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Histology of the cell : 

Histology of the cell Overview Plasma membrane Mitochondria Ribosome Endoplasmic reticulum Golgi complex Lysosome Cytoskeleton Nucleus

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Actin filaments Intermediate filaments Golgi complex Secondary lysosome Digested material in vacuole for exocytosis Smooth ER (SER) Rough ER (RER) Polyribosome Golgi vesicles Pinocytotis Plasma membrane Mitochondrion Nucleus Nucleolus Transfer vesicles Phagocytosis Typical cell

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Plasma Membrane Lipid bilayer with incorporated proteins and carbohydrates Primary function is segregation Selective barrier Recognition of specific substances for regulation of function

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Polar hydrophilic region Non-polar hydrophobic region Choline Phosphate Glycerol Fatty acid Phospholipid molecule is principle part of cell membrane

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Lipid molecules form lipid bilayer in water Hydrophobic layer (hate water) in middle of membrane Hydrophilic layers (love water) on outside of membrane

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Composition of lipid bilayer Extracellular space Cytoplasm Carbohydrates on glycolipids and glycoproteins serve as receptors for hormones (intercellular communication), cell adhesion, and attachment to extracellular matrix Integral proteins embedded in lipid layer Fatty acids (non-polar) Polar phosphate lipid Sugar chain of glycoprotein

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EM of plasma membrane and glycocalyx Three layers of plasma membrane Glycocalyx Glycocalyx: 1. External to cell membrane 2. Formed by carbohydrates of glycoproteins and glycolipids Extracellular space Staining of membrane: 1. Hydrophobic layer stains light 2. Hydrophilic layers stain dark

Functions of membrane proteins : 

Functions of membrane proteins Receptors for chemical signals, transducers (glycolipids & glycoproteins) enzymes Molecule transport into and out of cell (channel protein, pumps) Attachment sites for cytoskeletal filaments Attachment sites for extracellular matrix Actin cytoskeleton Channel protein Transmembrane protein Glycoprotein receptor Glycolipid receptor

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Cytoplasm Extracellular substance Extracellular space Endocytotic vesicle (endosome) Endocytosis 1. Pinocytosis: transport into cell by invaginated cell membrane engulfing fluid and small molecules 2. Phagocytosis: transport into cell by invaginated cell membrane engulfing large substance (e.g. bacterium, damaged cell)

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Exocytosis 1. Membrane-bound vesicle with stored substances 2. Fusion of membrane-bound vesicle to surface membrane 3. Expulsion of stored substances into extracellular space Extracellular space Cytoplasm 4. Membrane of fused vesicle added to surface membrane

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EM of formation of endocytotic vesicles Endocytotic vesicles Invagination of cell membrane to form endocytotic vesicles Microvilli (little fingers) of cell surface project into extracellular space

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Outer membrane Inner membrane Matrix Intermembranous space Crista Mitochondrion 1. Outer membrane: Contains pores for passage of molecules to/from cytosol and intermembranous space 2. Inner membrane: Contains enzymes for oxidative phosphorylation, electron transport system, ATP synthetase 3. Matrix: Contains circular DNA, RNA, mitochondrial proteins OM and IM = Outer and inner membranes C = Cristae EM

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Formation of ATP in mitochondrion (Heat produced) Matrix

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Typical mitochondrion with flat, shelf-like crista Mitochondrion of steroid secreting cell (adrenal cortex) has tubular crista Comparison of cristae of mitochondria in typical cells and steroid secreting cells

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Ribosome : Small subunit binds mRNA Large subunit forms peptide chain Ribosomes, mRNA, and tRNA form proteins RER: Rough endoplasmic reticulum is membrane-lined channels (cisterna) covered by polyribosomes. Peptides enters cisterna (ER lumen)

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Endoplasmic reticulum (ER) ER synthesizes and transports proteins and lipids 1. RER (Rough ER) is rough due to polyribosomes attached to outer membrane surface for protein synthesis; Stains basophilic; Composed of stacks of cisternae; Continuous with smooth ER. 2. SER (Smooth ER) lacks polyribosomes; Synthesizes steroid hormones and phospholipids; Composed of tubular cisternae. 3. Both RER and SER form transport vesicles (contain substance) that travel via cytoplasm to Golgi. Cistern is membrane covered space

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EM of rough endoplasmic reticulum (RER) Ribosomes on cytosolic surface Cisternae Stacks of flattened cisterna

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Golgi complex Golgi complex 1. Cis face receives transport vesicles 2. Trans face forms Golgi vesicles Containing final substance Golgi transport vesicle ER transport vesicle Functions of Golgi complex A. Gylcosylation of proteins B. Lysis of peptides to active form. C. Packaging, concentration, and storage of secretory products

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Function of specific cisternae and types of Golgi vesicles Gycosylation of proteins and lipids Types of vesicles formed from trans face of Golgi 1. Vesicles transport newly formed cell membrane for addition to surface membrane 2. Lysosomes (for intracellular digestion) 3. Secretory vesicles for release of substance to extracellular space (e.g. hormones) by exocytosis Phosphorylation of proteins New membrane formed Trans Golgi Middle Golgi Surface membrane Extracellular space 1. Sorting of molecules into specific vesicles by 2. Lysis of peptides to active product 3. Additional glycosylation of proteins and lipids Cis Golgi

