Introduction to Cells

1. Introduction to Cells • Cells – the smallest living units in our bodies • Organelles – “little organs” – carry on essential functions of cells • Enzymes – direct chemical reactions in cells • Metabolism – the sum of all chemical reactions in the cell

2. Introduction to Cells • Cells have three main components • Plasma membrane • Cytoplasm • Nucleus

3. Structure of a Generalized Cell Figure 2.1

4. The Plasma Membrane • Plasma membrane defines the extent of the cell • Structure of membrane • Fluid mosaic model (lipid bilayer) • Types of membrane proteins • Integral proteins – firmly imbedded in, or attached to lipid bilayer • Peripheral proteins – attach to membrane surface

5. The Plasma Membrane Figure 2.2a

6. The Plasma Membrane • Functions – relate to location at the interface of cell’s exterior and interior • Provides barrier against substances outside the cell • Some plasma membranes act as receptors Keywords: phospholipids -- polar head, non-polar tail, hydrophilic, hydrophobic, bilayered.

7. The Plasma Membrane • Determines which substances enter or leave the cell • Membrane is selectively permeable • Diffusion – molecules move from a region where they are more concentrated to an area where they are less concentrated • Osmosis – the diffusion of water across a membrane

8. Endocytosis • Endocytosis – mechanism by which particles enter cells • Phagocytosis – “cell eating” • Pinocytosis – “cell drinking”

9. Receptor-mediated Endocytosis • Receptor-mediated endocytosis • Plasma proteins bind to certain molecules • Invaginates and forms a coated pit • Pinches off to become a coated vesicle

10. Exocytosis  Exocytosis – mechanism that moves substances out of the cell  Substance is enclosed in a vesicle  The vesicle migrates to the plasma membrane  Proteins from the vesicles (v-SNAREs) bind with membrane proteins (t-SNAREs)  The lipid layers from both membranes bind, and the vesicle releases its contents to the outside of the cell

11. Exocytosis Figure 2.4

12. Cellular Diversity • Specialized functions of cells relates to: • Shape of cell • Arrangement of organelles

13. Cellular Diversity • Cells that connect body parts or cover organs • Fibroblast – makes and secretes protein component of fibers • Erythrocyte – concave shape provides surface area for uptake of the respiratory gases • Epithelial cell – hexagonal shape allows maximum number of epithelial cells to pack together

14. Cells that Connect Body Parts or Cover Organs Figure 2.16 (1)

15. Cellular Diversity • Cells that move organs and body parts • Skeletal and smooth muscle cells • Elongated and filled with actin and myosin • Contract forcefully

16. Cells that Move Organs and Body Parts Figure 2.16 (2)

17. Cellular Diversity • Cells that store nutrients • Fat cell – shape is produced by large fat droplet in its cytoplasm • Cells that fight disease • Macrophage – moves through tissue to reach infection sites

18. Cells that Store Nutrients and Cells that Fight Disease Figure 2.16 (3), (4)

19. Cellular Diversity • Cells that gather information • Neuron – has long processes for receiving and transmitting messages Figure 2.16 (5)

20. Cellular Diversity • Cells of reproduction • Oocyte (female) – largest cell in the body • Contains many copies of organelles for distribution to daughter cells • Sperm (male) – possesses long tail for swimming to the egg for fertilization Figure 2.16 (6)

21. Developmental Aspects of Cells • Youth – begin as a fertilized egg • Cells in embryo • Exposed to chemical signals (hormones and local peptides) • Chemicals channel cells into specific pathways of development • Cell specialization leads to structural variation of cell types Keywords: Apoptosis, dysplasia, hyperplasia, hypertrophy, necrosis.

22. Aging (emphasis on cellular events) • Aging – a complex process caused by a variety of factors • Free radical theory • Damage from byproducts of cellular metabolism • Radicals build up and damage essential molecules of cells • Radicals present in air pollution, radiation, certain foods • Peroxidase and Catalase breakdown radicals in cytosol (Vit. E, C, beta-carotene and selenium) • Mitochondrial theory – a decrease in production of energy by mitochondria weakens and ages our cells

23. Aging continued: • Immune theory – manufactures antibodies to fend of foreign invaders somehow start to attack bodies own cells. • Glucose theory – glucose added randomly btw adjacent protein molecules • Cell division and Genetic theory – experiments on human cells outside body show there is a limit to number of times cells will divide - is this is a genetically programmed event? - if so, aging part of our genetic blueprint. • Telomeres – “end caps” on chromosomes • Telomerase – prevents telomeres from degrading