CHEM 153A Midterm 2 Exam Questions with Correct Answers Latest Update 2025/2026

CHEM 153A Midterm 2 Exam Questions with Correct Answers Latest Update 2025/2026 Rotate the bond of the linear sugar, tip it on its side, the hydroxyl at C5 acts as a nucleophile and attacks the carbonyl. - Answers What mechanism allows for the formation of cyclic sugars? They differ only in the newly formed chiral carbon (after ring formation). Can be α vs β. Glucose the α anomer is trans and the β anomer is cis (both pointing up!) - Answers What are anomers? Cyclization is a reversible process. Depending on what side the nucleophile attacks, the orientation of the OH on the C1 can be pointing up or down. - Answers How can the sugar anomers interconvert? - Answers α-D-Glucopyranose - Answers β-D-Glucopyranose the connection to other monosaccharides - Answers What does the anomeric carbon serve as? It can as long as it is not the monomer using the anomeric carbon to bind. Whichever molecule that is using the anomeric carbon in a bond is the one that cannot linearize and switch forms. If both anomeric carbons (the carbons bound to two oxygens) are blocked it cannot linearize since the ring cannot open or close. - Answers Can a given sugar linearize and switch forms? covalent bonds that form between the hemiacetal group of a carbohydrate and a hydroxyl group on another compound (like other carbohydrates). This is how polysaccharides form. - Answers Glycosidic bonds lactose - Answers β-1,4-glycosidic bonds maltose - Answers α-1,4-glycosidic bond sucrose - Answers α-1, β-2-glycosidic bond polysaccharide of β-D-glucose that's used for structure in plants. Has an alternating structure. Has β-1,4 linkages that can form strong intrachain and interchain hydrogen bonds. - Answers Cellulose Nope! - Answers Can human enzymes break down β linkages? The alternating structure of cellulose causes the hydrogens to be in an optimal position to form strong intrachain and interchain hydrogen bonds. - Answers How does the structure of cellulose affect its strength? a polysaccharide of α-D-glucose that's used for energy storage in plants. It is a starch. Human enzymes can break down α linkages and utilize for energy. Just regular 1,4 linkages. - Answers Amylose amylose is not a straight chain. It's in a helix because the helix optimizes H bonding and makes the structure more stable. There is about 8 glucose residues per turn. - Answers is amylose straight chain or branched? a polysaccharide of α-D-glucose that's used for energy storage in animals. Has α-1,4 and α-1,6 every 8-10 residues creating a branch - Answers Glycogen It is branched since multiple branches reduce the time it takes for breakdown and utilization. - Answers Is Glycogen branched or straight chained? a class of organic compounds that are insoluble in water, and soluble in organic solvents. - Answers Lipids they are part of cell membranes - Answers How are lipids useful in structure? They are long term energy stores compared to carbohydrates since they are harder to break down and utilize. They need to be broken down and used in cellular respiration. - Answers How do lipids compare to carbohydrates as energy stores? carboxylic acids with open chains. Can be saturated or unsaturated based on whether they have double bonds. - Answers Fatty acids fatty acid that contains more than one double bond in its backbone - Answers polyunsaturated fatty acid Count the number of carbons in the entire chain starting from the carboxylic acid. Count the number of double bonds in the entire chain. Counting back from the last carbon in the fatty acid, find the first carbon with a double bond. - Answers Omega naming If there are more carbons in a fatty acid chain, the LDFs are happening between fatty acids. If there are more LDFs, it takes more energy to break them apart. Hence why when there are more carbons in a fatty acid, the melting point is higher. - Answers What is the relationship between length of a fatty acid and melting point? Double bonds create kinks in the fatty acid structure, since they're cis. Unsaturated fatty acids cannot align properly with other fatty acids because of those kinks. This causes melting point to decrease, because the IMFs between fatty acid chains are not as strong since they cannot align as closely to form those strong LDFs. - Answers What is the relationship between degree of unsaturation and melting point? esters derived from glycerol and three fatty acids, constitute 90% of dietary lipids, major form of metabolic energy in humans. AKA TAGs - Answers Triacylglycerols TAGs are long term energy storage, while carbohydrates are short term. TAGs are less oxidized than carbohydrates, which makes them better for energy storage. - Answers How do TAGs compare with carbohydrates as energy storage molecules? TAGs are broken down during lipolysis, where they are broken into their individidual fatty acids and glycerol. Those fatty acids are fed into beta oxidation, which oxidizes the fatty acid to reduce NAD+/FAD and generate acetyl-CoA. 1 acetyl-CoA is generated per 2 carbon atoms, so the longer the fatty acid, the more energy it can produce. - Answers How are TAGs broken down? What is the basic metric telling you how much energy (relative amount, not absolute) you can get from a TAG? Increase osmotic pressure because they are hydrophilic, which why they are in chains and not just existing as free monosaccharides. Their hydrophilicity also makes them easier to transport. - Answers How do carbohydrates affect osmotic pressure? They do not increase it by much since they are hydrophobic. This makes them harder to transport. - Answers How do TAGs affect osmotic pressure? Lipoproteins - Answers How do lipids get transported? a composite structure, a phospholipid monolater wuth several apolipoproteins. The inside is packed with various lipids but mostly TAGs and cholesterol. - Answers Lipoproteins Membranes form spontaneously in aqueous environments with the right lipids that have the right fatty acid chain length. - Answers How do membranes form? phospholipid bilayer - Answers The cell membrane is comprised of ions, because they can't pass through the hydrophobic environment. They require ion channels to get through. - Answers Cell membranes have low permeability for