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DNA
What is DNA video
• http://learn.genetics.utah.edu/content/begin/
tour/index.html
• Video united streaming Hershey and Chase
Experiment: “DNA Carries Genetic Material”
A Segment of: Greatest Discoveries with Bill
Nye: Genetics (2:05)
In the nucleus of a cell, wound up as
chromosomes is the chemical: Deoxyribonucleic
Acid
A Nucleotide: has 3 pieces
• Phosphate group
• Deoxyribose Sugar
• Nitrogen Base
Nucleotides form a repeating pattern
In 1953, Watson and Crick created
their historic model of the shape of
DNA: the double helix.
COLD SPRING HARBOR LABORATORY ARCHIVES
Dna Structure:
http://www.hhmi.org/biointeractive/paireddna-strands Howard Hughes medical institute
Chargaff’s Ratio:
http://www.hhmi.org/biointeractive/chargaffsratio
DNA replication:
http://www.hhmi.org/biointeractive/dnareplication-schematic
http://mw.concord.org/modeler/ molecular
workbench DNA to proteins
Double Helix
• DNA consists
of two long,
twisted chains
made up of
nucleotides.
http://publications.nigms.nih.gov/thenewgenetics/images/ch1_nucleotide.jpg
Nucleotide
http://www.accessexcellence.org/RC/VL/GG/images/nucleotide2.gif
BASES
• The bases in DNA nucleotides are adenine,
thymine, cytosine, and guanine.
• Adenine bonds to Thymine
• Guanine bonds to Cytosine
DNA game
• http://nobelprize.org/educational_games/me
dicine/dna_double_helix/index.html
The Secret to Life
• Discovering the structure “one of the greatest
scientific breakthroughs of the 20th century”
• Video on united streaming: “The Double
Helix” A Segment of: Greatest Discoveries
with Bill Nye: Genetics (4:04)
The Nobel Prize in Physiology or Medicine
1962
"for their discoveries concerning the molecular
structure of nucleic acids and its significance for
information transfer in living material"
Francis Crick
1/3 of the prize
United Kingdom
James
Watson
1/3 of the prize
USA
Maurice Wilkins
1/3 of the prize
United Kingdom and New
Zealand
Other scientists involved
• Rosalind Franklin
• Took pictures using x ray crystallography
discovered:
– DNA is helical (twisted)
– DNA is made of two strands of
nucleotides.
http://gandt.blogs.brynmawr.edu/files/2009/03/rfranklin.jpg
Scientists whose work added pieces of
the DNA structure puzzle
What was their experiment what did it prove:
• Fredrick Griffith:
• Oswald Avery:
• Alfred Hershey and Martha Chase:
• Erwin Chargaff:
• Rosalind Franklin
DNA Replication
• definition: DNA making
a copy of itself.
• Complimentary bases:
each strand of DNA can
be used to make the
other strand
• Each new DNA double
helix is ½ original and ½
new
http://www.brown.edu/Courses/BI0032/gentherp/dnarep.gif
Diagram from textbook
• The process is “semiconservative
DNA replication and protein synthesis online simulation
• http://ri-itest.portal.concord.org/preview/ molecular workbench
Select "Biology: Activities", then "DNA to proteins". You do not need to
have logged in with user name and password.
• http://www.pbs.org/wgbh/aso/
tryit/dna/#
DNA Polymerase enzymes
• This is the enzyme joins
complementary bases
on the “unzipped” DNA
strand.
• It also “proofreads” the
new strand to make sure
it is copied correctly.
Protein Synthesis
for animations of the transcription and translation processes
see molecular workbench:
http://ri-itest.portal.concord.org/preview/
Select "Biology: Activities", then "DNA to proteins". You do
not need to have logged in with user name and password.
See Page 2
Page 3
Protein Synthesis
• DNA is the code that instructs a cell to make proteins.
• Proteins make up roughly ½ of the material in cells and are an
important part of the chemical reactions that cells do.
• Proteins are made of polypeptides – chains of amino acids.
Protein Synthesis happens in two parts:
• Transcription: DNA
transcribed into mRNA
• Translation: mRNA is
used to put together
amino acids forming
proteins
DNA versus RNA
• DNA
–
–
–
–
has deoxyribose sugar
is double stranded
is only in the nucleus
Bases: Adenine, Thymine, Cytosine,
Guanine
• RNA
–
–
–
–
has ribose sugar
is single stranded
is in the nucleus & cytoplasm outside
Bases: Adenine, Uracil, Cytosine,
Guanine
Transcription
• DNA is separated and
messenger RNA bases
pair up to the DNA to
form a strand of mRNA.
