Cell Morphology: Cytoplasm Organelles PDF

CELL MORPHOLOGY Institute for medical histology and embryology Ass. Prof. Irena Kostadinova Petrova  Cytoplasm Kytos cell Plasma liquid medium in cells The word plasma denotes matter that does not fully correspond to any of the three aggregate states that can be used...

CELL MORPHOLOGY Institute for medical histology and embryology Ass. Prof. Irena Kostadinova Petrova  Cytoplasm Kytos cell Plasma liquid medium in cells The word plasma denotes matter that does not fully correspond to any of the three aggregate states that can be used to describe a matter (gaseous, liquid, solid) Structural components of the cytoplasm Cytosol Cell organelles Cellular inclusions Cytoskeleton Topographic regions of the cytoplasm Cortex Cytocenter, centrosome Endoplasma Topographic regions of the cytoplasm  Cytosol H2O aminoacids, proteines, enzymes, nucleotides, RNK, glucose, ATP, ions…  Cell organelles Лизозоми Visualization of the structural components of the cytoplasm Light microscopy ТЕМ – electron microscopy СЕМ – electron microscopy  Cell organelles Organelles Membranous Nonmembranous organelles organelles  mitochondria  ribosomes  rough endoplasmic  Centrioles reticulum  smooth endoplasmic reticulum  Golgi apparatus  lysosomes  peroxisomes  Function: Ribosomes Protein synthesis small unit big unit Structure of the ribosomes Small subunit – one rRNA molecule and 33 different proteins. Sedimentation coefficient: 40S. Large subunit – three rRNA molecules and 40 different proteins. Sedimentation coefficient: 60S.  Synthesis of ribosomes rRNK - nucleolus Polypeptide chains - cytoplasm Association of rRNA and proteins and creation of ribosomal subunits - nucleus Ribosomal subunits pass through the nuclear pores into the cytoplasm, where they bind and show their activity  Protein synthesis Ribosomal function Binding sites of iRNK and tRNK One iRNA binding site Two tRNA binding sites The small subunit serves to decode the genetic message The large subunit is the catalyst for the formation of peptide bonds Free ribosomes Monoribosomes (monosomes) – individual ribosomes scattered throughout the cytoplasm Polyribosomes (polysomes) – ribosomes, interconnected with the mRNA chain, located in the cytoplasm. Membrane-bound ribosomes Polyribosomes are bound to the membrane of the endoplasmic reticulum (ER) mRNA carries a message that codes for the sequence of amino acids in the proteins that the cell needs to synthesize Free polyribosomes: synthesize proteins that remain in the cytoplasm of the cell (hemoglobin, contractile proteins, keratin, peripheral membrane proteins, mitochondrial proteins). Membrane-bound polyribosomes: mainly synthesize proteins that leave the cell (hormones and enzymes) and proteins that remain in the cell (lysosomal enzymes and membrane proteins). Visualization of ribosomes with a scanning electron microscope Scan – electron micrograph of ribosomes, they are observed as spherical bodies Decoding the message from mRNK (translation) and synthesis of polypeptide chains  Visualization of ribosomes with a light microscope Due to the presence of rRNA, ribosomes have an affinity for basic dyes  Endoplasmic reticulum A complex membrane system that encloses flattened, oval or tubular spaces (cisterns, vesicles or tubules) that communicate with each other (anastomose) and form a reticulum (network).  Rough endoplasmic reticulum Primary function: Protein synthesis A complex membrane system that encloses mostly flattened spaces (cisterns), and polyribosomes are bound to its surface. rER: mainly synthesizes proteins that leave the cell (hormones and enzymes), and also proteins that remain in the cell (lysosomal enzymes and membrane proteins). The membrane is an extension of the nuclear membrane, and the spaces communicate with the perinuclear space. Rough endoplasmic reticulum Active cell – dilated cisternae. Weakly active cell – flattened cisternae. Rough endoplasmic reticulum  Basophilia of the rough endoplasmic reticulum Cells of exocrine pancreas (that produce large amount of enzymes) show basophilic staining of the cytoplasm due to the preasense of rough endoplasmatic reticulum  Cells with intensive protein synthesis Glandular cells that produce protein secrets: pancreatic exocrine cells Cells that produce intercellular matrix (fibroblasts, chondroblasts, osteoblasts, odontoblasts, ameloblasts) Cells that produce specific proteins - immunoglobulins (plasma cells) Cells that constantly renew their integral proteins (nerve cells)  Creation of membrane proteins and their integration into the cell membrane Cell membrane proteins are synthesized in the rER and then move in transport vesicles to the Golgi apparatus. Oligosaccharide chains (glycosylation) are added to many membrane proteins in the Golgi apparatus. When glycosylation and other posttranslational modifications are complete, mature membrane proteins are