Mod+6+Reading+Guide

The main point of Module 6 is to identify carboxylic acids, esters, and the many different kinds of lipids they produce while being able to pinpoint the function of these molecules within living systems especially as they relate to the transport of molecules into and out of a cell through cell membranes.
 * __Module 6 Reading Guide: Acids, Esters, and Lipids__**

-Summary: A **Carboxylic Acid** contains a hydroxyl group attached to a carbonyl group. To name carboxylic acids, you replace the -e of the alkane name with -oic acid. Then the carbon chain is numbered beginning with the caboxylic acid to name substituents from the chain. Similarly, in an aromatic benzoic acid, substituents are numbered starting with the carboxylic acid group as carbon 1. Ortho, meta, and para may be used to show substituents as well. p.579 includes some common names for carboxylic acids. A primary alcohol can be oxidized to an aldehyde which can be oxidized to a carboxylic acid.
 * __16.1: Carboxylic Acids__**

-Struggling Topic 1: Is there a difference in the wording of the oxidation of an alcohol where it would be complete or incomplete. For example, HW problem 16.9 asks to draw the product of the oxidation of an alcohol. I first drew the aldehyde thinking that the compound would be oxidized once. If the question wanted to ask for this, would it ask you to oxidize the alcohol once? Should the question be more clear and ask for the product of the complete oxidation of the given compound, or should we assume that it will be oxidized twice?

-Struggling Topic 2: Is there a time when a carboxylic acid could be further oxidized to add alcohols to other carbon atoms in the molecule? Eventually could it have a carboxylic acid group on both ends of the molecule?

__**16.3: Esters**__ -Summary: An **Ester** is a carboxylic acid with the --H replaced by an alkyl group. **Esterification** is a type of chemical reaction where an alcohol reacts with a carboxylic acid under heat with an acidic catalyst, such as sulfuric acid to form water and an ester.

-Struggling Topic 1: Does esterification explain what would happen instead of having a two-sided carboxylic acid? See 16.1's struggling topic 2.

-Struggling Topic 2: Esterification always requires a proton donor (acid catalyst) to form water and an ester. Is this reaction revered in a similar way as the Hydrolysis that happens in the breaking down of large carbohydrates? Don't they both use water in the breaking down of larger compounds?

__**17.1 Lipids**__ -Summary: **Lipids** are organic molecules that are soluble in organic solvents but not in water. **Waxes** are formed from a fatty acid with a long-chained alcohol. **Triacylglycerols** are formed from a glycerol bonded to three fatty acids. **Glycerophospholipids** are formed from a glycerol bonded to two fatty acids and a PO4 bonded to an Amino alcohol. **Sphingolipids** include a sphingosine bonded to a fatty acid and a PO4 bonded to an Amino alcohol. **Glycosphingolipids** inlucde sphingosine bonded to a fatty acid and a sugar. **Steroids** have a nucleus of four fused carbon rings and do not contain fatty acids/cannot be hydrolyzed.

-Struggling Topic 1: Steroids don't seem like they should be grouped with the other groups of lipids. It seems like steroids are structurally much more simple than the other types of lipids. Is it that both steroids and the other kinds of lipids are insoluble in water but are soluble in other organic solvents that places them in the same group?

-Struggling Topic 2: Which of the Lipid sub-groups should we be familiar with? It seems like all of these groups are covered in our objectives, but 17.1 was a very broad overview of these groups.

__**17.2 Fatty Acids**__ -Summary: **Fatty acids** are long carbon chains with a carboxylic acid group at one end. These are insoluble in water because of their long nonpolar carbon chains (usually10-20 carbons long). **Saturated fatty acids** have only single bonds between carbon atoms, **monounsaturated fatty acids** have 1 double bond between carbon atoms, and **polyunsaturated fatty acids** have two or more double bonds between carbon atoms. Unsaturated fatty acids can be cis or trans, and cis bonds have a much larger impact on the molecule's properties than trans bonds do. Saturated fatty acids are usually solids at room temperature with higher melting points than unsaturated fatty acids which are usually liquids that have lower melting points. **Prostaglandins** are hormone like substances formed from a 20 carbon fatty acid with a hydroxyl groups on carbon 11 and 15 and a trans double bond at carbon 13. Some prostaglandins produce inflammation, pain, and muscle contraction in the body.

-Struggling Topic 1: Which fatty acids should we recognize and be familiar with? Mod 6 objectives don't specifically label any that we should know, but the HW questions did ask us to look some up and identify some of their properties.

-Struggling Topic 2: How are prostaglandins related to fatty acids in properties? It sounds like they have related structures. It appears as though prostaglandins are oven bent in a U shape for their carbon chain. I don't think this is the case with fatty acids. What causes this difference, and how does it affect their properties?

