Download DNA and the Genetic Code

DNA and the
Genetic Code
1
DNA
• 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.
2
Nucleic Acids
• Nucleic 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.
3
DNA Structure
DNA is made up of three units including:
I. A ribose sugar
Ribose
Deoxyribose
Ribose and deoxyribose differ in that ribose
has an OH group on carbon 2 whereas
deoxyribose has only a hydrogen attached.
4
DNA Structure
DNA is made up of three units including
I. A ribose sugar
The phosphates
II. A phosphate group
are attached at
5
3
carbons 3 & 5.
This defines the
direction of the
chain.
Phosphate
Deoxyribose
The phosphate groups alternate with the ribose
sugar and are attached at carbon 3 and at carbon 5
5
DNA Structure
DNA is made up of three units including
I. A ribose sugar
II. A phosphate group
III. A nitrogen (amine) base
There are four different amine bases:
adenine, thymine, cytosine, and guanine.
6
A Nucleotide
Cytosine
The DNA strand is made up of alternating deoxyribose and
phosphate groups with a nitrogen base attached as a side
chain.
7
DNA Structure
DNA is made up of three units
1. A ribose sugar
2. A phosphate group
3. 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
carbon 1 of the deoxyribose
sugar.
Adenine
Cytosine
8
DNA Structure
DNA is made up of three units:
1. A ribose sugar
2. A phosphate group
3. A nitrogen (amine) base
• These three molecules make
up a nucleotide.
• A DNA strand is a sequence
of nucleotides.
• The phosphates are attached
at carbon 3 and carbon 5.
• The nitrogen bases are side
chains at carbon 1.
Adenine
Cytosine
9
DNA 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
10
Complimentary Bases
• Because of their size
and their 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
11
Hydrogen 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
12
DNA Structure -- Hydrogen Bonding
• Adenine and Thymine form a base pair
13
DNA Structure Hydrogen
Bonding
• Guanine and Cytosine
14
Base 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
15
DNA 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.
16
DNA Shape
• This color enhanced
image taken by the
Scanning Tunneling
Electron Microscope
shows a double helix
17
DNA 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
18
DNA 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
19
DNA 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.
20
Gene Correspondance for Neuropilin-1
Species
bp
NP-1 Sense Primer
Macaque
Human
Rat
-1422
1419
ACCCGCACCTCATTCCTACATCAATGAGTGGCTCCAAATAGACCTGGGGG
ACCCGCACCTCATTCCTACATCAATGAGTGGCTCCAAATAGACCTGGGGG
ACCCTCACCCCACCCATACATCAATGAATGGCTCCAAGTGGACCTGGGAG
1472
1469
AGGAGAAGATCGTGAGGGGCATCATCATTCAGGGTGGGAAGCACCGAGAG
AGGAGAAGATCGTGAGGGGCATCATCATTCAGGGTGGGAAGCACCGAGAG
ATGAGAAGATAGTAAGAGGTGTCATCATTCAAGGTGGGAAGCACCGAGAA
1522
1519
AACAAGGTATTCATGAGGAAGTTCAAGATCGGGTACAGCAACAACGGCTC
AACAAGGTGTTCATGAGGAAGTTCAAGATCGGGTACAGCAACAACGGCTC
AACAAAGTGTTCATGAGGAAGTTCAAGATCGCCTACAGTAACAATGGTTC
1572
1569
CGACTGGAAGATGATCATGGACGACAGCAAACGCAAGGCAAAGTCTTTTG
GGACTGGAAGATGATCATGGATGACAGCAAACGCAAGGCGAAGTCTTTTG
TGACTGGAAAATGATCATGGATGACAGCAAGCGCAAGGCTAAGTCTTTTG
1622
1619
AGGGCAACAACAACTATGACACACCTGAGCTGCGGACTTTTCCAGCTCTC
AGGGCAACAACAACTATGATACACCTGAGCTGCGGACTTTTCCAGCTCTC
AAGGCAACAACAACTATGACACACCTGAGCTCCGGGCCTTTACACCTCTC
1672
1669
TCCACGCGATTCATCAGGATCTACCCCGAGAGAGCCACTCATGGCGGACT
TCCACGCGATTCATCAGGATCTACCCCGAGAGAGCCACTCATGGCGGACT
TCCACAAGATTCATCAGGATCTACCCCGAGAGAGCCACACATAGTGGGCT
1722
1719
-NP-1 Anti-sense Primer (reverse)
GGGGCCCCGAATGGAGCTGCTGGGCTGTGAAGTGGAA
GGGGCTCAGAATGGAGCTGCTGGGCTGTGAAGTGGAA
CGGACTGAGGATGGAGCTACTGGGCTGTGAAGTAGAA
Macaque
Human
Rat
Macaque
Human
Rat
Macaque
Human
Rat
Macaque
Human
Rat
Macaque
Human
Rat
Macaque
Human
Rat
21
Protein 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
22
RNA 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
1. RNA is a single strand rather than a
double helix
2. Deoxyribose is replaced with ribose
3. The nitrogen base thymine is replaced
with uracil
23
RNA Structure
• Ribose has a slightly different structure
from deoxyribose.
