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Transcript
Cell Notes Part One The Nucleus Nucleolus Ribosomes Endomembrane System Outer Nucleus The outer membrane of the nucleus is composed of TWO lipid bilayers Attached outside this layer are ribosomes Enbedded within this layer are pore complexes which control what enter or leave the nucleus Inner Nucleus The inner wall of the nuclear membrane is lined with a netlike complex of protein filaments called the Nuclear Lamina that aids in maintaining the shape of the nucleus Chromatin is a substance composed of DNA and proteins that appears as a gray, grainy diffuse mass in a non-dividing cell. (the only other areas where DNA can be found are mitochondria and some chloroplasts) However, when the cell divides, this coils and condenses to form chromosomes The Nucleolus is a mass of dense granules and fibers which produces ribosomes out of ribosomal RNA and proteins(There may be more than one in a cell) Ribosomes Ribosomes participate in and are the site of protein synthesis Ribosomes have a small and large subunit Ribosomes may be free (in cytoplasm) or bound ( to outside of nucleus or Endoplasmic Reticulum) Free ribosomes make proteins used in the cytosol of the cell Bound ribosomes usually make those destined for use outside the cell or inside membranes within the cell The Endomembrane System Membranes related by physical continuity or by passing vesicles between one another Includes: Nuclear envelope Endoplasmic Reticulum Golgi Apparatus Lysosomes Vacuoles Plasma membrane Notice the differences between the smooth and rough ER as well as the cisternae and cisternal space Functions of the Smooth ER Synthesis of lipids (oils, phospholipids, steroids) Example: sex hormones and steroids in vertebrates in Smooth ER of testicle, ovarian & adrenal cells Metabolism of carbohydrates Example: hydrolysis of glycogen in the liver produces glucose phosphate which enzymes made in Smooth ER remove so glucose can enter the bloodstream Continued…… Detoxification of Drugs and Poisons Example: Smooth ER adds hydroxyl groups to drugs like alcohol and barbiturates to aid the body in flushing them out Contraction of Muscle Cells Example: ER membrane pumps ions into the ER against the concentration gradient. When a nerve stimulation occurs, calcium ions go rushing back across the membrane and contraction begins. Functions of the Rough ER Synthesis of secretory proteins Example: bound ribosomes make proteins like insulin and the ER attaches small carbohydrates called oligosaccharides to them. ER wraps membranes of transport vesicles around them and they bud from transitional surface of ER and go where they are needed. Continued………. Membrane production Rough ER makes phospholipids and membrane proteins, causing the membrane itself to grow or new parts to be transported to where they are needed. The Golgi Apparatus Flattened membranous sacs called cisternae In stacks Has a receiving side or cis face and a shipping side or trans face Cis face is usually facing ER and trans face gives rise to vesicles which travel to other sites “Teams” of enzymes needed for specific modifications are located in each cisternae Functions of The Golgi Modification of products of the ER by removing or adding monosaccharides Production of macromolecules such as pectins Transport of products to and fusion with the plasma membrane Modifies,Produces, Sorts and Ships Lysosomes Membranous sacs of digestive enzymes Made by Rough ER and Golgi Inside an acidic pH (5) is maintained by the lysosome because hydrogen ions are pumped into it from the cytosol (cytoplasm) Can aid in digestion by breaking down (by Hydrolysis) macromolecules (polysaccharides like starch, etc.) Can aid in the recycling of nutrients within the cell by breaking them down and releasing them into the cytoplasm for use again by the cell. Continued……. Lysosomes can also be involved in geneticallyprogrammed tasks, like making fingers in unborn humans, reducing a tail in a tadpole as it turns into a frog, etc. In some one-celled animals and in macrophages, lysosomes fuse with vacuoles to digest prey. Vacuoles Larger than vesicles Membranous sacs Can function as: storage sites for food (food vacuoles) water removal machines (contractile vacuoles) Plant Vacuoles Most plant cells have a large central vacuole The membrane that separates the vacuole from the rest of the cell is called the tonoplast. The tonoplast is part of the endomembrane system and selectively transports substances across its membrane. Functions of Plant Vacuoles Storage sites for substances dangerous to the plant Storage sites for pigments in flowers Storage sites for organic compounds needed by the plant cell May act as plant defenders by storing substances that make animals reluctant to eat them The Dynamic Cell Cells can vary the numbers of free and bound ribosomes according to its metabolic needs They can program their own deaths Modify their