First exam

Question 1

Oils are lipids. Which statement best explains why oil and water don’t mix?
Responses

If you try to mix oil and water, the two will separate almost immediately.

Oils and waxes are frequently used as water repellents—often as a coating on the surface of furniture or automobiles.

The C-C and C-H bonds that dominate oil molecules interact with each other—not water.

Answer 1

The C-C and C-H bonds that dominate oil molecules interact with each other—not water.

Question 2

Explain how saturation relates to hydrophobic interactions

Answer 2

Lipids:
Saturated hydrocarbon chains pack together more tightly than unsaturated chains, so are held together more tightly by hydrophobic interactions.

Question 3

Lipids vary a great deal in fluidity. Waxes, for example, are solid at room temperature while oils are liquid. Predict which of the following attributes are typical of the hydrocarbon chains in waxes versus more-fluid lipids. Select all that apply.
Responses

The hydrocarbon chains of waxes are saturated; those found in oils are not.

The hydrocarbon chains of waxes are polyunsaturated—meaning that they contain more than one double bond.

The hydrocarbon chains of waxes are longer than the chains found in oils.

Unlike oils, the hydrocarbon chains of waxes contain atoms other than C and H.

Answer 3

The hydrocarbon chains of waxes are saturated; those found in oils are not.
The hydrocarbon chains of waxes are longer than the chains found in oils.
Unlike oils, the hydrocarbon chains of waxes contain atoms other than C and H.

Question 4

Fats contain highly electronegative oxygen atoms, which carry a partial charge. Which of the following is the most logical explanation for why fats are not soluble in water?
Responses

Numbers and geometry: C-O and O-H bonds are very few in number compared with nonpolar bonds, and the few O atoms are “buried” by hydrophobic groups.

The oxygen atoms in fats are less electronegative than the oxygen atoms in water, so carry less of a partial charge.

If fats were soluble in water, they could not perform their various functions in organisms, starting with energy storage and metabolism.

Answer 4

Numbers and geometry: C-O and O-H bonds are very few in number compared with nonpolar bonds, and the few O atoms are “buried” by hydrophobic groups.

Question 5

Each fatty acid found in a fat consists of a long hydrocarbon chain that ends in a carboxl group (COOH, or O=C-OH). Why is “fatty acid” an appropriate name?
Responses

Fats vary in structure because they can contain more than one type of fatty acid, and because fatty acids vary in the length and saturation of their hydrocarbon chains.

“Fatty” refers to the long hydrocarbon chain; the carboxyl group acts as an acid by dropping a proton, just like the carboxyl groups in amino acids.

Carbon can form a total of four covalent bonds, so the C in the carboxyl group of a fatty acid can form a C-C bond with the hydrocarbon chain.

Answer 5

“Fatty” refers to the long hydrocarbon chain; the carboxyl group acts as an acid by dropping a proton, just like the carboxyl groups in amino acids.

Question 6

Why is “phospholipid” an appropriate name?
Responses

These molecules contain a phosphate group (“phospho”) and a hydrocarbon tail that does not interact with water (“lipid”).

The two hydrocarbon chains that make up the tail can be long or short and saturated or unsaturated.

The head region has a polar group that adds to the strongly hydrophilic nature of the phosphate group.

Answer 6

These molecules contain a phosphate group (“phospho”) and a hydrocarbon tail that does not interact with water (“lipid”).

Question 7

Cholesterol is an example of what class?

Answer 7

Steroids: type of lipid

Question 8

The R-groups on the amino acids that make up either end of the molecule carry full charges or polar groups. But the R-groups that hang off the a-helix in the middle of this molecule are not polar or charged. Is this molecule amphipathic?

Responses

Yes, because the entire molecule is hydrophilic.

Yes, because some regions are polar and will interact with water while other regions are not polar and will not interact with water.

No, because more than one region is polar.

Yes, because the entire molecule is hydrophobic.

Answer 8

Yes, because some regions are polar and will interact with water while other regions are not polar and will not interact with water.

Question 9

How do amphipathic lipids behave in water?

Answer 9

vesicle formation:
The hydrophobic tails of the phospholipids interact with each other, while the hydrophilic heads interact with water molecules inside and outside the vesicle.

Question 10

Which of the following is the best characterization for a process that is spontaneous?

Answer 10

It is energetically favorable and results in products that are more stable.

Question 11

What does it mean to say that vesicle formation is spontaneous?

