Download DNA - Experiments and Discoveries

Chapter #12 – DNA, RNA, &
Protein Synthesis
I. DNA – experiments & discoveries
A. Griffith and Transformation
Frederick Griffith – British scientist who
experimented with bacterial strains of
pneumonia in mice & discovered
transformation.
Transformation – process in which one strain
of bacteria is changed by a gene or genes from
another strain of bacteria, ex : rough,
harmless bacteria becoming smooth &
disease-causing.
Griffith & Transformation
B. Avery and DNA
Oswald Avery – Canadian
biologist who repeated
Griffith’s work & found that
DNA causes transformation in
bacteria.
-His work showed that DNA
stores & transmits genetic info
from one generation of an
organism to the next.
C. The Hershey-Chase Experiment
Alfred Hershey & Martha Chase – American
scientists who experimented with radioactive
markers in viruses & concluded that the genetic
material of the bacteriophage was DNA, not
protein.
Virus – nonliving particles smaller than a cell that
can infect living organisms.
Bacteriophage – (“bacteria eater”) type of virus
that infects bacteria.
-Scientists conclude that genes are made of DNA.
Alfred Hershey & Martha Chase
D. Components & Structure of DNA
DNA – (Deoxyribonucleic acid) nucleic acid that contains
the sugar deoxyribose; the molecule of heredity.
-DNA (nucleic acid) is made up of nucleotides.
Nucleotides of DNA have 3 basic parts :
1. A 5-carbon sugar called deoxyribose.
2. A phosphate group.
3. A nitrogenous (nitrogen-containing) base.
-There are 4 kinds of nitrogenous bases found in DNA :
1. Adenine (A)
2. Guanine (G)
3. Cytosine (C)
4. Thymine (T)
Structure of DNA
The 4 bases can be divided into 2 major groups :
Purines – have 2 rings in their structures & include
adenine & guanine.
Pyrimidines – have 1 ring in their structure & include
cytosine & thymine.
-The backbone of the DNA molecule is formed by sugar &
phosphate groups of each nucleotide & the nitrogenous
bases stick out sideways from the chain.
-Nucleotides can be joined together in any order to make
different sequences of bases.
Chargaff’s Rule :
In any sample of DNA, the percentages of guanine &
cytosine bases are nearly equal & the percentages of
adenine & thymine bases are nearly equal.
Rosalind Franklin
Rosalind Franklin – British
scientist who used a technique
called X-ray diffraction to
Record information about the
structure of DNA.
-Her work revealed that DNA is
shaped like a helix (twisted
strands like the coils of a spring).
James Watson and Francis Crick
James Watson & Francis Crick
– American biologist & British
physicist who built the first
accurate structural model of
DNA, after viewing Rosalind
Franklin’s work.
-Watson & Crick’s model of
DNA was a double helix, in
which 2 strands were wound
around each other.
The Twisted Ladder
-A double helix looks like a twisted ladder or a spiral staircase.
-In DNA, hydrogen bonds only form between certain
nitrogenous bases in the double helix to hold it together, this
is known as base pairing.
-Every adenine molecule binds with a thymine and every
cytosine molecule binds with a guanine.
Applying Concepts :
*Given this sequence, determine the
bases that would match it in a double
helix : A
C
G
T
C
T
G
C
A
G