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cell
basic functional unit of all living things
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plasma membrane (cell membrane)
- bounds the cell together
- encloses the nucleus and cytoplasm
- separates internal metabolic events from the external environment
- controls the movement of materials into and out of the cell
- is a double lipid bilayer
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cytoplasm
consists of specialized bodies (organelles) suspended in cytosol
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cytosol
consists of water and dissolved substances such as proteins and nutrients
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peripheral proteins
proteins may attach loosely to the inner or outer surface of the membrane
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integral proteins
proteins that may extend into the membrane
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transmembrane proteins
integral proteins may span across the membrane appearing at both surfaces
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phospholipid membrane
- selectively permeable
- small, uncharged, polar molecules, & hydrophobic molecules freely pass across the membrane
- large polar molecules and all ions are permeable
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proteins
in the plasma membrane provide a wide range of functions
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channel proteins
provide open passageway through the membrane for certain hydrophilic (water-soluble) substances such as polar and charged molecules
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ion channels
allow the passage of ions across the membrane
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gated channels
- ion channels in nerve and muscle cells
- open and close in response to specific chemical or electrical stimuli to allow the passage of specific ions (like Na+ and K+)
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porins
proteins that allow the passage of certain ions and small polar molecules through membranes
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aquaporins
found in the plasma membranes of certain cells (kidneys and plant roots) dramatically increase the passage of H2O molecules
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carrier proteins
- USE energy (ATP) to transport materials across the membrane
- when energy is used it's called active transport
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active transport
- carrier protein that uses energy
- materials are actively transported
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Na+-K+ pump
uses ATP to maintain higher concentrations of Na+ and K+ on opposite sides of the plasma membrane
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recognition proteins
- give each cell a type of unique identification
- these proteins are glycoproteins because they have short polysaccharide chains attached
- oligosaccharide part of the glycoprotein extends away from the surface of the membrane
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adhesion proteins
attach cells to neighboring cells or provide anchors for the internal filaments and tubules that give stability to the cell
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receptor proteins
- provide binding sites for hormones or other trigger molecules
- in response or trigger molecules, a specific cell response is activated
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cholesterol
- molecules distributed throughout the phospholipid bilayer provide some rigidity to the plasma membranes of animal cells.in plant cells they are called sterols
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glyocalyx
- carbohydrate coat that covers the outer face of the cell wall of some bacteria and the outer face of the plasma membrane of certain animals cells
- consists of various oligosaccharides that are attached to the membrane phospholipids and proteins
- may provide adhesive capabilities, barrier to infection, or markers for cell-cell recognition
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organelles
bodies within the cytoplasm that serve to physically separate the various metabolic reactions that occur within cells
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nucleus
- bounded by the nuclear envelope that consists of two phospholipid bilayers
- contains DNA
- serves as the site for the separation of chromosomes during cell division
- you can also see one or more nucleoli, concentrations of DNA in the process of manufacturing the components of ribosomes
- where ribosomes are made
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chromatin
- DNA which is spread out within the nucleus as a threadlike matrix
- found inside nucleus
- major components are DNA and histone
- functions: package DNA into a smaller volume to fit in the cell, strengthen the DNA to allow mitosis and meiosis, and to serve as a mechanism to control expression and DNA replication
- contains genetic material-instructions to direct cell functions
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chromosomes
- shape:rod-shaped bodies
- when cells begin to divide, the chromatin condenses into rod-shaped bodies
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histones
serve to organize the lengthy DNA
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nucleosomes
coiled bundles from chromosomes
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ribosomes
- subunits manufactured in nucleus
- consist of RNA molecules and proteins
- in the cytoplasm: assist in the assembly of amino acids into proteins
- two subunits: 60S & 40S move across the nuclear envelope and into the cytoplasm where they are assembled into a single 80S
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Svedberg
- S (ex. 40S, 60S, 80S)
