Cell Cytoplasm and Cell Nucleus ANA 215 PDF

CELL CYTOPLASM & CELL NUCLEUS  OUTLINE/OBJECTIVES At the end of the lecture, the student should have acquired adequate knowledge on: 1. Evolvement of multicellularity and cell specialization 2. Composition of cell cytoplasm 3. Different zones of the cytoplasm 4. Membrane-bound...

CELL CYTOPLASM & CELL NUCLEUS  OUTLINE/OBJECTIVES At the end of the lecture, the student should have acquired adequate knowledge on: 1. Evolvement of multicellularity and cell specialization 2. Composition of cell cytoplasm 3. Different zones of the cytoplasm 4. Membrane-bound organelles 5. Non-membrane- bound organelles 6. Cell nucleus 7. Components of the nucleus 8. Applied & Clinical Anatomy 2  INTRODUCTION From prokaryotic to eukaryotic cells Evolvement of multicellularity cell specialization The hallmark of multicellular life is the ability of diverse cellular types to work together to allow development, physiologic responses, & reproduction of the entire organism as a whole 3  CELL Nucleus Cytoplasm – Expresses most of functions of cell – Dependent on nucleus for direction, renewal & regeneration – Nucleus/Cytoplasmic ratio varies; 1:3-5 4  CYTOPLASM (I) Homogeneous, generally clear jelly-like material that fills cells Consists of cytosol & cellular organelles, except the nucleus Cytosol is made up of water, salts & organic molecules & many enzymes that catalyze reactions Cytosol makes up ~70 % of the cell volume Aqueous component of the cytoplasm (~80%) is composed of ions & soluble macromolecules such as enzymes, carbohydrates, different salts & proteins, as well as a great proportion of RNA The cytoplasm's watery component is also known as 5 hyaloplasm  CYTOPLASM (II) The watery component can be more or less gel-like or liquid depending on the milieu's conditions & the activity phases of the cell. In the 1st case, it can be referred to as cytogel & is a viscid solid mass. In the 2nd case, called cytosol In general, margin regions of the cell are gel-like and the cell's interior is liquid 6  ZONES OF CYTOPLASM (I) 7 ZONE A  Cytocentrum- Contains centrioles & centrosphere. May be bounded by microtubles and surrounded by Golgi app  ZONES OF CYTOPLASM (II) 8 ZONE B  Endoplasm- Solvated. Most organelles are here. Cytoplasmic streaming occurs here, carrying the the cytoplasmic organelles in rapid movement ZONE C  Ectoplasm- Gelated. Capable of rapid sol-gel transformation. Rich in microfilaments  CELL ORGANELLES Cytoplasm cytosol non- membranous organelles membranous organelles  Non-membranous Organelles  Cytoskeleton  Centrioles  Ribosomes  Cytoskeleton 4 major components: 1. Microfilaments (mostly actin) 2. Intermediate filaments 3. Thick filaments (composed of myosin subunits) 4. Microtubules (composed of tubulin subunits) Functions: support & movement of cellular structures & materials 11 2 centrioles direct formation of In 9+0 array mitotic spindle 12 Compare Centriole with Cilium, Flagellum, Stereocilium In 9+2 array 13  At a glance Microvilli – 1 µm long, 0.08 µm wide Centrioles – 0.3-0.5 µm in length, 0.15 µm wide Cilium – 5-10 µm in length, 0.2 µm wide Flagellum – 100 µm long Stereocilia – Longer than microvilli; nonmotile 14  Microvilli 15  Inside microvilli are clusters of actin filaments that are cross-linked to each other & to the surrounding plasma membrane  ATP supplies the energy for the propelling actions of cilia  Ribosome A sedimentation coefficient of 70S. ~20 x 30 nm. Can be dissociated into a large subunit (50S) & a small subunit (30S) 60% RNA + 40% ________ Fixed vs, free ribosomes 16  Ribosomes Ribosomes contain RNA & are therefore intensely basophilic- the cytoplasm of cells rich in ribosomes stain with basophilic dye such as haematoxylin Free ribosomes synthesize soluble proteins for cytoplasm & nucleus 17  Fixed Ribosomes All protein synthesis begins on free polyribosomes. mRNAs of proteins (destined for segregation in ER) contain xtra sequence of bases that code for Signal Sequence (20-24 aa)- recognized & bound by Signal Recognition Particle- blocks further elongation until mRNA is attached to rER. SRP-ribosome complex is in turn bound by docking proteins located on rER. SRP is then released allowing transcription to proceed Ribophorins I & II on rER bind to ribosomes & form a channel for newly synthesized proteins 18 Membranous Organelles 19 Mitochondrion / -a 20  MITOCHONDRIA  0.5-1 µm wide; up to 10 µm in length  Tend to accumulate in areas of high metabolic activity such as apical ends of ciliated cells, in the middle piece of spermatozoa, or at the base of ion-transferring cells Functions:  Transformation of chemical energy of the metabolites in cytoplasm into one that is easily accessible to the cell Number:  Number in a cell reflect its general energy requirement. 