Understanding Cell Growth, Division, and Regulation in Biology

1. Cell Growth and Reproduction Section 10.1 and 10.2 Biology

2. 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-to-volume ratio must be high; 6/1; cell has trouble transporting materials in/out of the cell if it’s too low like 2/1

3. 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

5. Cell division 10.2

6. 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)

7. Cell Cycle (3 stages) • Sequence of growth (interphase), nuclear division (mitosis), and cytoplasmic division (cytokinesis) of a cell

8. Interphase (1st stage) • G1 – growth phase – cell gets bigger and develops • S – synthesis phase – DNA in nucleus is copied • G2 – growth phase – preparation for mitosis; produce more organelles, enzymes, centrioles are replicated, etc.

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

10. 4 stages to mitosis • Prophase - prepare • Metaphase - middle • Anaphase - away • Telophase – two cells

12. 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

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

14. 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

15. 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

17. Cytokinesis (3rd 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)

18. 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

21. 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

22. 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

23. 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

24. 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