Cells and Tissues

1. Cells and Tissues

2. Overview of Cellular Basis of Life • Cells – the unit/building block of all living things • Many elements make up cells, some of which are electrolytes (atoms that carry an electrical charge)

3. Overview of Cellular Basis of Life • Cells are also about 60% water and are continually bathed in interstitial fluid • Cells vary in length from 2 μm to 1 m or more • Cells vary in function

4. Anatomy of a Generalized Cell • Although cells are different, there are common parts and functions to all cells, described by a generalized cell: • 1. Nucleus – the “headquarters” of the cell. The genetic material, deoxyribonucleic acid (DNA), that contains instructions for building proteins and for cell reproduction is contained here

5. Anatomy of a Generalized Cell • There are 3 distinct regions of the nucleus: • 1a. Nuclear Membrane (Envelope) – a double membrane that binds the nucleus. Between the two membranes is a space. At times, the two layers fuse, creating nuclear pores that penetrate the fused regions. The membrane encloses a jelly-like fluid called nucleoplasm

6. Anatomy of a Generalized Cell • 1b. Nucleolus (pl. nucleoli)– Small dark-staining, essentially round bodies found in the nucleus. The site where ribosomes are assembled. • 1c. Chromatin – A combination of DNA and protein formed when a cell is not dividing. When cells divide, chromatin condenses and coils to form chromosomes.

7. Anatomy of a Generalized Cell • 2. Plasma Membrane – fragile, transparent barrier that contains the cell contents and separates them from the surrounding environment. • Has a core of 2 lipid layers in which protein molecules float. Most of the lipid portion is phospholipid and cholesterol. • Proteins are responsible for specialized functions of the membrane, being binding receptors, channels, or carriers.

8. Anatomy of a Generalized Cell • 2a. Microvilli– tiny fingerlike projections on the plasma membrane that increase cell surface area to speed absorption

9. Anatomy of a Generalized Cell • 2b. Membrane Junctions– where cells come together. • Tight junctions– adjacent plasma membranes fuse together, forming an impermeable junction • Desmosomes– anchoring junctions that prevent cells under mechanical stress from being pulled apart • Gap junctions– allow communication between cells through the connection by hollow cylinders (connexons)

10. Anatomy of a Generalized Cell • 3. Cytoplasm – the cellular material outside the nucleus and inside the plasma membrane that contains three major components: • 3a. Cytosol– semitransparent fluid that suspends other elements, nutrients, and solutes1

11. Anatomy of a Generalized Cell • 3b. Organelles– the metabolic machinery of the cell. Each organelle is engineered to carry out a specific cellular function. • 3c.Inclusions– chemical substances that may or may not be present.

12. Anatomy of a Generalized Cell • 4. Ribosomes – tiny, dark, round bodies made of ribosomal RNA (rRNA). They are the sites of protein synthesis. Some are free floating in the cytoplasm, others are attached to membranes.

13. Anatomy of a Generalized Cell • 5. Endoplasmic Reticulum (ER) – a system of fluid-filled cisterns that coil through the cytoplasm that provides a network for transport throughout the cell. • 5a. Rough ER – ER studded with ribosomes. Essentially all building materials of cellular membranes are formed here.

14. Anatomy of a Generalized Cell • 5b. Smooth ER – A continuation of rough ER (no attached ribosomes), but does not play a role in protein synthesis. Functions in cholesterol synthesis and breakdown, fat metabolism, and detoxification.

15. Anatomy of a Generalized Cell • 6. Golgi Apparatus – stack of flattened membranous sacs that modifies and packages proteins. Proteins for export pinch off via secretory vesicles.

16. Anatomy of a Generalized Cell • 7. Lysosomes – membrane sacs containing powerful digestive enzymes, they function in the breakdown of worn-out cells and foreign substances. • Lack of oxygen or excess vitamin A results in lysosome rupture and self-digestion of the cell.

17. Anatomy of a Generalized Cell • 8. Peroxisomes– membranous sacs containing powerful oxidase enzymes that use O2 to detoxify harmful substances and “disarm” free radicals (highly reactive chemicals with unpaired electrons) by converting them to H2O2. Catalase then converts H2O2 to water.

18. Anatomy of a Generalized Cell • 9. Mitochondrion (pl. mitochondria) – tiny sausage-shaped organelles. Their wall has a double-membrane. The outer membrane is smooth, but the inner has protrusions called cristae. The processes that use O2 to break down food to generate ATP take place here.

19. Anatomy of a Generalized Cell • 10. Cytoskeleton– elaborate network of protein structures that extends throughout the cytoplasm that provides structure and movement for the cell.

20. Anatomy of a Generalized Cell • 10a. Intermediate Filaments – help form desmosomes and provide resistance against pulling forces on the cell. • 10b. Microfilaments – involved in cell motility and producing changes in cell shape. • 10c. Microtubules – determine the shape of a cell and distribution of organelles and are important during cell division.

21. Anatomy of a Generalized Cell • 11. Centrioles – rod-shaped bodies close to the nucleus that form the mitotic spindle during cell division.

22. Anatomy of a Generalized Cell • 12. Cell Projections • 12a. Cilia– whiplike cellular extensions that move substances along the cell surface. • 12b. Flagella – longer than cilia, these extensions move the cell itself.

