Lesson 2.1 - DNA & Inheritance Flashcards
Mendel’s work (1900)
Chromosomes observed (genotype), but unclear how it was connected to phenotype
T.H. Morgan’s Group (1920s)
Showed that genes were carried on chromosomes; [20] proteins assumed to be genetic material; fruit flies
Who initially performed the transforming principle?
Microbiologist Griffith
Transforming Principle concluded that…
something from heat-killed S cells transformed live R cells; standard assumption was that proteins were responsible
Transforming Principle Results (1928)
Smooth strains = virulent, rough strains = avirulent
Indirect evidence supporting hypothesis that DNA is genetic material
- Using dyes that bind to DNA showed that
- DNA doubles during “S” phase of cell cycle
- Diploid (2n) and haploid (n) exists
- After meiosis, gametes have 1/2 of DNA
What are the results of the transforming principle (1944)?
R cells were transformed by DNA from heat-killed S cells; example of HGT
Who performed transforming principle (1944)?
Avery, MacLeod, & McCarty
Chargaff’s Rule
Purines = Pyrimidines (A = T, G = C)
No organism was 50/50 (e.g. Virus QX174 did not fit data bc single stranded)
Rosalind Franklin (1951)
- Analyzed DNA helix with X-ray crystallography
- Turn every 3.4 nm, Diameter of 2.0 nm
How does X-ray crystallography work?
Create 2-D images by defracting rays onto plate
How did the 3-D structure of DNA came to be?
- (1953) Models built using following data:
- Alpha-helix by Franklin & Wilkins
- Width & no. bases per turn by Franklin & Stokes
- Purine = Pyrimidine by Chargaff
Purine Bases
Adenine, Guanine
Pyrmidine Bases
Cytosine, Thymine (DNA), Uracil (RNA)
Who won the Nobel Prize in Physioology or Medicine (1962)?
Francis Crick, James Watson, & Maurice Wilkins
Structure of DNA
- Nitrogenous base
- Pyrimidine (1-ring)
- Purines (2-ring)
- Pentose (5C) deoxyribose
- Phosphate (PO4) group
- Major (2.2 nm) & Minor (1.2 nm) groove
How is DNA synthesized?
- Connect sugar of one nucleotide, and phopshate of next
- Occurs via a phosphodiester link/bond, creating a backphone
- 5’ of PO4 of incoming nucleotide and 3’ OH
What is the Hershey & Chase experiment (1952)?
- Bacteriophage T2 infects E. coli
- Protein: 35S
- DNA: 32P
- Demonstrated that DNA (not protein) transferred, & is genetic material = inheritance
DNA sequences are always written…
5’ to 3’
Deoxyribose sugar structure
Ribose sugar structure
3 Hypothesis Models for DNA Replication
Semiconservative, Conservative, and Dispersive
What is the Meselson - Stahl experiment?
- Each round E.coli in 15N (red) medium was transfered to a 14N (orange) medium, DNA sediments halfway.
- Supports semiconservative model
DNA polymerase can only add nucleotides to the _____ end of a growing DNA strand.
free 3’-OH
DNA Replication Overview (terms: primase, primer, polymerase, leading and lagging strand, ligase)
-
Primase binds to template strand, synthesizes RNA primer
- Starts with RNA dNTPs, then DNA dNTPs
- DNA polymerase III synthesizes DNA
- Leading strand synthesized continously
- Lagging strand (Okazaki fragments) ligated by ligase
Why is the lagging strand looped during DNA synthesis?
It allows both strands to be synthesized concurrently by inverting the lagging strand
Replisome
Proteins that unwind DNA and synthesize new strands
Helicase
untwists and separates template DNA strands at replication fork
Single-strand binding proteins
keep unpaired template strands apart during replication
Gyrase
removes knots or create twists in duplex DNA; cuts ds DNA and passes one through the other
Ligase
catalyze phophodiester bond formation between new DNA; links Okazaki fragments together
Sliding ß-clamp
guides DNA polymerase and assists other proteins/enzymes
Topoisomerase IV
passes one ds DNA through another; cuts ds DNA
Bacteria & Archaea divide by…
-
Binary Fission
- Replication from single origin (ori)
- Plasmids - 1 ori site
- Replication around cirlce requires primer w/ available 3’-OH
- Replication from single origin (ori)
E. coli uses _________ to cut one of the chromosomes to separated interlocked chromosomes.
Topoisomerase IV
DNA Polymerase I (Characteristics, Function)
- 5’ - 3’ Polymerization: +
- 3’ - 5’ Exonuclease: +
- 5’ - 3’ Exonuclease: +
- Function: Joins Okazaki fragments
DNA Polymerase II (Characteristics, Function)
- 5’ - 3’ Polymerization: +
- 3’ - 5’ Exonuclease: +
- 5’ - 3’ Exonuclease: -
- Function: Restarted stalled polymerase
DNA Polymerase III (Characteristics, Function)
- 5’ - 3’ Polymerization: +
- 3’ - 5’ Exonuclease: +
- 5’ - 3’ Exonuclease: -
- Function: Main replicase
DNA Polymerase IV (Characteristics, Function)
- 5’ - 3’ Polymerization: +
- 3’ - 5’ Exonuclease: -
- 5’ - 3’ Exonuclease: -
- Function: Repairs damaged DNA
DNA Polymerase V (Characteristics, Function)
- 5’ - 3’ Polymerization: +
- 3’ - 5’ Exonuclease: -
- 5’ - 3’ Exonuclease: -
- Function: Repairs damaged DNA, translesion, DNA synthesis
3’ - 5’ Exonuclease function
- Makes cut at misplaced base; proofreading technique; can stop and go backwards
- Bacterial DNA polymerase I, II, and III
Nucleotide Excision Repair System (Cause of damage, solution)
- Damage caused by UV radiation & chemicals
- e.g. Pyrimidine dimers (covalent bond b/t adjacent pyrimidines)
-
Nuclease cuts out damaged strand
- Gap filled by DNA polymerase & ligase
