Cellular Structure & Function

1. Cellular Structure & Function Part 1: Organization of the Human Body

2. The Cell • Building block of the all organisms, from single-celled to human. • 200 Types of cells in the human body, categorized by cell shape. • Cell size limited by the volume and surface area ratio. • If the cell is too big, it cannot support itself or absorb nutrients/excrete wastes effeciently.

3. Classes of Cell Shapes • Squamous: Thin & flat cells covering surfaces or lining “tubes” • Example: Skin, lining of the esophagus • Cuboidal: Square or cube shaped; approximately as wide as they are tall. • Example: Liver cells • Columnar: Much taller than they are wide. • Example: Lining of the intestines • Spheroid: Egg cells and fat cells; round or oval. • Fusiform: Thick in the middle and tapered towards the ends. • Example: Smooth muscle cells • Stellate: Star-shaped cells. • Example: Some nerve cells

4. Cell Theory • Based on Robert Hook, Theordore Schwann, & Louis Pasteur • Modern Cell Theories’ Generalizations: • All organisms are composed of cells and cell products. • The cell is the simplest structural and functional unit of life. • All functions and structures are ultimately due to the activities of cells. • Cells come only from pre-existing cells. • The cells of all species have many fundamental similarities.

5. General Cell Structure • Cells have the following general structures: • Cell Membrane • Cytoplasm • Nucleus • Intracellular Organelles

7. Cell Membrane • All cells are surrounded by a plasma membrane made up of proteins and lipids • Composition and function differ from one area of the body to the other. • Bilayer of lipids with diverse proteins embedded in it • 98% of membrane molecules are lipids • 75% of these are phospholipids

8. Cell Membrane • Phospholipid Bilayer: • Two phospholipid layers thick • Hydrophilic heads facing the water on each side of the cell membrane. • Hydrophobic tails directed toward the center of the membrane (avoiding the water) • Membrane is dynamic and “fluid”

9. Cell Membrane • Cell Membrane is the target site of many pharmaceutical agents • Proteins only make up 2% of the molecules in a plasma membrane, but are larger then lipids and make up around 50% of the membrane weight.

10. Cell Membranes • Integral or Transmembrane Proteins: Pass across the plasma membrane and are responsible for many functions. Integral proteins function as… • Receptors: Specific for one messenger • Second-messenger Systems: Triggered by messengers that bind with surface receptors • Enzymes: Produce second messengers and help with digestion in the small intestine • Channel Proteins: These molecules have “pores” & allow passage of water & other solutes through the membrane • Carriers: Also called “PUMPS” they actively transport molecules into the cell utilizing ATP in the process

11. Glycocalyx • The “fuzzy” coat external to the plasma membrane on all animal cells, including humans • Acts as an “identification” tag that enables the body to distinguish its own healthy cells from transplanted tissue, invading organism, and diseased cells.

13. Surface Extensions • Surface extensions aid in absorption, movement, and sensory processes. • Microvilli: Extensions of the plasma membrane; serve primarily to increase a cell’s surface area; best developed in cells that specialized in absorption (e.g. the cells lining the small intestine)

15. Surface Extensions • Cilia: Multiple hair-like processes that project from the surface of the cell • Nonmotile Primary Cilium: Nearly every human cell has a single nonmotile primary cilium. • Play a role in balance in the inner ear. • Motile Cilia: Less widespread but occur widely in respiratory tract and fallopian tubes; “wave” to help move materials through internal tubes

17. Surface Extensions • Flagella: A single whip-like structure much longer than cilia. • The only functional flagellum in humans is the tail of the sperm cell.

19. Cytoplasm • Cytoplasm: The fluid that is contained inside the plasma membrane. • Crowded with fibers, tubules, passageways, and compartments. • Contains cytoskeleton (supportive framework) and intracellular organelles embedded in the cytosol or Intracellular fluid (ICF). • Extracellular fluid (ECF) is the fluid outside the cell.

21. Nucleus • Nucleus: The structure at the center of the cell containing the genetic information for the organism. • Nucleic Acid: DNA or RNA. • DNA is the principle type of nucleic acid contained in the cell nucleus. • DNA contains the genetic code for organisms and is involved in protein synthesis, cell division (mitosis), and reproduction of the organism.

23. Plasma Membrane • Plasma Membrane: Acts as a barrier and gateway between the cytoplasm and the extracellular fluid. • Selectively Semi-Permeable: The plasma membrane lets some things through and blocks other things; this is tremendously important in clinical practice!

24. Plasma Membrane • Methods of Transporting Substances: Passive and Active transport. • Passive Transport includes… • Filtration • Diffusion • Osmosis • Active Transport requires ATP and includes… • Active transport • Vesicular transport

26. Filtration • Filtration: The process by which particles are driven through a filter, or selectively permeable membrane, via hydrostatic pressure exerted on a membrane by water. • Example: Coffee Filter • Weight of water forces water through the grounds and coffee filter. • Filter holds back the larger particles (coffee grounds) • Most important filtration in the human body occurs in the capillary wall – transfer of water, salts, nutrients, etc. from blood stream to tissue and extracellular fluid & wastes to kidneys

28. Simple Diffusion • Simple Diffusion: The net movement of particles from an area of higher concentration to an area of lower concentration. • The result of constant, spontaneous movement of molecules known as Brownian Movement. • Concentration Gradient: When the concentration of a substance differs from one point to another. • Movement occurring down or with the concentration gradient is movement from the higher concentration area to the lower.

29. Simple Diffusion • IF the membrane is semi-permeable and permeable to that substance, than diffusion will occur. • IF the membrane is not permeable to the substance, it will not diffuse across the membrane.

