1. Chapter 4 Energy and Metabolism

2. 4.1 A Toast to Alcohol Dehydrogenase
Binge drinking is currently the most serious drug problem on college campuses
Alcohol dehydrogenase (ADH), helps break down ethanol and other toxic compounds
Ethanol and its breakdown products damage liver cells, leading to alcoholic hepatitis or cirrhosis of the liver

3. Alcohol Dehydrogenase
Figure 4.1 Alcohol dehydrogenase.
This enzyme helps the body break down
toxic alcohols such as ethanol, thus making
it possible for humans to drink beer,
wine, and other alcoholic beverages.

4. 4.2 Life Runs on Energy Energy The capacity to do work
Work occurs as a result of energy transfers
Example: A plant cell powers glucose synthesis by absorbing light energy from the sun
Some energy is lost during every transfer or conversion

5. Laws of Thermodynamics
First law of thermodynamics
Energy cannot be created or destroyed
Energy can be converted from one form to another and transferred between objects or systems
Second law of thermodynamics
Energy tends to disperse spontaneously
Some energy disperses at each energy transfer, usually in the form of heat

6. One-Way Flow of Energy
Living things maintain their organization by harvesting energy from someplace else
Energy flows in one direction through the biosphere (starting mainly from the sun) then into and out of ecosystems
Energy in chemical bonds is a type of potential energy

7. Potential Energy Figure 4.3 Illustration of potential
energy. By opposing
the downward pull
of gravity, the rope
attached to the rock
prevents the man from
falling. Similarly, a
chemical bond keeps
two atoms from moving
apart.

8. Material Recycle
Energy inputs drive a cycling of materials among producers and consumers
Producers and then consumers use energy to assemble, rearrange, and break down organic molecules that cycle among organisms throughout ecosystems

9. One-Way Flow of Energy
A) Energy In. Sunlight energy reaches environments on Earth. Producers in those environments capture some of the energy and convert it to other forms that can drive cellular work.
sunlight energy
Producers
B) Some of the energy captured by producers ends up in the tissues of consumers.
Nutrient Cycling
Consumers
Figure 4.2 Animated! A one-way flow of
energy into living organisms compensates for a
one-way flow of energy out of them. Energy inputs
drive a cycling of materials among producers and
consumers.
C) Energy Out. With each energy transfer, some energy escapes into the environment, mainly as heat. Living things do not use heat to drive cellular work, so energy flows through the world of life in one direction overall.

10. 4.3 Energy in the Molecules of Life
Cells store and retrieve energy by making and breaking chemical bonds in metabolic reactions
Some reactions require a net input of energy – others end with a net release of energy

11. Chemical Reactions Reaction Process of chemical change Reactant
Molecule that enters a reaction
Product
A molecule remaining at the end of a reaction

12. Energy Inputs and Outputs in Chemical Reactions
Chemical bonds hold energy – the amount depends on which elements take part in the bond
Cells store energy in chemical bonds by running energy-requiring reactions, and access energy by running energy-releasing reactions

13. Energy Inputs and Outputs in Chemical Reactions6
glucose
C6H12O2
oxygen O2
Energy
A) energy in
B) energy out
Figure 4.4 Energy inputs and outputs in
chemical reactions.
A Some reactions convert molecules with lower
energy to molecules with higher energy, so they
require a net energy input to proceed.
B Other reactions convert molecules with higher
energy to molecules with lower energy, so they end
with a net energy output. 6 6
carbon dioxide CO2
water H2O

14. Why the Earth Doesn’t Go Up in Flames
Molecules of life release energy when combined with oxygen, but not spontaneously – energy is required to start even energy-releasing reactions
Activation energy
Minimum amount of energy required to start a reaction

15. Difference between energy of reactants and products
Activation Energy
Reactants:
2 H O2
Activation energy
Difference between energy of
reactants and products
Products: 2H2O
Energy
Figure 4.5 Animated! Activation energy. Most reactions, including
energy-releasing ones such as burning wood cellulose, will not begin
without at least a small input of energy. This activation energy is shown
in the graph above as a bump in an energy hill. Reactants in this example
have more energy than the products. Activation energy keeps this and
other energy-releasing reactions from starting spontaneously.
Time

