Chapter 3
If a DNA double helix is 100 nucleotide pairs long and contains 25 adenine bases, how many guanine bases does it contain?
75
What do DNA, proteins, and fats have in common?
They contain carbonyl groups.
Which of the following is true of pleated sheet foldings within a polypeptide? -Its loops are held in place mainly by disulfide bridges. -They are part of the polypeptide's quaternary structure. -The side chains are parallel to the plane of the sheet. -They depend on regular occurrence of CO and NH. -All the above.
They depend on regular occurrence of CO and NH.
What do the three main forces that stabilize protein tertiary structure have in common?
They involve the side chains.
Why don't cells rely more on disulfide bridges to stabilize the folding of proteins?
They make the protein rigid. Many proteins change their shape as they work.
True or false? Enzymes in the digestive tract catalyze hydrolysis reactions.
True
True or false? Guanine and uracil are examples of nitrogenous bases.
True
True or false? Peptidoglycan is a polysaccharide found only in bacteria.
True
A function of cholesterol that does not harm health is its role _____.
as a component of animal cell membranes
Which of these is a polysaccharide? -sucrose -cellulose -galactose -glucose -lactose
cellulose
The secondary structure of a protein results from _____.
hydrogen bonds
The two strands of a DNA double helix are held together by _____ that form between pairs of nitrogenous bases.
hydrogen bonds
In the reaction that builds a fat,________ groups react with ________ groups.
hydroxyl; carboxyl
The amino acid lysine has an amino group in its side chain. In a protein, a scientist replaced every lysine with serine (side chain -CH2OH). The alteration made the protein's folding ...
less sensitive to pH.
What is the complementary DNA sequence to 5' ATGCATGTCA 3'?
5' TGACATGCAT 3'
_____ is the most abundant organic compound on Earth.
Cellulose
Which statement is true of organic molecules? -(a) An organic molecule can have many functional groups. -(b) Some organic molecules contain carbon atoms; others do not. -(c) Organic molecules are only made by living organisms. -Both (a) and (b). -(a), (b), and (c).
(a) An organic molecule can have many functional groups.
A food company hydrogenated a barrel of fat. The treatment ... -(a) made the fat less fluid. -(b) made the fat less saturated. -(c) lengthened the fat tails. -(d) put more bends (kinks) in the fat tails. -Both (a) and (d).
(a) made the fat less fluid.
Amino groups ... -(a) act as bases in water. -(b) contain nitrogen atoms. -(c) occur in proteins. -Just two of the preceding answers are true. -(a), (b), and (c).
(a), (b), and (c).
Polymers that contain sugars ... -(a) may store hereditary information. -(b) may store energy. -(c) may protect cells. -Both (b) and (c). -(a), (b), and (c).
(a), (b), and (c).
Some of the strongest biological structures (e.g., beaks and claws) are made of many molecules of the protein keratin. What else is true of structures made of keratin? -(a) Disulfide bridges bind the proteins together. -(b) Each protein is a single long alpha helix. -(c) Hair is another example. -Both (a) and (b). -(a), (b), and (c).
(a), (b), and (c).
Which statement is true of sucrose? -(a) It's a disaccharide. -(b) It contains glucose. -(c) It's table sugar. -Both (a) and (c). -(a), (b), and (c).
(a), (b), and (c).
Which statement expresses a real difference between DNA and RNA? -(a) DNA can make a double helix; RNA cannot. -(b) DNA is much longer than RNA. -(c) DNA has more kinds of bases than RNA. -Both (a) and (b). -(a), (b), and (c).
(b) DNA is much longer than RNA.
What do fats, steroids, and waxes have in common? -(a) Moderate polarity. -b) Low solubility in water. -c) They occur in membranes. -Both (a) and (c). -Both (b) and (c).
(b) Low solubility in water.
