Medicine 1-PBL Trans (1st Sem) PDF

MEDICINE 1- PBL Trans (1ST SEM) Lecture / Week 2/ Book-based Embryo-Origin-Inheritance-Fertilization-Implantation SPECIALIZED CELLS AND THEIR GENERAL...

MEDICINE 1- PBL Trans (1ST SEM) Lecture / Week 2/ Book-based Embryo-Origin-Inheritance-Fertilization-Implantation SPECIALIZED CELLS AND THEIR GENERAL CELL CELLULAR ACTIVITY body's building blocks providing structure for the body’s tissues and General Cellular Specialized Cell(s) organs Activity ingesting nutrients and converting them to energy Movement Muscles and other performing specialized functions contractile EUKARYOTES AND PROCARYOTES Form adhesive and tight Epithelial cells junctions between cells Prokaryotic Cell Synthesize and secrete Fibroblasts, cells of bone components of the and cartilage extracellular matrix Convert physical and Neurons and sensory chemical stimuli into cells action potentials Synthesis and secretion Cells of digestive glands of degradative enzymes Synthesis and secretion Cells of mucous glands of glycoproteins Eukaryotic Cell Synthesis and secretion Certain cells of the of steroids adrenal gland, testis, and ovary Ion transport Cells of the kidney and salivary gland ducts Intracellular digestion Macrophages and neutrophils Lipid storage Fat cells Metabolite absorption Cells lining the intestine Present organelles in eukaryotes: Endoplasmic reticulum Mitochondria CELL STRUCTURES Cytoskeleton Larger ribosomes The cell contains highly organized physical Membrane-bound nucleus structures called intracellular organelles, which are critical for cell function. Component structure functions nucleoplasm Plasma Phospholipid Acts as a physical Nuclear Double Separates nucleus membrane bilayer barrier to enclose envelope membrane from cytoplasm containing cell contents; boundary cholesterol regulates material between and proteins movement into and cytoplasm (integral out of the cell; and nuclear and establishes and contents; peripheral) maintains an continuous and some electrical charge with rough carbohydrate difference across endoplasmic s (externally); the plasma reticulum forms a membrane; selectively functions in cell Nuclear pore Openings Allow passage of permeable communication through the materials between boundary of nuclear the cytoplasm and the cell envelope nucleoplasm, including Cilia Short, Move substances ribonucleic acid numerous (eg, mucus and (RNA), protein, membrane dissolved materials) ions, and small extensions over the cell water-soluble supported by surface molecules microtubules, which occur Nucleolus Large, Functions in on prominent synthesis of exposed structure ribosomes membrane within surfaces of the nucleus some cells Cytoplasm Contents of Responsible for Microvili Numerous Increase membrane cells between many cellular thin surface area for the processes membrane greater absorption plasma folds membrane projecting and nuclear from the free envelope cell surface; supported by Cytosol Viscous fluid Provides support microfilament medium with for organelles; s dissolved serves as the solutes (eg, viscous fluid Flagellum Long, Propels sperm ions, medium through singular proteins, which diffusion membrane carbohydrate occurs extension s, lipids) supported by microtubules; Organelles Membrane-b Carry out specific present ound and metabolic activities on sperm non of the cell cells membrane-b ound Nucleus Large Houses the DNA structures structure that serves as the enclosed genetic material for Rough Extensive Modifies, within directing protein endoplasmic interconnecte transports, and a double synthesis reticulum d stores proteins membrane; (rough ER) membrane produced by contains network that attached chromatin, varies ribosomes; nucleolus, in shape (eg, these proteins are and cisternae, secreted, become Batch Sahaya | 2  tubules); components of the Mitochondria Double Synthesize most ribosomes plasma membrane, membrane-b ATP during aerobic attached on or ound cellular respiration cytoplasmic serve as enzymes organelles by digestion of fuel surface of lysosomes containing a molecules (eg, circular glucose) in the Smooth Extensive Synthesizes, strand of presence of oxygen endoplasmic interconnecte transports, and DNA (genes reticulum d stores lipids (eg, for producing (smooth ER) membrane steroids); mitochondrial network metabolizes proteins) lacking carbohydrates; ribosomes detoxifies drugs, Ribosomes Organelles Engage in protein alcohol, and composed of synthesis: Bound poisons; forms both protein ribosomes produce vesicles and and proteins that are peroxisomes ribosomal secreted, RNA (rRNA) incorporated into Golgi Series of Modifies, packages, that are plasma membrane, apparatus several and sorts materials organized and within elongated, that arrive from the into both a lysosomes; free flattened ER in transport large and ribosomes produce saclike vesicles; forms small proteins used within membranous secretory vesicles subunit; may the cell structures and lysosomes be bound to a membrane Vesicles Spherical-sh Transport