-Summary: A **wax** is an ester of a saturated fatty acid and a long-chain alcohol (14-30 cabons each). **Triacylglycerols** (fats and oils) are storage molecules for fatty acids in the body and are triesters of glycerol (a trihydroxy alcohol) and fatty acids. Triacylglycerols are the major form of energy storage for animals. **Fats** are triacylclycerols that are solids at room temperature, and **oil**s are triacylglycerols that are usually liquid at room temperature. Some oils are made of monounsaturated, polyunsaturated, or even mostly saturated fatty acids. The amounts of saturated monounsaturated, and polyunsaturated fatty acids affect the melting points of these fats, oils, and waxes. Generally speaking, animal fats have higher melting points than vegetable oils because animal fats are more saturated.
 * __17.3 Waxes, Fats, and Oils__**

-Struggling Topic 1: With the proper enzymes for digestion, could waxes be broken down and used for cellular respiration? It seems reasonable that they could since they are made of fatty acids much like triacylglycerols are.

-Struggling Topic 2: How do we tell that a triacylglycerol that is a solid at room temperature could be an oil like palm oil and coconut oil? It seemed like the definition for fat was that they must be triacylglycerols that are solids at room temperature. Is it because palm oil and coconut oil are plant products rather than animal fats?

__**17.4 Chemical Properties of Triacylglycerols**__ -Summary: **Hydrogenation** allows oils to be partially saturated to make them semi-solid or even completely solid at room temperature by converting a double bonded carbon pair to a single bond. **Hydrolysis** is when triacylglycerols are split by water in the presence of strong acids or digestive enzymes (lipases). The produces of hydrolysis are the water soluble glycerol and three fatty acids. **Saponification** is a reaction of a triacylglycerol with a strong base to form a glycerol and salts of fatty acids (soaps). NaOH produces a solid soap, and KOH produces a liquid soap. Polyunsaturated oils produce softer soaps.

-Struggling Topic 1: The amount of hydrogenation of vegetable oils affects the melting point of these semi-solids. I feel like there are many different viewpoints about the health effects of such compounds. Some seem to say that saturated fats are bad because of their cholesterol while others seem to say that at least the saturated fats aren't hydrogenated like the semi-solid spreads. Is there a correct answer to these questions, or are these both possibly correct based on the needs of a specific person's diet?

-Struggling Topic 2: Does the order of the fatty acids in a triacylglycerol make a difference for the molecule's properties? I would assume that different fatty acids contribute to different triacylglycerols, and it seems reasonable that the middle fatty acid might behave differently than the two "outside" fatty acids.

__**17.5 Glycerophospholipids**__ -Summary: **Glycerophospholipids** are lipids that are similar to triacylglycerols except that one hydroxyl group of glycerol is replaced by a phosporic acid and an amino alcohol bonded through a phosphodiester bond. **Lecithins** and **cephalins** are two types of glycerophospholipids. Lecithins contain choline and cephalins contain ethanolamine and sometimes serine. These glycerophospholipids contain polar and nonpolar regions. The ionized alcohol and phosphate portion, or head, is polar and can hydrogen bond with water. The two fatty acids connected to the glycerol form a nonpolar tail. These glycerophospholipids are found in cell membranes and myelin sheaths throughout the body because they can help transport other molecules using their polar and nonpolar sides.

-Struggling Topic 1: Since Lecithins and cephalins are both glycerophospholipids, but lecithins contain choline and cephalins contain ethanolamine and sometimes serine, does this mean that ethanolamine and serine have more similar properties than choline? What causes these two to be significantly enough different to be in a separate group from the lecithins?

-Struggling Topic 2: The objectives for Mod 6 discuss knowing the uses of lecithins and cephalins in the body and why they are used this way. In the book in 17.5, all we know so far is that these are involved in cell membranes and nerve cells. Is there more we should know about these? Currently I cannot say the practical differences between lecithins and cephalins. I am hoping that 17.6-17.8 will give me a better understanding of these.

__**17.6 Sphingolipids**__ -Summary: **Sphingolipids** also have polar and nonpolar regions with a long-chain amino alcohol connected to a fatty acid, phosphate, and an amino alcohol. **Ceramide** is produced when the NH2 group in sphingosine bonds to a fatty acid using an amide link. A sphingolipid forms when the OH group forms and ester bond with a phosphate attached to an amino alcohol. **Sphingomyelin** is an abundant sphingolipid that makes up the white matter of the myelin sheath that surrounds nerve cells, and it is formed from a sphingosine linked to a phosphate ester of choline. **Glycosphingolipids** are sphingolipids that contain carbohydrates such as monosaccharides bonded by a glycosidic bond where the OH of the ceramide would have been. These are important components of nerve membranes and muscle cells. **Cerebrosides** is a glycosphingolipid where the OH of the ceramide has been replaced by galactose. These molecules are important in cellular recognition and tissue immunity in cell membranes. **Gangliosides** are similar to cerebrosides but contain two or more monosaccharides. These are important in the membranes of neurons, and they act as receptors for hormones, viruses and some drugs.

