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organize the chemical activities of cells. |
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provide structural order for metabolism by compartmentalizing the inside of the cell into organelles. |
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are composed of a bilayer of phospholipids with embedded and attached proteins. Biologists call this structure a fluid mosaic |
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is a “mosaic” in having diverse protein molecules embedded in its “fluid” framework – the phospholipid bilayer.
Most components of the cell membranes move around – they are not stuck in one place!
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are found only in animal cell membranes – keeps membrane fluid and stable. |
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Membrane Proteins Perform Many Functions |
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Some proteins help maintain cell shape and coordinate changes inside and outside the cell through their attachment to the cytoskeleton & ECM.
Some proteins function as receptors for chemical messengers (signaling molecules) from other cells in a process called signal transduction.
Some membrane proteins function as enzymes.
Membrane proteins may participate in the intercellular junctions that attach adjacent cells to each other.
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Membrane Proteins Perform Many Functions |
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Some membrane glycoproteins are involved in cell-cell recognition.
Example: Attached sugar molecules act as ID tags that enable cells of your immune system to know if a cell is you or foreign!
Membranes may exhibit selective permeability, which means some substances can cross more easily than others.
Certain ions and glucose require help in the form of transport proteins to get in and out of the cell.
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the key ingredient of biological membranes, spontaneously self-assemble into simple membranes. This was a critical step in the origin of the first cells.
Below a test tube with phospholipids and water is shaken – the phospholipids naturally organize into bilayers.
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When molecules diffuse across a membrane without any work by the cell (no output of energy required).
2) When molecules diffuse down their concentration gradient. In other words molecules move from an area of higher concentration to an area of lower concentration.
Eventually, the molecules reach equilibrium where the concentration of molecules is the same throughout.
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is the tendency of particles to spread out evenly in an available space. |
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Most of the traffic across cell membranes occurs by |
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phospholipid bilayer of a membrane by diffusion |
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Small, non-polar or hydrophobic molecules such as O2 and CO2 easily cross the |
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Many kinds of substances cannot diffuse freely across membranes because they’re too big, are polar, or have a charge. So they need the help of a transport protein in a process called |
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is a type of passive transport so it doesn’t require energy and relies on a concentration gradient (substance moves from high to low concentration). |
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Sugars e.g. glucose, amino acids, ions, and water (its polar) use ? to cross cell membranes. |
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in some cells (kidney cells, plant cells, red blood cells) rapid transport of water is critical and is made possible by a protein channel called an |
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The diffusion of water across a selectively permeable membrane is called |
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is a type of passive transport so it doesn’t require energy and relies on a concentration gradient (water moves from high to low concentration) |
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water (a solvent) travels from a solution of high solvent concentration (lower solute concentration) to one of lower solvent concentration (higher solute concentration). |
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is a term that describes the ability of a solution to cause a cell to gain or lose water |
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Isotonic (iso = same) solution |
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: A solution having the same solute concentration as inside the cell. The cell volume will not change. |
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Hypotonic (hypo = below) solution |
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The solute concentration is lower outside the cell (and the solvent concentration is higher). Water molecules move into the cell, and the cell will expand and may burst |
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Hypertonic (hyper = above) solution |
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The solute concentration is higher outside the cell (and the solvent concentration is lower). Water molecules move out of the cell and the cell will shrink. |
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1) Expend energy (Use the energy molecule, ATP).
2) Move a substance against its concentration gradient (go from low to high concentration).
Active transport is critical in nerve cells (neurons) for them to generate a nerve impulse. |
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In active transport, a cell must |
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is used to export bulky molecules, such as proteins or polysaccharides |
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(endo = inside) is used to import substances useful to the cell. |
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“Cell-eating”. The consumption of solid particles e.g. food, cell debris, bacteria, by the plasma membrane wrapping around the object forming a vacuole. |
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“Cell-drinking”. The bulk transport of fluids containing dilute solutes into the cell with a vesicle. |
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Receptor-Mediated Endocytosis |
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: The plasma membrane forms a pit with receptor proteins in it. Receptors bind with specific substances and the pit pinches into the cell’s cytoplasm. Cells use this method to bring cholesterol into the cell. |
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is simply the capacity to perform work. |
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is the energy of motion. Moving objects perform work by transferring motion to other matter.
