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Earth Sciences 1081A/B Lecture Notes - Lecture 6: Taphonomy, Abrasive Blasting, Disarticulation

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28 Jun 2022

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Western University

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Earth Sciences 1081A/B

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Document Summary

Lecture 15: to be or not to be. Focus: factors that influence the preservation of dead remains and how dead remains become body fossils. Defined as the study of post-mortem processes (physical, chemical and biological factors) Misconception that fossils are dead remains that turn into rocks. Reality: less than 5% of all remains of living things actually become fossilized, and survive into the geologic record. After an organism dies, its tissues are destroyed due to different factors: macroscopic level: Large scavengers take their share of soft tissues and will separate and scatter some of the hard parts. Insects lay eggs on dead remains; their larvae have a field day on the tissue that has started to decompose (zombifying) Microbes break down dead organic matter further at the molecular level. Decay often proceed from the inside out (in animals, gut bacteria can jump-start the process) Hard parts are preferentially preserved but rarely preserved together.

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Related Questions

Do Enzymes Physically Attach to Their Substrates?

When scientists first began to examine the chemical activities of organisms, no one knew that biochemical reactions were catalyzed by enzymes. The first enzyme was discovered in 1833 by French chemist Anselme Payen. He was studying how beer is made from barley: First, barley is pressed and gently heated so its starches break down into simple two-sugar units; then yeasts convert these units into ethanol. Payen found that the initial breakdown requires a chemical factor that is not alive and that does not seem to be used up during the process-a catalyst. He called this first enzyme diastase (we call it amylase today).

Did this catalyst operate at a distance, increasing the reaction rate all around it, much as raising the temperature of nearby molecules might do? Or did it use physical contact, actually attaching to the molecules whose reaction it catalyzed (its "substrate")?

The answer was discovered in 1903 by French chemist Victor Henri. He saw that the hypothesis that an enzyme physically binds to its substrate makes a clear and testable prediction: In a solution of substrate and enzyme, there must be a maximum reaction rate. When all the enzyme molecules are working full tilt, the reaction simply cannot go any faster, no matter how much more substrate you add to the solution. To test this prediction. Henri carried out the experiment whose results you see in the graph, measuring the reaction rate (V) of diastase at different substrate concentrations (S).

1. Making Inferences As S increases, does V increase? If so, in what manner-steadily, or by smaller and smaller amounts? Is there a maximum reaction rate?

2. Drawing Conclusions Does this result provide support for the hypothesis that an enzyme binds physically to its substrate? Explain. If the hypothesis were incorrect, what would you expect the graph to look like?

3. Further Analysis If the smaller amounts by which V increases are strictly the result of fewer unoccupied enzymes being available at higher values of S, then the curve in Henri's experiment should show a pure exponential decline in V-mathematically, meaning a reciprocal plot (1/V versus 1/S) should be a straight line. If some other factor is also at work that reacts differently to substrate concentration, then the reciprocal plot would curve upward or downward. Fill in the reciprocal values in the table to the right, and then plot the values on the lower graph (1/S on the x axis and 1/V on the y axis). Is a reciprocal plot of Henri's data a straight line?