What are the three parts of a DNA nucleotide?
A deoxyribose sugar attached to a phosphate group and one of four organic bases.
What are the four bases found in DNA?
Adenine (A) and guanine (G) which are purines and cytosine (C) and thymine (T) which are pyrimidines.
What is the difference between purines and pyrimidines?
Purines (A and G) have double-ring structures and pyrimidines (C and T) have single-ring structures.
What is Chargaff’s rule?
In any DNA molecule the amount of A always equals the amount of T and the amount of G always equals the amount of C.
What is a double helix?
The shape of the DNA molecule - two strands wound around each other like a winding staircase.
What forms the “rails” of the DNA double helix?
The sugar and phosphate groups of the nucleotides.
What forms the “steps” of the DNA double helix?
The paired nitrogenous bases of nucleotides from opposite strands.
Which bases pair with each other in DNA?
Adenine (A) pairs with thymine (T) and guanine (G) pairs with cytosine (C).
Why does A pair with T and G pair with C?
Because hydrogen bonding between the bases is specific - A and T form two hydrogen bonds and G and C form three hydrogen bonds.
What does it mean for the two DNA strands to be complementary?
The sequence of one strand completely determines the sequence of the other - each strand is a mirror image of the other through specific base pairing.
What is DNA replication?
The process of copying DNA before cell division.
What enzyme unwinds the DNA double helix to begin replication?
Helicase.
What enzyme builds new DNA strands during replication?
DNA polymerase - it reads along a template strand and adds the correct complementary nucleotide at each position.
What is a primer in DNA replication?
A short section of nucleotides added by a separate enzyme to begin the new strand because DNA polymerase cannot start a strand from scratch.
What is the replication fork?
The point where the parent DNA molecule unwinds and replication is actively occurring.
What is the leading strand?
The new DNA strand built continuously in the 5’ to 3’ direction moving toward the replication fork.
What is the lagging strand?
The new DNA strand built in short segments moving away from the replication fork - each segment begins with its own primer.
What direction can DNA polymerase only build a new strand?
In the 5’ to 3’ direction - new nucleotides can only be added to the 3’ end of a growing strand.
What is DNA ligase?
The enzyme that seals the gaps between DNA segments on the lagging strand after primers are removed - joining them into one continuous strand.
How accurate is human DNA replication?
Very accurate - roughly one mutation per 30 million base pairs replicated or about 100 to 200 new mutations per generation.
What is a mutation?
A change in the nucleotide sequence of the genetic message.
What is a point mutation?
A mutation that changes one or only a few nucleotides in a gene - including base substitutions and insertions or deletions.
What is a base substitution mutation?
A mutation in which one nucleotide is replaced by a different nucleotide - can change the amino acid encoded at that position.
What is a frameshift mutation?
A mutation caused by the insertion or deletion of a nucleotide that shifts the reading of the entire gene message out of register.