• mRNA takes the code
from the DNA in the
nucleus to the ribosome
in the cytoplasm
DNA
mRNA
Adenine
=
Uracil
Cytosine
=
Guanine
Thymine
=
Adenine
Guanine
=
Cytosine
Transcription
• mRNA made from DNA
• mRNA travels out of
nucleus
http://biology.northwestcollege.edu/biology/b1010lab/DNApuz.htm
Translation
• A Ribosome attaches to
mRNA
• 3 bases of mRNA (codon)
pair with 3 bases of tRNA
(anticodon)
• The proper amino acid is
transferred to the ribosome
by the tRNA.
• Ribosome attaches amino
acids to form protein
(polypeptide chain)
mRNA = messenger RNA
tRNA= transfer RNA
Translation
• tRNA “anticodon”
matches to mRNA
“codon”
• Amino Acids connected
to form polypeptide
chain (protein)
mRNA and tRNA
• Messenger RNA, mRNA
– Takes DNA code from
nucleus to ribosome
• Transfer RNA, tRNA
– Each tRNA has 1 amino acid
attached to it to transfer
them to the ribosome
Deciphering the genetic code
Which codon = which amino acid?
Use a genetic code tool to help figure it out.
• Multiple codons code
for the same amino
acid
• 20 amino acids combine in
unique ways to form
different proteins.
Practice
• Transcribe the following DNA
– TACTTGGCA
– AUGAACCGU
• Translate the following mRNA into tRNA
•
-AUGAACCGU
-UACUUGGCA
How many codons are contained in this
example
-
•
3
What amino acids are coded for by the m RNA
codons?
- methionine, asparagine, arginine
Polypeptide chain
• The polypeptide was started with the “start”
codon of mRNA (AUG) which codes for
methionine
• Amino acids continue to attach to each other
until a “stop” codon from the mRNA instructs
the polypeptide chain to be release from the
ribosome.
http://learn.genetics.utah.edu/content/begin/dna/transcribe/images/ttsidebar.gif
DNA Fingerprinting
• The chemical structure of everyone's DNA is the
same.
• The order of bases making up everyone’s DNA is
different.
• Every person can be identified by the sequence of
their base pairs.
Website create a DNA fingerprint
http://www.teachersdomain.org/ass
et/tdc02_int_creatednafp2/
The process of DNA fingerprinting
1. Extract DNA
2. Use chemicals to cut the long strands of DNA into much
smaller segments. Each segment has a specific length, but all
of them share the same repeating sequence of bases (or
nucleotides).
3. Use a process called gel electrophoresis to separate these
repeating segments according to length.
4. Next, they introduce a small set of radioactive "markers" to
the sample. Photographic film, which darkens when exposed
to the radioactive markers, identifies the location of all
marked sample segments.
5. This film, then, becomes the DNA "fingerprint" that forensic
investigators analyze. Compare
Mutation
http://highered.mcgraw-hill.com/sites/0072552980/student_view0/chapter9/animation_quiz_5.html
What is a mutation? A mutation is a change in the DNA sequence.
Germline mutations, which can affect reproductive cells, can be passed on to
offspring.
Somatic mutations, which affect other cells, cannot be passed on.
• When one nucleotide is replaced with another, it is called a substitution mutation.
For example, changing ATCG to ATAG.
• When a nucleotide is added into the sequence, it is called an insertion mutation.
For example, changing ATCG to ATGCG.
• When a nucleotide is lost from the DNA sequence, it is called a deletion mutation.
For example, changing ATCG to ACG.
The result of mutation
• a silent mutation. This is a change from one codon to another that codes for
the exact same amino acid. It has no effect on the amino acid sequence of
the resulting protein.
• Stop codons don't code for an amino acid, as do other codons. Instead, they
signal the end of the protein. Inserting a stop codon into the sequence will
cause translation to stop there.
• A frame-shift occurs when an insertion or deletion
shifts nucleotides over, while the reading frame
stays in place.
Substitution mutation:
G changed to A
What is the result of this substitution?
Gene mutation versus chromosomal
mutation
• Gene mutations result from changes of a
single gene, a small portion of a chromosomes
• Chromosomal mutation result from changes in
a whole chromosome and affect many genes