Lecture 7 Chromosome structure 022218.pptx

Lecture 7 Chromosome structure 022218.pptx - REMINDER FIRST...

Info icon This preview shows pages 1–11. Sign up to view the full content.

View Full Document Right Arrow Icon
REMINDER FIRST MID-TERM IS NEXT WEEK: THURSDAY, MARCH 1 TAKE ADVANTAGE OF MONDAY TUTORING HRS AT SKIRBALL LEARNING CENTER!
Image of page 1

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Chromosome territories in a chicken cell nucleus. Each chromosome is marked with a distinct color. Each is confined to its own, well-defined territory. IMPORTANT POINTS REGARDING CHROMOSOME STRUCTURE: a) eukaryotic chromosomes are organized into chromatin b) chromatin is essential for chromosome structure c) chromatin state is important for gene expression: defines “euchromatin” and “heterochromatin”
Image of page 2
EUKARYOTIC CHROMOSOMES a) Eukaryotes have multiple linear chromosomes compacted in the nucleus b) The degree of compaction is enormous: 1.8 meters of DNA is packed into a 5 micrometer ( m = micron) nucleus (actual size of nucleus varies among cell types/organisms) . 1.8m = 1.8 x 10 6 m/5 m = 0.36 x 10 6 = 360,000 – fold compaction ! c) We do not fully understand how this is accomplished d) The DNA and associated proteins of a chromosome constitute the “chromatin” e) Proteins that organize chromosomes are essential and provide a mechanism for chromosome organization, condensation, segregation, and control of gene expression.
Image of page 3

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Chromosome compaction overview Figure: Maeshima, K. et al. Chromosoma 123:225. 2014 String of nucleosomes is known as “10 nm fiber” – first described by Flemming in 1800’s Actual diameter of the “10nm fiber” is 11nm and includes: a. Histone octamer = “core” b. ~146bp , 2nm diameter DNA helix wrapped around this histone “core” c. Linker DNA , 20-80bp d. Overall repeat unit in the 10nm fiber includes ~ 165 to ~220bp of DNA, depending on linker length Some controversy about “regular” folding into 30nm fiber (solenoid) vs irregular folding
Image of page 4
NUCLEOSOME The nucleosome is responsible for the first level of compaction (~7X) Linked nucleosomes form the 10nm fiber, or ‘beads on string’
Image of page 5

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
NUCLEOSOME Figure 11.6 HISTONE CORE : two molecules of each histone H2A, H2B, H3, and H4 = 8 total proteins = “octamer” Fifth type of histone = H1 (see later); not part of the nucleosome All histone proteins are highly conserved among eukaryotes
Image of page 6
HISTONES 1. Small = 11-14kD (kiloDaltons), basic proteins, rich in Lys. 2. H1 is a bit larger than the others (23kD) 3. Histones neutralize the negative charges of the DNA so that it can be compacted (would otherwise tend to self-repel)
Image of page 7

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
NUCLEOSOME Nucleosome structure: Remember that the nucleosome is 11nm in diameter, and 5.7nm in thickness Figure 11.7 11nm 5.7nm Notice: there are two molecules of each histone in a nucleosome
Image of page 8
The DNA around the nucleosome (1.75 turns) is the ‘core DNA ’; ~146 bp (many investigators quote 147bp ) The DNA between nucleosomes is called the “linker DNA” Linker varies in length , both among organisms and among cell types in the same organism (~20bp to 80bp).
Image of page 9

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Figure 11.6
Image of page 10
Image of page 11
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern