cell division

dat bio ch. 5

what is the cell cycle in 2 steps

1. interphase

2. M phase

what are the 4 parts of interphase (in order)

G1, G0 , S, G2

Go Sam Go Make Cake

G - gap phase 1 (G1) of interphase

S - synthesis phase of interphase

G - gap phase 2 (G2) of interphase

M - mitosis of M phase

C - cytokinesis of M phase

G1 phase

cell grows in prep for cell division and checks for fav conditions; if favorable, then cell proceeds ot S phase

what happens during G0 (part of G1)

cell still carries out functions but not preparing for division

Cells that will not divide (e.g., neurons) are permanently in G₀.

To divide, cells must exit the G₀ stage and enter G₁

S phase

cell replicates its genome and centrosome

genome

all DNA in cell

centrosome

organelle that aids in cell division

G2 phase

• organelles replicated and DNA assessed for errors

  • checks mitosis promoting factor aka maturation promoting factor levels → sufficient amount needed to proceed to M phase

M phase

stage in cell cycle for karyokinesis and cytokinesis occur

types of karyokinesis in eukaryotes

• mitosis + meiosis

  • utilize microtubule organizing centers

prokaryotes perform………

binary fission

• genome replicates while cell division occurs (no S phase)

  • no microtubule organizing center

microtubule organizing centers

• centrosome → MTOC in animal cells; replicate during S phase so each daughter cell gets one

• form spindle apparatus, which guides chromosomes during karyokinesis

• centrosomes made of pair of centrioles

• pericentriolar material surrounds centrioles, responsible for microtubule nucleation

microtubules are made of …

tubulin

what are centrioles

hollow cylinders oriented at 90 degrees

• attached by interconnecting fibers

• made of 9 microtubule triplets (9×3 array)

cilia and flagella

made up of 9 microtubule doublets with two singlets in the center (9+2 array)

types of microtubule types

• polar

• astral

• kinetochore

polar microtubule type

connect centrosomes and push them to opposite sides of the cell

astral microtubule type

attach to cell membrane to orient centrosome

kinetochore microtubule type

attach kinetochore

during which phase of the cell cycle does DNA replication occur

S phase

cell cycle has functional limitations and cell-specific regulations to …

help prevent uncontrolled growth (cancer)

ex of functional limitations

• surface to volume ratio (S/V)

• genome to volume ratio (G/V)

surface to volume ratio

cell volume becomes too large for surface area of plasma membrane to support → decrease in S/V leads to cell division

genome to volume ratio

cell volume becomes too large for genome to support → decrease in G/V leads to cell division

ex of cell-specific regulations

• cell cycle checkpoints

• cyclin-dependent kinases (CDKs)

• growth factors

• anchorage dependence

• density dependence

• density dependent inhibition

cell cycle checkpoints

• G1 restriction - conditions are favorable to grow and eventually divide

• end of G2 - accurately replicated genome & sufficient MPF levels

• M checkpoint - microtubules properly attached to chromosomes

cyclin-dependent kinases

phosphorylate certain molecules in order to signal cell cycle progression

• activated by cyclin, a protein that cycles through stages of synthesis and degradation

growth factors

bind plasma membrane receptors to signal growth and cell division

anchorage dependence

cells divide only when attached to an external surface

density dependent inhibition

halting of cell division when cell density is too high

an increase in cyclin will ___ cell division

increase

genome

all DNA in the cell

chromatin

loosely winded DNA + protein complex

chromosome

separate DNA molecules that make up the genome

sister chromatids

identical copies of the same chromosome

dyad

identical sister chromatids joined to form an X shape

centromere

region connecting sister chromatids

kinetochore

proteins that associate with microtubules in cell division

stages of mitosis

1. prophase

2. metaphase

3. anaphase

4. telophase

5. cytokinesis

prophase

• chromatin condenses into chromosomes

• nucleolus and nuclear envelope disappear

• spindle apparatus forms

metaphase

spindle apparatus guides chromosomes to metaphase plate (midpoint of cell) in single file

prometaphase

prior to metaphase, nuclear envelope fragments and spindle apparatus attaches to kinetochores

anaphase

• kinetochore microtubules shorten to pull sister chromatids apart

  • sister chromatids are now considered individual chromosomes - chromosome count doubles

cleavage furrow

in animals, cytokinesis begins in late anaphase with the formation of __. contractile ring of actin microfilaments and myosin motors that pinches cell into two

telophase

• chromosomes have separated, nuclear membrane and nucleolus reforms

• chromosomes decondense into chromatin

  • spindle apparatus disappears

cytokinesis

→ completes once cells complete split

• in plant cells, __ only begins in telophase with the formation of a cell plate, ends up producing middle lamella