16. Energy In, Energy Out
Cells store energy by running energy-requiring reactions that build organic compounds
Cells harvest energy by running energy-releasing reactions that break the bonds of organic compounds

17. energy-requiring reactions energy-releasing reactions
Energy In, Energy Out
small molecules
(e.g., carbon dioxide, water)
organic compounds (carbohydrates, fats, proteins)
energy-requiring reactions
A) Cells store energy in the chemical bonds of organic compounds.
small molecules (e.g., carbon dioxide, water)
organic compounds (carbohydrates, fats, proteins)
energy-releasing reactions
Figure 4.6 Cells store and retrieve energy in
the chemical bonds of organic molecules.
B) Cells retrieve energy stored in the chemical bonds of organic compounds.
Figure 4-6 p67

18. 4.4 How Enzymes Work
Enzymes make chemical reactions proceed much faster than they would on their own
Enzyme
Protein or RNA that speeds a reaction without being changed by it
Substrate
Reactant molecule specifically acted upon by an enzyme
An enzyme’s particular substrates bind at its active site

19. How an active site works
enzyme
substrates
A) An active site is complementary in shape, size, polarity, and charge with the enzyme’s substrates.
active site
B) The active site squeezes substrates together, influences their charge, or causes some other change that lowers activation energy.
How an active site works
C) The reaction proceeds and the product leaves the active site. The enzyme is unchanged, so it can work again and again.
Figure 4.7 How an active site works.

20. How an active site works
Figure 4.7 How an active site works.
D) For simplicity, enzymes and active sites are often depicted as blobs or geometric shapes. This model shows the actual contours of an active site in an enzyme (hexokinase) that adds a phosphate group to six-carbon sugars. A phosphate group is meeting up with a glucose molecule in the active site. 20

21. Factors That Influence Enzyme Activity
Regulatory molecules affect an enzyme by binding directly to its active site; or elsewhere on the enzyme
Each enzyme works best within a characteristic range of temperature, pH, and salt concentration
When conditions break hydrogen bonds, an enzyme changes its characteristic shape (denatures), and stops working

22. Regulatory molecule binding to enzymes
substrates
enzyme
regulatory molecules
Figure 4.8 Regulatory molecule binding to enzymes. Some types of regulatory
molecules (red) bind to an enzyme in a place other than the active site. This binding
changes the shape of the enzyme in a way that enhances or inhibits its function.

23. Enzymes and pH
Figure 4.9 Enzymes, temperature, and pH.

24. Enzymes and Temperature
Figure 4.9 Enzymes, temperature, and pH.

25. Cofactors
Cofactor
A metal ion or a coenzyme that associates with an enzyme and is necessary for its function
Coenzyme
An organic cofactor
Unlike enzymes, it may be modified by a reaction
Example: coenzyme NAD+ + electrons + H → NADH

26. ATP and Phosphorylation
ATP functions as a coenzyme in many reactions
When a phosphate group is transferred to or from a nucleotide, energy is transferred along with it
Phosphate-group transfers (phosphorylation) to and from ATP couple energy-releasing reactions with energy-requiring ones

27. Phosphorylation

28. Metabolic Pathways
Cells concentrate, convert, and dispose of most substances in enzyme-mediated reaction sequences
Metabolic pathway
Series of enzyme-mediated reactions by which cells build, remodel, or break down an organic molecule

29. Linear and Cyclic Metabolic Pathways

30. Controlling Metabolism
Various controls over enzymes allow cells to conserve energy and resources by producing only what they require
Concentrations of reactants and products
Feedback inhibition
Mechanism by which a change that results from some activity decreases or stops the activity

31. X Feedback Inhibition reactant enzyme 1 intermediate enzyme 2
Figure 4.10 Animated!
Feedback inhibition. In this example,
three kinds of enzymes act in
sequence to convert a substrate to a
product, which inhibits the activity
of the first enzyme.
enzyme 3
product

