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Properties of DNA

Brother Gregory speaks to his class,

The subject for today is the discovery, structure and replication of DNA. You must follow the lesson, answer the questions, then complete the research investigation, if required.

Let us begin .......

Friedrich Miescher discovered DNA (and RNA) in the pus cells of surgical bandages while working in the new department of natural sciences in the University of Tubingen.

At first called nuclein, this new material had an unusual chemical composition. It contained a unique ratio of phosphrous and nitrogen, much different from any other biological substance known at the time. So, it was first considered to be nothing more than a store house of these two elements.

Slowly, however, the chemical composition of the "nuclein" was investigated. Kossel found the nitrogenous bases in a solution of nuclein that had been boiled in water. Later, Levene discovered the deoxy-ribose sugar in "thymus nucleic acid" (DNA).

The nitrogenous bases were chemically linked to the sugar molecules to form the building blocks of DNA (and RNA); the nucleotides.

As you proceed through this lesson, test yourself as you go by answering some of these "true/false" questions.

Discovering the structure - a very BIG molecule.

It took, however, another 50 years before the structure of the DNA molecule was revealed. From its behavior in a variety of instruments, it was realized that DNA was a polymer, and that its molecules were very large indeed.

The three dimensional structure of the DNA molecule was shown to be an alpha-helix by research done by a variety of research and researchers in England in the 1950's. This 3D picture of the DNA explained how this molecule could act as the agent of heredity, but left a lot of other questions unanswered.

In living cells, DNA molecules are always guarded and protected, especially when they are not being used. Very long lengths of DNA are packaged into complex, multidimensional structures called "chromosomes".

another view
semi-
conservative

bacterial
chromosomes

eukaryotic
chromosomes

DNA replication - copying the information

It is possible to carry out experiments that show how the DNA molecules in chromosomes are replicated. These experiments show that the two halves of the DNA molecule separate and then act as the template for the synthesis of their complementary half. This is called "semi-conservative" DNA synthesis.

During replication the two strands of DNA are first separated. A "fork" opens at the point of replication and enzymes pair up nucleotide bases with their complements on the exposed DNA strands. These nucleotide triphosphates are then joined together to form a new, complementary strand.

Research investigation
check your schedule to see if this is required
The Curse of Amun
DNA research Investigation
Concept questions
for the lesson

check your schedule to see if this is required
DNA Molecule Set
Concept Questions and personal question page
Required Readings
for the lesson
Key Concepts
biopolymers -|- DNA -|- nucleotides -|- role
e-textbook
Table of Contents -|- Discovery -|- Components -|- Size

Double Helix -|- Chromosomes -|- Replication -|- Stages

Departments
Topic Menu -|- Monomers and Polymers

Polynucleotides

Graphics
Nucleotide -|- Nitrogenous Bases

DNA-|- Double Helix

Science@a Distance
© 2001, Professor John Blamire