Lecture #9 Flashcards
What are the three parts to a DNA nucleotide?
Phosphate group, five-carbon sugar, and nitrogenous bases
What are the 4 nitrogenous bases?
Adenine, Guanine, Cytosine, and Thymine
Nucleotides are connected by …?
phosphodiester bonds
Is DNA polar or non-polar?
polar
What identifies the 5’ end of a DNA strand?
free phosphate group
What identifies the 3’ end of a DNA strand?
free hydroxyl group
how are the DNA strands held together?
with hydrogen bonds between the bases
What is the most common form of DNA?
B-DNA
What is one characteristic of B-DNA?
Contains a major and minor groove
What are eukaryotic chromosomes composed of?
DNA, RNA, Histones, Non-Histone proteins, and non-chromatin nuclear constituents
How many levels of condensation are there in eukaryotic chromosomes?
3
What occurs during the first level of chromosomes in eukaryotic chromosomes?
Packaging DNA into nucleosomes – produces a 10nm fibre
How is DNA packed into nucleosomes?
DNA links between core histones of nucleosomes, 146 bp of DNA wrapped 1 ¾ turns around the histone octamer
What is the final steps in the first level of condensation?
DNA is wrapped around a nucleosome core of 8 histone proteins and anchored by a 9th
There are two molecules of each histones: H2A, H2B, H3, H4 in the nucleosomal core plus one molecule of Histone H1 to further stabilizer the structure
What happens during the second level of condensation in eukaryotic chromosomes?
an additional folding or supercoiling of the 11 nm fibre to produce a 30 nm fibre
What does the second level of condensation in eukaryotic chromosomes involve?
nucleosomal interactions, Histone H1 and the solenoid and zig-zag DNA structure
What happens during the third level of condensation in eukaryotic chromosomes?
Attachment of the 30nm fibre at many positions to a (non-histone) protein scaffold
What are telomeres?
consists of 500-3000 copies of the DNA sequence repeated on the ends of chromosomes
What are three important factors of telomeres?
Resist degradation by DNases, Prevent fusion of chromosomal ends, and facilitate replication of the ends of the linear DNA
What are centromeres?
Provides the point of attachment of sister chromatids and of chromosomes to microtubules in the mitotic spindle
What is the structure of the metaphase chromosome?
consists of a 30nm fibre
What is a metaphase chromosome?
DNA in its most condensed form
