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 and 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. Membrane Proteins • Integral or intrinsic • Extend from one surface to the other • Peripheral or extrinsic • Attached to either the inner or outer surfaces of the lipid bilayer

12. Marker Molecules • Allow cells to identify one another or other molecules

13. Channel Proteins • Nongated ion channels • Always open • Ligand gated ion channel • Open in response to small molecules that bind to proteins or glycoproteins • Voltage-gated ion channel • Open when there is a change in charge across the plasma membrane

14. Regulating Traffic Across Membranes II. Passive Transport: Diffusion and Facilitated diffusion • Diffusion : net movement • of a substance down • a concentration gradient. • Solutes diffuse from high to low concentration. • Continues until a dynamic equilibrium is reached. • No requirement for energy expense (passive) • Examples: • Uptake of O2 by cell performing respiration • Elimination of CO2 from cell

15. Diffusion of solutes across a membrane Each dye diffuses down its own concentration gradient.

16. Facilitated diffusion • Passive transport • Transport proteins speed the movement of molecules across the plasma membrane. • Channel protein and Carrier protein required • Channel protein : aquaporins, ion channels • Carrier protein

17. Osmosis • Diffusion (passive transport) of water across a selectively permeable membrane • Direction of water movement is determined by the difference in total solute concentration, regardless of type or diversity of solutes. • Water moves always from high concentration solution to low concentration solution.

18. Water balance of living cells • Tonicity : the ability of a solution to cause a cell to gain or lose water • Isotonic: no net movement of water across the membrane (normal). • Hypertonic : the cell loses water to its environment (crenation). • Hypotonic : the cell gains water from its environment (lysis).

19. Questions 0 An artificial cell consisting of an aqueous solution enclosed in a selectively permeable membrane has just been immersed in a beaker containing a different solution. The membrane is permeable to water and to the simple sugars glucose and fructose but completely impermeable to sucrose. • Glucose? • Fructose? • Hypotonic/Hypertonic? • Water?

20. Active Transport • Requires the cell to expend energy: ATP • Transport proteins pump molecules across a membrane against their concentration gradient. • “Uphill” transport • Maintain steep ionic gradients across the cell membrane (Na+ , K+ , Ca++ , Mg++ , Cl-) Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ inside outside

21. An Example of Active Transport: The Sodium-Potassium Pump

22. Passive and Active Transport

23. More examples of active transport • Exocytosis • Removing large particles out of the cell with a vesicle • Endocytosis • Ingesting large particles • Pinocytosis: “Cell drinking” • Phagocytosis: “Cell eating”

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

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

26. 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

27. 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

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

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

30. 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

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

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

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

34. Peroxisomes and Proteasomes • Peroxisomes • Smaller than lysosomes • Contain enzymes to break down fatty and amino acids • Hydrogen peroxide is a by-product of breakdown • Proteasomes • Consist of large protein complexes • Include several enzymes that break down and recycle proteins in cell

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

36. 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

37. Mitosis

38. Mitosis

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

40. Protein Synthesis • The process of using DNA to form proteins • Involves two steps: • Transcription • Translation

41. Genetic Information • Uses 2 main forms of genetic information: • DNA Deoxyribonucleic Acid • Double stranded • Sugar: Deoxyribose • Stays in the nucleus • Bases: A T G C • RNA Ribonucleic Acid • Single stranded • Sugar: Ribose • Can leave the nucleus • Bases: A U G C

42. Transcription • DNA unwinds • One strand of the double helix is used as a template • Nucleotides line up along the DNA and form a copy, called mRNA • Once completed, DNA winds back up and mRNA leaves

43. mRNA must be spliced before it leaves the nucleus ( immature RNA) • Enzymes remove noncoding areas called introns, and coding regions called exons are spliced back together • The result is a shorter, coding strand of mRNA • Every 3 bases on mRNA is a codon

44. Codons • Codes for amino acids • 64 codons can code for 20 different amino acids

45. Translation • mRNA binds to a ribosome • tRNA binds to ribosome along the codon and reads which amino acid it codes for • tRNA finds the specific amino acids • For every codon, the tRNA brings the amino acids • Amino acids link together forming a proteins • Peptide bonds link each amino acid together.

46. Translation

47. 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

48. Overview of Cell Metabolism

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