7.1 DNA Structure and Replication

Question 1

One difference between eukaryotic DNA and prokaryotic DNA

Answer 1

eukaryotic DNA is associated with proteins called histones while prokaryotic DNA is “naked”

Question 2

Histones

Answer 2

proteins used to package DNA into structures called nucleosomes

Question 3

Nucleosome

Answer 3

consists of a central core of 8 histone proteins with DNA coiled around the proteins
the 8 protein (octamer) consists of 2 copies of 4 different types of histones
a short section of “linker” DNA connects one nucleosome to the next
an additional histone protein (H1) serves to bind the DNA to the core particle - binds in such a way to form a structure called the 30nm fibre that facilitates further packing
supercoiling

Question 4

DNA Replication

Answer 4

topoisomerase: releases strain that develops ahead of the helicase
helicase: unwinds the DNA
single-stranded binding proteins: keep the strands apart long enough to allow the template strand to be copied
DNA primase: creates 1 RNA primer on the leading strand and many on the lagging strand
DNA polymerase III: adds nucleotide bases
DNA ligase: connect the gaps between fragments

Question 5

Non-coding regions of DNA

Answer 5

only some DNA code for the production of polypeptides (coding sequences)
most of the eukaryotic genome is non-coding
sequences used as a guide to produce tRNA and rRNA
regulation of gene expression (enhancers, silencers)
highly repetitive DNA sequences (satellite DNA) - telomeres (on ends of chromosomes, protective function)
the enzymes that replicate DNA cannot continue replication all the way to the end of the chromosome if cells went through the cell cycle without telomeres they would lose the genes at the ends of the chromosomes sacrificing the repetitive sequences found in telomeres serves a protective function