BS 161 EXAMINATION SCRIPT 2026
COMPLETE ANSWERS
◉ phosphodiester linkage Answer: bond between nucleotides in
nucleotide chain to form polynucleotide/ sugar phosphate backbone
◉ how do phosphodiester bonds attach? Answer: from the 5' to 3'
◉ what direction does DNA code? Answer: 5' ---> 3'
◉ What are nitrogenous bases? Answer: Adenine, Thymine, Guanine,
Cytosine, Uracil
◉ 2 types of nitrogenous bases Answer: purines and pyrimidines
◉ What are purines? Answer: Adenine and Guanine
◉ What are pyrimidines? Answer: cytosine, thymine, uracil
◉ What pyrimidine base is found • Only in RNA?
Only in DNA? Answer: Uracil
Thymine
,◉ What pyrimidine base is in both RNA & DNA? Answer: Cytosine
◉ How do the nitrogenous bases bond to each other? Answer:
hydrogen bonds that are anti parallel
◉ Franklin and Wilkins (1952) Answer: -determined DNA was
helical via X-ray diffraction studies
-DNA is 2nm and there is a turn of the helix every 3.4nm
◉ conservative hypothesis of DNA replication Answer: strand opens
up, each strand is a template strand and copies itself, the two new
strands attach and two original strands come back together
◉ semiconservative hypothesis of DNA replication Answer: strand
splits, each makes its own copy and attaches to its copy (parent &
daughter strands)
◉ dispersive hypothesis of DNA replication Answer: strands open up
and DNA fragments, new little copies are made in the fragments; new
DNA are hybrids of the DNA of the parent strands, patch work cut up
DNA together
◉ If DNA replication were conservative, after 1 round of replication
the tube would have contained... Answer: 2 bands--> a gold/gold
double helix above a blue/blue double helix
,◉ Requirements for DNA replication Answer: -template of DNA
-an enzyme to make a copy
-RNA primer
-nucleotides to assemble the polymers/nucleic acids
◉ replication fork Answer: a Y-shaped point that results when the
two strands of a DNA double helix separate so that the DNA molecule
can be replicated
◉ what holds two DNA strands apart? Answer: Single Stranded
Binding Proteins
◉ What end can new nucleotides be added to? Answer: on the 3' end
◉ What enzyme makes a copy of the template strand of DNA
Answer: DNA polymerase
◉ 2 types of DNA strands Answer: leading and lagging
◉ what is the RNA primer that initiates DNA replication Answer:
DNA primase
◉ how many polymerase III on each strand of DNA and how many
are continuous Answer: 2 and 1 is continuous
, ◉ Prokaryotic DNA replication Answer: * bacteria have a single
circular loop chromosome (DNA is circular)
* Replication can occur in one or both directions
* Process always occurs in a 5' to 3' direction
* begins at origin of replication
* strands are separated, unwound, DNA polymerase enzyme binds to
each side of opening and begins copying
* When both DNA polymerases meet at a termination region,
replication ends and the two copies are separated
◉ where does DNA stop replicating in prokaryotic DNA replication
Answer: Termination site
◉ What are primosomes? Answer: DNA helicase and DNA primase
◉ DNA helicase Answer: unwinds DNA; breaks the bonds and can
create a replication bubble
◉ DNA primase Answer: synthesizes RNA primers; so DNA can be
built off RNA primer
◉ single strand binding proteins Answer: bind to the unpaired DNA
strands, keeping them from re-pairing/ stabilizes them
◉ What forms the last phosphodiester linkage Answer: DNA ligase
COMPLETE ANSWERS
◉ phosphodiester linkage Answer: bond between nucleotides in
nucleotide chain to form polynucleotide/ sugar phosphate backbone
◉ how do phosphodiester bonds attach? Answer: from the 5' to 3'
◉ what direction does DNA code? Answer: 5' ---> 3'
◉ What are nitrogenous bases? Answer: Adenine, Thymine, Guanine,
Cytosine, Uracil
◉ 2 types of nitrogenous bases Answer: purines and pyrimidines
◉ What are purines? Answer: Adenine and Guanine
◉ What are pyrimidines? Answer: cytosine, thymine, uracil
◉ What pyrimidine base is found • Only in RNA?
Only in DNA? Answer: Uracil
Thymine
,◉ What pyrimidine base is in both RNA & DNA? Answer: Cytosine
◉ How do the nitrogenous bases bond to each other? Answer:
hydrogen bonds that are anti parallel
◉ Franklin and Wilkins (1952) Answer: -determined DNA was
helical via X-ray diffraction studies
-DNA is 2nm and there is a turn of the helix every 3.4nm
◉ conservative hypothesis of DNA replication Answer: strand opens
up, each strand is a template strand and copies itself, the two new
strands attach and two original strands come back together
◉ semiconservative hypothesis of DNA replication Answer: strand
splits, each makes its own copy and attaches to its copy (parent &
daughter strands)
◉ dispersive hypothesis of DNA replication Answer: strands open up
and DNA fragments, new little copies are made in the fragments; new
DNA are hybrids of the DNA of the parent strands, patch work cut up
DNA together
◉ If DNA replication were conservative, after 1 round of replication
the tube would have contained... Answer: 2 bands--> a gold/gold
double helix above a blue/blue double helix
,◉ Requirements for DNA replication Answer: -template of DNA
-an enzyme to make a copy
-RNA primer
-nucleotides to assemble the polymers/nucleic acids
◉ replication fork Answer: a Y-shaped point that results when the
two strands of a DNA double helix separate so that the DNA molecule
can be replicated
◉ what holds two DNA strands apart? Answer: Single Stranded
Binding Proteins
◉ What end can new nucleotides be added to? Answer: on the 3' end
◉ What enzyme makes a copy of the template strand of DNA
Answer: DNA polymerase
◉ 2 types of DNA strands Answer: leading and lagging
◉ what is the RNA primer that initiates DNA replication Answer:
DNA primase
◉ how many polymerase III on each strand of DNA and how many
are continuous Answer: 2 and 1 is continuous
, ◉ Prokaryotic DNA replication Answer: * bacteria have a single
circular loop chromosome (DNA is circular)
* Replication can occur in one or both directions
* Process always occurs in a 5' to 3' direction
* begins at origin of replication
* strands are separated, unwound, DNA polymerase enzyme binds to
each side of opening and begins copying
* When both DNA polymerases meet at a termination region,
replication ends and the two copies are separated
◉ where does DNA stop replicating in prokaryotic DNA replication
Answer: Termination site
◉ What are primosomes? Answer: DNA helicase and DNA primase
◉ DNA helicase Answer: unwinds DNA; breaks the bonds and can
create a replication bubble
◉ DNA primase Answer: synthesizes RNA primers; so DNA can be
built off RNA primer
◉ single strand binding proteins Answer: bind to the unpaired DNA
strands, keeping them from re-pairing/ stabilizes them
◉ What forms the last phosphodiester linkage Answer: DNA ligase
