DNA: The Molecule of Heredity
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.