Chapter5 sections+1 4
-
Upload
bigdanny -
Category
Technology
-
view
834 -
download
0
Transcript of Chapter5 sections+1 4
Chapter 5 Gases
Chapter 5
Ground Rules of Metabolism
(Sections 5.1 - 5.4)
5.1 A Toast to
Alcohol Dehydrogenase
Metabolic processes build and break down organic molecules such as ethanol and other toxins
Alcohol breakdown directly damages liver cells, and interferes with normal processes of metabolism
Currently the most serious drug problem on college campuses is binge drinking
Alcohol Metabolism
The enzyme alcohol dehydrogenase helps the liver break down toxic alcohols (ethanol)
Figure 5.1 Alcohol metabolism. Alcohol dehydrogenase helps the body break down toxic alcohols such as ethanol. This enzyme makes it possible for humans to drink beer, wine, and other alcoholic beverages
5.2 Energy and the World of Life
There are many forms of energy:
Kinetic energy, potential energy
Light, heat, electricity, motion
Energy cannot be created or destroyed (first law of thermodynamics)
Energy can be converted from one form to another and thus transferred between objects or systems
Energy Disperses
Energy tends to disperse spontaneously (second law of thermodynamics)
A bit disperses at each energy transfer, usually as heat
Entropy is a measure of how dispersed the energy of a system has become
Key Terms
energy
The capacity to do work
kinetic energy
The energy of motion
entropy
Measure of how much the energy of a system is dispersed
Key Terms
first law of thermodynamics
Energy cannot be created or destroyed
second law of thermodynamics
Energy tends to disperse spontaneously
Kinetic Energy
Figure 5.2 Demonstration of a familiar type of energy: motion, or kinetic energy.
Entropy
Entropy tends to increase, but the total amount of energy in any system always stays the same
Figure 5.3 Entropy. Entropy tends to increase, but the total amount of energy in any system always stays the same
Fig. 5.3, p. 76
Entropy
Time
heat energy
Stepped Art
Entropy
Figure 5.3 Entropy. Entropy tends to increase, but the total amount of energy in any system always stays the same
Work
Work occurs as a result of an energy transfer
A plant converts light energy to chemical energy in photosynthesis
Most other cellular work occurs by transfer of chemical energy from one molecule to another (such as transferring chemical energy from ATP to other molecules)
Energys One-Way Flow
Living things maintain their organization only as long as they harvest energy from someplace else
Energy flows in one direction through the biosphere, starting mainly from the sun, then into and out of ecosystems
Producers and then consumers use energy to assemble, rearrange, and break down organic molecules that cycle among organisms throughout ecosystems
Energy Conversion
It takes 10,000 pounds of feed to raise a 1,000-pound steer
About 15% of energy in food builds body mass; the rest is lost as heat during energy conversions
Figure 5.4 It takes more than 10,000 pounds of soybeans and corn to raise a 1,000-pound steer. Where do the other 9,000 pounds go? About half of the steers food is indigestible. The animals body breaks down molecules in the remaining half to access energy stored in chemical bonds. Only about 15% of that energy goes toward building body mass. The rest is lost during energy conversions, as heat.
Energy Flow
Energy flows from the environment into living organisms, and back to the environment
Materials cycle among producers and consumers
Fig. 5.5, p. 77
Consumers animals, most fungi, many protists, bacteria
nutrient cycling
Producers plants and other self-feeding organisms
sunlight energy
Energy Flow
Figure 5.5 Energy flows from the environment into living organisms, and then back to the environment. The flow drives a cycling of materials among producers and consumers.
Animation: One-Way Energy Flow and Materials Cycling
Potential Energy
Energys spontaneous dispersal is resisted by chemical bonds
Energy in chemical bonds is a type of potential energy, because it can be stored
potential energy
Stored energy
Key Concepts
Energy Flow
Organisms maintain their organization only by continually harvesting energy from their environment
ATP couples reactions that release usable energy with reactions that require it
Animation: Energy Changes in Chemical Work
5.3 Energy in the Molecules of Life
Every chemical bond holds energy the amount of energy depends on which elements are taking part in the bond
Cells store and retrieve free energy by making and breaking chemical bonds in metabolic reactions, in which reactants are converted to products
Key Terms
reaction
Process of chemical change
reactant
Molecule that enters a reaction
product
A molecule that remains at the end of a reaction
Chemical Bookkeeping
In equations that represent chemical reactions, reactants are written to the left of an arrow that points to the products
A number before a formula indicates the number of molecules
The same number of atoms that enter a reaction remain at the reactions end
Chemical Bookkeeping
2H2O(water)
Fig. 5.6, p. 78
Stepped Art
Reactants
4 hydrogen atoms+ 2 oxygen atoms
Products
4 hydrogen atoms+ 2 oxygen atoms
2H2(hydrogen)
O2(oxygen)
Chemical Bookkeeping
Figure 5.6 Chemical bookkeeping. In equations that represent chemical reactions, reactants are written to the left of an arrow that points to the products. A number before a formula indicates the number of molecules. Atoms shuffle around in a reaction, but they never disappear: The same number of atoms that enter a reaction remain at the reactions end.