sequestered within secretory vesicles that leave the Golgi apparatus. These vesicles move to and fuse with the cell membrane, thereby incorporating the new membrane proteins (along with the vesicle's lipid bilayer) into the cell membrane. Smooth endoplasmic reticulum Smooth endoplasmatic reticulum Connecting the sER to the rER on one side and the Golgi apparatus on the other Primary function: Lipid synthesis neutral lipids steroid hormones glycogenolysis detoxication Well developed cisternae of smooth endoplsmic reticulum Cells in: hepar adrenal cortex testis ovarium  Smooth endoplasmic reticulum Smooth endoplasmic reticulum in the cytoplasm of kidney cells. Apart from the synthesis of lipids, it also produces membrane-bound proteins. sER in skeletal muscle cells Sarcoplasmic reticulum  Rough and smooth endoplasmic reticulum  Golgi apparatus 6 – 8 disk-shaped cisternae that do not communicate between themselves The central part of the cisternae is narrower and their ends are widened  Cis face Medial part Trans face Cis or forming face is oriented towards ER Trans or maturing face is oriented towards cell membrane  Golgi apparatus Primary function Synthesis of: glycoproteins, glycolipids, glycosaminoglycans, proteoglycans Modification and packaging of proteins and lipids synthesized in the ER Cell membrane renewal Constitutive secretion – secretory vesicles are directed directly to the plasmalemma (characteristic of goblet cells) Transport vesicles Secretory vesicles supstrat Regulated secretion – secretory vacuoles are temporarily deposited in the cytosol, and their content is condensed many times (secretory granules). Their secretion is released when there is adequate stimulation for it (cells that secrete hormones). Regulated secretion – secretory granules A cell from the exocrine pancreas that synthesizes digestive enzymes and releases them into the small intestine through drainage channels.  hydrolase enzymes Primary lysosomes – are formed by budding of vesicles from the trans-Golgi network. They are filled with hydrolase enzymes. They are covered with a clathrin coat that is lost immediately after separation from the Golgi apparatus.  Secretory Constitutive vesicles Regulated secretion secretion Golgi apparatus (TEM) Golgi apparatus (SEM) The Golgi apparatus is named after its inventor, the Italian histologist Camillo Golgi, who discovered the organelle in 1898 while researching neurons. Visualization of the Golgi apparatus with a light microscope is difficult (silver impregnation technique - Defano staining in which the Golgi apparatus is seen as a group of dark spots. The cells in the image are intestinal epithelial cells. Mitochondria Energy center Mitochondria create and store energy in the form of adenosine triphosphate (ATP). Energy is obtained by metabolizing glucose and fatty acids through the Krebs cycle and oxidative phosphorylation. Energy is needed for both biosynthetic and motile (moving) activities of cells.  Structure Outher mitochondrial membrane Inner mitochondrial membrane – with folds called cristae, which greatly increase its surface. Cristae are most numerous in the mitochondria of highly active cells. Intermembrane space Matrix – gel containing numerous enzymes, mitochondrial DNA and RNA. The surface of the inner membrane is lined with many multimeric protein complexes resembling globular units on short stalks. They are known as ATP synthetases (oxisomes) that generate most of the cell's ATP.  Mitochondrial matrix Enzymes Mitochondrial DNA and RNA Ribosomes Matrix granules Krebs cycle and oxidative phosphorylation enzymes Matrix granules: depot of Ca++ and Mg++ Mitochondrial DNA Mitochondrial DNA is circle shaped Due to the presence of their own DNA and protein synthesis system, mitochondria have some similarities with bacteria. They are therefore believed to originate from some aerobic bacteria The child inherits the mitochondrial DNA only from the mother through the cytoplasm of the oocyte Mitochondria  Permeability of mitochondrial membranes The inner mitochondrial membrane is significantly impermeable to ions (electrochemical gradient across the membrane) due to the presence of the protein cardiolipin. The channel that runs through the oxisome (enzyme complex) allows protons to flow through it, down the electrochemical gradient, and across the membrane back into the intermembrane space. During the penetration of protons through the oxisomes, energy is released, which the oxisomes use for the synthesis of ATP from ADP.  mitochondria During cell division, each daughter cell receives ½ of the number of mitochondria. Furthermore, their number can increase with the growth and division of mitochondria.  