CELLS AND TISSUES

1. CELLS AND TISSUES Cell Parts

2. Basic Cell • defined as the structural and functional unit of all living things - as small as 1/1000th of an inch (bacteria) - as large as 4 feet (certain nerve cells) • Shape: - disc shaped, thread-like, cube-like, etc. • Functions: - protection, hormones, chemical regulation, gas exchange, cleanse blood

3. Main Regions of a Cell • plasma (cell) membrane • cytosol (cytoplasm) • organelles - specialized highly organized structures for specific cellular activities • inclusions - temporary structures

4. Plasma (cell) Membrane • outer layer of the cell • fragile barrier • separates internal components of the cell from the external environment • contains cell contents • two lipid layers - protein molecules are suspended between lipid layers

5. Plasma (cell) Membrane (cont.) • unique structure which determines which substances enter or leave the cell • Consists of: - phopholipids - cholesterol - proteins

6. Functions of Membrane Proteins • channels • enzymes • transportation of substances across membrane • receptor sites for hormones, neurotransmitters, or nutrients • cytoskeleton anchors • cell identity markers

7. Cytoplasm • outside nucleus • inside plasma membrane • site of most cellular activities • Major elements include: - cytosol - inclusions - organelles

8. Cytosol • viscous, transparent, gel-like • 75% H2O + solid components: - proteins, carbohydrates, lipids, and inorganic substances - inorganic substances and smaller organic substances soluble in H2O are present as solutes - larger organic compounds are found as colloids (semi-solid matrix)

9. Organelles • little organs • specialized structures • characteristic appearances • specific roles in growth, maintenance, repair, and control • chemically different with one another

10. Nucleus • Three distinct components: - nuclear membrane - nucleoli - chromatin

11. Nucleus (cont.) • largest organelle in the cell • usually oval or spherical - conforms to shape of the cell • contains genetic material (DNA) • controls cellular functions • directs cellular activities • surrounded by nuclear membrane

12. Nuclear Membrane • double layer • bound to nucleus • encloses nucleoplasm in which nucleoli and chromatin are suspended • has large pores

13. Nucleoli • little nucleus • dense body • composed mostly of RNA and protein • ribosome production (migrate through pores in nuclear envelope and enter cytoplasm) • disappear during cell division and reappear in daughter cells

14. Chromatin • loosely coiled fibers of DNA and associated proteins • before cell division DNA duplicates, chromatin fibers coil and shorten to form chromatids • one of two spiral filaments joined at the centromere which make a chromosome

15. Ribosomes • tiny, round dark bodies • sites of protein synthesis • contain ribosomal RNA (rRNA)

16. Endoplasmic Reticulum • system of membrane-enclosed tubules or channels that coil and twist; called cisterns • continuous with nuclear envelope • serves as minicirculatory system • provides surface area for chemical reactions • Two types: - granular and agranular

17. Endoplasmic ReticulumGranular • rough • studded with ribosomes which synthesize protein • temporary storage area • together with Golgi body it synthesizes and packages molecules that will be excreted from the cell

18. Endoplasmic ReticulumAgranular (smooth) • site of fatty acid, phospholipid, and steroid synthesis • inactivates or detoxifies chemicals such as alcohol, pesticides, and carcinogens

19. Golgi Apparatus (body or complex) • stacks of flattened sacs with bulges at ends • located close to nucleus • modifies, packages, and secretes proteins and lipids • as proteins accumulate in sacs, the sacs swell; swollen sac pinches off to form vesicles that travel to cell membrane

20. Route of Proteins for Export ribosomes rough ER transport vesicles Golgi body secretory vesicles release to exterior of cell

21. Lysosomes • membrane-enclosed vesicles • formed in Golgi body • contain powerful digestive enzymes (as many as 40) responsible for breaking down molecules • can also digest worn-out cell structures (autophagy) and foreign substances

22. Peroxisomes • membrane sacs similar to lysosomes but smaller • contain enzymes that use molecular oxygen to oxidize organic substances • detoxify potentially harmful substances that may enter the bloodstream (e.g., free radicals) • especially important in liver and kidneys

23. Mitochondria(powerhouse of the cell) • sausage-shaped fluid filled sacs • double membrane wall • outer wall is smooth • inner wall - series of folds called cristae • cristae provide surface area for cellular respiration (only occurs if O2 is present) • enzymes on cristae catalyze reactions that generate ATP

24. Cytoskeleton • responsible for cell movement and for movement of organelles and chemicals within the cell • Network of protein structures: - microfilaments - microtubules - intermediate filaments

25. Microfilaments • rod-like structures • formed from the protein actin • in muscle tissue - actin filaments (thin) and myosin (thick) slide past one another to produce contraction • in non-muscle - actin filaments support and shape

26. Microtubules • larger than microfilaments • straight, slender cylindrical structures - contain the protein tubulin • support and shape cells • movement of substances

27. Intermediate Filaments • medium size • strong and tough • provide structural reinforcement

28. Centrosome • cytoplasmic material • within centrosome is pair a of rod-shaped bodies called centrioles - lie at right angles to each other - during cell division, centrioles direct formation of mitotic spindle - like mitochondria, they contain DNA and control self replication

29. Cilia • minute projection extending from cell surface • contain ten pairs of microtubules • act to move substances along cell surface • beat rhythmically to move fluids or particles over cell surface

30. Flagella • long whip-like projections extending from free cell surface • act to propel a cell • contain ten pairs of microtubules • tail of sperm is a flagellum