Deck 2: Molecules and Membranes

Question 1

Water is an ideal solvent in cells because it

A) has low heat of vaporization.
B) is a polar molecule that can form hydrogen bonds with itself and with other polar molecules.
C) dissolves nonpolar molecules.
D) contracts when it freezes.

Answer 1

B

Question 2

In polysaccharides, sugars are linked together by means of _______ bonds.

A) phosphodiester
B) peptide
C) glycosidic
D) hydrophobic

Answer 2

C

Question 3

Sugars can cyclize if they contain _______ or more carbons.

A) four
B) five
C) six
D) seven

Answer 3

B

Question 4

A few sugars joined together are called a(n)

A) glycoside.
B) oligosaccharide.
C) polysaccharide.
D) starch.

Question 5

The major bonds in glycogen are _______ glycosidic bonds.

A) α(1→4)
B) α(1→6)
C) β(1→4)
D) β(1→6)

Question 6

Cell membranes are composed principally of

A) carbohydrates.
B) nucleic acids.
C) phospholipids.
D) proteins.

Question 7

Lipids play a major role in cells as

A) a form of energy storage.
B) components of cell membranes.
C) part of the cell signaling function.
D) All of the above

Question 8

Fatty acids are stored in fat droplets in the form of

A) triacylglycerols.
B) phospholipids.
C) cholesterol.
D) glycolipids.

Question 9

Which of the following molecules stores the most chemical energy per unit of weight?

A) Carbohydrates
B) Lipids
C) Proteins
D) Nucleic acids

Question 10

Sphingomyelin contains two hydrocarbon chains linked to

A) glycerol.
B) choline.
C) serine.
D) glycine.

Question 11

An amphipathic molecule is

A) water-soluble.
B) water-insoluble.
C) part water-soluble and part water-insoluble.
D) hydrophilic.

Question 12

RNA in cells can serve as a

A) regulator of gene expression.
B) carrier of information from the nucleus to the cytoplasm.
C) catalyst or enzyme.
D) All of the above

Question 13

Complementary base pairs form _______ bonds to direct replication of DNA.

A) hydrogen
B) phosphodiester
C) glycosidic
D) covalent

Question 14

Which of the following is not a way in which DNA differs from RNA?

A) DNA contains deoxyribose sugars.
B) DNA is usually a double-stranded molecule.
C) DNA contains thymine as one of its bases.
D) DNA can form hydrogen bonds with complementary sequences.

Question 15

Nucleotides function in cells as all of the following except

A) building blocks of nucleic acids.
B) carriers of chemical energy.
C) intracellular signal molecules.
D) defenders against infection.

Question 16

In DNA,

A) G pairs with T and A pairs with C.
B) G pairs with A and C pairs with T.
C) G pairs with C and A pairs with T.
D) G pairs with C and U pairs with A.

Question 17

Polymerization of nucleotides to form nucleic acids involves the formation of _______ bonds.

A) peptide
B) phosphodiester
C) glycosidic
D) hydrogen

Question 18

The main difference between double-stranded DNA (dsDNA) and single-stranded DNA (ssDNA) is that

A) dsDNA has bases that include thymine (T), while ssDNA has bases including uracil (U).
B) dsDNA has strands oriented in an antiparallel fashion, while ssDNA does not.
C) dsDNA cannot undergo translation while ssDNA can leave the nucleus to undergo translation.
D) dsDNA has 5' to 3' polarity while ssDNA does not.

Question 19

A researcher is trying to determine the contents of a viral genome. Upon chemical analysis, the nucleic acid is found to contain 27% cytosine, 27% adenine, 23% uracil, and 23% guanine. Based on this data, the viral genome most likely consists of

A) single-stranded DNA.
B) double-stranded DNA.
C) single-stranded RNA.
D) double-stranded RNA.

Question 20

Serine, threonine, asparagine, and glutamine are all _______ amino acids.

A) basic
B) acidic
C) polar
D) nonpolar

Question 21

Which of the following is not a basic amino acid?

A) Arginine
B) Glutamine
C) Histidine
D) All of the above are basic amino acids.

Question 22

Proteins are polymers of how many different amino acids?

A) 16
B) 20
C) 24
D) 36

Question 23

In the primary structure of a protein, amino acids are joined together by _______ bonds.

A) peptide
B) phosphodiester
C) glycosidic
D) hydrophobic

Question 24

The scientist who first determined the complete amino acid sequence of a protein (insulin) was

A) Christian Anfinsen.
B) Frederick Sanger.
C) Linus Pauling.
D) John Kendrew.

