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

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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