Understanding Cell Anatomy: Structure, Function, and Transport Mechanisms

1. Anatomy & Physiology Chapter 3: Cells Chapter 4: Tissues and Membranes

2. Cells • Smallest living subunit of a multicellular organism • Single-celled microorganisms • Function and survive independently • Examples: amoebas, bacteria

3. Human cells • Work together • Function interdependently • Variable in shape, size, function • Microscopic

4. Cell Structure • Common structural features of human cells • Cell membrane • Nucleus (except for mature RBC) • Cytoplasm • Cell organelles

5. Cell Membrane • Also called plasma membrane • Composed of: • Phospholipids • Cholesterol • proteins

6. Cell Membrane Phospholipids • Exist as a bilayer • One layer each on outer and inner surface of cell membrane • Allows lipid-soluble chemicals to enter or leave the cell via diffusion • Cholesterol • Stabilizes membrane by decreasing its fluidity

7. Cell membrane proteins • Functions • Form channels or pores • Allow chemical to pass (water, ions) • Transporters • Carrier enzymes, bring substrates in • Antigens • Identifying markers on cell outer surface • Receptor sites • Shape allows a bond/fit with hormone

8. Cell membrane • Selective permeability • Allows only certain substances to pass through

9. Nucleus • Inside the cytoplasm • Bounded by the nuclear membrane • Double-layer membrane with pores • Contains: • 1/more nucleoli • chromosomes

10. Nucleus • Contents: • Nucleoli • Spherical shaped group of DNA, RNA, & proteins • Forms ribosomal RNA • Chromosomes • Long threads of chromatin • Made of DNA & proteins • 46 chromosomes in humans

11. Chromosomes • Associated proteins • Structural framework for chromatin coils • Regulatory proteins • Gene • The genetic code for one protein • Very few genes are active in any cell

12. Cytoplasm • Watery solution between the cell membranes and the nucleus • Minerals, gases, organic molecules, cell organelles are here • Cytosol • Water portion of the cytoplasm • Numerous chemical reactions occur here

13. Cell Organelles • Endoplasmic reticulum (ER) • Network of membranous tubules • Extends from nuclear membrane to cell membrane • Passageway for transport of materials needed for cell functions • Rough ER: has ribosomes, makes proteins • Smooth ER: no ribosomes, makes lipids

14. Organelles • Ribosomes • Made of protein and ribosomal RNA • Some on rough ER, some in cytoplasm • Site of protein synthesis • Proteasome • Organelle composed of enzymes (proteases) • Destroys unnecessary proteins

15. Organelles • Golgi apparatus • Flat, membranous sacs • Site of carbohydrate synthesis • Exocytosis via packaging in sacs that break off • Lysosomes • Single-membrane sacs of digestive enzymes • Destroys invaders, damaged cell parts

16. Organelles • Mitochondria • Oval organelles with double membrane • Inner membrane folds are cristae • Site of aerobic reactions & energy production (make ATP) • Contain their own genes (mDNA) • Mitochondria duplicate themselves during cell division

17. Organelles • Centrioles • Pair of rod-shaped structures • Perpendicular to each other • Organize spindle fibers during cell division to divide chromosomes • Cilia/ Flagella • Mobile thread-like projection through cell membrane • Anchored by a basal body • Provide motility • Cilia is shorter than flagella

18. Organelles • Microvilli • Folds of surface of cell membrane • Increase surface area & absorption

19. Cellular Transport Mechanisms • Methods of moving materials in or out of the cells • Osmosis • Diffusion • Facilitated diffusion • Active transport • Filtration • Phagocytosis • Pinocytosis

20. Diffusion • Movement of molecules from an area of greater concentration to an area of lesser concentration • Occurs along a concentration gradient • Occurs due to constant motion of the molecules in gases, liquids, and solids

21. Diffusion • Slow process • Effective across microscopic distances • Examples: diffusion of oxygen from inspired air into capillary blood, diffusion of carbon dioxide in the opposite direction

22. Osmosis • Diffusion of water through a selectively permeable membrane • Goes along a concentration gradient of water also • Examples: • Small intestine mucosal cells absorb water from food by osmosis • Kidney tubule cells reabsorb water from urine by osmosis

23. Osmosis: terminology • Solutes • Dissolved substances in fluids • May be salts, sugars, acids, bases • Osmotic pressure • Pressure created by the concentration of solutes in a fluid (in solution) • A type of factor that determines the movement of water through membranes

24. Osmosis • Standard reference point: • NaCl concentration in human cells: 0.9% • Isotonic: has same concentration of salt as human cells (blood plasma) • Hypotonic: has a lower concentration (distilled water 0% salt) • Hypertonic: has a higher concentration (seawater, 3% salt)

25. Facilitated Diffusion • Molecular movement from an area of higher concentration to one of lower concentration WITH some assistance • Facilitators: • Transporters/carrier enzymes: these are part of the cells membranes • Examples: glucose or amino acid diffusion into cells

26. Active Transport • Movement of molecules from an area of lesser concentration to an area of greater concentration • Requires energy (ATP) • Moves molecules against a concentration gradient

27. Active Transport • Examples: • Sodium pumps • In nerve & muscle cells • Pump Na+ ions outside the cell • Glucose & AA absorption • in small intestine cells

28. Filtration • Movement of water & dissolved materias from an area of higher pressure to an area of lower pressure through a membrane • Energy required is mechanical force • Examples: • Blood pressure in various blood vessels and tissues • Filtration pressure in the kidney capillaries

