Section 8.5 notes
Section 8.5 notes MCB 252
Popular in Cells, Tissues & Development
verified elite notetaker
Popular in MCBA - Cell Biol & Anatomy
This 3 page Study Guide was uploaded by Noopur Walia on Thursday October 6, 2016. The Study Guide belongs to MCB 252 at University of Illinois at Urbana-Champaign taught by Good, E in Fall 2016. Since its upload, it has received 9 views. For similar materials see Cells, Tissues & Development in MCBA - Cell Biol & Anatomy at University of Illinois at Urbana-Champaign.
Reviews for Section 8.5 notes
Report this Material
What is Karma?
Karma is the currency of StudySoup.
You can buy or earn more Karma at anytime and redeem it for class notes, study guides, flashcards, and more!
Date Created: 10/06/16
Exam II Study Guide (T extbook chapter notes) Section 8.5 – Structural Organization of Eukaryotic Chromosomes - 5 major types of histone proteins: H1, H2A, H2B, H3, and H4 (rich in positively charged basic amino acids which interact with the negatively charged phosphate groups in DNA) - the “string” is composed of free DNA, called “linker” DNA, connecting bead like structures termed nucleosomes (contain about 147 bp) - core is an octamer containing two copies each of histones H2A, H2B, H3, and H4 - The amino acid sequences for the four core histones (H2A, H2B, H3 and H4) are highly conserved between distantly related species - Minor histone variants – (i.e. H2AX is a special form of H2A) (i.e. H3 is replaced by CENP-A), most minor histones variants differ only slightly in sequence from the major histones and these slight changes in histone sequences may influence the stability of the nucleosome as well as its tendency to fold into the 30 nm-fiber - Histone tails – required for chromatin to condense from the beads on a string conformation in the 30 nm fiber; histone tails are subject to multiple post translational modifications such as acetylation, methylation, phosphorylation and ubiquitination - H4K16 = particularly important for the folding of the 30 nm fiber; When it is acetylated, the chromatin tends to form the less condensed “beads on a string” conformation conducive for transcription and replication - An observation indicates that the histone acetylation is associated with a less condensed form of a chromatin - Histone Acetyl Transferases (HATs) – acetylate specific lysine residues in histones, are required for the full activation of transcription of a number of genes - Complete repression of many yeast genes requires the action of Histone Deacetylases (HDACs) that remove acetyl groups of acetylated lysines from histone tails - Other histone modifications: Lysine E-amino groups can be methylated; the N of lysine E amino groups can be methylated once, twice or three times; Arginine side chains can be methylated, the O in the hydroxyl groups of serine and threonine side chains can be reversibly phosphorylated – each of these post translational modification contributes to the binding of chromatin associated proteins that participate in the control of chromatin folding and the ability of DNA and RNA polymerases to replicate - Heterochromatin – condensed regions of chromatin, usually contain histone H3 modified by methylation of lysine 9, H4K16 is generally non-acetylated in heterochromatin which allows it to interact with neighboring nucleosomes and stabilize chromatin folding into the 30nm fiber - Euchromatin – less condensed (most DNA transcribed regions), usually contain histone H3 modified by acetylation of lysine 9 - Histone code of modified amino acids is read by proteins that bind to the modified tails and in turn promote condensation or decondensation of the chromatin (i.e. of such protein is Heterochromatin protein 1 – HP1) o The chromodomain of HP1 binds to the H3 N terminal tail only when it is di or trimethylated at K9 o HP1 also contains a chromoshadow domain – in addition to binding itself, this domain also binds the enzyme that methylated H3K9 which results in the nucleosomes adjacent to a region of HP1 containing heterochromatin also become methylated at K9. - Epigenetic – when DNA in heterochromatin is replicated, the histone octamers that are di- or trimethylated at H3K9 become distributed to both daughter 2 chromosomes along with a equal number of newly assembled histone octamers (pg. 333-334) - X chromosome inactivation in Mammalian females – example of epigenetic control; Each female mammal has 2 X chromosomes; during early embryonic development, random inactivation of either one of the two chromosomes occurs in each somatic cell which results in a dosage compensation which is a process that ensures that cells of females express proteins encoded on the X chromosome at the same levels as the cells of males which have only one X chromosome o Hypoacetylation of lysines, di and trimethylation of histone H3 lysine 27 and a lack of methylation at histone H3K4 o X chromosome inactivation is another example of an epigenetic process; that is, a process that affects the expression of specific genes and is inherited by daughter cells but is not the result of a change in DNA sequence - Structural Maintenance of Chromosome (SMC) proteins – non histone proteins are critical for maintaining the structure of condensed chromosomes during mitosis (pg. 336) Section 9.5 – Molecular Mechanisms of Transcription Repression and Activation - 3
Are you sure you want to buy this material for
You're already Subscribed!
Looks like you've already subscribed to StudySoup, you won't need to purchase another subscription to get this material. To access this material simply click 'View Full Document'