DNA
Chapter 12
DNA
 Holds our genetic information
Like a library
 Important for mitosis to occur
 Biologists had to discover the chemical
nature of DNA to determine that it is
responsible for our genetic information
Griffith and Transformation
 Transformation: when a strain of bacteria is changed by a
gene or genes from another bacteria
 Experiment
 Inject mice with bacteria containing virus for pneumonia
 Smooth colonies = have bacterial infection
 Rough colonies = harmless bacteria
Griffith and Transformation
 If the virulent colonies were killed with heat and mixed with harmless
bacteria, then the harmless bacteria get transformed into virulent bacteria
 Some factor of the bacteria was tranformed to harmless bacteria
http://www.quia.com/files/quia/users/hlrbiology/Animations/08_DNA_and_Proteins/Griffith_Mouse_Experiment.swf
Avery and DNA
 Wanted to repeat Griffith’s experiment
 Treated heat-killed virulent bacteria with enzymes
 One enzyme destroyed RNA and proteins
 Another enzyme destroyed ONLY DNA
Lethal
Virus
Avery and DNA
 Results showed that
Lethal
Virus
bacteria treated with DNA
destroying enzyme did not
transform harmless
bacteria into virulent
bacteria
 It is the DNA that stores
the genetic information
from one generation to
the next
Lethal
Lethal
Non Lethal
Hershey-Chase
 Bacteriophage: a virus that
infects bacteria ONLY
 Scientists wanted to see
what gets injected into a
bacteria to cause infection
 Used a radioactive marker
for DNA and protein
Hershey Chase
 After infection, the bacteria that had radioactive marker on DNA
showed that it is the DNA that is inserted into the bacteria
 Results: DNA from the virus is what causes infection
Hershey-Chase Experiment
DNA Structure
 Monomer of DNA is a
nucleotide
 5-carbon sugar
 Phosphorous group
 Nitrogenous base
 4 Nitrogenous bases in DNA
 Adenine
 Guanine
 Thymine
 Cytosine
DNA Structure
 Backbone of DNA is the
sugar and phosphate
 Nitrogenous bases stick out
of side to form latter rungs
 These bases are repeated
in a pattern that form our
genetic code
DNA Structure
 Chargaff’s Rule
 Scientist that discovered a pattern between the 4 bases
 Same percentage of Adenine as Thymine
 Same percentage of Guanine as Cytosine
 Scientists still not sure how they match up though
DNA Structure
 Rosalind Franklin
 Scientist that worked with X-ray diffraction
 Used X-rays on a portion of DNA and the results showed an X
pattern
DNA Structure
 Watson & Crick
 Scientists that were
able to understand
Rosalind’s X-ray
picture
 Result: DNA has a
double helix pattern
where the
nitrogenous bases
face each other
DNA Structure
 DNA has a double helix pattern
 Looks like a ladder twisted up
 The sides of the ladder are the sugar and
phosphate and the rungs of the ladder are the
nitrogenous bases paired up
 The adenine binds to thymine
 The guanine binds to cytosine
 This concluded Chargaffs’s rule  base pairing
DNA and Chromosomes
 Prokaryotes
 Lack nucleus and organelles
 DNA floats as a circle in the
cytoplasm
 Eukaryotes
 1000 times more DNA than
prokaryotes
 DNA is located in nucleus
 Specific number of chromosomes
 Ex: Humans have 46
chromosomes
DNA and Chromosomes
 DNA Length
 DNA is very long
 DNA is coiled up into a very
small space because it is in
chromatin form
 Chromosome Structure
 Tightly packed chromatin is
wrapped around small
proteins called histones
 When chromatin gets super
coiled you create a
chromosome
DNA Replication
 Each strand of DNA is
needed to be a template
for a new strand of DNA
to be produced
 Since you can use one
strand to make the
other side, they are said
to be complementary
Duplicating DNA
 Before mitosis occurs, DNA needs to be
duplicated first during interphase
 When DNA duplicates, its called
replication
 DNA molecules separates into two
strands, then produces two new
complementary strands following the
rules of base pairing
 Each strand serves as a template for the
new strand
How Replication Occurs
 Enzymes help make new strands of DNA
 One enzyme called helicase “unzips” the DNA, separating the base pairs
 DNA polymerase adds new bases to pair up with the template
 This enzyme also proofreads to make sure everything matches
 What would be the matching bases to the part of DNA shown below?
