Mitosis and Meiosis Flashcards
G1 Phase
Organelles/ other cyt. comp. replicate/ form.
Cell incr in size
S Phase
DNA duplicated and chromatids form within the nucleus
Histones produced
G2 Phase
Spindle proteins synthesised.
Chr checked for error and repaired as nec
Second growth phase
What does mitosis ensure regarding daughter cells?
Ensures daughter cells produced during cell division have exactly the same chr makeup as parent cell
How does mitosis differ from cytokinesis?
Mitosis is div of chr
Cyt is div of cell into 2 daughter cells
What does G1 check?
1: Cell reached crit size
2: Enough nutr avail for next stages to take place
3: Nec growth factors in place
4: No DNA damage
If req are met what happens?
And if not??
yes: S phase- DNA synth takes place
no: G0 resting phase
What does G2 check?
DNA rep (during S phase) has taken place acc and no DNA damage.
If all good mitosis happens
What is cancer?
Uncontr cell div- mitosis out of control
What does cancer inv in rel to mitosis?
Cannot enter G0- inv breakdown in ability to regulate checkpoints of cell to reg process of cell div
How does Vincristine work?
Inhibits the formation of microtub- binds to tubulin in microtub and stops spindle fibres contracting and pulling chromatids apart- prev ANAPHASE
How do antimetabolites i.e Fluouracil work?
S phase inhib- prev DNA synth i.e Fluouracil inhibits enzyme inv in making nucleotides that cont base thymine- prev DNA synth
When is the support of histones particularly important?
When chromatin condenses to form visible chr during nuclear div
How is a nucleosome formed?
Histone proteins folded into compact stacks and DNA coils tightly around stack to form this str
What is diploidy?
Situation in which a cell has 2 sets of chr i.e a pair of each type
What is haploidy?
Situation in which a cell has a single set of unpaired (non-homologous) chr
Why are homologous chromosomes not id?
But what is similar about them?
Carry the same genes in same seq along l. as partner chr does.
Not identical as alleles for small no. genes may differ in 2 chr
Prophase
Chromatin condenses to form chr
Centrioles in animal cells move towards opposite poles
Spindle begins to form
As each chr continues to condense, 2 chromatids joined at centromere become apparent
Nucleolus disappears
Nucl membr breaks down
Metaphase
chr consisting of 2 chromatids align along equator and join at centromeres to spindle fibres
Anaphase
Centromeres attaching 2 chromatids of each chr split
Contr of spindle fibres pull chr of sister chromatids apart
Sister chromatids move towards opposite ends
Telophase
Cleavage furrow forms in animals
Each chromatid now a sep chr
2 groups of chr reach opposite poles of cell
A new nuclear env forms around each group
Chr decondense and bec more visible
Nucleolus reappears
Spindle dis as its broken down
Describe difference between cytokinesis of animal and plant cells:
Animal: cleavage furrow forms as cell surf membr invaginates and eventually splits the cell in two
Plant: cell plate precursor to a new cell wall is laid down along the centre of the cell. GA plays imp role in syth mat needed in the form of the new wall
How does meiosis differ from mitosis?
Only takes place in reprod organs
Inv 2 div resulting in 4 daughter cells
Chr arrangements in daughter cells are both different from each other and different from the parent cell
Prophase I
As chr condense it becomes apparent that homologous chr have paired and lie alongside each other- each pair is known as a bivalent
Chromatids appears- chr in a bivalent are entwined at points called chiasmata
Chromatids may break @ chiasmata and rejoin with dif chromatids resulting in crossing over or recombination