cellular or free in aped material cytosol membrane bound sacs; Cytoskeleton Organized Maintains contain network of intracellular various types protein structural support of materials filaments and and organization of to be hollow cells; participates in transported tubules,inclu cell division; through the ding facilitates cell microfilament movement s, Lysosomes Spherical-sh Digest microbes or intermediate aped materials (eg, filaments, membrane ingested by the cell, and bound worn-out cellular microtubules organelles components, or the formed from entire cell) Microfilaments s Actin Maintain cell shape; the Golgi protein support microvilli; apparatus; monomers separate two cells contain organized during cytokinesis digestive into two thin, (a process of cell enzymes intertwined division); facilitate protein change in cell Peroxisomes Smaller, Detoxify specific filaments shape; participate spherical-sha harmful substances (actin in muscle ped either produced by filaments) contraction membrane-b the cell or taken ound into the cell; Intermediate Various Provide structural organelles engage in beta filaments protein support; stabilize formed from oxidation of fatty components junctions between the ER or acids to acetyl CoA cells through fission; Microtubules Hollow Maintain cell shape contain cylinders and rigidity; oxidative composed of organize and move enzymes tubulin organelles; support Batch Sahaya | 3  PLASMALEMMA protein cilia and flagella; participate in vesicular transport; plasma membrane” or “cell membrane” separate envelops the cell chromosomes thin, pliable, elastic structure (7.5 to 10 during the process nanometers thick) of cell division Composed of lipids, proteins, and carbohydrates Centrosome Amorphous Organizes 55% proteins, 25% phospholipids, 13% region microtubules; cholesterol, 4% other lipids, 3% carbohydrates. adjacent to participates nucleus; in mitotic spindle contains a formation during pair of cell division centrioles Proteasomes Large, Degrade and digest barrel-shape damaged or d protein unneeded proteins; complexes ensure quality of located in exported proteins both the cytosol and PLASMA MEMBRANE AND THEIR FUNCTIONS nucleus Inclusions Aggregates Serve as temporary Fluid Mosaic Model of specific storage for these types of molecules The membrane consists of a bimolecular lipid layer with molecules proteins inserted in it or bound to either surface. These (eg, melanin proteins comprise a moveable mosaic within the fluid protein, lipid bilayer, move laterally (lateral diffusion) an often glycogen, or restricted by: lipid) cytoskeletal attachments tight junctions CYTOPLASM Major components of the cell that surrounds the nucleus which contains the hereditary and genetic material. Batch Sahaya | 4 DIFFERENT STRUCTURES OF PLASMA MEMBRANE invariably protrude to the outside of the cell forming a mesh network. Membrane Lipids FUNCTIONS OF PLASMA MEMBRANE Physical Barrier - establishes a flexible boundary, protects cellular contents, and supports cell structure. The cell membrane separates substances inside and outside the cell. Selective Permeability - regulates entry and exit of ions, nutrients, and waste molecules through the membrane. Transport - carrier proteins or channels are incorporated within the membrane which allows passage of polar, large molecules (proteins), water-soluble molecules Communication - proteins in the cell membrane act as receptors that recognize and respond to molecular signals. Phospholipid Bilayer - are thin, amphipathic, double-layered film of lipids. TRANSPORT ACROSS THE PLASMA MEMBRANE Cholesterol - mainly help determine the degree of permeability (or impermeability) of the bilayer to Passive transport water-soluble constituents of body fluids. Diffusion: Simple Diffusion - High area of concentration to Membrane Proteins an area of low concentration w/o energy expenditure & transport proteins. Facilitated diffusion - High area of concentration to an area of low concentration w/o energy expenditure but with transport proteins. Osmosis - Lower solute concentration to an area of higher solute concentration via specific channels called “Aquaporins” Active transport Primary Active Transport Secondary Active Transport (cotransport) Contransport (Symport) Countertransport (Antiport) Bulk transport Endocytosis cells engulf external substances, bringing them into the cell Integral Proteins - act as carrier proteins for transporting Exocytosis substances that otherwise could not penetrate the lipid expel materials in vesicles, vesicle bilayer. fuse with the plasma membrane Includes transmembrane proteins which are Receptor-mediated ion channels or carrier proteins Peripheral Proteins - often attached to integral proteins. It TRANSPORT ACROSS THE PLASMA MEMBRANE functions almost entirely as enzymes or as controllers of transport of substances through cell membrane pores. Cytosol: jelly-like fluid portion of cytoplasm where Membrane Carbohydrates “Glycocalyx” particles are dispersed such as neutral fat