Question 25

Anfinsen's experiments on denatured ribonuclease showed that

A) protein denaturation is irreversible.
B) proteins can renature to regain their activity only with the assistance of specialized enzymes.
C) proteins have unique amino acid sequences.
D) the conformation of the folded protein is determined by its amino acid sequence.

Question 26

Which of the following are involved in forming the tertiary structure of proteins?

A) H bonds
B) Hydrophobic interactions
C) Ionic bonds
D) All of the above

Question 27

The interaction of two α and two β subunits to form a functional hemoglobin molecule is an example of _______ structure.

A) primary
B) secondary
C) tertiary
D) quaternary

Question 28

Like other catalysts, enzymes

A) increase the rate of reactions without being consumed in reactions.
B) shift the chemical equilibrium from more reactants to more products.
C) do not alter the chemical equilibrium between reactants and products.
D) Both a and c

Question 29

Enzymes act by

A) lowering the overall free energy change of a reaction.
B) decreasing the distance reactants must diffuse to find each other.
C) increasing activation energy.
D) decreasing activation energy.

Question 30

A reaction in which the substrate glucose binds to the enzyme hexokinase and the configuration of both molecules changes is an example of

A) a lock-and-key mechanism.
B) an induced fit mechanism.
C) competitive inhibition.
D) allosteric inhibition.

Question 31

Because of the central role that one amino acid plays in the mechanism by which proteins are cleaved by the enzymes trypsin and chymotrypsin, these enzymes are called _______ proteases.

A) histidine
B) lysine
C) arginine
D) serine

Question 32

The trypsin substrate binding site contains an aspartate residue, which is able to form an ionic bond with which amino acids in its polypeptide substrates?

A) Lysine or arginine
B) Glutamate or glutamine
C) Leucine or phenylalanine
D) Serine or threonine

Question 33

Coenzymes are

A) enzymes in the same pathway.
B) proteins that form dimeric enzymes.
C) small molecules that work with an enzyme to enhance reaction rate.
D) small molecules that allosterically regulate enzymes.

Question 34

Which statement describes the most common relationship of the inhibitor molecule to the allosteric enzyme in feedback inhibition of enzyme activity?

A) The inhibitor is the substrate of the enzyme.
B) The inhibitor is the final product of the metabolic pathway.
C) The inhibitor is the product of the enzyme-catalyzed reaction.
D) The inhibitor is a metabolically unrelated signal molecule.

Question 35

In allosteric regulation, binding of a small regulatory molecule to an enzyme _______ enzyme activity.

A) inhibits
B) stimulates
C) may stimulate or inhibit
D) neither stimulates nor inhibits

Question 36

Proteins can be covalently modified by the addition of phosphate groups to all but which of the following amino acids?

A) Arginine
B) Threonine
C) Serine
D) All of the above

Question 37

The fundamental building block of cellular membranes is

A) the glycolipid.
B) the phospholipid.
C) cholesterol.
D) protein.

Question 38

Common factors affecting membrane fluidity include

A) length of phospholipid fatty acid chains.
B) temperature.
C) number of double bonds in the fatty acid chains.
D) All of the above

Question 39

Cholesterol affects membrane fluidity by

A) increasing membrane fluidity at all temperatures.
B) decreasing membrane fluidity at all temperatures.
C) decreasing membrane fluidity at high temperatures and increasing membrane fluidity at low temperatures.
D) increasing membrane fluidity at high temperatures and decreasing membrane fluidity at low temperatures.

Question 40

Phospholipids in a membrane commonly

A) move laterally in the plane of the bilayer.
B) rotate within the bilayer.
C) move from one bilayer to the other.
D) Both a and b

Question 41

The role of double bonds in the fatty acid tails of membrane phospholipids is to

A) help stabilize the membrane.
B) react with adjacent double bonds.
C) increase membrane fluidity.
D) interact with membrane proteins.

Question 42

The currently accepted model of membrane structure is called the _______ model.

A) lipid bilayer
B) unit membrane
C) lipid raft
D) fluid mosaic

Question 43

The fluid mosaic model of cell membranes was proposed by

A) Frye and Edidin.
B) Singer and Nicolson.
C) Gorter and Grendel.
D) Watson and Crick.

