Lecture1 cytology

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2. Cell Components Nucleus Cytoplasm Cytoskeleton Cell surface 3. Plasma Membrane All eukaryotic cells are enveloped by a limiting membrane composed of phospholipids, cholesterol, proteins, and chains of oligosaccharides covalently linked to phospholipids and protein molecules. The cell, or plasma, membrane functions as a selective barrier that regulates the passage of certain materials into and out of the cell and facilitates the transport of specific molecules. 4. Membrane phospholipids, such as lecithin and cephalin, consist of two long, nonpolar chains linked to a charged (hydrophilic) head group. Cholesterol is also a constituent of cell membranes. Within the membrane, phospholipids are most stable when organized into a double layer with their hydrophobic (nonpolar) chains directed toward the center of a membrane and their hydrophilic (charged) heads directed outward. 5. Cholesterol breaks up the close packing of the phospholipid long chains, and disruption makes membrane more fluid. The cell controls the fluidity of the membranes through the amount of cholesterol present. 6. Plasma membrane The fluid mosaic model of membrane structureMain components; 1. Phospholipids 2. Cholesterol 3. Proteins 4. Chains of oligosaccharides 7. Plasma membrane 8. Plasma membrane Phospholipids -phosphatidylcholine(lecithin) -phosphatidylethanolamine(cephalin) Structure: 2 nonpolar (hydrophobic) hydrocarbon chains linked to one charged(hydrophilic) head group 9. Cholesterol -breaks up the close packing of the phospholipid long chains,and as a consequence plasma membranes become more fluid 10. Proteins 1. Integral proteins -directly incorporated within the lipid bilayer 2. Peripheral proteins -exhibit a looser association with membrane surfaces.They can be easily removed from the cell membranes with salt solutions 11. In order to regulate the transport of molecules, there are two types of proteins in the cell: - carrier proteins - transport proteins. The two types of transport proteins are: - channel - carrier protein. Transport is either active or passive. Active transport is moving molecules against the concentration gradient and energy is required in the form of ATP. 12. Glycocalyx -a fuzzy carbohydrate-rich region on the external surface of the cell -composed of carbohydrate chains linked to a membrane proteins and lipids and of cell-secreted glycoproteins and proteoglycans 13. Plasma membrane 14. Plasma membrane-transport The plasma membrane is the site at which materials are exchanged between the cell and its environment Endocytosis-bulk uptake of material through the plasma membrane 15. Passive transport is moving molecules down the concentration gradient and no energy is required. Examples of passive transport are diffusion, which moves from high concentration to low concentration and osmosis, which is the diffusion of water molecules. 16. The Nucleus Its enclosed by the nuclear envelope and contains: - nuclear lamina - nucleolus - chromatin 17. Nucleus The nucleus is the site of deoxyribonucleicacid (DNA) replication and trascription of DNA into precursor ribonucleic acid (RNA) molecules. It contains all of the enzymes required for replication and repair of newly senthesized DNA, as well as for trascription and processing of precursor RNA molecules. 18. Nuclear envelope -Is double membrane containing pores -The outer nuclear membrane is continuous with the endoplasmic reticulum 19. Nucleolus contains three morphologically distinc zones: - granular zone found at periphery; contains ribosomal precursor particles in various stages of assembly - fibrillar zone centrally located; contains ribonuclear protein fibrils - fibrillar center- contains DNA that is not being transcribed 20. Chromatin Is a complex of: DNA histone proteins and nonhistone proteins 21. DNA A doublestranded helical molecule that carries gentic information of the cell 22. Histone proteins Positively charged proteins enriched with lysine and arginine residues. They are important in forming two types of structures in chromatin: - nucleosomes - solenoid fibers The nucleosomes are the basic repeating units of the chromatin fiber. Schematic representation of a nucleosome. This structure consists of a core of 4 types of histones (2 copies of each)H2A, H2B, H3, and H4and one molecule of H1 or H5 located outside the DNA filament. 23. Nonhistone proteins Include enzymes involved in nuclear functions such as:- replication - transcription - DNA repair - regulation of chromatin function They are acidic of neutral proteins. 24. Forms of chromatin - Heterochromatin - highly condensend, transcriptionally inactive - Euchromatin a more extended form of DNA, which is potentially transcriptionally active. 