-Struggling Topic 1: Many groups of lipids are listed and described in this section. Very few seem to be related to the objectives of Mod 6. It sounds like these are unique and important to the body's ability to function properly, but which of these do we need to be familiar with? It appears from the objectives that only sphingolipids and glycosphingolipids should be included on our quizzes.

-Struggling Topic 2: With so many different groups of lipids in this section, do you have any tips for keeping them straight? So far I picture these sphingolipids as "opposite" from the glycerophospholipids because the sphingolipids have a double bond in the sphingosine group where the glycerophospholipids have a phosphate group bonded to part of the glycerol. Are there other hints/suggestions for keeping these grouped correctly?

__**17.7 Steroids: Chloresterol, Bile Salts, and Steroid Hormones**__ -Summary: **Steroids** are compounds with a steroid nucleus that consits of three cyclohexane rings and one cyclopentane ring fused together. Steroids do not hydroliyze to give fatty acids and alcohols. The carbons are numbered and the four rings in the nucleus are designated A, B, C, and D beginning with the carbons in ring A and ending with the two methyl groups. **Cholesterol** is one of the most important steroids in the body and has an OH group on carbon 3 where many steroids have carbonyl groups. It also includes a double bond between carbon 5 and 6, and methyl groups at carbon 10 and 13. Cholesterol is important in cell membranes, myelin sheathes, and brain/nerve tissues. Cholesterol is a factor in heart disease because of the way it can accumulate as plaque in the arteries. **Bile salts** are made in the liver from cholesterol and are used much like soaps to break down fat. These also help the body absorb cholesterol. Too much cholesterol can cause precipitates that form gallstones. **Lipoproteins** are particles that form from phospholipids and proteins to become water soluble. These include cholesteryl esters, the prevalent form of cholesterol in the blood, that are formed by the esterification of the OH group in cholesterol with a fatty acid.

-Struggling Topic 1: The homework questions and objectives seemed to want to know the uses of cholesterol and bile salts in the body, but it seemed like there was lots of information in this section that we didn't need to know. Is there a relation of these steroids to the objectives that I have missed?

-Struggling Topic 2: Does the difference between the "good" and "bad" cholesterol have to do with the ease with which these molecules are removed from the system? It seemed like the "good" cholesterol was used mostly for removing excess cholesterol from the tissues for elimination while the "bad" cholesterol was likely to be deposited in the arteries if its concentration is greater than it needs to be.

__**17.8 Cell Membranes**__ -Summary: Cell membranes are mostly composed of a double row arrangement of phospholipids called the **lipid bilayer**. These bilayers form with the nonpolar, hydrophobic, tails towards the center of the bilayer and the polar, hydrophilic, head towards the outsides of the bilayer (one side out to the inside of the cell, and on side to the outside of the cell). The model for biological membranes is called the **fluid mosaic model** because the lipid bilayer is not a rigid fixed structure. This is due to the cis double bonds in the phospholipids that do not fit closely together. **ATP** is used in active transport to move Na+ and K+ ions against he concentration gradient. Facilitated diffusion is used for Cl-, HCO3-, and glucose molecules. Diffusion can be used for O2, urea, and water.

-Struggling Topic 1: Usually I teach my students that the size of the molecules is the primary reason why some molecules must use facilitated diffusion rather than diffusion. Why then does Cl- need facilitated diffusion when water, O2, and urea can diffuse through the membrane. Wouldn't Cl- be smaller than urea and water?

-Struggling Topic 2: Active transport is used mostly to move Na+ and K+ ions against their concentrations into and out of the cells. What other molecules are commonly transported using active transport and ATP?

A. How clearly the author communicated individual topics -17.7 - the author did a good job communicating examples and of steroid molecules in the body. These are present in cholesterol, bile salts, hormones, and lipoproteins. The author also gave many specific examples of these compounds and showed how they are used in the body.
 * __Critiques of this chapter:__**

B. Specifics about the amount of content (did you need more examples?) -17.6 - this section included many new types of lipids that are used in the body, and each group was given at least one example and use in the body. If these are to be understood as part of a group of many molecules, then we should be exposed to more than one example from each group. The way it was presented suggests to me that only the few examples that were presented are initially relevant to my understanding of the group's properties.

C. Chapter's place in the overall text -16.3 - it is appropriate that 16.3 comes after learning about alcohols, aldehydes, and ketones because writing the esterification equations requires familiarity with these other organic compounds. It would be far to challenging to introduce esterification without first having built an understanding of alcohols and aldehydes.