Cytology Lecture Two PDF

Cytology Lecture two Cell  Introduction Cells are the basic structural and functional unit of the living organism showing a variety of functional specializations which perform all the activities necessary for the survival, growth and reproduction of the organism It is a self replicating...

Cytology Lecture two Cell  Introduction Cells are the basic structural and functional unit of the living organism showing a variety of functional specializations which perform all the activities necessary for the survival, growth and reproduction of the organism It is a self replicating, self regulating and self governing biological system Metabolism (absorption, synthesis, respiration and excretion), Growth and regeneration Irritability (excitability) Movement Reproduction Aging and death  Cont.… Number (around 100 trillion (1012) cells Type (more than 250 named cell types) Shape (round, oval, columnar, multipolar, polygonal, cylindrical, fusiform, pyramidal, pyriform, etc.) Size (5µm - 120µm in diameter) Functions  Cellular Functions in Some Specialized Cells Function Specialized Cell(s) Movement Muscle cell Synthesis and secretion of enzymes Pancreatic acinar cells Synthesis and secretion of mucous Mucous-gland cells substances Synthesis and secretion of steroids Some adrenal gland, testis, and ovary cells Ion transport Cells of the kidney and salivary gland ducts Intracellular digestion Macrophages and some white blood cells Transformation of physical and chemical stimuli into Sensory cells nervous impulses Metabolite absorption Cells of the intestine 4/4/2023 Fikre B. 5 Cont.… nucleus circle=cuboid cell flat=squamous cell WBCs10,000 under normal condition exceeds 10,000 when there's an infection round=cuboid cell Components of Eukaryotic Cell 1. Cell membrane 2. Cytoplasm 3. Karyoplasm (Nucleus)  1. Cell membrane dont forget to search up the three types trilaminar laminar layers In electron micrographs of osmium-stained tissue, appears as trilaminar layer, each layer 2.5 nm in diameter Because all membranes have this appearance, it is called the unit membrane  Cell membrane about 7.5 nm thick Biochemically made by the following components 1. Lipids volunme 90% weight 50% 2. Proteins volume 10% weight 50% 3. Carbohydrates  Phospholipids 75% Such as phosphatidylcholine (lecithin) With an amphipathic character (both hydrophobic and hydrophilic) Arranged in a bilayer, each with: Hydrophilic polar phosphate-containing head - towards water Hydrophobic nonpolar pair of fatty acid tails – away from water  Cholesterol Modulate the fluidity and movement of all membrane components maintaining the structural integrity of the plasma membrane  Proteins 50% w/w in the plasma membrane Most are globular proteins forming the following two groups: 1. Integral membrane proteins intrinsic 2. Peripheral membrane proteins extrinsic  Integral membrane proteins Some protrude from only one membrane surface, while others are transmembrane proteins and protrude from both sides  Peripheral membrane proteins Are more loosely associated, mostly on the inner membrane surface Bound to the polar groups of the membrane phospholipids or integral membrane proteins Usually functions as part of the cytoskeleton or an intracellular secondary messenger proteins of the cell those which are found inside the cell  Cell membrane proteins Functionally there are 6 broad categories of membrane proteins as: 1. Pumps 2. Channels 3. Receptors 4. Linkers 5. Enzymes 6. Structural proteins  Carbohydrates Occur as oligosaccharide attached to plasma membrane proteins as glycoproteins and lipid as glycolipids Branch and project from the outer surface of the outer leaflet of the plasma membrane They form a cell coat called glycocalyx that participates in: Cell adhesion to the extracellular matrix Binding of enzymes and antigens to the cell surface. Cell-to-cell recognition and interaction Organization of the cell membrane Are asymmetrical because of: Different composition of lipids Peripheral proteins are mainly on inner leaflet Oligosaccharides are on outer leaflet  Functions of the cell membrane 1. Selective permeability & transportation 2. Communication 3. Physical barrier 4. Intercellular connections  2. Cytoplasm It is the cellular material outside the nucleus but within the plasma membrane; consists of the following: Cytosol - cellular fluid (mainly water) with dissolved proteins, salts, sugars, and other solutes Organelles - ultramicroscopic structures that perform various cellular functions; ribosomes, ER, mitochondria, etc. Cytoskeleton - protein filaments and tubules that provide support, movement within the cell; cellular