Download Chapter 1 The Framework of Biology

Chapter 7 The Master Molecule of Life: DNA – Structure and
Function
CHAPTER OUTLINE
7.1 DNA is the master molecule of life.
DNA contains the code for the development and maintenance of life through the
production of proteins and is capable of being copied and passed from parent to
offspring.
Studies in the early 1900s laid down the groundwork for the discovery of the structure of
DNA.
Many years of work by many scientists led to the discovery of the structure of DNA.
Included in the group are Fred Griffith, Oswald Avery, Alfred Hersey, and Margaret
Chase. Fred Griffith discovered that free genetic material could be taken up by bacteria.
Avery continued the study of bacterial transformation, extracting the fibrous DNA
molecule. Hershey and Chase used bacteriophage to find that DNA, not protein, was the
genetic material.
7.2 Scientific sleuthing: the discovery of the structure of DNA.
As study continued, Linus Pauling continued his work with model building, while
Maurice Wilkins and Rosalind Franklin studied DNA using x-rays. Francis Crick and
James Watson gathered all the data and constructed a model of DNA that proved to be
correct, a discovery for which they were awarded the Nobel Prize.
7.3 The structure of DNA is a double helix.
The DNA molecule is a double strand of nucleotides, or double helix, resembling a
twisted ladder. The sides of the ladder are the sugar and phosphate units, one side
running in a 3' to 5' bonding arrangement, the other arranged 5' to 3'. The rungs of the
ladder are matched bases: adenine to thymine or cystosine to guanine.
The DNA in cells combines with proteins to form chromosomes.
The entire complement of DNA within each cell is divided into segments called
chromosomes. In order to compact the DNA molecule, it is wound around proteins into
structures called nucleosomes.
7.4 The structure of DNA allows genetic information to be transferred from parent
to offspring.
The genetic code is responsible for directing protein formation and also must be passed
from parent to offspring.
The double helix contains the mechanism for inheritance.
DNA replication is run by DNA helicase, DNA polymerase and DNA ligase.
7-1
7.5 DNA directs the synthesis of proteins.
DNA controls cellular processes through the production of proteins.
A sequence of nucleotides codes for a sequence of amino acids.
Genetic information is the code for specific amino acids. The code for a protein is called
a gene; the entire DNA sequence in an organism is its genome.
RNA plays important roles in the process of protein synthesis.
Messenger RNA, mRNA, transfer RNA, tRNA, and ribosomal RNA, rRNA, are all
involved in protein synthesis. rRNA molecules may be called ribozymes.
DNA directs the synthesis of proteins by the process of transcription and translation.
The genetic code is comprised of sets of three bases called codons. Transcription is the
formation of an mRNA from DNA controlled by RNA polymerase. Translation is the
formation of a chain of amino acids from mRNA on a ribosome. tRNA brings the
appropriate amino acid, matching the tRNA anticodons to the mRNA codon. An mRNA
strand fits into a ribosome using three binding sites, A-site, P-site, and E-site, for
attachment of the tRNA and binding of amino acids.
7.6 DNA helps to explain the unity and diversity of life.
The genetic code is a universal code across all life forms. Mutations within the genetic
code allow for changes in organisms, creating diversity of life forms. Scientists have
discovered other ways in which genetic information can change including gene transfer
and gene duplication.
7.7 How do you know? Conquering tuberculosis.
Understanding the genetic code and how it works, especially the specific information
being revealed today, helps scientists combat disease.
What do you think?
Astrology is presented to stimulate critical thinking about science.
7-2