Animation: Chemical Bookkeeping
Energy In, Energy Out
In most reactions, free energy of reactants differs from free energy of products
Reactions in which reactants have less free energy than products are endergonic they will not proceed without a net energy input
Reactions in which reactants have greater free energy than products are exergonic they end with a net release of free energy
Key Terms
endergonic
Energy in
Reaction that converts molecules with lower energy to molecules with higher energy
Requires net input of free energy to proceed
exergonic
Energy out
Reaction that converts molecules with higher energy to molecules with lower energy
Ends with a net release of free energy
Energy In, Energy Out
Fig. 5.7, p. 78
Free energy
energy out
energy in
2H2O
O2
2H2
1
2
2H2O
Energy In, Energy Out
Figure 5.7 Energy inputs and outputs in chemical reactions. 1 Endergonic reactions convert molecules with lower energy to molecules with higher energy, so they require a net energy input in order to proceed. 2 Exergonic reactions convert molecules with higher energy to molecules with lower energy, so they end with a net energy output.
Why Earth Does Not Go Up in Flames
Earth is rich in oxygenand in potential exergonic reactions; why doesnt it burst into flames?
Luckily, energy is required to break chemical bonds of reactants, even in an exergonic reaction
activation energy
Minimum amount of energy required to start a reaction
Keeps exergonic reactions from starting spontaneously
Activation Energy
Fig. 5.8, p. 79
O2
Free energy
2H2
Activation energy
Products: 2H2O
Difference between free energy of reactants and products
Reactants:
Activation Energy
Figure 5.8 Activation energy. Most reactions will not begin without an input of activation energy, which is shown here as a bump in an energy hill. In this example, the reactants have more energy than the products. Activation energy keeps this and other exergonic reactions from starting spontaneously.
Animation: Activation Energy
ATPThe Cells Energy Currency
ATP is the main currency in a cells energy economy
ATP (Adenosine triphosphate)
Nucleotide with three phosphate groups linked by high-energy bonds
An energy carrier that couples endergonic with exergonic reactions in cells
ATP
Fig. 5.9a, p. 79
A Structure of ATP.
ribose
adenine
three phosphate groups
ATP
Figure 5.9 ATP, the energy currency of cells.
Phosphorylation
When a phosphate group is transferred from ATP to another molecule, energy is transferred along with the phosphate
Phosphate-group transfers (phosphorylations) to and from ATP couple exergonic reactions with endergonic ones
phosphorylation
Addition of a phosphate group to a molecule
Occurs by the transfer of a phosphate group from a donor molecule such as ATP
ATP and ADP
Fig. 5.9b, p. 79
B After ATP loses one phosphate group, the nucleotide is ADP (adenosine diphosphate); after losing two phosphate groups, it is AMP (adenosine monophosphate)
ribose
adenine
AMP
ATP
ADP
ATP and ADP
Figure 5.9 ATP, the energy currency of cells.
ATP/ADP Cycle
Cells constantly use up ATP to drive endergonic reactions, so they constantly replenish it by the ATP/ADP cycle
ATP/ADP cycle
Process by which cells regenerate ATP
ADP forms when ATP loses a phosphate group, then ATP forms again as ADP gains a phosphate group
ATP/ADP Cycle
Fig. 5.9c, p. 79
energy out
ADP + phosphate
energy in
C ATP forms by endergonic reactions. ADP forms again when ATP energy is transferred to another molecule along with a phosphate group. Energy from such transfers drives cellular work.
ATP/ADP Cycle
Figure 5.9 ATP, the energy currency of cells.
Animation: Mitochondrial Chemiosmosis
5.4 How Enzymes Work
Enzymes makes a reaction run much faster than it would on its own, without being changed by the reaction
catalysis
The acceleration of a reaction rate by a molecule that is unchanged by participating in the reaction
Most enzymes are proteins, but some are RNAs
Substrates
Each enzyme recognizes specific reactants, or substrates, and alters them in a specific way
substrate
A molecule that is specifically acted upon by an enzyme
Active Sites
Enzyme specificity occurs because an enzymes polypeptide chains fold up into one or more active sites
An active site is complementary in shape, size, polarity, and charge to the enzymes substrate
active site
Pocket in an enzyme where substrates bind and a reaction occurs
An Active Site
Fig. 5.10a, p. 80
An Active Site
Figure 5.10 An example of an active site. This one is in a hexokinase, an enzyme that phosphorylates glucose and other six-carbon sugars.