Which statement is true of nucleic acids? -(a) rRNA positions amino acids along mRNA. -(b) mRNA binds amino acids together to make proteins. -(c) mRNA is part of the ribosome. -(d) DNA carries information for making RNA. -Both (b) and (d).
(d) DNA carries information for making RNA.
A residue in the middle of a polypeptide has −CH3 as its side chain or R group. How many atoms does the residue contain?
10
If a strand of DNA has the nitrogen base sequence 5'-ATTTGC-3', what will be the sequence of the matching strand?
3'-TAAACG-5'
A phosphate group contains _________ oxygen atoms.
4
Which of the following statements about the formation of polypeptides from amino acids is true? -A bond forms between the carboxyl functional group of one amino acid and the amino functional group of the other amino acid. -The reaction occurs through the addition of a water molecule to the amino acids. -Polypeptides form by condensation or hydrolysis reactions. -A bond can form between any carbon and nitrogen atom in the two amino acids being joined.
A bond forms between the carboxyl functional group of one amino acid and the amino functional group of the other amino acid.
How does a carbonyl group differ from a carboxyl group?
A carboxyl group contains H; a carbonyl does not.
Which of the following is NOT true of protein quaternary structure? -A quaternary protein cannot have fewer than two carboxyl groups. -A single polypeptide may have quaternary structure. -Hydrogen bonds may hold the polypeptides in contact.
A single polypeptide may have quaternary structure.
Which linkage forms the backbone of a nucleic acid? -A sugar-base-phosphate linkage -A base-phosphate linkage -A sugar-base linkage -A sugar-phosphate linkage
A sugar-phosphate linkage
How does an aldehyde group differ from a ketone group?
Aldehydes, but not ketones, have H bound to C=O.
Which statement is true of phospholipids? -(a) Their synthesis uses fatty acids. -(b) Some of their tails have double bonds. -(c) They all ionize. -All the above. -Both (a) and (b).
All the above.
Which complex carbohydrate contains only a-1,4-glycosidic linkages? -Cellulose -Amylopectin -Glycogen -Amylose
Amylose
Which of the following is not attached to the central carbon atom in an amino acid? -An amino functional group -A carboxyl functional group -An oxygen -A side chain ("R group")
An oxygen
Which of the following complex carbohydrates is listed with its correct function? -Amylose: main component of plant starch -Chitin: constituent of bacterial cell walls -Starch: primary energy-storage molecule in animals -Cellulose: structural component of plant cell walls
Cellulose: structural component of plant cell walls
The presence of many C-C and C-H bonds causes fats to be ... -(a) rich in energy. -(b) insoluble in water. -(c) low in energy. -Both (a) and (b). -Both (b) and (c).
Both (a) and (b).
Which statement is true of the side chains that occur in proteins? -(a) Some of them contain only C and H. -(b) Some of them contain carboxyl groups. -(c) None of them join the backbone at more than one point. -Both (a) and (b). -All the above.
Both (a) and (b).
Which statement is true of hydroxyl groups? -(a) They ionize more often when bound to C=O than when bound to CH2. -(b) They are negative ions. -(c) All alcohols and sugars have them. -Both (a) and (c). -Both (a) and (b).
Both (a) and (c).
Fats vary with respect to the number of ...
C atoms in the tails and double bonds in the tails.
Which statement helps most to explain why life is based on carbon compounds? -C makes strong bonds with O. -Each C atom makes three covalent bonds. -C-C bonds are as strong as C-O bonds. -C is very abundant in non-living nature. -All of the above.
C-C bonds are as strong as C-O bonds.
Identify the empirical formula of a free amino acid whose side chain is just H. -C2H4O2N -C2H5O2N -CH6O2N -C2H5ON -None of the above.
C2H5O2N
In a protein, peptide bonds connect ...
C=O to N-H.
A certain protein is not very sensitive to pH. It may have many side chains with ________ groups.
CH2OH
The helical foldings of proteins are stabilized mainly by bonds between ...
