Post on 25-Dec-2015
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/paired-dna-strands Howard Hughes medical instituteChargaff’s Ratio: http://www.hhmi.org/biointeractive/chargaffs-ratio DNA replication: http://www.hhmi.org/biointeractive/dna-replication-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/medicine/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 CrickJames Watson
Maurice Wilkins
1/3 of the prize 1/3 of the prize 1/3 of the prize
United Kingdom USA 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 “semi-conservative
DNA replication and protein synthesis online simulation
• http://www.pbs.org/wgbh/aso/tryit/dna/#
• http://ri-itest.portal.concord.org/preview/ molecular workbenchSelect "Biology: Activities", then "DNA to proteins". You do not need to
have logged in with user name and password.
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 Synthesisfor 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
Click on this
Click on this
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
mRNA
mRNA codes for amino acid
chain
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 codeWhich 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– T A C T T G G C A– A U G A A C C G U
• Translate the following mRNA into tRNA- A U G A A C C G U - U A C U U G G C A
• 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 fingerprinthttp://www.teachersdomain.org/as
set/tdc02_int_creatednafp2/
The process of DNA fingerprinting
1. Extract DNA2. 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
Mutationhttp://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