Cell Cycle Division Biology I Cell Division All

Cell Cycle & Division Biology I

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.

Cell Division 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. Reasons for Cell Division: • Cell growth • Repair & replacement of damaged cell parts • Reproduction of the species

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 somatic (body cells) have 23 pairs of chromosomes or 46 chromosomes (diploid or 2 n number) • The 2 chromatids of a chromosome pair are called homologues (have genes for the same trait at the same location)

Chromosome Numbers • Human reproductive cells (gametes) sperms & eggs, have one set or 23 chromosomes (haploid or n number) • Every organism has a specific chromosome number Organism Chromosome Number (2 n) 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. • A form of asexual reproduction in yeast and corals.

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 S phase G 1 interphase Mitosis -prophase -metaphase -anaphase -telophase G 2

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: – G 1: cell growth – S (synthesis): DNA synthesis – G 2: prepare for cell division

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

Prophase • Longest phase of mitosis • Nucleolus disappears • Chromatin condenses into chromosomes, 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 late prophase early prophase centrioles spindle fibers aster fibers nuclear envelope disappearing centromere

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 centrioles aster fibers spindle fibers metaphase plate

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, chromatids now chromosomes aster fibers spindle fibers centrioles

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) 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

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? 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? each

Answer: • 20 chromosomes

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