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Lysosomes for intracellular digestion of cellular components and extracellular particulate matter Lysosomes 1. Hydrolytic enzymes synthesized in RER, transferred to Golgi, and packaged as lysosomes. Enzymes work at low pH. 2. Membrane of lysosomes prevents leakage of enzymes into cytoplasm preventing self-digestion of cell. 3. Extracellular matter can be taken up by endocytosis to form phagocytic vesicle (phagasome); Lysosome fuses with vesicle and releases hydrolytic enzymes for digestion. 4. Intracellular matter (old organelles) enclosed in phagocytic vesicle that fuses with lysosome for self-digestion. 5. Indigestible matter is retained in vesicle now called residual body. 6. Residual bodies in long-lived cells form lipofuscin (age pigment). 7. Digestable material diffuses into cytoplasm. Phagocytic vesicle

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EM of Golgi complex Cis face of Golgi Trans face of Golgi Dilated vesicle with synthesized substance about to bud off from Golgi SER Transport vesicles from RER RER with synthesized granular matter in cisterna High power view of RER below RER Secretory vesicles

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EM of lysosomes and secondary lysosomes Membrane (M) -bound vesicles containing acid hydrolases (C) Membrane-bound lysosomes contain acid hydrolases Secondary lysosomes formed by fusion of lysosome (hydrolytic enzymes) with phagocytic vacuole

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Peroxisomes Peroxisome 1. Small membrane bound vesicle 2. Oxidize substance by removing hydrogen, which is transferred to oxygen to make hydrogen peroxide 3. Catalase breaks down hydrogen peroxide which can damage cell Peroxisomes Glycogen granules for storage of carbohydrate

Cytoskeleton : 

Filamentous proteins form internal framework of cell Attach to membranes and other filaments via anchoring and joining proteins Functions Shape of cell Intracellular transport Anchoring to other cells and extracellular matrix Three types of filaments Microfilaments Intermediate filaments Microtubules Cytoskeleton

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Microfilaments Gobular proteins (g-actin) form actin filaments (F-actin) Polymerize at “+” end and depolymerize at “-” end of F-actin filament; Filaments constantly forming and breaking down Form filamentous cross-linked meshwork (cell cortex) beneath plasma membrane of cell Anchor to cell membrane via transmembranous proteins of plasma membrane of cell Interact with myosin proteins (thick filaments) for contractile forces as in muscle contraction Actin filament polymerizing from G -actin at “+” end and depolymerizing at “-” end to form free G-actin Cell membrane Actin filament Actin linking protein Cell cortex

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EM of microfilaments and microtubules Actin filaments (AF) Microtubules (MT, tubular structure)

Microtubules form tubular structures : 

Formed from alpha and beta subunits Polymerize (+) end and depolymerize (-) end Stable in cilia; Transitory in mitotic spindles Emerge from microtubule organizing bodies (e.g. basal bodies, centrosomes) Microtubules form tubular structures Alpha-tubulin Beta-tubulin Microtubule (-) end EM cross-section of microtubules and tubulin subunits Microtubule Cross-section of microtubule and subunits Cross-section: Ring of 13 subunits

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Cilia (motile ) and centrioles (microtubule organizing center) Cilium Cilium 1. Covered by cell membrane 2. Central core with nine pairs of outer microtubules and a central pair of tubules (9 +2) 3. Nexin is linking protein A Centrosome Centriole Triplet of microtubules Protein links Centriole 1. Bundle of nine microtubule triplets 2. Centrosome is a microtubule organizing center made of one pair of centrioles oriented perpendicular to the other EM of cross-section of centriole

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Cilia on apical cell membrane of ciliated cells Lumen Cilia sweep fluid across apical surfaces of cells in epithelium (sheet of cells) Cilia Basal Bodies

Nucleus: Contains DNA : 

Nucleolus Nuclear pore Nuclear envelope Heterochromatin Euchromatin Nucleus: Contains DNA Nucleus Stains basophilic with hematoxylin Contains nucleolus for formation of ribosomal RNA subunits Nuclear membrane has pores for two-way transfer between cytosol and nucleus Outer nuclear membrane Continuous with RER Encloses perinuclear space Inner nuclear membrane Lamins are filamentous proteins attached to proteins of inner nuclear membrane; form a nuclear skeleton Two types of chromatin Euchromatin Actively transcribing DNA Light stained region of nucleus in LM or EM Heterochromatin Inactive DNA not being transcribed Dense stained regionclose to nuclear membrane RER

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EM of nucleus Euchromatin Heterochromatin Nucleolus Heterochromatin Euchromatin Mitochondria Perinuclear space in nuclear envelope

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Nuclear pores in nuclear membrane Inner and outer nuclear membranes Nucleus Nuclear membranes and pores Nucleus Cytoplasm Nuclear pore EM of nuclear membranes and pores Denotes nuclear pore Perinuclear space

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Step one in formation chromatin and chromosomes: Nucleosome Nucleosome 1. DNA wrapped around a basic protein called a histone 2. Globular structures of nucleosome form “pearls on a necklace” Histones DNA

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Steps one, two and three in formation of chromatin and chromosomes Nucleosome beads Chromatin formed from winding of nucleosome beads into filaments Chromosome (condensed chromatin) formed during cell replication Histone DNA Nucleosome

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Cell storage products: Lipid vacuoles and glycogen particles LM of lipid vacuoles in adrenal steroid secreting cells EM of lipid vacuoles in adrenal steroid secreting cell Lipid vacuoles Nucleus Lipid vacuoles Mitochondrion Glycogen particles prominent in liver cells Lipid vacuoles provide ready source of lipid precursor for steroid hormone synthesis Glycogen particles provide a ready supply of glucose after conversion

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Cell storage products: Pigments Exogenous (from without) - Carotene (plants) - Dusts (smoking) - Minerals (tattoo) Endogenous (from within) - Hemoglobin (hemosiderin, bilirubin, biliverdin) - Melanin - Lipofuscin (residual bodies)

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