DNA
It’s not just for college anymore!
Web Sites
• DNA structure and replication animation
http://207.207.4.198/pub/flash/24/menu.swf
• Overview of gene expression
http://www.genomicseducation.ca/animations/gene_expression.asp
• DNA Models & Translation model
http://www.indigo.com/models/dna-models.html
Learning Goals for DNA & Genetics
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Know structure/function of DNA
Know DNA is genetic material
Illustrate how DNA specifies traits
Understand mutations are change in DNA
sequence
• Understand relationship between
mutations in DNA and expressed
phenotype
What Is DNA
• Deoxyribonucleic acid
– Everyone knows this?
• Molecule of heredity
– Constitutes our genes
– Genes are stretches of DNA sequence
– DNA is present in each cell
– Passed on to gametes and into progeny
What is DNA, Really
• Polymer of nucleotides
• Polymer? Nucleotides?
• Polymer
– A large molecule that is a series of joined smaller
molecules
• Nucleotides
– The small molecules that make up the large DNA
polymer
DNA Concepts
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•
•
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Genes
Chromosomes
Complementary base-paired double helix
Polymer of nucleotides
The sequence of nucleotides is the
information of DNA
DNA Concepts
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•
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DNA controls traits of organism
Traits pass from parent to offspring
DNA is copied during cell division
DNA is present in sex cells
DNA is passed from parent to offspring
Why are DNA Concepts Difficult?
• Chemical names?
– Deoxyadenosine, purine, pyrimidine
• Chemical processes?
– base pairing, hydrogen bonds
• Genetic principles?
– DNA replication
– Mutations
– Chromosome segregation & assortment
Why is DNA So Difficult?
• Chemical Names
– Deoxyadenosine monophosphate
– Pyrimidine
• Persons Names
– Martina Navratilova
– Hakeem Olajuwon
How About Pictures + Names
A
B
C
E Hakeem Olajuwon
__
F Purine
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C Kareem Abdul-Jabbar
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H Deoxyadenosine monophosphate
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B Pyrimidine
D
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G Martina Navratilova
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D Deoxycytidine monophosphate
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A Nadia Comaneci
__
F
G
E
H
Nucleotides
The building blocks of DNA
Nucleotide Structure
Base always
attached here
Phosphates are
attached there
Nucleotides
Adenosine monophosphate
Cytidine monophosphate
Guanosine monophosphate
Uridine monophosphate
Deoxyadenosine monophosphate
Deoxycytidine monophosphate
Deoxyguanosine monophosphate
Deoxythymidine monophosphate
Nucleotide Polymerization Reaction:
Phosphodiester Bond Formation
Order of Nucleotides
• As nucleotides join the strand they
generate a sequence
• Inherent fidelity of DNA replication
TAAGTGTACACGTA
ATTCACATGTGCAT
TAAGTGTACACGTA
TAAGTGTACACGTA
TCACATCGTAAGTGTACACGTA
AGTCCGATCGTAACTGGGTCACATCGTAAGTGTACACGTA
AGTCCGATCGTAACTGGG
||||||||||||||||||||||
||||||||||||||||||||||||||||||||||||||||
||||||||||||||||||
TCAGGCTAGCATTGACCCAGTGTAGCATTCACATGTGCAT
TCAGGCTAGCATTGACCC
AGTGTAGCATTCACATGTGCAT
ATTCACATGTGCAT
TAAGTGTACACGTA
ATTCACATGTGCAT
DNA Sequence
• Human Genome Project
– sequencing the human genome
• What does “sequencing” mean?
– To determine the order of the nucleotides in the human DNA
molecules
– Human DNA molecules are our chromosomes
– Each chromosome is a DNA double helix
– Each DNA double helix is two single DNA molecules intertwined
– Each single DNA molecule is a chain of nucleotide units
– Sequencing is the method to determine what the exact order of
units is in this chain
Gene
Expression
DNA
Gene
Transcription
RNA (messenger RNA)
Translation
Protein
(sequence of
amino acids)
Functioning of proteins within living
cells influences an organism’s traits.
A Gene is a Transcription Unit
Terminator
Promoter & Regulatory
sequences
Coding sequences
DNA
Transcription
mRNA 5
3
Start
codon
Ribosome binding site
Open
reading
frame
Stop
codon
Transcription
Coding
Overview of gene expression
AC
Translation
Translation Elongation
aa-tRNA entry
Peptidyl
transferase
Translocation
Termination
Translation
The code is 3 letter words, but what about
punctuation?
cbab
GROWANDNOWTHECATSAWTHEDOGBUTDIDNOTRUNENDSEW
• Code written in three letter words - codons
• Ribosomes must start at the right place to read
the message
• There are three frames, but only one is read to
give an intelligible message
• Need a start codon (NOW) and a stop codon
(END) to define the frame to use
• frame b
– NOW THE CAT SAW THE DOG BUT DID NOT RUN
Reading Frames & Mutation Types
• Frame shift mutations
– Original reading frame is frame a
– Insertions or deletions shift the reading frame
a
b
c
ROWANDNOWTHECATSAWTHEDOGBUTDIDNOTRUNENDSEW
^
a
b
c
ROWNDNOWTHECATSAWTHEDOGBUTDIDNOTRUNENDSEW
Reading Frames & Mutations
a
b
c
ROWANDNOWTHECATSAWTHEDOGBUTDIDNOTRUNENDSEW
• Once a ribosome begins translation in a particular
frame (a) it does not shift frames
• Therefore, if a mutation shifts the reading frame in
the mRNA, the ribosome will read the wrong frame.
^
a
b
c
ROWANDNOWTHECATSAWTHEADOGBUTDIDNOTRUNENDSEW
NOW THE CAT SAW THE ADO GBU TDI DNO TRU NEN DSE W..
Reading Frames & Mutations
a
ROWANDNOWTHECATSAWTHEDOGBUTDIDNOTRUNENDSEW
• A change that creates a stop codon is a
non-sense mutation
• Generates a truncated protein
^^
a
ROWANDNOWTHECATSAWTHEDOGBUTENDNOTRUNENDSEW
NOW THE CAT SAW THE DOG BUT END
Reading Frames & Mutations
a
ROWANDNOWTHECATSAWTHEDOGBUTDIDNOTRUNENDSEW
• A change that creates a different codon is a
mis-sense mutation
• Generates a protein with an altered
sequence
^
a
ROWANDNOWTHECATSAWTHEHOGBUTDIDNOTRUNENDSEW
NOW THE CAT SAW THE HOG BUT DID NOT RUN END
Molecular Basis of Phenotype
Effect of Mutations
• Sickle cell disease
– single nucleotide change AT