globules, glycogen granules, ribosomes, secretory vesicles, and 5 Membrane carbohydrates occur almost invariably in important organelles. combination with proteins or lipids. ○ glycoproteins Important organelles: ○ glycolipids Endoplasmic reticulum The glyco portion of these molecules almost A.1. Rough endoplasmic reticulum Batch Sahaya | 5  A.2. Smooth endoplasmic reticulum Golgi apparatus vacuole Mitochondria - is the powerhouse energy of the cells, and is self replicating No limiting membrane Enclosed by the nuclear Lysosomes - A vesicular organelles that envelope breaks from golgi apparatus then disperse throughout the cytoplasm Does not consist of Consists of chromosomes chromosomes Intracellular digestive system (hydrolytic enzymes) : Rich in RNA Rich in DNA 1. Damaged cellular structure 2. Food particles that have been ingested by the cell GERM LAYERS 3. Unwanted matter such as bacteria Peroxisomes Ectoderm ←The ectoderm layer will differentiate into the 1. Formed by self-replication (budding nervous system, skin, and many sensory organs. off from SER) 2. Oxidases rather than hydrolases Derivatives of Ectoderm: (lysosomes) 3. Catalase: oxidase enzyme present in Surface Ectoderm (Epidermal layers of the skin) large quantities in peroxisome gives rise to: 4. Catabolize long chain fatty acids Epidermis (epidermal cells of the skin, hair, nails) Glands (sweat glands, sebaceous glands, CYTOSKELETON mammary glands) a dynamic network of protein filaments that Sensory structures (lens of the eye, inner ear extends throughout the cytoplasm of the cell. structures) Other structures (enamel of teeth, anterio Ectoplasm: actin filaments in the outer zone of the cell pituitary gland) 1. Microfilaments (Active filaments) Neuroectoderm differentiates into two main 2. Microtubulin components: 3. Intermediate filaments Neural tube (CNS) - forms the CNS including the brain, spinal cord, and retina and optic nerve. NUCLEUS AND NUCLEOLUS Nervous system: Brain and Spinal cord (CNS) PNS Sensory organs (eyes and ears) Skin and Related Structures: Epidermis Hair Nails Sweat glands Mammary glands Mesoderm ← It is the middle germ layer and is NUCLEOLUS NUCLEUS responsible for forming many of the internal structures and systems in the body. A sub-organelle in the A large spherical nucleus organelle found in Musculoskeletal System eukaryotic cells Bones Cartilage Composed of dense Composed of a nuclear Skeletal muscles fibrillar component, envelope, pores, lamina Circulatory System dibrillar center, granular nucleoplasm, Heart component and nuclear chromosomes, nucleolus Blood vessels Batch Sahaya | 6  Blood cells Pigment Cells: Lymphatic vessels Excretory and Reproductive System Melanocytes - Cells that produce melanin and Kidneys are responsible for pigmentation of the skin, Ureters hair, and eyes. Gonads (ovaries and testes) Reproductive ducts Craniofacial Cartilage and Bone: Dermis of the skin Connective tissue layer under the epidermis Skull and Jaw Bones: Some bones and cartilage of the face and neck, including the Endoderm ← It is the innermost germ layer and forms pharyngeal arches. the linings of many internal structures and organs, particularly within the gastrointestinal and respiratory Connective Tissue: systems. Dermis of the Face and Neck: Connective Digestive system tissue layers beneath the skin. Epithelial lining of the gastrointestinal tract Adipose Tissue: Fat cells (except the mouth and anus, which are ectodermal) Endocrine Cells: Liver pancreas Adrenal Medulla: Cells that produce Respiratory system adrenaline (epinephrine) and noradrenaline Epithelial lining of the respiratory tract (trachea, (norepinephrine). bronchi, lungs) Parafollicular Cells of the Thyroid: Cells that produce calcitonin. Neural Crest ← Group of cells that develop from the ectoderm and give rise to various structures, including Cardiovascular System: peripheral nerves and facial cartilage. Outflow Tract of the Heart: Parts of the heart Formation: and major blood vessels. The neural crest forms during neurulation, a process that follows gastrulation. TISSUES OF THE HUMAN BODY Migration: Epithelial - composed of closely aggregated Neural crest cells migrate extensively polyhedral cells with very little extracellular throughout the embryo to various regions, substance. These cells have strong adhesion following specific pathways that lead them to and form cellular sheets that cover the surface their final destinations. of the body and line its cavities. Location: Outer layer of the skin, lining of respiratory, Derivatives of Neural Crest Cells digestive, urinary, reproductive tracts, and glands. Neural crest cells are multipotent, meaning Nervous - ransmits electrical impulses they have the potential to develop into many different cell throughout the body, allowing for types and contribute to various structures in the body. communication between the brain, spinal cord, Here are some key derivatives: and other body parts. Location: tissue brain & spinal cord, nerves of the Peripheral