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E. If the thread was the true thickness of DNA it would have easily fit into the relatively
large capsule, but still would have become tangled if it did not have an efficient packing
structure.
Read pg. 291-294 Do Q#1-6, 8 and 9 pg. 294
Read pgs. 295-298 Do Q#1-7 pg. 298
Section 6.5 Questions, page 294
1. The following structures are in order of size from smallest to largest: histone,
nucleosome, solenoid, and chromosome.
2. Given:
length of a nucleus, LN = 10–5 m
length of a solenoid, LS = 3 × 10–8 m
Required:
number of solenoids that can fit sided by side in the nucleus, NS
Solution:
Step 1. Divide the length of the nucleus by the length of a solenoid.
NS = LN ÷ LS
= (10–5 m) ÷ (3 × 10–8 m)
NS = 3.3 × 102
Statement: This nucleus can fit 300 solenoid structures side by side within it.
3. DNA wraps tightly around the histone complex because of polar and ionic interactions.
The histones are positively charged and the DNA is negatively charged.
4. Answers may vary. Sample answer:
DNA-packing Strategies
Prokaryotes
Eukaryotes
- contain circular
- contains linear
chromosomes
chromosomes
- uses supercoiling to - use chromatin and
5. Answers may vary.
Sample
answer: Due to
the volume
of DNA that must be replicated
increase
packing
histones
to increase
in eukaryotic cells, efficiency
as compared to bacteria, packing
the process
would
efficiencysimply take too long in
eukaryotic cells -if there
were only
one replication
site.telomeres
An alternative
hypothesis is that
free floating
DNA
- contains
to
the small size of the circular chromosomes ofprotect
bacteria
prevents
replication
from occurring
the ends of
in more than one spot simply due to the lack chromosomes
of space; multiple sites cannot be unwound
simultaneously in bacteria.
- DNA contained in a
6. (a) Methylation occurs when a methyl group
is added to a molecule. Some arginine and
nucleus
lysine side chain residues undergo post-translational methylation.
5. The
Answers
may
vary.refer
Sample
answer:ofDue
the volume
of DNADNA
that must
be replicated
(b)
histone
“tails”
to regions
the to
histone
that modulate
accessibility
in eukaryotic
cells, asThe
compared
to bacteria,
theand
process
simply
takemethylated
too long in
within
a nucleosome.
tails contain
arginine
lysinewould
residues
that are
Copyright
© cells
2012 if
Nelson
Education
Ltd.
Chapter 6:site.
DNA:
Hereditary
Molecules
of Life 6.5-1
eukaryotic
there
were
only
one
replication
An
alternative
hypothesis
and demethylated to modulate structure and/or interactions of the core histone tails,isorthat
to
the small
size ofsites
the for
circular
chromosomes
bacteria prevents replication from occurring
serve
as binding
ancillary
proteins orofenzymes.
more than
one
spotSample
simply answer:
due to the
lack of space; multiple
sites cannot
be unwound
7.inAnswers
may
vary.
Immunodeficiency,
centromeric
instability,
and
simultaneously
in
bacteria.
facial dysmorphism (ICF) syndrome is a very rare autosomal disorder caused by a
6. (a) Methylation
when encoding
a methyl group
is added to a molecule.
Some arginine
and
mutation
to the geneoccurs
(DNMT3B)
DNA methyltransferase-3B
resulting
in
lysine
side
chain
residues
undergo
post-translational
methylation.
hypomethylation of histone proteins. ICF is a very serious disease characterized by facial
(b) The histone
“tails” refer
to regionsrespiratory
of the histone
that modulate
DNA
dysmorphism,
recurrent
and prolonged
infections,
infections
of accessibility
the skin and
within
a
nucleosome.
The
tails
contain
arginine
and
lysine
residues
that
are
methylated
digestive system, and variable immune and immunoglobulin deficiencies. Since
histones
andinvolved
demethylated
to modulate
structureofand/or
interactions
of the
core that
histone
tails, or to
are
in the most
basic structure
DNA coiling,
I would
expect
histone
serve as
binding
for ancillary
proteins or enzymes.
defects
could
havesites
serious
consequences.
Answers
vary. Sample
answer: Immunodeficiency,
instability,
8.7.The
benefitmay
to having
large non-coding
repeating sections centromeric
in the telomeres
of DNAand
is
facial
dysmorphism
(ICF) syndrome
is a being
very rare
disorder Some
causedDNA
by a at the
that
these
protect the coding
regions from
lost autosomal
during replication.
mutation
to the gene
(DNMT3B)
encoding
end
of the strand
is removed
and not
replacedDNA
withmethyltransferase-3B
every replication. Theresulting
presenceinof nonhypomethylation
of histone
proteins.coding
ICF is regions
a very serious
diseaseofcharacterized
by facial
coding
regions protects
the important
in the centre
the DNA strand.
dysmorphism,
recurrent
and
prolonged
respiratory
infections,
infections
of
the
skin
9. During the organisms’ first replications there will be little effect of losing the non- and
digestive
system,
variable
immune
and
immunoglobulin
deficiencies.
Sincecan
histones
coding
regions.
Theand
larger
the regions
are,
presumably
the longer
the organisms
are involved
in thesuffering
most basic
of DNA
coiling, Istarts
would
that histone
reproduce
without
anystructure
effects. The
real problem
as expect
the organism
defects
could
have
serious
consequences.
undergoes continued reproduction. Eventually there will be no more non-coding regions
8. The
to having
large
non-coding
sections
the telomeres
DNA is
left
in thebenefit
telomeres
and the
coding
regions repeating
of the DNA
will beinaffected.
Losingoftelomere
that these
protectlimits
the coding
from being
losttherefore
during replication.
Some DNA at the
regions
probably
the ageregions
a cell might
achieve,
limiting lifespan.
end of the strand is removed and not replaced with every replication. The presence of noncoding regions protects the important coding regions in the centre of the DNA strand.