Cell Growth and Reproduction Section 10 1 and

Cell Growth and Reproduction Section 10. 1 and 10. 2 Biology

Limits to cell growth § Diffusion – diffusion slows w/larger distances § DNA – DNA can only control the needs of a small cell § Cell Size - Surface area-tovolume ratio must be high; 6/1; cell has trouble transporting materials in/out of the cell if it’s too low like 2/1

§ The larger the cell, the lower the ratio (surface area to volume), the harder to transport materials. § Solves these problems with cell division (making 2 new cells) § Cell Division – when a cell gets too large to control or function efficiently, cell division takes place

Cell division 10. 2

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 (3 stages) § Sequence of growth (interphase), nuclear division (mitosis), and cytoplasmic division (cytokinesis) of a cell

§ § § Interphase (1 st stage) G 1 – growth phase – cell gets bigger and develops S – synthesis phase – DNA in nucleus is copied G 2 – growth phase – preparation for mitosis; produce more organelles, enzymes, centrioles are replicated, etc.

Mitosis – PMAT (2 nd stage) § nuclear division § yields two daughter nuclei that are genetically identical § used for growth and healing

4 stages to mitosis §Prophase - prepare §Metaphase - middle §Anaphase - away §Telophase – two cells

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

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 § 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 (3 rd stage) § § § Cytoplasmic Division Begins during anaphase In animal cells a furrow / ring starts to develop in the middle of the cell membrane (pinching of the middle)

Cytokinesis § In plants, you start to develop a cell plate (starts in middle of the 2 cells) § Ring contracts until it completely separates the two new nuclei and about ½ organelles into each new cell

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

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

Apoptosis – programmed cell death § Normal part of development for most cells in a multi-celled organism (50 - 70 billion cells die each day in the average human adult. ) § Once cells stop dividing or specializing; special enzymes will break it down & scavenger WBCs come & clean up