• Ribose has an –OH group on carbon 2
rather than a H as in deoxyribose.
24
RNA v DNA
• The structure of Uracil differs only
slightly from Thymine
Uracil
Thymine has
a methyl side
group
Thymine
25
Messenger 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
26
Messenger RNA
• Messenger RNA (mRNA)
acts as a template for
protein synthesis
• It has the same sequence
of bases (in the 5' to the 3'
direction) as the DNA
strand that holds the gene
sequence.
• mRNA strands can range
from 300 to as many as
7000 nucleotides.
• The length depends on the
size and the number of
proteins related to the
code.
27
Transfer 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.
28
Transfer RNA
• tRNA molecules are
covalently attached to
the corresponding
amino-acid at one end,
and at the other end
they have a triplet
sequence (called the
anti-codon) that is
complementary to the
triplet codon on the
mRNA.
• All tRNA molecules are
in the range ~70-90
nucleotides. They have
a molecular weight of
~25,000
29
RNA Codons
U
UUU
U
UUC
UUA
UUG
C
Phe
Leu
CUU
C
A
CUC
CUA
UCU
UAU
UCC
UAC
UCA
Ser
UAA
UCG
UAG
CCU
CAU
CCC
CCA
Pro
CAC
CAA
CUG
CCG
CAG
AUU
ACU
AAU
ACC
AAC
AUC
Ile
AUA
AUG
G
Leu
A
ACA
AAA
ACG
AAG
GUU
GCU
GAU
GUC
GCC
GAC
GUA
GUG
Met
Thr
Val
GCA
GCG
Ala
GAA
GAG
G
Tyr
Term.
His
Gln
Asn
Lys
Asp
Glu
UGU
UGC
Cys
UGA
Term.
UGG
Trp
CGU
CGC
CGA
Arg
CGG
AGU
AGC
AGA
AGG
Ser
Arg
GGU
GGC
GGA
GGG
Gly
30
Ribosomal RNA
• Ribosomal RNA (rRNA) is one of the
structural components of a cell structure known
as a Ribosome.
• Ribosomes structurally support and catalyze
protein synthesis.
31
DNA Replication During Cell
Division
• During cell replication
the DNA unwinds and
each strand builds a
new complimentary
strand.
32
RT-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
33
RT-PCR and DNA Replication
NP-1
400
300
bp
bp
Cyclo
200
bp
Primers
100
bp
CTRL
EARLY
MID
MID
LATE
LATE
MENSE
RT-PCR gel showing relative amounts of NP-1
using cyclophilin as an internal standard.
34
DNA Sequencing
Dr. Lee Hood (Univ. of Washington) invented a device
that can sequence the bases for a DNA fragment.
35
Forensic 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)
36
DNA Fingerprinting Process
DNA fingerprinting is a multistep process.
37
Forensic DNA Analysis
• Used to identify
people in criminal
cases.
• Used to establish
identity, paternity
and ancestry.
• Used to study
evolutionary
changes in species.
38
Forensic 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
39