32. X reactant enzyme 1 intermediate enzyme 2 intermediate enzyme 3
Figure 4.10 Animated!
Feedback inhibition. In this example,
three kinds of enzymes act in
sequence to convert a substrate to a
product, which inhibits the activity
of the first enzyme.
enzyme 3
product
Stepped Art
Figure 4-10 p70

33. Electron Transfers
Electron transfer chains allow cells to harvest energy in manageable increments
Electron transfer chain
An array of membrane-bound enzymes and other molecules that accept and give up electrons in sequence

34. Uncontrolled Energy Release
glucose +
oxygen
carbon dioxide +
water
A) Glucose and oxygen react (burn) when exposed to a spark. Energy is released all at once as light and heat when carbon dioxide and water form.
Figure 4.11 Comparing uncontrolled and controlled energy release.

35. Controlled Energy Release1
glucose +
oxygen H+ 2
carbon dioxide +
water 3
Figure 4.11 Comparing uncontrolled and controlled energy release.
1 An input of activation energy
splits glucose into carbon dioxide,
electrons, and hydrogen ions (H+).
2 Electrons lose energy as they
move through an electron transfer
chain. Energy released by electrons
is harnessed for cellular work.
3 Electrons, hydrogen ions, and
oxygen combine to form water.

36. ANIMATION: Allosteric inhibition

37. 4.5 Diffusion and Membranes
Spontaneous spreading of molecules or ions through a liquid or gas

38. Diffusion Rate
How quickly a particular solute diffuses through a particular solution depends on five factors:
1. Size
2. Temperature
3. Concentration
4. Charge
5. Pressure

39. Concentration Gradient
The number of molecules or ions per unit volume of a fluid
Concentration gradient
Difference in concentration of a substance between adjoining regions of fluid

40. Selective permeability of lipid bilayers
carbon dioxide
ions;
glucose and other polar organic molecules
gases
oxygen
lipid bilayer
water
Figure 4.12 Animated! Selective permeability
of lipid bilayers. Hydrophobic molecules, gases,
and water molecules can cross a lipid bilayer on
their own. Ions in particular and most polar organic
molecules such as glucose cannot.

41. Tonicity
When fluids on either side of a selectively permeable membrane differ in solute concentration, water diffuses across the membrane in a direction that depends on tonicity:
Hypotonic: Low solute concentration relative to another fluid
Hypertonic: High solute concentration relative to another fluid
Isotonic: Same solute concentration relative to another fluid

42. Osmosis
When a selectively permeable membrane separates two fluids that are not isotonic, water will diffuse from the hypotonic fluid into the hypertonic one
Osmosis
Diffusion of water across a selectively permeable membrane between two fluids that are not isotonic
If extracellular fluid is not isotonic, cell volume changes
Cells in hypertonic fluid shrink
Cells in hypotonic fluid swell

43. Osmosis selectively permeable membrane Figure 4.13 Animated! Osmosis.
Water moves across a selectively permeable membrane
that separates two fluids of differing solute
concentration. The fluid volume changes in the two
compartments as water diffuses across the membrane.
selectively permeable membrane

44. Effects of tonicity in human red blood cells
Figure 4.14 Animated! Effects of tonicity in human red blood cells (A–C) and iris petal cells (D,E).
A) Red blood cells immersed
in an isotonic solution do not
change in volume. The fluid
portion of blood is normally
isotonic with cytoplasm.
B) Red blood cells
immersed in a hypertonic
solution shrivel up as water diffuses out of them.
C) Red blood cells
immersed in a hypotonic
solution swell up as water
diffuses into them.

45. Osmosis and Turgor In plant cells, turgor counters osmosis Turgor
Pressure that a fluid exerts against a wall, membrane, or other structure that contains it
Osmosis continues until two fluids are isotonic, or until pressure against the hypertonic fluid counters the movement

46. Effects of tonicity in plant cells
Figure 4.14 Animated! Effects of tonicity in human red blood cells (A–C) and iris petal cells (D,E).
D) Osmotic pressure
keeps plant parts erect.
These cells in an iris petal
are plump with cytoplasm.
E) Cells from a wilted iris petal.
The cytoplasm shrank, and
the plasma membrane has
pulled away from the cell wall.

