Cell Cycle & Division Biology I

Cell Division Cell Division: All cells are derived from preexisting cells (Cell Theory) Cell division is the process by which cells produce new cells Cell division differs in prokaryotes (bacteria) and eukaryotes (protists, fungi, plants, & animals) Cells grow in number, not in size. Reasons for Cell Division: Cell growth Repair & replacement of damaged cell parts Reproduction of the species How often do cells divide? Some cells must be repaired often such as cells lining the intestines, white blood cells, skin cells with a short lifespan. Other cells DO NOT divide at all after birth such as muscle, nerve cells, brain cells, female egg cells.

Chromosomes & Their Structure The plans for making cells are coded in their DNA. DNA, deoxyribose nucleic acid, is a long thin molecule that stores genetic information. DNA is organized into molecules called chromosomes.

Chromosomes & Their Structure Chromosomes are made of protein & a long, single, tightly- coiled DNA molecule visible only when the cell divides. When a cell is NOT dividing the chromosome (DNA) is less visible & is called chromatin.

Chromosomes & Their Structure Centromeres hold duplicated chromosomes together until they are separated in cell division. When DNA makes copies of itself before cell division, each half of the chromosomes is called a sister chromatid. –Each sister chromatid contains identical genetic information.

Chromosomes & Their Structure

Chromosome Numbers Humans somatic or body cells have 23 pairs of chromosomes or 46 chromosomes (diploid or 2n number) The 2 chromatids of a chromosome pair are called homologues (have genes for the same trait at the same location) Human reproductive cells or gametes (sperms & eggs) have one set or 23 chromosomes (haploid or n number) Every organism has a specific chromosome number OrganismChromosome Number (2n) Human46 Fruit fly8 Lettuce14 Goldfish94

Types of Reproduction Asexual Reproduction –Reproduction of cells involving only ONE parent. –The organism will make a copy of itself. Produces identical offspring. –Types: Binary Fission (bacteria) Mitosis (most eukaryotic cells) Vegetative propagation Budding

Binary Fission

Vegetative Propagation Form of asexual reproduction in plants. Part of the plant detaches from the parent plant to form their own organism. Genetically identical to parent.

Budding A form of asexual reproduction in the plant in which a new organism develops from an outgrowth of the parent. Genetically identical to the parent plant.

Types of Reproduction Sexual Reproduction –Reproduction that involves TWO parents –Produces offspring that are genetically diverse. –Happens in the sex cells (sperm and egg) which are called gametes.

Cell Cycle Mitosis -prophase -metaphase -anaphase -telophase G1G1 G2G2 S phase interphase

Cell Cycle The cell cycle includes 3 main parts: interphase, mitosis, and cytokinesis. –Mitosis = nuclear division –Cytokinesis = division of the cytoplasm

Interphase The longest stage of the cell cycle. Called the resting stage because the cell isn’t dividing. Consists of 3 stages: –G1: cell growth –S (synthesis): DNA synthesis –G2: prepare for cell division

Interphase 1. G 1 (gap) phase:  Main growth stage  Cell increases in size  Cell makes organelles 2. S phase:  Copying of all of DNA’s instructions (DNA Replication)  DNA in the form of chromatin (not visible) 3. G 2 (gap) phase:  Preparation time for mitosis/meiosis (cell division)  Cell continues growing  Needed proteins produced

Mitosis

Prophase Longest phase of mitosisLongest phase of mitosis Nucleolus disappears chromosomes sister chromatidsChromatin condenses into chromosomes, consisting of two sister chromatids. CentriolesCentrioles move apart (not found in plants). Spindle fibers centriolescentromeres.Spindle fibers form and attach from centrioles to centromeres. Nuclear membrane disappears.

Prophase late prophase early prophase centrioles spindle fibers centromere nuclear envelope disappearing aster fibers

Prophase Animal CellPlant Cell

Metaphase Shortest phase of mitosis Chromosomesmiddle of cellChromosomes line up across the middle of cell (center of cell – equator of cell). The centromere of each chromosome attaches to spindle fibers.

Metaphase metaphase plate centrioles spindle fibers aster fibers

Metaphase Animal CellPlant Cell

Anaphase Sister chromatidsSister chromatids separate and move apart. chromatids chromosomesAfter separation, chromatids are now considered chromosomes. chromosomesDuring this phase, the cell contains twice the normal number of chromosomes. elongateCell begins to elongate. At the end, there are equal numbers chromosomes of chromosomes at the poles.

Anaphase sister chromatidschromosomes No longer sister chromatids, now chromosomes centrioles spindle fibers aster fibers

Anaphase Animal CellPlant Cell

Telophase Nuclear membrane reappears. Nucleolus reforms. ChromosomesChromosomes uncoil and appear as chromatin again. In the end, two genetically identical nuclei are present. Cytokinesis begins.

Telophase cleavage furrow (cytokinesis) nuclear membrane reforming nucleolus reappears

Telophase Animal CellPlant Cell

Cytokinesis Division of the cytoplasm of the cell and its organelles into two new daughter cells. Cytokinesis differs between plants and animals: –Animals: a cleavage furrow forms to make the circular shape. –Plants: a cell plate forms where new cell wall will be to make the rectangular shape. cell plate

Cytokinesis Animal Cell: cleavage furrow Plant Cell: cell plate

2 daughter cells identical to original Parent cell Chromosomes are copied and double in number Chromosomes now split

Question: chromosomes eachA cell containing 20 chromosomes at the beginning of mitosis would, at its completion, produce cells containing how many chromosomes each?

Answer: 20 chromosomes20 chromosomes

Question: 40chromatids chromosomes eachA cell containing 40 chromatids at the beginning of mitosis would, at its completion, produce cells containing how many chromosomes each?

Answer: 20 chromosomes20 chromosomes

Cancer is Uncontrolled Mitosis: Mitosis must be controlled, otherwise growth will occur without limit (cancer) Control is by special proteins produced by oncogenes CANCER