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Cells: The Living Unit
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Cells – general 4 aspects of cell theory –
A cell is the basic structural & functional unit of life Cell properties directly relate to the properties of life The activity of an organism depends on the activities of individual and collective cells Principle of complementarity – Activities of cells are dictated by specific structures of cells Continuity (the smooth working) of life is based on a cellular level Cells come from pre-existing cells
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Cells – general cont. Characteristics of cells –
Cells vary greatly in their size, shape, and function All cells are composed primarily of carbon, hydrogen, nitrogen, and oxygen (CHON) All cells have the same basic parts & some common functions All general cells contain a plasma membrane, cytoplasm, and nucleus
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Cell diversity
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Plasma membrane structure
Defines the extent of the cell Separates bodies major fluid components Intracellular fluid within cells Extracellular fluid outside cells The plasma membrane is composed of a double layer of phosopholipids embedded with smaller amounts of cholesterol and glycolipids and proteins
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Plasma membrane structure cont.
Fluid mosaic model = Membrane structure composed of a double layer (bilayer) of lipid molecules with protein molecules dispersed in it. Proteins which “float” within the bilayer form an ever changing mosaic pattern Composed of… Double layer of phospholipids (lying tail to tail with their polar heads exposed to the water inside and outside the cell) embedded with cholesterol, proteins, and glycolipids
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Plasma membrane structure cont.
Surfaces of the plasma membrane – Outside surfaces of the cell contain more lipids Contains glycolipids (sugar lipid) Helps to make the outer surface more polar Inside contains integral proteins, phospholipids, & cytoskeleton Phospholipids – Modified lipid containing phosphorus 2 components – Hydrophilic – Polar “head” Has a charge Water loving Hydrophobic – Nonpolar “tail” Does not have a charge Water hating
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P.M.
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Plasma membrane structure cont.
Plasma membrane proteins – Integral proteins are firmly inserted into the plasma membrane Have both hydrophobic and hydrophilic regions Some protrude from only one side of the plasma membrane Usually involved in receptors for hormones or chemical messengers or act as chemical relay messengers Transmembrane proteins span the entire plasma membrane Mainly involved in transport Channel proteins – Have a pore in which water soluble molecules pass Carrier proteins – Bind to substances to move them through the membrane
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P.M
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Plasma membrane structure cont.
Peripheral proteins are not embedded in the plasma membrane, but attach to integral proteins or to phospholipids Can be removed w/o disturbing the plasma membrane Contain filaments that helps support the membrane on the cytoplasmic side Some involved in changing the cells shape (during division) The glycocalyx is the fuzzy, sticky, carbohydrate-rich area surrounding the cell “sugar covering” Provides a highly specific biological markers Recognize self from non-self
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P.M.
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Specialization of the plasma membrane
Microvilli – “shaggy hairs” Fingerlike extensions of the plasma membrane that increase the surface area of the cell Most often found in cells with an absorptive function Kidneys and intestines Contains actin – Contractile protein that helps stiffen the microvilli to keep them erect
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Specialization of the plasma membrane cont.
Membrane junctions – Many cells are close together and in tight communities Glycoproteins act as the cells “adhesive” Wavy contours of cells edges allow cells to stick together in a tongue and grove fashion Special membrane junctions are formed Tight Junctions Desmosomes Gap Junctions
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Specialization of the plasma membrane cont.
Tight junctions Integral proteins on adjacent cells fuse together to form impermeable junctions Prevents molecules from passing through the extracellular space between cells
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Specialization of the plasma membrane cont.
Membrane junctions cont. - Desmosomes – Anchoring junctions Scattered like rivets to prevent the cells separation Held together by linker proteins that extend from the plaque on the cytoplasmic face Linker proteins span from one cell to the other & attach themselves to the other cells plaque Reduces the chances of ripping the cell when tension is applied
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Desmosomes
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Specialization of the plasma membrane cont.
Membrane junctions cont. – Gap junctions – Communication junction Allows chemical substances to pass between adjacent cells Connected by connexons – hollow tubules that allow the cells to communicate because their cytoplasm's are so close Allows small molecules to pass between two cells In electrically charged tissues
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Gap junctions
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P.M. Functions – general Cells are “bathed” in interstitial fluid –
Contains important substances cells need to survive Cells extract nutrients to remain healthy Where the cells eject their waste The plasma membrane is a selectively permeable barrier, regulating how substances pass into and out of the cell Allows some substances to pass while excluding others
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P.M. Functions cont. Solute – Solvent – Concentration gradient –
Substance being dissolved within a solution Ex. Sugar, salt, calcium, etc. Solvent – Substance in which solutes are dissolved “vat” in which substances are dissolved Typically water Concentration gradient – The difference in solute concentration inside and outside the cell
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Passive processes Passive processes – Does not require energy (ATP)
Move substances down (or with) a concentration gradient Substances move from areas of higher concentration to areas of lower concentration Types – Diffusion Simple diffusion Facilitated diffusion Osmosis Filtration
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Passive processes Diffusion –
The tendency of molecules/ions to scatter evenly throughout the environment Substances move directly through the plasma membrane if its… Lipid soluble Small enough to pass through membrane channels Assisted by carrier proteins Goal of diffusion – to reach equilibrium – where molecules are moving equally in all directions – there is no net movement – molecules are balanced on each side
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Passive processes cont.
