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DNA
Chapter 10 – Ms. Colabelli
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 S.pneumoniae
 Smooth colonies = virulent (disease causing)
 Rough colonies = harmless bacteria
Griffith and Transformation
 If the virulent colonies were killed with heat & mixed with harmless
bacteria, the harmless bacteria get transformed into virulent bacteria
 Some factor of the harmless bacteria was transformed to become
virulent
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
 Used two enzymes that destroyed proteins, and RNA
 Another enzyme destroyed ONLY DNA (nucleic acids)
Lethal
Virus
Avery and DNA Results
 Results: bacteria treated
Lethal
Virus
with DNA destroying
enzyme did not transform
harmless bacteria into
virulent bacteria
 It must be 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
DNA and protein
Hershey Chase Results
 After infection, the bacteria that had radioactive marker on DNA
showed that it is the DNA that is inserted into the bacteria
 Results: genetic material of the bacteriophage was DNA and not
protein
http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter14/animations.html#
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 figure out
what Rosalind’s X-ray
pattern meant
 Result: DNA has a
double helix pattern
where the
nitrogenous bases
face each other in the
middle
DNA Structure
 DNA has a double helix pattern
 The sides of the ladder are the
sugar and phosphate
 Rungs of the ladder are the
nitrogenous bases paired up
 The bond between two nitrogenous
bases is a hydrogen bond
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
 Monomer of DNA is a
nucleotide
 Phosphorous group
 5-carbon sugar
 Nitrogenous base
 4 Nitrogenous bases in DNA
 Adenine
 Guanine
 Thymine
 Cytosine
DNA Structure
 Chargaff’s Rule
 Scientist that discovered a peculiar trend between the 4 bases
 Same percentage of Adenine as Thymine
 Same percentage of Guanine as Cytosine
 Adenine binds to Thymine
 Guanine binds to Cytosine
DNA Replication
 Process by which DNA is
copied in a cell before
division
 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
Replicating DNA
 Step 1: DNA molecules separates into two strands with
help from enzyme named helicase
 Breaks hydrogen bonds between bases
 Creates a replication fork
Replicating DNA
 Step 2: Enzyme named DNA polymerase adds new
nucleotides to other side of template strand
 This forms new hydrogen bonds
DNA Polymerase can only
move in one direction (3’-5’)
so you have one strand that
leads and one that lags
To join the gaps between
lagging strands and enzyme
(ligase) come and binds
them
Replicating DNA
 Step 3: Once the DNA is replicated, the
DNA polymerase releases
http://www.youtube.com/watch?v=zdDkiRw1PdU
How Replication Occurs
 Enzymes help make new strands of DNA
 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?
Eukaryotes vs. Prokaryotes
 Eukaryotes
 Long rod shaped chromosomes
 Replication starts in certain points on the
chromosome
 Try to be as effective and time efficient
 Prokaryotes
 Circular chromosome
 Replication begins in one place
 Ends once the DNA polymerase meets its
starting point
 Very fast
Protein Synthesis
 Two parts process to make a protein from
a segment of DNA
 Part one: Transcription
DNA  RNA
 Part two: Translation
RNA  Protein
RNA
 Made of nucleotides
 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
RNA
 Three types of RNA
 mRNA
 Messenger RNA
 rRNA
 Ribosomal RNA
 tRNA
 Transfer RNA
RNA
 Messenger RNA
 This is a copy of complimentary strand of DNA
 Eventually will code for a protein to be made
RNA
 Ribosomal RNA
 RNA found in ribosomes (organelles in the cell)
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
 Step 1: RNA polymerase binds to a promoter and unwinds
the strands
 Step 2: RNA polymerase adds free RNA nucleotides that are
complimentary to DNA strands
 Once this is made it is called pre-mRNA
 Step 3: RNA polymerase reaches a termination signal and
releases
http://www.zerobio.com/drag_oa/protein/overview.htm
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 certain protein
 These unnecessary parts are called introns
 Introns get cut out of pre-mRNA
 Before leaving the nucleus, mRNA needs to get a 5’ cap and poly A tail to
finalize the RNA strand
The Genetic Code
 Proteins are made of
amino acids
 There are 20 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 = AGCGTGCCAATT
 RNA = UCG-CAC-GGU-UAA
 Amino acids = Ser-His-Gly-STOP
The Genetic Code
 Each three letter codon represents an amino acid
 DNA = TACCGTCCGGTCATC
 RNA = AUG-GCA-GGC-CAG-UAG
 Amino acids = Met-Ala-Gly-Gln-STOP
http://learn.genetics.utah.edu/content/molecules/transcribe/
Translation
 Taking mRNA and making a protein
 Occurs in the cytoplasm on a ribosome
 Step 1: 2 ribosomal subunits bind to mRNA and a tRNA
molecule. The tRNA molecule matches to the codon of the
mRNA sequence
 The first amino acid is always
Methionine
 If mRNA = AUG, then tRNA = UAC
 The tRNA has the anti-codon
Translation
 Step 2-3: As tRNA brings
new amino acids to the
ribosome, past ones break
off leaving just amino acids
bonded to each other
 Step 4: This continues until
one of the three STOP
codons is met
 Step 5: ribosomal units
break down and the amino
acid strand goes through
protein folding
http://www.zerobio.com/drag_oa/protein/translation.htm
The Human Genome
 The entire genome sequence of a human
 3.2 billion base pairs in our 23 chromosomes
 We now need to learn what each of these sequences code for
 This will help with curing diseases and prevention of others
http://www.youtube.com/watch?v=TCsWBMMXewE
http://www.youtube.com/watch?v=F5LzKupeHtw