29. Phagocytosis & Pinocytosis • Endocytosis: cellular engulfment of something, making it intracellular • Phagocytosis: • WBC engulfing invading organism • Pinocytosis: • Stationary cells engulfing small molecules that attach to their membranes (kidney tubules reabsorption of protein)

30. Genetic Code & Protein Synthesis • Genetic code • Sequence of bases (A,T, C, G) • Genome • Total genetic information in the 46 chromosomes of the human • Approximately 3 billion base pairs • Gene • Genetic code for a single protein

31. Genes & Protein Synthesis • Other aspects of genes: • Some segments are shuffled or used in various combinations • Each protein is a specific AA sequence so the gene is the DNA code for that sequence of amino acids (AA’s) • Triplet or codon • The sequence of 3 bases in the DNA molecule that codes for a specific one of the amino acids • Some triplets signal the start & end of the protein

32. RNA & Protein Synthesis • Functions of RNA • Gene expression • Product of how the gene is apparent to the observer • Messenger RNA (mRNA) • Molecular intermediary between chromosomes & ribosomes • Transfer RNA (tRNA) • Transfers AA’s to mRNA triplets

33. How a Protein is Made: • Segment of DNA (a gene) uncoils • Hydrogen bonds of the base pairs break • Now the double helix of DNA in that part of the chromosome is single stranded DNA for the length of that gene

34. How a Protein is Made • RNA nucleotides and enzymes make a single strand (SS) of nucleotides that is complementary (opposite) copy of that SS DNA • This process is called transcription • The copy is called mRNA • Chemical information is now transmitted from DNA to RNA

35. Protein Synthesis • The mRNA leaves the nucleus and attaches to the cytoplasmic ribosomes. • This mRNA has the codon information • The gene coils up into its double helix form in the chromosome

36. Protein Synthesis • Cytoplasmic tRNA has anticodons • Triplet that is complementary to the mRNA’s triplets • The tRNA picks up a specific AA and deposits them on the triplets in mRNA in ribosomes. (translation) • Ribosomal enzymes catalyze peptide bond formation between the AA’s

37. Protein Synthesis • Protein leaves ribosome • May be transported by ER to other parts of the cell • May be packaged by Golgi apparatus to be secreted from the cell

38. Genetic Diseases • A mistake in the DNA bases or triplets may be copied by mRNA and lead to a malfunctioning protein • Example: Sickle Cell Anemia • Error in the 6th amino acid of the beta chains of the hemoglobin molecule • HbS has valine instead of glutamic acid in normal hemoglobin (HbA)

39. Sickle Cell Anemia • Most common genetic disorder among people of African descent • Recessive genetic disease • 1% have disease, 9% have trait • HbS crystallizes in low oxygen states • RBC form abnormal shapes (sickles or cresents) • clog & rupture capillaries • RBC rupture, causing hypoxia & anemia

40. Cell Division • Process by which a cell reproduces itself • Types of cell division: • Mitosis • Meiosis

41. Mitosis • The division of one cell with the diploid # (double the usual #) of chromosomes into 2 identical cells • Cell needs to double its chromosomes prior to mitosis • DNA replication = process by which each chromosome is copied • Chromatids = DNA strand & its attached copy • Replication takes place during interphase (time between cell divisions)

42. Stages of Mitosis • Prophase • Chromosomes coil & become visible, attached at centriole • Nuclear membrane disappears • Centrioles move to opposite ends of cell, spindle fibers become organized • Metaphase • Chromatid pairs line up at cell’s equator with centromeres attached to spindle fiber • Centromeres divide

43. Stages of Mitosis • Anaphase • Each chromosome is now separate • Now two sets of chromosomes (diploid) • Spindle fibers pull chromosomes toward the poles • Telophase • Chromosomes reach poles, uncoil • Nuclear membranes reform

44. Mitosis • Cytokinesis • Cytoplasm divides, new cell membranes form • Mitosis replaces damaged cells after injury • Occurs variably in different areas of the body • Examples: • Mitosis occurs in skin, GI mucosa, bone marrow • Mitosis in heart and CNS insufficient

45. Mitosis Problems: Cancer • Benign growth • No invasion of nearby normal tissue • Cancer (malignancy) • Invades & destroys nearby local tissue and may spread to distant areas of the body • Metastasis • The distant spread of a malignancy beyond its area of origin

46. Cancer Terminology • Mutation • Error or change in the DNA that may bring about a nonfunctional protein • Replicated during interphase • Carcinogen • Substance that increases the chance of mutation or abnormal mitoses and cancer • Chemotherapy • A medication which destroys cancers, often by interference with cell division or other cell processes

47. Meiosis • A more complex type of cell division that forms gametes • Gametes =egg and sperm cells • Cell with diploid # of chromosomes divides twice • End result = 4 haploid gametes • Haploid = half the usual chromosome #

48. Meiosis • Meiosis • In females: oogenesis • In males: spermatogenesis • Fertilization • The union of the two haploid gametes • Restores the normal number of chromosomes from 23 each to 46 total in the fertilized egg

49. Cellular Aging • May occur through deterioration of telomeres (the ends of chromosomes) • Telomeres eventually are lost over time & cell divisions and genes are lost

50. Cell Aging • Deterioration of chaperone proteins • These ensure proper shaping of other proteins & disposal of damaged proteins • Involved in cataract development and neurodegenerative diseases • Alzheimer, Parkinson, & Huntington’s Diseases