The Biological Basis of Life – Part 1
- Sir Francis Crick: 1916-2004
- He discovered the structure of DNA
- Was very important in deciphering the genetic code*
- DNA, to RNA to proteins
Cells, the Basic Units of Life
- Cells are the basic units of life.
o Bacteria and more complex cells known as eukaryotes
- Cells of bacteria and blue-green algae lack nuclear membrane. These
unicellular organisms are known as prokaryotes.
- Cells of other life forms, including multicellular plants and animals, have a
nucleus in which the genetic material is organized on chromosomes. These
organisms are composed of eukaryotic cells.
- A representation of the typical prokaryote and eukaryote cells is shown in
the next slide.
Prokaryotic vs. Eukaryotic Cells
- Eukaryotic have a nucleus so the genetic information is found there
o DNA is located in the nucleus of the cell
o And in the cytoplasm, there are important organelles found, including
o (mitochondria DNA is passed from the mother)
DNA, the Molecule of Life
- The instructions to carry out all the activities required by most living
systems are stored in a molecule called DNA (deoxyribonucleic acid). Some
life forms are based on a related molecule, RNA (ribonucleic acid).
- The structure of DNA was deciphered more than 50 years ago (1953) by
Francis Crick and James Watson.
- Let’s review the structure of this important molecule, key for the
transmission of the instructions of life from generation to generation.
- It has not escaped our notice that the specific pairing we have postulated
immediately suggests a possible copying mechanism for the genetic material
o They were able to explain how the genetic material was past from one
generation to the next
Other Researchers Involved in the Race to Find the Structure of the DNA
- Rosalind Franklin
o Chemists who specialized in x-ray picture of moleucules
- Maurice Wilkins
o DNA was the molecule that was responsible for genetic material (this
was known but the structure was unknown) o It was known that the basis (components of DNA) has different
A was similar to T while C was similar to G
- Linus Pauling
o Everyone thought he was going to be the one who would find the
structure of DNA
o In 1953, he proposed
The Structure of DNA
- Key elements of the DNA molecule are the nitrogenous bases, nitrogen
containing ring compounds of two main classes, purines and pyrimidines
o These rings contain nitrogen
o There are two structures that are important for bones
o Purine – adamines and guatamine (A and G)
Have two rings
o Pyrimidines – C and T
Have one ring
- Nucleotides consist of a nitrogen-containing base, a five carbon sugar
(deoxyribose, in the case of DNA, ribose in the case of RNA), and phosphate
- Nucleotides are the basic units of nucleic acids.
- Free nucleotides have three phosphate groups deoxyadenosine triphosphate
- When they are incorporated into DNA, they lose two of the three phosphates
- Nitrogenous bases can form hydrogen bonds with one another
- Adenine forms two hydrogen bonds with thymine,
- Guanine forms three hydrogen bonds with cytosine
- This is how when DNA separates, you are able to figure out the pairing strand
that will be newly synthesized
- DNA is a polymer made of deoxynucleotides
- Nucleotides are linked together via phosphodiester bonds