- expresses how readily a product a product forms a sediment in a centrifuge, a larger values represents larger and heavier products
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endoplasmic reticulum (ER)
- consists of stacks of flattened sacs involved in the production of various materials
- often closely related to nucleus
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rough ER
- has ribosomes attached
- creates glycoproteins by attaching polysaccharide groups to polypeptides as they are assembled by the ribosomes
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smooth ER
- without ribosomes
- responsible for various activities including the synthesis of lipids and hormones, especially in cells that produce these substances for export from the cell
- liver cells:breaks down toxins, drugs, and toxic by products from cellular reactions
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golgi apparatus
- group of flattened sacs arranged like a stack of bowls
- modify and package proteins and lipids into vesicles
- these vesicles release their contents to the outside of the cell
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lysosomes
- vesicles from a golgi apparatus that contain digestive enzymes
- break down food, cellular debris, and foreign invaders
- low pH (acidic) are favorable to the activity of the enzymes (inside lysosome)
- enzymes that escape from the lysosome remains inactive in the neutral pH of the cytosol
- do no occur in plant cells
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peroxisomes
- breaks down various substances (H2O2, fatty acids, and amino acids)
- common in liver and kidney because they break down toxic substances
- plants cells: modify by-products of photorespiration
- germinating seeds: break down store fatty acids to help generate energy for growth
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mitochondria
carry out aerobic respiration, which is energy (form of ATP) is obtained from carbohydrates
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chloroplasts
- carry out photosynthesis
- plant process of incorporating energy from sunlight into carbohydrates
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cytoskeleton
- internal structure of the cytoplasm
- microtubules, intermediate filaments, and microfilaments establish the shape or coordinate movements (all are proteins fibers)
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microtubules
- made of tubulin (protein)
- provide support and motility for cellular activities
- found in spindle apparatus and in the flagella and cilia
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spindle apparatus
guides the movement of chromosomes during cell division
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intermediate filaments
provide support for maintaining the shape of a cell
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microfilaments
- made of the protein actin and are involved in cell motility
- found in the muscle cells and in cells that move by changing shape such as phagocytes
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phagocytes
white blood cells that wander throughout the body attacking bacteria and other foreign invaders
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transport vesicles
move materials between organelles or between organelles and the plasma membrane
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food vacuoles
- temporary receptacles of nutrients
- often merge with lysosomes whose digestive enzymes break down food
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storage vacuoles
- seen in plants
- sotre starch, pigments, and toxic substances
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central vacuoles
- large bodies occupying most of the interioir of certain plant cells
- when fully filled-they exert turgor (pressure) on the cell walls and maintains rigidity in the cell
- store nutrients and carry out functions otherwise assumed by lysosomes in animal cells
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contractile vacuoles
specialized organelles in single-celled organisms that collect and pump excess water out of the cell
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extracellular region
- region outside the plasma membrane
- ex: cell wall, extracellular matrix
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cell walls
- found in plants, fungi, protists, and bacteria
- develop outside the plasma membrane and provide support for the cell
- plants: made of cellulose (made from B-glucose)
- fungi: made of cellulose and chitin
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chitin
- cell walls of fungi
- modified polysaccharide differing from cellulose in that one of the hydroxyl group is replaced by a group containing nitrogen
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extracellular matrix
- found in animals in the area between adjacent cells
- area is occupied by fibrous structural proteins, adhesion proteins, and polysaccharides secreted by cells
- matrix provides mechanical supports and helps bind adjacent cells together
- most common substance in this region is the protein collagen
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cell junctions
serve to anchor cells to one another or to provide a passageway for cellular exchange
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anchoring junctions
protein attachments between adjacent animal cells
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desosome
- an anchoring junction
- consists of proteins that bind adjacent cells together, providing mechanical stability to tissues
- associated with protein filaments that extend into the interior of the cell and serve to hold cellular structures together
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tight junctions
- tightly stitched seams between animal cells
- completely encircles each cell, producing a seal that prevents the passage of materials between the cells
