Biol 201- Chapter 2

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

-H bonds -Hydrophobic interactions -Ionic bonds

Lipids play a major role in cells as

-a form of energy storage. -components of cell membranes. -part of the cell signaling function

Like other catalysts, enzymes

-increase the rate of reactions without being consumed in reactions -do not alter the chemical equilibrium between reactants and products

Common factors affecting membrane fluidity include

-length of phospholipid fatty acid chains -temperature. -number of double bonds in the fatty acid chains

Phospholipids in a membrane commonly

-move laterally in the plane of the bilayer. -rotate within the bilayer

RNA in cells can serve as a

-regulator of gene expression. -carrier of information from the nucleus to the cytoplasm. -catalyst or enzyme

Proteins are polymers of how many different amino acids?

20

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

5ʹ to 3'

The mitochondrial inner membrane is about _______ protein

75%

Fully folded proteins typically have polar side chains on their surfaces, where electrostatic attractions and hydrogen bonds can form between the polar group on the amino acid and the polar molecules in the solvent. In contrast, some proteins have a polar side chain in their hydrophobic interior. Which of the following would not occur to help accommodate an internal, polar side chain?

A hydrogen bond forms between a polar side chain and an aromatic side chain

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

Active

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

Arginine

The pyrimidine bases in DNA are

Cytosine and Thymine

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

DNA can form hydrogen bonds with complementary sequences.

Approximately 50% of the chemical reactions in cells are catalyzed by enzymes

False

Each membrane phospholipid contains 3 fatty acid chains

False

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

False

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

False

One conclusion derived from the Singer and Nicolson fluid mosaic model of membrane structure is that integral membrane proteins are freely soluble in water

False

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

False

Sugars can cyclize if they contain _______ or more carbons.

Five

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

Frederick Sanger

In DNA

G pairs with C and A pairs with T

Which of the following is not a basic amino acid?

Glutamine

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

Glyosidic

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

Hydrogen

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

Lipids

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?

Lysine or arginine

A few sugars joined together are called a(n)

Oligosaccharide

The fluid mosaic model of cell membranes was proposed by

Singer and Nicolson.

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

The inhibitor is the final product of the metabolic pathway

Cholesterol is an amphipathic molecule.

True

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

True

Coenzymes function in conjunction with enzymes to carry chemical groups between substrates.

True

RNAs can be enzymes

True

Some enzymes participate directly in the chemical reactions they catalyze

True

Sphingomyelin is a serine-based phospholipid

True

The activity of enzymes can be controlled by the binding of small molecules, by interaction with other proteins, and by covalent modifications

True

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

True

The sugar groups of glycolipids and glycoproteins are found on the outer surface of the plasma membrane

True

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

activation; transition

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

adenosine 5ʹ-triphosphate (ATP)

Passive transport molecules

allow small molecules across membranes

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

alpha-helical; hydrophobic

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

amphipathic

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

an induced fit mechanism

Integral membrane proteins are those that

are directly associated with membrane lipids

Coenzymes serve as _______ of several types of chemical groups.

carriers

Steroid hormones are derivatives of

cholesterol

Steroid hormones are derivatives of the membrane lipid _______.

cholesterol

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

consumed (altered permanently, used up); equilibrium

Enzymes act by

decreasing activation energy

Cholesterol affects membrane fluidity by

decreasing membrane fluidity at high temperatures and increasing membrane fluidity at low temperatures

Nucleotides function in cells as all of the following except

defenders against infection

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.

distal (distant, far); conformational (shape)

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

disulfide

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

dsDNA has bases that include thymine (T), while ssDNA has bases including uracil (U).

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 _______.

enzymes (enzymatic catalysis)

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

fluid mosaic

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

hydrophobic amino acids

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

increase membrane fluidity

Transmembrane proteins that span the membrane are

integral membrane proteins

Water is an ideal solvent in cells because it

is a polar molecule that can form hydrogen bonds with itself and with other polar molecules

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

lipids (phospholipids, amphipathic lipids); bilayer (phospholipid bilayer)

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

may stimulate or inhibit

An amphipathic molecule is

part water soluble and part water insoluble

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

peptide

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

peripheral membrane proteins

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

phosphodiester

Cell membranes are composed principally of

phospholipids

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

polar

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.

positively (+); negatively (‒)

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

prenyl groups

The unique functions of different membranes are primarily due to their

proteins

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

quaternary

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

selectively bind the molecule to be transported, change configuration, and release it on the other side

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

selectively; channel (carrier); carrier (channel)

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

serine

Sphingomyelin contains two hydrocarbon chains linked to

serine

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

single-stranded RNA

Coenzymes are

small molecules that work with an enzyme to enhance reaction rate.

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

small; uncharged

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

starch; glycogen

Anfinsen's experiments on denatured ribonuclease showed that

the conformation of the folded protein is determined by its amino acid sequence

The fundamental building block of cellular membranes is

the phospholipid

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

thymine

Fatty acids are stored in fat droplets in the form of

triacylglycerol's

The most abundant molecules in cells are

water

Transmembrane proteins can span the lipid bilayer as

α helices

The major bonds in glycogen are _______ glyosidic bonds.

α(1→4)