Unit I, chapter-2 Cellular level of organization.
- 1. Unit:-I, Chapter:-2 Cellular level of organization Represented By, Mr. Audumbar Mali. (Assistant Professor) Sahyadri College of Pharmacy Methwade BP101T. Human Anatomy And Physiology-I (Theory)
- 2. CELL •A cell is the basic, living, structural and functional unit of living organisms. •There are about 200 different types of cells in our body. •All cells produced by the process of cell division. •Cell biology is the study of cellular structure and function. •Structure of the cell is intimately related to its function.
- 3. PARTS OF ACELL 1. Plasma membrane 2. Cytoplasm a) Cytosol b) Organelles 3) Nucleus
- 4. The plasma membrane •Structure: • The membrane is composed of proteins and lipids (phospholipids). • It bind together by non covalent forces • The phospholipid molecules have head which is electrically charged and hydrophilic in nature. A tail which has nocharge and hydrophobic in nature. • In this layer the sugar molecule is embedded in between them.
- 5. Functions • Protection • Barrier • Shape of the cell • Cell junction • Cell movement • Selective permeability • Impulse transmission
- 6. Cytoplasm • The cytoplasm has two components a) Cytosol: • It is the fluid portion of cytoplasm that contains water (75-90 %), ions, amino acids, proteins, lipids, ATPand waste products. b) Organelles: 1. Ribosomes 2. Endoplasmic reticulum (smooth & rough) 3. Golgi complex 4. Mitochondria 5. Nucleus
- 7. 1. Ribosomes • These are tiny granules composed of RNA & protein. • They synthesize protein from amino acids using RNA. • When this is present in free units in the cytoplasm, the ribosomes make proteins for use within the cell. • Ribosomes are also found on the outer surface of the nuclear envelope and rough endoplasmic reticulum where they manufacture proteins for export from the cell.
- 8. 2. Endoplasmic Reticulum •It is the series of interconnecting membranous canals in the cytoplasm. There are 2 types of endoplasmic reticulum 1. Smooth endoplasmic reticulum: • Here is lack of ribosomes 2. Rough endoplasmic reticulum: • This is studded with ribosomes that synthesize proteins.
- 9. 3. Golgi apparatus • It consist of stack of closely folded flattened membranous sac. • It present in all cells but is larger in those cells that synthesize and export proteins. • The proteins move from ER to golgi apparatus where they are ‘packaged’ into membrane bound vesical called secretory granules. • The vesicles are stored and when needed more to plasma membrane, through which the proteins are exported.
- 10. 4. Nucleus • Every cell in the body has nucleus, with exception of mature RBC. • Skeletal muscle and some other cell contain several nuclei. • It is the larger organelle of the cell and is contained within the nuclear envelope. • The nucleus contains body’s genetic material which directs all metabolic activities of the cell. •This consist of 46 chromosomes, which are made from DNA.
- 11. 5. Mitochondria • This is also called ‘Power House’of cell. • They are involved in the aerobic respiration. The process by which chemical energy is made available in the cell. • This energy is in the form of ATP which release energy when the cell break it down. • Synthesis of ATP is most efficient in the final stage of aerobic respiration. A process requiring oxygen.
- 12. TRANSPORT OF MATERIAL ACROSS THE CELL •Motion of substances in and out of the cell •Cell membranes are Selectively permeable •Two Types of Transport Mechanisms: 1. Passive Transport 2. Active Transport
- 13. Membrane transport •Passive transport is movement of molecules through the membrane in which no energy is required from the cell •Active transport requires energy expenditure by the cell
- 14. 1. Passive Transport •Passive transport is movement of molecules through the membrane in which no energy is required from the cell. • Molecules move in response to a concentration gradient. - A concentration gradient is a difference between the concentration on one side of the membrane and that on the other side. •Passive transport mechanisms only movement substances along the concentration gradient.
- 15. 1. Passive Transport •Passive transport mechanisms only movement substances along the concentration gradient: - Substances move from an area of high concentration to an area of low concentration
- 16. 1. Passive Transport •Mechanisms of Passive Transport: 1. Diffusion -movement of solute molecules from high solute concentration to low solute concentration 2. Osmosis -movement of solvent water from high solvent concentration to low solvent concentration
- 17. Diffusion • Diffusion is movement of solute molecules from high concentration to low concentration.
