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DNA, PROTEIN
SYNTHESIS,
& Mutations
Chapters 12
Pages 287-308
Chapter 12:
I.
Section 1
History
A. Frederick Griffith- 1928
- Tried to figure out how bacteria
made people sick.
- Heat killed, disease-causing
bacteria passed “something” along
to harmless bacteria.
- He called this process
“Transformation.”
B. Oswald Avery- 1944
- Determined DNA is the molecule of
inheritance and not proteins.
– Did this by destroying other cell parts
piece by piece.
C. Alfred Hershey & Martha Chase- 1952
Hershey & Chase – determined that DNA
transmits genetic information from parent to
offspring, & not any other molecule
• Worked with bacteriophages – viruses that
invade bacterial cells
• Used bacteriophages with radioactive
markers (1952)
Structure of Bacteriophage
• Protein coat –
outer covering
• DNA – inner core
Hershey & Chase
• One bacteriophage had radioactive
phosphorus-32 in its DNA & was used to infect
a bacterial cell
• The other had radioactive sulfur-35 in its
protein coat & was used to infect a bacterial cell
• Both bacterial cells were examined
• Only the bacteriophage with P-32 was inside
the bacterial cell, proving that DNA is the
material that transmits genetic info
Hershey and Chase
D. Erwin Chargaff- Late 1940’s
• Found there are 4 bases in a DNA
molecule
– Adenine, Guanine, Cytosine and Thymine
• Found that the amount of A = T and G = C
E.
Rosalind Franklin (1952)
• Franklin used X-ray diffraction to get
information about the structure of DNA
• Was able to tell that DNA had an “X” like
structure where the strands are twisted
around each other
• All of these discoveries
led to the following….
F. Watson and Crick
- The discovery of the structure of
DNA was made in 1953 by two
scientists named James Watson &
Francis Crick.
- Watson & Crick proposed that DNA
is shaped like a “twisted ladder.”
- This twisted ladder is also called a
“Double Helix.”
- They used the
findings of the other
scientists for their model.
II.
DNA
A. What is DNA ?
• Stands for Deoxyribonucleic acid
• Functions:
1. Transmit genetic info. to
next generation
2. Controls all cell activities,
including protein synthesis
B. Structure of DNA
- DNA is made of nucleotides.
1. Nucleotides consist of the following:
a. Deoxyribose – a sugar
b. A Phosphate Group
c. A Nitrogen Base
1. Four possibilities
a. Adenine (A)
b. Guanine (G)
c. Cytosine (C)
d. Thymine (T)
- These nucleotide bases join together
to form a long single strand.
- Each long single strand of nucleotides
connects to “another” single strand of
nucleotides.
- The two strands are held together by
hydrogen bonds.
C. Base Pairing Rules
1. Adenine always pairs with Thymine.
2. Cytosine always pairs with Guanine.
- The different order of these bases is
what makes organisms different.
Example:
Strand 1: A – G – T – T – C – T – A – G
Strand 2: T – C – A – A – G – A – T – C
Sample Exercise:
Strand 1: C – G – A – T – G – T – A – C
Strand 2:
–
–
–
–
–
–
–
Sample Exercise:
Strand 1: T – C– A – A – C – G – C – C
Strand 2:
– – – – – – –
- The more closely related two organisms
are the more alike the order of their
nucleotides in their DNA will be.
Example:
Humans  Chimps Gorillas Orangutans
Purines vs. Pyrimadines
• Adenine and Guanine are PURINES
• Thymine and Cytosine are PYRIMIDINES
• Remember:
Purines and Pyrimidines
• Purines can only pair with pyrimidines due
to their size and shape.
III. DNA Terminology
A. Chromosomes
- Tightly compacted strands of DNA
found when a cell is dividing! (Needs
to be compact to fit in a small space!)
- Hold all genetic information.
- Chromosomes are passed on to an
offspring by its parents.
Examples:
Fruit Fly = 8
Humans = 46 Shrimp = 254
Chimps = 48 Chicken = 78
Gorilla = 48 Wolf
= 78
B.
Chromatin
- When a cell is not dividing, DNA is in the
form of chromatin.
- Loosely packed DNA that is wrapped
around proteins (called histones)
C. Genes
- A section of DNA on a chromosome that
codes for a specific protein.
IV. DNA Replication SECTION 2
A. DNA is copied before a cell divides so
that each new cell has it’s own genetic
copy.
B. There are 4 main steps:
STEP 1:
- DNA is unzipped by the enzyme
HELICASE and now two single
strands begin to unwind.
- Hydrogen bonds are broken.
- This is called a replication fork
STEP 2:
- Each unwound strand of DNA acts as a
template to produce two new strands of
DNA.
STEP 3:
- An enzyme named DNA Polymerase will
read each unwound strand and join new
complimentary nucleotides to each.
STEP 4:
- This occurs until the whole strand is
replicated.
- Now there are two
identical DNA molecules.
-
Each strand contains
one original and
one complimentary
strand.
Click image
for animation!