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Gregor Mendel
1866 - Paper on inheritance in peas
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Sutton
1902 (Sutton) Genes located on chromosomes
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Watson and Crick
1953 - DNA double helix
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Kary Mullis
1986 - Polymerase Chain Reaction
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1996
Dolly the Cloned Sheep
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1995-2005
Several genomes completely sequenced
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Biochemical reactions require
Enzymes
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Gene products (examples and necessary)
- Enzymes are gene products
- Gene products are necessary for metabolism and growth
Many genetic diseases involve defective enzymes
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Fruit Fly
Drosophila melanogaster
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Bacterium
Escherichia coli
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Roundworm
Caenorhabditis elegans
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Thale Cress Plant
Arabidopsis thaliana
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Baker's Yeast
Saccharomyces cerevisiae
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Why are model organisms used in laboratories?
- Short generation time
- Manageable numbers of progeny
- Easily adaptable to the lab
- Inexpensive to maintain
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DNA structure
Deoxyribonucleic Acid - Double Helix
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Primary structure
Nucleotide sequence
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Secondary structure
Alpha helix
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Tertiary structure
Higher order folding
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Length of E. coli DNA
4.64X10^6 base pairs
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Length of H. sapiens DNA
6X10^9 base pairs
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Width of DNA double helix
2 nm
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Number of base pairs wrapped around histone
145-147
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Number of times DNA wraps around histone
1.76
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Amount of linker DNA
30-50 base pairs
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Histone proteins
- Structural
- H1 & H5 - Linker
- H2A, H2B, H3, and H4 - Core
- Strongly alkaline proteins
- Only in Eukaryotic cells
- Form spools around which DNA winds
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Nucleosomes
Histones + DNA
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Chromatosome
Nucleosome with one bound linker histone
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Where does H1 attach to the core particle?
Where the DNA joins and leaves
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Solenoid
- 30 nm fiber of chromatin
- Helical winding of at least five nucleosome strands
- Six connected loops form a ROSETTE
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Chromatid
One of two idenitcal copies of DNA making up a duplicated chromosome
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Centromere
- Join sister chromatids
- Help control the cell cycle by inhibiting anaphase until all the spindles are attached
- Kinetochore proteins bind to them
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Telomeres
- Serve as caps that stabilize chromosome ends
- Provide a means for replicating the ends of chromosomes
- Characteristic Nucleotide sequences
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Useful properties to describe chromosomes:
- Size
- Number
- Position of centromere
- Nucleolar organizers number and position
- Chromomere patterns
- Heterochromatin patterns
- Banding patterns
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Types of Chromosomes
- Metacentric
- Submetacentric
- Acrocentric
- Telocentric
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Are X and Y homozygous?
YES
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Heterochromatin
- Highly condensed
- Transcriptionally inactive
- Dark when stained
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Euchromatin
- Lightly packed
- Usually under active transcription
- Light when stained
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Banding patterns
Transverse bands along the length of the chromosomes
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G-bands
- Made visible with Giemsa stain
- Rich in A-T bonds
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R-bands
- Visible with reversed Giemsa stain
- rich in G-C bonds
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Other types of stains
- C- constitutive heterochromatin
- T- telomeres
- NOR- nucleolar organizer
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Nucleolar organizer
A chromosomal around which the nucleolus forms, a site of tandem repeats of the rRNA genes.
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Nucleolus
visible region in nucleus where portions of the ribosomes (rRNA) are being assembled.
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Chromomere patterns
- Little thickenings along the chromosome, easily viewed during prophase of mitosis and meiosis.
- Especially large chromomeers are called "knobs."
- Unkown function
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Cell cycle
- Series of events that takes place in a cell leading to its division
- Two periods: interphase and mitosis
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Interphase
Time where the cell grows and duplicates DNA
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Mitosis
Cell splits itself into two daughter cells
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Three sub phases of Interphase
G1, S, G2
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G1
Cell grows and carries out normal activities
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S
Cell replicates its chromosomes (DNA)
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G2
Cell replicates its organelles and prepares for division
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Is interphasal DNA uncoiled?
- Yes!
- In G1 or G2- Chromatin is NOT condensed - chromosomes are long strands of chromatin.
- S- DNA replication occurs
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G0 Phase
- Gap Zero
- Period in the cell cycle where cells exist in a quiescent state
- Typical cells that rarely divide (neurons, heart muscles)
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Cell cycle check points
- Used by the cell to monitor and regulate the progress of the cell cycle
- Prevent cell cycle progression at specific points, allowing verification of necessary phase processes and replair of DNA damage
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p53
- When malfunctioning is responsible for more than half of cancer cells
- Plays an important role at both G1/S and G2/M checkpoints
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G1/S Checkpoint
Key decision (restriction point): whether the cell should divide, delay division, or enter a resting stage.
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G2/M Checkpoint
- Check for potential DNA damage to ensure cell is ready for Mitosis
- Postreplication checkpoint
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