Cell Growth and Reproduction Section 8.2 Biology

What Limits Cell Size?  Diffusion – diffusion slows w/larger distances  DNA – DNA can only control the needs of a small cell  Cell Size - Surface area-to- volume ratio must be high; 6/1; cell has trouble transporting materials in/out of the cell

Purpose of Cell Division  When a cell gets too large to control or function efficiently, cell division takes place  Results in 2 cells identical to the parent cell  Old cells are replaced; new cells produced as an organism grows

Chromosomes  Chromosomes are carriers of our genetic material & must be copied & transmitted accurately  Chromosomes are tightly coiled chromatin.  Most of the time our chromosomes exists as chromatin (long strands of DNA wrapped around proteins called histones)

Cell Cycle  Sequence of growth, nuclear division, and cytoplasmic division of a cell

Interphase – cell spends most of it’s time in this phase

Interphase  G1 – growth phase – cell gets bigger and develops  S – synthesis phase – DNA in nucleus is copied  G2 – growth phase – more growing and developing; produce more organelles, enzymes, centrioles are replicated, etc.

Mitosis - PMAT  nuclear division  yields two daughter nuclei that are genetically identical  used for growth and healing

Prophase – 1 st stage of mitosis

Prophase  Chromatin condenses into chromosomes, 2 identical strands of DNA attached by a centromere  Centrioles move to opposite ends of the cell  Nuclear envelope and nucleolus disappear  Spindle starts to appear

METAPHASE

Metaphase  Chromosomes line up about midway between the centrioles  Spindle fibers attach to chromosomes at centromeres

Anaphase

Anaphase  Centromeres are pulled apart as spindle fibers contracts  Chromatids (half of a chromosome) are pulled in opposite directions  Chromatids are pulled to opposite ends of the cell

Telophase

Telophase  Chromatids complete journey to the ends of the cell  Chromatin is formed as DNA elongates  Nuclear envelope forms around each set of DNA  Spindle disappears  Nucleoli appear in each nucleus

Cytokinesis  Cytoplasmic Division  Begins during anaphase  Furrow / ring starts to develop in the middle of the cell membrane

Cytokinesis  In plants, you start to develop a cell plate  Ring contracts until it completely separates the two new nuclei and about ½ organelles into each new cell

Results of Mitosis  Unicellular organisms remain as single cells  Multicellular organisms - cell growth results in cell specialization & organization for a complex organism  Cells > Tissues > Organs > Organ systems

Results of Mitosis  Cells – still the basic level of organization  Tissues are groups of cells working together to perform a specific function  Organs – tissues organized in various combinations  Organ systems – multiple organs

Control of the cell cycle  8.3

Control of the Cell Cycle  cyclins (proteins) regulate cell growth  Internal regulators – only move to the next phase of the cell cycle when the previous phase is complete

Control of the Cell Cycle  External regulators – if there is room, a cell divides; if neighboring cells are touching, cell growth is inhibited because space is scarce

Apoptosis – programmed cell death  Normal part of development for most cells in a multi-celled organism  Once cells stop dividing or specializing; special enzymes will break it down and scavenger WBCs come and clean up the mess

Cancer  Uncontrolled cell growth  Tumors are cells that do not respond to cell regulators  Cells could also become “immortal”; they don’t finish cell development and die, so new cells just build up

Cancer Causes  2 nd leading cause of death in the US  Caused by genetic & environmental influences  Env. Factors include: smoking, air/water pollution, viral infections, & UV exposure

Cancer prevention  Diets low in fat, high in fiber  Lots of fruits, veggies, and grain products  Foods high in Vit. A, C & E, & the mineral calcium  Exercise & no smoking