Biology Study Guide Exam 2 Chapter 6 A Tour of the Cell Cell Fractionation a useful technique for studying cell structure and function it takes cells apart and separates major organelles and other subcellular structure from one another The centrifuge spins test tubes holding mixtures of disrupted cells at a series of increasing speeds forming a pellet at the bottom of the test tube At lower speeds the pellet consists of larger components and at higher speeds the pellet consists of smaller components Cell fractionation enables researchers to prepare specific cell components in bulk and identify their functions Basic features of all cells o Plasma membrane o Semifluid substance called cytosol cytoplasm o Chromosomes carry DNA o Ribosomes make proteins Only organisms of the domains Bacteria and Archaea consist of prokaryotic cells Protists fungi animals and plants all consist of eukaryotic cells Eukaryotic cells are characterized by having o DNA in a nucleus that is bounded by a membranous nuclear envelope o Membrane bound organelles o Cytoplasm in the region between the plasma membrane and nucleus o Eukaryotic cells are generally much larger than prokaryotic cells Prokaryotic Cells are characterized by having o No nucleus DNA in an unbound region called the nucleoid o No membrane bound organelles o No internal membranes Major difference b t prokaryotic and eukaryotic cells in the location of their DNA o Eukaryotic Cells most of the DNA is in the nucleus which is bounded by a double membrane True Nucleus o Prokaryotic Cells the DNA is concentrated in a region that is not membrane enclosed called the Nucleoid Before Nucleus Nucleus the organelle of a Eukaryotic cell that contains the genetic material I the form of Chromosomes made up of chromatin o The nuclear envelope encloses the nucleus separating its contents from the cytoplasm It is a double membrane o Within the nucleus the DNA is organized into discrete units called chromosomes which are structures that carry genetic information o The complex of DNA and proteins making up chromosomes are called chromatin Ribosomes are the cellular components that carry out protein synthesis o They are made up of ribosomal RNA and protein o Not membrane bounded and thus are not considered organelles o Free ribosomes are located in the cytosol Synthesis proteins that are free in the cytoplasm o Bound ribosomes are located on the outside of the endoplasmic reticulum ER or the nuclear envelop Synthesis proteins associated with membrane Trans membrane proteins Generally make proteins that are destined for insertion into membranes for packaging o Bound and Free ribosomes are structurally identical and ribosomes can alternate between the two roles The endomembrane system is the internal membranes of a Eukaryotic cell it is made up of the nuclear envelope endoplasmic reticulum Golgi apparatus lysomes vacuole and plasma membrane o The membranes of this system are related either through direct physical continuity or by the transfer of membrane segments as tiny vesicles The Endoplasmic Reticulum ER an extensive membranous network continuous with the outer nuclear membrane and composed of ribosome studded rough and ribosome free smooth regions o Accounts for more than half the total membrane in many eukaryotic cells o Consists of a network of membranous tubules and sacs called cisternae o The ER separates the cisternae space from the cytosol o Biosynthetic Factory Smooth ER Functions o Outer surface lacks ribosomes o Functions in diverse metabolic processes which include synthesis of lipids metabolism of carbohydrates detoxification of drugs and poisons and storage of calcium Rough ER Functions o Has bound ribosomes which secrete glycoproteins proteins covalently bonded to carbohydrates o Distributes transport vesicles proteins surrounded by membranes o Is a membrane factory for the cell Golgi Apparatus Shipping and Receiving Center o Stacks of flat membranous sacs cisternae that modify store and route products of the ER and synthesize some products notably noncellulose carbohydrates Cisternae is not physically connected o Functions of the Golgi apparatus Modifies products of the ER Manufactures certain macromolecules Sorts and packages materials into transport vesicles o Cis face is usually located near the ER and acts as the receiving side of the Golgi o Trans face is the shipping side of the Golgi Lysosomes Digestive Compartments o A lysosomes is a membranous sac of hydrolytic enzymes that can digest macromolecules o Lysosomal enzymes can hydrolyze proteins fats polysaccharides and o Lysosomal enzymes work best in the acidic environment inside they o Some types of cells can engulf another cell by phagocytosis which forms nucleic acids lysosome a food vacuole o A lysosome fuses with the food vacuole and digests the molecules o Lysosomes also use enzymes to recycle the cell s own organelles and macromolecules a process called autophagy Mitochondria and Chloroplasts change energy from one from to another o Mitochondria are the sites of cellular respiration a metabolic process that uses oxygen to drive the generation of ATP by extracting energy from sugars fats and other fuels o Chloroplasts found in plants and algae are the sites of photosynthesis This process in chloroplasts converts solar energy to chemical energy by absorbing sunlight and using it to drive the synthesis of organic compounds such as sugars from carbon dioxide and water o Peroxisome an oxidative organelle o Mitochondria and Chloroplasts have similarities with bacteria Enveloped by a double membrane Contain free ribosomes and circular DNA molecules Their autonomous they grow and reproduce somewhat independently in cells o Endosymbiont theory Mitochondria and chloroplasts originated as prokaryotic cells engulfed by a host cell The engulfed cell and its host then evolved into a single organism Mitochondria Chemical Energy Conversion o Mitochondria are found in nearly all eukaryotic cells including those of plants animals fungi and most unicellular eukaryotes o Some cells have on large mitochondria but more often a cell has hundreds or even thousands of mitochondria the number correlates with the cell s level of metabolic activity o Mitochondria have two membranes The outer membrane is smooth but the inner membrane is convoluted with infoldings called cristae o Mitochondrial matrix the compartment of the mitochondrion enclosed by the inner membrane and containing enzymes and substrates for
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