C10: How Cells Divide

Human chromosomes are found inside the ___. Each human inherits ___ from each parent and have a total of ___ chromosomes (___ pairs). 22 pairs (chromosome 1-22) of them are ___, which is said to be ___ as they are almost ___. The 23rd pair (__/__) determines ___.

nucleus, 23, 46 (23 pairs), autosome, homologous, identical, XX/XY, sex

What is a chromosome, DNA and gene?

A chromosome is consisted of a DNA molecule that wraps around histone proteins and folds into a compact structure.

DNA of a single chromosome is one long continuous double-stranded molecule.

Genes are segments of DNA which will code for protein.

What is the sequence of chromosomal organisation in eukaryotes?

DNA → Nucleosome → Solenoid → Chromatin Loop → Rosettes of Chromatin loops → Mitotic Chromosome

Describe level 1 in sequence of chromosomal organisation in eukaryotes.

Level 1: DNA Double Helix - Each chromosome contains a long, double-stranded DNA molecule, which requires further packaging to fit in nucleus.

Describe level 2 in sequence of chromosomal organisation in eukaryotes.

Level 2: Nucleosomes - Nucleosome is the basic structure when DNA wraps around histone proteins and is made up of DNA duplex coiled around 8 histone proteins every 147 base pairs (bp). Histones are positively charged and strongly attracted to negative charged phosphate groups of DNA. Nucleosomes wrap into higher order coils → solenoids.

Describe level 3-6 in sequence of chromosomal organisation in eukaryotes.

Level 3: Solenoid - The nucleosomes are further coiled into a solenoid.

Level 4: Chromatin loop - This solenoid is then organised into looped domains

Level 5: Rosettes of chromatin loop - Final organisation is unknown, but it appears to involve further radial looping into rosettes around a pre-existing scaffolding of protein.

Level 6: Mitotic chromosome - Highly condensed chromosome before cell divides.

Cell cycle: 1st gap phase,G1, involves ___ & ___ for ___ ___. During S phase, a ___ of the ___ is ___. 2nd gap phase, G2, prepares cell for ___. During ___, ___ ___ are ___. ___ ___ the cell into two cells with ___ ___.

growth and preparation for DNA synthesis, copy of genome is synthesised, mitosis, mitosis, replicated chromosomes are partitioned, Cytokinesis divides, identical genomes

Interphase: a period between ___ ___ and is the period of time when the cell ___ and ___ in ___ ___ ___ and can extend for days/weeks (while __ phase lasts for about __ hour in mammalian cells).

cell division, grows and engages in diverse metabolic activities, M phase, 1 hour

G1 phase: Cell ___ and ___ ___ ___ ___, organelles ___.

S phase: ___ of ___ to form ___ ___.

G2 phase: Cell ___ and ___ for mitosis

M phase: further divided into 2 stages: ___ & ___.

grows and carries out normal metabolism, duplicate;

replication of DN, sister chromatid

grows and prepares

mitosis & cytokinesis

Mitosis is the process of ___ ___ to produce __ ___ cell identical to ___ cell and is important for the ___ and ___ of an organism. Cytokinesis ___ ___ the cell into 2 daughter cells with ___ ___.

cell division 2 daughter cells, parent, growth and maintenance , physically splits, identical genomes

Phases of mitosis: ___→ ___→___→ ___→___.

PPMAT: Prophase, Prometaphase, Metaphase, Anaphase, Telophase

Prophase: ___ ___ and become ___, and appear as __ ___ ___ held together at the ___. ___ is ___; ___ and ___ are ___; ___ ___ breaks down; ___ ___ assembles (not in plants). __ ___ move to ___ ___ forming ___ ___ and ___ array of ___ (___) begins to form.

Chromosomes condense, visible, 2 sister chromatids, centromere; Cytoskeleton is dissembled; Golgi and ER are dispersed; Nuclear envelope, Mitotic spindle; 2 centrioles, opposite poles, radial, microtubules (asters)

Prometaphase: Chromosome ___ to ___ at the ___. Each chromosome is oriented such that the ___ of ___ ___ are ___ ___ ___ from ___ ___. Chromosomes move to ___ of cell.

attaches, microtubles, kinetochores, kinetochores of sister chromatids attached to microtubles from opposite poles, equator

Metaphase: All chromosomes are aligned at ___ of the cell called ___ ___and are attached to ___ ___ and are ___ ___.

equator, metaphase plate, opposite poles, under tension

Anaphase: ___ (___) holding ___ of ___ ___ are ___, ___ ___ ___. ___ ___ are ___ to ___ ___ (Anaphase A); ___ ___ ___ ___ (Anaphase B).

Proteins (cohesins), centromeres of sister chromatids are degraded, freeing individual chromosomes; Sister chromatids are pulled to opposite poles; Spindle poles move apart

Telophase: ___ ___ ___: