1. Ground Rules of Metabolism
Chapter 5

2. 5.1 Energy and the World of Life
Energy: The capacity to do work
Potential energy (Example: chemical bonds)
Kinetic energy (Energy of motion)

3. Two Laws of Thermodynamics
1. Energy cannot be created or destroyed
It can be converted from one form to another and transferred between objects or systems
The energy transfer most pertinent to living systems in the conversion of light to chemical energy via photosynthesis
2. Entropy tends to increase
Energy tends to disperse spontaneously
Some energy disperses at each energy transfer, usually in the form of heat
Therefore, living systems need a constant input of energy to maintain their organization

4. One-Way Energy Flow

5. Energy In, Energy Out Chemical reactions
Reactants (molecules in)
Products (molecules out)
Endergonic reactions (energy-requiring)
Exergonic reactions (energy-releasing)
Chemical reactions in cells are nearly always coupled – an input of energy is coupled by an output of energy

6. Exergonic and Endergonic Reactions

7. 5.2 ATP in Metabolism Adenosine triphosphate (ATP) Phosphorylation
Main energy carrier between cell reaction sites
ADP/ATP cycle
Phosphorylation
Phosphate-groups transfer to and from ATP
When a phosphate is added to a molecule (endergonic reaction) it is coupled to the exergonic reaction of the lost of a phosphate from the molecule “giving up” the phosphate

8. ATP: Energy Currency of Life

9. 5.3 Enzymes in Metabolism Activation energy Enzymes are catalysts
Minimum energy needed to start a reaction
Enzymes are catalysts
Speed reaction rates by lowering activation energy
Most are proteins (some RNAs)
catalyze every synthesis (condensation reactions) and decomposition (hydrolysis) reaction in cells

10. Activation Energy

11. Enzyme Action Active site How enzymes lower activation energy
Specific site of enzyme molecule where reactions occur
Creates a microenvironment that is more favorable for the reaction
How enzymes lower activation energy
By concentrating substrate molecules
By orienting substrates to favor reaction
By inducing fit between substrate and active site
Activation energy allows enzyme to bring substrate to transition state

12. Enzyme Action: Hexokinase

13. 5.4 Controls Over Enzymes
Enzymatic reactions are carefully controlled in cells via
competitive inhibition = when a molecule similar to the substrate attaches to the active site and blocks its access to the actual substrate
Allosteric sites = a physical site on the enzyme molecule distinct from the active site
Molecular bonding to the allosteric site can enhance or inhibit enzyme function by changing the shape of the enzyme molecule

14. Allosteric Control

15. Feedback Inhibition – results from inhibition

16. Enzymes and the Environment
Each enzyme functions best within a characteristic range of temperature, salt concentration, and pH

17. Enzymes and pH

18. 5.5 Metabolism – Organized, Enzyme-Mediated Reactions
Cells concentrate, convert, and dispose of most substances in orderly, enzyme-mediated reaction sequences called metabolic pathways
Biosynthetic pathways
Construct large molecules from smaller ones
Require energy
Photosynthesis
Main biosynthetic pathway in the biosphere
Autotrophs

19. Degradative Pathways Degradative pathways Aerobic respiration
Break down molecules to smaller products
Release usable energy
Aerobic respiration
Main degradative pathway in the biosphere
Heterotrophs

20. Main Metabolic Pathways

21. REDOX Reactions Oxidation–reduction (redox) reactions
Electron transfers used in metabolic pathways
Electron transfer includes a transfer of energy
Electron transfer chains
Take part in organized sequences of reactions in photosynthesis and aerobic respiration
Electrons are passed from one molecule to the next “moving’ energy along the way

22. Controlled Energy Release

23. Key Players in Metabolic Pathways

24. 5.6 Diffusion, Membranes, and Metabolism
Concentration of a substance
Number of atoms or molecules in a given volume
Concentration gradient of a substance
A difference in concentration between two regions – a higher concentration versus a lower concentration
Effects the movement of substances via diffusion

25. Diffusion Diffusion Diffusion rates are influenced by:
Net movement of molecules to a region where they are less concentrated
Diffusion rates are influenced by:
Temperature
Molecular size
Gradients of pressure, charge, and concentration

26. Diffusion

27. Diffusion and Membrane Permeability
Selective Permeability

28. How Substances Cross Membranes: Diffusion, Passive and Active Transport

29. How Substances Cross Membranes: Endocytosis and Exocytosis

30. Three Types of Endocytosis
Receptor-mediated endocytosis
Substance binds to surface receptors
Pit forms endocytotic vesicle
Phagocytosis (“cell eating”)
Amoebas use pseudopods to engulf prey

31. Endocytosis and Exocytosis

32. Phagocytosis

33. 5.7 Working With and Against Gradients
Many solutes cross membranes through transport proteins (open or gated channels)
Facilitated diffusion (passive transport) does not require energy input
Solute diffuses down its concentration gradient through a transporter
Example: Glucose transporters

34. Facilitated Diffusion

35. Active Transport
Active transporters require ATP energy to move a solute against its concentration gradient
Maintain gradients (concentration differences) across cell membranes
Example: Calcium pumps
Cotransporters move two substances at the same time
Example: Sodium-potassium pump

36. Active Transport: Calcium Pump

37. 5.8 Which Way Will Water Move?
Osmosis
The diffusion of water across a selectively permeable membrane
Water molecules follow their concentration gradient, influenced by solute concentration –
Water moves from an area of lower solute (higher water) concentration to an area of higher solute (lower water) concentration

38. Osmosis

39. Tonicity
Relative concentrations of two solutes separated by a semipermeable membrane
Hypertonic fluid (higher solute concentration)
Hypotonic fluid (lower solute concentration)
Isotonic solutions (two solutions with the same tonicity)

40. A Tonicity Experiment

41. Osmosis and Hydrostatic Pressure

42. 5.10 Night Lights Bioluminescence
Fluorescent light released by enzyme-mediated reactions in organisms