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 …