chromosome and cell division mw% + Flashcards
Name the components of a eukaryotic chromosome structure?
- Telomere
- Centromere
- Heterochromatin
- Euchromatin
What is the function of a telomere?
- 5’-TTAGGG-3’ repeats
- Prevent end-replication problem
- Protects the end of the chromosome from deterioration or from fusion with neighboring chromosomes.
Describe the components of the cell cycle?
- Interphase:
- G0: Exit from cell cycle. Stopped undergoing mitosis indefinitely
- G1 : Cell growth. Metabolically active; duplicates organelles and cytosolic components and centrosome replication begins
- S: DNA Replication
- G2: Preperation for mitosis. Cell growth continues; enzymes and other proteins are synthesized; centrosome replication completed.
- Mitotic phase
Prophase
- Chromosomes condense
- Nuclear membrane disappears
- Spindle fibres are made from the centriole
Metaphase
- Chromosomes aligned at the equator of the cell
- Fibre attaches to each centriole (on chromosomes Kinetochore )
- Maximum condensation of chromosome
Note: Long protein fibers called microtubules extend from the centrioles in all possible directions, forming what is called a spindle fibres
Anaphase
- Sister chromatids separate at centromere
- Separate longitudinally
- Move to opposite ends of cell
Telophase
- New nuclear membranes form
- Each cell contains 46 chromosomes (diploid)
Cytokineses
- Cytoplasm separates
- Two new daughter cells
What are centromeres?
- Constricted region joining sister chromatids
- Repetitive DNA sequences
- Site of kinetochore (where the spindle fibers attach during cell division to pull sister chromatids apart)
- Protein complex that binds to microtubules
- Required for chromosome separation during cell division
What are the componets of chromatin?
Heterochromatin
–Condensed structure
–Silenced genes
Euchromatin
–Open structure
–Active genes
Chromatin structure
- DNA packaged with histone proteins to form chromatin
- Histones have positive charge
- Packaged into units called nucleosomes
- From ‘solenoid’ structure
What is the purpose of packaging DNA?
- Negatively charged DNA neutralised by positive charged histone proteins
- DNA takes up less space
- Inactive DNA can be folded into inaccessible locations until required
Briefly describe Meiosis
- Cell division in germ cells: spermatogonium and oogonium
- Diploid cells (in ovaries and testes) divide to form haploid cells
- Chromosomes are passed on as re-arranged (recombined) copies
–Creates genetic diversity
Gametogenesis
- Oogenesis = process of egg formation
- Spermatogenesis = process of sperm formation
- Both go though several stages, with different timing in males and females
- Sperms go through more cell divisions than eggs do – more chance of mutation
What is fertilisation?
- Two haploid cells form 1 diploid cell (zygote) – develops into embryo
- Whether sperm contain an X or Y chromosome determines if embryo is female (XX) or male (XY)
- Embryo contains an assortment of genes from each original parent – more genetic diversity
- Mitochondria (and their DNA) come only from mother via the egg – maternal inheritance
What does X-inactivation in female mammals prevent?
- Double dose of gene products
- As all female mammals have wX chromosomes, X-inactivation prevents them from having 2X as many X chromosome gene products as males, who only possess a single copy of the X chromosome
Extragenic sequences
•Tandemly repeated (nucleotide repeat) DNA sequences
Meiosis and recombination pic
Karyotype
- Karyotype is a test to identify and evaluate the size, shape, and number of chromosomes in a sample of body cells.
- Extra or missing chromosomes, or abnormal positions of chromosome pieces, can cause problems with a person’s growth, development, and body functions.
Fluorescent in situ hybridisation (FISH)
a molecular cytogenetic technique that uses fluorescent probes that bind to only those parts of the chromosome with a high degree of sequence complementarity
Types of FISH
(telomere pic)
- Unique sequence probes
- Centromeric probes
–Useful for determining chromosome number
•Telomeric probes
–Useful for detecting subtelomeric rearrangements (Subtelomeres are segments of DNA between telomeric caps and chromatin)
•Whole chromosome probes
–Cocktail of probes covering different parts of a particular chromosome
–Used with different fluorescent dyes
–Spectral karyotype
–Useful for detecting translocations and rearrangements
