Transcript Nucleic Acids - Fort Bend ISD / Homepage

Nucleic Acids
DNA & RNA
Where did we find Genes and who
Discovered Them?
 In 1928 a man named Frederick Griffith was
trying to figure out how bacteria made
people sick.
– What caused pneumonia
 Griffith’s Experiment was the key in
discovering Genes.
Griffith’s Experiment
 Grew 2 strains of bacteria:
– Strain 1 –smooth colonies (disease)
– Strain 2 –rough colonies (harmless)
 Mice injected with the smooth bacteria got
pneumonia and died.
 Mice injected with the rough bacteria did not get
sick at all.
 Griffith wondered if maybe the bacteria that was
lethal (smooth) produced a poison.
Griffith’s Experiment Continued
 To find out if the disease causing bacteria
(smooth) made a poison he took some of it,
heated it, and injected it into mice.
 So what do you think happened?
Griffith’s Experiment Continued
 That is right all the mice survived!!
 So, the bacteria was not making a chemical
poison that was causing the mice to die, so
what was?
 He did a second experiment…..
Griffith’s Second Experiment
 This time he took the heat killed disease
causing bacteria (smooth) and mixed it with
the live harmless bacteria (rough).
– Neither should make the mice sick.
 So what do you think happened to the mice
this time?
Griffith’s Second Experiment
 Many of the mice developed pneumonia and
died.
– Their lungs were filled with the disease causing
bacteria.
 So how did this happen? If the disease
causing bacteria was heated and killed how
did it make the mice sick?
– The heat killed disease causing bacteria passed
their information to the live harmless strain in a
process known as Transformation.
Transformation
 The process in which one strain of bacteria
is changed by a gene or genes from another
strain of bacteria.
Griffith’s Conclusion
 Some information from the heat killed
disease causing bacteria (smooth) were
transferred into the harmless bacteria
(rough).
 And thus Genes were discovered….
Avery and DNA
 In 1944 Oswald Avery decided to take
Griffith’s experiment one step farther.
 They added an enzyme that breaks down
DNA. They then did Griffith’s experiment
and this time the mouse did not die.
– This experiment proved that the information was
being carried by genes, and that those genes
are made of DNA.
The Components and Structure of
DNA
 DNA is a long molecule made up of
nucleotides.
– Nucleotide:
 5 carbon sugar (Deoxyribose)
 Nitrogen base
 Phosphate group
 DNA is made up of 4 kinds of nitrogen
bases……
Kinds of Nitrogen Bases
 Adenine and Guanine: Purines
– Purine bases have 2 ring structures
 Cystosine and Thymine: Pyrimidines
– Pyrimidine bases only have 1 ring structures
The Components and Structure of
DNA Continued
 The backbone of a DNA chain is made up of
the sugar and phosphate groups of each
nucleotide.
Sugar and
Phosphate
Back Bone
Chromosomes and DNA
 Where in our bodies do we find our DNA?
– Inside of the nucleus.
DNA
 In the nucleus there are chromosomes which store
our DNA.
Chromosome
Cell
Nucleus
Chromosomes Structure
 Each chromosome has both DNA and proteins
in it.
– Chromatin: DNA coiled or wrapped around a
histone (protein).
 Many histones packed together are called a nucleosome.
 Basically a chromosome is made up of DNA
wrapped around proteins, coiled together to
form nucleosomes that coil up into supercoils
called a CHROMOSOME.
The structure of a Chromosome
Chromosome
DNA
Double
Helix
Supercoils
Histones
Nucleosomes