Topic 9 How Does Life Use Energy?

1. Topic 9How Does Life Use Energy? Dr. George Lapennas Dept. of Biology

2. Nature of science: Search for mechanistic explanations – ones that predict events based on underlying rules and structures, rather than attributing events to the whims of god(s).

3. Explanations for behavior of non-living matter Scientists have developed theories that successfully explain natural phenomena such as motion, gravity, energy, and chemical reactions

4. Explanations for behavior of non-living matter were … - developed on relatively simple systems - but also apply to more complex non-living systems, such as the mechanism of a clock

5. Clock face

6. Behavior of man-made mechanisms involves laws of physics and chemistry, together with their structure (shapes and arrangement of their parts)

8. Can life also be understood mechanistically (vs vitalistically)?

9. Quick review of special characteristics of living things (organisms)

10. 1. Growth

11. 2. Development (changes other than growth during individual lifetime)

12. 3. Reproduction (involves inheritance)

13. 4. Ordered, complex structure; adaptation

14. 5. Movement (esp. animals)

15. 6. Sensitivity/Responsiveness

16. 7. Consciousness/Rationality

17. 8. Evolution (change over generations)

18. 9. Use of energy

19. An early mechanistic success: Harvey’s partial explanation of the pumping and circulation of the blood

20. Some 19th century steps from a vitalistic toward a mechanistic understanding of life

21. 1. The cell theory Living things are made up of large numbers of tiny units called “cells” that come from previous cells Prerequisite technical advance: Invention of the microscope (early 1600’s)

22. Structure of an animal cell

23. Structure of a plant cell

24. 2. In vitro (in glass) synthesis of organic molecules Wohler’s 1828 in vitro synthesis of urea, etc. Eventually, chemists learned to synthesize everything in vitro that organisms synthesize in vivo. General conclusion: There are no unique laws of chemistry operating within living organisms.

25. 3. The fermentation controversy “Fermentation” – chemical transformations that had only been observed in association with living things, including … - souring of milk - fermentation of fruit/grain, producing alcohol and carbon dioxide - putrification and decay of dead animals and plants

26. Do fermentations require presence of living organisms? Buchner (1897) observed fermentation of fruit juice by cell-free extract of yeast, yielding alcohol and carbon dioxide (CO2) Conclusion: Living cells are not required for fermentation – only need some materials that were present within the cells (now known to be enzymes - proteins that act as catalysts to speed up reactions).

27. 4. Cryptobiosis Does life irreversibly end when life processes cease? or … Can life processes be stopped and later re-started, so long as necessary structures have been preserved intact? Can the “clock” of life be stopped and then re-started?

30. Conclusion: Life processes only depend upon the presence of certain matter in a certain structural arrangement. That matter and structure can persist during drying or freezing when all processes cease. Life processes can resume upon restoration of water or thawing.

31. Why did mechanistic explanations take so long to develop in biology? - Because living things are much more complex than anything else that scientists study - Many other discoveries had to be made before the mechanisms of biological structures and processes could be effectively investigated.

32. Machinery of life: 4 classes of organic “macro-molecules” assembled from building blocks 1. Proteins (structural; catalytic “enzymes”) 2. Nucleic acids (DNA, RNA; instructions for inheritance as the structure of proteins) 3. Polysaccharides (energy storage; structure) 4. Complex lipids (energy storage; cell membranes)

33. Protein building blocks – amino acids

34. Protein structure – primary structure

35. Protein structure – secondary structure

36. Protein structure – tertiary structure

37. Protein function

38. DNA (molecule of inheritance)

39. Living matter seems to obey the same laws of physics and chemistry as non-living matter Conservation of mass Conservation of momentum Gravitation Chemical properties of elements Laws of thermodynamics

40. Laws of thermodynamics In any isolated system (no matter or energy can enter or leave the system), including the entire universe: First Law – the total amount of energy is constant, though it can change form.

41. Laws of thermodynamics In any isolated system (no matter or energy can enter or leave), including the entire universe: First Law –total amount of energy is constant, though it can change form. Second Law – Whenever anything actually happens, the entropy (disorder) of the system increases.

42. Laws of thermodynamics In any isolated system (no matter or energy can enter or leave), including the entire universe: First Law –total amount of energy is constant, though it can change form. Second Law – Whenever anything actually happens, the entropy (disorder) of the isolated system increases. - “Time’s Arrow” points in the direction of increasing entropy (disorder) of the universe. - Changes that would reduce the entropy of the universe cannot occur

43. “Spontaneous” changes= changes that can happen = “downhill” changes

44. “Spontaneous” processes can happen

45. Two old hypotheses about animals’ use of food 1. Assimilation- food is added to the body for growth or to replace material lost through “wear and tear”

46. Two hypotheses about animals’use of food 1. Assimilation - food is added to body for growth or to replace material lost through “wear and tear” 2. Combustion - food is somehow “burned” within the body, like fuel in a fire, generating heat, and being consumed in the process

47. Reinterpretation of combustion and animal respiration by Lavoisier Lavoisier (late 1700’s)… - Overthrew phlogiston theory and applied new knowledge of gases to combustion - Flames and animals do not produce phlogiston, - Both consumeoxygen (O2) and releasecarbon dioxide (CO2) and heat

48. “Slow combustion” Lavoisier had observed a quantitative similarities between burning charcoal and a living animal. They hypothesized that animals carry out a “slow combustion” of fuel (process now called cellular respiration). They believed that the function of cellular respiration was to make heat.

49. What do we know now about the use of food? - Blood carries digested food from intestine and oxygen from lungs throughout body, where cells take them up through walls of capillaries.

50. What do we know now about the use of food by animals? - Blood carries digested food from intestine and oxygen from lungs throughout body, where cells take them up through walls of capillaries. - Cells both ASSIMILATE food and use it as FUEL FOR CELLULAR RESPIRATION