Chapter 6. Ground Rules of Metabolism

Transcription

1 Chapter 6 Ground Rules of Metabolism

2 Alcohol dehydrogenase removes ethanol molecules from the liver

3 Binge Drinking by State (Source Centers for Disease Control and Prevention (CDC). Rank States Amount # 1 Wisconsin: 21.8% # 2 North Dakota: 20.4% # 3 Minnesota: 19.8% # 4 Iowa: 18.9% # 5 Rhode Island: 18.2% # 6 Nevada: 18% = 7 Pennsylvania: 17.6% = 7 Nebraska: 17.6% # 9 Illinois: 17.5% # 10 Delaware: 17.4% # 36 Oregon: 13.1% # 52 Tennessee: 8.2%

4 What Is Energy? Capacity to do work Forms of energy Potential energy Kinetic energy Chemical energy

5 First Law of Thermodynamics The total amount of energy in the universe remains constant Thus, energy is neither created or destroyed (except through matter-energy conversion, i.e. nuclear energy) Energy can be converted from one form to another (i.e., from potential to kinetic energy)

6 Energy Conversions What are examples of energy conversion? Example: skydivers falling from an airplane Example: detonating bomb

7 Second Law of Thermodynamics No energy conversion is 100% efficient Any energy transformation (as between different forms of chemical energy) always produces some waste heat, representing a loss of usable energy Thus, usable energy is always being lost within organisms and ecosystems, and needs to be replaced by fresh sources of usable energy

8 Simple Ecosystem Model ENERGY LOST Energy continually flows from the sun. Usable energy comes from sunlight Some energy is captured by plants (producers) producers Some energy is captured by animals eating the plants, or others that eat animals (consumers) NUTRIENT CYCLING consumers Usable energy is lost during each phase, and must be replaced by more sunlight

9 What Can Cells Do with Energy? Energy inputs become coupled to energy-requiring processes Cells use energy for: Chemical work Mechanical work Electrochemical work

10 Reactions, Downhill (Exergonic) If a reaction is running downhill, it is releasing chemical energy as it occurs Example: burning of paper, which is made of cellulose, which is made in turn of glucose

11 Exergonic Reactions Energy is released from the burning of glucose Products of combustion have less energy than starting substance glucose, a high energy reactant + 6O 2 ENERGY OUT low energy products 6 6

12 Reactions, Uphill (Endergonic) If a reaction is running uphill, it is absorbing chemical energy as it occurs Example: CO 2 and H 2 O do not spontaneously assemble into glucose, cellulose, starch

13 Endergonic Reactions Energy input required (as in sunlight, below) Product (glucose) has more energy than the starting substances (water and carbon dioxide) glucose, a high energy product + 6O 2 low energy reactants 6 ENERGY IN (sunlight) Photosynthesis

14 Photosynthesis, Respiration Photosynthesis: 6CO 2 + 6H 2 O + sunlight C 6 H 12 O 6 + 6O 2 Respiration: C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + energy Photosynthesis and respiration are opposite, symmetrical processes Photosynthesis (by plants) supports respiration (by all plants and animals)

15 The Role of ATP ATP (adenosine triphosphate) is the main energy carrier in cells It is produced by respiration (dismantling of glucose and other large energy-containing food molecules) Cells then use the energy in ATP to power most of their endergonic processes three phosphate groups base (adenine) sugar ATP (note similarity to nucleotides of DNA)

16 ATP/ADP Cycle ATP (energy resources available to cell) cellular work reactions that release energy ATP ADP + Pi reactions that require energy (e.g., synthesis, breakdown, or rearrangement of substances; contraction of muscle cells; active transport across a cell membrane)

17 ATP/ADP Cycle ATP (adenosine triphosphate) is formed from ADP (adenosine diphosphate) + inorganic phosphate (P i ), mostly in the mitochondria ATP formation requires energy input (obtained from the energy in food) When ATP gives up a phosphate group to power an endergonic reaction, ADP is formed ATP later re-forms from ADP and P i Regenerating ATP by this ATP/ADP cycle helps drive most metabolic reactions

18 ATP Usage Example: Active Transport Ca ++ Ca ++ ATP Ca ++ Ca ++ Ca ++ Ca ++ ADP energy input energy output Ca ++ Ca ++ P i Calcium ion (Ca ++ transport is essential for muscle function Ca ++ ions must be concentrated into small compartments ATP provides energy for transport proteins to push the ions against their concentration gradient (uphill)

19 What is an enzyme?

20 Enzyme Structure and Function Enzymes are a special class of proteins Enzymes are catalytic molecules A catalyst either causes or accelerates a chemical reaction, without itself being consumed in the reaction Enzymes greatly speed up chemical reaction rates (sometimes by factors of millions or billions of times)

21 Features of Enzymes 1) Enzymes do not make anything happen that could not happen on its own (therefore, if a reaction is energetically unfavorable, it won t happen, even with an enzyme) 2) Reactions do not permanently alter or use up enzyme molecules

22 Enzymes in Nepenthes release the nitrogen from insects captured in the plant

23 More Features of Enzymes 3) The same enzyme usually works for both the forward and reverse reactions. 4) Each type of enzyme recognizes and binds to only certain substrates.

24 Activation Energy For a reaction to occur, an energy barrier must be surmounted Example: to ignite paper, we must first light a match Enzymes make the energy barrier smaller starting substance energy released by the reaction activation energy without enzyme activation energy with enzyme products

25 Some Factors Influencing Enzyme Activity Allosteric regulators Feedback inhibition Temperature ph Salt concentration

26 Effect of Temperature Small increase in temperature increases molecular collisions, reaction rates High temperatures disrupt bonds and destroy the shape of active site

27 Effect of ph Activity rates of three different enzymes Which is (are) probably active in the stomach?

28 Effect of ph Pepsin (in stomach) Trypsin (in intestine)