Jan 15 Flashcards
(22 cards)
What is Genetics?
Study of heredity and variation in cells, individuals and populations
What is Gene ?
functional unit of heredity and variation (hence genetics is simply the study of genes)
Molecular genetics is…?
The study of structure and function of genes at the molecular level
Why do we want to study molecular genetics ?
- Human Health - better understanding of human diseases resulting in new therapeutics and diagnostics, matching organ donors,
- Forensics : crime, paternity tests, sources of food, poisoning outbreaks
- Agriculture - superior crops and livestock:”pharm” animals
- Environment - molecular ecology(specifies identification and diagnosis for conservation and species-habitat relationships): genetic engineering microbes for bioremediation
- Evolutionary biology : phylogenetic and phylogenomics
Why sequence genomes?
To understand how the types and abundance of RNA and proteins result in phenotype of an organism, we need to identify all the genes in the genomes
What is gene expression?
“Turning on” a gene to produce RNA and proteins
Turning the genotype into the phenotype
Follows the central dogma of biology
Transcription —> RNA (coding and non coding)—->translation ——> protein
Protein expression? Enzymes? Structural proteins? Signalling proteins?
The type and abundance of proteins in the cell
- although DNA is the information molecule that directs protein expression, proteins ultimately determine the phenotype of the cell bcs they control every reaction in a cell
-enzymes : catalyses the synthesis and transformation of all bio molecules
-structural proteins : maintenance of a cell shape
-signalling proteins : hormones and receptors
Phenotypic variation? What makes individuals different from 1 another’s?
- different alleles (slight variation in gene sequence results in changes in amino acid sequence of proteins)
- Different regulation of gene and protein expression
3.Gene for eye colour : -alleles for eye pigment gene: blue, green , brown etc
-amount of gene and protein expression; pale vs deep colour - Unique alleles and differential regulation of thousands of genes among Individuals leads to countless phenotypic possibilities in a population
- Individuals that possess similar alleles and gene regulation leads to more similar protein expression and phenotypes (immediate family, relatives)
Chromosome theory of inheritance
-scientists noted that chromosomes fit Mendel’s hypothesis
-individuals have 2 copies of each chromosome
-similar (homologous) chromosomes separate independently during meiosis
-Gametes : have 1 copy of each chromosome
-Zygotes : are a random combo of 2 gametes
Chromosomes are composed of both _____ and ____,
But ______ make up 50-60 %
-composed of ___ _______ acids
-millions of possible __ structures
- complex enough to store ______ information
But ____ make up 40-50%
-composed of 4 _______ _____
- simple and limited 3D structures
-thought to play a _________ role
Proteins and DNA,
Proteins,
-20 amino acids,
-3D structures
-Heritable information
DNA
- nucleic acids
- structural role
Establishing DNA as the hereditary molecule (3 classical experiments)
1.Griffith : discovered _____ _________ that genetically _______ ________ streptococcus pneumonia
2. Avery, Macleod & McCarthy : identified ____ as the molecule that transforms __.___________
3. Hershey and chase : found the final evidence establishing ____ as the ______ molecule
- Genetic transformation that genetically altered (transforms)
- DNA, S. pneumonia
- DNA as the hereditary molecule
Streptococcus pneumoniae
Bacterial pathogen that causes pneumonia in mammals A significant cause of child mortality before the development of antibiotics and vaccines
-smooth (s) strain : each bacterium is surrounded by a polysaccharide capsule
-the s strain is virulent : capsule protects S cells from the immune system well enough to cause infection
- Rough (R) strain: lacks polysaccharide capsule, cannot evade the immune system, therefore, benign .
Streptococcus pneumoniae
Bacterial pathogen that causes pneumonia in mammals A significant cause of child mortality before the development of antibiotics and vaccines
-smooth (s) strain : each bacterium is surrounded by a polysaccharide capsule
-the s strain is virulent : capsule protects S cells from the immune system well enough to cause infection
- Rough (R) strain: lacks polysaccharide capsule, cannot evade the immune system, therefore, benign .