Question 44

The unique functions of different membranes are primarily due to their

A) proteins.
B) phospholipids.
C) cholesterol molecules.
D) glycolipids.

Question 45

The mitochondrial inner membrane is about _______ protein.

A) 0%
B) 10%
C) 42%
D) 75%

Question 46

Integral membrane proteins are those that

A) directly associate with membrane lipids.
B) associate with the membrane indirectly.
C) do not span the lipid bilayer.
D) None of the above

Question 47

Transmembrane proteins that span the membrane are

A) peripheral membrane proteins.
B) covalently linked to membrane lipids.
C) integral membrane proteins.
D) active transporters.

Question 48

Transmembrane proteins can span the lipid bilayer as

A) α helices.
B) β turns.
C) unstructured chains.
D) Both a and c

Question 49

Membrane proteins can be anchored to the cytosolic face of the plasma membrane by

A) sugar groups of glycolipids.
B) prenyl groups.
C) sugar groups of glycoproteins.
D) None of the above

Question 50

Phospholipid bilayers are permeable only to molecules that are _______ and _______.

A) large; uncharged
B) large; charged
C) small; uncharged
D) small; charged

Question 51

Passive transport molecules

A) allow small molecules across membranes.
B) are peripheral proteins.
C) can transport against a concentration gradient.
D) use the energy of ATP to transport molecules.

Question 52

Molecules that traverse a membrane against their concentration gradient do so by _______ transport.

A) active
B) passive
C) carrier-mediated
D) channel-mediated

Question 53

Channels form pores through which molecules of appropriate size and charge can cross a membrane. By contrast, carrier proteins

A) actively transport molecules.
B) selectively bind the molecule to be transported, change configuration, and release it on the other side.
C) require ATP.
D) transport a molecule against its concentration gradient.

Question 54

Plants store glucose in the form of _______, and animals store glucose in the form of _______.

Question 55

Because phospholipids consist of hydrophobic hydrocarbon chains and hydrophilic head groups, they are _______ molecules.

Question 56

Steroid hormones are derivatives of the membrane lipid _______.

Question 57

RNA contains uracil in place of the _______ found in DNA.

Question 58

Polymerization of DNA and RNA always occurs in the _______ direction.

Question 59

The purine base adenine is found in DNA and in the principal form of chemical energy in cells, _______.

Question 60

The side chains of basic amino acids such as lysine and arginine are _______ charged while those of acidic amino acids such as aspartic acid and glutamic acid are _______ charged at normal cellular pH.

Question 61

In most proteins, α helices and β sheets fold into globular domains with _______ on the inside.

Question 62

The two polypeptide chains in insulin are held together by _______ bonds.

Question 63

Proteins associated with a membrane by protein-protein interactions are called _______.

Question 64

Under the mild conditions of temperature and pressure that are compatible with life, most biological reactions are so slow that they would not occur in the absence of _______.

Question 65

Enzymes increase reaction rates without either being _______ themselves or altering the _______ of the reaction.

Question 66

Enzymes reduce the _______ energy required to reach the _______ state in a chemical reaction.

Question 67

Coenzymes serve as _______ of several types of chemical groups.

Question 68

In allosteric regulation of enzyme activity, the regulatory molecules bind to a site that is _______ from the active site of the protein, producing a _______ change in the protein that affects substrate binding to the active site.

Question 69

The formation of cell membranes is based on the capacity of _______ to form a _______.

Question 70

Integral membrane proteins typically possess _______ segments of 20−25 amino acids that traverse the membrane and are rich in _______ amino acids.

Question 71

Cell membranes are _______ permeable to small, uncharged molecules, while transport of larger polar or charged substances through membranes occurs via _______ or _______ proteins.

Question 72

Most proteins interact with other proteins through covalent protein-protein interactions.

Question 73

The function of glycogen, starch, and cellulose is to store glucose.

Question 74

The glucose molecules in cellulose are joined by β(1→4) bonds.

Question 75

Cholesterol is an amphipathic molecule.

Question 76

Each membrane phospholipid contains 3 fatty acid chains.

Question 77

Sphingomyelin is a serine-based phospholipid.

Question 78

RNAs can be enzymes.

Question 79

Christian Anfinsen and colleagues showed in the 1950s that proteins contain all the information to spontaneous fold into an active enzyme. Yet sixty years later, we can still not predict the three-dimension shape of a protein from its amino acid sequence.

Question 80

Enzymes accelerate reactions and affect the end equilibrium concentration of reactants and products.