BIO 1330 Chapter 7: Inside the Cell
BIO 1330 Chapter 7: Inside the Cell BIO 1330
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This 9 page Class Notes was uploaded by mythical.mm on Tuesday September 27, 2016. The Class Notes belongs to BIO 1330 at Texas State University taught by Dr.Debelica in Fall 2016. Since its upload, it has received 4 views. For similar materials see Functional Biology 1330 in Biology at Texas State University.
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Date Created: 09/27/16
Chapter 7 Inside the Cell Cells are the fundamental unit of life All cells have: o Proteins: perform most of the cell’s functions o Nucleic Acids: store, transmit and process information o Carbohydrates: provide chemical energy, carbon, support and identify o Plasma Membrane: serves as a selectively permeable membrane barrier Based on morphology, or form, cells are divided into two fundamental types: o Eukaryotes have a membrane bound nucleus o Prokaryotes lack a membrane bound nucleus Based on phylogeny, or evolutionary history, organisms are divided into three domains: o Bacteria: prokaryotic o Archaea: prokaryotic o Eukarya: eukaryotic Bacterial and Archaeal Cell Structure: o Recent advances reveal that prokaryotes are more complex than previously thought o They contain a single, circular chromosome composed on DNA and proteins, genes that code for polypeptides, tightly coiled to fit inside the cell and located in a region called the nucleoid o They also may contain small, circular DNA molecules called plasmids o Prokaryotes also have ribosomes which are macromolecular machines that consist of RNA molecules and protein and are used for protein synthesis o Many prokaryotes have internal photosynthetic membranes that convert energy in sunlight to chemical energy and develop from folds of the plasma membrane o Some bacteria have membrane bound compartments called organelles o Organelles perform specialized tasks, including storing calcium ions, holding magnetite crystals to serve as a compass and organizing enzymes for building organic compounds o Bacteria and archaea contain protein fibers that form the basis of the cytoskeleton, assist in cell division and maintain the cells shape Plasma Membrane: o Consists of a phospholipid bilayer o Has proteins that either span the bilayer or attach to one side o Creates a distinct internal environment o Inside the membrane, all the contents of a cell (excluding the nucleus in eukaryotes) is called the cytoplasm The Cell Wall: o Forms a protective “exoskeleton” o Most prokaryotes have a cell wall composed of a tough, fibrous layer that surrounds the plasma membrane o Many species have an additional layer outside the cell wall that is composed of glycolipids External Structures: o Many prokaryotes have structures that grow from the plasma membrane o Flagella: long filaments that rotate to propel the cell o Fimbriae: needlelike projections that promote attachment to other cells or surfaces Eukaryotic Cell Structure: o Eukaryotes range in size from microscopic algae to 100-meter tall redwood trees o Protists, fungi, plants and animals are all eukaryotic (multicellular or unicellular) o Eukaryotic cells are generally larger than prokaryotic o Have a large surface-to-volume ratio o Organelles break up the large cell volume into smaller membrane bound organelles o Separation of incompatible chemical reactions o Increasing the efficiency of chemical reactions o The # Differences Between Eukaryotic and Prokaryotic: o Eukaryotic cells are generally larger o Prokaryotic chromosomes are in a nucleoid regions and eukaryotic chromosomes are enclosed in the nucleus o Eukaryotic cytoplasm in compartmentalized into a large number of distinct organelles The Nucleus: o Large and highly organized o Double membrane= nucleus envelope studded with pore like openings and the inside surface is linked to the nucleus lamina (lattice sheet of fibrous proteins) o Has a distinct regions called the nucleolus where ribosomal RNA is synthesized and ribosome subunits are assembled o Center for information storage and processing o Contains the cells chromosomes Ribosomes: o Complex molecular machines that manufacture proteins o Lack a membrane so are not considered organelles o Some ribosomes ae free in the cytosol (manufacture proteins that remain in the cytosol or are imported to other organelles) and some are attached to the endoplasmic reticulum (manufacture proteins with other fates) Endoplasmic Reticulum: o An organelle that is an extension of the nuclear envelope o Rough and smooth endoplasmic reticulum o Rough ER: o Is studded with ribosomes o Synthesizes proteins that will be: Shipped to other organelles Inserted into the plasma membrane Secreted to the cell exterior o As proteins are manufactured on the surface of RER proteins are folded and processed inside of the lumen of RER o Proteins