dna & protein synthesis chapters 12 & 13, pages 287-333
TRANSCRIPT
Chapter 12: Section 1I. 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.”
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)
- 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
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.
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.