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Human cells contain how many DNA?
6 billion base pair
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DNA structure
- Primary - Nucleotide sequence
- Secondary - Double stranded helix
- Tertiary - Higher Order Folding (Supercoiling)
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Overrotated molecules of DNA
Positive Supercoiling
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Underrotated molecules of DNA
Negative Supercoiling
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Enzyme that adds or remove rotations by temporarily breaking nucleotide strands, rotating ends and rejoining broken ends
Topoisomerase
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Supercoiling advantages:
- Easier during replication and transcription
- Can be packed into smaller spaces
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Unersgoes normal condensation and decondensation
Euchromatin
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Remains highly condensed throughout cell cycle.
Heterochromatin
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Type of Chromatin that exists at telomeres and centromeres
Heterochromatin
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Name 5 chromatin histones
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DNA wrapped 2 x around octamer histone proteins
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Chromatosome
Nucleosome plus H1 histone
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Localized swelling of chromosome, showing active transcription
Chromosomal puffs
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Gian chromosomes, unusual, due to replication without cell divisions
Polytene chromosomes
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Stable alterations in chromatin structure (methylation) that can be passed ont o cells or individual organisms. They do not alter DNA sequence, can be reversed and often influenced by environmental factors.
Epigenetic Genes
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Contain centromeric sequences that are bidnign sites for kinetochore
Centromeres
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"End Caps" that keep DNA from degrading usually consist of repeating units of A/T followed by G/C (End of chromosome)
Telomeres
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Binds to telomeres overhang to prevent repair
Shelterin
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Amount of DNA per cell
C-value
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During Denaturation which requires more heat?
G/C or A/T why?
G/C requires more heat because it has 3 hydrogen bonds connecting them versus A/T only has 2 h bonds
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Annealing of 2 DNA from different sources
Hybridization
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DNA sequences that are only repeated once or at the most a few times. Make up 25-50% of protein encoding genes
Unique Sequence DNA
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Repeating DNA. 150-300 bp
rRNA
tRNA
Moderately Repeating DNA
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Tandem Repeating Sequences
Repetitive sequences, one after another
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Interspersed Repetitive DNA
Include LINE, SINE
Scattered throughout genome
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AKA Satellite DNA, less than 10bp in lenght
no known function
Highly repetivie DNA
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3-12 bp in length added on both sides of transposable elements
short flanking direct repeats
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mobile DNA sequences able to insert at many different locations
transposable elements
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9-40 bp inverted DNA sequences, complements of each other. Exist at many ends of transpoable elements.
terminal inverted repeates
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the movement of a transposalbe element from one location to another
transposition
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transposition - 3 steps
- staggered breaks
- transposable element joined to single stranded ends of target DNA
- DNA replicated at single strand gaps
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some transposable elements tranpose as DNA
DNA transposons
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elements that transpose through a RNA intermediate
retrotransposons
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Copy and Paste transposition
Replicative transposition
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Cut and Paste transposition
Non-replicative transposition
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