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 …