Download DNA Lab

Irene
Kim
November
20,
2012
DNA
Model‐Building
Deoxyribonucleic
Acid,
often
known
as
the
DNA,
is
the
molecule
of
inheritance
for
all
organisms
on
Earth.
It
is
a
three
dimensional
double
helix
of
repeating
nucleotides.
The
sides
of
a
double
helix
are
formed
by
the
alternating
sugar
and
phosphate
that
are
joined
together
by
covalent
bonds.
There
are
10
nucleotides
per
every
turn,
about
3.4nm
per
helical
turns.
The
“back
bone”
of
the
DNA
is
made
of
a
ring
shaped
sugar
called
deoxyribose,
and
phosphoric
acid
(one
phosphorus
with
four
oxygen).
The
two
single
strands
of
DNA
connect
to
each
other
with
hydrogen
bonding
at
their
nitrogen‐containing
bases:
adenine,
guanine,
cytosine,
and
thymine.
Adenine
and
guanine
are
purines,
meaning
that
they
are
double
ringed.
On
the
other
hand,
cytosine
and
thymine
(and
Uracil
in
RNA)
are
pyrimidine,
meaning
that
they
are
single
ringed.
In
1950,
Chargaff
found
that
the
four
bases
are
found
in
all
organisms
but
the
proportion
varied
from
one
to
another.
He
realized
that
in
the
DNA
of
every
organism,
the
amount
of
adenine
was
similar
to
the
amount
of
thymine,
and
the
amount
of
guanine
was
similar
to
the
amount
of
cytosine.
This
was
the
beginning
of
Chargaff’s
rules,
stating
that
A
=
T
and
G
=
C.
Later
on,
Watson
and
Crick’s
DNA
model
explained
the
theory
behind
Chargaff’s
rules.
From
looking
at
the
x‐ray
picture
of
DNA,
Watson
and
Crick
had
enough
clues
to
infer
that
the
DNA
is
a
helix
with
two
strands
that
have
a
constant
width
apart.
While
making
the
model,
they
realize
that
the
purine
bases
are
twice
as
large
as
pyrimidine
bases;
therefore,
they
must
pair
up
with
each
other
to
keep
a
regular
width
apart.
They
concluded
that
the
DNA
is
a
three
dimensional
double
helix
with
the
strands
complementary
to
each
other.
The
base‐pairing
rule
states
that
A
and
T
always
pair
together
and
that
G
and
C
always
pair
together,
due
to
their
sizes
and
ability
to
form
hydrogen
bonds
with
another.
The
DNA
Replication
is
during
the
Synthesis
(S)
stage.
It
is
basically
copying
information
from
a
single
chromatid,
and
making
another
identical
chromatid,
which
becomes
two
sister
chromatids.
DNA
RNA
Transcription
Protein
Translation
The
DNA
helicase
stimulates
the
unzipping
of
the
nucleotide
base
pairs
(places
along
the
chromosome.
The
hydrogen
bonds
are
broken
and
the
bases
on
each
strand
are
exposed
to
act
as
a
template
for
the
new
set.
Free
nucleotides
pair
with
the
bases
exposed
as
the
template
strands
unzips.
DNA
polymerases
bond
these
together
to
form
new
strands.
As
a
result,
there
are
two
identical
molecules
of
DNA,
each
with
one
strand
from
the
original
molecule
and
one
new
strand.
DNA
replication
is
semiconservative
as
one
old
strand
is
conserved,
one
new
strand
is
made,
and
finally,
combined
together
to
form
one
DNA
molecule.
Transcription
is
copying
the
sequence
of
DNA
(A,
T,
G,
C)
to
produce
an
identical
strand
of
mRNA
gene
that
is
later
translated
into
a
sequence
of
amino
acids
that
create
protein.
For
most
eukaryotic
cells,
transcription
occurs
inside
the
nucleus.
During
or
soon
after
it
is
finished,
the
mRNA
exits
through
the
membrane
pores
and
translation
happens
in
the
cytoplasm.
The
mRNA
is
only
made
when
the
cell
needs
that
particular
segment
of
the
DNA,
allowing
the
cell
to
adjust
in
different
demands.
As
replication
begins,
transcription
is
beginning
as
well
by
RNA
polymerase.
RNA
polymerase
recognizes
transcription
start
site
of
gene
and
transcription
complex
(of
RNA
polymerase
and
other
proteins)
begins
to
unwind
segments
of
DNA
until
the
strands
are
apart
from
each
other.
RNA
polymerase
binds
to
the
promoter
region
of
the
DNA
strand
and
the
factors
encourage
the
start
of
transcription.
It
strings
together
an
identical
strand
of
mRNA
nucleotides,
using
one
strand
of
DNA
as
template
(A
with
U,
C
with
G)
strand
with
the
same
base
pairing
system
as
replication.
The
growing
RNA
strand
hangs
freely
until
it
is
detached,
as
DNA
helix
zips
back
together
in
shape.