- 18. Diffusion •There are two types of diffusion I. Simple Diffusion II. Facilitated Diffusion
- 19. I. Simple Diffusion •Substances pass directly through the cell membrane •The cell membrane has limited permeability to small polar molecules, water, and ions •The motion of water across the membrane is known as osmosis
- 20. diffusion depends on the •The rate (molecules/s) of simple degree of concentration gradient •As the gradient reaches equilibrium, diffusion slows •At equilibrium, substances pass in and out of the membrane at equal rates
- 21. II. Facilitated Diffusion •Substances must pass through transported proteins to get through the cell membrane. •The cell membrane is selectively permeable. •Carrier proteins bind to the molecule that they transport across the membrane.
- 22. II. Facilitated Diffusion •Selective permeability: integral membrane proteins allow the cell to be selective about what passes through the membrane. -Channel proteins have a polar interior allowing polar molecules to pass through. -Carrier proteins bind to a specific molecule to facilitate its passage.
- 23. Ion Channels
- 24. Carrier Proteins Carrier proteins bind to a specific molecule to facilitate its passage.
- 25. Osmosis •Osmotic concentration is determined by the concentration of all solutes in solution.
- 26. 16 2. Active Transport Active transport • Requires energy – ATP is used directly or indirectly to fuel active transport • Able to moves substances against the concentration gradient - from low to high concentration - allows cells to store concentrated substances •Requires the use of carrier proteins
- 27. Active transport
- 30. 20 Bulk Transport Bulk transport of substances is accomplished by 1.Endocytosis – movement of substances into the cell 2.Exocytosis – movement of materials out of the cell
- 31. 21 Bulk Transport •Endocytosis occurs when the plasma membrane envelops food particles and liquids. 1. phagocytosis – the cell takes in particulate matter 2.pinocytosis – the cell takes in only fluid 3. receptor-mediated endocytosis – specific molecules are taken in after they bind to a receptor
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- 34. Intercellular space in closely packed tissue is about 20nm. The cells are bound together by the specific adhesive glycoprotein. Epithelial cells adhere to each other through glycoproteins called Cadherins Modified cell membranes contributing in cohesion and communication are called Cell junctions Cell Junctions
- 35. There are three types of Cell Junctions 1. Tight Junctions or Occluding Junctions 2. Adhering Junctions 3. Communicating Junctions Types of Cell Junctions
- 36. Found in epithelial tissues Also known as “Tight Junctions” Do not allow passage of small molecules form impermiable membrane. Types: Zonula Occludens Fascia Occludens 1. Tight Junctions
- 37. Encircles the entire cell perimeter Occludes the intercellular space Series of focal fusions The adjacent cell membranes approach each other, outer leaflets fuse, diverge again then fuse again At fusions sites specific trans membranous proteins named (Occludins, and Claudins) perform the binding function Less in PCT and more in the intestinal mucosa Zonula Occludens
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- 39. A strip like tight junction of limited extent Found between the endothelial cells of the blood vessels Fascia Occludens
- 40. Anchoring junctions Provide cell-cell or cell to basal lamina adherence Types: Zonula adherens Fascia adherencs Macula adherens (Desmosomes) Hemidesmosomes Adhering Junctions
- 41. A belt like junction No fusion of cell membranes Trans membranous glycoprotein “E-cadherin” occupies intercellular gap E-cadherin links to adherent proteins in cytoplasm which are: Catenin Vinculin Zonula Adherens
- 42. Structurally it is similar to Zonula adherence But its cell junction is strip-like and (not ring-like or belt-like) i.e. Cardiac muscle cells. Fascia Adherens
- 43. Macula adherins are commonly known as desmosomes “Spot-weld” like junctions Randomly distributed along lateral plasma membranes of the cells in simple epithelium In stratified epithelium it is distributed throughout the plasma membrane It is also found in cardiac muscle cells 2. Desmosomes
- 44. Cell membrane in the region of junctions are seen further apart (30mm) than the usual gap Electron dense attachment plaques are located opposite to each other on the cytoplasmic aspects Intermediate filaments of the cytoskeleton are anchored to the attachment plaques Two types of transmembranes glycoproteins named Desmocolins and Desmogleins provide adherence Desmosomes
