Cell Cycle & Division Biology I

Reasons for Cell Division: Cell growth Repair & replacement of damaged cell parts Reproduction of the species 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.   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 Human reproductive cells or gametes (sperms & eggs) have one set or 23 chromosomes (haploid or n number) Every organism has a specific chromosome number 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) Organism Chromosome Number (2n) Human 46 Fruit fly 8 Lettuce 14 Goldfish 94

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 Bacteria, cyanobacteria, and most single celled organisms reproduce by 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 G1 G2 Mitosis S phase interphase -prophase -metaphase -anaphase -telophase G1 G2 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. G1 (gap) phase: 2. S phase: 3. G2 (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. G2 (gap) phase:  Preparation time for mitosis/meiosis (cell division)  Cell continues growing  Needed proteins produced

Mitosis Division of the nucleus occurs first (mitosis) Mitosis is asexual reproduction. Only ONE parent cell Daughter cells are genetically identical Mitosis consists of four stages – Prophase, Metaphase, Anaphase, Telophase

Mitosis

Stages of Mitosis Prophase Metaphase Anaphase Telophase

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

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

Prophase Animal Cell Plant Cell

Metaphase Shortest phase of mitosis Chromosomes 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 Cell Plant Cell

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

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

Anaphase Animal Cell Plant Cell

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

Telophase cleavage furrow (cytokinesis) nucleolus reappears nuclear membrane reforming nucleolus reappears

Telophase Animal Cell Plant 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 cell plate

Cytokinesis Animal Cell: cleavage furrow Plant Cell: cell plate

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

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

Answer: 20 chromosomes

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

Answer: 20 chromosomes

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

Mitosis