The question states that molecule A is heavier than molecule B. This could result from several reasons. First, molecule A could be a double stranded DNA and molecule B could be a single stranded RNA. This will allow the DNA molecule to be a lot heavier than its RNA counterpart. Second, molecule A could contain more purines (adenine and guanine) than molecule B). Recall that purines are two membered rings whereas pyrimidines (uracil, cytosine and thymine) are one membered rings. This means purines have more atoms and, therefore, have a higher molecular weight.

We are not given enough information to determine the identity or the distribution of nitrogenous bases in molecule A and B; therefore, we cannot conclude any of the given statements.

DNA and RNA molecules contain four types of nitrogenous bases. Guanine, cytosine and adenine are found in both whereas thymine is only found in DNA and uracil is only found in RNA. This means that DNA molecules will have more Thymine bases than RNA molecules. Another difference between DNA and RNA molecule is the type of pentose sugar. RNA contains ribose sugar whereas DNA contains deoxyribose. Deoxyribose contains one less hydroxyl group than ribose; therefore, DNA molecules have more deoxygenated sugars than RNA.

Think of it as this. CUT the PY (pie) PYrimidines. PURe As Gold. PURines. A will pair with T (and U in RNA). G will pair with C. The deamination of cytosine makes uracil, which is in RNA. 

In a biochemistry course, we often rely on important information that was learned during general and organic chemistry. One important concept to remember is chirality. A molecule is chiral if it is not superimposable on its mirror image. These molecules lack a plane of symmetry.  

It is a common mistake for students to think that all amino acids are chiral. While most amino acids are chiral, glycine is in fact achiral. Remember, the side chain on glycine is simply a hydrogen. The central carbon therefore is connected to two hydrogens, and is not a stereocenter.

Spinghomyelin has a head group of phosphotidylcholine, which makes sphingomyelin a phospholipid. None of the other lipids have phosphates, and therefore are not phospholipids. 

To answer this question we need to recall the structure of the different macromolecules. Proteins are made up of amino acids, nucleic acids are made up of nitrogenous bases, phosphate groups and 5-carbon sugars, carbohydrates are made up of monosaccharides, and most of the lipids are made up of a three-carbon glycerol molecule attached to varying numbers of fatty acids and other molecules. If there are three fatty acids attached to three of the carbons of glycerol, then it is classified as a triglyceride. If there are two fatty acids and a phosphate group, then it is a phospholipid; therefore, the molecule mentioned in this question is phospholipid. Recall that phospholipids are mainly found in cellular membranes, such as plasma membrane.

Note that certain lipids such as cholesterol and sphingolipids don’t have 3-carbon backbone molecule with fatty acids. They are organized in a different manner. Cholesterol is a ring structure with four rings and hydroxyl group whereas sphingolipids are synthesized from sphingosine.

Recall that there are four main nonpolar vitamins (lipids): vitamins A, D, E, and K. Vitamin A is an important vitamin for proper functioning of eye and can be found in foods containing carotene, such as carrots. Vitamin D is involved in the absorption of key minerals such as iron, calcium, and phosphate. It is usually obtained through sun exposure. Vitamin E is an antioxidant and is used to prevent the effects of reactive oxygen species (free radicals). Finally, Vitamin K is a clotting factor that is essential to repair and clot damaged endothelial walls and tissue.

Decreased levels of lipids will actually increase the absorption of these essential lipid vitamins. The body will try to absorb even the slightest amount of vitamins in diet to compensate for the depletion of these vitamins; therefore, the rate of absorption of Vitamin D will increase.

Phospholipids, as the name implies, require a phosphate head group attached to two fatty acid tails. Their polar phosphate head groups and non-polar fatty acid tails are perfect for a bi-layer membrane, where 2 layers of phospholipids are arranged such that their non-polar tails face each other and their polar phosphate head groups face outwards.

The correct answer is "sterols." The most common sterol in animals is cholesterol, which is an important structural component of cell membranes and the precursor to steroid hormones. Acetyl-CoA is not a lipid but is a precursor to cholesterol itself. The other answers are lipids with other functions. While phospholipids are an important part of cell membranes, they are not precursors to steroid hormones.

Glucose is a monosaccharide that is utilized for energy production in cells. Decrease in glucose levels in blood and tissues will lead to decreased production of energy (ATP) and, subsequently, will cause the person to be lethargic. Recall that glucose undergoes glycolysis to create products that will eventually undergo Krebs cycle and/or oxidative phosphorylation to generate ATP.

Glycogen is a storage molecule found typically in liver. It is made up of numerous glucose molecules bonded together by glycosidic bonds. If there is a decrease in blood glucose levels, liver initiates the breakdown of glycogen to individual glucose molecules and deposits these molecules in the blood; therefore, this patient’s liver will break down glycogen and create individual glucose molecules.

Fatty acid is another type of macromolecule used to synthesize energy. If there is a decrease in levels of glucose, fatty acids from adipose tissue and muscle will be mobilized and released into the blood. These fatty acids will now travel to tissues and supply energy (by generating ATP).