in cytoplasm
100-250 A's at 3' end
5' cap
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
tRNAs that carry amino acids
Ribosomes
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?
Acceptor > Peptidyl > Exit
How is translation initiated?
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?
Occurs when stop codon enters A site
Release factor recognizes stop codon, hydrolyzes ester bond with P site, releasing aa chain
Reverse transcriptase
enzyme that transcribes RNA to cDNA (lacks introns)
RNA --> RNA:DNA --> cDNA (dsDNA)
Pleiotrophy
a single gene controls the expression of many phenotypic traits
ie Sickle Cell Anemia
cDNA
intron free complementary DNA
can be inserted into a plasmid
Vector
helps carry DNA into cell
ie plasmids, virus
Open Reading Frame (ORF)
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
