ASSIGMENT DISCUSSION
chu98
Mader_Essentials_7e_LecturePPT_Ch05_ACCESS.pptxChapter 5
The Dynamic Cell
Essentials of Biology
SEVENTH EDITION
Sylvia S. Mader Michael Windelspecht
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5.1 What Is Energy?
Energy is the capacity to do work.
Our biosphere gets its energy from the sun.
Two basic forms of energy
Potential energy—stored energy
Kinetic energy—energy of motion
Two forms are converted back and forth.
During conversions, some lost as heat.
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Figure 5.1 Potential Energy Versus Kinetic Energy
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Calorie and Kilocalorie
Measuring energy
Food energy is measured in calories.
Calorie—amount of heat required to raise temperature of 1 g of water by 1°C
Kilocalorie or calorie = 1,000 calories
Value listed on food packages
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Energy Laws
Two energy laws
First law—conservation of energy
Energy cannot be created or destroyed, but it can be changed from one form to another.
Second law
Energy cannot be changed from one form to another without a loss of usable energy.
Heat is the least usable form of energy.
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Entropy 1
Entropy:
Every energy transformation leads to an increase in the amount of disorganization or disorder.
Entropy—relative amount of disorganization
Only way to maintain or bring about order is to add energy.
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Entropy 2
Entropy, continued
Our universe is a closed system.
All energy transformations increase the total entropy of the universe.
Energy provided by the sun allows plants to make glucose from the more disorganized water and carbon dioxide.
Some of sun’s energy is lost as heat.
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Figure 5.2a Cells and Entropy
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Figure 5.2b Cells and Entropy
Unequal distribution of hydrogen ions
Equal distribution of hydrogen ions
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5.2 ATP: Energy for Cells
Adenosine triphosphate (ATP)
Energy currency of cells
Cells use ATP to carry out nearly all activities.
One nucleotide along with three phosphate groups makes it unstable.
Easily loses a phosphate group to become adenosine diphosphate (ADP)
Continual cycle of breakdown and regeneration
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Figure 5.3 ATP
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Figure 5.4 The ATP Cycle
ATP releases energy quickly.
Amount of energy released is usually just enough for a biological purpose.
Breakdown can be easily coupled to an energy-requiring reaction.
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Coupled Reactions
Coupled reactions:
Energy-releasing reaction can drive an energy-requiring reaction.
Usually, energy-releasing reaction is ATP breakdown.
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Figure 5.5 Coupled Reaction
ATP breakdown provides the energy for muscle movement.
Myosin combines with ATP.
ATP breaks down.
Release of ADP + P causes myosin to change shape and pull on the actin filament.
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The Flow of Energy
The flow of energy:
Activities of chloroplasts and mitochondria enable energy to flow from the sun through all living things.
Photosynthesis—solar energy used to convert water and carbon dioxide into carbohydrates
Food for plants and other organisms
Cellular respiration—carbohydrates broken down and energy used to build ATP
Useful energy is lost with each transformation.
Living things dependent on constant in/out of solar energy
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Figure 5.6 Flow of Energy
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(leaves): ooyoo/Getty Images; (woman): Karl Weatherly/Photodisc/Getty Images
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Humans and Energy
Humans are also involved in the cycling of molecules between plants and animals and in the flow of energy from the sun.
Inhale oxygen, eat plants and animals
Energy rich foods allow us to produce the ATP required to maintain our bodies and carry on activities.
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5.3 Metabolic Pathways and Enzymes
a. Active enzyme and active pathway
b. Feedback inhibition
c. Inactive enzyme and inactive pathway
Metabolic pathway—series of linked reactions
The letters
represent enzymes.
Protein molecules that function as organic catalysts speed up reactions.
Can only speed up possible reactions
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Figure 5.7 Enzymatic Action
Enzymes
Act on substrates
May facilitate breakdown or synthesis reactions
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Enzyme’s Active Site
Enzyme’s active site
Accommodates substrate
Like a lock and key—specific to one substrate
Induced fit model—undergoes slight shape change to accommodate substrate
Change in shape facilitates reaction
Active site returns to original shape after releasing product(s)
Enzymes are not used up by the reaction.
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Enzyme Inhibition
Enzyme inhibition:
Occurs when an active enzyme is prevented from combining with its substrate.
Cyanide is a poison because it binds to and inhibits cytochrome c oxidase.
Penicillin interferes with a bacterial enzyme that kills the bacteria.
