BIO SCI 99 Lecture Notes - Lecture 3: Leucine, Deoxycytidine Monophosphate, Spindle Apparatus
12 Sep 2018
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LECTURE 3
DNA compaction: Beads on a String
• Histone core + ~150bp DNA
• Histone H1
DNA Compaction: 30nm filament
• Two models to explain how nucleosomes position themselves
• Dependent on histone H1, histone tails
• Solenoid model (one-start helix)
• Zigzag model (two-start helix)
DNA Compaction: Chromosome
• Dependent on chromosome scaffold (protein)
What is a chromosome?
QUESTION: Chromosomes contain:
A. Centromere
B. Telomere
C. Origin of Replication
D. A & C
E. A, B, & C
What is a Chromosome?
• Contains:
• Origin of Replication (ORI) - where replication starts
Histones
• Histone core
• H2A, H2B, H3, H4
• Histones highly
conserved
• High % of (+) AA
• Histone tails
• Flexible
• Highly modified - Ac,
P, Me, Ub, etc
• Mediate inter-
nucleosome
connections
• Centromere: attachment point for proteins that link the chromosome to the mitotic
spindle at metaphase (MITOSIS)
• Telomere: ends of DNA, protects against the end replication problem
• Exp. Construction of artificial chromosomes in yeast
• Examined transformation of plasmid in yeast
How do we know which yeast acquire the plasmid - Selection marker:
Leu2∆ yeast does NOT have leu2 gene
What is a colony: collection of cells that grow on a plate
In this scenario, why does a colony form? 6 colonies on the plate (each colony arise from one
cell); cells are all similar in the colony because they all arise from the same cell. They are
observable, even if plate doesn’t have leucine and we start with knockout strain that doesn’t
contain leucine, because the knockout strain was transformed with the plasmid to allow the gene
to express and survive in the conditions
• Only the cell that picks up the plasmid picks up the Leu2 and survives
What is a Chromosome - ORI
*** Selective media: does NOT contain leu/NO origin of replication (ORI) aka no
leucine
QUESTION: Will we see colonies?
A. Yes
B. No
Why or why not?
• NO because there is no leucine; therefore it won't be able to grow.
• It needs ORI (which this is lacking)
• We introduced a plasmid without Leu2 gene meaning no ORI
• NO plasmid = NO leu
Document Summary
Histones: histone core, h2a, h2b, h3, h4, histones highly conserved, high % of (+) aa, histone tails, flexible, highly modified - ac, P, me, ub, etc: mediate inter- nucleosome connections. Dna compaction: beads on a string: histone core + ~150bp dna, histone h1. Dna compaction: 30nm filament: two models to explain how nucleosomes position themselves, dependent on histone h1, histone tails, solenoid model (one-start helix, zigzag model (two-start helix) Dna compaction: chromosome: dependent on chromosome scaffold (protein) Question: chromosomes contain: centromere, telomere, origin of replication, a & c, a, b, & c. Construction of artificial chromosomes in yeast: examined transformation of plasmid in yeast. How do we know which yeast acquire the plasmid - selection marker: What is a colony: collection of cells that grow on a plate. 6 colonies on the plate (each colony arise from one cell); cells are all similar in the colony because they all arise from the same cell.