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- 46. These junctions serve to anchor the epithelial cells to the basal lamina A hemidesmosome is a spot like adhering junction which gives appearance of a half desmosome In hemidesmosome transmembrane linker proteins are integrins The cytoplasmic intermediate filaments of keratin are inserted in to the attachment plaque Hemidesmosomes
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- 48. Characterized by presence of minute tubular passageways Provide direct cell to cell communication Tubular passages allow movement of ions and other small molecules between adjacent cells Communicating Junctions
- 49. Gap junction also called the “Nexus” which are communication junctions, occur frequently between the epithelial cells Also found in cardiac muscle cells, smooth muscles, neurons, astrocytes, and osteocytes Plasma membrane of the adjoining cells are closely opposed with a gap of only 2nm The gap junction contains closely packed numerous tubular intercommunicating channels 3. Gap Junction
- 50. The lumens of the channels of gap junction have an average diameter of 1.5nm These channels permit free passage of ions, sugar and amino acids In cardiac and smooth muscles the gap junction provides electrical coupling of the adjacent cells Gap junctions are frequently found in embryonic cells Gap Junctions
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- 53. Cells belonging to renewing population undergoes a sequence of events which are repeated over and over again The cycle is divided in to two parts M PHASE: in which mitosis occurs (30 to 60 minutes) INTERPHASE: it is intervening period between two cell divisions consist of three sub phases 1 The G1 Phase -During this phase synthesis of RNA and proteins occur s -Cell size is restored to normal -The duration of G1 is about 8 hours Cell Cycle
- 54. 2 The S-Phase: -During this synthesis of DNA takes place -It results in preparation of exact replica of genetic material and duplication of centrioles -Duration is 8 hours 2 G2 Phase: - It is period between the end of S phase and beginning of mitosis -During this process production and accumulation of energy for mitosis takes place -Duration is 2 to 4 hours Cell Cycle
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- 57. Mitosis • The process of cell division which results in the production of two daughter cells from a single parent cell. • The daughter cells are identical to one another and to the original parent cell.
- 58. Mitosis can be divided into stages 1. Interphase 2.Prophase 3. Metaphase 4.Anaphase 5. Telophase
- 59. Interphase The cell prepares for division DNA replicated Organelles replicated Cell increases in size
- 60. Chromosomes become visible under LM Threads become shorter and thicker consist of two chromatids joined by centromere Nucleoli disappears Centrioles separates and migrate to each pole and starts giving out mitotic spindle Prophase The cell prepares for nuclear division
- 61. Chromosomes line up at the center of the cell Spindle fibers attach from daughter cells to chromosomes at the centromere Equatorial plate is formed Microtubules of mitotic spindle are attached at centromere Microtubules exert pull on chromosomes Metaphase The cell prepares chromosomes for division
- 62. Spindle fibers pull chromosomes apart ½ of each chromosome (called chromatid) moves to each daughter cell Chromatids separate and move to respective poles as an independent chromosome In human cell two identical sets of 46 chromosomes move to the opposite poles Anaphase The chromosomes divide
- 63. A constriction called cleavage furrow appears in the middle of elongated cell Nuclear envelop is formed enclosing chromosomes 2 nuclei form Cell wall pinches in to form the 2 new daughter cells Telophase The cytoplasm divides
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- 65. Mitosis -- Review Interphase Prophase Metaphase Anaphase Telophase Interphase
- 67. • Meiosis is the type of cell division by which germ cells (eggs and sperm) are produced. • One parent cell produces four daughter cells. • Daughter cells have half the number of chromosomes found in the original parent cell Meiosis
- 68. During meiosis, DNA replicates once, but the nucleus divides twice. Four stages can be described for each division of the nucleus. Meiosis
- 69. Prophase is much longer consisting of five stages 1. Leptotene: Chromosomes becomes visible in the nucleus 2. Zygotene: Homologus chromosomes come together along their entire length and synapses are formed 3. Pachytene: Chromosomes become thicker and shorter Each chromosome pair is called bivalent 4. Diplotene: Chromosomes began to separate along their length. Each bivalent consists of four chromatids 5. Diakinesis: Separation of chromosomes continue. Nucleolus and the nuclear envelop disappears Prophase
