AP Biology : Identify structure and purpose of carbohydrates, lipids, proteins, and nucleic acids

Study concepts, example questions & explanations for AP Biology

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Example Questions

Example Question #73 : Biochemical Concepts

Which of the following are not hydrophilic molecules?

Possible Answers:

Nucleic acids

Starch

Lipids

Sugar

Amino acids

Correct answer:

Lipids

Explanation:

Hydrophilic means "water loving." Hydrophobic means "water fearing." Recall from your general chemistry, "like dissolves like" with regards to solubility. This means that hydrophobic molecules can be dissolved in hydrophobic solvents, and vice versa. Lipids such as oil and cholesterol are hydrophobic molecules and are thus insoluble in water. A good rule of thumb is that all acids are soluble in water. We know sugar is soluble in water, and starch has a similar molecular structure as sugar; it consists of many sugar molecules in a chain.

Example Question #42 : Macromolecules

A(n) __________ fat contains no double bonds in the fatty acid chain.

Possible Answers:

Phosphorylated

Trans

Unsaturated

Saturated

Cis

Correct answer:

Saturated

Explanation:

A saturated fat contains no double bonds in its fatty acid chain. Just remember that saturated means the fat is saturated with hydrogens. Double bonds eliminate two hydrogen atoms per occurrence, and are present in unsaturated fats.

Example Question #12 : Identify Structure And Purpose Of Carbohydrates, Lipids, Proteins, And Nucleic Acids

How many fatty acid chains do phospholipids have?

Possible Answers:

Three

Four

One

Two

Correct answer:

Two

Explanation:

Phospholipids contain two fatty acid chains bound to a hydrophilic head (usually glycerol). Fats (triglycerides) contain three.  

Example Question #75 : Biochemical Concepts

How many fatty acid chains are contained in a typical molecule of "body fat?"

Possible Answers:

One

Two

Four

Three

Correct answer:

Three

Explanation:

Body fat, also known as triglycerides or triacylglycerols have three fatty acid chains. These hydrocarbon tails are hydrophobic, and they are each attached to the glycerol head, which is hydrophilic via ester linkages. Adipose tissue is a type of connective tissue that plays a structural and protective role, provides stored energy, and helps regulate body temperature.  

Example Question #14 : Identify Structure And Purpose Of Carbohydrates, Lipids, Proteins, And Nucleic Acids

A lipid with three fatty acids linked to glycerol is a __________.

Possible Answers:

phospholipid

triglyceride

steroid

diacylglycerol

Correct answer:

triglyceride

Explanation:

A fat is a lipid with three fatty chains linked by an ester linkage to glycerol.

Example Question #51 : Macromolecules

A chain of 4 to 28 carbons with a carboxyl group at one end is a __________.

Possible Answers:

fatty acid

phospholipid

polypeptide

steroid

Correct answer:

fatty acid

Explanation:

A fatty acid consists of a hydrocarbon chain (carbons bound to hydrogen), with even numbers of carbons from 4 to 28, and a carboxyl group at one end. A triglyceride consists of three fatty acids with their carboxyl end bound to glycerol via an ester bond.

Example Question #52 : Macromolecules

The heads of phospholipids are __________.

Possible Answers:

hydrophilic

hydrocarbons

lipophilic

hydrophobic

Correct answer:

hydrophilic

Explanation:

The heads of phospholipids contain a glycerol group and a phosphate group. Both of these groups contain atoms other than hydrogen and carbon, so they are not hydrocarbons. Since phosphate is negatively charged, and glycerol contains oxygens, this part of the molecule is water soluble. In other words, it is hydrophilic, lipophobic, and polar. 

Example Question #53 : Macromolecules

In a cell membrane, phospholipids are arranged in a __________.

Possible Answers:

micelle

bilayer

monolayer

trilayer

Correct answer:

bilayer

Explanation:

Phospholipids are arranged in bilayers with the hydrophilic heads of pointing out towards the aqueous solutions inside and outside the cell. The hydrophobic tails point towards each other and are in the interior of the membrane. This unique structure allows cells to be water soluble, yet have a protective membrane that is selectively permeable to small, uncharged, hydrophobic molecules such as gasses and steriod hormones. Micelles are spheres of fatty acids in solution, where their heads are on the surface of the sphere, and their tails aggregate in the center of the sphere, avoiding the aqueous environment. Micelles are usually formed by lipids with single fatty acid tails, not two, as is seen in phospholipids. 

Example Question #12 : Identify Structure And Purpose Of Carbohydrates, Lipids, Proteins, And Nucleic Acids

A lipid that consists of two fatty acids and a phosphate group linked to glycerol is a __________.

Possible Answers:

monoglyceride

carbohydrate

steroid

phospholipid

Correct answer:

phospholipid

Explanation:

A phospholipid has two fatty acid tails, which consist of hydrocarbons with even numbers of carbons ranging from 4 to 28, and a phosphate group attached to a glycerol head, which is hydrophilic. Monoglycerides contain only one fatty acid chain bound to a glycerol head, and triglycerides contain three fatty acid chains. 

Example Question #18 : Identify Structure And Purpose Of Carbohydrates, Lipids, Proteins, And Nucleic Acids

What is the resulting molecule if a triacylglycerol has one of its fatty acid chains replaced with a phosphate group?

Possible Answers:

Saturated fatty acid

Diglyceride

Phospholipid

Steroid

Correct answer:

Phospholipid

Explanation:

A fat (triglyceride/triacylglycerol) consists of three fatty acids linked to glycerol. A phospholipid consists of two fatty acids and a phosphate group linked to glycerol. Thus removing a fatty acid from a triglyceride and replacing it with a phosphate group will yield a phospholipid. Diglycerides contain similar structures to triglycerides, but only have two fatty acid chains bound to the glycerol head. Steroids are lipids, but do not contain fatty acids. Rather they contain four hydrocarbon rings, and they are all derived from cholesterol. The saturation of a fatty acid refers to the presence of hydrogens anywhere they can potentially be present. A saturated fatty acid is said to be saturated with hydrogens.

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