2000 in heptocytes. Few in resting lymphocytes  Mature RBCs lack mitochondria; rely mainly on glycolysis for energy supplies 21  Composition:  Mainly proteins. Lipids present to a lesser degree, along with small quantities of DNA & RNA Membranes:  Outer & inner  Inner memb have folds (cristae) projected into the organelle 2 Spaces:  Intramembranous, continuous with the intracristal spaces  Intercristal/Matrix space- enclosed by the inner memb & is in turn penetrated by the cristae 22  Cristae  Cristae more numerous & complex in cells with high metabolic rate than in relatively inactive ones  Most have flat, shelf-like cristae, however, cells that secrete steroids frequently contain tubular cristae Permeability of membranes  Outer memb freely permeable to many substances b/c of the presence of large nonspecific channels formed by porins while inner permeable to only a narrow range of molecules. Presence of cardiolipin in inner membrane may contribute to this relative 23 impermeability  Cristae increase the internal surface area of mitochondria, & is on these that enzymes & other compounds involved in the oxidative phosphorylation & e- transport systems are located  B/w the cristae is an armophous matrix rich in protein & containinig some DNA & RNA. In the matrix are rounded e--dense granules rich in Ca & Mg 24   Enzymes for Krebs cycle & fatty acid β-oxidation reside within the matrix space  Inner memb contains cytochromes b, c, c1, a, & a3, the F1 ATPase associated with the mechanism of oxidative phosphorylation & certain dehydrogenases, particularly those for succinate & NADH 25   Extra mitochondrial metabolic pathway generates acetyl-CoA, which enters the mitochondria. A-CoA combines with oxaloacetate to form citric acid  Decarboxylation rxns produce CO2 + 4 pairs of H atoms removed by reactions catalyzed by dehydrogenases. The H atoms ultimately react with O to form H2O  Thru the action of cytochromes a, b & c, co- enzymes Q & cytochrome oxidase, the e- transport system is capable of releasing energy that is captured at 3 points of this system thru 26 formation of ATP from ADP & Pi   Under aerobic conditions the combined activity of extramitochondrial glycolysis & the citric acid cycle as well as the e- transport system gives rise to 36 molecules of ATP/ mole of glucose  This is 18x energy obtainable under anaerobic circumstances when only the glycolytic pathway is utilized 27  Smooth & Rough ER (I) Chambers = cysternae Function: Synthesis  Storage  Transport 28  Smooth & Rough ER (II) Granular/rough/rER has fine granules, ribosomes of ribonucleo-protein (RNP), l5 nm in diameter, in clusters studding the outer surface of the parallel membranes – related to protein synthesis Agranular/smooth lacks the ribosomes & is more tubular – associated with cholesterol metabolism among other things 29  the Endoplasmic reticulum and protein synthesis The principal function of the rough endoplasmic reticulum is to segregate proteins from the cytosol that are destined for export or intracellular use. All protein synthesis begins on polyribosomes that are attached to the endoplasmic reticulum. During post-translational modification of polypeptides, the signal-recognition particle inhibits further polypeptide elongation until the signal-recognition polypeptide- polyribosome complex binds to the docking protein. 30  The Endoplasmic reticulum and protein synthesis Rough endoplasmic reticulum participates in the contraction process in muscles cells, where it appears in a specialized form, called the sarcoplasmic reticulum. Smooth endoplasmic reticulum is abundant in liver cells, where it is responsible for the oxidation, conjugation, and methylation processes employed by the liver in the detoxification of noxious substances. 31  Golgi Apparatus (I) Complex transit region of smooth-surfaced tubules, sacs & flat chambers varying considerably in size Packaging & shipping of proteins Cell membrane renewal Vesicles depart from trans/maturing/releasing face 32  Golgi Apparatus (II) Concentrates, modifies & packages certain secretory products to await transport to the cell membrane for release, or application to some intracellular purpose Glycoconjugates are finished by adding remaining sugars (using glycosyltransferases), e.g., in cartilage & mucus-secreting goblet cells May be more than one in large cells 33  LYSOSOMES (I) Round, single-membrane-limited, darkly staining bodies without cristae & containing hydrolytic enzymes 34  Lysosomes are dense spheroidal membrane-bound bodies, 8- 18 nm in diameter. can be detected histochemically by the enzyme acid phosphatase under both light and electron microscopy. contain high concentrations of the enzyme urate oxidase. are numerous in cells active in phagocytosis of large particles and in cells with a high turnover of organelles. contain enzymes that are strongly glycosylated, and are maintained at a high pH by proton pumps in the lysosomal membranes. 