- 70. A spindle of microtubules is produced by centrioles Equatorial plate is formed The bivalent chromosome pairs align in the centre of the spindle Metaphase
- 71. Chromosomes of homologous pairs completely separates and move to the opposite poles No division of centromere occurs and the whole chromosomes move to opposite poles Anaphase
- 72. Nuclei are reconstructed The parent cell is divided in to two daughter cells Each daughter cell contains haploid (23) chromosomes Each chromosome is double structured consisting of two sister chromatids Telophase
- 73. Meiosis II
- 74. Differences in Mitosis & Meiosis Mitosis Asexual Cell divides once Two daughter cells Genetic information is identical Meiosis Sexual Cell divides twice Four haploid daughter cells Genetic information is different
- 75. General principles of cell communication •Cell signaling is part of a complex system of communication that governs basic activities of cells and coordinates cell actions. •The ability of cells to perceive and correctly respond to their microenvironment is the basis of development, tissue repair, and immunity as well as normal tissue homeostasis. Classification These signals can be categorized based on the distance between signaling and responder cells. Signaling within, between, and among cells is subdivided into the following classifications: 1. lntracrine signals are produced by the target cell that stays within the target cell. 2. Autocrine signals are produced by the target cell, are secreted, and affect the target cell itself via receptors. Sometimes autocrine cells can target cells close by if they are the same type of cell as the emitting cell. An example of this is immune cells.
- 76. 3. Juxtacrine signals target adjacent (touching) cells. These signals are transmitted along cell membranes via protein or lipid components integral to the membrane and are capable of affecting either the emitting cell or cells immediately adjacent. 4. Paracrine signals target cells in the vicinity of the emitting cell. Neurotransmitters represent an example. 5. Endocrine signals target distant cells. Endocrine cells produce hormones that travel through the blood to reach all parts of the body. 6. Some cell-cell communication requires direct cell-cell contact. Some cells can form gap junctions that connect their cytoplasm to the cytoplasm of adjacent cells.
- 77. (a) Contact-dependent signaling: In which two adjacent cells must make physical contact in order to communicate. This requirement for direct contact allows for very precise control of cell differentiation during embryonic development. In the worm Caenorhabditis elegans, two cells of the developing gonad each have an equal chance of terminally differentiating or becoming a uterine precursor cell that continues to divide. The choice of which cell continues to divide is controlled by competition of cell surface signals. One cell will happen to produce more of a cell surface protein that activates the Notch receptor on the adjacent cell.
- 78. (b) Endocrine signaling: Many cell signals are carried by molecules that are released by one cell and move to make contact with another cell. Endocrine signals are called hormones. Hormones are produced by endocrine cells and they travel through the blood to reach all parts of the body. Specificity of signaling can be controlled if only some cells can respond to a Particular hormone. (c) Paracrine signaling: Paracrine signals such as retinoic acid target only cells in the vicinity of the emitting Cell. Neurotransmitters represent another example of a paracrine signal. Some signaling molecules can function as both a hormone and a neurotransmitter. For example, epinephrine and norepinephrine can function as hormones when released from the adrenal gland and are transported to the heart by way of the blood stream.
- 79. (d) Synaptic signaling: Synaptic signaling is a special case of paracrine signaling (for chemical synapses) or juxtacrine signaling (for electrical synapses) between neurons and target cells. Signaling molecules interact with a target cell as a ligand to cell surface receptors, and/or by entering into the cell through its membrane or endocytosis for intracrine signaling. This generally results in the activation of second messengers, leading to various physiological effects.
- 80. References: 1. Presentation on Introduction To Human Anatomy & Physiology, By Mr. Abhay Shripad Joshi. 2. Human Anatomy and Physiology-I, By Dr. Mahesh Prasad, Dr. Antesh Kumar Jha, Mr. Ritesh Kumar Srivastav, Nirali Prakashan, As per PCI Syllabus. Page No. 1.7 to 1.22. 3. www.google.com.
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