membranes Cell Notes Part Two Mitochondria and Chloroplasts Cytoskeleton Extracellular Matrix Cell Surfaces and Junctions Mitochondria Found in nearly all eukaryotic cells Site of cellular respiration Have DNA that makes specific proteins on its own ribosomes Number within a particular cell will depend on that cell’s metabolic activity Move and replicate themselves Enclosed by 2 lipid bilayers embedded with proteins Continued……… Narrow area between inner and outer membranes is called the intermembrane space Inner membrane curved upon itself with infoldings called cristae Within the inner membrane is the mitochondrial matrix, the area where DNA and enzymes and ribosomes are found Cristae gives more surface area for chemical reactions needed in cellular respiration like the Krebs Cycle Chloroplast A plastid (membranous sacs with various functions in plants) Two membranes enclose it with a narrow intermembrane space Within the inner membrane are stacks of thylakoids(thylakoid stacks are called grana),that have inner spaces of their own as well as the stroma, or fluid area where DNA, ribosomes and enzymes are involved in the chemical reactions of photosynthesis like the light reactions and the Calvin Cycle. Peroxisomes Specialized compartments Enclosed by one membrane Transfer hydrogen to oxygen Both makes and degrades hydrogen peroxide Can split in two when more are needed Can break down fatty acids and convert them to sugars in plant seeds Cooperate with mitochondria and chloroplasts in certain metabolic functions The Cytoskeleton Network of fibers that: support allow movement regulation of biochemical activities Three types of fibers: microtubules microfilaments intermediate filaments Microtubules Hollow rods Largest of all 3 types of fibers Wall of tubulin which is made of two polypeptide subunits (alpha and beta) Separate chromosomes during cell division Provide “tracks “ for organelles with motor molecules(ex: vesicles) Bear compression forces Centrosomes Microtubules grow out from a pair of centrioles within centrosomes Active during cell division Allow movement of chromosomes Each centriole composed of a ring of 9 triplet microtubules Cilia and Flagella Specialized arrangements of microtubules make up these organelles They are a core of microtubules surrounded by the extension of the plasma membrane. Ring of nine double microtubules with a pair at their center Anchored to a basal body, which is structurally identical to a centriole. Movement of Cilia & Flagella Pairs of microtubules have extensions made of dynein, a protein that can change shape(with the help of ATP) These shape changes allow these extensions to grip other doublets and “walk” along them which results in bending the cilia or flagella This coordinated bending allows them to move which allows them to function in a number of important ways. (sperm to swim to the egg, cilia to clean air passages, etc. ) Microfilaments Solid rods built from intertwined strands of actin ( a globular protein) Bear tension forces Examples of functions: act to contract muscles with myosin(protein) pinch off cytoplasm in dividing cells contract and push cytoplasm forward in amoebae allow cytoplasmic streaming in plants Intermediate Filaments Bear tension forces There are many types that are specialized depending on the cell All are proteins called keratins More permanent than microtubules and microfilaments Especially important in reinforcing the shape of the cell and the fixed position of some organelles like the nucleus Cell Surfaces and Junctions Plant cells have complex structures called cell walls composed of polysaccharides (like cellulose) and proteins They construct a primary cell wall and then a secondary cell wall Between them lies a sticky polysaccharide structure called the middle lamella Plant cells connect via channels through the walls called plasmodesmata Extracellular Matrix Outside animal cells lie a complex of structures called the ECM The ECM consists of glycoproteins like collagen and proteoglycans and fibronectins. Collagen fibers are embedded in a network of proteoglycans Some cells are attached to the ECM by fibronectins which attach to receptor proteins (integrins) Some communication between the cell and the ECM occurs through Integrins, receptor proteins Intercellular Junctions Plant cells are connected to and continuous with the membranes of other cells through the plasmodesmata. It allows water and solutes and sometimes nucleic acids to pass from one cell to another. Macromolecules can move via fibers in the cytoskeleton through the same passage. Animal Cell Junctions Tight junctions: membranes of neighboring cells are fused preventing leakage between membranes Desmosomes: fasten cells together into strong sheets (act like nails or rivets) Gap Junctions: provide channels for cytoplasm between neighboring cells (in the heart this allows close coordination for heartbeat (contractions of the heart muscle)