Title: DNA and the Genetic Code
1DNA and the Genetic Code
2DNA
- First isolated from the nuclei of cells in 1869
- Oswald Avery (1944) presented evidence that
suggested that nucleic acids were involved in the
storage and transfer of genetic information. - Erwin Chargaff found that the DNA always contains
the same relative amounts of certain pairs of
amine bases. There are always equal amounts of - adenine and thymine
- guanine and cytosine.
- James Watson and Francis Crick in 1953 determined
the structure of DNA as a double helix - Rosalind Franklin created the early X-ray
diffraction pictures of DNA
3Nuclei Acids
- Nuclei acids fall into two classes,
- DNA
- RNA
- RNA, or Ribonucleic Acid, is built on the
ß-D-ribofuranose ring. - DNA, or deoxyribonucleic acid, is based on a
modified ribofuranose ring in which the -OH group
on the second carbon atom has been removed.
4DNA Structure
- DNA is made up of three units including
- A ribose sugar
Ribose
Deoxyibose
Ribose and deoxyribose differ in that ribose has
an OH group on carbon 2 whereas deoxyribose has
only a hydrogen attached.
5DNA Structure
- DNA is made up of three units including
- A ribose sugar
- A phosphate group
Phosphate
Deoxyribose
The phosphate groups alternate with the ribose
sugar and are attached at carbon 3 and at carbon 5
6DNA Structure
- DNA is made up of three units including
- A ribose sugar
- A phosphate group
- A nitrogen (amine) base
There are four different amine bases adenine,
thymine, cytosine, and guanine.
7Nucleotide
- The DNA strand is made up of alternating
deoxyribose and phosphate groups with a nitrogen
base attached as a side chain
Cytosine
8DNA Structure
- DNA is made up of three units
- A ribose sugar
- A phosphate group
- A nitrogen (amine) base
The amine bases are side branches to a strand
made of alternating phosphate and deoxyribose
sugars These bases are attached at carbon1 of
the deoxyribose sugar
Adenine
Cytosine
9DNA Structure
- DNA is made up of three units
- A ribose sugar
- A phosphate group
- A nitrogen (amine) base
- These three molecules make up a nucleotide.
- A DNA strand is a sequence of nucleotides.
Adenine
Cytosine
10DNA Structure
- DNA consists of two strands of nucleotides.
These strands are wound together in a spiral
known as a double helix - The amine bases hold the strand together
- with a
- sequence
- of hydrogen
- bonds
11Complimentary Bases
- Because of their size and ability to hydrogen
bond, the amine bases exist in complimentary
pairs in the DNA double helix - Adenine always bonds with Thymine and Guanine
always bonds with Cytosine
12Hydrogen Bond Alignment
- The size and shape of the amine bases is such
that hydrogen bonds can only form at specific
sites - Adenine only bonds with Thymine
- Guanine only bonds with Cytosine
- Therefore they form complimentary base pairs
13DNA Structure -- Hydrogen Bonding
- Adenine and Thymine form a base pair
14DNA Structure Hydrogen Bonding
15Base Pair Sequence
- The sequences of bases appears to be random but
in reality nothing is farther from the truth.
The base pair sequence contains the code by
which proteins are synthesized in the cell
16DNA Structure
- In the double helix of a DNA molecule, the two
strands are not parallel, but interwoven with
each other. - The helix makes a turn every 3.4 nm, and the
distance between two neighboring base pairs is
0.34 nm. - There are about 10 pairs per turn.
- The intertwined strands make two grooves of
different widths, known as the major groove and
the minor groove. - These grooves may facilitate binding with
specific proteins.
17DNA Shape
- This color enhanced image taken by the Scanning
Tunneling Electron Microscope shows a double helix
18DNA Replication
- In human beings there are 23 pairs of chromosomes
- Chromosomes are effectively a very long DNA
sequence. This DNA sequence replicates itself
during cell division - As the DNA double helix partially unzips as the
hydrogen bonds between the nitrogen bases are
broken - Sugar and base units are picked up from the
surrounding solution. - Since only A T and G-C combinations can occur
the new strand is a complimentary replicate of
the existing DNA
19DNA Replication
- When cells divide the DNA must is replicated
exactly - As the DNA unzips new complimentary strands are
formed. - These new strands are exact replicas of the
previously existing strands
20DNA and the Genetic Code
- Genes are long sequences of DNA that code for the
formation of proteins - Typical genes are often thousands of base pairs
long - Not all of the DNA strand appears to have genetic
information - The sequence for a particular gene is very
specific.