Feedback inhibition
When a product is in abundance, it competes with substrate for active site
An end product of a pathway can inhibit the first enzyme in the pathway—binds to a site other than active site to cause shape change—which shuts the entire pathway down
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Figure 5.8a Feedback Inhibition—Active Enzyme and Active Pathway
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Figure 5.8b Feedback Inhibition
b. Feedback inhibition
When a product builds up—the body doesn’t need more
Product binds to enzyme and changes its shape
Loss of shape = loss of function
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Figure 5.8c Feedback Inhibition, concluded
c. Inactive enzyme and inactive pathway
Now the substrate can’t bind to enzyme and the reaction stops
When the product gets low, enzyme will go back to original shape.
Enzyme starts working again.
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Energy of Activation
Energy of activation:
Molecules frequently do not react with each other unless activated.
Energy of activation (
)—energy needed to cause
molecules to react with one another
Enzymes lower the amount of energy required.
Enzymes bring substrates into contact and even sometimes participate in the reaction.
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Figure 5.9 Energy of Activation (E sub a)
A LOWER hurdle is easier/faster to get over
A LOWER energy of activation makes a reaction easier/faster
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5.4 Cell Transport
Plasma membrane regulates traffic in and out of the cell.
Selectively permeable—some substances pass freely, some transported, some prohibited
Three ways to enter
Passive transport—substances move from higher to lower concentration, no additional energy is required.
Active transport—substances move from lower to higher concentration, additional energy is required.
Bulk transport—movement independent of gradients, additional energy is required.
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Passive Transport
Passive transport:
No energy required for simple diffusion
Molecules move down their concentration gradient until equilibrium is reached.
Cell does not expend additional energy—molecules already in motion.
Some molecules slip between phospholipids.
Facilitated diffusion—others use transport protein specific to molecule
Water uses aquaporins—this explains faster than expected transport rate.
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Figure 5.10 Simple Diffusion Demonstration
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Figure 5.11 Facilitated Diffusion
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Figure 5.12 Osmosis Demonstration
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Figure 5.13 Osmosis in Animal and Plant Cells—Isotonic Environment
Effect of osmosis on cells
Isotonic solution
No net gain or loss of water
Concentration of water same on both sides of the membrane
0.9% saline isotonic to red blood cells
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Figure 5.13 Osmosis in Animal and Plant Cells—Hypotonic Environment
Hypotonic solution
Concentration of water outside cell greater than inside cell
Cell gains water.
Animal cells may lyse or burst
Plant cells use this to remain turgid.
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Figure 5.13 Osmosis in Animal and Plant Cells—Hypertonic Environment
Hypertonic solution
Concentration of water outside cell less than inside cell
Cell loses water.
Animal cells shrink.
Plant cells undergo plasmolysis and may wilt.
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Figure 5.14 Active Transport
Active transport:
Cells expend energy to move molecules against a concentration gradient.
Requires transport protein
Sodium–potassium pump is important in maintaining gradient of ions used in the nerve impulse conduction.
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Figure 5.15 Sodium–Potassium Pump
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Bulk Transport
Bulk transport:
Macromolecules are often too large to be moved by transport proteins.
Vesicle formation takes them in or out of cell.
Exocytosis—movement out of cell
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Figure 5.16a Bulk Transport—Exocytosis
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Figure 5.15b Bulk transport—Endocytosis
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Endocytosis
Endocytosis—movement into cell
Phagocytosis—cell surrounds, engulfs, and digests particle
Pinocytosis—vesicle forms around liquid or small particles
Receptor-mediated endocytosis—receptors for particular substances found in coated pit—selective and more efficient.
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Figure 5.17 Receptor-Mediated Endocytosis
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Figure 5.1 Potential Energy Versus Kinetic Energy - Text Alternative
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Plants capture solar energy and store it as potential energy in different parts of the plant like fruits, stems, and leaves. When a man eats a fruit, the potential energy enters his body where it is transformed into kinetic energy when he moves from one location to another. At every stage of the energy flow, some energy is also lost as heat.
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Figure 5.2a Cells and Entropy - Text Alternative
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The photo on the left depicts a clean, organized room with everything in its right place. The right photo shows a dirty, disorganized room with items strew on the bed and the floor.
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Figure 5.3 ATP - Text Alternative
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The structure of ATP consists of adenine, ribose, and triphosphate bonded together.
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Figure 5.4 The ATP Cycle - Text Alternative
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The ADP combines with a P utilizing the energy from cellular respiration to give ATP. ATP releases energy for cellular activity (for example, protein synthesis, nerve conduction, muscle contraction) and breaks down into ADP and P. The structure of ADP consists of adenine, ribose, and diphosphate bonded together.
