DNA
DNA
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Deoxyribonucleic Acid
Contains the genetic code
Polymers of nucleotides
Nucleotide- sugar ,phosphate ,base
DNA use deoxyribose sugar
4 Bases in DNA
• Adenine binds to Thymine
• Cytosine binds to Guanine
• A-T-T-G-G-C-G-T-A strands are bound to
• T-A-A-C-C-G-C-A-T each other by H bonds
Discovery of DNA
• Watson and Crick discovered shape and
make up of DNA
• Looks like a twisted ladder
• Double helix
• Sequence of bases determines genetic
information
• The closer the sequence is between 2
organisms-the closer related they are.
DNA REPLICATION
• Needed during mitosis and meiosis
• Each strand serves as a template to make
a whole new strand•
Semi-conservative method
• 1. Helicase breaks the H bonds between
bases
• 2. DNA unzips
• Free floating nucleotides attach to empty
base pair
• DNA polymerase bonds nucleotide in
place
• Continues until whole chain is replicated
on both sides.
• Produce 2 strands of DNA- each has an
old side and a new side
• This is how genetic information passed to
new cells during mitosis
New generations during meiosis
We use DNA to make Proteins
• Information to make proteins is located on
DNA
• Proteins are polymers of Amino Acids held
together by peptide bonds
• AA—AA-- AA -- AA – AA
• Use RNA (ribose nucleic acid) as a go
between the code on the DNA and the
protein
Differences between RNA and DNA
RNA
DNA
Sugar
Ribose
Deoxyribose
# of strands
1
2
Base
Uracil replaces thymine
Thymine
3 Types of RNA
• mRNA(messenger)- brings instructions
from DNA to ribosome
• rRNA(ribosomal)- binds to mRNA and
assembles the amino acids
• tRNA(transfer)- delivers amino acid to
rRNA
Transcription
• mRNA enters nucleus
to make copy of DNA
(just one side)
• mRMA moves to
ribosome
Translation
• At the ribosome the mRNA binds to
ribosome(rRNA)
• tRNAs bring over the correct amino acid
according to the base sequence on mRNA
• Amino Acids bonded together by peptide
bonds.
• New protein breaks off and moves to Golgi
body for processing
• Every three bases on the mRNA is called
a codon.
• Each codon has an anti codon sequence
on a tRNA molecule
• Each codon codes for a specific amino
acid- so each tRNA will bring over a
specific amino acid
Codons
DNA
A
T
G
G
C
A
T
G
A
mRNA
U
A
C
C
G
U
A
C
U
tRNA
A
U
G
C
C
A
U
G
A
Codon Chart
• A codon chart displays the amino acid for
each codon.
• Even though there are only 20 amino
acids there are 64 possible combinations
of triplets using the 4 bases
• So… there can be more than one codon
for each amino acid
• There is 1 start codon (AUG-Methionine)
• There are 3 stop codons
• 61 other codons code for amino acids
• www.youtube.com/watch?v=B6O6uRb1D3
8
• www.youtube.com/watch?v=ncjIiD51hQk&
NR=1
• Not all DNA codes for proteins
• Exons code for genetic information
• Introns are filler DNA or nonsense code
Genetic Changes
• MUTATION- any change in the DNA
sequence of bases
• Causes- replication error(mitosis/meiosis)
transcription
chemical agent
external agent
• If error occurs in mitosis- result will be
seen in individual like cancerous cell
• If error occurs during meiosis- result will
be seen in offspring
Point Mutation
•
Single base pair change
1. Deletion C-T-A-G
2. Insertion C-T-A-G
3. Wrong Base C-T-A-G
C-T-G
C-T –G-A-A-G
C-T-T-G
Frame Shift Mutation
• Reading of codons starts at wrong spotwill lead to incorrect amino acid sequence
A-U-G-G-U-U-A-C-G-A-C-A
Methionine-valine-threonine-threonine
A-U-G-G-U-U-A-C-G-A-C
Tryptophan-leucine-arginine
Chromosomal Alterations
• Affect whole chromosomes- not just one
base
• Deletion A-B-C-D
A-B-D
• Insertion A-B-C-D
A-B-C-B-C-D
• Inversion A-B-C-D
A-C-B-D
• Translocation A-B-C-D
X-Y-A-B-C-D
X-Y-Z
Z
• Spontaneous mutations just happen
• Exposure to external agents like sun and
chemicals can a take long time to cause
mutation
• There are repair mechanisms that read the
DNA strand during replication and correct
mistakes.