Topic 7.1: DNA Structure Flashcards
Describe the structure of DNA, including the antiparallel strands, 3’ - 5’ linkages and hydrogen bonding between purines and pyrimidines (6)
The carbon atoms in deoxyribose are numbered, with the nitrogenous bases attach to C1 and the phopshate group is attached to C5
Nucleotides are joined by a covalent phosphodiester bond between the C5 phosphate group and the C3 hydroxyl group
Hence one nucleotide strand runs 5’ - 3’
The nitrogenous bases interact via hydrogen bonding (complementary base pairing)
Adenine (A) and thymine (T) share 2 hydrogen bonds
Guanine (G) and cytosine (C) share 3 hydrogen bonds
In order for the bases to associate (i.e. face each other), one strand must run antiparallel to the other (this antiparallel strand runs 3’ - 5’)
Double stranded DNA forms a double helix, with 10 nucleotides per turn and the structure containing both major and minor grooves
How many hydrogen bonds between Adenine and Thymine?
2 hydrogen bonds
How many hydrogen bonds between Guanine and Cytosine?
3 hydrogen bonds
Outline the structure of nucleosomes (4)
The DNA double helix contains major and minor grooves on its outer diameter, which expose chemical groups that can form hydrogen bonds
The DNA of eukaryotes associates with proteins called histones
DNA is wound around an octamer of histones (146 bases and 1.65 turns of the helix per octamer)
The octamer and DNA combination is secured to a H1 histone, forming a nucleosome
What are the two main functions of nucleosomes?
Nucleosomes serve two main functions:
They protect DNA from damage
They allow long lengths of DNA to be packaged (supercoiled) for mobility during mitosis / meiosis
What is the difference between unique/single copy sequences and repetitive sequences in respect to proportion of the genome?
Unique/Single Copy Sequences: small proportion of genome (1.5%)
Repetitive Sequences:
higher proportion of genome
What is the difference between unique/single copy sequences and repetitive sequences in respect to how many times it occurs in the genome?
Unique/Single Copy Sequences: occurs once in the genome
Repetitive Sequences: occurs many times
What is the difference between unique/single copy sequences and repetitive sequences in respect to length of base sequence?
Unique/Single Copy Sequences: long base sequences
Repetitive Sequences: short base sequences (typically 5-300 bases)
What is the difference between unique/single copy sequences and repetitive sequences in respect to genes?
Unique/Single Copy Sequences: usually genes
Repetitive Sequences: not genes
What is the difference between unique/single copy sequences and repetitive sequences in respect to translation?
Unique/Single Copy Sequences: may be translated
Repetitive Sequences: never translated
What is the difference between unique/single copy sequences and repetitive sequences in respect to mutation?
Unique/Single Copy Sequences: low rate of mutation
Repetitive Sequences: higher rate of mutation
What is the difference between unique/single copy sequences and repetitive sequences in respect to variability among individuals?
Unique/Single Copy Sequences: very similar between individuals
Repetitive Sequences: varies greatly between individuals
What is the difference between unique/single copy sequences and repetitive sequences in respect to DNA profiling?
Unique/Single Copy Sequences: not used for DNA profiling
Repetitive Sequences: used for DNA profiling
What is the difference between unique/single copy sequences and repetitive sequences in respect to examples?
Unique/Single Copy Sequences: Exons are examples of unique sequences
Repetitive Sequences: Introns are examples of repetitive sequences
Define Intron
Intron: A non-coding sequence of DNA within a gene (intervening sequence) that is cut out by enzymes when RNA is made into mature mRNA
