Cell Cycle

cell cycle components

1. interphase (G1, S, G2)

2. mitotic phase (mitosis, cytokinesis)

mitosis function

growth & repair, asexual reproduction

mitosis in prokaryotes is called

binary fission

mitosis occurs in

somatic cells

in mitosis, a … cell splits into two … cells

diploid, identical & diploid

mitosis technical definition

separation of replicated chromosomes and thus the division of nuclei

cytokinesis technical definition

division of cytoplasm

interphase overview

• first step of cell cycle, 90% of cell’s lifespan

• the phase in between divisions

• growth stage

G1 phase of interphase

• primary growth phase, typically the longest

• grows, absorbs nutrients, metabolic functions

• organelle replication

S phase of interphase

• DNA replication

• short phase

G2 phase of interphase

• shorter growth phase, prepares for mitosis

G1 checkpoint

• after G1

• checks for DNA damage, nutrients, growth factors/signals

G2 checkpoint

• right before G2, after S

• checks for proper DNA replication/integrity

• if both G1 and G2 is passed, the cell may proceed to mitosis

malfunction of the checkpoints can lead to

unregulated cell division → cancer

early prophase

• chromatin condenses → chromosomes

• mitotic spindle begins to form and helps organize chromosomes

• nuclear envelope breaks down, nucleolus disappears

why use chromosomes and not chromatin directly?

more likely to be transferred without breaking down; evolutionary advantage

mitotic spindle structure

• consists of microtubules (polymers of proteins) that originate from a pair of centrioles in a centrosome

late prophase/prometaphase

• mitotic spindle aligns the chromosomes; attaches to the kinetochores, a patch of protein at the centromere (the area where sister chromatids attach)

• not all spindles bind to chromosomes

metaphase

• chromosomes are lined up at the center (metaphase plate/equator)

• spindle checkpoint: microtubules are properly aligned and attached to the 2 kinetochores per chromosome

anaphase

• sister chromatids pulled apart toward opposite ends (each is now its own chromosome)

• spindle contracts & elongates the cell

improper separation of sister chromatids is called

nondisjunction

telophase (reverse of prophase)

• mitotic spindle breaks down

• nuclear envelope reforms around the two poles

• chromosomes decondense

cytokinesis

• animal cells: a cleavage furrow (microfilaments) forms and splits

• plant cells: a cell plate forms and divides

meiosis occurs in

germ cells

meiosis function

sexual reproduction

meiosis produces four … cells from one … cell

haploid, diploid

prophase I

• chromosomes condense

• nuclear envelope breaks down

• homologous pairs of chromosomes join and form tetrads → recombination, increasing genetic variation

• spindle forms

metaphase I

• tetrads align across the metaphase plate

anaphase I

• each tetrad is separated from its homologue

telophase I & cytokinesis I

• cell divides into two haploid cells, each with differing DNA

• nuclear envelope reforms, chromosomes decondense

after meiosis I

some cells enter a rest phase/interphase II

meiosis II steps

• similar to mitosis

• due to recombination during prophase I, the four daughter cells are genetically different

spermatogenesis

• all daughter cells are viable sperm

• organelles are destroyed

oogenesis

• only 1 of 4 daughter cells are viable (this one receives the most cytoplasm/organelles)

• the other 3 are polar bodies that are reabsorbed

• mitochondrial DNA is inherited via matrilineal inheritance