Ch. 7: Cell Division Flashcards
2 phases of cell division
nuclear division (mitosis/ meiosis) and cytokinesis
First step in mitosis/ meiosis
condensation of chromatin into chromosomes
Chromosome
2 identical sister chromatids joined at centromere
each chromatid consists of single tightly coiled DNA
Diploid vs. Haploid cell
diploid: 2 copies of every chromosome (2n)
haploid: 1 copy of every chromosome (n)
M phase
mitosis and cytokinesis
Prophase (mitosis)
first stage of mitosis
nucleoli disappear and chromatin condenses into chromosomes
nuclear envelope breaks down
mitotic spindle forms: microtubules develop from MTOCs and connect to centromeres at kinetochore
Metaphase (mitosis)
second stage of mitosis
chromosomes align at metaphase plate
ends when microtubules at kinetochores pull chromosome apart into two chromatids (chromosomes)
Anaphase (mitosis)
third stage of mitosis
sister chromatids pulled apart to opposite poles
microtubules not attached to chromosomes push poles farther apart to elongate cell
Telophase (mitosis)
fourth (final) stage of mitosis
nuclear envelope is restored around each pole, nuclei form and chromosomes disperse into chromatin
Mitotic spindle
fibers of microtubule proteins that form during prophase
consist of: spindle microtubules, centrosome, asters
attach to chromosomes at kinetochore to assist in their movement
Kinetochore
structure of proteins on centromere of DNA chromosome
attachment site for microtubules and move chromosome to pole from which the microtubules extend, opposite pole attaches and starts tug-of-war
Cell plate
cytokinesis in plants
vesicles originating from Golgi bodies migrate to plane between the two newly forming nuclei, membranes of vesicles fuse to form two new plasma membranes and the contents form cell plate, which develops into the new cell wall
Cleavage furrow
actin filaments between two newly forming nuclei shorten and act like purse strings to pull plasma membrane to center, forming a groove = cleavage furrow to split the two cells
Interphase
3 stage growth: G1, S, G2
G1: cell growth
S: DNA synthesis (make 2 chromatids)
G2: all materials for next mitosis prepared, cell growth
Meiosis
meiosis I (homologous chromosome pairs) and meiosis II (chromosomes/ chromatids)
Prophase I (meiosis)
begins like prophase in mitosis: nucleolus disappears, chromatin condenses to chromosomes, nuclear envelope breaks down and spindle forms
homologous chromosomes pair with each other in synopsis, during which crossing over can happen at region called chiasmata
Metaphase I (meiosis)
homologous chromosome pairs align at metaphase plate, microtubules from each pole attach to kinetochore and pull homologous pairs apart
Anaphase I (meiosis)
homologues uncouple as they’re pulled to opposite poles
Telophase I (meiosis)
new nuclei form and new cells form and all that jazz
daughter cells haploid
Mitosis is similar to which process in meiosis
meiosis II
its literally the same thing except no replication so result are haploid (1 chromosomes in each)
Types of genetic recombination (3)
crossing over, independent assortment of chromosomes, joining of gametes
Crossing over
only in meiosis I
during prophase I, nonsister chromatids of homologous chromosomes exchange pieces of genetic material
Independent assortment of homologues
during metaphase I, homologues of each pair of homologous chromosomes go to opposite poles, the separation is random for each homologous pair
Joining of gametes
bc sexual reproduction requires gametes of two individuals, new combos are created
which sperm fertilizes the egg is random (faster swimmer)
Surface-to-volume ratio (cell limit)
want large S:V ratio
as cell grows, volume increases faster than surface area so it limits how much the cell can grow to efficiently be able to support diffusion of oxygen in and waste out
Genome-to-volume ratio (cell limit)
chromosomes in nucleus (genome) control cell by producing substances that make enzymes and molecules to regulate cell… when cell grows, volume increases but genome stays same size so limits how much cell can grow
Regulation of cell cycle
at specific points of cell cycle, cell evaluates internal and external conditions to determine whether to go through
think border control/ airport security
G1 checkpoint
at end of G1 phase
quality of DNA evaluated, if can’t be repaired then cell performs apoptosis (death), if nutrients missing G1 phase might be extended to get proper conditions
G2 checkpoint
at end of G2 phase
evaluates accuracy of DNA replication and signals whether or not to start mitosis
M checkpoint
during metaphase
ensures that microtubules are properly attached to all kinetochores at metaphase plate before division c continues w/ anaphase (and non-disjunction occurs)
Cyclin-dependent kinases (CDKs) (internal cell cycle regulation)
proteins responsible for advancing cell past checkpoints and through cell cycle
- CDKs are kinases: phosphorylate other proteins to activate
- CDKs activated by cyclins: cyclins attach to create conformational change
Mitosis-promoting factor (or maturation-promoting factor) (MPF)
cyclin-CDK complex that advances the cell through G2 checkpoint
each checkpoint has its specific CDK that advances it through
Growth factors (external cell cycle) regulation
plasma membranes have receptors for growth factors that stimulate cell to divide
Ex: platelet-derived growth factor (PDGF)
Density-dependent inhibition (external cell cycle regulation)
cells stop dividing when surrounding cell density reaches certain max
Ex. petri dish
Anchorage dependence (external cell cycle regulation)
most cells only divide when they are attached to external surface, like flat surface of neighbor cell or petri dish
Cancer (cells)
uncontrolled cell growth and division: disease of cell cycle
transformed cells go on w/out checkpoints, density-dependent inhibition, anchorage dependence or any regulatory mechanisms
