Download - DNA: D eoxyribo n ucleic A cid
DNA: Deoxyribonucleic Acid
Image from http://www.pratt.duke.edu
What do you know about DNA?• My 10 year old says “Mom,
everyone knows all about DNA.”
• OK… so what do you know?
By the way… I “googled” the term DNA and it returned
2.6 MILLION images!
Image from www.blockbuster.com
The Double Helix
• Another image from GATTACA …
Image from www.movieforums.com
• The Double Helix is held together by “Hydrogen Bonding”
• Gives the Helix specificity• Chargaff’s Rule (1950): [A] = [T] and [G] = [C]
refuted the previously held understanding of the “Tetranucleotide Hypothesis”
A=T and G-C
Images from:The Creative Science Quarterly: www.scq.ubc.ca and http://en.wikipedia.org/wiki/Phoebus_Levene
A Closer Look at the Anatomy of the
Double Helix
• While the base pairs are holding things together in the middle…
• the sugars and phosphates are holding things together along the sides.
• The strands in the Double Helix are “antiparallel”
Image from: http://whyfiles.org
The sugar in DNA is “DEOXYRIBOSE”
• The DNA Double Helix is wound around a set of proteins call “Histones” which allow for efficient packaging of the DNA into Chromosomes
• The Chromosomes are then packaged into the Nucleus of the Cell
Structure : Function
Replication
Image from healthanddna.com
"It has not escaped our notice that the specific pairing that we have postulated immediately suggests a possible copying mechanism for the genetic material."Nature 171, 737–738 (1953)
• The structure of the double helix provides a means for Replication
• DNA copied into more DNA… exactly the same
• Watson and Crick: 1953 paper in Nature described not only the double helix structure but MORE IMPORTANTLY identified the double helix as a mechanism for replication
• The mechanism (“semi-conservative replication” was not proven experimentally until 1957, by Meselson and Stahl.
Transcription• One strand of the DNA is copied
into an RNA strand• The RNA strand serves as a
messenger (mRNA) that goes out into the cytoplasm to direct the synthesis of the corresponding protein
• RNA’s and their function studied in the late 1950’s and well into the 1960’s
http://www.dnai.org/timeline/Image from http://www.le.ac.uk/ge/genie/vgec/he/expression.html
Translation• The RNA is translated
into Protein• Proteins are NOT
nucleic acids... They are made of amino acids
• Notice that the Ribosome (the blob here) is focused on three nucleotides – that is the “CODON”
Image from http://www.dorlingkindersley-uk.co.uk
Not to over simplify…• This image shows
that Translation occurs outside the nucleus
• And that tRNA is involved in the protein synthesis process
• REGULATION – or Gene expression can be controlled at many different stages of the process
? HeLa Cells• Cancer
– Uncontrolled cell growth due to errors in regulation
– Errors could be in any part of the process
– Errors are called Mutations– Mutations can be genetic,
environmental (virus, carcinogen, or various forms of energy); damage to the DNA can be cumulative
Image from www.smithsonianmag.orgQuote from Cancer Res. 59 (1): 141–50
In the case of HeLa, the cervical cancer was caused by a Human Papillomavirus (HPV-18) which integrated itself into a normal gene and then caused five different mutations including “numerical and structural chromosomal aberrations”
Virus• Virus are nucleic acids – HPV,
HIV, polio, herpes, adenovirus (cold) etc…
• They are received into a cell where they insert their viral genetics into the cell’s normal routine and take over
• New virus are produced, killing the cell, taking over more cells, and wearing down the immune system
Gene Therapy
• DNA can be inserted – therapeutically – into a cell in order to cause the cell to synthesize a missing or dysfunctional protein.
Gene therapy has been used successfully in clinical trials for Cystic Fibrosis, some eye diseases, lung cancer, melanoma …
Still in development
Genetic Engineering(Transgenics)
• Insert DNA from one species into another species in order to acquire a new trait or characteristic.
• Common today in agriculture for improving yield (anti-pest genes) and marketability (harvest time, shipping, storage, shelf-life)
DNA …