Cell Division & Mitosis

RUSSELL BIOLOGY

RHODES AP BIO

Multicellular organisms are made of cells and cell products

Multicellular organisms have divided from a single cell

Most cells are specialized

Regeneration is a limited property

Cells must form 3-D organism with specialized tissues in specific locations

Zebra fish (Danio rerio) grows new fin when attacked by Knifefish (Notopterus notopterus)

10.1 Overview: The Cycle of Cell Growth and Division

STEPS

Cell growth and everyday activity like making proteins from accessible DNA regions called genes and making of new organelles and structures

DNA replication

DNA (chromosomes) segregated into equal parts; even distribution

DNA moved into two new nuclear regions

Cytoplasm divided; fairly even distribution

2 new cells; genetically identical to each other and the parent

PURPOSES

Growth

Maintenance

Repair

Reproduce

Concepts DNA is chemical that stores information

Genes are regions of chromosomes that code for proteins

A-T, C-G (Purines and pyrimidines)

Double helix

Chromosomes are individual and linear

Replication

Chromosomes that have replicated are called sister chromatids and are joined at kinetochores by centromeres, forming arms

Cell division is used for

Growth = larger organisms

Replacement = due to wear and tear

Repair = to fix wounds

Reproduction of single celled eukaryotes

Duplicates

Chromosomes are replicated

Cells produced are identical genetically to each other AND to the cell produced

In meiosis cells generated have potential to be genetically different and contain ½ the DNA of the parent cell = gametes

Partitioning of Chromosomes

2 copies of each chromosome = Diploid;

These are homologous meaning they have the same genes in the same positions and sequences

1 copy of each chromosome = haploid

“ploidy “ refers to chromosome sets

Chromosomes replicate into sister chromatids ( for a phase there are 4 of each)

Sister chromatids move apart in Segregation

Each cell gets one of each set of chromatids; pairs of homologous chromosomes creating CLONES

10.2 Overview: The Mitotic Cell Cycle Cell Cycle = Interphase + Mitosis + Cytokinesis

Interphase

Between NUCLEAR divisions

Phases of Mitosis

Prophase

Prometaphase

Metaphase

Anaphase

Telophase

Cytokinesis

Animal cells “furrow” with a band of microfilaments pinching the cell into two

Plant cells deposit material for new cell wall starting at midpoint

Concepts

Chromatid

Kinetochore

Spindle

Centrosome

centriole

Microtubules

Metaphase plate (plane)

Segregation

Page 207

Interphase = between divisions G1 = chromosomes as chromatin, dark nucleus, everyday protein synthesis; cell growth

S= synthesis or REPLICATION of DNA; chromosomes are sister chromatids

G2 = cohesions; centrosomes have replicated; new organelles

G0 = sometimes cells are suspended and won’t divide again (not the typical scenario)

Mitosis= division of eukaryotic nucleus Prophase= chromosomes visible (chromatids); nucleus disintegrating;

centrosomes moving and creation of spindle occurring Prometaphase= nucleus gone, spindle formed; kinetochores attached to spindle; tugging starts to

move chromosomes to metaphase plane

Metaphase= chromosomes aligned at spindle midpoint

Anaphase= kinetochores separate and chromatids/ now chromosomes move toward poles along the spindle microtubules; cohesions are cut

Telophase= two separate nuclei (piles of chromosomes at the poles) now begin to uncoil and become chromatin, nuclei are rebuilt; cytokinesis has started; clones will be created

Cytokinesis= physical division of cytoplasm Animal = cleavage furrow

Plant= cell plate

10.3 Overview: Formation and Action of the Spindle

Plant cells

No centrosomes – spindle forms around nucleus

Animal cells

Centrosomes divide and two parts move apart

Microtubules form creating the spindle

Kinetochore microtubules

Pole to kinetochore of chromosome

Motor proteins of kinetochore WALK chromosome along microtubule

Motor proteins at poles pull kinetochore microtubules

Movement is species and cell-type specific

Anaphase

Non-kinetochore microtubules

Pole to overlap region at metaphase plane without chromosomes

Overlap region is reduced and cell lengthens

10.4 Overview: Cell Cycle Regulation Check points for starting critical phases

Internal check points

Cyclin and cyclin dependent protein kinases (Cdk)

Cyclin + phosphate (phosphorylation) = Cdk

Initiate or regulate 4 key events

G1, G1/S, S and M

External check points

Surface receptors and binding sites for proteins

Growth hormones, peptide hormones, surface groups, matrix

Speed/ slow/ stop

Contact inhibition

Cancer

Control of cell cycle is lost, continuous and uncontrolled growth of cells = mass

oncogenes

SEE PAGE 217 Control proteins called Cyclins regulate function of many checkpoints

Cyclins are proteins (work based on concentration) and Cdk are enzymes (function when phosphorylated and connected to cyclin) and cause action to occur

1. G1/S checkpoint

Cell is stopped ; waiting for extracellular signals, checking for DNA damage; needs growth factor to procede.

MAIN check point; once past G1/ S committed to mitosis

2. G2/M checkpoint

Stopped before Mitosis if DNA didn’t replicate

Insure identical daughter cells

3. Mitotic Spindle checkpoint

Check at metaphase to see if chromosomes and kinetochores attached to spindle; insures even distribution of DNA

MPF Maturation Promoting Factor

10.5 Overview: Cell Division in Prokaryotes

Replication of DNA caused by enzymes

Two circles of DNA migrate to opposite ends of cell

Move as they are attached to CM and cell is elongating

CW grows inward to create two cells

“ Theta replication”

“Binary fission”