The Cell

Cell Theory

• Cells are fundamental units of life
• All organisms are composed of cells
• All cells come from preexisting cells
• same as studying life
• Life is continuous- we can trace back to cells

Cells like to keep a good surface area to volume ratio

• Volume determines metabolic activity per unit of time
• Surface area determines how many substances enter and leave
• Basically need a high ratio so that enough nutrients can enter and waste can exit for the processes to happen
• Cells increase surface area by folding

Cell Membrane

• made of lipids
• Selectively permeable barrier that helps maintain homeostasis
• Important in communication and receiving signals
• Has proteins for binding cells   * Plasmodesmata are membrane-lined channels found in plants that transport substances and connect them   * Extracellular matrices are found in animals     * Like a string of webs connected to the membrane that hangs outside       * Integrin connects the extracellular matrix to the membrane       * Connected to microfilaments in the cell membrane and the collagen outside       * for cell movement, the protein changes shape and detach     * Fibrous component is collagen, gel-like component is proteoglycans       * collagen is a protein, proteoglycans are proteins and polysaccharides       * contribute to physical properties of bone, cartilage, skin, bone, and other tissues       * help filter materials like in kidneys       * orient cell movement and repair   * Cell junctions protrude through and between cells to bind them together     * Tight junction       * prevents substances moving in the space between the cells     * Desmosomes       * allows for substances to move in the matrix between cells     * Gap junction       * run between membrane pores, allows for substances to pass through them
• Cell Wall   * Bacteria     * have cell wall containing peptidoglycan (amino sugars and saccharides)     * some bacteria have a additional outer cell wall, very permeable     * some have slimy layer of polysaccharides called the capsule     * some bacteria, including cyanobacteria, contain molecules in membrane that can photosynthesize   * plants     * semi-rigid, provides support and limits its volume     * cellulose     * gel-like matrix contains proteins and polysaccharides     * act as barrier to infection     * contributes to form during growth

Organelles

• found in the cytoplasm along cytosol, which is water and dissolved particles
• Ribosomes   * sites of protein synthesis   * translates the nucleotide sequence of a messenger RNA into a polypeptide   * both types of cells, has a large and a small subunit   *   * each subunit consists of ribosomal RNA and protein   * not membrane bound organelles   * they are free in the cytoplasm, in the rough endoplasmic reticulum, or in mitochondria or chlorplast   * in prokaryotes they float freely in the cytoplasm
• Nucleus   * usually largest organelle   * where DNA is stored and replicated   * where DNA is transcribed to RNA   * contains nucleolus     * where ribosomes are made from RNA and proteins   * two membranes called the nuclear envelope     * has pores for substances to pass through   * In the nucleus, DNA combines with proteins called chromatin to make chromosomes     * strand of DNA encoded with genes   * outer membrane is continuous with the endoplasmic reticulum
• endomembrane system   * nuclear envelope, endoplasmic reticulum, golgi apparatus, and lysosomes
• vesicles   * membrane-bound shuttles that transport substances between components and the membrane
• Endoplasmic reticulum   * network of interconnected membranes in the cytoplasm, large surface area   * Rough endoplasmic reticulum     * ribosomes attached to surface     * newly made proteins enter the RER lumen, and are modified then tagged for delivery to specific locations       * transported in vesicles that pinch off of the ER     * all secreted proteins and most membrane proteins pass through RER     * Polypeptides also transported to RER while synthesizing       * folded into tertiary structure       * many combine with carbohydrate groups, becoming glycoproteins         * important in recognition and interaction between cells   * Smooth Endoplasmic Reticulum     * more tubular (like coral, RER is wall-y), no ribosomes     * chemically modifies small molecules like drugs and pesticides     * site of glycogen degradation     * synthesis of lipids and steroids     * stores calcium ions, important for cell responses
• Golgi Apparatus   * flattened sacs (cisternae) and small membrane enclosed vesicles   * further modifies proteins from the RER   * concentrates, packages, and sorts proteins   * adds carbs to proteins   * site of polysaccharide synthesis for plant cell walls   * three regions     * cis: recieves     * trans: exports in vesicles to the membrane or lysosomes     * medial: medial
• Lysosomes   * primary lysosomes originate from golgi apparatus   * contain hydrolases (digestive enzymes), macromolecules are hydrolyzed into monomers   * macromolecules enter the cell through phagocytosis     * part of the membrane encloses the material and a phagosome is formed     * phagosomes then fuse with primary lysosomes to make secondary lysosomes     * secondary lysosomes hydrolyze food molecules   * phagocytes are cells that specialize in taking in materials and breaking them down   * autophagy is the programmed destruction of cell components (materials and organelles) using lysosomes   * lysomal storage diseases happen when lysosomes fail to break cell components down
• Mitochondria   * energy-rich molecules begin breaking down in the cytosol   * then it enters the mitochondria where it gets turned into ATP   * need more energy=more mitochondria   * 2 membranes     * outer-very porous     * extensive folds called cristae increase surface area   * fluid filled matrix contains enzymes, DNA, and ribosomes
• peroxisomes   * collect and break down toxic by-products of metabolism (ex. H2O2) using special enzymes
• plant organelles   * plastids     * some are used for storage     * give plants their color     * chromoplasts     * leucoplasts (starch)   * chloroplast     * chlorophyll, photosynthesis, anabolic reaction     * two membranes     * internal membranes called thylakoids       * granum- stack of thylakoids, converts light energy into chemical energy       * stroma- aqueous matrix around grana         * contains ribosomes and DNA, synthesizes carbs   * glyoxysomes     * convert lipids into carbs for growth
• vacuoles   * mainly in plants and fungi   * storage of waste in toxins, deters herbavores   * structure for plants, water enters vacuole through osmosis, creates turgor pressure   * reproduction- colors attract pollinators   * catabolism- enzyme in seed vacuoles hydrolyze stored food for early growth   * contractile vacuoles can get rid of water by pumping it out and moving the cell

Cytoskeleton

• some rod-shaped bacteria have network of actin-like, helical structures that help maintain shape
• supports and maintains cell shape
• holds organelles in position and can move them
• involved in cytoplasmic streaming (things in cell move)
• interacts with extracellular stuff to hold cell in place
• dynamic instability   * filaments can lengthen or shorten with more assembly or detachment     * actin and myosin interact to contract muscles
• motor protein   * any protein that causes movement
• 3 components
• microfilaments   * helps a cell or its parts move   * determines shape   * made from actin monomers that attach in the plus end and detach at the minus     * actin is a protein, important in muscle contraction
• intermediate filaments   * 50 kinds, 6 classes   * tough, ropelike, no dynamic instability   * anchor cells in place
• microtubules   * thickest cytoskeleton component   * rigid internal skeleton for some cells or regions   * framework for motor proteins   * made from dimers of protein tubulin, chains of dimers surround a hollow core   * \     * and - ends, dynamic instability   * polymerization - rigidity, depolymerization- collapse   * form internal skeleton for cellular appendages   * cilia     * short, usually many     * stiffly moves cell     * can move fluid over a stationary cell   * flagella     * some prokaryotes use flagella to move     * one or two, longer, push or pull cell through water   * cilia and flagella microtubules are arranged in 9+2 pattern     * doublets- 9 fused pairs of tubules form a cylinder     * one unfused pair in center     * motion occurs when doublets slide past each other     * dynein       * motor protein that can change shape, causes sliding     * nexin       * crosslinks doublets and prevents sliding, so it bends     * kinesin       * combines with vesicles that walk along the microtubule

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