Answer 11

phospholipids “naturally” form vesicles in water because they are more stable that way. The stability is based in
part on 1) hydrophobic interactions among the hydrocarbon tails on phospholipids in a bilayer
part 2) on hydrogen bonding between water molecules and the hydrophilic heads on phospholipids.

Question 12

lipid:

Answer 12

Lipid: A molecule that does not dissolve in water.

Question 13

Indicate which of the following statements about C, O, H, and N atoms are correct.

The number of covalent bonds each can form is hydrogen (1), oxygen (2), nitrogen (3), and carbon (4).

O is so electronegative that all of the covalent bonds it forms are polar — even the O=O double bonds in atmospheric oxygen (O2).

Their relative electronegativities are C = H < N &laquo_space;O.

Nitrogen is found in nucleotides and nucleic acids but not in amino acids or proteins.

C-C and C-H bonds are nonpolar, so organic molecules that contain all or mostly all C and H atoms don’t contain partial charges, can’t participate in H-bonds, and tend not to dissolve in

Answer 13

The number of covalent bonds each can form is hydrogen (1), oxygen (2), nitrogen (3), and carbon (4).

Their relative electronegativities are C = H < N &laquo_space;O.

C-C and C-H bonds are nonpolar, so organic molecules that contain all or mostly all C and H atoms don’t contain partial charges, can’t participate in H-bonds, and tend not to dissolve in

Question 14

Difference between ribose and deoxyribose?

Answer 14

ribose: sugar in deoxyribonucleic acid (DNA)
deoxyribose: sugar in ribonucleic acid (RNA)

Question 15

Suppose you are analyzing a glycan you have never seen before. Where would you find the glycosidic linkages?

Answer 15

Between each of the monosaccharide subunits in the long chain that forms the glycan.

Question 16

In your body, different types of cells (along with structures inside cells) are distinguished in part by specific, small glycans that are attached to their surfaces and function as “street addresses” or “zip codes.” Which of the following is the most logical explanation for why these glycans can function so effectively as unique molecular identifiers?

When long chains of monosaccharides are joined by b-glycosidic linkages and then bonded to each other in some way, they form tough structural sheets or fibers.

If a-glycosidic linkages form a branching network of glucose molecules, the resulting glycan can play an important role in energy storage and metabolism.

High variation in the structure of monosaccharides and how they attach to each other, along with differences in size, makes a large number of unique “addresses” or “zip codes” possible.

Answer 16

High variation in the structure of monosaccharides and how they attach to each other, along with differences in size, makes a large number of unique “addresses” or “zip codes” possible.

Question 17

Glycan:

Answer 17

a polymer made up of monosaccharides joined by glycosidic linkages.

Question 18

Carbohydrates:

Answer 18

a family of molecules that includes both monosaccharides and glycans.

Question 19

Life scientists point to two interrelated abilities to define life. What are they?

Answer 19

The ability to produce more new individuals
Metabolism (taking in resources and processing them into the products needed to sustain activity and grow)

Question 20

Are viruses alive?

Answer 20

No, Because they can only replicate by “stealing” resources from organisms, most biologists don’t consider them to be alive.

Question 21

What molecules are found in cell membranes?

Answer 21

The basic structure of a cell membrane is a phospholipid bilayer.

Question 22

What stabilizes the phospholipid bilayer in a cell membrane? (This is another way of asking, why does a phospholipid bilayer exist?) Select all that apply.
Responses

Hydrogen bonding between water molecules inside or outside the cell and polar or charged R-groups on proteins at the cell surface (either interior or exterior).

Hydrophobic interactions among the tails on phospholipids

Hydrogen bonding between hydrophilic heads on phospholipids and water molecules inside the cell.

Hydrophobic interactions between the tails on phospholipids and nonpolar R-groups on membrane proteins.

Answer 22

Hydrophobic interactions among the tails on phospholipids

Hydrogen bonding between hydrophilic heads on phospholipids and water molecules inside the cell.

Hydrogen bonding between hydrophilic heads on phospholipids and water molecules outside the cell.

Question 23

Why don’t fats form lipid bilayers and thus the basic structure of the cell membrane, instead of phospholipids? Choose the single best answer.
Responses

The hydrocarbon tails on fats are so long—and especially if the tails are saturated and thus straight—that they form strong hydrophobic interactions that stabilize fat as clumps or globules, not bilayers.

If the tails of lipids are long enough and straight enough—like waxes or butter—the hydrophobic interactions among lipids are strong enough to make them solid at room temperature.

Fats do not have polar or charged groups that can interact with water.

Question 24

Transmembrane proteins are amphipathic.

Answer 24

true