Nervous System: body, sensory organs of the body Sensory ganglia - Neurons in the dorsal root Muscle - Facilitates movement of the body and ganglia that relay sensory information its parts. It plays roles in posture, heat Autonomic ganglia - Neurons that control production, and movement of substances within involuntary functions (sympathetic and the body. parasympathetic ganglia). Location: Bones, cartilage, tendons & ligaments, Enteric nervous system - Neurons that control blood fat the gastrointestinal tract. Batch Sahaya | 7  Connective - Provides structural and nutritional support, stores energy, and helps in tissue Cilia- long highly motile apical structures, larger repair. than microvilli and containing internal arrays of microtubules. EPITHELIUM LATERAL SURFACES a tissue in which cells are bound tightly together structurally and functionally to form a sheetlike or tubular structure with little extracellular material between the cells. Cells in epithelia each have an apical side facing the sheet’s free surface and a basal side facing a basement membrane and underlying connective tissue. often specialised for absorption or transcytosis, pinocytosis of material at the apical side and exocytosis at the basolateral side (or vice versa). exhibit continuous renewal, with the locations of Tight junctions, or zonulae occludens: are the stem cells and rates of cell turnover variable in most apical of the junctions. "Zonula" indicates various specialised epithelia. that the junctions form bands completely Features: encircling each cell, and "occludens" refers to Highly cellular, with little or no extracellular the membrane fusions that close off the space material present between cells between the cells. Thus, the principal function Joining cells form specialised intercellular of the tight junction is to form a seal that connections called cell junctions prevents the flow of materials between Polarity with differences in structure and epithelial cells. function between the apical and the basal surface. Adherens junction or zonula adherens Avascular; nutrients must enter the tissue by diffusion or absorption from underlying tissues encircles the cell, usually immediately below or the surface. the zonula occludens, and provides for the firm adhesion of one cell to its neighbours. Main Functions: Cell adhesion is mediated by cadherins, Protect - barrier formation transmembrane glycoproteins of each cell that Absorption - nutrient uptake bind each other in the presence of Ca2+ Secretion - production of Substances Desmosome or macula adherens, as the Filtration- selective permeability name implies, this junction resembles a single Sensation - sensory reception “spot-weld” and does not form a belt around the Excretion- waste removal cell. Absorption and Transport- transport of materials Desmosomes are disc-shaped structures at the Formation of Membranes - serous surface of one cell that are matched with membranes identical structures at an adjacent cell surface. EPITHELIAL CELLS Gap junctions- Mediate intercellular communication rather than adhesion or APICAL SURFACES occlusion between cells. Connexins form hexameric complexes called connexons Microvilli - small membrane projections with cores of actin filaments that generally function Hemidesmosomes - (Gr. hemi, half + desmos to increase epithelial cell’s apical surface are + soma). These adhesive structures resemble a for absorption. half-desmosome ultrastructurally, clustered transmembrane proteins that indirectly link to Stereocilia- long microvilli with specialized cytokeratin intermediate filaments are integrins. mechanosensory function in the cells of the inner ear and for absorption in tissues of male Focal adhesion/ focal contact reproductive tract. Batch Sahaya | 8  Although resembling hemidesmosomes The excretory ducts of salivary and sweat superficially, focal adhesions are smaller, more glands numerous, and consist of integrins linked ➔ Columnar - Covering the ovary, thyroid indirectly to bundled actin filaments, not Conjunctiva lining the eyelids, where it is both intermediate filaments. protective and mucus secreting. Relatively rare CLASSIFICATION OF EPITHELIAL CELLS ➔ Transitional - Bladder, ureters, renal calyces Pseudostratified ➔ Lining of trachea, bronchi, nasal cavity FEATURES OF BASAL MEMBRANE Simple epithelia- one cell layer Stratified epithelia- two or more layers Pseudostratified - thick and appear to have Basal lamina: All epithelial cells in contact with several cell layers connective tissue have at their basal surfaces a sheet of Transitional- specialised to stretch (e.g., extracellular structure. urinary bladder lining). Lamina densa: Consisting of a network of fine fibrils Lamina lucida : The basal laminae may have Cell Morphology electron-lucent layers on one or both sides of the dense layer. Squamous - thin cells Cuboidal- cell width and thickness roughly Basement membrane: often thicker due to the fusion of similar the basal lamina from each epithelial layer. Columnar - cells taller than they are wide The most macromolecular components of basal laminae Simple epithelia are: Squamous - Lining of vessels (endothelium); 1. Laminin: These are large glycoprotein - Serous lining of cavities; molecules that self-assemble to form a lace-like - Pericardium, pleura, peritoneum sheet immediately below the cells' basal poles (mesothelium) where they are held in place by the Cuboidal- Covering the ovary, thyroid transmembrane integrins. Columnar - Lining of intestine, gallbladder Stratified epithelia 2. Type IV collagen: Monomers of type IV ➔ Squamous - collagen contain three polypeptide chains and “Keratinized” (packed with keratin self-assemble further to form a felt-like sheet filaments) - epidermis of skin, where associated with the laminin layer. it helps prevent dehydration from the tissue. 3. Entactin (nidogen), a glycoprotein, and “Non-keratinized” (relatively sparse perlecan, a proteoglycan with heparan sulfate keratin) - lines moist internal cavities side chains: (eg, mouth, esophagus, and vagina) where water loss is not a problem. ❖ These glycosylated proteins and others serve to link together the laminin and type IV collagen ➔ Cuboidal- Covering the ovary, thyroid sheets. Relatively rare Batch Sahaya | 9 Reticular lamina These proteins are produced by cells of the connective tissue and form a layer below the basal lamina. ❖ Type III Collagen ❖ Type VII Collagen Basal laminae: Simple structural and filtering functions influence cell polarity Regulate cell proliferation and differentiation by binding and concentrating growth factors Influence cell metabolism and survival Organise the proteins in the adjacent plasma a tough, durable form of supporting connective membrane and serve as pathways for cell tissue, characterized by an extracellular matrix migration (ECM) with high concentrations of GAGs and Contain the information necessary for many proteoglycans, interacting with collagen and cell-to-cell interactions, such as the enervation elastic fibers. of enervated muscle cells its function involves having a firm consistency that allows the tissue to bear mechanical CONNECTIVE TISSUES stresses without permanent distortion. its resiliency and smooth, lubricated surface, BONE cartilage provides cushioning and sliding regions within skeletal joints and facilitates bone movements. BLOOD COMPONENTS a specialized connective tissue composed of calcified extracellular material, the bone matrix, and three major cell types (3 O’s) as Osteocytes, Osteoblasts, and Osteoclasts They are lined on their internal and external a specialized connective tissue consisting of surfaces by layers of connective tissue cells and fluid extracellular material called containing osteogenic cells. The endosteum plasma. elements circulating in the plasma are on the internal surface surrounding the marrow erythrocytes(red blood cells), leukocytes cavity and the periosteum on the external (white blood cells), and platelets. surface. Its main function is to work as a distributing vehicle, transporting O2, CO2 metabolites, CARTILAGE hormones, and other substances to cells throughout the body. Batch Sahaya | 10  also participates in heat distribution, the regulation of body temperature, and the NERVOUS TISSUE maintenance of acid-base and osmotic balance. MUSCLE TISSUE The nervous system's supporting structures include various components that provide structural and functional support to neurons. components are collectively known as the contains bundles of very long, multinucleated neuroglia or glial cells, along with the extracellular cells with cross-striations. contraction is quick, matrix and connective tissue coverings associated with forceful, and usually under voluntary control. the central and peripheral nervous systems. Muscle connective tissue can be divided into three primary layers: Epimysium, Perimysium, and Endomysium. EMBRYOBLAST AND TROPHOBLAST DEVELOPMENT Epimysium- the outermost layer that surrounds the entire muscle, helps to protect muscles from friction against other muscles and bones, and maintains the integrity of the muscle tissue. Perimysium- layer surrounds bundles of muscle fibers known as fascicles. provides pathways for blood vessels and nerves to reach the muscle fibers, aiding in the transmission of force generated by the muscle fibers. Endomysium- innermost layer that surrounds individual muscle fibers. provides an extracellular matrix that helps maintain the position of muscle fibers and facilitates the exchange of metabolites between muscle fibers and capillaries. Blastocyst formation - occurs 5 days after fertilization Blastocyst is formed when the embryo reaches the uterine cavity. Batch Sahaya | 11  Embryoblast (Inner cell mass)- contributes to Interphase the formation of embryo and fetus. collective term for the phases of the cell cycle Trophoblast (Outer cell mass)- contributes to when cells grow and replicate their DNA the development of the placenta. G1 - longest and most variable phase of the cell cycle; APOPTOSIS