21Gene Correspondance for Neuropilin-1
Species bp NP-1 Sense Primer Macaque
-- ACCCGCACCTCATTCCTACATCAATGAGTGGCTCCAAATA
GACCTGGGGGHuman 1422
ACCCGCACCTCATTCCTACATCAATGAGTGGCTCCAAATAGACCTGGGGG
Rat 1419 ACCCTCACCCCACCCATACATCAATGAA
TGGCTCCAAGTGGACCTGGGAGMacaque
AGGAGAAGATCGTGAGGGGCATCATCATTCAGGGTGGGAAGCACCGAGAG
Human 1472 AGGAGAAGATCGTGAGGGGCATCATCAT
TCAGGGTGGGAAGCACCGAGAGRat 1469
ATGAGAAGATAGTAAGAGGTGTCATCATTCAAGGTGGGAAGCACCGAGAA
Macaque AACAAGGTATTCATGAGGAAGTTCAAG
ATCGGGTACAGCAACAACGGCTCHuman 1522
AACAAGGTGTTCATGAGGAAGTTCAAGATCGGGTACAGCAACAACGGCTC
Rat 1519 AACAAAGTGTTCATGAGGAAGTTCAAGA
TCGCCTACAGTAACAATGGTTC Macaque
CGACTGGAAGATGATCATGGACGACAGCAAACGCAAGGCAAAGTCTTTTG
Human 1572 GGACTGGAAGATGATCATGGATGACAGC
AAACGCAAGGCGAAGTCTTTTGRat 1569
TGACTGGAAAATGATCATGGATGACAGCAAGCGCAAGGCTAAGTCTTTTG
Macaque AGGGCAACAACAACTATGACACACCTG
AGCTGCGGACTTTTCCAGCTCTCHuman 1622
AGGGCAACAACAACTATGATACACCTGAGCTGCGGACTTTTCCAGCTCTC
Rat 1619 AAGGCAACAACAACTATGACACACCTGA
GCTCCGGGCCTTTACACCTCTCMacaque
TCCACGCGATTCATCAGGATCTACCCCGAGAGAGCCACTCATGGCGGACT
Human 1672 TCCACGCGATTCATCAGGATCTACCCCG
AGAGAGCCACTCATGGCGGACTRat 1669
TCCACAAGATTCATCAGGATCTACCCCGAGAGAGCCACACATAGTGGGCT
-NP-1
Anti-sense Primer (reverse) Macaque
GGGGCCCCGAATGGAGCTGCTGGGCTGTGAAGTGGAAHuman
1722 GGGGCTCAGAATGGAGCTGCTGGGCTGTGAAGTGGAARat
1719 CGGACTGAGGATGGAGCTACTGGGCTGTGAAG
TAGAA
22Protein Synthesis
- DNA is found in the chromosomes which are found
in the nucleus of the cell - DNA stores the genetic code for an organism
through its sequence of the nitrogen bases - The genetic code is transferred via RNA to the
ribosomes in the cytoplasm outside of the cell
nucleus where protein in synthesized - The information required for protein synthesis
is passed through a similar unzipping and
replication process
23RNA and Protein Synthesis
- The transfer of information for building proteins
is then accomplished by the RNA. - RNA is similar to DNA but there are some
important differences - RNA is a single strand rather than a double helix
- Deoxyribose is replaced with ribose
- The nitrogen base thymine is replaced with Uracil
24RNA
- Ribose has a slightly different structure from
deoxyribose - Ribose has an OH group on carbon 2 rather than a
H as in deoxyribose
25RNA
- The structure of Uracil differs slightly from
Thymine
Uracil
Thymine
26Messenger RNA
- Messenger RNA or mRNA copies and carries the
genetic code from the DNA template within the
cell nucleus to the ribosomes where proteins are
synthesized. - It essentially aligns itself with the DNA and
produces a complimentary copy
27Transfer RNA
- Transfer RNA acts as an amino acid carrier in the
formation of proteins - Through a decoding mechanism it facilitates the
addition of an amino acid to a peptide chain
forming a protein - It directs the insertion of amino acids in the
proper sequence in the poly peptide chain through
sets of three nitrogen bases known as codons
28RNA Codons
29RT-PCR or Reverse Transcriptase Polymerase Chain
Reactions
- RT-PCR was first developed by Cary Mullis for
which he was awarded the Nobel Prize in
Chemistry - Replicated DNA can be then separated and
classified
- This process allows the DNA from very small
amounts of - cellular material to be replicated
- DNA is extracted and broken down into smaller
fragments - using restriction enzymes
- The DNA is then replicated and separated using
gel - electrophoresis
30RT-PCR and DNA Replication
RT-PCR gel showing relative amounts of NP-1 using
cyclophilin as an internal standard.
31DNA Sequencing
Lee Hood (Univ. of Washington invented a device
that can sequence the bases for a DNA fragment.
32Forensic DNA Analysis
- The DNA fragment contains codons that code for
proteins - It also contains regions where there is no coded
message in the base sequence
- The application of a restriction enzyme cuts this
part of - the DNA into fragments.
- The sequence and hence the fragment sizes are
unique - for each individual (Except for Identical Twins)
33Forensic DNA Analysis
- Used to identify
- people in criminal
- cases
- Used to establish identity, paternity
- and ancestry.
- Used to study evolutionary
- changes in species
34Forensic DNA Analysis
- DNA evidence is only as good as the person
performing the tests. Care must be taken to
guard against contamination for legal evidence to
stand. - Chain of evidence rules