skeleton Inclusions - chemicals such as glycogen, fat, and pigments Cytosol, cytoplasm matrix (or ground substance) In between the three dimensional cytoskeletal structure Contains proteins, electrolytes, and metabolites dissolved in water (which makes 75-90%) Could generally be divided into an inner and outer domains  Organelles Metabolically active structures include: 1. Endoplasmic reticulum 2. Golgi complex (bodies or apparatus) 3. Lysosomes 4. Peroxisomes (microbodies) 5. Mitochondria 6. Endosomes and phagosomes 7. Proteasomes 8. Ribosomes 9. Cytoskeleton i. Microtubules ii. Microfilaments iii. Intermediate filaments 10. Centrioles  Endoplasmic reticulum Convoluted network of anastomosing membrane channels (cisternae ) of various shapes Show transfer vesicles which bud and move to the Golgi complex Are of two types: 1. Rough or granular endoplasmic reticulum 2. Smooth or agranular endoplasmic reticulum  Rough or granular endoplasmic reticulum (RER) Show continuity with the outer nuclear membrane Have docking proteins as receptors for ribosomes, and glycoprotein ribophorins Synthesize proteins for sequestration For export For proteins of the ER, the Golgi apparatus, Lysosomes or the cell membrane Transport molecules through cisternal space Under LM appear as basophilic patches formerly termed as: – Ergastoplasm in glandular cells – Nissl bodies in neurons they secret neuro transmiters  Smooth or agranular endoplasmic reticulum (SER) Have more tubular or vesicular cisternae than the RER is sacular Functions in: o Synthesis of phospholipids and steroids o Lipid metabolism o Glycogen breakdown o Detoxification o Transport molecules through cisternal space o Store and release calcium ions in the striated muscle cells as sarcoplasmic reticulum  Golgi complex (Golgi body or Golgi apparatus) Stalk of 3-10 discrete flattened and slightly curved bag-like channels or cisternae surrounded by vesicles Has the following two surfaces: a. Forming, convex, entry, cis face Closest to the nucleus Surrounded by small transfer vesicles (vesicles in) b. Maturing, condensing, exit, trans face Usually concave Has condensing vacuoles (vesicles out) and secretory granules  Golgi complex (Golgi body or Golgi apparatus) Functions in: Synthesis of polysaccharides Glycosylate proteins and lipid forming, respectively glycoproteins & proteoglycans and glycolipids Sulfate glycosaminoglycans Packaging of secretory products Concentration and storage of secretory products  Lysosomes Electron dense usually spherical bodies with a diameter of 0.05 - 0.5 μm Contain more than 40 hydrolytic enzymes (cause hydrolysis of a chemical bonds, breaking down bigger molecules), most commonly acid hydrolyases such as proteases, nucleases, phosphatase, phospholipases, sulfatases, and β-glucuronidase Most active at an acidic pH (5.0)  Peroxisomes (microbodies) Are like the lysosomes, but slightly larger in diameter (0.2–0.5 μm) Contain more than 40 oxidative enzymes that: – Produce hydrogen peroxide (H2O2) to kill microorganisms and detoxifies toxic agents Complement certain functions of the SER and mitochondria in the metabolism of lipids and other molecules Replicate by budding of precursor vesicles from the ER or fission of preexisting peroxisomes  Mitochondria Large spherical, filamentous or rod-shaped with diameters of 0.5-1 μm and 2-7 μm long Have double membranes a. Outer porous smooth membrane - containing many transmembrane proteins called porins that form channels b. Inner less porous membrane o Makes cristae Shelf-like in many cells Tubular in steroid secreting cells Able to rapidly changing shape, fusing together and dividing by fission  Mitochondria Have two spaces a. Intermembrane space (outer chamber, intracristal) b. Matrix space (intercristal space), which contains: o Enzymes, water, solutes, and granules that bind Ca2+ and Mg2+ o Mitochondrial ribosomes o mRNA, tRNA and rRNA o Circular DNA Like those of prokaryotic cells Are maternal  Endosomes and phagosomes Endosomes are membrane bound structures in the cell May be released at other side in transcytosis Phagosomes are found in the forms of: 1. Hetrophagosomes - ingested 2. Autophagosomes – self 3. May fuse with lysosomes forming the hetrophagolysosomes and autophagolysosomes  Proteasomes A cylindrical structure made of four stacked rings, each composed of seven proteins including proteases Degrade denatured or nonfunctional polypeptides tagged for degradation with a small protein called ubiquitin  Ribosomes About 20 × 30 nm in size Composed of : 1. Several types of ribosomal RNA (rRNA) 2. Specific ribosomal proteins Have large and small subunits Found in two forms: free