DNA: Structure and Function

DNA Structure• Deoxyribonucleic

acid.• A macromolecule

composed of two strands of monomers called nucleotides.

• These strands are joined in the middle by hydrogen bonds.

• The strands twist around one another forming a double helix.

http://cancergenome.nih.gov/media/DNAKit_illustration_image.jpg

Nucleotide Structure• 5-C sugar –

deoxyribose• Phosphate

group• Nitrogen

containing base -4 of two types– Adenine – Guanine– Cytosine– Thymine http://www.msu.edu/course/isb/202/ebertmay/drivers/nucleotide.jpg

Types of Nitrogen Bases

• Purines – have two rings in their structure– Adenine – Guanine

• Pyrimidines – have one ring in their structure– Thymine – Cytosine

http://student.ccbcmd.edu/~gkaiser/biotutorials/dna/images/DNAbases.jpg

Nitrogen Base Pairing• Bases pair in

a specific pattern.

• A purine always bonds to a pyrimidine

• Adenine bonds to thymine.

• Guanine bonds to cytosine.

Nitrogen Base Pairing• The bases are held

together by weak hydrogen bonds. 

• The sides of the DNA ladder are composed of alternating sugar and phosphate and are called “backbones”.

Discovery of DNA Structure

• This structure was discovered by the work of James Watson and Francis Crick.

• These two scientists viewed x-ray images of DNA crystals that were created by Rosalind Franklin and Maurice Wilkins.

http://www.peace-files.com/ICELANDIC_FILES/QF-R-08/02_A-DNA-Sagan.gif

Functions of DNA

• DNA is the molecule of heredity.

- It provides instructions for cell functioning and is a blueprint for the production of proteins that do the work of the cell.

• DNA must be able to copy itself exactly. - This process is called replication. - Enzymes control the process.

Replication – Overview

        DNA “unzips” down its H-bonds

        One strand then acts as a template for the production of a new strand

        Each new DNA molecule has one old strand of nucleotides and one new strand.

Control Of Cell Activities• DNA is copied

into RNA. (transcription)

• RNA in turn controls the production of proteins. (translation)

• Proteins then do the work of the cell.

Frequently Asked Questions• Why is DNA “twisted”

• Who named it DNA?

• Does the sound of your voice come from DNA?

• Do twins have the same DNA?

Why is DNA “twisted”

• This is caused by the bond angles of the covalent bonds between the carbons in ribose and the oxygen in the phosphate group.

• http://madsci.org/posts/archives/2001-12/1007667362.Bc.r.html

Who named it DNA?

• DNA was named for the chemical components of the molecule – deoxyribonucleic acid- a result of cumulative work among scientists

• Francois Jacob on the naming of RNA http://www.dnalc.org/view/15273-Who-named-messenger-RNA-Fran-ois-Jacob.html