characterized by active RNA and protein synthesis Apoptosis- programmed cell death, degrading and an increase in cell volume all cellular components in a regulated process. S - characterized by DNA replication, histone synthesis, and the beginning of centrosome duplication PROCESS OF NEURULATION G2 - short duration; accumulation of synthesized proteins takes place Postmitotic cells can enter a quiescent state called the G0 phase while differentiating. Differentiated cells like liver cells can re-enter the cell cycle under certain conditions. Terminally differentiated cells, such as muscle and nerve cells, generally do not re-enter the cell cycle. Mitogens or growth factors - protein signals from the extracellular environment that triggers reactivation of cell cycle in the G0 cells by binding to cell surface receptors to initiate a kinase signaling cascade Cyclins - a family of cytoplasmic proteins that regulate CELL CYCLE overall cell cycling the regular sequence of events that cells undergo to produce new cells Cyclin-Dependent Kinase (CKD) - an enzyme consists of repeated cycles of macromolecular activated by cyclins that phosphorylates target proteins to synthesis (growth) and division (mitosis) before regulate progression through the cell cycle cells differentiate Mitosis Four Distinct Phases of the Cell Cycle a cell division wherein a parent cell divides and 1. Mitosis each of the two daughter cells receives a 2. G1 chromosomal set identical to that of the parent 3. S cell 4. G2 the only cell cycle phase that can be routinely distinguished with the light microscope Duration of Cell Cycle Phases Mitotic Phase Cellular Activity Diagram Prophase - Nucleolus Early Prophase disappears - Chromatin condenses into discrete chromosomes with duplicate sister chromatids joined at the Late Prophase centromere. Batch Sahaya | 12  cytoplasm and organelles into two daughter cells, each with one nucleus. ese checkpoints monitor the quality of specific Metaphase - Chromosomes cell activities further condense - Kinetochores, (G1/S), Metaphase/anaphase, and G2/M large protein checkpoint complexes at the ThProgression to the next phase of the cycle centromere, does not occur until all activities of the attach to the preceding phase are completed satisfactorily mitotic spindle - The cell becomes more spherical - Microtubules align chromosomes at the equatorial plate. Anaphase - Sister chromatids (now individual chromosomes) separate. - Chromosomes move toward opposite spindle poles. - Movement is driven by microtubule Meiosis motor proteins and changes in a specialized process involving two unique and microtubule closely associated cell divisions that occurs length as spindle only in the cells that will form sperm and egg poles distance cells increases. Two key features characterize meiosis: Telophase - Chromosomes 1. During synapsis, homologous chromosomes reach spindle pair up, undergo DNA breakage and repair, and poles and start to de-condense exchange genetic material through crossovers, - Spindle resulting in unique gene combinations in germ microtubules cells. depolymerize 2. Haploid cells, each with one chromosome from and nuclear each pair, combine during fertilization to form a envelope diploid zygote, which can develop into a new reassembles individual. around daughter chromosomes Mitosi - Actin-myosin First Meiotic Division contractile ring forms at the cell Prophase - prolonged in the first meiotic division and is equator - The contractile usually divided into the following stages: ring creates a cleavage furrow, Leptotene - chromosome becomes visible and dividing the condensed, sister chromatids of each chromosome are closely placed Batch Sahaya | 13  Zygotene - synapsis or conjugation (pairing of homologous chromosomes), paired chromosomes are called bivalent or tetrad chromosomes Pachytene - the two chromatids of each chromosome become distinct; a crossing over occurs ○ Crossing over - the process where central chromatids from each CELL MATURATION chromosome coil and cross over at multiple points the process by which a cell becomes fully ○ Chiasmata - the points where developed or differentiated chromatids cross and become adherent to each other Maturation often involves: Diplotene - homologous chromosomes separate apart from each other a. Differentiation - cells morph to become - The “loose” pieces become attached to the specialized for specific tasks opposite chromatid, resulting in exchange of b. Functional development - cells acquire the genetic material between the chromatids specific functions and abilities required for their roles in the body Metaphase - The 46 chromosomes align at the spindle's c. Physiological changes - cells may change in equator, with paired chromosomes positioned close size, shape, and structure to better perform together (similar to mitosis) their functions Anaphase- One chromosome from each pair moves to each pole of the spindle, resulting in daughter cells with 23 chromosomes, each consisting of two