Cell Growth and Division Cell Size l 8

Cell Growth and Division

Cell Size l 8 micrometers in diameter to 1 meter with small diameters. l Most cells are between 2 and 200 micrometers in diameter. l Human Body: – Smallest: sperm cells – Largest: ovum – Longest: nerve cells l Largest Living Cell- Ostrich Egg (unfertilized)

Comparison of Cell sizes

Cell Size Limitations l Cell must be small – Large need more food – Must export waste l Rate of Diffusion – Size : diffusion slower and less efficient. l DNA (molecule where critical information stored) Too large “Information Crisis” – Cell cannot survive unless • enough DNA to support protein needs • cell activities are carried out quickly and efficiently

Cell Size Increase Not enough cell membrane to adequately supply the cell interior with enough oxygen, water, and food. Result: Cell Death

Surface area-to-volume ratio As cell’s size increases, its volume increases much faster than its surface area.

Surface Area and Volume Surface Area: 6 (# of sides) x A Volume: A x A X A • Cube doubled • Outside Grows by 4 x • Inside grows by 8 x

Cell Growth and Reproduction

Asexual Versus Sexual Reproduction Asexual l Genetically identical offspring l Single Cell – ex. Bacteria l Multi Cellular- Break off and new organism produced – ex. Hydra Sexual l Offspring inherit genetic information from each parent. l Most plants and animals, some single celled organisms.

Asexual Versus Sexual Reproduction l l Asexual Survival Strategy Better the conditions the faster reproduce, better chance of survival, As long as conditions favorable; genetically identical has advantages Lack of diversity a disadvantage when conditions change and are not favorable. Sexual l Different survival strategy l Finding a mate, growth and development take more time. l Genetic diversity; better tolerate change

Both Sexual and Asexual l Ex. Yeast l Mostly asexual, however, may under certain conditions reproduce sexually.

Cell Theory All cells come from pre-existing cells! Cell division results in two cells that are identical to the original parent cell.

Prokaryotic Cells l Lack nucleus & many organelles l DNA molecule found in cytoplasm l Most contain single, circular DNA with all genetic information

Chromosomes Chroma (Greek) “colored” Soma “body” Genetic information is bundled into packages of DNA

Structure of the Eukaryotic Chromosome l Exist as CHROMATIN—Long strands of DNA wrapped around proteins. l Microscope—Plate of spaghetti

Components • Sugar-Deoxy-ribose – derived from ribose sugarone less oxygen • Phosphate Group backbone • 4 Nitrogen Bases-In complementary base pairs held by hydrogen bonds • Adenine & Thymine • Cytosine &Guanine

CHROMOSOMES Make it possible to separate DNA precisely during cell division

A series of events the cells go through as they grow and divide • During cell cycle, a cell grows, prepares for division, and divides to form two daughter cells. • CELL CYCLE

Prokaryotic Cell Cycle Regular pattern of growth, DNA replication, and cell division that can take place under ideal conditions l Just beginning to understand process l Form of reproduction called Binary Fission. l Result-two genetically identical cells. l

Cell Cycle – Interphase-Period of cell cycle b/w cell division • most of the cell’s metabolic functions are carried out • chromosomes are replicated • LONGEST of Cell Cycle – Cell Division (M Phase) • Mitosis when nuclear division occurs, leading to the formation of two daughter cells. • The division of the cytoplasm, called cytokinesis, follows mitosis. • Length of cell cycle depend on the type of cell

Eukaryotic Cell Cycle

Interphase: Cell prepares for Mitosis l Cell grows in size l Carry on metabolism l Chromosomes are duplicated for cell division.

Interphase G 1 Phase: Cell Growth • Most cell growth • Increase in size • Synthesize new proteins and organelles

Interphase Continued G 2 Phase: Preparing for Cell Division S Phase “S” Synthesis DNA is synthesized when chromosomes replicated. l Result: Cell has 2 x as much DNA l l Shortest phase of Interphase l Organelles and molecules required for cell division are produced. l Result: Cell ready for division l

Helicase-(Enzyme) unzips/breaks hydrogen bonds b/w base pairs Nitrogen Bases

M Phase l Produces 2 daughter cells l “M” comes from Mitosis l Cell division relatively quick l Includes Mitosis and Cytokinesis – Mitosis-division of the cell nucleus • 2 daughter cells produced with genetic information – Cytokinesis-division of the cytoplasm

Mitosis: A period of nuclear division

Mitosis l Prophase l Metaphase l Anaphase l Telophase

Prophase l 1 st / longest phase of mitosis. l Chromatin coils up (condenses)chromosomes. l Duplicate chromosomes become visible l Two halves of the double structure are called sister chromatids. (Exact Copies of each other) l Centromere—holds together sister chromatids.

Prophase continued… l Nucleus disappears l Nuclear envelope and nucleolus disintegrate. l Animals—centrioles migrate to opposite end of the cell. l Centriole—Small, dark, cylindrical structures that are made of microtubules and are located just outside the nucleus. (animal cells only)

Prophase continued… l Spindle—A football shaped, cage-like structure consisting of thin fibers made of microtubules.

Metaphase: Second stage of mitosis l Chromosomes l One sister chromatid’s spindle fiber extends to one pole, and the other extends to the opposite poles (ensures a complete set of chromosomes) – – – Line up at center of cell Attach to the spindle fibers via centromeres. Pulled by spindle fibers and line up on the midline (equator).

Anaphase: Third Phase of Mitosis l Separation of sister chromosomes – Centromeres split apart and chromatid pair separate – Pulled apart by the shortening of the microtubules in the spindle fiber.