made in the RER: Carry messages to other cells Act as a membrane transport or pump Catalyze reactions o Smooth ER: o Lacks ribosomes o Contains enzymes that catalyze reactions involving lipids that: Synthesize lipids needed by the organism Break down lipids and other molecules that are poisonous o Is a reservoir for Caions Golgi Apparatus: o Is formed by a series of stacked flat, membranous sacs called cisternae o Has a distinct polarity, or sidedness o The cis (on the side) surface is closest to the nucleus o The trans (across) surface is orientated toward the plasma membrane o Processes, sorts, and ships proteins synthesized in the rough ER o The cis side receives products from the rough ER and the trans side ships them out to other organelles or the cell surface o Membranous vesicles carry materials to and from the organelle Lysosomes: o Recycling centers found only in animal cells o Contain o Approximately 40 different enzymes o Digest macromolecules and export monomers to the cytosol o Acid hydrolases o Work best at a pH of 5 o Proton pumps in membrane maintain low internal pH o Synthesized in the ER o Processed in the Golgi apparatus o Shipped to lysosomes o Lysosomes+ Golgi apparatus+ ER= endomembrane system o Produces, processes and transports proteins and lipids Vacuoles: o Large, membrane bound structures found in plants and fungi o Functions: o Some are specialized for digestion o Most are used to store water and ions to help the cell maintain its normal volume o In seeds, they are filled with proteins o In flower petals or fruits, they contain pigments o May contain noxious compounds to protect leaves and stems from being eaten Peroxisomes: o Originate as buds from the ER o Center of redox reactions o Liver cell peroxisomes contain enzymes that oxidize the ethanol in alcoholic beverages o Specialized plant peroxisomes, called glyoxysomes, oxidize fats to form an energy storage compound o Oxidation often produced hydrogen peroxide o In peroxisomes the enzyme catalase “detoxifies” it Mitochondria: o POWER HOUSE o Supple ATP to cells o Two membranes: o The inner one is folded into a series of sac like cristae o The solution inside the inner membrane is mitochondrial matrix o Have their own mitochondrial DNA (mtDNA) o Manufacture their own ribosomes Chloroplasts: o Most plant and algal cells have chloroplasts, where photosynthesis takes place o Have three membranes: o Innermost membrane contains flattened sacs called thylakoids which are arranged in stacks called grana o Surrounding the thylakoids is the stroma o Chloroplasts contain their own DNA and manufacture their own ribosomes o Chloroplasts and mitochondria may once have been free living bacteria o Endosymbiosis theory: bacteria ere engulfed and a mutually beneficial relationship evolved o Mitochondria and chloroplasts contain their own DNA o Synthesize their own small ribosomes o Grow and divide independently of cell division Cytoskeleton: o Composed of protein fibers o Gives cells shape and structural stability o Aids in cell movement o Transports materials within the cell o Organizes the organelles and other cellular structures into cohesive whole The Eukaryotic Cell Wall: o Fungi, algae and plants have a stiff outer cell wall that gives structural support to the cell o Rods, or fibers of a carbohydrate, run through a stiff matrix made of other polysaccharides and proteins Putting Parts into a Whole: o Size and number of different types of organelles correlate with cell’s specialized function o Cells are dynamic living things that have interacting parts and contain constantly moving molecules The Dynamic Cell: o Your body’s cells use and synthesize approximately 10 million ATP molecules per second o Cellular enzymes can catalyze more than 25,000 reactions per second o Each membrane phospholipid can travel the breadth of its organelle or cell in under a minute o Hundreds of trillions of mitochondria are completely replaced about 10 days Nuclear Envelope: o Perforated with openings called nuclear pore complexes o Connects inside of nucleus with the cytosol o Consists of about 30 different proteins o RNA and ribosomes going out o Proteins needed in the nucleus going in o Nucleotides go in o Nuclear proteins contain a 17 amino-acid-long nuclear localization signal (NLS) that serves as a zip code that marks them for transport through the nuclear pore complex The Endomembrane System: o Manufactures+ships+recycles cargo o 1) protein enters ER o 2) proteins exit ER o 3) proteins enter Golgi apparatus o 4) proteins exit the Golgi apparatus o 5) protein is secreted from the cell o 6) proteins are folded o 7) carbohydrate side chains that serve as indicators for shipment are added (glycosylation) o 8) glycoprotein is ready to be shipped to next destination o Moving from the ER to the Golgi Apparatus: o Proteins are transported in vesicles that bud off from the