Answers to End-of-Chapter Questions – Brooker et al ARIS site

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Answers to End-of-Chapter Questions – Brooker et al ARIS site
Chapter 3
Test Yourself Questions
1. Molecules that contain the element ___________ are considered organic molecules.
a. hydrogen
b. carbon
c. oxygen
d. nitrogen
e. calcium
Answer: b. Organic molecules contain the element carbon.
2. ___________ was the first scientist to synthesize an organic molecule. The organic molecule
synthesized was _________.
a. Kolbe, urea
b. Wöhler, urea
c. Wöhler, acetic acid
d. Kolbe, acetic acid
e. Wöhler, glucose
Answer: b. Wohler synthesized urea in 1828.
3. The versatility of carbon to serve as the backbone for a variety of different molecules is due to
a. the ability of carbon atoms to form four covalent bonds.
b. the fact that carbon usually forms ionic bonds with many different atoms.
c. the abundance of carbon in the environment.
d. the ability of carbon to form covalent bonds with many different types of atoms.
e. both a and d.
Answer: e. Carbon atoms can form up to four covalent bonds and can form covalent bonds with many
different atoms. These are just two of the characteristics of carbon bonding that allows for the large
variety of organic molecules that can be found in nature.
4. _________ are molecules that have the same molecular composition but differ in structure and/or
bonding association.
a. Isotopes
b. Isomers
c. Free radicals
d. Analogues
e. Ions
Answer: b. Isomers are molecules that have the same molecular composition but differ in structural
arrangement and/or bonding associations.
5. ____________ is a storage polysaccharide commonly found in the cells of animals.
a. Glucose
b. Sucrose
c. Glycogen
d. Starch
e. Cellulose
Answer: c. Glycogen is a storage polysaccharide commonly found in animal cells.
6. In contrast to other fatty acids, essential fatty acids
a. are always saturated fats.
b. cannot be synthesized by the organism and are necessary for survival.
c. can act as building blocks for large, more complex macromolecules.
d. are the simplest form of lipids found in plant cells.
e. are structural components of cell membranes.
Answer: b. Essential fatty acids cannot be synthesized and must be obtained from through the diet.
They are necessary for survival.
7. Phospholipids are said to be amphipathic, which means these molecules
a. are partially hydrolyzed during cellular metabolism.
b. are composed of a hydrophilic portion and hydrophobic portion.
c. may be poisonous to organisms if in combination with certain other molecules.
d. are molecules composed of lipids and proteins.
e. all of the above.
Answer: b. The term amphipathic describes molecules that have a hydrophilic portion and a
hydrophobic portion.
8. The monomers of proteins are __________ and these are linked by polar covalent bonds commonly
referred to as _______________ bonds.
a. nucleotides, peptide
b. amino acids, ester
c. hydroxyl groups, phosphodiester
d. amino acids, peptide
e. monosaccharides, glycosidic
Answer: d. Proteins are polymers of amino acids linked by peptide bonds.
9. The ________ of a nucleotide determines whether it is a component of DNA or a component of RNA.
a. phosphate group
b. five-carbon sugar
c. side chain
d. fatty acid
e. both b and d
Answer: b. The 5-carbon sugar distinguishes between nucleotides that are ribonucleotides versus
deoxyribonucleotides.
10. A ________ is a portion of protein with a particular structure and function.
a. peptide bond
b. domain
c. phospholipid
d. wax
e. monosaccharide
Answer: b. A protein domain is a sequence of amino acids within a protein that folds up into a specific
structure and carries out a particular function.
Conceptual Questions
1. Define isomers.
Isomers - Two structures with an identical molecular formula but with different structures and characteristics.
2. List the four classes of organic molecules and give a function of each.
Answer:
a. Carbohydrates – energy storage and structural support
b. Lipids – energy storage and components of membranes
c. Proteins – many functions including enzymes, defense, transport, structure, contraction
d. Nucleic acids – information storage, gene expression
3. Explain the difference between saturated and unsaturated fatty acids.
Answer: Saturated fatty acids are saturated with hydrogen and have only single bonds while
unsaturated fatty acids have some double bonds.
Experimental Questions
1. Before the experiments conducted by Anfinsen, what were the common beliefs among scientists
about protein folding?
Answer: Many scientists assumed that protein folding was directed by some cellular factor, meaning
some other molecule in the cytoplasm. Others assumed that protein folding was determined somehow
by the ribosome because this organelle is primarily responsible for synthesizing proteins.
2. Explain the hypothesis tested by Anfinsen.
Answer: Anfinsen was testing the hypothesis that the information necessary for determining the threedimensional shape of a protein is contained within the protein itself. In other words, the chemical
characteristics of the amino acids that make up a protein will determine the three-dimensional shape.
3. Why did Anfinsen use urea and β-mercaptoethanol in his experiments? Explain the result that was
crucial to the discovery that the tertiary structure of a protein is dependent on the primary structure.
Answer: The urea disrupts hydrogen bonds and ionic interactions that are necessary for protein folding.
The mercaptoethanol disrupted the S-S bonds that also form between certain amino acids of the same
polypeptide chains. Both substances essentially allow the polypeptide chain to unfold, disrupting the
three-dimensional shape.
Anfinsen removed the urea and mercaptoethanol from the protein solution by dialysis. After removing
the urea and mercaptoethanol, Anfinsen discovered that the protein refolded into its proper threedimensional shape and became functional again. This was important because the solution contained
only the protein and lacked any other cellular material that could possibly assist in protein folding. This
demonstrated that the protein could refold into the functional conformation.
Collaborative Questions
1. Discuss several types of carbohydrates.
Answer:
Monosaccharides - These are the most simple out of the sugars. A prime example of this type of sugar
is glucose which is used by many organisms to make ATP.
Disaccharides - These consist of two monosaccharides bonded together. Sucrose is an example of this
type of sugar. This is accomplished through a condensation reaction by removing hydrogen from one
monosaccharide and a hydroxyl from the other.
Polysaccharides - These consist of many monosaccharides bonded together. Some examples of
polysaccharides are:
Glycogen – this is the storage form of glucose in animals.
Starch – this is the storage form of glucose in plants.
Cellulose – this molecule serves as a support molecule in plants.
2. Discuss some of the roles that proteins play in organisms.
Answer:
Protection - protect organisms from attack against disease. Organisms develop specific proteins to fight
against specific diseases.
Enzymes - increase the rates of chemical reactions. Without these proteins metabolism would grind to a
halt.
Gene expression and regulation - involved in transcribing genes, regulating genes, and synthesizing
polypeptides.
Cell signaling - are needed for a cell to communicate with other cells and with the environment.
Motor proteins - allow cellular movements.
Transporters - allow the movement of ions and molecules across cellular membranes.
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