Cell Growth and Reproduction

Limits to Cell Growth Two reasons cells cannot continue to grow larger indefinitely: (1) The larger a cell becomes, the more demands the cell places on its DNA. As cell gets bigger, it does not make extra copies of DNA. (2) Cell has more trouble moving enough nutrients and wastes across the cell membrane.

Cell Reproduction Before it becomes too large, a growing cell divides forming two “daughter” cells. The process by which a cell divides into two new daughter cells is called cell division.

Cell Division The Cell Cycle is a series of events a cell goes through as it grows and divides.

Cell Division Before the cell divides, it must first copy its genetic information before cell division begins. Two stages for cell division: (1) mitosis – division of the nucleus (2) cytokinesis – division of the cytoplasm

Mitosis Reproduction by mitosis is asexual, because the daughter cells are genetically identical to the parent cell

Chromosomes Chromosomes are composed of DNA and proteins and pass genetic information from one generation to the next Humans have 46 chromosomes (23 pairs). One of each pair from mom and one from dad

Chromosomes Chromosomes are visible only during cell division, when they condense into compact, tightly coiled structures

Chromosome VS Chromatid Before cell division occurs, each chromosome is replicated or copied. Because of this, each chromosome has two identical “sister” chromatids. When the cell divides the sister chromatids separate from each other, so that one chromatid goes into each of the new cells

Chromosomes In humans, only chromosome pairs 1-22 reproduce via mitosis, because these chromosomes include somatic (body) cells. Examples of somatic cells include: muscle, blood, bone, and skin cells.

Chromosomes The purpose of mitosis in multicellular organisms is growth and repair of damaged tissues. The purpose of mitosis in unicellular organisms is replication (creating a new organism).

Cell Cycle The cell cycle is the series of events that cells go through as they grow and divide Consists of 4 phases: 1. M phase – mitosis and cytokinesis 2. S phase – chromosome replication 3. G1 and G2 phases – “gaps” of time with intense growth and activity

Interphase Consists of three phases: 1. G1 phase 2. S phase

G1 Phase The G1 phase is a period of activity in which cells do most of their growing. Cells increase in size and synthesize new proteins and organelles.

S phase The S phase is a period in which chromosomes are replicated and the synthesis of DNA (DNA replication) occurs

G2 Phase Shortest of the three phases of interphase Many organelles and molecules required for cell division are produced. When G2 phase is over, cell is ready to enter M phase and begin cell division

Mitosis – time of cell reproduction Mitosis process can last from a few minutes to several days. Four phases included: Prophase Metaphase Anaphase Telophase

Prophase Prophase is the longest phase of mitosis Chromatin condenses into chromosomes Nuclear envelope dissolves Centrioles move to poles Spindle fibers form Centromere = Center of chromosome Centrioles = organize spindle, that will help separate chromosomes during division Spindle = microtubules that guide chromosomes

Prophase

Metaphase - short Chromosomes line up at the equator Microtubules connect centromere to spindle

Anaphase Centromeres split and sister chromatids separate to become individual chromosomes

Telophase Chromosomes uncoil and nucleus reappears

Cytokinesis Cytokinesis = division of cytoplasm making 2 new daughter cells Animal cells Plasma membrane pinches along equator Forms 2 new cells Plant Cells Cell plate laid across equator Cell membrane forms around each cell New cell walls form

Results of Mitosis 2 new cells with identical chromosomes as parent cell Unicellular organisms Organism multiplied Multicellular organisms Cell growth and reproduction Tissue – groups of cells that work together Organs – tissues organize in various combos Organ Systems – multiple organs

Cancer Malignant growth resulting from uncontrolled cell division May be caused by environmental factors Or by changes of enzyme production Genes are segments of DNA that controls the production of a protein portion just before DNA replication. This is the key control period

Cancer: Mistake in Cell Cycle Form masses of tissues called tumors – deprive normal cells of nutrients Cancer cells enter circulatory system and spread – form new tumors 2nd leading cause of death 1st heart disease

Cause Genetic and environmental Different countries different types Cigarette smoke Air and water pollution UV rays Viral infections

Prevention Life Healthy Lifestyle Diets low in fat and high in fiber Fruits, veggies, grain products Vitamins and minerals A,C,E, Calcium Exercise