CO and NH.
Which part of an amino acid is always acidic? -Carboxyl functional group -Side chain ("R group") -Amino functional group -None of the above
Carboxyl functional group
An amino acid residue in a protein differs from a free amino acid in having ... -(a) one less H. -(b) one less OH. -(c) one less H and one less OH. -Either (a) or (b). -Could be any of the above.
Could be any of the above.
Which statement helps to explain how DNA stores hereditary information? -DNA contains four kinds of nitrogenous bases. -DNA contains 20 kinds of amino acids. -DNA is made from thousands of kinds of monomers. -DNA is a self-replicating type of protein. -DNA binds a master copy of each kind of protein.
DNA contains four kinds of nitrogenous bases.
What do phosphoglycerides and fats have in common?
Ester linkages.
What does cholesterol have in common with sex hormones? -Four linked rings. -Fatty acids. -Ester linkages. -Causes heart disease. -Strong polarity.
Four linked rings.
What holds the strands of the DNA double helix together?
Hydrogen bonds between purines and pyrimidines.
A certain amino acid side chain ionizes at low pH but not at very high pH. What else is true of this side chain?
It contains an amino group.
A major limitation of the ribbon model of a protein is:
It gives a false sense of open space in the protein.
For good health, you don't want your body to run the LDL part of this diagram faster than the HDL part because ...
LDL cholesterol is stored; HDL cholesterol is destroyed.
Which molecule is not a carbohydrate? -Starch -Lipid -Cellulose -Glycogen
Lipid
Which of the following statements about monosaccharide structure is true? -A six-carbon sugar is called a pentose. -Aldoses and ketoses differ in the position of their hydroxyl groups. -All monosaccharides contain carbon, hydrogen, oxygen, and nitrogen atoms. -Monosaccharides can be classified according to the spatial arrangement of their atoms.
Monosaccharides can be classified according to the spatial arrangement of their atoms.
Which biological activity does NOT directly involve proteins? -Sensing light. -Changing the shape of a cell. -Defending cells against viruses. -Breaking food polymers into smaller molecules. -None of the above; proteins are involved in all of them.
None of the above; proteins are involved in all of them.
Which monomers make up RNA? -Nucleotides -Simple sugars -Polymers -Amino acids
Nucleotides
Which functional group has the most different ionized forms? -Sulfhydryl -Carbonyl -Carboxyl -Phosphate -Hydroxyl
Phosphate
Which lipid is most amphipathic? -Cholesterol -Phospholipid -Fat -Wax -Triglyceride
Phospholipid
Dr. Haxton told one of his students, "To move in the bloodstream, fats need the help of phospholipids." What would a good student say?
Phospholipids are most important for ... Yes. Nonpolar molecules aren't compatible with water.
Which polymers are composed of amino acids? -Proteins -Monomers -Carbohydrates -Nucleic acids
Proteins
Which of these is NOT a lipid? -cholesterol -steroids -RNA -phospholipid -wax
RNA
Which structure is not a component of a nucleotide? -Sulfhydryl Oxygen group -Phosphate group -Nitrogen-containing base -Pentose
Sulfhydryl Oxygen group
Which atom is most likely to have a δ + charge? -The N in an amino group. -The S in a sulfhydryl group. -An O that is involved in a hydrogen bond. -An O in a carboxyl group. -The C in a carbonyl group.
The C in a carbonyl group.
What will probably be the effect on a protein if you replace the amino acid proline with the amino acid glycine (side chain -H) at several points?
The altered protein will have longer helices than before.
Which factor is most important in determining a protein's optimum pH? -The pH of the protein's environment. -The number of backbone carboxyl groups. -The sensitivity of hydrocarbon side chains to pH. -The locations of side-chain carboxyl groups. -The number of amino groups in the protein's backbone.
The locations of side-chain carboxyl groups.