Telophase: 4 th phase of mitosis l Chromosomes reach opposite poles of cell. l Prophase changes are reversed (independent existence). l Chromosomes unwind; Spindle breaks down; nucleolus reappears; new nuclear envelope forms each set of chromosomes; new double membrane begins to form.

Cytokinesis l l Cytoplasm division Animal Cells—Membrane is drawn inward until the cytoplasm is pinched into two nearly equal parts. l Plant Cells—(cell membrane not flexible enough to draw inward because of rigid cell wall) Cell plate forms b/w the divided nuclei. Gradually, cell plate develops into cell membrane that separates two daughter cells.

Result of Mitosis Two new cells with chromosome sets identical to those of the parents; Carry out same function of parent cells; Grow and divide like parent cells. l Tissues: group of cells that work together to do a specific function. l Organs: group of two or more tissues organized to perform complex activities within an organism. l Organ Systems: Multiple organs that work together to perform specific life function. l

Cell Cycle

Purpose of Cell Division and Mitosis l Keep total cell number in a mature organism relatively constant, l Replace worn-out or damaged cells, l Enable a multicellular organism to grow to adult size.

Control of Cell Cycle Cell cycle l 24 to 48 hours l less then an hour l never divide only mature l. Most muscle and nerve never divide A mistake in the cell cycle can lead to cancer.

Cell Regulation l Injury occurs-cells divide rapidly, healing process begins, as near completion, slows down, everything returns to normal l Cyclin-a protein that regulates timing of cell cycle l Regulatory Proteins-Proteins that control cell cycle (both inside and outside cell) – Functions: slow down or stop cell division, start cell division, etc – Internal Regulators- allow cell to proceed only when certain events have occurred – External Regulators-Respond to events outside cell. • Growth factors-stimulate growth and division of cells.

Control of the Cell Cycle l Enzymes – Begin and drive the cell cycle – Control the cycle through its phases. l Cell can lose control (uncontrolled dividing) – failure to produce certain enzymes – production of other enzymes at the wrong time. l Cancer is the result of uncontrolled cell division.

Cell Death due to injury l Apoptosis-Cell may be programmed to die (self-destruction) – Controlled steps to death • Cell and its chromosomes shrink • Parts of cell membrane break off • Neighboring cells clean up cell’s remains

Causes of loss of control of cell cycle l Environmental Factors l Changes in enzyme production – Enzyme production is directed by genes located on the chromosome. – A gene is a segment of DNA that controls the production of a protein. l Many studies point to portion of interphase just before DNA replication as being a key control period.

Cancer: A mistake in the Cell Cycle Expressed as cancer when something prompts the damaged genes into action.

Cancer l Cancerous cells form masses of tissue called tumors that deprive normal cells of nutrients. l Late Stages: Cancer cells enter the circulatory system and spread throughout the body (Metastasis), forming new tumors that disrupt the function of organs, organ systems, and ultimately the organism.

In Cancer Cells • There is no awareness of surroundings. • Cells do not stop dividing when crowded. • Cells do not stop after a set number of divisions. • Cells do not enter a resting state. • Cells divide faster and take less time to complete the cycle.

Cancer: 2 nd Leading Cause of death in the United States (heart disease #1) Environmental and Genetic Factors l Cigarette smoke l Air l Water pollution l Exposure to UV Radiation l Viral Infections l Instogram, Facebook and Twitter l p 53 (gene halts cell cycle)

Treatments l Surgery (tumor removal) l Chemotherapy-Chemical compounds that kill cancer cells and/or slow growth – Interfere with healthy cells – Serious side effects l Radiation

Cancer Prevention l Link between healthy lifestyle and the incidence of cancer. l Diets low in fat and high in fiber. l Minimal amounts of fat. l Vitamins and minerals; carotenoids, vitamins A, C, and E and calcium. l Daily exercise l No smoking l Don’t use Instogram, Face Book and Twitter

Cell Differentiation l Human body-estimated one hundred trillion cells. l Embryo-developmental stage of a multicellular organism; organism's cells become more and more differentiated and specialized for specific function.

Differentiation During development of an organism, cells differentiate into many types of cells 9959 cell with precisely determined functions

Stem Cells and Development l Totipotent-cells that are able to develop into any type of cell found in the body. l Blastocyst- after about 4 th day of development human embryo forms; a hollow ball of cells with a cluster of cells inside (inner cell mass); differentiation occurs – Outer cells form tissue that will attach to mom – Inner cells mass becomes the embryo

Pluripotent Cells that can develop into MOST, but not all, of body’s cell types. Ex. Inner cell mass (can not form tissues surrounding embryo

Stem Cells Unspecialized cells from which differentiated cells develop

Stem Cells l Embryonic Stem Cells-found in early embryos – 1998 researchers from way to grow in culture – Can make different types of cells; sperm made from embryonic stem cells were used to generate live mice.

Adult Stem Cells l Cells that differentiate to renew and replace cells in the adult body-limited potential l Multipotent-cells that can develop into many types of differentiated cells. – Most only produce type of cells of given organ or tissue • Eg-adult stem cells in bone marrow can develop into several types of blood cells; while brain stem cells can produce neurons (nerve cells)

Frontiers in Stem Cell l Important to human health l Use of undifferentiated cells to repair or replace badly damaged cells and tissues. l Ethical Issues – Embryonic stem cells (from early embryos) • Embryo‘s entitled to rights and protections of human beings. • Government funding-political issue • Ethical issue of life and death – Technology solutions becoming available