Honors and AP Biology Homework Chapter 5: Enzyme Functions
Textbook assignment: Chapter 5: The Working Cell, sections 10-16. Read through the end-of-chapter summary and do a mental self-test using the multiple choice questions.
- 5.10 This is a very basic overview of the concept of energy, its forms, and the processes of changing energy from one form to another. We will be spending several chapters looking at how organisms store and release energy, so be sure that you understand the difference potential and kinetic energy and can recognize the two forms. Each of the laws of thermodynamics discusses how energy changes form: it cannot be created or destroyed, but it can be changed to useless forms of random heat.
- 5.11 Chemical reactions all require activation energy to get started, but the overall rearrangement of atoms from reactant molecules to product molecules may ultimately require more energy from the system's surroundings (endergonic reactions), or release energy into these surroundings (exergonic reactions). In human metabolic systems, endergonic reactions which require energy input must get this energy from exergonic reactions that release energy.
- 5.12 ATP is a short name for a fairly simple chemical, adenosine triphosphate, that can store and release energy easily. The adenosine molecule can take on a "tail" with one, two, or three phosphate molecules. AMP is adenosine monophosphate -- a one-phosphate long tail tied to the adenosine group. ADP is adenosine s -- which has two phosphates in the tail. ATP is adenosine triphosphate with three phosphate groups in the tail. Each phosphate bond stores energy that can be released when these bonds are broken. Pay especial attention to Fig. 5.12A, which puts all the concepts together.
- 5.13 Remember that even spontaneous reactions, ones that release energy, require some starter or activation energy. The amount of net energy from the reaction doesn't change with the use of an enzyme, but the activation energy can be reduced, which makes it easier to start the reaction at body temperatures.
- 5.14 In organisms, each step of a reaction where bonds are broken or reformed is controlled by a specific enzyme. You will not need to memorize the names of enzymes for most reactions, but you do need to understand the mechanism or process involved. Here, we use the analyg of a lock and key: the enzyme must fit the particular reactants for the reaction. The controls work both ways: certain useful reactions won't occur without an enzyme, and many harmful reactions can't occur without an enzyme either!
- 5.15 Cells use enzyme inhibitors and activators to control enzyme function and start or stop metabolic processes, depending on circumstances. For example, if a particular enzyme facilitates lactose breakdown (a milk sugar). If lactose is present, it acts as a substrate to bond to the enzyme and the reaction can begin. In this case, the substrate is the activator. But suppose we have a situation where substrate A binds to the enzyme, which then facilitates a reaction to produce molecule B. If we have a lot of molecule A, we may get more than we need (or is healthy) of molecule B. But if molecule B itself binds to the enzyme as either a competitive or non-competitive inhibitor, it will stop its own production. This is negative feedback and is an important type of process used by most cells to control production of various molecules.
- 5.16 Anything that affects the shape of the enzyme will affect its ability to function, either destroying that ability or improving it. We will need to use the concept of cofactors when we talk about cellular respiraiton (next chapter) and vitamins (next spring). Be sure that you understand the implications of temporarily disrupting enzyme function and permanently disrupting it. By creating a temporary disruption, a cell can actually control when certain reactions occur. But a permanent disruption means that the cell can never perform the function that the destroyed enzyme makes possible. This is okay if the cell doesn't need to do a specialized activity any more, say, after it has developed to a certain level of specialization. But if the function is essential to the health of the cell, disruption of the enzyme controlling the function becomes life-threatening.
Read the following weblecture before chat: Energy and Enzymes
Take notes on any questions you have, and be prepared to discuss the lecture in chat.
Perform the study activity below:
Chat Preparation Activities
- Essay question: The Moodle forum for the session will assign a specific study question for you to prepare for chat. You need to read this question and post your answer before chat starts for this session.
- Mastery Exercise: The Moodle Mastery exercise for the chapter will contain sections related to our chat topic. Try to complete these before the chat starts, so that you can ask questions.
- Required: Complete the Mastery Exercise with a score of 85% or better.
- Optional: Test yourself with the textbook multiple choice questions and note any that you miss that still don't make sense. Bring questions to chat!
- Go to the Moodle and take the quiz for this chapter.
Read through the lab for this week; bring questions to chat on any aspect of the lab, whether you intend not perform it or not. If you decide to perform the lab, be sure to submit your report by the posted due date.
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