[BOTAONE-LE2] cell division

Cell division

is an integral part of the cycle, the life of a cell from formation to its own division.

The ability of organisms to reproduce best distinguishes living things from non-living matter.

The continuity of life is based upon the reproduction of cells or cell division.

Unicellular organisms

Division of one cell reproduces the entire organism.

Multi cellular eukaryotes

• They depend on cell division for the development of a fertilized cell, growth, and repair.

Meiosis & mitosis

2 types of cell division

Mitosis

retains the number of chromosomes in the dividing cells.

Meiosis

reduces the chromosome # of the dividing cells into half.
→ E.g. from diploid (2n) to haploid (n)

Binary fission

In prokaryotes, An asexual type of reproduction where DNA is copied and the cell splits. Usually for bacteria

Chromosomes

DNA in cells is divided into long chains called..

Histones

What is wrapped around chromosome DNA to organize it

Nucleosome

What is the unit of DNA wrapped around histones called

• simplest packing strand of DNA

• 146 bp (base pair) DNA wrapped around histone octamer

chromatin

“thin” genetic material

• chromosomes are spread out & not identifiable

Sister chromatids

• At the start of mitosis they condense & take the form shown

• The replicated chromosomes stay together and are called

• are attached at the centromere by proteins called cohesins

• The other side of the centromeres contain other proteins called kinetochore

Interphase

A cell performs all of its regular functions & gets ready to divide

> metabolic activity is very high

The longest out of all the cell cycles

interphase, G0, G1, S, G2

the cell cycle

G1 (Gap)

cells are recovering from an earlier cell division and are synthesizing components for cell growth and DNA synthesis.

S (Synthesis)

- DNA replication occurs

G2 (Gap)

cells are making gure all the DNA was replicated correctly.

(checking)

→A little more growth, the chromosomes start to undergo condensation, becoming tightly coiled

MITOSIS

for growth, development, and repair

Asexual reproduction (yields genetically identical cells)

Occurs in somatic (body) cells

Is divided into four phases:

Prophase, Metaphase, Anaphase, Telophase

Prophase

• Chromosomes shorten and become visible.

• Centrioles move to opposite sides of the animal cell.

• Nuclear envelope disappears

• Spindle Apparatus begins to form.

Metaphase

• Chromosomes line up along the center of the cell called the "metaphase plate"

• Chromosomes attach to spindle fibers.

• Spindle fibers are now clearly visible.

Spindle Apparatus

consists of two distinct sets of microtubules.
→ Each set extends from one of the cell poles.
→ Two sets overlap at the spindle equator.
Moves chromosomes during mitosis.

Phragmoplast

In animal spindle fibers originate from centrioles. in plant cells, what forms like a scaffold for cell plate assembly

G1

Any cell that is going to divide must enter this phase

• This is the period before DNA synthesis begins

• G stands for gap and the number refers to the gap between cell division and DNA synthesis

• Here the cell makes ER, ribosomes, and cytosol to make 2 functional cells

• before a cell starts dividing, the chromosomes are duplicated

• This process produces sister chromatids

• Homologous chromosomes are identical pairs of chromosomes.

• One inherited from mother and one from father

• made up of sister chromatids joined at the centromere.

What are the 3 main points to describe the structure of chromosomes

chromatid, kinetochore, microtubules, sister chromatid, chromosome, centromere

Parts of a chromosome (5-6 enumerate)

G2

This phase spans the time from the completion of

DNA synthesis to the onset of cell division

• Following DNA replication, the cell spends about

2-5 hours making proteins prior to entering the M phase

Function of proteins works: as enzymes

M phase

This is the process that separates the duplicated sister chromatids of the parental cell into 2 nuclei

Mitosis refers specifically to the division of the nucleus of the cell

preprophase band

The orientation of the division plane is determined by a band of cytoskeletal elements called the ..

• In plant cell instead of centrioles they have thickening of cytoplasm (guide for cell division)

Prophase

• nuclear membrane disintegrates

• nucleolus disappears

• chromosomes condense

• mitotic spindie begins to form between centrioles

• kinetochores begin to mature and attach to spindle

nucleus disappears

Nuclear membrane disappears in plant cells

Metaphase

kinetochores attach chromosomes to mittic spindle and align them along metaphase plate at equator of cell

Anaphase

• When the cell divides, the sister chromatids separate

• Two daughter cells are produced

• Each has a complete and identical set of chromosomes

• kinetochore microtubules shorten, separating chromosomes to opposite poles

• polar microtubules elongate, preparing cell for cytokinesis

Vesicles containing cell wall material

Cell plate formation

New cell wall

Then finally daughter cells

In plant cells they conduct telophase like:

(note: that there will be a size difference)

Telophase (cytokinesis)

• Nuclear envelope forms around both sets of chromosomes.

• DNA uncoils

• Spindle and Astral fibers completely disappear

• Cytokinesis happens with most (but not all) cells Cytoplasm and organelles move (mostly equally) to either side of the cell.

• Cell membrane "pinches" to form two separate cells.

Meiosis

Similar in many ways to mitosis.

Several differences

Occurs only in sex cells

Yields gametes (= eggs and sperm or spores)

Involves two cell devisions (meiosis 1 & 2)

Results in four haploid cells

Leads to genetic variations

Meiosis 1 (prophase 1, metaphase 1, anaphase 1, telophase 1)

First cell division for gametes

Meiosis 2 (prophase 2, metaphase 2, anaphase 2, telophase 2)

Second cell division for gametes

MEIOSIS I: PROPHASE I

Synapsis and crossing over occurs

Areas of homologous chromosomes connect in areas called chiasmata.

Synapsis

pairing of homologous chromosomes

Crossing over

exchange of segments of homologous chromsomes

MEIOSIS I: METAPHASE I

Alignment of pairs of homologous chromosomes at the metaphase plate.

MEIOSIS I: ANAPHASE I

Splitting of the pairs of homologous chromosomes and subsequent movement to opposite poles

MEIOSIS I: TELOPHASE I

Cytokinesis results in two haploid cells (n)

MEIOSIS II

• DNA does not double

• Stages occur like regular mitosis (Prophase Il, Metaphase II, Anaphase Il, Telophase Il)

• Cytokinesis results to four haploid cells (n)

• Cells are not identical in this phase due to the crossing over that happened during meiosis 1.

CELL CYCLE CONTROL SYSTEM

the cell cycle appears to be driven by specific chemical signals present in the cytoplasm.

The sequential events of the cell cycle are directed by a distinct cell cycle control system, which is similar to a clock.

The clock has specific checkpoints where the cell cycle stops until a go-ahead signal is received.

complete the S, G2, and M phases and divide.

If a cell receives a go-ahead signal at the G1 checkpoint, it will usually….

exit the cycle, switching into a nondividing state called the G0 phase

If the cell does not receive the go-ahead signal, it will

Cyclins

Cyclin dependent kinases (Cdks)

Two types of regulatory proteins are involved in cell cycle control:

Cyclins

• Proteins produced in synchrony with the cell cycle.

• Regulate passage of the cell through cell cycle checkpoints.

Cyclin-dependent kinases (Cdks)

• Enzymes that drive the cell cycle

• Activated only when bound by a cyclin

• The activity of this regulatory progein rises and falls with changes in concentration of its cyclin partner

Malnutrition-promoting factor (MPF)

• Is a cyclin-Cdk complex that triggers a cell's passage past the G2 checkpoint into the M phase.