31. Diffusion Rates • Diffusion Rates: Important to cell survival because they determine how quickly a cell can acquire nutrients or rid itself of wastes. • Factors affecting diffusion rate: • Temperature: The higher the temp, the faster the diffusion rate. • Molecular Weight: Heavy molecules diffuse more slowly. • Membrane Surface Area: The more surface area the faster the diffusion rate. • “Steepness” Of Concentration Gradient: The greater the concentration difference, the faster the diffusion. • Membrane Permeability: The permeability of the membrane. • Diffusion Distance: Distance diffusion occurs across. • Facilitated Diffusion: Whether a solute binds to a specific transporter (changes the shape and releases the solute on the other side of the membrane).

32. Osmosis • Osmosis: The diffusion of water through a selectively permeable membrane from the area of higher water concentration to the area of lower water concentration. • The higher solvent (water) concentration area has a low solute concentration. • The higher solute concentration has a low solvent concentration.

33. Tonicity • Tonicity: The ability of a solution to affect the fluid volume and the pressure in a cell. • If a solute cannot pass through a plasma membrane, but remains more concentrated on one side of the membrane than on the other, it triggers osmosis.

34. Tonicity • Hypotonic Solution: Area surrounding a cell has a lower concentration of nonpermeating solutes than the intracellular fluid. • Cells absorb water, swell, and lyse (burst). • Hypertonic Solution: Area surrounding cell has a higher concentration of nonpermeating solutes than the intracellular fluid. • Cells will lose water and crenate (shrivel). • Isotonic Solution: The area surrounding the cell has the same total concentration of nonpermeating solutes as the intracellular fluid. • Cells will neither loose nor gain water molecules & do not change size or shape.

35. Active Transport • Active Transport: The carrier-mediated transport of a solute through a plasma membrane but against a concentration gradient. • Utilizes ATP and energy to move against the normal concentration gradient from an area of low concentration to high concentration. • Example: The sodium-potassium pump.

36. Sodium-Potassium Pump • Used to regulate the balance of sodium and potassium within the cell. • 1 ATP molecule exchanges 3 sodium atoms (Na+) for 2 potassium (K+) atoms. • Keeps the potassium higher and sodium lower within the cell. • Plasma membrane continuously leaks Na+ and K+, so the pump keeps the balance corrected. • Na+ and K+ play a critical part in nerve impulses and cardiac function.

37. Vesicular Transport • Vesicular transport moves large particles and droplets of fluid or numerous molecules through the plasma membrane all at once. • Endocytosis: Vesicular processes that bring matter into the cell. Two types: • Phagocytosis: “Cell eating” where foreign particles are engulfed (e.g. monocytes) • Pinocytosis: “Cell drinking” where droplets of extracellular fluid containing molecules used by cells are taken in. • Exocytosis: Vesicular processes that release matter from the cell.

38. Organelles • Organelles: The internal structures within a cell that carry out specific functions. • Some are surrounded by one or two layers of a unit membrane and are therefore referred to as “membranous organelles.” • Membranous Organelles: Nucleus, mitochondria, lysosomes, endoplasmic reticulum, golgi complex. • Non-Membranous Organelles: Ribosomes, centrosome, centrioles, basal bodies.

39. Membranous Organelles: Nucleus • Nucleus: The largest organelle, spheroid in shape. • Most cells have a single nucleus • Skeletalmuscle cells have multiple nuclei • Mature red blood cells are anuclear – have no nucleus. • Liver cells are multinuclear • Nucleus surrounded by nuclear envelope or membrane • Nucleoplasm: The material contained within the nucleus. • Includes… • Chromatin (DNA and protein) • Nucleoli (produces ribosomes)

41. Membranous Organelles: Endoplasmic Reticulum (ER) • Endoplasmic Reticulum: “Little network within the cytoplasm” • A system of interconnected channels that extend through the cytoplasm and reach the nuclear membrane. • Channels called Cisternae • Two Types: • Rough Endoplasmic Reticulum: Channels are covered with ribosomes (synthesize proteins). • Smooth Endoplasmic Reticulum: Extends from the Rough ER to form membranous tubules network.

42. Membranous Organelles: Endoplasmic Reticulum (ER) • Smooth ER synthesizes steroids & lipids • Rough ER is responsible for detoxifying alcohol and other drugs • Rough ER most abundant in cells that produce large amounts of proteins – such as those in the digestive glands • Skeletal and cardiac muscle contain extensive networks of smooth ER that store and release calcium to trigger muscle contraction.

44. Membranous Organelles: Golgi Complex • Golgi Complex: The small system of cisternae which synthesize carbohydrates and put the finishing touches on protein and glycoprotein synthesis. • Primary function is to package protein into membrane-bound golgi vesicles • Some become secretory vesicles and store cell products such as breast milk & digestive enzymes • Some of these can become lysosomes

46. Membranous Organelles: Lysosomes • Lysosomes: A package of enzymes which are bounded by a single unit membrane – usually produced by the Golgi complex • Primary function is to hydrolyze or digest proteins, nucleic acids, complex carbohydrates, and phospholipids • Autophagy: The digestion of surplus cells by their own lysosomal enzymes (as in the liver).

48. Membranous Organelles: Peroxisomes • Peroxisomes: Resemble lysosomes but are smaller and contain different enzymes (oxidase) and are not produced by the Golgi Complex\

50. Membranous Organelles: Mitochondria • Mitochondria: Organelles specialized for synthesizing ATP • Power-house of cells • Bean shaped • Outer and inner membranes • Generate most of the cell’s ATP • Cristae contain enzymes for aerobic respiration • Matrix enclosed in the inner membrane; site of oxidation of organic molecules; contains DNA and ribosomes.