- characteristics of cells lining the digestive tract where materials are required to pass through cells to penetrate the blood stream
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communicating junction
- passageways between cells that allow the transfer of chemical or electrical signals
- 2 types: gap junctions & plasmodesmata
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gap junctions
- narrow tunnels between animal cells that consist of proteins called connexins
- proteins prevent the cytoplasm from each cell from mixing, but allows the passage of ions and small molecules
- allow communication between cells through the exchange of materials or through the transmission of electrical impulse
- channel proteins of 2 adjacent cells that are closely aligned
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connexins
proteins prevent the cytoplasm from each cell from mixing, but allows the passage of ions and small molecules
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plasmodesmata
- narrow channels between plant cells
- narrow tube of endoplasmic reticulum ,(desmotubule) surrounded by cytoplasm and plasma membrane, passes through the channel
- material exchange occurs through the cytoplasm surrounding the demotubule
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plant cells vs animal cells
- presence of cells wall, chloroplasts, central vacuoles in plants cells (absent in animals)
- presence of lysosomes, centrioles, and cholesterol in animal cells (absent in plants)
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eukaryotes
all organism except for bacteria, cyanobacteria, archaebacteria
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prokaryotes
- bacteria, cyanobacteria, archaebacteria
- lack all the organelles
- have plasma membrane, DNA molecule, ribosome, cytoplasm, and cell wall
- do not have a nucleus
- single "naked" DNA molecule without the protein that is associated with the DNA in eukaryotic chromosomes
- ribosomes are smaller (70S,50S,30S)
- cells walls of bacteria and cyanobacteria (when present) are constructed from peptidoglycan
- cell wall of cyanobacteria contains various polysaccharides, NOT peptidoglycan, cellulose, or chitin
- flagella are not constructed microtubules
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peptidoglycan
polysaccharide protein molecule
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bulk flow
collective movement of substances in the same direction in response to a force or pressure
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passive transport
- process describes the movement of substances from a region of higher to lower concentration
- do not require energy
- "down" a concentration gradient
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simple diffusion
- net movement of substances from an area of higher concentration to an area of lower concentration
- random, constant, independent motion
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osmosis
- diffusion of water molecules across a selectively permeable membrane
- turgor pressure: osmotic pressure that develops when water enters the cells of plants and microorganisms
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dialysis
diffusion of solutes across a selectively permeable membrane
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plasmolysis
movement of water out of a cell that results in the collapse of a cell
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facilitated diffusion
- diffusion of solutes or water through channel proteins in the plasma membrane
- water can pass through plasma membrane without the aid of special proteins, aquaporins increase the rate of transfer by facilitated diffusion
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countercurrent exchange
describes the diffusion of substances between two regions in which substances are moving by bulk flow in opposite directions
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active transport
- movement of solutes against a gradient and requires the expenditure of energy (ATP)
- transport proteins in the plasma membrane transfer solutes such as small ions, amino acids, and monosaccharides across the membrane
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vesicular transport
uses vesicles or other bodies in the cytoplasm to move macromolecules or large particles across the plasma membrane
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exocytosis
describes the process of vesicles fusing with the plasma membrane and releasing their contents to the outside of the cell
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endocytosis
- describes the capture of a substance outside the cell when the plasma membrane merges to engulf it.
- 3 types: phagocytosis, pinocytosis, receptor-mediated
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phagocytosis
- "cellular eating"
- occurs when undissolved material enters the cell
- plasma membrane wraps around the solid material and engulfs it forming a phagocytic vesicle
- phagocytic vesicles then attack and engulf the material
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pinocytosis
- "cellular drinking"
- occurs when dissolved substances enter the cell
- plasma membrane folds inward to form a channel allowing the liquid to enter
- plasma membrane closes off the channel encircling the liquid to make a vesicle
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receptor-mediated
- endocytosis occurs when specific molecules in fluid surround the cell bind to specialized receptors that concentrate in coated pits in the plasma membrane
- membrane pits, receptors, and specific molecules fold inward and the formation of a vesicle follows
- proteins that transport cholesterol in blood and certain hormones target specific cells by receptor-mediated endocytosis
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