Mitosis and Cell Division

Binary fission

simple process that bacteria use to copy their cells

Binary fission: step 1

cell replicates its DNA / chromosome

Binary fission: step 2

the cytoplasmic membrane elongates and separates DNA molecules / copies of ribosomes are made

Binary fission: step 3

cross wall and plasma membrane start to form

Binary fission: step 4

cross wall and plasma membrane form completely

Binary fission: step 5

daughter cells are produced

Some cells divide all the time

cells on surface like skin and mucous are constantly being shed from the body and need to be replaced so that cells in these tissues are always dividing to replace the lost cells

Some cells divide when signaled to divide

some cells in organs like the liver don’t normally divide, but may be triggered to divide if the organ is damaged

Some cells don’t usually divide

most cells in the nervous tissue of humans don’t divide / for example: nerve damage in the spine can’t be repaired because the nerve cells aren’t dividing

Two major parts of the cell cycle

interphase: growth phase consisting of G1, S, and G2 / mitosis and cytokinesis: dividing phase consisting of prophase, metaphase, anaphase, and telophase

Gap 1 (G1)

1st phase of interphase, cells are active and functioning, cell growth occurs, all cell content is copied except for DNA

G1 checkpoint

checkpoint conditions: cells large enough to divide, signals tell cell to divide, cells must have nutrients, DNA is in good condition

Synthesis (S)

cells copy their DNA, copied DNA proceeds to G2

Gap 2 (G2)

work done in S phase is checked

G2 checkpoint

checkpoint conditions: DNA not damaged, all chromosomes copied, signals tell cell to proceed to mitosis

Diploid (2n)

cells contain pairs of homologous chromosomes / humans: 46 total chromosomes

Haploid number (n)

cell contains one homolog / humans: 23 pairs of chromosomes

Sister chromatids

two exact copies attached to each other at centromere

Mitotic spindle

made of microtubules, microtubules work with dynein motor to move structures in cells, dynein and other proteins form protein clusters (kinetochores), motor proteins walk along microtubules to move chromosomes within cell

Kinetochores

protein clusters that attach to replicated chromosomes at the centromeres

Prophase

chromosomes coil up and become visible, nuclear envelope breaks down for spindle to reach into cell center, mitotic spindle attaches to chromosomes, nucleoli break down and become invisible

Metaphase

cells organize chromosomes by lining them up in the middle of spindle, checkpoint present to make sure all chromosomes are attached to spindle, cells cannot continue until it passes M-checkpoint

Anaphase

replicated chromosomes separated so each sister chromatid can go to opposite sides of cell, chromatids are separated carefully so each new cell gets one, separated chromatids are called chromosomes

Telophase

chromosomes uncoil and become invisible, nuclear membrane reforms, spindle breaks down, nucleoli reform and becomes visible

Cytokinesis

separation of cytoplasm, forms two distinct cells after chromosomes separate and nuclear membrane reforms, occurs differently in plant and animal cells since plants have cell walls

Cytokinesis: animal cell

a contractile ring forms that constricts the cell inward, called a cleavage furrow

Cytokinesis: plant cell

a plate forms down the middle that separates the cell into two

Euchromatin

less condensed and used

Heterochromatin

more condensed and not used

Cdks

cyclin-dependent kinases

Cyclins

proteins that regulate progress of eukaryotic cells through cell cycle, amounts increase and decrease during cell cycle, bind to partner proteins (cdks), binding to cdks forms activated complexes that trigger events in cell cycle

Cyclins in G1

cyclins bind to cdks and form a complex, complex triggers cells to get chromosomes ready for replication

Cyclins in S

cyclins bind to cdks and form complex (S-phase promoting factor), promoting factor enters nucleus and helps trigger DNA replication

Cyclins in G2

cyclins bind to cdks to form M-phase promoting factor / promoting factor triggers: spindle formation, nuclear envelope breakdown, condensation of chromosomes, triggers a process that separates sister chromatids during M-phase

Cyclins at the end of a phase

destroyed so the phase ends and a new one starts