Diffusion cont – Move from areas of higher concentration to areas of lower concentration – move down the concentration gradient Molecules move very quickly & erratically Bounce off each other They don’t like to be close they naturally move to areas where numbers are lower (move from high to low) The greater the concentration difference the faster the diffusion process Movement occurs due to the kinetic energy of the molecules The smaller the molecule the faster the diffusion Warmer the temp the faster the diffusion
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Diffusion
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Passive processes cont.
Diffusion cont. – Simple diffusion – Unassisted diffusion of lipid-soluble or very small particles Substances that are nonpolar Oxygen, carbon dioxide, alcohol, fat-soluble vit Down the concentration gradient Facilitated diffusion - Substances are moved through the plasma membrane by binding to protein carriers or by membrane channels Transport proteins change shape to allow substances (glucose & simple sugars) through Transported down the concentration gradient
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Passive processes
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Passive processes cont.
Osmosis – Diffusion of water Water is polar, but it is a small molecule that can slip through the plasma membrane as the membrane changes shape Occurs until solute concentrations are balanced Movement occurs due to solute concentrations Water moves when solute concentrations differ Requires less energy to move water than a solute Osmolarity – the total number of all solute particles w/in a solution Osmotic pressure – the cells ability to resist further (net) water movement – when solute concentrations are equal
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Osmosis
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Passive processes cont
Osmosis cont. – Tonicity – A solutions ability to change the tone or shape of cells by altering their internal water volume The number of nonpenetrating solutes Isotonic – Solutions with the same concentration of nonpenetrating solutes on either side of the cell or the total solute concentration Solutes are equal inside and outside the cell Cells keep their “normal” shape because there is no net movement of water Body fluids = isotonic
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Passive process cont. Osmosis cont. – Hypertonic – Hypotonic –
Solutions with high concentrations of solutes Cells loose water trying to equalize the solutes Loosing water causes them to shrink or crenate Hypotonic – Solutions that contain fewer solutes The solution bathing the cell is more dilute than the cell itself Cells take on water as it tries to equalize the lower number of solutes on the inside of the cell Cells take on so much water they eventually burst or lyse Rehydrating – sports drinks, cola, and apple juice are hypotonic increasing the amount of water cells absorb, causing rehydration
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Tonicities
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Passive processes cont.
Filtration – A pressure-driven process that forces water and solutes through a membrane or capillary wall by fluid or hydrostatic pressure Passive processes Involves a pressure gradient that pushes the solute fluid (filtrate) from higher-pressure areas to lower-pressure areas Not a selective process Anything that is small enough will be pushed, by pressure, through the plasma membrane
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Active processes Cells use energy, ATP, to move substances against their concentration gradient Active transport – Uses solute pumps to move substances against their concentration gradient Energy is needed either directly or indirectly Provide movement for substances who can’t pass by diffusion Ions such as Na+ and K+ need a protein transport (solute pump) to move across the membrane against their concentration (moving them uphill)
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Active processes cont. Active transport cont. –
Primary active transport – Energy provided directly by the hydrolysis of ATP Causes the transport protein to change shape which pumps the bound solute across the membrane Sodium potassium pump K+ higher inside the cell Na+ higher outside the cell They leak across the plasma membrane along their concentration gradient – the pump is needed to keep K+ higher inside and Na+ higher outside
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Active processes cont. Active transport cont. –
Secondary active transport – The driving forces of primary transport can indirectly drive the transport of other solutes As sodium is transported it drags other solutes with it – they are cotransported (sugars and amino acids) Even though solutes are cotransported which is passive – they would not be able to be transported w/o the energy required movement of sodium
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Active transport
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Active transport cont. Active transport cont – Vesicular transport –
Means by which large particles (macromolecules) & fluids are transport across the plasma membrane Energized by ATP Two types – Endocytosis Exocytosis
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Active transport cont. Vesicular transport – Exocytosis –
“out of the cell” Used to move substances from inside the cell to the extracellular environment Hormone secretion, neurotransmitting, ejection of waste, mucus secretion Substance to be secreted is enclosed in a membranous sac called a vesicle
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Exocytosis
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Active transport cont. Endocytosis – “into the cell”
Move substances into the cell using protein-coated vesicles Clathrin-coated Non-clathrin-coated (Caveolae or coatomer) Moved into the cell by extensions of the plasma membrane
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Active transport cont. Endocytosis cont –
