Ch 10: Cell Division

what are the 2 functions of cell divisions?

1. growth, maintenance, and repair of cells and tissues

2. single-celled organisms use cell division to reproduce

prokaryotic genome

• consists of 1 double-stranded circular DNA molecules

  • resides in nucleoid

• additional smaller loops of DNA called plasmids may be present

  • not necessary for normal growth (non-essential)

  • may have important information for cell function

  • exchange of plasmids with other cells allows gene transfer in prokaryotes (in same generation → cell division may not be necessary)

eukaryotic genome

• consists of several double-stranded DNA molecules in the form of chromosomes

• stored in nucleus

the number of chromosomes in the cell nucleus varies among _______

species

true or false. within a species, chromosome number is consistent, but may vary with developmental stage or specific cell type

true

somatic cells

typically have 2 matched sets of chromosomes

• diploid (2n)

• 1 set of homologous chromosomes from each parent

  • nearly completely identical (<1% difference)

• X and Y chromosomes are not homologous in humans

  • heterologus

gametes

have half the number of chromosomes (23)

• eggs and sperm cells

• haploid (1n)

eukaryotic DNA must be __________ into compact chromosomes to fit into the ________

condensed, nucleus

organization of eukaryotic chromosomes from loose to tight

DNA double helix, DNA wrapped around histone, nucleosomes coiled into a chromatin fiber, further condensation of chromatin, duplicated chromosome

which is accessible: euchromatin or heterochromatin?

euchromatin

packaging of eukaryotic chromosomes

• short stretches of DNA wrap around a core of 8 histone proteins

• histone DNA complex and connecting DNA (string)

• this structure coils to form a chromatin fiber

• fibrous proteins further pack each chromosome

histone DNA complex

nucleosome

connecting DNA (string)

linker DNA

true or false. eukaryotic DNA must be condensed into compact chromosomes to fit into the nucleus

true

how much DNA is a cell?

6 ft

cell cycle order:

G1, S, G2, Mitosis, Cytokinesis

cell cycle 2 major phases

interphase and mitotic phase

interphase has 3 parts

G1, S, G2

G1 Phase (first gap)

change is not evident but cell is accumulating resources and energy

S Phase - DNA synthesis occurs

• identical copies of DNA molecules (sister chromatids) are joined at the centromere fibers

• centrosomes produce mitotic spindles to move chromosomes

• in animal cells centrosomes are associated with centrioles

  • help organize cell division

G2 Phase (second gap)

• energy is replenished

  • organelles reproduce and cytoskeleton breaks down

what is the first step in the mitotic phase?

karyokinesis: nuclear division

what is the second step in mitotic phase

cytokinesis: cytoplasmic components physically separate into 2 daughter cells

prophase

• nuclear envelope breaks down

• membranous organelles (ex. golgi complex, endoplasmic reticulum) disperse to edge of cell

• nucleolus disappears

• centrosomes being migration to poles

• microtubules of spindle form and push apart

• sister chromatids coil tighter

  • aided by condensin proteins

what stage does the nuclear envelope break down?

prophase

what stage do the membranous organelles disperse to the edge of the cell?

prophase

what stage does the nucleolus disappear?

prophase

what stage do centrosomes begin migration to poles, microtubules of spindle form push apart, and sister chromatids coil tighter?

prophase

prometaphase

• sister chromatids develop a protein kinetochore in the centromeric region

  • attaches chromatids to spindle microtubules

• polar microtubules contribute to cell elongation

what causes the cell to elongate in prometaphase?

the overlapping microtubules interacting with each other

what stage do the sister chromatids develop a protein kinetochore in the centromeric region?

prometaphase

what stage do the polar microtubules contribute to cell elongation?

prometaphase

metaphase

• chromosomes line up along metaphase plate

• sister chromatids remain attached by cohesion proteins

  • maximally condensed

what stage do the chromosomes line up along the metaphase plate?

metaphase

in what stage are the sister chromatids still attached by cohesin proteins?

metaphase

anaphase

• cohesin proteins degenerate

  • chromatids separate

• separated sister chromatids move in opposite directions toward centrosomes

• cell elongates

what stage do cohesin proteins degenerate and chromatids separate?

anaphase

what stage do the separated sister chromatids move in opposite directions toward the centrosomes, making the cell elongate?

anaphase

telophase

• chromosomes reach opposite poles and begin to decondense

• spindles depolymerize into tubulin monomers that will form cytoskeletal repurposed components for daughter cells

• nuclear envelopes form around the chromosomes

• nucleosomes appear within the nuclear area

what stage do the chromosomes reach opposite poles and begin decondense?

telophase

what stage do the spindles depolymerize into tubulin monomers that will form cytoskeletal repurposed components for daughter cells

telophase

what stage does the nuclear envelope form around the chromosomes and nucleosomes appear within the nuclear area?

telophase

cytokinesis in animal cell

• forms cleavage furrow to separate into 2 daughter cells

  • cleavage furrow contains actin filament

cytokinesis in plant cell

vesicles forming cell plate → wall to create 2 daughter cells

G₀ Phase

• cells not actively preparing to divide (quiescent)

• influenced by environmental or growth factors

• cardiac muscle cells and central nervous system cells remain here permanently