Unlike
DNA,
mRNA
has
oxygen
in
ribose,
which
keeps
it
from
being
double
stranded.
Deoxyribose
doesn’t
have
oxygen,
allowing
the
two
strands
to
connect.
Also,
adenine
pairs
with
uracil
instead
of
thymine
in
mRNA.
Translation
is
a
process
that
converts
an
mRNA
message
to
a
polypeptide
that
make
up
protein.
A
codon
is
a
genetic
unit
of
a
three‐nucleotide
sequence,
which
is
coded
for
one
amino
acid.
This
process
happens
in
the
cytoplasm
of
the
cell
and
takes
a
lot
of
energy.
Before
it
actually
starts,
the
small
ribosomal
subunit
binds
to
the
mRNA
strand.
The
exposed
codon
attracts
a
complementary
tRNA
molecule
bearing
an
amino
acid
and
the
tRNA
anticodon
pairs
with
the
mRNA
codon.
The
ribosome
pulls
the
mRNA
strand
through
itself
one
codon
at
a
time.
As
the
strand
moves,
the
start
codon
and
its
complementary
tRNA
molecule
shifts
into
the
second
site
(P
site)
inside
the
large
subunit.
The
ribosome
also
helps
form
a
peptide
bond
between
two
amino
acids
and
breaks
the
bond
between
tRNA
molecule
and
amino
acid.
The
tRNA
that
entered
from
A
site
moves
to
P
site,
leaving
A
site
open.
This
exposes
the
next
mRNA
codon
and
the
process
continues
as
another
complementary
tRNA
molecule
is
attracted
to
the
exposed
mRNA
codon.
The
tRNA
in
the
P
site
now
moves
to
E
(exit)
site,
and
the
tRNA
exits
the
ribosome
to
be
charged
with
another
amino
acid
in
the
cytoplasm.
The
ribosome
moves
down
the
mRNA
strand
while
attaching
new
amino
acids
to
the
growing
protein,
until
it
reaches
a
stop
codon.
The
ribosome
and
protein
are
both
released.
Sickle
cell
anemia
is
a
dangerous
illness
caused
from
a
single
change
in
a
single
nucleotide.
According
to
Peachey,
these
blood
cells
have
an
irregular
shape
and
only
last
for
half
of
what
its
supposed
to
live.
During
replication,
a
point
mutation
can
occur
when
an
incorrect
base
is
substituted
during
base
substitution.
A
single
base
substitution
can
lead
to
many
serious
consequences
such
as
the
sickle
cell
anemia.
If
tautomeric
shift
occurs
during
base
pairing,
things
such
as
adenine
bonding
with
cytosine
could
happen.
This
small
change
in
the
nucleotide
will
affect
the
mRNA,
as
it
will
be
created
off
the
incorrect
template.
This
will
result
in
a
change
in
a
codon
that
leads
to
a
different
amino
acid
in
the
protein.
Like
mentioned
in
the
worksheet,
a
single
incorrect
codon
that
led
to
an
incorrect
amino
acid
in
the
protein
can
cause
the
formation
of
things
such
as
sickle
cell
anemia.
In
the
case
of
sickle
cell
anemia,
Peachey
mentions,
“The
sixth
DNA
triplet,
CTC,
has
been
changed
to
CAC
(the
nitrogenous
base
thymine
is
replaced
by
adenine
in
the
mutant
gene)”
(para.
4).
Normally,
the
amino
acid
would
be
glutamic
acid,
which
is
very
hydrophilic.
However,
the
because
of
the
mutation,
the
amino
acid
is
now
valine,
which
is
very
hydrophobic.
As
a
result,
it
causes
the
shape
of
the
blood
cells
to
change
into
“stiff
rod‐like
structure”.
This
shape
no
longer
allows
the
hemoglobin
to
load
and
unload
oxygen
properly.
Abnormal
hemoglobin
leads
to
sickling
of
red
blood
cells.
This
causes
rapid
destruction
of
sickled
cells,
clumping
of
cells
and
interference
with
blood
circulation,
and
collection
of
sickle
cells
in
the
spleen.
This
at
the
end
could
lead
to:
• Skull
deformation
• Weakness
and
fatigue
• Impaired
mental
fuction
• Poor
physical
development
• Heart
failure
• Pneumonia
• Rheumatism
• Paralysis
• Abdominal
pain
• Kidney
failure
(Based
on
diagram
from
Peachey,
R.
Sickle‐Cell
Anemia:
Example
of
a
"Beneficial
Mutation"?)
Bibliography
Peachey,
R.
(n.d.).
Sickle‐Cell
Anemia:
Example
of
a
"Beneficial
Mutation"?
Retrieved
November
19,
2012,
from
Creation
Science
Association
of
British
Columbia:
http://www.creationbc.org/index.php?option=com_content&view=article&i
d=113
&Itemid=
Johnson, G., Ph.D., & Raven P., Ph.D. (2006). Biology. Orandlo, Fl., Holt, Rinehart
and Winston.