Micrographs for MT 1 (2).pptx

Midterm 1 Micrographs & Schematic Images Sample preparation in LM involves the following sequence of steps (a): Fixation: Small pieces of tissue are placed in solutions of chemicals that cross-link proteins and inactivate degradation, which preserves cell and tissue structure. Dehydration: The tissu...

Midterm 1 Micrographs & Schematic Images Sample preparation in LM involves the following sequence of steps (a): Fixation: Small pieces of tissue are placed in solutions of chemicals that cross-link proteins and inactivate degradation, which preserves cell and tissue structure. Dehydration: The tissue is transferred through a series of increasingly concentrated alcohol solutions, ending in 100%, which removes all water. Clearing: Alcohol is removed in organic solvents in which both alcohol and paraffin are miscible. Infiltration: The tissue is then placed in melted paraffin until it becomes completely infiltrated with this substance. Embedding: The paraffin-infiltrated tissue is placed in a small mold with melted paraffin and allowed to harden. 3D structure The sections appear microscopically have only 2 dimensions: length and width. Missing components in front of and behind / above and below. Many tissue structures are thicker than the section. Round structures seen microscopically may be portions of spheres or tubes. Due to different orientations, two-dimensional (2D) appearance of structures depends on the plane of section. ✔For example: A single convoluted tube will appear Golgi apparatus in the thalamocortical relay neuron. N - nucleus, Golgi sacculi - red arrow, Golgi vesicles - blue arrow. Scale = 300 nm. Heterochromatin is disposed in three locations: Marginal chromatin is found at the periphery of the nucleus Karyosomes are discrete bodies of chromatin irregular in size and shape that are found throughout the nucleus. Nucleolar-associated chromatin is Each eukaryotic containswith about chromatin found in cell association billion bits the6 nucleolus. of information encoded in DNA structure, which has a total length of about 1.8 m. The length of the DNA molecule is 100,000 times longer than the nuclear diameter. ❖ A bit is the smallest piece of computer information. ❖ Byte: Is combinations of eight bits, Represent one character of data. For example, the word "cat" has https://slideplayer.com/slide/ 13104863/ Folding of DNA is accomplished by the formation of a unique nucleoprotein complex - chromatin, which consists of DNA and structural proteins. Further folding of chromatin produces chromosomes. Each human cell contains 46 chromosomes. Chromatin proteins include 5 basic proteins –histones along with other nonhistone proteins. A unique feature of chromatin Several orders of DNA packing in chromatin during chromatin condensation of mitotic prophase. ▪ The 2-nm DNA double helix, followed by the association of DNA with histones to form 11-nm filaments of nucleosomes connected by the DNA (“beads on a string”). ▪ Nucleosomes on the DNA then interact in a manner not well understood to form a more compact 30-nm fiber. ▪ For transcription, DNA forms 300 nm loops that remain tethered to and stabilized by interactions with protein scaffolds. ▪ Protein scaffold makes up a central framework at the long axis of each chromosome. ▪ Heterochromatin is not transcribed and remains more highly condensed. The nucleolus Is a generally spherical Is highly basophilic subdomain of nuclei in cells Is actively making proteins The intense basophilia of nucleoli is due not to heterochromatin but to the presence of densely concentrated ribosomal RNA (rRNA) that is ✔ Transcribed ✔ Processed ✔ Complexed into ribosomal subunits in nucleoli. In cells requiring intense ribosome production for synthesis of proteins during growth or secretion – ≥1 Chromosomal regions with the genes for rRNA organize ≥1 nucleoli. rRNA are processed in the nucleolus, Structure of nucleolus is not homogeneous are quickly associated with the ribosomal andGranular subregions with proteins Fibrillar and different staining characteristics reflect Regions of euchromatin and heterochromatin display variable electron densities with the transmission electron microscope (TEM). An active nucleus typically has much diffuse, lightstaining euchromatin and smaller subdomains of electrondense heterochromatin (H), with many of these associated at the periphery with the nuclear lamina. The more heterogeneous electron- ▪ Fibrillar and Granular subregions with different staining characteristics reflect stages of rRNA maturation. ▪ rRNA are processed in the nucleolus, quickly associated with the ribosomal proteins and exported to the cytoplasm through the nuclear pores. ▪ Fibrillar centers - Contain DNA loops of five different chromosomes (13, 14, 15, 21, and 22) that contain - rRNA genes, - RNA polymerase I - Transcription factors. x15,0 00. Electron micrograph of the nucleolus. This nucleolus from a nerve cell shows fibrillar centers (FC) surrounded by the fibrillar (F) and ▪ Fibrillar material (pars fibrosa) granular (G) materials. Such a network of both – contains ribosomal genes that materialsis referred to as the nucleolonema. The rRNA, DNA-containing genesfor the rRNA, are actively undergoing and specifi c proteins are localized in the The transcription