47. 3D ANIMATION: Osmosis

48. ANIMATION: Selective Permeability

49. 4.6 Membrane Crossing Mechanisms
Gases, water, and small nonpolar molecules can diffuse across a lipid bilayer
Most other molecules and ions cross only with the help of transport proteins
Each type of transport protein moves a specific ion or molecule across a membrane

50. Passive and Active Transport
Passive transport
Concentration gradient drives a solute across a cell membrane through a transport protein
Requires no energy input
Example: glucose transporters
Active transport
A transport protein uses energy (ATP) to pump a solute across a cell membrane against its concentration gradient
Example: calcium pump

51. Passive Transport of Glucose
Extracellular Fluid
glucose
Figure 4.15 Animated! Passive transport of
glucose.
Cytoplasm

52. Passive Transport of Glucose

53. Passive Transport of Glucose

54. Active Transport of calcium ions
Extracellular Fluid
calcium ion
Figure 4.16 Animated!
Active transport of calcium ions.
Cytoplasm

55. Active Transport of calcium ions
Figure 4.16 Animated!
Active transport of calcium ions.
ADP + phosphate

56. Active Transport of calcium ions
Figure 4.16 Animated!
Active transport of calcium ions.

57. Cotransport Cotransporter
Active transport protein that moves two substances across a membrane in opposite directions at the same time
Example: sodium-potassium pump
ATP powers an active transport protein that pumps Na+ out of and K+ into a cell

58. Cotransport: Sodium-Potassium Pump
Extracellular Fluid
Figure 4.17 The sodium–potassium pump. This active
transport protein (gray) transports sodium ions (Na+) from
cytoplasm to extracellular fluid, and potassium ions (K+) in
the other direction. The transfer of a phosphate group ( P )
from ATP provides energy required for transporting the ions
against their concentration gradient.
ADP
Cytoplasm

59. Membrane Trafficking
Patches of membrane constantly move to and from the cell surface as vesicles that fuse with or pinch off from the plasma membrane
The lipid bilayer reseals itself when the membrane is disrupted

60. Endocytosis and Exocytosis
Process by which a cell takes in a small amount of extracellular fluid by a ballooning inward of its cellular membrane
Exocytosis
Process by which a cell expels a vesicle’s contents to extracellular fluid by merging the vesicle with the plasma membrane

61. Membrane Crossings Figure 4.18 Animated! Membrane crossings.
A plasma membrane is a hub of activity: Molecules and
ions (colored balls) are constantly flowing into and out
of a cell via transport proteins embedded in its plasma
membrane. Vesicles are also taking in or expelling bulk
amounts of solutes and much larger particles.
1 Endocytosis begins as a small patch of plasma membrane
sinks inward.
2 As the membrane balloons into the cell, it wraps
itself around a small volume of extracellular fluid, along
with the solutes or particles it contains.
3 The balloon pinches off inside the cell as a vesicle,
which may deliver its contents to an organelle.

62. Phagocytosis Phagocytosis (“cell eating”)
Endocytic pathway by which cells such as macrophages and other white blood cells engulf particles such as microbes or cellular debris
Amoebas also are phagocytic cells

63. Phagocytosis Figure 4.19 Animated! Phagocytosis. This micrograph shows
a phagocytic white
blood cell engulfing
several Tuberculosis
bacteria (red).

64. 3D ANIMATION: Process of Secretion

65. ANIMATION: Active and Facilitated Diffusion

66. 4.7 A Toast to ADH (revisited)
Alcohol dehydrogenase (ADH) converts ethanol to toxic acetaldehyde, which is then converted to acetate by ALDH

67. Alcoholic liver disease
Figure 4.20 Alcoholic liver disease.

68. Alcoholic liver disease
Figure 4.20 Alcoholic liver disease.

69. Alcoholic liver disease
Figure 4.20 Alcoholic liver disease.

70. Digging Into Data: pH anomaly of Ferroplasma enzymes

71. Digging Into Data: pH anomaly of Ferroplasma enzymes
Figure 4.21 pH anomaly of Ferroplasma enzymes.