Download Ch. 16 - ltcconline.net

Lake Tahoe Community College
Fall Quarter
Bio 101
Instructor: Sue Kloss
________________________________________________________________________________________________
Chapter 16 - Molecular Biology of the Gene
________________________________________________________________________________________________
The study of the DNA molecule and its basis in heredity is called molecular biology.
I. DNA is the genetic material
A. Viruses
1. protein coats and DNA.
2. They gain entry into our cells
3. hijack the cell’s machinery
4. inserts own DNA into the cell’s DNA.
B. Viruses that infect bacteria are widely used as tools
1. bacteriophages (or phages)
2. experiments performed with phages showed that DNA is the hereditary material
II. The Structure of Genetic Material
A. Review - DNA and RNA are polymers
1. DNA and RNA are nucleic acids
a. long chains (polymers)
b. nucleotide structure
2. nucleotides joined by covalent bonds
3. phosphate group
4. usually reside in the nucleus
5. nitrogenous bases
6. RNA has ribose instead of deoxyribose - it has one less oxygen atom
a. instead of thymine, RNA has a nitrogenous base called Uracil (U)
B. DNA structure
Race to find structure of DNA was huge in the science world
1. A & T, C & G – base pairing
2. hydrogen bonds
3. purines pair with pyrimidines
4. double helix
5. semiconservative and antiparallel
II. DNA Replication
A. DNA replication depends on specific base pairing
1. essential to reproduction - a complete set of genetic instructions is passed down from each generation
2. must copy the instructions precisely
3. old genes serve as template for the new
4. template model for replicating DNA
5. since A always pairs with T and C with G
a. each new molecule is semiconsevative
6. complex process chemically, though simple in concept
B. DNA replication
1. begins at origins of replication
2. Helicase proteins attach to DNA, untwist the helix
a. single stranded binding proteins
b. Topoisomerase
c. Primase and RNA primer
3. replication fork
4. parent strands have many origins of replication
5. thousands of can be present at once in eukaryotes
6. all bubbles merge
7. 2 new daughter strands of DNA molecule
C. Elongating a new strand
1. elongation is catalyzed by DNA polymerases
2. DNA polymerase adds nucleotides
3. DNA’s sugar phosphate backbones are antiparallel
4. Leading strand v lagging strand
a. DNA polymerases add nucleotides to the 3’ end
b. a daughter strand can grow only in the 5’ - 3’ direction
III.
c. one daughter strand synthesized continuously
d. other DNA polymerase III must work from the fork outwards; synthesized in pieces
e. DNA ligase clips (ligates) the pieces together - Okazaki fragments
f. protein interactions facilitate efficiency
5. DNA pols cannot initiate the synthesis of a polynucleotide
a. primer
b. template strand
c. available nucleotides
6. Proofreading/repair - only about 1 mismatch/10 billion nucleotides linked
a. DNA polymerase proofreads
b. lots of damage can occur to DNA
c. almost 100 repair enzymes are known in E coli, 130 in humans
7. DNA ligase also “proofreads”
8. DNA polymerase and ligase also repair DNA harmed by radiation
9. DNA replication ensures that all somatic cells have a full set of genetic instructions
10. Also allows DNA to continue to next generation in inheritance
Chromatin structure is based on successive levels of DNA packing
A. DNA packing in eukaryotic chromosomes helps regulate gene expression
1. Histones
2. linker DNA
B. Higher levels of DNA packing
1. the beaded string
2. protein scaffold into domains
3. DNA packing tends to prevent transcription and translation
4. Also, for a gene to be transcribed, the histones must loosen their grip on the DNA molecule.
a. heterochromatin
b. euchromatin
C. chemical modifications of packing affects gene activity
Ch 16 Lesson Objectives
1. Explain why researchers originally thought protein was the genetic material.
2. Explain how Watson and Crick deduced the structure of DNA and describe the evidence they used.
3. Explain the significance of the research of Rosalind Franklin.
4. Diagram the structure of DNA. Explain the base-pairing rule and describe its significance.
5. Describe the semiconservative model of replication.
6. Describe the process of DNA replication, including the role of the origins of replication and replication forks.
7. Explain the role of DNA polymerases in replication.
8. Define antiparallel and explain why continuous synthesis of both DNA strands is not possible.
9. Distinguish between the leading strand and the lagging strand.
10. Explain how the lagging strand is synthesized even though DNA polymerase can add nucleotides only to the 3’ end.
11. Describe the significance of Okazaki fragments.
12. Diagram the roles of DNA ligase, primer, primase, helicase, topoisomerase, and single-strand binding proteins.
13. Explain the roles of DNA polymerase, mismatch repair enzymes, and nuclease in DNA proofreading and repair.
14. Describe the current model for progressive levels of DNA packing in eukaryotes.
15. Explain how histones influence folding in eukaryotic DNA.