Ch.8 DNA Structure and Analysis, Organization in Chromosomes Flashcards
Chromosomes
Theory of inheritance
Proof that genetic info is passed on with the chromosomes (1940s)
Chromosomes
Genetic info
Chromosomes consist of nucleic acids and proteins. Which one carries the genetic info?
Criteria for Genetic Material
To serve as genetic material, a molecule must be able to: Replicate (by themselves, autonomously) Store information Express information Allow variation by mutation
Central Dogma
DNA -> RNA -> protein
DNA makes RNA (transcription), which makes proteins (translation)
Proof that Genetic info is stored in DNA
In organisms and many viruses, the genetic info is encoded in DNA (some viruses also RNA).
Until 1944: what chemical component makes up genes and is the actual genetic material?
Why the doubt?
Thera are 21 different amino acids but only 4 different nucleotides. (ppl were in favor of proteins being the genetic material - could chemically analyze proteins and DNA)
Can the incredible diversity of life really be based on just 4 nucleotides?
Transformation (Griffith 1929)
Mouse experiment
The traits of being virulent and smooth coating were passed from bacteria to bacteria through transformation
Transformation in vitro (petri dish)
Sia and Dawson transformed bacteria in vitro ans showed that the mouse host plays no role in transformation.
DNA mediates transformation
Avery, MacLeod, McCarty (1944) used specific enzymes to degrade DNA, RNA, or proteins.
DNAse treatment eliminated transformation activity.
Proof that DNA must be the carrier of information.
Hershey and Chase Experiment
Life cycle of a T-even bacteriophage as known in 1952.
Attachment of phage tail fibers to bacterial wall.
What enters the cell and directs phage reproduction?
Phage genetic material (?) is injected into bacterium.
Phage reproduction cycle begins.
Components accumulate; assembly of mature phages occurs.
Cell lysis occurs and new phages released.
Hershey and Chase Experiment 1952
Phosphorus Isotope
Phage T2 added to E.coli in radioactive medium.
Phosphorus isotope.
Phosphorus isotope in DNA
Phosphorus isotope in next generation of virus.
(Were able to radioactively mark DNA or proteins.
Proof that virus consists of DNA and proteins- DNA injected into the bacteria and carries the info.)
Hershey and Chase Experiment 1952
Sulphur Isotope
Phage T2 added to E.coli in radioactive medium.
Sulphur isotope.
Sulphur isotope in protein. (not a component of DNA)
No Sulphur isotope trace in next generation of virus.
(Were able to radioactively mark DNA or proteins.
Proof that virus consists of DNA and proteins- DNA injected into the bacteria and carries the info.)
The genetic material of tobacco mosaic virus RNA
Fraenkel-Conrat (1957) mixed proteins from one virus strain with RNA from another virus strain. When tobacco leaves were infected, the resulting virus offspring was always genotypically and phenotypically identical to the parent strain from which the RNA was obtained.
Concluded - RNA carries information
Eukaryotes Indirect evidence
Close correlation between gametes and diploids in amt of DNA and number of chromosome sets.
No such correlation between gametes and diploids for proteins.
Eukaryotes Direct evidence
Recombinant DNA technology (ex: human insulin gene transferred and expressed into a bacterium) Transgenic animal (ex: Human DNA microinjected into fertilized mouse egg, human B-globin gene, expressed in mouse and transmitted to progeny)
Nucleic acids: Structure of DNA and RNA
Understanding the structure of nucleic acids is cruical to understanding how heredity works on the molecular level.
DNA is usually double stranded with adenine paired with thymine and guanine paired with cytosine.
RNA is usually single stranded and contains uracil in place of thymine.
Nucleic acids structure
Polymers made of nucleotides monomers.
Nucleotides are composed of
1. phosphate group
2. pentose (sugar with 5 carbon atoms): Ribose (in RNA) and 2- in Deoxyribose (in DNA)
3. Cyclic nitrogen-containing base: pyrimidines and purines.
Pyrimidines
Uracil, Cytosine, Thymine
Purines
Adenine, Guanine
Triphosphates
Serve as precursor molecule during nucleic acid synthesis (dNTPs in PCR reactions).
ATP and GTP: Adenosine triphosphate and guanine triphosphate.
-large amt of energy involved in adding/removing terminal phosphate group
4 different deoxyribonucleotides
Deoxythymidine monophosphate, dTMP
Deoxycytidine monophosphate, dCMP
Deoxyadenosine monophosphate, dAMP
Deoxyguanosine monophosphate, dGMP
The phosphate group is attached to the 5’ carbon atom.
The nitrogenous base is attached to the 1’ carbon atom.
(monomers of DNA)
Structure of a polynucleotide chain
Chain single nucleotides together to form polymer.
Phosphodiester linkage (C-O-P-O-C) joins the nucleotides.
The polynucleotide chain is directional.
“Five prime end” upstream
“tree prime end” downstream
The Double Helix
Watson and Crick inferred the DNA double helix model based on 2 discoveries
1) Chargaff’s rule
2) Rosalind Franklin’s x-ray crystallography pictures of DNA molecules.
Chargaff’s Rule (1947)
Measure content of DNA and always find same amounts of G and C and same of A and T - all the %s add up to 100%.
A and T and C and G are present in the DNA molecules in equal amounts.
This is bc of complementary nucleotides pairing in the DNA double helix.
Rosalind Franklin: X-ray Diffraction Pattern of DNA
DNA helical structure.
Bases are stacked perpendicular with a periodicity of 0.34 nm.
The DNA double helix
Right handed double helix, the 2 polynucleotide chains are coiled around each other in a spiral
Covalent bonds
Strong chemical bonds formed by sharing of electrons between atoms.
- In bases and sugars
- In phosphodiester linkages (chaining nucleotides)
Hydrogen bonds
Weak bond between an electronegative atom and a hydrogen atom (electropositive) that is covalently linked to a second electronegative atom.
Strands are bonded with these. Break easily with heat.
Hydrophobic bonds. Van der Waals interactions
The association of nonpolar groups with each other when present in aqueous solutions because of their insolubility in water.
Opposite polarity of the 2 strands
Structure
Bonds
Run in opposite directions of each other.
Sugar phosphate backbone.
Bases in the core.
A-T bonded with 2 H bonds.
C-G bonded with 3 H bonds.
Apply heat and break H bonds, strands separate. Cool down and bonds will form again.
Complementary base-pairing - only possible if bases are arranged in a certain way.
Strands run opposite ways
5’-> 3’
3’ -> 5’