chromatids. CELLULAR RESPIRATION Telophase - Two daughter nuclei are formed, in which the a catabolic reaction taking place in the cells division of the nucleus is followed by division of the the process by which cells break down cytoplasm. nutrients to release energy Conversion of nutrients in the human body: Carbohydrates - converted into glucose Proteins - converted into amino acids Fats - converted into fatty acids Adenosine Triphosphate Known as the cell's energy currency due to its continual turnover Composed of adenine (nitrogenous base), ribose (pentose sugar), and three phosphate radicals. ATP energy conversion: The first meiotic division is followed by a short ATP splits a phosphoric acid radical to form interphase without DNA duplication. adenosine diphosphate (ADP) Mitosi ○ The released energy is used for Second Meiotic Division cellular processes. Resembles mitosis. Key functions include Due to crossing over in the first division, synthesizing substances daughter cells have unique genetic content and muscle contraction Differences between mitosis and meiosis Chemiosmotic mechanism - refers to the overall process for formation of ATP Batch Sahaya | 14 Stages of Cellular Respiration 1. Glycolysis 2. Pyruvic acid conversion 3. Krebs cycle (citric acid cycle) 4. Electron transport chain Krebs Cycle (Citric Acid Cycle) a series of enzyme catalyzed reactions where acetyl-CoA is oxidized to form carbon dioxide and coenzymes are reduced, which generate ATP in the electron transport chain occurs in the mitochondrial matrix Glycolysis the primary step of cellular respiration the process in which glucose is broken down to produce energy takes place in the cytoplasm of a cell Electron-transport chain converts redox energy from NADH and FADH2 into a proton-motive force, which synthesizes ATP through conformational changes in ATP synthase electrons transfer from organic compounds to oxygen and release energy through the created chemical gradient that can be used to power oxidative phosphorylation Pyruvate oxidation this process is crucial for ATP regeneration, cycling ATP into ADP and back approximately Pyruvate, formed in glycolysis, enters the 300 times a day mitochondrial matrix Pyruvate undergoes oxidative decarboxylation, producing two molecules of Acetyl CoA the reaction is catalyzed by the pyruvate dehydrogenase enzyme Batch Sahaya | 15  Specificity: a particular codon always code for the same amino acid Universality: its specificity has been conserved from very early stages of evolution, with only slight differences in the manner in which the code is translated Degeneracy: each codon corresponds to a single amino acid, a given amino acid may have more than one triplet coding Nonoverlapping and Commaless: code is read from a fixed starting point as a continuous sequence of bases, take three at a time ○ Eg. AGCUGGAUACAU read as AGC/UGG/AUA/CAU TYPES OF RNA Directly involved in protein synthesis: 1. messenger RNA (mRNA) - produced in the nucleus - carries the code for the synthesis of proteins - mRNA Comprises only 5% of all RNA in the cell. - Polycistronic mRNA-Carries information for more than 1 gene (prokaryote) GENETIC CODE - Monocistronic mRNA- Carries information for only 1 gene (eukaryote) Codon transfer RNA (tRNA) set of three-letter combinations of nucleotides - small RNA molecule - Collection of these codons, once transcribed to mRNA, - carry​the​amino​acids​to​the ribosome with makes up the genetic code Anticodon its anticodon - three-nucleotide sequence found on tRNA that binds to - It contains a high percentage of the corresponding mRNA sequence unusual bases ex. Dihydrouracil. - Site of protein synthesis is covalently Nucleotide Bases of DNA attached to the 3' end. Adenine (A) Thymine (T) - Makes up 15% of the RNA in the cell. Guanine (G) ribosomal RNA (rRNA) Cytosine (C) - Component of ribosomes and serves as the organelle of translation Purine - exported to the cytoplasm to help Adenine-Thymine(DNA)/Uracil (RNA) translate the information in mRNA Pyrimidine Guanine-Cytosine into protein. - 64 possible three-base combinations, 61 code for the - Make up 80 percent of the total RNA. 20 common amino acids and three signal termination of protein synthesis Participate in mRNA splicing or modulation of gene expression: START Codon: AUG STOP Codon: UAA, UAG, UGA precursor messenger RNA (pre-mRNA) - ​large, immature, single strand of RNA that is Characteristics processed in the nucleus to form mature mRNA Batch Sahaya | 16  ○ introns - removed in the RNA 1. Initiation splicing ○ exons - retained in the mRNA - enzyme ​RNA ​polymerase ​(RNAP) binds to the promoter region of DNA. small nuclear RNA (snRNA) - RNA polymerase separates the DNA strands -​directs the splicing of pre-mRNA to - providing single-stranded template form mRNA. - when the RNAP binds with the promoter, it microRNAs (miRNA) signals the DNA to unwind so the enzyme can -​regulate gene transcription and read the bases in one of the DNA strand translation. - enzyme can now make a