25. Cytoplasm components -Endoplasmic reticulum -Golgi Apparatus -Lysosomes -Peroxisomes -Mitochondria 26. Endoplasmatic Reticulum 27. Endoplasmatic Reticulum Exists in two forms: -Rough endoplasmatic reticulum (RER) -Smooth endoplasmatic reticulum (SER) 28. Rough endoplasmatic reticulum - RER is a single, lipid bilayer continuous with outer nuclear membrane. Its organized into stacks of large flattened sacs called cisternae that are studded with ribosomes on the cytoplasmic side. - RER synthesizes proteins that are destined for the Golgi apparatus, secretion, the plasma membrane and lysosomes. - RER is very prominent in cells that are specialized of proteins destined for secretion (e.g., pancreatic cells) 29. Smooth endoplasmic reticulum SER is a network of membranous sacs, vesicles, andtubules continuous with the RER, but lacking ribosomes. SER contains enzymes involved in the biosynthesis of phospholipids, triglycerides, and sterols. 30. Functions of SER 1.Detoxification Reactions / hepatocytes / These are reactions that make compounds soluble so that they can be excreted. Two types of reactions that increase solubility are: - Hydroxylation reactions - conjugation reactions 31. Functions of SER 2.Glycogen Degradation and Gluconeogenesis 3.Steroid synthesis / Leydig cells in testis and adrenal gland cells / 32. Functions of SER 4.Reactions in Lipid Metabolism Lipolysis begins in the SER with the release fatty acid from triglyceride. The SER is also the site where lipoprotein particles are assembled 33. Functions of SER 5.Sequesration and Release of Calcium Ions In striated muscle the SER is known as sarcoplasmic reticulum (SR). The sequestration and release of calcium ions takes place in the SR. 34. Golgi Apparatus 35. Consists of disc-shaped smooth cisternae that are assembled in stacks (dictyosomes) Associated with numerous small membrane-bound vesicles. 36. The Golgi apparatus has two distinct faces: The cis (forming) face associated with RER The trans (maturing) face is often oriented toward the plasma membrane. The transmost region is a network of tubular structures known as the trans-Golgi network. 37. Functions of Golgi apparatus Proteins and LipidsAG is the site of posttranslational modification and sorting of newly synthesized proteins and lipids. Glycoproteins Further modification of the carbohydrate moiety of glycoproteins produces complex and hybrid oligosaccharide chains. This determines which proteins remain in the Golgi apparatus or leave the Golgi apparatus to become secretory proteins, lysosomal proteins, or part of the plasma membrane. 38. Mitochondria 39. Mitochondria - two membranes - synthesizes adenosine triphosphate (ATP) - contain their own doublestranded circular DNA, and make some of their own proteins - have several compartments 40. Outer membrane - is smooth, continuous, and highly permeable - contains an abundance of porin, an integral membrane protein that forms channels in the outer membrane 41. Inner membrane Is impermeable to most small ions and small molecules. -The inner membrane has numerous infoldings, called cristae. The cristae greatly increase the total surface area. They contain the enzymes for electron transport and oxidative phosphorylation. The number of mitochondria and the number of cristae per mitochondrion are proportional to the metabolic activity of the cells in which they reside. 42. Intermembrane compartment It is the space between the inner and outer membranes. Contains enzymes that use ATP to phosphorylate other nucleotides. 43. Matrix Is enclosed by the inner membrane and contains: -dehydrogenases- oxidize many of the substrates in the cell , generating reduced NADH (nicotinamide adenine dinucleotid) and reduced FADH2 (adenine dinucleotide) for use by the electron transport chain and energy generation. -a double-stranded circular DNA genome- encodes a few of the mitochondrial DNA is always inherited from the mother, resulting in the maternal transmission of diseases of energy metabolism. -RNA, proteins, and ribosomes- although there is some protein synthesis, most mitochondrial proteins are synthesized in the cytoplasm and are transferred into the mitochondria. 44. Ribosomes 45. Ribosomes Composed of RNA and protein Consist of large (60s) and small (40s) subunits Assembled in the nucleus and transported to the cytoplasm through the nuclear pores The large ribosomal subunits are synthesized in the nucleolus, whereas the small subunits are synthesized in the nucleus. 46. Polysomes Ribosomes often form polysomes, which consist of a single messenger RNA (mRNA) that is being translated by several ribosomes at the same time. The ribosomes move on the mRNA from the 5 end toward 3 end. The two ribosomal subunits associate on the mRNA with the small subunit binding first. 47. Forms of ribosomes-Free polysomes are the site of synthesis for proteins destined for the nucleus, peroxisomes, or mitochondria. -Membrane-associated polysomes are the site of secretory proteins, membrane proteins, and lyzosomal enzymes. 48. Peroxisomes 49. Peroxisomes are