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Figure 5.5 Coupled Reaction - Text Alternative
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The reaction takes place as follows: Myosin assumes its resting shape when it combines with ATP. ATP splits into ADP and P, causing myosin to change its shape and allowing it to attach to actin. Release of ADP and causes myosin to again change shape and pull against actin, generating force and motion.
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Figure 5.6 Flow of Energy - Text Alternative
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Chloroplasts present in green plants trap solar energy and convert it into chemical energy (carbohydrate) through photosynthesis. Oxygen and heat are released during the process. Mitochondria convert chemical energy to ATP molecules, which are stored in cells. Cells use this stored energy in chemical work, transport work, and mechanical work. During cellular respiration in mitochondria, carbon dioxide and water are produced, which are utilized by chloroplast during photosynthesis.
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5.3 Metabolic Pathways and Enzymes - Text Alternative
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a. The first substrate S binds with the active site of enzyme E1 with another binding site also. Further, multiple enzymes E2, E3, and E4 also react in the metabolic pathway, and finally, end product P is formed.
b. The binding forms a product enzyme complex in which the shape of the active site is changed.
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Figure 5.8a Feedback Inhibition—Active Enzyme and Active Pathway - Text Alternative
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The first substrate S binds with the active site of enzyme E1 with another binding site also. Further, multiple enzymes E2, E3, and E4 also react in the metabolic pathway, and finally, end product P is formed.
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Figure 5.8b Feedback Inhibition - Text Alternative
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The binding forms a product enzyme complex in which the shape of the active site is changed.
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Figure 5.9 Energy of Activation (E sub a) - Text Alternative
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A curve labeled with enzyme starts from the reactants, reaches a small peak, and slopes down to the product. The energy of activation needed is less. A curve labeled without enzyme starts from the reactants, reaches a bigger peak, and slopes down to the product. The energy of activation needed is high.
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Figure 5.10 Simple Diffusion Demonstration - Text Alternative
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The diagram is discussed as follows:
a. A purple crystal of dye is placed in water at the bottom of the aquarium. Its molecular view shows separate groups of water and dye molecules.
b. After some time, the water of the aquarium starts turning purple. Due to the beginning of diffusion, the water and dye molecules are somewhat mixed in its molecular view.
c. After the passage of some more time, the water of the aquarium turns completely purple. The molecular view of the dye shows the equal distribution of water and dye molecules as a result of complete diffusion.
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Figure 5.11 Facilitated Diffusion - Text Alternative
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It shows a carrier protein embedded in the plasma membrane of a cell. The solute particles outside the cell enter the cell through the carrier protein.
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Figure 5.12 Osmosis Demonstration - Text Alternative
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The setup consists of a thistle tube with the broad end covered by a semipermeable membrane filled with 10% salt solution. It is immersed in a beaker containing 5% salt solution. After sometime, the concentration of the beaker solution becomes more than 5% and the solution in the thistle tube becomes less concentrated (less than 10%).
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Figure 5.14 Active Transport - Text Alternative
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From the left, the first diagram shows solute molecules outside of a cell moving toward the transport protein embedded in the bilayer of the plasma membrane. The adenosine triphosphate present inside the cell provides energy for the movement of the solutes. In the second diagram, the transport protein holds a solute by changing its shape accordingly. The breakdown of adenosine triphosphate molecules releases adenosine diphosphate and one phosphate group. The released phosphate group attaches to the transport protein towards the interior of the cell. The third diagram shows the release of the solute to the inside of the cell. The arrowheads show the direction of the movement of the solute. The phosphate group now dissociates from the transport protein, which again causes its shape to change.
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Figure 5.15 Sodium–Potassium Pump - Text Alternative
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The enlarged diagrams show a carrier protein with the phospholipid bilayer at the sides, along with the sodium and potassium cations. The six steps are as follows:
1. Carrier protein has a shape that allows it to take up three sodium cations.
2. Adenosine triphosphate (ATP) is split, and phosphate group attaches to carrier.
3. Change in shape results and causes carrier to release three sodium cations outside the cell.
4. Carrier has a shape that allows it to take up two Potassium cations.
5. Phosphate group is released from carrier.
6. Change in shape results and causes carrier to release two Potassium cations inside the cell.
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Figure 5.16a Bulk Transport—Exocytosis - Text Alternative
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A vesicle is formed inside the cell which fuses with the plasma membrane and ultimately discharges the vesicle content to the outside of the cell.
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Figure 5.15b Bulk transport—Endocytosis - Text Alternative
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It shows a vesicle-like pit formed inside the plasma membrane which ultimately forms a vesicle and moves inside the cell.
