Molecular Biology Exam 1 – Core Concepts:
DNA Structure, Base Pairing & Synthesis |
Questions Provided with A+ Graded
Rationales Latest Updated 2026
What is a nucleotide?
monomer of nucleic acids
What is a nucleotide made up of?
phosphate, 5 carbon sugar, nitrogenous base
What is a nitrogenous base made up of?
purines (adenine and guanine) and pyrimidines (cytosine, uracil, and thymine)
What is the sequence of DNA
5'-3'
What is a nucleoside made up of?
5' carbon sugar and nitrogenous base
What does each nitrogen base bind to and how many hydrogen bonds?
Adenine to thymine (2 hydrogen bonds) Cytosine to guanine (3 hydrogen bonds)
Why do the different bases have different amounts of bonds?
A and T have less bonds because they don't stack as well. This gives them different levels of
entropy.
Where are adenine and thymine base pairs normally found?
At the beginning of a sequence, usually promoters
What do hydrogen bonds do?
hold the nitrogen bases together and help them align
How do the hydrogen bonds in rna and dna differ?
, in RNA the pattern can be variable which leads to a variety of 3D structures
in DNA the pattern is the double helix
What is this structure?
nucleotide
What is this structure?
nucleoside
What is the polarity of the double helix
They are antiparallel and run 5'-3'
What joins the sugar phosphate
backbone?
phosphodiester bonds
Why does DNA go 5'-->3'?
The 3'OH provides the attachment for the next nucleotide
What is the first modification to the nucleotides?
removing the 2'OH of ribose to make deoxyribose
What is it called when you remove the hydroxyl off of the 2' and 3' on ribose on a nucleoside
dideoxynuceloside
What are the common modifications on a nucleotide
methylation, additions, substitutions, deamination
What are dideoxynucleotides used for?
sequencing bc they stop the chain bc there's nothing to be attachment to the 3' ends
How does azidothymidine (AZT) work?
substitution of an N3 on 3' bc that's where we can terminate the joining of nucleotide. This
prevents the PPDE bond and prevents the RNA genome from being reverse transcribed into
DNA. This stops the reproduction of the virus
What is azidothymidine?
inhibits the reverse transcriptase of retroviruses, such as HIV
DNA Structure, Base Pairing & Synthesis |
Questions Provided with A+ Graded
Rationales Latest Updated 2026
What is a nucleotide?
monomer of nucleic acids
What is a nucleotide made up of?
phosphate, 5 carbon sugar, nitrogenous base
What is a nitrogenous base made up of?
purines (adenine and guanine) and pyrimidines (cytosine, uracil, and thymine)
What is the sequence of DNA
5'-3'
What is a nucleoside made up of?
5' carbon sugar and nitrogenous base
What does each nitrogen base bind to and how many hydrogen bonds?
Adenine to thymine (2 hydrogen bonds) Cytosine to guanine (3 hydrogen bonds)
Why do the different bases have different amounts of bonds?
A and T have less bonds because they don't stack as well. This gives them different levels of
entropy.
Where are adenine and thymine base pairs normally found?
At the beginning of a sequence, usually promoters
What do hydrogen bonds do?
hold the nitrogen bases together and help them align
How do the hydrogen bonds in rna and dna differ?
, in RNA the pattern can be variable which leads to a variety of 3D structures
in DNA the pattern is the double helix
What is this structure?
nucleotide
What is this structure?
nucleoside
What is the polarity of the double helix
They are antiparallel and run 5'-3'
What joins the sugar phosphate
backbone?
phosphodiester bonds
Why does DNA go 5'-->3'?
The 3'OH provides the attachment for the next nucleotide
What is the first modification to the nucleotides?
removing the 2'OH of ribose to make deoxyribose
What is it called when you remove the hydroxyl off of the 2' and 3' on ribose on a nucleoside
dideoxynuceloside
What are the common modifications on a nucleotide
methylation, additions, substitutions, deamination
What are dideoxynucleotides used for?
sequencing bc they stop the chain bc there's nothing to be attachment to the 3' ends
How does azidothymidine (AZT) work?
substitution of an N3 on 3' bc that's where we can terminate the joining of nucleotide. This
prevents the PPDE bond and prevents the RNA genome from being reverse transcribed into
DNA. This stops the reproduction of the virus
What is azidothymidine?
inhibits the reverse transcriptase of retroviruses, such as HIV
