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Transcript of 05 Lecture Ppt
5-1
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Chapter 5Dynamic Activities
of Cells
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Living Things Transform Energy
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5.1 Energy makes things happen
Energy - the capacity to do work Chemical energy present in organic molecules
and is the direct source of energy for living things
Potential energy is stored energy Kinetic energy is energy in action
Calorie - the amount of energy to raise the temperature of 1 g of water by 1° Celsius
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Figure 5.1 Potential energy versus kinetic energy
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5.2 Two laws apply to energy and its use
1st law of thermodynamics—the law of conservation of energy Energy cannot be created or destroyed, but it
can be changed from one form to another
2nd law of thermodynamics Energy cannot be changed from one form to
another without a loss of usable energy Entropy - disorder increases because it is difficult
to use heat to perform more work
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Figure 5.2 Flow of energy from the sun to an animal that eats a plant
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5.3 Cellular work is powered by ATP
ATP (Adenosine TriPhosphate) - the energy currency of cells Cells use ATP to perform nearly all activities
Exergonic reactions Energy exits the reaction
Endergonic reactions Energy enters the reaction
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Figure 5.3A The ATP cycle
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5.4 ATP breakdown is coupled to energy-requiring reactions
Coupled reactions occur in the same place, at the same time energy-releasing (exergonic) reaction drives an
energy-requiring (endergonic) reaction
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Figure 5.4 Muscle contraction occurs when it is coupled to ATP breakdown
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Enzymes Speed Chemical Reactions
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5.5 Enzymes speed reactions by lowering activation barriers
Enzyme - usually a protein molecule that functions as an organic catalyst to speed a chemical reaction without itself being affected by the reaction Enzymes lower energy of activation
(Ea)
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Figure 5.5 The energy of activation (Ea) is lower when an enzyme is involved
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5.6 An enzyme’s active site is where the reaction takes place
Each enzyme is specific to its reaction Substrate(s) – reactants in an enzymatic
reaction Substrates combine with an enzyme, forming an
enzyme-substrate complex
The enzyme’s active site, binds with the substrate(s) Induced fit model the enzyme is induced to
undergo a slight alteration to achieve optimum fit with the substrate
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Figure 5.6 Enzymatic action
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5.7 Enzyme speed is affected by local conditions
Substrate Concentration More substrate means more chance encounters
between substrate molecules and the enzyme Temperature
warmer temperatures cause more effective encounters between enzyme and substrate
pH A change in pH can change the enzyme’s shape and
disrupt normal interactions Cofactors
The presence of molecules like coenzymes or vitamins allow enzymes to be active
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Figure 5.7A The effect of temperature on the rate of an enzymatic reaction
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5.8 Enzymes can be inhibited noncompetitively and competitively
Metabolic pathway - series of linked reactions Enzyme inhibition occurs when a molecule (the
inhibitor) binds to an enzyme and decreases its activity
Noncompetitive inhibition – inhibitor binds to the enzyme at a location other than the active site
Competitive inhibition – inhibitor and the substrate compete for the same active site
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Figure 5.8 Metabolic pathways and noncompetitive inhibition. In the pathway, A–E are substrates, E1–E5 are enzymes, and F is the end product of the pathway.
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APPLYING THE CONCEPTS—HOW BIOLOGY IMPACTS OUR LIVES
5.9 Enzyme inhibitors can spell death
Cyanide can be fatal because it binds to a mitochondrial enzyme necessary for the production of ATP
Sarin is a chemical that inhibits an enzyme at neuromuscular junctions, where nerves stimulate muscles
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The Plasma Membrane Has Many and Various Functions
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5.10 The plasma membrane is a phospholipid bilayer with embedded proteins
Plasma membrane is a fluid phospholipid bilayer Polar head of a phospholipid is hydrophilic, while the
nonpolar tails are hydrophobic Fluid-mosaic model – proteins embedded in
the membrane form a mosaic within the phospholipid bilayer Cholesterol molecules are steroids that lend support
to the membrane Glycolipids and glycoproteins – lipids and proteins
carrying carbohydrate chains
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Figure 5.10 Fluid-mosaic model of plasma membrane structure
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5.11 Proteins in the plasma membrane have numerous functions
Channel proteins have channels that let molecules to move across the membrane
Carrier proteins combine with a molecule to help it move across the membrane Differentially permeable - only certain substances
can pass through Receptor proteins have a binding site for a
specific molecule Enzymatic proteins carry out metabolic
reactions Junction proteins form various types of
junctions between cells
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Figure 5.11 Functions of plasma membrane proteins
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APPLYING THE CONCEPTS—HOW BIOLOGY IMPACTS OUR LIVES
5.12 Malfunctioning plasma membrane proteins can cause
human diseases Diabetes Type 2 - insulin binds to receptor protein, but
the number of carriers sent to the plasma is not enough Too much glucose in the blood, which spills over into the urine
Color Blindness – Usually three types of photopigment proteins in plasma membrane within photoreceptor cells Some people lack of functional red or green photopigment
Cystic Fibrosis (CF) - Usually, chloride ions pass easily through a plasma membrane channel protein When not regulated, a thick mucus appears in the lungs and
pancreas damaging the lungs and contributing to an early death
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Figure 5.12 Cystic fibrosis is due to a defective CF gene and defective CF channel proteins
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The Plasma Membrane Regulates the Passage of Molecules
Into and Out of Cells
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5.13 Simple diffusion across a membrane requires no energy
Simple diffusion – molecules move down concentration gradient until equilibrium is achieved and they are distributed equally
Dissolved gases can diffuse readily through the phospholipid bilayer How oxygen enters and carbon dioxide exits
cells How oxygen enters blood, and carbon dioxide
leaves the blood from air sacs in the lungs
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Figure 5.13 Some molecules can simply diffuse across a membrane
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5.14 Facilitated diffusion requires a carrier protein but no energy
Facilitated diffusion – certain molecules cross membranes by combining with a carrier protein The carrier proteins are thought to be specific.
Figure 5.14 During facilitated diffusion, a carrier protein assists solute movement across the membrane
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5.15 Osmosis can affect the size and shape of cells
Osmosis - diffusion of water across a differentially permeable membrane due to concentration differences Solution contains both a solute and a
solvent Solvents dissolve solutes
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Figure 5.15A During osmosis, net movement of water is toward greater solute concentration
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How Osmosis Affects the Size and Shape of Cells
Isotonic solutions (iso, same as) - concentration of water is the same on both sides of the membrane
Hypotonic solution (hypo, less than) - Outside the cell, the concentration of solute is
less, and the concentration of water is greater, than inside the cell
hypertonic solution (hyper, more than) - Outside the cell, the concentration of solute is more, and the concentration of water is less, than inside the cell
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Figure 5.15B Osmosis in animal and plant cells
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5.16 Active transport requires a carrier protein and energy
Active transport, molecules or ions move through the plasma membrane, accumulating on one side of the cell Movement of molecules against their
concentration gradients requires both a carrier protein and ATP
Sodium-potassium pump undergoes a change in shape when it combines with ATP allowing it to combine alternately with sodium ions and potassium ions
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Figure 5.16 During active transport, a substance moves contrary to its concentration gradient
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5.17 Bulk transport involves the use of vesicles
Bulk transport occurs when fluid or particles are brought into or out of a cell by vacuole formation, called endocytosis or by evagination, called exocytosis Phagocytosis occurs when the material taken in is
large Pinocytosis occurs when vesicles form around a
liquid or around very small particles Receptor-mediated endocytosis - receptors for
particular substances are found at one location in the plasma membrane
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Figure 5.17 Bulk transport into the cell is by endocytosis
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Connecting the Concepts: Chapter 5
Energy is the ability to do work, to bring about change, and to make things happen
A cell is dynamic because it carries out enzymatic reactions
Exchanges across the plasma membrane allow the cell to continue to perform its usual reactions Few reactions occur without enzymes, which are proteins,
because they lower the energy of activation with their substrate ATP, the universal energy “currency” of life, get energy-
requiring (endergonic) reactions going The plasma membrane is called the gatekeeper of the
cell because its numerous proteins allow only certain substances to enter or exit