DNA Structure
What does the abbreviation DNA stand for?
Deoxyribonucleic Acid
What does it mean that DNA replication is “semi-conservative”?
It means that each new DNA molecule contains one original (parent) strand and one newly synthesized strand.
Why do both strands of DNA replicate differently?
Because DNA is antiparallel and DNA polymerase can only synthesize in the 5′→3′ direction
What is a wild-type allele?
The allele present on the vast majority of chromosomes (the most commonly observed)
DNA repair enzymes are in a constant race with what molecular process that can lock in mutations?
Replication (if DNA replicates before enzymes can repair mutations, the mutation becomes heritable)
Name the three components of a nucleotide.
Sugar, Phosphate, Nitrogenous Base
What does it mean for DNA to have polarity?
Each strand has a direction, with a 5′ end and a 3′ end, and DNA polymerase can only synthesize new DNA in the 5′ → 3′ direction.
What are the fragments of DNA created on the lagging strand called?
Okazaki Fragments
What is the difference between monomorphic and polymorphic genes?
Genes with one common allele are considered monomorphic, while genes with several common alleles in natural populations are polymorphic.
What do we call naturally occurring mutations?
Spontaneous Mutations
Identify which nitrogenous bases are purines and which are pyrimidines.
Purines: Adenine (A) and Guanine (G)
Pyrimidines: Cytosine (C) and Thymine (T)
What are the two stages of DNA replication?
Initiation, Elongation.
What is the enzyme that adds new bases?
DNA Polymerase
What is the difference between forward and reverse mutations?
A forward mutation occurs when a wild-type allele changes to a different allele, which can be either dominant or recessive relative to the original.
A reverse mutation, or reversion, restores a mutant allele back to the wild type.
By definition, what is a protein?
Polymers made of amino acids.
How do purines and pyrimidines differ structurally, and why is this difference important for base pairing?
Purines have two rings
Pyrimidines have one ring.
What is the replication fork?
The replication fork is the Y-shaped region where the DNA double helix is unwound so that each strand can serve as a template for replication. It’s where DNA synthesis actively occurs.
What is the name of the enzyme that unzips DNA?
Helicase
What are the three main types of mutations that can affect a nucleotide sequence?
Insertions, Deletions, Substitutions.
What do we call chains of hundreds to thousands of amino acids linked by peptide bonds?
Polypeptides
Explain Chargaff’s ratios and describe how they contributed to the model of DNA.
The amount of adenine (A) equals thymine (T), and the amount of guanine (G) equals cytosine (C). (1:1 ratio)
What is the difference between the leading strand and lagging strand of DNA?
The leading strand is synthesized continuously toward the replication fork, while the lagging strand is synthesized discontinuously away from the fork in short Okazaki fragments that are later joined by ligase.
What is the name of the enzyme that binds fragments on the lagging strand together?
Ligase
What is the difference between transitions and transversions?
Transitions – a purine (A ↔ G) replaces another purine, or a pyrimidine (C ↔ T) replaces another pyrimidine.
Transversions – a purine is replaced by a pyrimidine, or a pyrimidine is replaced by a purine.
What is the difference between a mutagen and a carcinogen?
A mutagen is any agent that causes changes (mutations) in the DNA sequence of a cell.
A carcinogen is any substance or agent that causes or promotes the formation of cancer.