23. Anatomy of a Generalized Cell • Animal Cell Diagram

24. Cell Physiology • Most cells have the ability to: • Metabolize • Digest foods • Dispose of wastes • Reproduce • Grow • Move • Respond to a stimulus (irritability)

25. Cell Physiology • The fluid on both sides of the plasma membrane is a solution(homogeneous mixture of 2 or more components) • The substance present in the largest amount is the solvent • The substances present in smaller amounts are solutes

26. Cell Physiology • The intracellular fluid(nucleoplasm and cytosol) is a solution containing small amounts of gases, nutrients and salts dissolved in water • The interstitial fluid that continuously bathes the cells is similar

27. Cell Physiology • The plasma membrane is selectively permeable (allows some substances to pass through while excluding others) • Typical only of healthy, unharmed cells

28. Cell Physiology • Movement of substances through the plasma membrane happens in 2 ways: • 1. Passive Transport – substances are transported across the membrane without energy input from the cell • 2. Active Transport – cell provides ATP that drives the transport process

29. Cell Physiology • There are 2 types of passive transport: • 1a. Diffusion– the process by which molecules/ions tend to scatter themselves throughout available space. • The movement is from a region of higher concentration to a region of lower concentration (moving down their concentration gradient)

30. Cell Physiology • The speed of diffusion is affected by molecule size and temperature • The plasma membrane allows molecules to diffuse if: • They are small enough to pass through its pores • They can dissolve in the fatty portion of the membrane

31. Cell Physiology • The unassisted diffusion of solutes is simple diffusion • The diffusion of water through a selectively permeable membrane is osmosis • Diffusion that utilizes carrier proteins for assistance is facilitated diffusion

32. Cell Physiology • The tendency of a solution to hold water or take water in is osmotic pressure • The ability of a solution to change the size/shape of cells by altering their water content is called tonicity

33. Cell Physiology • Isotonicsolutions have the same solute and water concentrations as cells • Cells placed in isotonic solutions will exhibit no visible change • Hypertonic solutions contain more solutes than inside cells • Cells placed in hypertonic solutions will crenate (shrink)

34. Cell Physiology • Hypotonic solutions contain fewer solutes than inside cells • Cells placed in hypotonic solutions will lyse (burst)

35. Cell Physiology • 1b. Filtration – the process by which water and solutes are forced through a membrane by fluid/hydrostatic pressure. • The movement is from a region of higher pressure to a region of lower pressure (moving down their pressure gradient)

36. Cell Physiology • There are 2 types of active transport: • 2a. Solute Pumping – ATP is used to energize protein carriers called solute pumps. In most cases, substance move across concentration/electrical gradients • 2b. Bulk Transport – ATP helps to transport substances into/out of cells

37. Cell Physiology • Types of bulk transport: • Exocytosis – substances moving out of cells • Endocytosis – substances moving into cells • Phagocytosis – “cell eating” • Pinocytosis - “cell drinking”

38. Cell Physiology • Cell life cycle – series of changes a cell goes through from the time it is formed until it divides. There are 2 major periods: • Interphase – cell grows, carries on metabolic activities • Cell Division – cell reproduces itself

39. Cell Physiology • Prior to cell division, DNA is copied exactly (toward the end of interphase) • DNA helix uncoils and separates into 2 strands, each of which serve as a template • Nucleotides joint complementary base pairs: adenine (A) and thymine (T) and guanine (G) and cytosine (C)

40. Cell Physiology • Cell division consists of two parts: • 1. Mitosis – formation of two daughter nuclei • Prophase – chromatin coils to form chromosomes, which are made of two chromatids held together by a centromere. The centrioles separate and move toward opposite ends of the cell, directing the assembly of the mitotic spindle. By the end of prophase, nuclear membranes and nucleoli are broken down/disappeared and chromosomes are attached to spindle fibers by centromeres

41. Cell Physiology • Metaphase – chromosomes cluster and become aligned at the center of the spindle midway between the centrioles • Anaphase – the centromeres have split and the chromosomes move toward the ends of the cell

42. Cell Physiology • Telophase– chromosomes uncoil and become chromatin. The spindle breaks down/disappears, a nuclear membrane forms around the chromatin, and nucleoli reappear. • Depending on the type of tissue, mitosis takes 5 mins to several hours to complete

43. Cell Physiology • 2. Cytokinesis – the division of the cytoplasm. A cleavage furrow appears over the midline of the spindle and eventually squeezes the cytoplasmic mass into 2 parts. • At the end of cell division, 2 daughter cells exist • In some cases the cytoplasm is not divided, which leads to binucleate and multinucleate cells

44. Cell Physiology

45. Cell Physiology • DNA also serves as the blueprint for protein synthesis. • A gene is a DNA segment that carries the information for building one protein or polypeptide chain. • Proteins are key substances for all aspects of cell life • Enzymes are functional proteins that function as biological catalysts

46. Cell Physiology • Each sequence of three bases (triplet) calls for a specific amino acid. • The information in DNA is not useful without being “decoded”. • The decoder is ribonucleic acid (RNA)

47. Cell Physiology • There are three types of RNA molecules: • 1. Transfer RNA (tRNA) – small clover-leaf molecules • 2. Ribosomal RNA (rRNA) – helps form the ribosomes. • 3. Messenger RNA (mRNA) – long, single nucleotide strands that resemble half the DNA molecule

48. Cell Physiology • Protein Synthesis involves two major phases: • 1. Transcription – when complementary mRNA is made from DNA. • Each triplet on the DNA has a corresponding sequence on the mRNA called a codon

49. Cell Physiology • 2. Translation – when the information in mRNA molecules is “decoded” and used to assemble proteins. • Once the mRNA attaches to the ribosome, tRNA with the complementary codon (anticodon) transfers amino acids to the ribosome, where they are bound together by enzymes in the exact sequence specified by the mRNA.

50. Cell Physiology