The Eukaryotic Cell Cycle, Mitosis, and Meiosis

Ch 16

Cell division

the reproduction of cells

Eukaryotic cells follow two different sorting processes

Mitosis and Meiosis

Mitosis

two daughter cells receive the same amount of genetic material as the mother cell

Meiosis

needed for sexual reproduction; cells that have two sets of chromosomes produce daughter cells with a single set of chromosomes

Omnis cellula e cellula

Every cell originates from another cell

Cell cycle

highly regulated series of events that leads to cell division

Cytogenetics

field of genetics involving microscopic examination of chromosomes

Cells getting ready to divide

chromosomes become compact enough to be seen with a light microscope

Karyotype

an individuals complete set of chromosomes; reveals number, size, and form of chromosomes in an actively dividing cell

• two copies of each chromosome are joined together

Sister chromatids

2 copies of each chromosome are joined together

Autosomes

not sex chromosomes

• same in both males and females

• each homolog nearly identical in size and genetic composition

eg - both carry gene for eye color but one may have brown and the other blue

Sex chromosomes

1 pair in humans (X,Y)

• XX (female)

• XY (male)

Diploid

contains two complete sets of chromosomes, one from each parent

(2n) - 23 pairs of chromosomes in humans

Haploid

contains a single set of unpaired chromosomes 

(n) - gametes have 1 member of each pair of chromosomes

Gametes

sperm and eggs

Homologs

members of a pair of chromosomes

Homologous chromosomes (pair)

derived from the same chromosome

Stages of the cell cycle

G1 - first gap

S - synthesis of DNA

G2 - second gap

M - mitosis and cytokinesis

G1 phase

• cell growth occurs

• signaling molecules can cause cells to accumulate molecular changes that promote progression through the cell cycle

• gaining ATP

S phase

• chromosomes replicated to form a pair of sister chromatids

• after rep, a cell has twice as many chromatids as the umber of chromosomes in G1

• G1 = 46 chromosomes —> G2 = 92 chromatids

G2 phase

cell synthesizes proteins (ATP) needed for chromosome sorting and cell division; some growth may occur

M phase

mitosis and cytokinesis

Mitosis

division of one cell nucleus into two distributing duplicated chromosomes so that each daughter cell receives the same complement of chromosomes

(makes identical body cells)

Cytokinesis

follows mitosis to divide the cytoplasm into daughter cells

Cell cycle length

• several minutes in quickly growing embryos

• several months in slow-growing adult cells

• for fast dividing mammal cells (skin cells) - 10-24 hours

Cell dividing in 24 hours

• G1 - 11 hours

• S - 8 hours

• G2 - 4 hours

• M phase - 1 hour

Why divide?

Internal factors: cell cycle control molecules and checkpoints

External factors: environmental conditions, signaling molecules

Cyclins or cyclin-dependent kinases (cdks)

• responsible for advancing a cell through the phases of the cell cycle

• amount of cyclins varies through cycle

• cdks are kinases controlling cell cycle

  • must bind to a cyclin to be active

Three cell cycle checkpoints in eukaryotes

• G1 checkpoint (restriction point)

• G1 checkpoint

• Metaphase checkpoint

Checkpoint proteins

act as sensors to determine if the cell is in proper condition to divide

G1 checkpoint (restriction point)

proteins determine if conditions are favorable for cell division; search for DNA damage

G2 checkpoint

check for DNA damage and ensure that all of the DNA has been replicated; monitor the levels of proteins needed to advance through mitosis

Metaphase checkpoint

monitor the integrity of the spindle apparatus, prevents cells from incorrectly sorting their chromosomes during cell division

Progesterone

Mitotic spindle

responsible for organizing and sorting chromosomes during mitosis

• composed of microtubules

Centrosomes

organize the mitotic spindle and help regulate cell division

Micotubules

formed from tubules

3 types:

• astral - emanate away from region between the poles

• polar - project into the region between the poles

• kinetochore - attached to kinetochores of sister chromatids

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