Mitochondrial defects due to mutations in nuclear DNA or mitochondrial DNA (maternal inheritance) Mitochondria show morphological changes Muscle dysfunction Skeletal muscles are particularly sensitive to mitochondrial damage because they have a high-energy metabolism (high energy consumers). drooping of the upper eyelid difficulty swallowing weakness of the limbs  Lysosomes  Lysosomes are organelles (oval vesicles) surrounded by their own membrane.  They contain hydrolytic enzymes necessary for intracellular digestion (they break down bacteria, viruses, degenerated organelles, etc.).  They are numerous in cells responsible for various types of endocytosis.  Primary lysosomes Clathrin is a protein that plays a major role in the formation of enveloped vesicles Small vesicles, enveloped by a clathrin coat. They contain over 40 different types of hydrolases. They are created in the Golgi apparatus, and enzymes in the ER. Primary lysosomes are inactive lysosomes.  Primary lysosomes Secondary lysosomes (phagolysosomes) Autophagia Autophagia removal of its worn- out organelles He te Heterophagia ro ph digestion of ag substrates that i a enter the cell from the outside Tertiary lysosomes (residual bodies)  Tertiary lysosomes (residual bodies) Primary Secondary Tertiary lysosome lysosome lysosome (phagosome) (residual body) Terminal phase in lysosomal function They contain the remains of undigested ingredients (that's why they are named residual bodies)  Lipofuscin If the residual bodies accumulate in the cell, they form the pigment of aging - lipofuscin Example: some long-living cells: neurons, cardiac muscle cells  Visualization of lysosomes with TEM - electron microscope  In TEM, lysosomes (L) have the characteristic appearance of structures with high electron density (density). Located near Golgi cisternae (G) and centrioles (C)  Heterolysosomes, in which the digestion of the content is in progress, have a lower electron density. The cell is a macrophage with numerous fine cytoplasmic extensions (arrows)  Visualization of lysosomes by light microscope and toluidine blue staining Cells in the renal tubule show numerous purple lysosomes (L) in the cytoplasm between the basally located nuclei (N) and the apical ends of the cells. By a process of endocytosis, these cells actively ingest (swallow) small proteins from the lumen of the tubule, degrade the proteins in lysosomes, and then release the resulting amino acids for reuse. Staining: toluidine blue Spermatozoa in wet preparation lysosome-acrosome in the sperm head Hematoxillin-eosin stained sparmatozoa  Peroxisomes 0.2 – 0.5 µm Peroxisomes are membrane organelles similar to lysosomes. Small spherical bodies found throughout the cytoplasm. They differ from lysosomes by the type of enzymes (40) they possess They contain enzymes involved in the breakdown of various substances (amino acids, fatty acids) and in the breakdown of toxic substances.  Peroxisomes  Peroxisomes contain oxidative enzymes (for β-oxidation of fatty acids), catalases (antioxidants), peroxidases  They are responsible for protecting the cell from its toxic product: hydrogen peroxide  Skin fibroblast stained with fluorescent dyes Oxidative enzymes remove H+ from cells and H2O2 is produced which is used by phagocytes to destroy microorganisms. But due to its toxicity, peroxisomes (containing catalases – antioxidants) break it down into water and oxygen, thus protecting the cell from damage They self-replicate (by fission)  Similarities to mitochondria Peroxisomes, like mitochondria, contain enzymes that are synthesized in free polyribosomes in the cytosol of the cell, and then transported to the peroxisome matrix The ability to grow and replicate by fission Peroxisomes in skin fibroblasts  Cellular inclusions Cellular inclusions Glycogene in hepatocytes Fat droplets in adipocytes Pigments (melanin) in the epidermis of the skin Inclusions are cell products deposited in the cytoplasm: glycogen, fat droplets, pigments, etc. Glycogen Staining methode: PAS Glycogen in hepatocytes: polysaccharide that is stored in the cytoplasm of cells with pronounced metabolic activity Glycogen in hepatocytes HE – staining: the glycogen in hepatocytes with routine staining methods is lost, leaving bright areas in its place. Glycogen granules and mitochondria in a hepatocyte Fat droplets Triglyceride fat droplets. Cholesterol fat droplets. Unilocullar adipocyte Multilocullar adipocyte Cholesterol fatty droplets in the adrenal gland: zona fasciculata Pigments Melanin – in the cells of the basal layer of the epidermis of the skin Melanin – in pigment cells (melanocytes) in pigment connective tissue  Melanocytes and keratinocytes Melanocytes in the epidermis of the skin. The concentration of melanosomes is higher in the surrounding keratinocytes than in the cytoplasm of the melanocytes. Hemoglobin Myoglobin Bilirubin Rhodopsin and iodopsin Cytochrome pigments  Leydig – cells Protein inclusions in the form of crystals: Reinke–crystal  Lipofuscine In some long-lived cells (eg, neurons, cardiac muscle), residual bodies can accumulate and form granules of the pigment lipofuscin.