Lecture 7: Inside the Cell
Lecture 7: Inside the Cell 200001
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This 13 page Class Notes was uploaded by Olivia Sutton on Monday February 22, 2016. The Class Notes belongs to 200001 at Boston College taught by Danielle Taghian in Spring 2016. Since its upload, it has received 22 views. For similar materials see Molecules and Cells in Biology at Boston College.
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Date Created: 02/22/16
Lecture 7: Inside the Cell February 16, 2016 What’s Inside the Cell? There are two broad groupings of life: Prokaryotes: bacteria cells o Lack a membrane-bound nucleus & well-defined organelles o Contain only ribosomes and DNA o Some have endomembrane systems Eukaryotes: animal cells o Have a nucleus o Often have an extensive endomembrane system of organelles and cytoskeletal network The most numerous intracellular structure is the ribosome, which is the site of protein synthesis in all living organisms Basic Prokaryotic Cell Structure Plasma membrane surrounds the cytoplasm o Includes all the contents of the cell Few or no substructures separated from the rest of the cell by internal membranes Tough cell wall for protection, shape and structure Bacterial DNA is Supercoiled Nucleoid: supercoiled DNA in chromosome found in a localized area of the cell Allows 1 mm (500 cell lengths) of DNA to fit inside the cell! Protein-RNA Structure Function: protein manufacturing 10,000 ribosomes/cell Large subunit Small subunit Basic Prokaryotic Cell Wall Cell wall is called peptidoglycan (similar to a chain linked fence that gives the cell structure and protection) Bacteria is stained with a certain dye which makes the distinction between cell wall types Bacteria is classified as: o Gram positive Plasma membrane Periplasmic space Peptidoglycan o Gram negative Contains a plasma membrane, periplasmic space, peptidoglycan, and an outer membrane (lipopolysaccharide and protein) Has an additional lipid bilayer outside the cell wall (two bilayers) Some of the most lethal pathogens are this category Major Differences between Eukaryotes and Prokaryotes 1. Eukaryotic chromosomes are found inside the nucleus 2. Eukaryotic cells are larger 3. Eukaryotic cells contain extensive amounts of an internal membrane 4. Eukaryotic cells have a diverse and dynamic cytoskeleton a. Cytoskeleton is akin to the human skeletons i. Insoluble matrix ii. Can reassemble and all organelles would return to their original form Eukaryotic Cells Organelles: membrane-bound structures in the cell that have specific shapes and function o Allows cells to have a divided cytoplasm to compartmentalize specific functions o Increase chemical reaction efficiency by separating incompatible chemical reactions and grouping enzymes and substrates together Oxidation must only occur in the cytoplasm, otherwise it could destroy proteins in the cell The Nucleus Large and highly organized Structure o Nucleus is surrounded by a double-membrane nuclear envelope o Nucleus has a distinct region called the nucleolus (site of ribosome/RNA assembly) o Fibrous proteins that form a lattice Nuclear lamina, provides structure and shape Function o Information storage and processing Contains the cell’s chromosomes = digital code o Ribosomal RNA synthesis (in the nucleolus) Underlying the nucleus is its own cytoskeleton The Nuclear Envelope The nucleus is a highly organized information center for the cell Nuclear envelope: has two membranes, each consisting of a lipid bilayer & is continuous without the endoplasmic reticulum Endoplasmic reticulum is physically associated with nucleus Nuclear Pore Complex 50 proteins that provide a pore Links two series of membranes together The material that goes through these pores are very large, which is why the pores are so big Messenger RNA are long molecules So highly regulated that there is no need for energy mRNA gets sorted where some become exported through the pore while others stay in the endoplasmic reticulum (ER) Key Concept: How Are Molecules Imported into the Nucleus? Export: mRNA and ribosomes Import: proteins needed in the nucleus Energy is required for this to happen Proteins destined for the nucleus have a molecular “zip code” which allows them to enter the nucleus o Nuclear localization signal (NLS): the “zip code”; 17 amino- acids long The NLS of nucleoplasmin is the prototype of the ubiquitous bipartite signal (signal that exists everywhere) o Two clusters of amino acids separated by a spacer of about 10 amino acids Ribosomes Non-membranous (not considered organelles) Have large and small subunits, both containing RNA molecules and protein Can be attached to the rough ER or free in the cytosol (fluid part of the cytoplasm) Function: protein synthesis Rough Endoplasmic Reticulum Network of membrane-bound tubes and sacs studded with ribosomes The interior is called the lumen Is a continuous nuclear envelope Function o Ribosomes associated with the rough ER synthesize proteins o New proteins are folded and processed and multimeric proteins are assembled in the rough ER lumen o Proteins are glycosylated