DNA: The Molecule

of Heredity

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

• Pyrimidines –

have one ring in

their structure

– Thymine

– Cytosine

• Purines – have

two rings in their

structure

– Adenine

– Guaninehttp://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.