ribosomes and polyribosomes (polysomes)  Polyribosomes or polysomes Clustered along a single strand of mRNA, and occur as: 1. Free polyribosomes Found in the cytoplasm Synthesize structural proteins and enzymes for intracellular use 2. Attached polyribosomes Attached to the outer nuclear membrane and RER Produce proteins to be secreted, proteins of the ER, the Golgi apparatus, Lysosomes or the cell membrane  Cytoskeleton Gel-like network of protein filaments Include: 1. Microtubules 2. Intermediate filaments 3. Microfilaments  Microtubules Tubular with 24 nm outer diameter, 5 nm wall thickness and variable length up to many micrometers Wall is made by tubulin heterodimers Each with α-tubulin and β-tubulin protein molecules Arranged as thread like polymers called protofilaments 13 protofilaments, circumferentially form wall of a microtubule  Microtubules Contain microtubule-associated proteins (MAPs), Include: a. Kinesin o Transport vesicles towards the plus end b. Dynein o Move vesicles towards the minus end c. Dynamin o Motor for sliding microtubules in respect to each other, for activities such as elongation of axon at growth cone  Microtubules Functions include Intracellular transport Maintaining cell shape Intracellular compartmentalization Cell migration  Intermediate filaments Are 10-12 nm wide, between microtubules and microfilaments Unlike microtubules and actin filaments, are stable, conferring increased mechanical stability to cell structure and tensile strength Formed of tetramers of rod-like proteins making staggering helical cable-like bundles Intermediate filaments Several types, the most common ones include: 1. Lamins - in nuclear lamina of all types of cells 2. Keratin or Cytokeratin - in all epithelial cells 3. Vimentin - in mesenchylly derived cells 4. Desmin - in all muscle cells 5. Neurofilaments - in neurons 6. Glial fibrillary acid protein (glial filament) - in glial cells  Microfilaments (Actin Filaments) Measure 5 -7 nm in diameter Composed of polymers of globular G-actin monomers that assemble into a double- stranded helix of filamentous F-actin G-actin is added to preexisting filaments for growth and branching, but new filaments can also be formed  Microfilaments (Actin Filaments) Have various myosin motor transport cargo along F-actin. Movement is usually toward the (+) ends Interactions between F-actin and myosins form the basis for various cell movements, which include: Transport of organelles, vesicles, and granules in the process of cytoplasmic streaming Cytokinesis during mitosis Endocytosis Muscle and contractile cells contraction  Centrioles Located at the centrosome, near the nucleus and Golgi bodies Cylindrical shaped, as a pair, perpendicular to each other Made by 9 triplets of microtubules Each microtubule in the triplet share portion of its neighbor’s wall Surrounded by pericentriolar bodies or microtubule-organizing centers (MTOCs) The MTOCs contain γ-tubulin rings, each of which serves as the nucleation site for the growth of a single microtubule  Centrioles Functions include: dont forget the amount of centrioles in the shaft of flagella and body of cilia Control microtubule polymerization Transmit physical organizing forces Control movements of organelles and vesicles Form the poles of mitotic spindle apparatus Form basal bodies of cilia and flagella  Inclusions Metabolically inactive materials Include: 1. Lipid droplets 2. Glycogen granules 3. Various types of pigments 4. Crystals  Inclusions 1. Lipid droplets Mainly in the adipose cells, but also in many other cells Triglycerides as energy source and stored cholesterol for the synthesis of steroids  Inclusions 2. Glycogen granules As clusters of electron-dense bodies (rosettes) specially abundant in the hepatocytes and muscle cells Converted to glucose Inclusions 3. Pigments a. Hemosiderin Brown colored inclusion that accumulates within the macrophages Breakdown product of hemoglobin Inclusions b. Lipofuscin Yellowish-brown pigment that increase with increasing age Are residual bodies of lysosomal activities Inclusions c. Melanin Brownish pigment mainly in the cells of skin and hairs (melanocytes & keratinocytes), but also in some neurons and in the pigment epithelium of retina  Inclusions e. Carbon particles Mainly in macrophages located in the lungs  Inclusions d. Carotenoid A yellowish-orange-red pigment obtained from vegetables and fruits  Inclusions 4. Crystals May be crystalline form of certain proteins In humans crystals described include: Crystals of Reinke in the interstitial cells of Leydig of testis Crystals of Charcot-Böttcher in the Sertoli cells of testis  3. Nucleus Oval, elongated or flattened in shape. 