strand of mRNA with a complementary sequence of bases RNA is synthesized from DNA template 2. Elongation 3 steps: -Eukaryotic pre-mRNA have their ends 1. Initiation modifie 2. Elongation - Addition of 5’ cap and 3’ poly-A tail 3. Termination - pre-mRNA undergo splicing TRANSCRIPTION - Introns are chopped out - Exons are stuck back together -​occurs in nucleu - RNA polymerase moves along the DNA strand - synthesizes complementary RNA strand by adding nucleotides, making a chain that grows from 5’ to 3’ - adenine pairs with uracil in RNA 3. Termination - RNAP crosses a stop (termination) sequence in the gene on the DNA template - sequences called terminators signal the RNA transcript is complete - RNA polymerase and the newly synthesized RNA molecule detach from the DNA - example of a termination mechanism involves the formation of a hairpin in RNA Batch Sahaya | 17  2. Elongation Modified mRNA TRANSLATION -​occurs in cytoplasm 1. Initiation - methionine-carrying tRNA starts in the middle slot of the ribosome (P site - a fresh codon is exposed in another slot (A site - A site will be the “landing site” for the next tRNA, where the anticodon is complementary for the exposed codo - peptide bond is formed, when the matching tRNA arrived in the A site, that connects the amino acid togethe - this transfers the methionine from the first tRNA onto the amino acid of the second tRNA in the A site - methionine​forms​the N-terminus of the polypeptide, and the other amino acid - tRNA carrying methionine attaches to C-terminus. the small ribosomal unit - together they binds to the 5’ end of mRNA going in the 3’ direction, stopping when they reach the start codon - large ribosomal subunit joins the small subunit, forming a functional ribosome Batch Sahaya | 18  growth factor receptors and various cytoplasmic proteins. 3. Termination CELL DIFFERENTIATION - natural process through which a cell with less specificity develops and matures to become more distinct in terms of form and function.- - cell size, shape, polarity, metabolism, and responsiveness to signals change dramatically such that a less specialized cell becomes more - the ribosome reaches a stop codon specialized and acquires a more specific role- (UAA, UAG, or UGA) enters the A - undifferentiated is used to describe a cell (or a site tissue) that has not yet acquired a special - stop codons are recognized by structure and function proteins (release factors) which fit perfectly in the P site PROCESS: - terminates protein synthesis and release the ribosome - all cells in the body, begins with the fertilized egg called zygote - zygote divides to make more cells until it Molecular (Genetic) Control of becomes blastocysts which contain the Growth, Differentiation and stem cells Development - all stem cells contain the same full complement of DNA, but each type of Several genes and gene families cell only “reads” the portions of DNA play important roles in the - different cells regulate gene expression development of embryo. Most of with the use of various transcription these genes produce factors. transcription factors that control - primary mechanism of a gene genes are transcription of RNA. turned “on” or “off” Transcription factors play an - transcription factors are proteins that important role in gene affect the binding of RNA polymerase to expression as they can switch a particular gene on the DNA molecule genes on and off by activating or - transcription factors has a major role in repressing them. determining which genes are expressed Many transcription factors control in a cell before a cell is going to have a other genes, which regulate different areas of g fundamental embryological processes of induction, segmentation, migration, differentiation and apoptosis (programmed cell death). These fundamental differentiation factors are mediated by growth and differentiation factors, Batch Sahaya | 19  3. Endothelial stem cells which give rise to the endothelial cell types that line blood and lymph vessels 4. Mesenchymal stem cells which give rise to the different types of muscle cells ➔ Embryonic stem cells ➔ Fetal stem cells Growth Factors - This group of peptides controls cell growth and differentiation. Cell Surface Specialization enes ➔ Totipotent; first embryonic cells that arise from the division of the zygote are the ultimate stem cells ➔ Pluripotent; one that has the potential to differentiate into any type of human tissue but cannot support the full development of an organism ➔ Multipotent; has the potential to differentiate into different types of cells within a given cell lineage or small number of lineages ➔ Oligopotent; limited to becoming one of a few different cell types ➔ Unipotent; fully specialized and can only reproduce to generate more of its own specific cell type Stem Cell ➔ Adult stem cells 1. Epithelial stem cell, which gives rise to the keratinocytes 2. Hematopoietic stem cells which give rise to red blood cells, white blood cells, and platelets Batch Sahaya | 20 Batch Sahaya | 21