3 Types of Clathrin-coated vesicles Phagocytosis Pinocytosis Receptor-mediated endocytosis Phagocytosis – “cell eating” Cytoplasmic extensions = pseudopods – protrude from cell and cover/contain large/solid material Formed vesicle = phagosome Fuses with a lysosome to digest the contents
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Active transport cont. Endocytosis cont –
Pinocytosis (fluid phase endocytosis) Infolding of the plasma membrane Contains extracellular fluid w/ dissolved molecules Allows the cell to “sample” the contents of the extracellular fluid Important for cells that absorb nutrients
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Active transport cont. Receptor-mediated endocytosis –
Most common method for specific uptake Enzymes, insulin, hormones, and iron Flu viruses utilize this method to attack our cells Receptors = membrane proteins that only bind with certain substances Create a vesicle = coated pit Contents dissolved/utilized within the cell
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Enodcytosis
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Active transport cont. Non-clathrin-coated vesicles
Caveolae – inpocketings of plasma membrane Caveolin proteins Capture specific molecules (folate, tetanus toxin) Close association with lipid rafts, important for cell signaling Coatomer (COP1 and COP2) proteins Vesicular trafficking
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Membrane potentials A membrane potential is a voltage across the cell membrane that occurs due to a separation of oppositely charged particles. In a resting stage a cell exhibits a resting membrane potential – the cell is polarized – the inside of the cell is more negative than the outside Charge only exists at the membrane Charges within in the cell are neutral Determined by… Concentration gradient of potassium (K+) and sodium (Na+) More K+ within cells More Na+ in the extracellular fluid K+ diffuses out of the cell – cells is impermeable to Na+ Now more positive charges are outside the cell giving it its negative charge
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Cellular environmental interactions
Membrane receptors – Diverse groups of integral proteins and glycoproteins that serve as binding sites Function in: Contact signaling – Touching of cells Method for recognizing other cells Bacteria and viruses utilize this method Electrical signaling – Responding to the changes in voltage Neural and muscle tissue Chemical signaling – Job of most membrane receptors Nervous & endocrine systems
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Developmental aspects of cells
Aging – Due to wear-and-tear Accumulation of free radicals May be a result of autoimmune responses & progressive weakening of the immune system Apoptosis – Programmed cell death Cell suicide Cancer = cells fail to go through apoptosis Strokes & heart attacks increase the rate of apoptosis
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The rest of the material is not necessary for the test.
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Components of the cell The cytoplasm is the cellular material between the cell membrane and the nucleus, and is the site of most cellular activity. Major elements of the cytoplasm – Cytosol – Fluid in which the other cytoplasmic elements are suspended Largely water w/ salts, proteins, sugars & other solutes Cytoplasmic organelles – Major components/workings of the cell Cytoplasmic inclusions – Not a functional unit Chemical substances Ex: lipid droplet in a fat cell
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Components of the cell Organelles – Mitochondria – Ribosome –
Sausage-shaped organelle Powerhouse of the cell Produce ATP The more mitochondria – the more energy a particular cell needs Large quantities in liver and muscle cells Ribosome – Consist of proteins & ribosomal RNA Site of protein synthesis
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Components of the cell cont.
Endoplasmic reticulum – Continuous with the nuclear membrane “network within the cell” Two types – Rough endoplasmic reticulum – Contains ribosomes making it appear rough Manufactures all proteins secreted from the cell Produces components of the membranes Liver & secretory cells Smooth endoplasmic reticulum – Continuation of the RER Lipid & cholesterol synthesis Synthesis of steroid-based hormones (sex hormones) Absorbtion, synthesis & transort of fats Detoxification of drugs Breakdown of glycogen to form free glucose
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Components cont. Golgi apparatus – Lysosomes –
Moves & directs cellular proteins Modifies, concentrates, & packages proteins Proteins bud off in vesicles from the ER & bind with the golgi in order to be modified Golgi vessicles are created allowing proteins to be transferred to the plasma membrane in order to be excreted into the extracellular space Lysosomes – Involved in digestion & phagocytosis (bacteria, viruses, & toxins) Degrading nonfunctional/worn-out organelles Break down nonuseful tissues
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Components cont. Peroxisomes – Cytoskeleton –
Digestion of alcohol Cytoskeleton – Cells skeleton Supports cell structure & generates cell movements Centrosomes & centrioles – Organizes mircrotubules Arranged at right angles to each other Organize mitotic spindles Form base of cilia and flagella Cellular extensions – Cilia – Occur in large numbers Move together in order to move substances Propels other substances Flagella – Single Whip like motion Sperm Propels itself
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Nucleus Control center of the cell Nuclear envelope – Nuclear pores –
Binds the nucleus Double layer membrane Continuous with rough ER Nuclear pores – Regulates entry and exit of large particles Nucleoli – Site of ribosome production Contain DNA Chromatin – DNA (genetic materials) & histone proteins Nucleosomes – Eight histone proteins & DNA molecule Chromosomes – Condensed chromatin Utilized when cells are going to divide
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