Biology Chapter 12/13 S-G
DNA Replication
Blue=The Scientists
Green=DNA Replication
Red=RNA and Protein Synthesis
● The Genetic Material
○ During the 20th century, scientists were determined to
discover which part of a cell held the genetic material
○ Almost all scientists thought that the genetic material
was proteins
● Griffth
○ In 1928, Griffith was attempting to develop a vaccine
against pneumonia
○ Experiment
■ Griffith used 2 types of Bacteria
■ S strain bacteria
● Smooth and Harmful
■ R strain bacteria
● Rough and harmless
■ When Griffith gave the R strain bacteria the rat
lived, as expected when he gave the S strain
bacteria the mouse died
■ When Griffith gave the heat-killed S strain the
mouse lived because the proteins denatured
■ However, when Griffith mixed the R strain
bacteria with the heat-killed S strain the mouse
died
■ Meaning that there was some form of genetic
material left
○ Griffith was unable to identify the transformation that
took place, so he was not able to identify the genetic
material as DNA
○ Transformation
■ Process in which one strain of bacteria is changed
by a gene or genes from another strain of bacteria
● Oswald Avery
○ 1944
○ Researchers do not know whether the molecule that
holds genetic information is, proteins, lipids,
carbohydrates, RNA, or DNA
○ Avery performs Griffth’s experiment with a twist
○ Virus
■ A very tiny, simple nonliving particle that is
made of protein and nucleic acids (DNA or
RNA). Not visible to the naked eye only with a
powerful electron microscope
○ Capsid
■ The protein coat that protects the genetic material
and helps viruses attach and enter the host cell
○ 4 shapes of a virus
■ Crystals
■ Spheres
■ Cylinders
■ Spacecraft
○ In Avery’s experiments, they used identical extracts
from heat-killed S cells, and they used hydraulic
enzymes to kill either protein, DNA, or RNA. The
treatments were then mixed with R cells. Using the
process of elimination they were able to prove that
DNA was the hereditary material. Furthermore, his
colleagues were able to isolate DNA and show that it
possessed the same transforming ability as the
heat-treated extract
● Hershey and Chase
○ Used two different bacteriophages
○ Bacteriophages
■ Viruses that infect bacteria
○ Tagged the bacteriophages using a radioactive isotope
(trackers)
■ Phosphate 32 to trace DNA
■ Sulfur 35 to trace proteins
○ When the viruses are attached to the bacterium. There
was no radioactivity from the Sulfur 35 bacteriophage,
meaning that the bacteriophage's genetic info was not
proteins. However, when the Phosphate 32
bacteriophage was used, there was radioactivity in the
bacterium meaning that the genetic information is
DNA, not protein
○ Concluded, that DNA was the genetic material,
proteins weren’t, and it is the genetic material for ALL
LIVING CELLS
● DNA structure
○ Nucleotide
■ Monomer of nucleic acids made up of a 5-carbon
sugar, a phosphate group, and a nitrogenous base
○ Nitrogenous bases
■ Adenine
■ Thymine (IN DNA ONLY)
■ Guanine
■ Cytosine
■ Uracil (ONLY IN RNA)
○ A-T, G-C, or A-U (IN RNA)
○ DNA has a sugar-phosphate backbone
● Chargaff’s Rule
○ If I have a certain number of Cytosines I will have the
same number of Guanines. This applies to As and T’s
● Rosalind Franklin
○ 1950
○ Used X-Ray Diffraction to take photos of DNA
○ Coiled (Forming Helix)
○ Double-Stranded
○ Nitrogenous bases are in the center
○ Photo-51
○ However, her data was supposedly used without
credit, and she was often ignored because she was a
woman
● Watson and Crick
○ Francis Crick
■ British physicist
○ James Watson
■ American Biologist
○ Were building a 3D model of DNA
○ Used Franklin’s X-Ray without permission and
realized that the structure was a Double Helix
○ Ended up winning the Nobel Prize
● DNA Replication
○ Unwinding
■ Parental DNA molecule is “unzipped” (the weak
H bonds are broken b/w paired bases)
○ Complementary Base pairing
■ New complementary nucleotides are positioned
by the rules of base pairing. (A =T, C = G)
○ Joining (Semi conservative model)
■ Complementary (matching) nucleotides join to
form new strands. Each daughter DNA molecule
contains an old strand and a new strand.
○ Unwinding
■ Enzymes unwind DNA
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■ Enzymes split “unzip” double helix
■ The enzyme, DNA polymerase, finds and
attaches the corresponding Nitrogenous base
■ Each old/original strand serves as a template and
is matched up with a new strand of DNA
■ New helixes wind back up
DNA Structure
■ Antiparallel Strands
■ The 2 strands of DNA run in opposite directions
(Antiparallel)
■ Nitrogenous bases connect at the center
Basic Vocab
■ Origin of Replication
● Center of a Replication bubble
● The place where the DNA polymerase starts
working
■ Replication Bubble
● A portion of the strand that is getting copied
DNA Polymerase
■ Is only able to add nucleotides to the free 3’ end
of a growing DNA strand (Hydroxyl Group)
Leading Strand■ used by polymerases as a template for a
continuous complementary strand working
towards the replication fork unzipping it
Lagging strand
■ Copied away from the replication fork in short
segments called Okazaki fragments
○ DNA Polymerase and primers
■ The polymerase cannot initiate the synthesis of a
nucleotide
● Can only add nucleotides to the end of an
existing chain
■ To start a new chain requires a primer
● A short segment of RNA
○ Enzymes and important vocab
■ Topoisomerases
● Helps Supercoils/Winding (Prevents
Tangling)
■ Helicase
● Unzips the double helix
■ Single Strand proteins
● Keeps the Hydrogen bonds separated
■ Ligase
● Joins DNA molecules together
■ Primases
● Put RNA primers where DNA polymerase is
going to bind and make new strands
■