5-10 µm in diameter Composed of: 1. Nuclear envelope 2. Chromatin 3. Nucleolus 4. Nucleoplasm  Nuclear envelope Double membrane separated by perinuclear cisternal space (30-50 nm wide) 1. Outer nuclear membrane – Shows occasional continuities with the RER and has polyribosomes – Surrounded by a loose network of intermediate filament vimentin from its cytoplasmic aspect  Nuclear envelope 2. Inner nuclear membrane – Lined internally by nuclear (fibrous) lamina with intermediate filament lamins Contains specific lamin receptors and several lamina-associated proteins Functions include: – Serve as scaffolding for chromatin – Involved in nuclear organization, cell-cycle regulation, differentiation, and gene expression  Chromatin DNA and associated 5 basic proteins called histone, and nonhistone proteins Each of the 46 human DNA is about 40,000 μm long in average making a total of 1.8 - 2 meter long Located in a nucleus with a diameter of only 5 - 10 μm Undergo a super helical coiling to give repeating nucleosomes connected by short connecting strands  Chromatin A nucleosome is made by: 146-166 base pairs of the DNA strand wrapped twice around a core of a pair of 4 types of histones (H2A, H2B, H3 and H4) called an octamer The connecting strand as a 2-nm filament is made by 50-80 DNA base pairs with another type of histone (H1)  Chromatin Undergo further progressive super coiling and looping  Chromatin During interphase chromatin is identified as: 1. Heterochromatin transcriptionally inactive As dense basophilic staining by LM and dense granular regions by EM 2. Euchromatin transcriptionally active Lightly stained dispersed regions in the nucleus (not evident in the light microscope)  Heterochromatin Is found as: 1. Marginal chromatin – along the inner surface of the nuclear envelope associated with the fibrous lamina 2. Karyosomal chromatin – dispersed throughout the nucleus 3. Nucleolar associated chromatin – in the nucleolus 4. Bar body (sex chromatin) - one of the X chromosome , appears as drum stick appendage in the neutrophils  Nucleolus Round basophilic & non-membrane bound bodies Is site of rRNA synthesis and initial assembly of ribosomes Has a protein named nucleostemin that regulates the cell cycle and influences cell differentiation  Nucleoplasm Nuclear components other than the chromatin and nucleolus Although appear amorphous medium under microscopy it contains: Many proteins and other metabolites Intranuclear lamin-based structures Protein filaments of the nuclear pore complexes RNA transcription and processing apparatus  Cell Renewal Somatic cells may be classified according to their mitotic activity as: 1. Renewing cells – Slowly renewing cells – Rapidly renewing cells 2. Stable cells (quiescent cells)Eg: gamete cell 3. Static cells (permanent cell)Eg: cardiac muscle cells, neurons mucus cells 5-6 days skin cell up-to a month  Cell Cycle A self-regulated sequential events that controls cell growth and cell division The cell cycle stops at several checkpoints Driven by a family of cytoplasmic proteins called cyclins, cyclically synthesized and degraded during each cycle in response to intracellular or environmental signals  Cell Cycle In somatic cell is comprised of: 1. Interphase a. Gap1 (G1) phase b. Synthesis (S) phase c. Gap2 (G2) phase 2. Mitosis  The G1 (gap 1) phase Longest and most variable - a few hours to several days The cell: Gathers nutrients RNA and protein synthesis occurs Grow to the size of the parent cell Centrioles begin to duplicate  The G1 (gap 1) phase Monitored by 2 checkpoints: 1.G1 DNA-damage checkpoint Monitors the integrity of DNA If the DNA has irreparable damage it will most likely undergo programmed cell death (apoptosis)( n e c r o s i s )  The G1 (gap 1) phase 2. Restriction checkpoint – Is the most important checkpoint in the cell cycle – Cell self-evaluates its own replicative potential If requirements are met enter the S phase If requirements are not met cell cycle is paused and: 1. Attempt to remedy the problematic condition, or 2. Enter into G0 and awaiting further signals permanently (for static cell) or temporarily (for stable cells)  S (synthesis) phase Takes about 7.5 to 10 hours Undertake: DNA replication and doubling Histone synthesis Beginning of centrosome duplication Has S DNA-damage checkpoint Monitor quality of replicating DNA  G2 (gap 2) phase Is a period of : 1. Further cell growth and reorganization of cytoplasmic organelles 2. Examination of the replicated DNA by 2 checkpoints: a. G2 DNA-damage checkpoint b. The unreplicated-DNA checkpoint Prevents entry into the M phase before DNA synthesis is complete 4/4/2023 Fikre B. 74