ER, move away, fuse with the membrane on the cis face of the Golgi apparatus, and dump their cargo inside o In the Golgi Apparatus: o The Golgi apparatus is dynamic o New cisternae form at the cis face o Old cisternae break off from the trans face and are replaced by the cisternae behind them o Different cisternae contain different enzymes o Proteins enter the Golgi apparatus at the cis face and are modified as they move through Proteins: o Proteins are secreted out of the cell by exocytosis o 1) proteins bound for different destinations carry distinct tags o 2) proteins are sorted o 3) transport vesicles bud o 4) cytosolic and membrane proteins cause transport vesicles to attach and fuse at destinations o 5) vesicles deliver contents o Receptor-mediated endocytosis: o Uses receptors to bind macromolecules outside of the cell o Plasma membrane pinches in to form a vesicle that delivers cargo to early endosome o Early endosome is acidified and matures into late endosome, and eventually, the lysosome o Phagocytosis: o Brings smaller cell or food particles inside the cell to form a phagosome o Phagosome is delivered to lysosome which fuses with phagosomes and digests its contents o Autophagy: o Encloses a damaged organelle within a membrane, forming an autophagosome that is delivered to the lysosome and digested The Dynamic Cytoskeleton: o The cytoskeleton Is dense o Complex network of fibers o Help maintain cell shape by providing structural support o Is not a static structure like scaffolding used construction sites o Its fibrous proteins move and change to alter the cell’s shape, shift its contents and even move the cell itself o 3 Type: o Actin filaments (microfilaments): Smallest cytoskeleton elements Polymer actin molecules two strands coil around each other grouped together into long bundles or dense networks Usually found inside plasma membrane The two distinct ends are referred to as plus and minus ends Different rates of assembling actin subunits on each end The plus end grows faster than the minus end Actin filaments help define the cell’s shape Movement, with motor protein myosin (uses ATP) results in muscle contraction, cytokinesis (dividing cytoplasm curing cell division), and cytoplasmic streaming (flow of cytoplasm) Cell crawling is caused by actin filaments growing in one direction, moving the cell o Intermediate filaments: Are defined by size rather than composition Many types exist, each consisting of a different protein Provide structural support for the cell Are not involved in movement About 20 types of keratin (found in hair and nails) Nuclear laminas are intermediate filaments Nuclear lamins give the nucleus its shape, form a dense mush under the nuclear envelope, anchor the chromosomes and break up and reassemble the nuclear envelope when cells divide o Microtubules: Largest cytoskeletal elements Large hollo tubes made of tubulin dimers Have two polypeptides called α-tubulin and β-tubulin Have polarity Are dynamic Usually grow on their plus ends Originate from the microtubule organizing center (plus ends grow outward and radiate throughout the cell) In animal cells this center is called centrosome and it contains two bundles of microtubules called centrioles Provide stability Provide a structural framework for organelles Are involved in movement Separates chromosomes during cell division Serve as “railroad tracks” for vesicle transport o Vesicle transport requires a motor protein called kinesin o Kinesin uses ATP for mechanical work, the head region binds to microtubules and the tail region binds to transport vesicle o Kinesin “walks” along the microtubule through a series of conformational changes as it hydrolyzes ATP Flagella and Cilia: o Flagella are long, hair like projections (usually 1-3) o Cilia are short, hair like projections o Closely related to eukaryotic flagella o Usually more numerous than flagella o Prokaryotic flagella: o Helical rods made of a protein called flagellin o Move the cell by rotating the rod like a ship’s propeller o Are not surrounded by the plasma membrane o Eukaryotic flagella: o Consist of several microtubules o Move the cell by undulating (whipping back and forth) o Are surrounded by the plasma membrane o These two probably evolved independently o Although they have different movement their underlying organization is identical o A complex “9+2” arrangement of microtubules called an axoneme o Connected by links and spokes o The axenome attaches to the cell at the basal body (identical in structure to a centriole, aid sin growth of axenome) o How Does It Move: o The motor protein dynein o Dynein forms a set of arms between doublets, changes shape when ATP is hydrolyzed to “walk” up the microtubule, and moves dynein along microtubules toward the minus end o When dynein arms on only one side of the axoneme move, cilia and flagella bend which results in a swimming motion