Transcript AA G

Molecular Biology of the Gene
 1952—Hershey
& Chase
determine that DNA
rather than protein
carries genetic
information
 1953—Rosalind Franklin
captures image of DNA
with x-ray
crystalography
 1953—Watson & Crick
describe the doublehelix structure of DNA
 Comprised




Adenine
Thymine
Guanine
Cytosine
 Hydrogen

of 4 nucleotides
A-T, C-G
bonds attach nucleotides
 Happens
in S phase
of Interphase
 Semiconservative
replication

One parent strand
ends up in each
daughter DNA
 Helicase
separates hydrogen bonds between base
pairs.
 Occurs in multiple locations on DNA at the same
time
 DNA polymerase binds to each side of the “bubble”
 DNA
polymerase
moves along the
strand, attaching free
nucleotides to
complementary bases.

ALWAYS A-T and C-G!
 DNA
ligase splices
(links, ligates)
sections of DNA to
form one strand.
DNA
RNA
Double Helix
Single Strand
Thymine
Uracil
Inside Nucleus
Can Leave Nucleus
Entire genetic code
Only one gene
 Messenger



mRNA
Direct copy from DNA
Has codons
 Transfer



RNA
tRNA
Has anticodons
Binds to amino acids

Specific for each anticodon
 Ribosomal


RNA
RNA
rRNA
Comprises part of ribosomes
 Copy
of a gene made from the DNA
 Copy moves to ribosomes
 Protein is created from this “blueprint”
RNA Polymerase unravels part of the DNA strand
 The polymerase creates a template based on a
section of DNA. This is the mRNA.
 mRNA leaves the nucleus
 mRNA binds to ribosome
 tRNA carries an amino acid (AA), matches to a
section of the mRNA in the ribosome
 Another tRNA carries the next AA, the two AAs
bond
 tRNA leaves
 Subsequent AAs continue to bond, forming a
peptide chain
 At the end of the sequence, the peptide breaks
off into the cytoplasm, the ribosome releases
the mRNA, and the mRNA breaks apart to be
recycled.

 “The
process by which an mRNA
template, carrying the sequence of the
protein, is produced for the translation
step from the genome.”
 Copying
something to be read by someone
else in another place.
 In this case…copying the gene to be used
as an instruction manual to make protein
in another part of the cell.
 Initiation


RNA polymerase binds
to a specific part of the
DNA strand. This is the
gene.
Polymerase unravels
this part of the strand,
separating the base
pairs.
 Elongation



Polymerase begins to
slide along the DNA
Ribonucleotides match
to opposite base, then
bond
This creates a chain,
which is the mRNA
 Termination
Introns (unwanted
parts) are “cut out” and
removed
 Exons (coding parts) are
fused together
 A “cap” is put on the
end of the mRNA for
protection

DNA
C G C A T A A G C G A C T A G G C T T C A C C C G C T A A G A T
G C G T A T T C G C T G A T C C G A A G T G G G C G A T T C T A
C G C A U A A G C G A C U A G G C U U C A C C C G C U A A G A U
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fewmay
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aissequence
are
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double-stranded
A
typical
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DNA.
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has
average,
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introns,
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isthe
about
be ribosome
hundreds;
14kb
(14,000
a
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occur
using
molecule
concurrently
the
tobut
begin,
are
“trimmed”,
and
andthe
probably
base
process
before
pair
aids
is
poly-adenylation.
rules.
known
stability.
In
asRNA
RNA,
“splicing”.
“Capping”
Uracil
isIt
actually
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complementary
actually
istemplate.
also
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occurs
required
immediately
while
to
for
Adenine
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In
the
region
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the
gene,
Transcription:
the
DNA
unwinds
making
and
the
2 The
strands
a DNA
come
apart.
RNA
polymerase,
an
The
bases
incomplementary
the
introns
are
recycled.
There
are
several
hypothesis
about
the
origin
of
introns.
It
base
have
pairs)
none.
A typical
size
human
is
highly
intron
variable.
is
around
The
1dystrophin
kbfrom
but
it
can
gene,
be
encoding
hundreds
aof
muscle
kb.
On
protein,
average,
has
translation
The
and
DNA
stability.
strand
that
acts
splicing
as10-20
being
the
synthesis
and
template
synthesized.
poly-adenylation
begins.
strand
varies
are
from
known
gene
asisDNA
to
“RNA
gene.
processing”.
While
average
enzyme,
human
the
mRNA
key
molecule
molecule
for
has
the
about
manufacture
2,600
bases,
of
RNA
theG-C
from
size
highly
variable.
Thean
RNA
comes
Note
offisCapping,
the
the
DNA
complementary
template
which
reforms
pair
rules;
a75kb
double-stranded
A-T
and
molecule
has
been
suggested
that
some
may
have
abase
function
inthan
the
cell,
before
or
after
excision.
2.4Mb
(2.4
million
introns
base
pairs).
are
Typically,
times
there
larger
is
exons.
between
human
genes.

“Protein translation involves the transfer of
information from the mRNA into a peptide,
composed of amino acids. This process is
mediated by the ribosome, with the adaptation
of the RNA sequence into amino acids mediated
by transfer RNA.”
Taking something in a language you can’t use,
and making it into a language that you can use.
 In this case…taking the “language” of the DNA &
mRNA, which the cell can’t directly use, and
converting it into the “language” of proteins,
which the cell can use.

 Ribosomes
(two
subunits) are in
cytoplasm
 tRNA attaches to
amino acids in
cytoplasm
 Ribosome binds to the
beginning of the
mRNA chain
 Initiation




Starts with a 3-base
section of the
template, a “codon”,
specifically the “start
codon”
tRNA with matching
“anticodon” attaches
Another tRNA matches
to the next codon
Amino acids bond
 Elongation
Ribosome moves down
the mRNA one codon at
a time
 tRNA continues to
match codon to
anticodon, bringing
more AAs
 AAs bond, forming a
lengthening chain

 Termination



Ribosome reaches “stop
codon”
Creation stops, and a
release factor binds to
the stop codon
Ribosome releases,
polypeptide can be
modified and used,
mRNA is recycled
val
thr
gly
U G C
C C G
arg
phe
leu
C A U
met
G C G
A A G
Polypeptide
G A U
arg
U A C
G C U
Stop
C G C A U A U G C G A C U A G G C U U C A C C C G C U A A G
Start
mRNA
thr
 Transcription



Initiation
Elongation
Termination
 Translation



Initiation
Elongation
Termination
 Changes
in the DNA
sequence

Alterations in sequence
of nucleotides
 Altering
the DNA alters
the mRNA
 Altering mRNA changes
the codons
 Since amino acids are
specific for a codon,
the polypeptide chain
can be different during
translation