4

haploid

containng one set of chromosomes

diploid

containing tow sets of chromosomes, one from each parent

→ homologous chromosomes

homologous chromosomes

two different copies of the same chromosome in a diploid organism

mitosis vs meiosis

• mitosis: division of a diploid cell into two genetically identical diploid cells

• meiosis: two divisions of a diploid cell to produce four genetically distinct haploid daughter cells

meiosis is divided into

• meiosis I: homologous chromosomes separate

  • reductional division

• meiosis II: sister chromatids separate

somatic cells are…

diploid → 2n = 46

germ cells can…

divide via mitosis to form more diploid germ cells, or via meiosis to form haploid gametes

gametocytes are…

eukaryotic germ cells

gametes are…

haploid → n = 23

M1 - prophase I

• DNA condenses into chromosomes

• homologous chromosomes pair up/cross over & recombination occurs

• nucleolus and nuclear envelope disappear & spindle apparatus forms

synapsis (M1 - prophase I)

homol chromosomes pair up to form tetrads (aka bivalents)

synaptonemal complex

protein structure that forms between homologous chromosome during synapsis

chiasmata

site of crossing over leads to genetic recombination

• increases genetic diversity

M1 - metaphase I

• homologous chromosomes line up (double file) at the metaphase plate

• independent assortment increase genetic diversity

M1 - anaphase

homologous chromosomes are separated by shortening kinetochore microtubules

M1 - telophase I and cytokinesis

• the cytoplasm divides and two haploid cells form

• each chromosome is composed of two sister chromatids

• nuclear membrane and nucleolus reforms

M2 - prophase II

DNA condenses into chromosomes; spindle apparatus forms & nucleolus and nuclear envelope disappear

• NO CROSSING OVER

M2 - metaphase II

chromosomes line up (single file) at the metaphase plate

M2 - anaphase II

sister chromatids are separated by shortening kinetochore microtubules

• sister chromatids = individual chromosomes - chromosome count doubles

M2 - telophase II and cytokinesis

• cytoplasm divides and four haploid daughter cells form

• chromosomes decondense → chromatin

• spindle apparatus disappears, nuclear membrane and nucleolus forms

during what step of meiosis do homologous chromosomes separate from one another

anaphase I

During which stage of meiosis does the ploidy decrease from 2n to 1n?

a. meiosis I

b. meiosis II

meiosis I

how many chromosomes & chromatids are there in mitosis prophase

46; 92

how many chromosomes & chromatids are there in mitosis metaphase

46 ; 92

how many chromosomes & chromatids are there in mitosis anaphase

92 both

how many chromosomes & chromatids are there in mitosis telophase

92 both

how many chromosomes & chromatids are there in mitosis cytokinesis

46 both

how many chromosomes & chromatids are there in meiosis I prophase I

46 ; 92

how many chromosomes & chromatids are there in meiosis I metaphase I

46 ; 92

how many chromosomes & chromatids are there in meiosis I anaphase I

46 ; 92

how many chromosomes & chromatids are there in meiosis I telophase I

46 ; 92

how many chromosomes & chromatids are there in meiosis I cytokinesis I

23 ; 46

how many chromosomes & chromatids are there in meiosis II prophase II

23 ; 46

how many chromosomes & chromatids are there in meiosis II metaphase II

23 ; 46

how many chromosomes & chromatids are there in meiosis II anaphase II

46 both

how many chromosomes & chromatids are there in meiosis II telophase II

46 both

how many chromosomes & chromatids are there in meiosis II cytokinesis II

23 both

if a human cell undergoes mitosis, how many chromatids will be present in each daughter cell at the end of cytokinesis

46

karyokinesis

is the division of the nucleus, where one parent nucleus divides to form two daughter nuclei

cytokinesis

describes the division of the cytoplasm and cell membrane

During what phase of mitosis does cytokinesis begin in animal cells and plant cells, respectively?

Cytokinesis begins at the end of anaphase in animal cells. In contrast, cytokinesis starts in telophase in plant cells.

what structure cements neighboring plant cells together?

middle lamella