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DNA was
discovered in
1953 by James
Watson and
Francis Crick
What does DNA stand for?
• Deoxyribonucleic acid
DNA is located in the nucleus of cells
DNA: deoxyribonucleic acid,
controls the production of proteins
in the cell.
DNA & RNA
are both
polymers
The repeating
subunits of DNA &
RNA are nucleotides.
DNA Structure – The Twisted
Ladder
DNA Structure
DNA is made of nucleotides.
DNA nucleotides are made of:
1. Sugar (deoxyribose)
2. Phosphate
3. Nitrogen Base
A phosphate
group
A 5 carbon sugar
called deoxyribose.
A nitrogen
base
Nitrogen Base Pairing- Who
pairs with who?
The bases on one strand of the
DNA molecule are the exact
compliment of the bases on the
other strand. Thus, they are called
complimentary strands.
The sugar and
the phosphate
groups form the
backbone of
the DNA
molecule
The “rungs” of the
ladder are bonded
pairs of nitrogen
bases. The bases
are bonded
together by weak
hydrogen bonds.
Replication begins when the
enzyme DNA HELICASE
attaches to the DNA molecule
and unzips it by breaking the
hydrogen bonds between the
bases.
The DNA is separated into 2
strands. The unpaired bases on
each strand attract the unpaired
COMPLIMENTARY bases that float
around in the nucleus. They then
form new hydrogen bonds.
Next, an enzyme called DNA
POLYMERASE catalyzes the
formation of new sugar and
phosphate sides for each of the
2 new DNA molecules.
Two new DNA molecules
result from replication, with
the EXACT same code.
Each is one half of the
ORIGINAL DNA double
helix.
Replication occurs at MANY
points of the DNA molecule at
once. If not, it would take
3 days for one DNA molecule
to replicate. This way, it only
takes 3 minutes to replicate.
DNA contains the information
to MAKE proteins but does
not actually make it – RNA
does….
Look… no T’s
They are replaced by
U’s
Notice… only one strand…
not two like DNA – not a double
helix.
RNA’s sugar is
RIBOSE, not
deoxyribose like
DNA
mRNA – MESSENGER RNA is a
single strand of RNA that copies
DNA information during protein
synthesis.
It serves as a TEMPLATE for
assembling amino acid sequences
to make proteins.
tRNA – TRANSFER RNA is a single
strand of RNA that is folded back on
itself like a hairpin.
There are 20 forms of tRNA that
correspond to each of the 20 amino
acids which bind to them.
rRNA – RIBOSOMAL RNA, is
RNA in a globular form. They are
ribosomes!
What do ribosomes make?
Protein!!
To transcribe means to re-write or
to write something down.
RNA is transcribed from DNA
through this process…..
First, the enzyme RNA
POLYMERASE opens up
the DNA molecule.
1.
2. Next, RNA polymerase
attaches RNA bases floating
around in the nucleus to the DNA
bases. RNA polymerase also
builds a new SUGAR phosphate
backbone for the RNA molecule.
3. The transcription process
stops when a termination CODE
is reached on the DNA molecule.
RNA is then released & the DNA
closes back up……..
All three types of RNA are made
this way. RNA then leaves the
NUCLEUS through the nuclear
pores and enters the cytoplasm
where it joins up with
RIBOSOMES and proteins are
made.
Internet site
http://www.ncc.gmu.edu/dna/mRNAanim.htm
http://www.agresearch.co.nz/scied/search/m
olecular/dnatranscription.htm
DNA
RNA
Proteins
The GENETIC code is the system
that contains information needed
by cells for proper functioning. A
CODON is a group of 3 sequential
mRNA bases that recognize a
specific amino acid
Codons are UNIVERSAL.
For example, UUU is the codon for
the amino acid phenylalanine in
mice, men, & bacteria.
Every organism has the same
genetic code for proteins………
http://www.cat.cc.md.us/biotut
orials/protsyn/peptidea.html
Is the formation of protein
using the information coded
on DNA and carried out by
RNA
Amino acids must be in the proper
sequence for proteins to function
properly.
The number of different kinds of
proteins varies with the
COMPLEXITY of an organism.
1. MRNA enters the cytoplasm
from the nucleus and finds a
ribosome to hook up with.
2. tRNA’s then bring specific amino
acids to the ribosomes.
3. The ribosome attaches to an
AUG (start codon) on mRNA.
4. TRNA attaches itself to the
mRNA and passes its amino acid
off to the growing protein chain.
5. TRNA leaves and another tRNA
takes its place with a new amino
acid.
This process continues until a
STOP codon is reached and the
protein chain is complete and falls
off.
The part of the tRNA that attaches to
the codon is called the anticodon..
The three bases of the anticodon are
complimentary to a specific codon in
the mRNA.