Griffith’s experiments (the transforming principle) , how the dude published a paper while trying to develop vaccine, what was Griffith’s conclusion?
- Virulent bacteria (control#1)(mouse dies of pneumonia), 2.Nonvirulent bacteria (control#2) (mouse remains healthy), 3. Heat-killed virulent bacteria (they boil the crap out of the bacteria in water) (mouse remains healthy) 4. Heat- killed virulent bacteria & nonvirulent bacteria (mouse dies of pneumonia)
Griffith’s conclusion : some molecules (transforming principle) released when S cells died could genetically transformation that living R cells into S cells.
-Transformation was permanent and heritable ( all progeny cells in the colony were the same type)
What is the Chemicl nature of the transforming principle? (Avery, Macleodean & McCarthy)
Name the hypothesis, experimental approach and conclusion>
Hypothesis: transforming principle could be protein, DNA or rna - which one?
Experimental approach : eliminate each type of molecule in S cells and see whether transformation of R cells into the virulent (S) form still occurs?
Conclusion; if transformation stops when one type of molecule is absent, then this molecule is the transforming principle
The Avery experiment:
-Kill S cells, Lyse the cells (basically put into pressure blender and exploded the cells releasing all the macromolecules) , remove the lipids and sugars,
-Test 1 : they added protease (attacks and breaks down proteins), protease also chop polypeptides into their individual amino acids, basically eliminating that as macromolecule. {Test tube 1 will have no protein, lots of DNA, lots of RNA }
-Test 2: They took some of their solution and they added a ribonuclease (enzymes that chop up RNA molecules), the ribonuclease would eliminate all of the rna in test tube number 2 , but it would still have lots of DNA and lots of protein,
-Test 3 : Add DNAse (enzymes that break down DNA molecules), so test 3 would have no DNA, but lots of RNA and lots of protein
- Then they added living R cells into each tube
-Then they look for living S cells (transformation)
Test 1 - mice died (so protein prob not genetic material bcs there was no protein in the test tube
Test 2 - mice died (RNA, prob not genetic material bcs these bacteria became virulent when RNA wasn’t there
Test 3 - didn’t die and (they recovered living S cells from these mice, so DNA is the transforming principle and molecule that carries the genetic code!)
The nail In the coffin (or the phage in the bacterium as the case may be)
-that the Hershey & Chase experiment provided further evidence that DNA is the genetic material
-Used bacteriophage (viruses that infect bacteria) and its E.coli host to show that DNA is the transforming principle)
Picture of bacteriophage
Most viruses are genetic material encased in a little protein case. Basically that little top part where that’s labeled the head. That’s the structure of lots and lots of viruses. Bacteriophage are a little bit more complex, bcs they’ve got that bottom half that contains what we call tail fibres .
Picture of bacteriophage attached to an E Coli,
and so the E Coli is down there at bottom in that browny colour, and these viruses use their tail fibres to basically touch down like a lunar lander onto the bacterial surface, injects its genetic material on the inside and caused an infection .
Life cycle of a bacteriophage
-Lyric infection : massive reproduction of virus resulting in host cell lysis
-After attachment, the virus genetic material is injected into the host and the phage coat remains outside
-Viral DNA “takes over” the host, hundreds of copies are made, and progeny virus burst from the host
- DNA uses phosphorus (I.e phosphodiester bonds) but not sulfur
- Some amino acids use sulfut (I.e cysteine and methionine )but not phosphorus
-The experimenters developed 2 populations of virus: One with radioactive phosphorus (32P) in its DNA, one with radioactive sulfur (35S) in its proteins
Hersheys and Chase experiment: Does the bacteriophage injects DNA or protein into E. Coli
Results: Experiment 1: 35S not found in host cells or progeny virus particles
- protein isn’t a genetic material
- all the protein was removed after they threw those bacteria into the blender and those shells dissapeared
-the genetic material inside the bacteria reproduced using non-radioactive phosphorus and amino acids and none of the progeny virus were radioactive
Results : Experiment 2: 32P found in host cells and progeny virus particles
-DNA is the genetic material
