Functions of the Cell

1. Functions of the Cell • Basic unit of life • Protection and support • Movement • Communication • Cell metabolism and energy release • Inheritance

2. Cell Characteristics • Plasma Membrane • Outer cell boundary • Substances inside the cell membrane are intracellular • Substances outside the cell are extracellular. • Encloses an supports the cell contents.

3. Plasma Membrane • It attaches cells to the extracellular environment or to other cells. • The ability of cells to recognize and communicate with each other take place through the plasma membrane • It determines what moves into and out of cells.

4. Plasma Membrane • Ion movement by cells results in a charge difference across the plasma membrane called the MEMBRANE POTENTIAL • The outside of the plasma membrane is positively charged compared to the inside because there are more positively charged ions immediately on the outside of the plasma membrane and more negatively charged ions inside.

5. Plasma Membrane • The membrane potential allows cells to function like tiny batteries with a positive and negative pole. • It is an important feature of a living cell’s normal function.

6. Plasma Membrane • Consists of: • 45% -50% lipids • 45% - 50% proteins • 4% - 8% carbohydrates • The carbohydrates combine with lipids to form glycolipids • The proteins combine with lipids to form glycoproteins.

7. Membrane Lipids • 1st: Phosoplipids • Form lipid bilayer • Double layer of lipid molecules • They have a polar head (exposed to water inside and outside the cells) and a non polar tail (face one another in the interior of the plasma membrane.

8. Membrane Lipids • 2nd: Cholesterol • Interspersed among the phospholipids and accounts for about 1/3 of the total lipids in the plasma membrane. • The amount of cholesterol in a given membrane is a major factor in determining the fluid nature of the membrane. Which is critical to its function.

9. Membrane Lipids • Phospholipids form a lipid bilayer • Hydrophilic (water-loving) polar heads • Hydrophobic (water-fearing) nonpolar heads • Cholesterol: Determines fluid nature of membrane

10. Membrane Proteins • Many functions of the plasma membrane are determined by its proteins. • FLUID-MOSAIC MODEL: • The plasma membrane is neither rigid nor static in structure. • It is highly flexible and can change its shape and composition through time.

11. Movement through the Plasma Membrane • Diffusion • Osmosis • Filtration • Mediated transport mechanisms • Facilitated diffusion • Active transport • Secondary active transport

12. Osmosis • Diffusion of water (solvent) across a selectively permeable membrane • Important because large volume changes caused by water movement disrupt normal cell function • Cell shrinkage or swelling • Isotonic: cell neither shrinks nor swells • Hypertonic: cell shrinks (crenation) • Hypotonic: cell swells (lysis)

13. Filtration • Works like a sieve • Depends on pressure difference on either side of partition • Moves from side of greater pressure to lower • Example: In kidneys in urine formation

14. Endocytosis • Internalization of substances by formation of a vesicle • Types • Phagocytosis • Pinocytosis • Receptor-mediated endocytosis

15. Pinocytosis

16. Exocytosis • Accumulated vesicle secretions expelled from cell • Examples • Secretion of digestive enzymes by pancreas • Secretion of mucus by salivary glands • Secretion of mild by mammary glands

17. Cell Characteristics • Cytoplasm • Cytosol • Cytoskeleton • Cytoplasmic inclusions

18. Cytoplasm • Cellular material outside nucleus but inside plasma membrane • Cytosol: Fluid portion • Cytoskeleton: Supports the cell • Microtubules • Microfilaments • Intermediate filaments • Cytoplasmic inclusions

19. Organelles • Small specialized structures for particular functions • Most have membranes that separates interior of organelles from cytoplasm • Related to specific structure and function of the cell

20. Centrioles • In specialized zone near nucleus: Centrosome • Each unit consists of microtubules • Before cell division, centrioles divide, move to ends of cell and become spindle fibers

21. Cilia • Appendages projecting from cell surfaces • Capable of movement • Moves materials over the cell surface

22. Flagella • Similar to cilia but longer • Usually only one exists per cell • Move the cell itself in wavelike fashion • Example: Sperm cell

23. Microvilli • Extension of plasma membrane • Increase the cell surface • Normally many on each cell • One tenth to one twentieth size of cilia • Do not move

24. Ribosomes • Sites of protein synthesis • Composed of a large and small subunit • Types • Free • Attached to endoplasmic reticulum

25. Endoplasmic Reticulum • Types • Rough • Attached ribosomes • Proteins produced and modified • Smooth • Not attached ribosomes • Manufacture lipids • Cisternae: Interior spaces isolated from rest of cytoplasm

26. Golgi Apparatus • Modification, packaging, distribution of proteins and lipids for secretion or internal use • Flattened membrane sacs stacked on each other

27. Mitochondria • Provide energy for cell • Major site of ATP synthesis • Membranes • Cristae: Infoldings of inner membrane • Matrix: Substance located in space formed by inner membrane

28. Nucleus • DNA dispersed throughout • Consists of : • Nuclear envelope: Separates nucleus from cytoplasm and regulates movement of materials in and out • Chromatin: Condenses to form chromosomes during cell division • Nucleolus: Assembly site of large and small ribosomal units

29. Chromosome Structure

30. Overview of Cell Metabolism

31. Overview of Protein Synthesis

32. Overview of Protein Synthesis • Transcription • Copies DNA to form mRNA • tRNA carries amino acids to ribosome • Translation • Synthesis of a protein at ribosome

33. Translation

34. Cell Life Cycle • Interphase • Phase between cell divisions • Mitosis • Prophase • Metaphase • Anaphase • Telophase • Cytokinesis • Division of cell cytoplasm

35. Mitosis

36. Mitosis

37. Meiosis

38. Cellular Aspects of Aging • Cellular clock • Death genes • DNA damage • Free radicals • Mitochondrial damage