and large network formed by the granular and interstices of the nucleolonema. amounts of rRNA. ▪ Granular material (pars granulosa) – ▪ represents the site of initial the fibrillar materials is called the nucleolonema. rRNA is present in both granular and fibrillar material and is organized, respectively, as both granules and Morphologically distinct regions within a nucleolus. X35,000. FC - Small, light-staining areas are fibrillar centers, containing the DNA sequences for the rRNA genes (the nucleolar organizers). F - The darker fibrillar material surrounding the fibrillar centers consists of accumulating rRNA transcripts. G - More granular material of the nucleolus, contains mainly the large and small ribosomal subunits being assembled from rRNA and ribosomal proteins synthesized in the cytoplasm. H - Various amounts of heterochromatin are also found near the nucleolus. E - the euchromatin for the ribosomal subunits are localized in the interstices of this NE Genes - the nuclear envelope network and are transcribed by RNA polymerase I. C - cytoplasm After further processing and modification of rRNA by small nucleolar RNAs (snoRNAs), the subunits of rRNA are assembled using ribosomal proteins imported from the cytoplasm. The partially assembled ribosomal subunits (preribosomes) are exported The Nucleolus In addition, DNA, RNA, and retroviruses and their viral proteins interact with the nucleolus and cause redistribution of fibrillar and granular materials during the course of viral infection. These viruses can use components of the nucleolus as part of their own replication process. Evidence suggests that A nucleolus in a human fibroblast and its three distinct zones. viruses may target (A) View of entire nucleus. (B)High-power view of the the nucleolus and its nucleolus. components to favor A retrovirus a virus that and viralistranscription uses RNAtranslation as its genetic and material.perhaps When a alter retrovirus the cell infects a cycle cell, it a DNA tomakes promote viral copy of its genome that is replication. inserted into the DNA of the host cell. There are a variety of different retroviruses that Cell cycle ❖ G1 is the longest and the most variable phase during which the cell ▪ accumulates nutrients ▪ synthesizes ✔ RNA and ✔ proteins necessary for S phase – Replication of DNA Initiation of DNA synthesis. Duplication of DNA and formation of new chromatids. Chromosome replication is initiated at many different sites - replicons along the chromosomal DNA. Each replicon has a specifically assigned G2 phase ❖ Preparation for cell division. ❖ Examination of replicated DNA ❖ Reorganization of cytoplasmic organelles before entering the mitotic cycle. ❖ May be as M phase - Mitosis short as Nearly always includes both 1 hr in rapidly 1. Karyokinesis (division of the dividing cells. nucleus) and 2. Cytokinesis (division of the cell) Lasts about 1 hour. Mitosis takes place in several stages Separation of two identical daughter cells concludes the Bone cells, SEM Fibroblasts / Fibrocytes, LM Fibroblasts, TEM Basic stain: [dye]+ OHstains basophilic structures, e.g., nuclei, ribosomes, GAGs Acid stain: [dye]- H+ stains acidophilic structures, e.g., mitochondria, collagen https://ag.purdue.edu/arp/ Microscopy/Pages LM SEM Fibroblasts TEM Diagram of a plasma membrane showing the modified fluid–mosaic model. ❖ Cholesterol molecules are incorporated within the gaps ❖ The plasma membrane is a lipid bilayer between phospholipids equally ❖ Carbohydrate chains consisting primarily of on both sides of the ▪ attach to ✔ integral proteins ▪ phospholipid molecules, membrane. membran ▪ cholesterol, and ▪ Note the elevated area of the ✔ peripheral proteins ▪ protein molecules. lipid raft ▪ form ▪ The hydrophobic fatty-acid chains of ✔ is characterized by the high ✔ glycoproteins and phospholipidsface each other to form concentration of the inner portion of the membrane. glycosphingolipids and ✔ glycolipids. ▪ The hydrophilic polar heads form the cholesterol. extracellular and intracellular surfaces ✔ contains large numbers of Diagram of small intestine absorptive epithelial cells. a. All three cellular domains of a typical epithelial cell are indicated on the diagram. The junctional complex provides adhesion between adjoining cells and separates the luminal space from the intercellular space, limiting the movement of fl uid between the lumen and the underlying connective tissue. The intracellular pathway of fl uid movement during absorption b. This photomicrograph of a plasticembedded, thin section of intestinal epithelium, stained with toluidine blue, shows cells actively engaged in fl uid transport. Like the adjacent diagram, the intercellular spaces are prominent, refl Electron micrograph of microvilli on the apical surface of an absorptive cell. This electron micrograph shows the apical portion of absorptive cells with microvilli. Note that at this magnification, the plasma membrane displays its characteristic appearance, showing two electron-dense lines separated by an electron-lucent intermediate layer. The glycoproteins of the glycocalyx can be seen extending from the tips of the microvilli into the lumen. The relationship between the outer plasma membrane leaflet and the glycocalyx is particularly well demonstrated.