https://www.youtube.com/watch?v=zdDkiRw1PdU
Sections 3-4
RNA & Protein Synthesis
Structure of RNA
 Made of nuleotides
 Three differences between DNA
& RNA
 Sugar
 DNA = deoxyribose sugar
 RNA = ribose sugar
 RNA is single stranded
 RNA uses Uracil instead of
Thymine to bond with Adenine
Types of RNA
 Three types of RNA
 mRNA
 Messenger RNA
 rRNA
 Ribosomal RNA
 tRNA
 Transfer RNA
Types of RNA
 Messenger RNA
 This is a copy of complimentary strand of DNA
 Eventually will code for a protein to be made
Types of RNA
 Ribosomal RNA
 RNA found in ribosomes (organelles in the cell)
 Ribosomes are the factory for protein synthesis
Types of RNA
 Transfer RNA
 Help produce a protein from mRNA
 Brings amino acids (monomer of protein) to ribosome to bond
them together and make a whole protein
Transcription
 Taking DNA and making an RNA copy
 Occurs in the cell’s nucleus
 RNA polymerase opens the DNA and adds RNA copy to the
template
 Once this is made it is called pre-mRNA
RNA Editing
 Pre-mRNA is a rough draft to the final copy of mRNA
 Some parts of pre-mRNA are not needed to make a protein
 These unnecessary parts are called introns
 Introns get cut out of pre-mRNA
 Before leaving the nucleus, mRNA needs to get a cap and tail
to finalize the RNA strand
The Genetic Code
 Proteins are made of 20 possible amino acids
 In order to make a protein from a strand of mRNA, the mRNA is
read in a 3 letter sequence called codons
The Genetic Code
 Each three letter codon represents an amino acid
 DNA = AGCGTGCCA
 RNA =
 Codons =
 Amino acids =
The Genetic Code
 Each three letter codon represents an amino acid
 DNA = TACCGTCCGGTCATC
 RNA =
 Codons =
 Amino acids =
 Each three letter codon represents an amino acid
 DNA = AGCGTGCCAATT
 RNA =
 Codons =
 Amino acids =
http://learn.genetics.utah.edu/content/molecules/transcribe/
The Genetic Code
 RNA knows when to start and stop based on the codons read
 There is ONE start codon: AUG
 There are THREE stop codons: UAA, UAG, UGA
Translation
 Taking mRNA and making a protein
 Occurs in the cytoplasm on a ribosome
 tRNA brings specific amino acids to ribosome
 If mRNA = AUG, then tRNA = UAC
 The tRNA has the anti-codon
Translation
 As new tRNA brings amino acids to the ribosome, past ones break off
leaving just amino acids bonded to each other
 This continues until one of the three STOP codons is met
 Finished amino acid strand goes through protein folding
Mutations
 Changes in the DNA sequence that affect the cell
 Two types of mutations
 Gene mutation
 Chromosomal mutation
Gene Mutation
 Point mutation
 A change in one nucleotide in a DNA sequence
 Occur only in a single point of the DNA
 Can sometimes be a problem
 Frameshift mutation
 A change in the reading frame of DNA
 Since DNA is read in 3 letter codons, if there is
an insertion, deletion, or large change in these
codons the frame is changed
Chromosomal Mutation
 A change in the number of chrom0somes in the cell
 Four types
 Duplication
 Deletion
 Inversion
 Translocation