35 Lysosomes (II) 36  Shape-variable- rounded, elongated  Location- variable- centrally  Size- variable: 5-10 µm  Components: Nuclear envelope, Chromatin, Nucleolus & Nucleoplasm/Nuclear matrix 37  The outer membrane is usually continuous with rough endoplasmic reticulum.  The inner membrane is closely associated with the fibrous lamina.  During interphase the chromatin adjacent to centromeres of chromosomes is associated with fibrous lamina. 38  The euchromatin is electron- dense and appears as coarse granules in the electron microscope.  Chromatin is composed mainly of coiled strands of DNA bound to basic proteins.  Euchromatin seems to represent the more inactive metabolic state whereas heterochromatin is more active in the synthesis of RNA. 39 2 parallel unit membranes separated by a perinuclear cisterna: 40-70nm  Outer membrane usually continuous with rER  Inner membrane closely associated with a protein structure = fibrous lamina (80 – 300 nm in thickness) 40  The fibrous lamina [FL] is composed of 3 main pp called lamins, that form part of the nuclear matrix  During interphase chromatin adjacent to centromeres of chromosomes is associated with FL  Nuclear pores: ~70nm, bridged by e--dense membrane 41  Interphase form chromosomes. 2 types  Chromatin is composed mainly of coiled strands of DNA bound to basic proteins (histones) 42  Heterochromatin: e--dense & appears as coarse granules in the EM ; visible in the LM as basophilic clumps of nucleoprotein  Euchromatin: visible as an organized structure only in EM ◦ HC seems to represent the more inactive metabolic state whereas EC is more active in the synthesis of RNA 43  Involved in synthesis of ribosomes  Size directly related to synthetic activity of cell  Number can vary with cell cycle  In humans as many as 10 may form immediately after mitosis  As the cell progresses thru cell cycle, individual nucleoli fuse to form a single nucleolus 44  Spherical, up to 1µm in diameter 3 distinct components:  Nucleolar organizer DNA (Pars amorpha): sequences of bases that code for rRNA. In the human genome, 5 pairs of chromosomes contain nucleolar organizer; ~200 copies of DNA code for rRNA  Pars fibrosa: densely packed 5-10 nm ribonucleo protein fibre; consists of primary transcripts of rRNA genes, i.e., represents rRNA being transcribed from DNA 45  Pars granulosa: 15-20 nm granules (maturing ribosomes) ◦ Active ribosomes are not present in nucleus ◦ Proteins, synthesized in cytoplasm, become associated with rRNAs in the nucleolus ◦ Immature ribosomal subunits exit nucleus thru nuclear pores & enter cytoplasm where final maturation takes place 46 47 48  HC is often attached to the nucleolus  Large nucleoli seen in embryonic cells during proliferation and rapidly growing malignant tumours  The nucleolus is mostly pre- ribosomal RNA  Nucleoli are prominent in nerve & Sertoli cells. 49  Fills the space b/w the chromatin & nucleoli in nucleus  Composed mainly of ◦ Proteins ◦ Metabolites ◦ Ions ◦ Fibrous lamina 50  Small non-living, non-participating, poorly structured cell elements, very rarely seen in an intra-nuclear position; usually cytoplasmic  Non-motile material- often the result of metabolic activity of cells in which found  May represent a form of stored food, not immediately vital to life processes  Can be build-up of matter in vacuoles that can’t be broken down by cell's excretory process  Usually but not limited to structural proteins  Can also be an insoluble agent or drug  Also called metaplasm 51  Fat droplets, Amyloid bodies, alphasynuclein, or viral capsids  Negri bodies, Howell-Jolly bodies, Heinz bodies, Pappenheimer bodies, Intra-cytoplasmic parasites.  Lamellar bodies contain lipids to be secreted  Glycogen granules visible as dark l5-30 nm wide granules in EM, e.g., in cardiac muscle and liver cells  Secretion granules, e.g. zymogen, in pancreatic cells  Pigments, e.g., melanin (skin cells), lipofuscin (old neurons), and haemosiderin (natural), carbon (exogenous - from outside the body)  Crystals, e.g., in testicular interstitial cells  Bacteria and viral inclusion bodies (pathological) 52