Example: Pumping your legs to move bicycle pedals to get you and your bike to move forward |
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is the random movement of atoms or molecules. |
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is used to power photosynthesis. |
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is stored energy that matter possesses as a result of its location or structure. It can be converted to kinetic energy |
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is a form of potential energy available for release in a chemical reaction |
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is a branch of physics which deals with the energy and work of a system. |
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is the study of energy transformations that occur in a collection of matter. |
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first law of thermodynamics (law of energy conservation) |
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Energy is constant – it cannot be created or destroyed.
Energy can be changed or transformed from one form to another |
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second law of thermodynamics |
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Energy transformations or conversions increase the disorder (entropy) of the universe!
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Second Law of Thermodynamics |
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Every time energy is put to work or is converted from one form to another, some energy is lost as heat.
Heat is also a form of energy, but it is so chaotic, so unorganized, and so spread out that it cannot be put to work.
Any energy converted to heat radiates out of the system and so can no longer be put to use by the system.
All of the energy is conserved, but the energy that is converted to heat escapes the system and is no longer useful.
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Energy is transferred from organism to organism in the form of |
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about 34% the chemical energy stored in glucose is converted to energy for cell work; the rest is lost as heat energy. |
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(“energy inward”) require energy and yield products rich in potential energy. An example is photosynthesis |
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starts with energy-poor reactants (CO2 and H2O) and, using sunlight as energy, produces energy-rich sugar molecules. |
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(“energy outward”) release energy and yield products that contain less potential energy than their reactants. These reactions release the stored energy in covalent bonds of the reactants. |
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The total sum of an organism’s chemical reactions is called |
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uses energy released from exergonic reactions to fuel endergonic reactions in the cell. |
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adenosine triphosphate, powers nearly all forms of cellular work |
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ATP acts like a battery for storing and transporting energy.
ATP is the molecule of energy transfer in living systems.
Every reaction in the body that requires energy uses ATP. |
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is composed of a nitrogenous base (adenine) and a five-carbon sugar (ribose) – together they are called adenosine. The triphosphate group is composed of three negatively charged phosphate groups. |
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The energy in an ATP molecule is stored in the bonds between its |
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exergonic and endergonic reactions |
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ATP drives cellular work by coupling |
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Hydrolysis of ATP releases energy (exergonic reaction) by transferring its third phosphate to some other molecule in a process called |
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chemical, mechanical, and transport.
ATP drives all three of these types of work |
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There are three main types of cellular work |
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is a biological molecule, usually a protein, that acts as a catalyst. |
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increase the rate of chemical reactions without being consumed by the reaction |
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speed up the cell’s chemical reactions by lowering the activation energy needed for the reaction to begin. |
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The 1989 Nobel Prize in Chemistry was awarded jointly to Professors Altman and Cech for their discovery that RNA can act as an enzymes called |
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typically perform reactions on other RNA molecules, cleaving themselves or other strands, but they also perform other important reactions, such as the reaction that connects amino acids in the ribosome |
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Before any chemical reaction can begin there is an energy barrier that must be overcome |
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Energy must be absorbed to weaken bonds in the reactant molecules so they can break and form new bonds. This energy is called |
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An enzyme’s shape determines its |
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: A specific substance (reactant) on which an enzyme acts. Each enzyme recognizes only the specific substrate or substrates of the reaction it catalyzes. |
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A pocket or groove on the surface of the enzyme where the substrate(s) attaches |
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When the substrate is attached to the active site, an |
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enzyme-substrate complex is formed. |
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The interaction between a substrate molecule and the active site of an enzyme, which changes shape slightly to embrace the substrate more snugly like a handshake.
The substrate bonds are contorted or strained during the induced fit catalyzing the reaction |
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Most human enzymes work best at body temperature |
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Most enzymes work best near neutrality in the range 6-8 |
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cofactors such as metal ions (zinc, iron, and copper) in order to function. |
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Some enzymes require non-protein |
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coenzymes such as vitamins in order to function |
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Other enzymes require organic molecules called |
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are chemicals that interfere with an enzyme’s activity. |
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is a substance that reduces the activity of an enzyme by directly binding to the enzyme’s active site in place of the substrate |
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is a substance that blocks the activity of an enzyme without entering its active site; it binds elsewhere and changes the shape of the enzyme so that the active site no longer functions. |
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takes the place of a substrate in the active site.
Can be overcome by adding more substrate
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alters an enzyme’s function by changing its shape. |
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are important in regulating cell metabolism. |
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In some reactions, the product may act as an inhibitor of one of the enzymes in the pathway that produced it. This is called |
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it prevents cells from wasting valuable resources by making more of a particular product than is needed. |
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