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HCB Objectives 2 1. Identify/functions of: fluid-mosaic model: cell membrane is a fluid collection of phospholipids, proteins, and various other elements. When looked at from afar, these tiny elements form a “mosaic” phospholipid: main component of the cell membrane; has a hydrophilic head and hydrophobic tail cholesterol: lipid component of the cell membrane that increases intracellular permeability, but decreases cell membrane fluidity membrane proteins: a protein found in the plasma membrane transmembrane protein: a protein that spans the cell membrane (an integral membrane protein) lipid-linked protein: a protein bound to lipids on the plasma membrane (can be either extracellular or cytoplasmic; an integral membrane protein) integral membrane protein: a protein embedded in or covalently attached to the plasma membrane peripheral membrane protein: a protein that is not covalently attached to the plasma membrane glycocalyx: network of sugars covalently attached to membrane or membrane components submembrane cytoskeleton: composed of peripheral membrane proteins, gives stability to the membrane and anchors transmembrane proteins nuclear envelope: similar to cell membrane; inside of cell, membrane that surrounds the nucleus nuclear pore: similar to a channel in the cell membrane; allows larger elements to enter the nuclear space chromatin: DNA that is not tightly wound to make chromosomes euchromatin: least tightly wound DNA; may be wrapped around histones, but if so, is definitely not condensed. Appears as darker of the two chromatins under a microscope. heterochromatin: more condensed DNA; wrapped around histones and may be supercoiled. Appears as darker of the two chromatins under a microscope. histones: proteins in the nucleus that DNA wraps around. The “hair-curlers” for DNA “hair” nucleolus: the innermost and most prominent part of the nucleus. Where ribosomes are manufactured; thus, cells making lots of proteins will have larger nucleoli than those not actively synthesizing proteins RER: endoplasmic reticulum with ribosomes studded on it to give “rough” appearance. Active site of non-cytoplasmic protein manufacturing. signal peptide: first 20 or so amino acids that will send protein to the RER and is later cleaved by proteases in the RER. For shipping to lysosomal, secretory, or membrane-bound proteins. glycosylation: adding sugar to a newly translated protein destined for the lysosome, secretion, or the plasma membrane. Begins in the RER. golgi apparatus: cis, medial, and trans: site where proteins are trafficked after translation in the RER (cis first, then medial and trans). This is the “mail center” of the cell, proteins are processed here and shipped to their correct destination. mannose-6-phosphate: lysosomal signal put onto proteins in the golgi apparatus mannose-6-phosphate receptor: receptor on the lysosome to receive newly translated proteins membrane traffic: process whereby proteins come in and out of cell (elaboration in question 2) endosome: intracellular vesicle that forms after endocytosis of extracellular components. Endosomes later move on to become lysosomes either by maturing or fusing with a mature lysosome (process still unclear) lysosome: cellular vesicle filled with acid hydrolases (low pH); destructor of any intracellular elements (“the garbage compactor”). SER: endoplasmic reticulum without ribosomes involved in several processes (elaboration in question 2) mitochondrion: site of ATP synthesis in the cell cytoskeleton: intracellular component that gives cell shape and support thin filament/microfilatin/actin: smallest of the three filaments, exists in equilibrium between g-actin (single components, “globular”) and f-actin (bound strands, “filamentous”) Is extremely important for processes such as locomotion, cytokinesis, and attachment of cytoskeleton to plasma membrane intermediate filament: second largest filament; much more stable and long-lived than microfilaments; large family consisting of many different types. glial fibrillary acidic protein (GFAP): intermediate filament found in some types of glial cells nuclear lamin: intermediate filaments on inner surface of nuclear envelope keratin: very strong filaments that form tonofilaments radiating from desmosomes and hemidesmosomes. Extremely resistant to stress vimentin: intermediate filament in mesenchymal cells desmin: intermediate filament in muscle cells neurofilament: intermediate filament in neurons microtubule: largest of the 3 types of filaments, in equilibrium between filament and globular arrangements, made of tubulin in heterodimer spirals, 13 to a revolution. Important as “tracks” for protein shuffling (think about axonal transport in a neuron!) spindle fiber formation, and is the core of flagella and cilia. Anchored by centrioles microvillus: extension of cells with a core of microfilaments, nonmotile terminal web: network of thin filaments at the base of a microvillus that runs parallel to the cell membrane. Major support of thin filament core of microvillus centriole: paired cylindrical structures, important as anchors for microtubules in mitosis cilium: membrane covered mobile structure with microtubule core. Important for sweeping cells out of certain areas of the body flagellum: membrane covered mobile structure with microtubule core, larger than cilium, found in spermatozoa to provide motility basal body: inner core of cilia and microtubules arranged in typical 9 + 2 fashion whereby there are 9 pairs of microtubules radiating around the periphery with a central pair in the middle. Dynein attaches to the microtubule basal body to allow cilia/flagella to bend (the basis of its motility) 2. Major molecular components in plasma membrane: phospholipids, cholesterol, integral membrane proteins (transmembrane and lipid-linked). Associated with these major components are the glycocalyx, and the submembrane cytoskeleton. Molecular organization of chromatin: Chromatin can be classified as either euchromatin or heterochromatin. Heterochromatin is more tightly wound and is thus more dense and transcribed less. Because it is more dense it is more darkly stained in microscope slides Euchromatin is less tightly wound and is less dense; transcription occurs in euchromatin. It is more lightly stained in microscope slides. Euchromatin/heterochromatin ratios can tell you whether the cell is metabolically active or not (more euchromatin = more proteins production) Intracellular pathways followed by endocytosis: Cell receptors on the outside of the cell will be recycled along with components of the plasma membrane that the receptors are bound to. Ligands will be endocytosed and either transferred to a lysosome or will be broken down when the endosome matures into a lysosome. 3. 4. Major functions of SER: 1. Produces cholesterol 2. Produces steroid hormones 3. Helps cell regulate Ca2+ levels by storing and releasing it 4. Breaks down toxins (will grow more in presence of toxins – hypertrophy of SER shows that SER has been exposed to toxin) Major steps in synthesis of proteins: All proteins are translated from RNA after transcription of DNA in the nucleus. Cytoplasmic proteins are then translated by free ribosomes in the cytoplasm. All other proteins are translated on the RER and then sent to the Golgi for processing. Membrane proteins have hydrophobic regions that span the ER membrane during translation. Thus, when they are sent in vesicles to their destination, they are already stuck in the membrane and fuse with the membrane along with the vesicle. Secretory proteins are proteins sent in vesicles to the plasma membrane. When the vesicle fuses with the plasma membrane, the proteins are then sent out into the extracellular space. Lysosomal proteins are tagged with a mannose-6-phosphate in the cis-Golgi and are then sorted and sent to the lysosome where they bind to mannose-6-phosphate receptors.