Life Science 3 Lecture 1

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Molecular Biology

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The branch of biology that deals with the formation, structure, and function of macromolecules essential to life, such as nucleic acids and proteins, and especially with their role in cell replication and the transmission of genetic information.

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Biochemistry

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The study of chemical substances and vital processes occurring in living organisms.-in vitro (test tube)studies [proteins]

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Genetics

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The branch of biology that deals with heredity, especially the mechanisms of hereditary transmission and the variation of inherited characteristics among similar or related organisms-in vivo studies (living organism). [Going from one generation toe the next and how changing one gene affects the organism]

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Molecular biology techniques

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-Embrace in vitro analysis of mixtures of biological macromolecules.
-Utilize recombinant DNA technology
-frequently focus on model organisms where techinques have been developed to both take genes out and put them back in the genome
-focuses on DNA/RNA/proteins

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Organisms being studied

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-bacteria [middle sized]
-bacteriophages (bacterial viruses) [smallest]
-simple eukaryotes (yeast) [largest]

Smaller tend to be simpler to study.

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Bacteria

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1) free living single cell organism
2) single circular chromosome not surrounded by nucleus
3) membrane bound sack of proteins, molecules, and chemicals
4) best studied bacteria is e/ coli (doubles every 20 minutes and found in animal gut)
5) bacteria can grow in liquid media or on solid surface [generally agar[
6) bacteria are internally regulated to produce only the enzymes they require under certain growth conditions-metabolic regulation [don't make anything they don't need]

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Viruses

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1) genetic information plus protective covering
2) parasite: dependent on host for proteins and energy
3) viruses may infect bacteria [bacteriophages], plants [plant viruses], or animals [animal viruses]
4) composed of head and tail: the tail is where it attaches]
5) need right conditions to survive

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Yeasts

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1) single celled eukaryotes
2) grows in both liquid media and agar surface
3) has nuclear membrane and 16 linear chromosomes
4) increased complexity due to its compartmentalization though developmentally simple
5) can grow like bacteria

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Animal Cells Three types of laboratory cultures

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Laboratory cultures:
1) primary cell cultures: cells grow in special media for a limited time [internal clock that inhibits division after so many cell cycles]
2) tumor cells (transformed): cells grow indefinitely in culture [have lost control of cellular division]but harbor many mutations or chromosomal aberrations
3) embryonic stem cells: replicate indefinitely in culture and are pluripotent

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New Techniques to Study Molecular processes

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1) Ultracentrifuge
2) Electrophoresis
3) Electron microscope
4) radioisotopes
5) Column Chromatography
6) X-ray diffraction
7) protein sequencing
8) Hybridization
9) DNA sequencing
10) Recombinant DNA technology
11) DNA synthesis
12) Monoclonal antibodies
13) Polymerase Chain Reaction (PCR)
14) Genomics

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What type of chemical molecule is stable enough to contain genetic information, and yet capable of changing to a mutant form to allow for evolution? (Major question during the 1920s-1940s)

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Genetics and cell biology had shown by then that genetic information was contained on chromosomes (colored body--chromosomes differ in organisms). Chromosomes were made up of both DNA and protein (amino acid chains. Chemical molecule would need to be stable enough to contain genetic material, but able to change and evolve. Genetic information was in the DNA. Was this genetic information (genes) in DNA or proteins-most thought it was proteins.

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Why did many scientists believe that genes were contained in proteins?

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1) Proteins are more complex (alot more variance possible)
2) DNA was believed to play structural role in cell (only 4 building blocks)

-Most thought that there were beads of string-where the DNA was the string holding the proteins together.

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George Beadle and Edward Tatum: neurospora (bread mold)

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-Showed that each gene controlled a single protein (one gene: one hypothesis)
-If genes are proteins, how do they direct the synthesis of other proteins?
-Proteins were known to be a unique sequence of amino acids-how is this unique sequence synthesized?

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Three Experiments showing DNA is genetic material?

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1) Griffith Experiment (1928)
2) Avery, MacCleod McCarty Experiment (1944)
3) Hershey Chase Experiment (1952): Bacteriophage T2 Radioisotopes

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Griffith Experiment

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Dr. Griffith was working with two strains of Streptococcus pneumoniae:
-lethal strain contained polysaccharide capsule making it appear smooth (S) and allowing it to evade the host immune system [virulent]
-Non lethal strain was lacking the polysaccharide capsule giving it a rough (R) appearance. this strain was quickly removed from the host by the immune system. [non virulent]

Experiment 1: Lethal strain was killed with heat and injected into mouse to see if polysaccharide capsule alone could cause death. Mouse survived. Conclusion: polysaccharide capsule alone is not toxic. No chemicals toxic where needed living strain-->not a toxin.

Experiment 2: Lethal strain was killed with heat and mixed with the non lethal strain (R strain). When injected into a mouse the mouse died. Bacteria isolated from the lungs of the mouse were examined and found to be the S strain, not the R strain.
Conclusion: heat killed S strain can transform R strain into S strain
Modern Interpretation: Genetic information for polysaccharide coat is transferred from S strain into R strain.

Note: this experiment was designed to determine what was causing the bacteria to be pathogenic and an unattended outcome was insight into the nature of the gene.

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Avery, Macleod and McCarthy

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Follow up on Griffith's experiments:
-Showed transformation could take place in a mouse or in a test tube (Dawson)
-purified transforming activity from S cells to near homogeneity
-->What is it that transforms R-->S

Go from S cell-->lyse cell-->isolate DNA-->mix DNA with R cells-->Grow cells and find some are now S cells

Was transformation due to contaminant or DNA? Treated the extract with different enzymes to prove that DNA was transforming agent:
DNases: degrade DNA into components
RNases: degrade RNA into components
Proteases: degrade proteins into components

treat protease or RNA still transform while with DNase there is no transformation

Conclusion: DNase destroys ability of heat extract to transform R strain into S strain. DNA must contain the transforming activity. DNA must contain the genetic information.

*Not accepted by all