Biochemical Regulation of Xsome Formation and Segregation
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Transcript of Biochemical Regulation of Xsome Formation and Segregation
THE BIOCHEMICAL REGULATION OF CHROMOSOME FORMATION AND
SEGREGATION IN MITOSIS/MEIOSIS
By: GOSIFE DONALD OKOYEGENETICS 301
APRIL 13TH 2015
● Definition of Important Concepts○ Eukaryotic Chromosome○ Chromatin○ Chromatid
● Formation of the Eukaryotic Chromosome○ Biochemistry and regulation of nucleosome
formation○ Nucleosome packing (heterochromatin vs
euchromatin)○ Chromosome condensation
● Chromosomes during Mitosis and Meiosis○ Biochemical regulation of Mitosis and Meiosis
OVERVIEW
● EUKARYOTIC CHROMOSOMES: Structures resulting from the organization of nuclear DNA.
● CHROMATIN: A complex of macromolecules consisting of DNA, proteins and RNA. Basically resulting from packaging of DNA with histone proteins.
● CHROMATID: One copy of a duplicated chromosome usually joined to another via a centromere.
IMPORTANT CONCEPTS
NUCLEOSOMES: Histone proteins with DNA wrapped around them● DNA: Negatively charged● Histones: Positively charged
o Core (H2A, H2B, H3, H4)o Linker Histone (H1)
NUCLEOSOME FORMATION
● H3-H4 dimers assemble● DNA associates● H2A/H2B associate with
tetramer● Histone Octamer forms● H1 for higher order
packing
ASSEMBLY
● Individual Core Histone Proteins Aggregate unspecificallyo Random coil conformation in low ionic conditions
● Interacting Core Histones adopt similar and more stable secondary conformations fostering further interactions
● Interactions with DNA are also favoredThe resulting interactions produce modifiable tails.● Histone Chaperones
STABILITY OF HISTONE PROTEINS
● Binds Entry/Exit site of DNA to nucleosome
● Stabilizes Nucleosome
● Reduces nucleosomal mobility
● Guides higher order folding
● Accumulates in transcriptionally inactive regions
● Closely linked to DNA modification
H1 LINKER HISTONE
● Histone Acetyltransferases (HATs)
o Lysine Residues
● Histone Deacetylases (HDACs)
● Histone Methyltransferases (MTs)
o Lysine or Arginine residues
● Histone Demethylases (DMTs)
● Condensin: I and II
OTHER PROTEINS THAT REGULATE NUCLEOSOME PACKAGING
Chromatin Remodeling Complexes (CRC): ● establish a proper chromatin context for central
nuclear processes such as replication, DNA repair, and gene expression.
● move or evict nucleosomes to allow access to DNA for regulatory proteins that otherwise would be impeded by their binding to the nucleosomal DNA
● the mode of nucleosome movement and rearrangement is the topic of epic scientific debates
HIGHER ORDER PACKING
● Folding continues guided by CRC and other proteins.
● The microenvironments determine the rate of folding and the concentration of linker histones
● The folding pattern closely mimics the double-helix nature of DNA but in a much tighter form.
HIGHER ORDER PACKING continued...
REGULATION OF CHROMOSOMAL ACTIVITIES DURING MITOSIS/MEIOSIS
● PROPHASE: Chromosome Condense
● METAPHASE: Chromatids attach to mitotic spindle
equator
● ANAPHASE: Sister Chromatids separate and migrate
● TELOPHASE: Chromosome uncoils
MITOSIS AND THE CHROMOSOME
● Occurs during metaphase
● Determines if mitosis will
continue
MITOTIC CHECKPOINT
● Cohesin● BUB1 (Budding Uninhibited by
Benzimidazole-1)● MAD1/MAD2/MAD3● cdc20 (Cell Division Cycle 20)● Anaphase-Promoting Complex● Securin-Separase Complex● Cyclin-Dependent Kinase-1● BUBR1 (Budding Uninhibited by
Benzimidazole Related-1)
THE METAPHASE-ANAPHASE TRANSITION IS HIGHLY REGULATED
● cdc 20● cdc14 (Cell Division Cycle 14)
(phosphatase)● APC● Securin-Separase Complex● Separase● Cohesin
This represents the last regulated step of mitosis
THE METAPHASE -ANAPHASE TRANSITION IS HIGHLY REGULATED
● Very similar to mitosis
● Meiotic Crossover
o Regulation of number and distribution by DPY-
28
o A subunit of condensin
REGULATION OF CHROMOSOMES IN MEIOSIS
The Eukaryotic Cell is:● A master biochemist
● A master strategist........a grand chessmaster
IN SUMMARY
● "Chromatin Structures" by Original uploader was Richard Wheeler at en.wikipedia Later version(s) were uploaded by Seans Potato Business at en.wikipedia. - Transferred from en.wikipedia; Transfer was stated to be made by User:sevela.p.. Licensed under CC BY-SA 3.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Chromatin_Structures.png#/media/File:Chromatin_Structures.png
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