DNA Introduction Notes

Phenotype

• The observable characteristics or appearance of an organism.
• Examples:
  • Color of eyes or hair
  • Length of limbs or bodies

Phenotype and Genotype

• DNA contains the genetic instructions for an organism; it is the "Blueprint for Life."
• DNA contains genetic codes that determine the physical characteristics (phenotype) of an organism.
• The combination of our genes and DNA is called our genotype.

DNA Location and Structure

• DNA, or deoxyribonucleic acid, is found in the nucleus of plant, animal, and fungal cells.
• When the cell is not dividing, the complex of DNA and proteins exists in a mass of long, thin fibers called CHROMATIN within the nucleus.

Discovery of DNA Structure

• Based on work by Maurice Wilkins and Rosalind Franklin, James Watson and Francis Crick developed the first model of the DNA molecule.
• Watson, Crick, and Wilkins were awarded the 1962 Nobel Prize in Physiology and Medicine.
• Rosalind Franklin developed ovarian cancer and received no recognition from her peers.

DNA Structure

• The basic unit of DNA is the NUCLEOTIDE.
• Each nucleotide molecule consists of:
  • A phosphate group
  • A sugar group
  • A nitrogen base
• Watson and Crick described the shape of a DNA molecule as a double helix structure:
  • It consists of two strands or sides.
  • The two strands were joined together by “rungs”.
  • The whole structure was twisted like a spiral ladder.

Double Helix

• The sugar groups and phosphate groups form the "sides" of the double helix (or ladder).
• The nitrogenous bases form links between the sides (or the "rungs" of the ladder).

Nitrogenous Bases

• There are four nitrogenous bases:
  • A = adenine
  • T = thymine
  • C = cytosine
  • G = guanine
• Each cross-link consists of two nitrogenous bases.
  • Adenine always links to thymine (A to T)
  • Cytosine always links to guanine (C to G)

Complementary Base Pairing

• The bases can only pair up in one way.
• This characteristic is known as complementary base pairing.