Biology Homework Chapter 3: Proteins and Nucleic Acids
Textbook assignment: Chapter 3: The Molecules of Cells, sections 8-16.
Read through the end-of-chapter summary and do a mental self-test using the multiple choice questions.
- 3.8 Lipids are similar to sugars in that part of a lipid is composed of a polymer chain, in this case the monomers (CH2 and CH3 subunits). Where CH2 monomers exist, the "extra" bond becomes a double carbon bond, and the external H atoms "kink" the chain, causing these unsaturated chains to have lower melting points than "saturated" chains made up entirely of CH3 units. The non-monomer part of the lipid is a glycerol group that is hydrophilic, while the chain is hydrophobic. This causes groups of lipids to orient themselves in water so that the "phobic" tails are "inside" a circle of hydrophilic "heads".
- 3.9 Scientific Thinking Partially hydrogenating unsaturated fats produces compounds that hold their shape but supposedly are easier to digest than saturated fats. However, the process of hydrogenation produces transfats that studies show are statistically related to health problems including heart attacks. Two types of studies, prospective and retrospective, are used to establish health patterns. The Nurses Health Study started in 1976 provides evidence that trans fat consumption is a greater risk than saturated fat consumption
- 3.10 Lipids vary depending on the composition of the head and the number of tails associated with it. Study the differences in structures and functions of phospholipids, and steroids. Phospholipids add a phosphate ion to a simple lipid construction. Steroids molecules are four fused rings. (Another form of phospholipid is wax).
- 3.11 This is another unit on practical application of a concept to your health. Be sure that you understand what medical problems are inherit when using steroids to build body muscle.
- 3.12 The primary component of proteins are amino acids. Different proteins have different shapes; shape dictates function. All amino acids have a similar nitrogen and hydrogen complex (the amino group) bonded to a carbon and oxygen, and a carboxyl group, but different functional subunits (remember: the functional subunit is the part of the molecule that reacts with other molecules). These differences allow the amino acids to form chains of different shapes, and consequently different properties. We'll see how important this is shortly when we study enzymes in chapter 5. Compare the process of peptide chain formation to the formation of polysaccharides in 3.5 and fatty acids in 3.8. Be sure that you understand how dehydration synthesis and hydrolysis work.
- 3.13 Amino acids have localized areas of charge and H-bonds. When the peptides chains form, these local areas cause the chain to kink up, forming a particular shape. Exposure to salt, other acids or water, salts, and heat can break these weak bonds, change the shape of the protein, and make it fail to function.
- 3.14 Study the level of structures involved. Be sure that you understand how each level is held together. Each level twists to form a structure that can then be coiled and twisted on its own. In a way, this is like twisting strands of cotton to form threads, threads, to form yarn, then knitting the yarn to make a sweater.
- 3.15 The nucleic acids DNA and RNA form from small units called nucleic acids, bound by chemical bonds that create complex patterns. These patterns provide cells with the information needed to make thousands of different proteins that support individual steps in metabolic functions.
- 3.16 The monomers of the nucleic acids DNA and RNA are nucleotides, of which there are five primary kinds. Three (be sure you know which three) are found in both DNA and RNA, and of the remaining two, one is found only in DNA and one only in RNA--this is one of the ways in which the two kinds of nucleic acids differ. In DNA, two chains are bound together by hydrogen bonds to form a double helix shape, which protects the chain from accidental breakup.
- 3.17 Evolution Connection Studies of human DNA patterns indicate that the ability to produce lactase, an enzyme capable of breaking down milk fats into usable food components, is a "recent" adaptation in human development that appeared in Europe, aiding survival in a cold climate where animal fats were available year round.
Read the following weblecture before chat: Organic Molecules: Proteins and DNA
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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