Proteins synthesized by the rough ER have specific final destinations. Some proteins remain within the ER while others are sent to the Golgi apparatus. Proteins secreted from Golgi apparatus are directed to lysosomes or to the cell membrane, but others are destined for secretion to the cell exterior Smooth Endoplasmic Reticulum Lacks the ribosomes Function o Enzymes within the smooth ER synthesize fatty acids and phospholipids or break down poisonous lipids o Reservoir for Ca2+ ions Golgi Apparatus Is a series of stacked membranes with order (like pancakes) Formed by series of stacked flat membranous sacs called cisternae Function o Processes (carbohydrate modifications), sorts, and ships proteins synthesized in rough ER o Membranous vesicles carry materials to and from the organelle Cis; side that faces the ER Trans: side that faces the plasma membrane Golgi represents distinct functional compartments cis medial trans (stained with (mannosidase II) (nucleoside) diphosphatase) Mitochondria Have two membranes, with the inner one folded into a series of sac-like cristae. o The solution inside the cristae is called the mitochondrial matrix Mitochondria have their own DNA and manufacture their own ribosomes. Function o ATP production is a mitochondrion’s core function o The mitochondria also play important role in the process of apoptosis o Beta-oxidation is the catabolic process by which fatty acid molecules are broken down o Site where we make ATP and where lipids are degraded (recycles carbons) Peroxisomes Are globular organelles bound by a single membrane Function o Center of oxidation reactions o They are involved in the catabolism of very long chain fatty acids and biosynthesis of plasmalogens and etherphospholipids critical for the normal function of mammalian brains and lungs o Specialized peroxisomes in plants called glyoxysomes are packed with enzymes that oxidize fats to be used to store energy for the cell Lysosomes Membrane-bound structures containing approximately 40 different digestive enzymes Found in all animal cells Function o Used for digestion and waste processing o Enzymes break nucleic acids, carbs, lipids and proteins into monomer units o Hydrolases -> working pH 5.0 (acidic) Site where material is degraded (e.g proteins, macromolecules, polysaccharides) Amino acids get transported out and recycled What Are the Cellular Trafficking Pathways that Lead to Lysosomes? Materials are delivered to the lysosomes by four processes 1. Phagocytosis a. Ability for immune cells to endocytose large material from the outside of the cell 2. Autophagy a. Under certain conditions, the cell can digest certain organelles (organelle physically fuses with the lysosomes and starts degrading) 3. Endomembrane transport 4. Receptor-mediated Endocytosis a. Process where cell grabs something out of the bloodstream specifically and brings it in through the plasma membrane b. Forms a liposome like structure Endocytosis: process in which the cell membrane can pinch off a vesicle to bring outside material into the cell Why Receptor-mediated Endocytosis? It’s more specific Things that are brought in are macromolecules The receptor is a membrane domain When macromolecules fuses with the cell, it becomes deconstructed into their monomeric units When a receptor binds with an LDL, it triggers the plasma membrane into invagination Lysosome-dysfunction Lysosomal storage diseases are a group of approximately 40 rare inherited metabolic disorders that result from defects in lysosomal function Tay-Sachs disease was the first of these disorders to be described in 1881 Lysosomal disorders are triggered when a particular enzyme exists in too small an amount or is missing altogether. When this happens, substances accumulate in the cell. Lysosomal storage diseases affect mostly children and they often die at a young and unpredictable age The Endomembrane System Proteins are synthesized in rough ER, then move to the Golgi apparatus for processing, then travel to the cell surface or other destinations Some proteins stay in the endomembrane system, where they provide organelle-specific functions, either in the membrane or lumen of organelles Sent to various destinations: o Lysosomes o Plasma membrane o Secreted outside of cell The Secretory Pathway Hypothesis Summary: Cellular Proteins have Distinctive Molecular Address Labels Proteins that come out of Golgi (rough ER) o Have a molecular tag (e.g phosphorylated sugar) that puts them in correct transport vesicle o Transport vesicle also has tag that tells it to go to a particular destination Proteins synthesized in cytoplasm (on free ribosomes): o Also have zip codes to tell them to go to organelles not on the endomembrane system (e.g mitochondria) Cell Structure Correlates with Function o Type and quantity of organelle in each cell differs depending on function o Animal pancreatic cell: exports digestive enzymes—packed with ER and Golgi to support secretory capacity o Mast cell: manufactures histamine, stored in intracellular vesicles, ready for release upon degranulation
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