DNA & PROTEIN
SYNTHESIS
Chapters 12 & 13,
Pages 287-333
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. Avery- 1944
- Determined DNA is the molecule of
inheritance and not proteins.
– Did this by destroying other cell parts
piece by piece.
C. Hershey & Chase- 1952
- Studied viruses, non-living particles
that contain DNA.
- Discovered that DNA is the genetic
material responsible for
transformation.
Click for
animation!
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
Chargaff warned that “the technology of genetic engineering poses a greater
threat to the world than the advent of nuclear technology. An irreversible attack on
the biosphere is something so unheard of, so unthinkable to previous generations,
that I only wish that mine had not been guilty of”
II.
DNA (DeoxyRibo Nucleic Acid)
A. Discovery of Structure
- The discovery of the structure of
DNA was made in 1953 by two
scientists named Watson & Crick.
- Watson & Crick proposed that DNA
is shaped like a “twisted ladder.”
- This twisted ladder is also called a
“Double Helix.”
What about Rosalind Franklin?
• Watson and Crick used the data from
Rosalind Franklin and Maurice Wilkins Xray Crystallography to determine the
structure.
• Watson, Crick and Wilkins shared the
Nobel prize, Franklin was robbed!!
• Rosalind Franklin song
B. What is DNA made of?
- 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)
Nucleotide
- 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: C – G – A – T – G – T – A – 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
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!
- Hold all genetic information.
- Chromosomes are passed on to an
offspring by its parents.
Examples:
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.
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.
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!