Midterm 1 Micrographs & Schematic Images PDF

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. Dehydrat...

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. Trimming: The resulting paraffin block is trimmed to expose the tissue for sectioning (slicing) on a microtome. 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 histologically as many separate rounded or oval structures. Golgi apparatus in the thalamocortical relay neuron. N - nucleus, Golgi sacculi - red arrow, Golgi vesicles - blue arrow. Scale = 300 nm. (Rat, lateral geniculate nucleus). 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 chromatin found in association with the nucleolus. Each eukaryotic cell contains about 6 billion bits 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 https://slideplayer.com/slide/13104863/ longer than the nuclear diameter. Folding of DNA is accomplished by the formation of a unique nucleoprotein complex - chromatin, which consists of DNA and structural proteins. ❖ A bit is the smallest piece of computer Further folding of chromatin produces information. chromosomes. Each human cell contains 46 ❖ Byte: chromosomes. Is combinations of eight bits, Chromatin proteins include 5 basic proteins Represent one character of data. –histones along with other nonhistone proteins. For example, the word "cat" has three A unique feature of chromatin packaging permits characters, and it would be represented by three the transcriptional machinery to access those bytes. regions of the chromosomes that are required for A kilobyte (K or KB) is equal to 1,024 bytes. gene expression. 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 bottom drawing shows a metaphase chromosome, with maximum packing of DNA. ▪ The chromosome consists of two chromatids held together at the centromere.  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 Regions of euchromatin and heterochromatin Chromosomal regions with the genes for rRNA organize display variable electron densities with the ≥1 nucleoli. transmission electron microscope (TEM). Structure of nucleolus is not homogeneous An active nucleus typically has much diffuse, lightstaining euchromatin and smaller Fibrillar and Granular subregions with different staining subdomains of electrondense heterochromatin (H), with many of these associated at the characteristics reflect stages of rRNA maturation. periphery with the nuclear lamina. rRNA are processed in the nucleolus, The more heterogeneous electron-dense subdomain is the nucleolus (N), the site of rRNA are quickly associated with the ribosomal proteins and synthesis and ribosomal subunit assembly. X25,000. exported to the cytoplasm through the nuclear pores. ▪ 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 x15,000. - rRNA genes, - RNA polymerase I - Transcription factors. Electron micrograph of the nucleolus. This nucleolus from a nerve ▪ Fibrillar material (pars fibrosa) – contains cell shows fibrillar centers (FC) surrounded by the fibrillar (F) and ribosomal genes that are actively granular (G) materials. Such a network of both materialsis undergoing transcription and large referred to as the nucleolonema. The rRNA, DNA-containing amounts of rRNA. genesfor the rRNA, and specifi c proteins are localized in the interstices of the nucleolonema. ▪ Granular material (pars granulosa) – The network formed by the granular and the fibrillar ▪ represents the site of initial ribosomal materials is called the nucleolonema. assembly and contains densely packed preribosomal particles. rRNA is present in both granular and fibrillar material and is organized, respectively, as both granules and extremely fine filaments packed tightly together. 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 NE - the nuclear envelope C - cytoplasm Genes for the ribosomal subunits are localized in the interstices of this network and are transcribed by RNA polymerase I. 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 from the nucleus via nuclear pores for full assembly into mature ribosomes in the cytoplasm. 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 viruses may target the nucleolus and its components to favor viral transcription and translation and perhaps alter the cell cycle to promote viral replication. A nucleolus in a human fibroblast and its three distinct zones. (A) View of entire nucleus. (B)High-power view of the nucleolus. A retrovirus is a virus that uses RNA as its genetic material. When a retrovirus infects a cell, it makes a DNA copy of its genome that is inserted into the DNA of the host cell. There are a variety of different retroviruses that cause human diseases such as some forms of cancer and AIDS.  Cell cycle G2 phase ❖ Preparation for cell division. ❖ Examination of replicated DNA ❖ Reorganization of cytoplasmic organelles before entering the mitotic cycle. ❖ May be as short as 1 hr in rapidly dividing ❖ G1 is the longest and cells. the most variable S phase – Replication of DNA M phase - Mitosis phase during which Initiation of DNA synthesis. Nearly always includes both the cell Duplication of DNA and formation of new 1. Karyokinesis (division of the nucleus) chromatids. and ▪ accumulates nutrients Chromosome replication is initiated at 2. Cytokinesis (division of the cell) ▪ synthesizes many different sites - replicons along the Lasts about 1 hour. ✔ RNA and chromosomal DNA. Mitosis takes place in several stages ✔ proteins necessary for Each replicon has a specifically assigned Separation of two identical daughter DNA synthesis and time frame for replication during S phase. cells concludes the M phase. chromosome The S DNA-damage checkpoint monitors replication. quality of replicating DNA. Fibroblasts / Fibrocytes, LM Bone cells, SEM Fibroblasts, TEM Basic stain: [dye]+ OH- stains 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 between phospholipids ❖ The plasma membrane is a lipid bilayer consisting equally on both sides of the membrane. ❖ Carbohydrate chains primarily of ▪ Note the elevated area of the lipid raft ▪ attach to ▪ phospholipid molecules, ✔ is characterized by the high concentration ✔ integral proteins ▪ cholesterol, and of glycosphingolipids and cholesterol. ✔ peripheral membrane proteins ▪ protein molecules. ✔ contains large numbers of integral and ▪ form ▪ The hydrophobic fatty-acid chains of phospholipidsface peripheral membrane proteins. ✔ glycoproteins and each other to form the inner portion of the membrane. ✔ protrudes above the level of ✔ glycolipids. ▪ The hydrophilic polar heads form the extracellular and asymmetrically distributed phospholipids in intracellular surfaces of the membrane. the membrane bilayer (indicated by the different colors of the phospholipid heads). 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 b. This photomicrograph of a plastic-embedded, thin section space, limiting the movement of fl uid between the lumen and the of intestinal epithelium, stained with toluidine blue, shows underlying connective tissue. The intracellular pathway of fl uid cells actively engaged in fl uid transport. Like the adjacent movement during absorption (arrows) is from the intestinal lumen into the diagram, the intercellular spaces are prominent, refl ecting cell, then across the lateral cell membrane into the intercellular space, fl uid passing into this space before entering the underlying and, fi nally, across the basement membrane to the connective tissue. connective tissue. x1,250. 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. Glycoproteins of the glycocalyx include terminal digestive enzymes such as dipeptidases and disaccharidases. x100,000. (Pawlina, 2020)