Fig. 5.10a, p. 80
active site
enzyme
A Like other enzymes, hexokinases active sites bind and alter specific substrates. A model of the whole enzyme is shown to the left.
An Active Site
Figure 5.10 An example of an active site. This one is in a hexokinase, an enzyme that phosphorylates glucose and other six-carbon sugars.
Fig. 5.10b, p. 80
An Active Site
Figure 5.10 An example of an active site. This one is in a hexokinase, an enzyme that phosphorylates glucose and other six-carbon sugars.
Fig. 5.10b, p. 80
reactant(s)
B A close-up shows glucose and phosphate meeting inside the enzymes active site. The microenvironment of the site favors a reaction between the two substrate molecules.
An Active Site
Figure 5.10 An example of an active site. This one is in a hexokinase, an enzyme that phosphorylates glucose and other six-carbon sugars.
Fig. 5.10c, p. 80
An Active Site
Figure 5.10 An example of an active site. This one is in a hexokinase, an enzyme that phosphorylates glucose and other six-carbon sugars.
Fig. 5.10c, p. 80
product(s)
C Here, the glucose has bonded with the phosphate. The product of this reaction, glucose-6-phosphate, is shown leaving the active site.
An Active Site
Figure 5.10 An example of an active site. This one is in a hexokinase, an enzyme that phosphorylates glucose and other six-carbon sugars.
Lowering Activation Energy
Enzymes lower activation energy in four ways:
Bringing substrates closer together
Orienting substrates in positions that favor reaction
Inducing the fit between a substrate and the enzymes active site (induced-fit model)
Shutting out water molecules
induced-fit model
Substrate binding to an active site improves the fit between the two
Lowering Activation Energy
Fig. 5.11, p. 80
Free energy
Reactants
Products
Transition state
Activation energy with enzyme
Activation energy without enzyme
Time
Lowering Activation Energy
Figure 5.11 An enzyme enhances the rate of a reaction by lowering its activation energy.
Animation: Enzymes and Activation Energy
Effects of Temperature, pH, and Salinity
Each type of enzyme works best within a characteristic range of temperature, pH, and salt concentration:
Adding heat energy boosts free energy, increasing reaction rate (within a given range)
Most human enzymes have an optimal pH between 6 and 8 (e.g. pepsin functions only in stomach fluid, pH 2)
Too much or too little salt disrupts hydrogen bonding that holds an enzyme in its three-dimensional shape
Enzymes and Temperature
Fig. 5.12, p. 81
Temperature
Enzyme activity
temperature- sensitivetyrosinase
normal tyrosinase
40C (104F)
30C (86F)
20C (68F)
Enzymes and Temperature
Figure 5.12 Enzymes and temperature. Tyrosinase is involved in the production of melanin, a black pigment in skin cells. The form of this enzyme in Siamese cats is inactive above about 30C (86F), so the warmer parts of the cats body end up with less melanin, and lighter fur.
Animation: Enzymes and Temperature
Enzymes and pH
Fig. 5.13, p. 81
pH
trypsin
glycogen phosphorylase
pepsin
Enzyme activity
1 2 3 4 5 6 7 8 9 10 11
Enzymes and pH
Figure 5.13 Enzymes and pH. Left, how pH affects three enzymes. Right, carnivorous plants of the genus Nepenthes grow in nitrogen-poor habitats. They secrete acids and protein-digesting enzymes into a fluidfilled cup that consists of a modified leaf. The enzymes release nitrogen from insects that are attracted to odors from the fluid and then drown in it. One of these enzymes functions best at pH 2.6.
Help From Cofactors
Most enzymes require cofactors, which are metal ions or organic coenzymes in order to function
cofactor
A metal ion or a coenzyme that associates with an enzyme and is necessary for its function
coenzyme
An organic molecule that is a cofactor
Coenzymes and Cofactors
Coenzymes may be modified by taking part in a reaction
Example: NAD+ becomes NADH by accepting electrons and a hydrogen atom in a reaction
Cofactors are metal ions
Example: The iron atom at the center of each heme
In the enzyme catalase, iron pulls on the substrates electrons, which brings on the transition state
Antioxidants
Cofactors in some antioxidants help them stop reactions with oxygen that produce free radicals (harmful atoms or molecules with unpaired electrons)
Example: Catalase is an antioxidant
antioxidant
Substance that prevents molecules from reacting with oxygen
Key Concepts
How Enzymes Work
Enzymes tremendously increase the rate of metabolic reactions
Cofactors assist enzymes, and environmental factors such as temperature, salt, and pH can influence enzyme function
Animation: How Catalase Works
Albia Dugger Miami Dade College
Cecie StarrChristine EversLisa Starr
www.cengage.com/biology/starr