Which of the following statements about DNA structure is true? -The arrangement of the sugar-phosphate groups determines the genetic code. -DNA is always synthesized in the 3' to 5' direction. -The nucleic acid strands in a DNA molecule are oriented antiparallel to each other. -Phosphodiester bonds form between the phosphate group of one nucleotide and the 5' carbon of the adjacent nucleotide.
The nucleic acid strands in a DNA molecule are oriented antiparallel to each other.
Which of the following statements about nucleotide structure is false? -The phosphate group is bonded to the nitrogenous base. -The sugar is bonded to the phosphate group. -The nitrogenous base is bonded to the sugar. -The sugar can be either ribose or deoxyribose.
The phosphate group is bonded to the nitrogenous base.
Which fact results from the presence of both polar and nonpolar side chains in a protein? -Water has a strong effect on tertiary structure. -pH has a strong effect on secondary structure. -Proteins ionize when they are placed in water. -A protein's folding doesn't depend on the polarity of the environment. -Each protein has many functions.
Water has a strong effect on tertiary structure.
Which fact is most important in causing phospholipids to behave as they do in water? -Hydrogen is more electronegative than oxygen. -Water molecules make hydrogen bonds. -Nonpolar groups repel water. -Hydrocarbons attract one another. -Phosphate groups can bind together.
Water molecules make hydrogen bonds.
Glycogen is _____.
a polysaccharide found in animals
A biochemist modified a protein so the amino acid lysine occurred where the amino acid aspartic acid previously occurred. This change could ...
alter the protein's tertiary structure.
A functional group on a molecule in solution carries two H atoms at pH 9 and three H atoms at pH 3. The functional group is probably. . .
amino
Proteins are polymers of _____.
amino acids
The helical foldings in proteins ...
are kept folded by hydrogen bonds.
Amino acids are called "acids" because they ...
contain carboxyl groups in the backbone part.
When a protein has been unfolded enough to lose its function, the protein has been ...
denatured.
Non-ionized carboxyl groups cause a molecule to act as an acid because they ...
donate H+ ions to water.
In fat synthesis,________and fatty acids combine to make fats plus________.
glycerol; water
glucose + glucose —> _____ by _____.
maltose + water ... dehydration synthesis
To find the best source of phospholipids, look at ...
membranes.
Which of these is a source of lactose? -sugar beets -starch -milk -sugar cane -potatoes
milk
Among the forces that stabilize protein tertiary structure, hydrogen bonds are especially important because they are ...
more numerous than the other forces.
RNA nucleotides contain __________ than DNA nucleotides.
more oxygen
Which of these is rich in unsaturated fats? -butter -lard -olive oil -a fat that is solid at room temperature -beef fat
olive oil
What type of bond joins the monomers in a protein's primary structure?
peptide
Tertiary structure is NOT directly dependent on _____.
peptide bonds
A nucleotide is composed of a(n) _____.
phosphate group, a nitrogen-containing base, and a five-carbon sugar
It is difficult for molecules to pass through the phospholipid bilayer because ...
polar molecules attract one another.
Phospholipids are most important for ...
preventing leakage from cells.
The information in DNA tells a cell how to make ...
proteins, DNA, tRNA.
To make a disulfide bridge, it's necessary to ...
remove two H atoms.
In a membrane, the________of the phospholipids in one monolayer face the________of the phospholipids in the other monolayer.
tails; tails
If you measure the amounts of the bases in any sample of DNA, you'll find that ...
the amount of A + the amount of G = the amount of T + the amount of C.
DNA and mRNA differ with respect to ...
the kind of sugar they contain.
The most unsaturated fats have ...
the most double bonds.
If you were to analyze a DNA sample from a eukaryotic cell, you would find that:
the number of purines equals the number of pyrimidines and the number of guanines equals the number of cytosines.
The sequence of polar and nonpolar side chains has a strong effect on a protein's folding mainly because ...
water attracts polar but not nonpolar groups.
