Protein Synthesis Review Answers
1. Chromosomes contain information that is used for constructing proteins.
More specifically, the sequence of nucleotides in the DNA of a chromosome
determines the sequence of amino acids in a protein. The sequence of amino
acids in a proteins determines the properties of that protein.
2. Two types of molecules present in a chromosome are (1) protein and (2)
DNA. The DNA contains genetic information and the protein helps hold the
DNA in proper position.
3. Two of the major functions of proteins in cells are (1) serving as enzymes
(and thereby controlling which chemical reactions occur in a cell) and (2)
serving as structural material from which parts are constructed. Specific
proteins may have other functions. For example, hemoglobin is a protein whose
primary function is to transport oxygen in red blood cells, and antibodies are
proteins whose function is to protect against the invasion of antigens (i.e.,
"foreign materials").
4. A protein molecule is a polymer constructed of units called amino acids.
5. Humans, like other kinds of living organisms, use twenty different kinds of
amino acids to build proteins. Most proteins will not contain all twenty of these
different amino acids. Many proteins will have multiple copies of some amino
acids. Remember that some proteins contain hundreds or even thousands of
amino acids; since only twenty different kinds of amino acids are available,
some of the amino acids must be used many times.
6. Human cells may have hundreds or even thousands of different kinds of
protein molecules. Some types of cells will have more kinds of proteins than
other cells.
7. The "building blocks" of nucleic acids (i.e., DNA and RNA) are nucleotides.
8. The three components of a nucleotide are (1) a five carbon sugar, (2) a
phosphate, and (3) a nitrogen base. The nitrogen base will be either (1) adenine,
(2) thymine, (3) uracil, (4) cytosine, or (5) guanine.
9. Four different kinds of nucleotides are used to build molecules of DNA.
Each of these nucleotides contains one of the following nitrogen bases: (1)
adenine, (2) thymine, (3) cytosine, or (4) guanine.
10. Four different kinds of nucleotides are used to build molecules of RNA.
Each of these nucleotides contains one of the following nitrogen bases: (1)
adenine, (2) uracil, (3) cytosine, or (4) guanine.
11. Nucleotides containing thymine are present in molecules of DNA but not in
molecules of RNA.
12. Nucleotides containing uracil are present in molecules of RNA but not in
molecules of DNA.
12a. A nucleotide containing either thymine or uracil is complementary to a
nucleotide containing adenine.
12b. A nucleotide containing guanine is complementary to a nucleotide
containing cytosine.
12c. A nucleotide containing adenine is complementary to a nucleotide
containing uracil.
13. The nucleotides containing adenine, cytosine, and guanine are present in
both DNA and RNA.
14. DNA molecules are double stranded ("ladder like") while RNA molecules
are single stranded. DNA molecules may contain nucleotides with thymine but
not uracil, while RNA molecules may contain nucleotides with uracil but not
thymine. DNA contains deoxyribose sugar; RNA contains ribose sugar.
15. Three kinds of RNA molecules are: (1) messenger RNA, abbreviated
mRNA; (2) transfer RNA, abbreviated tRNA; and (3) ribosomal RNA,
abbreviated rRNA.
16. All types of RNA molecules are manufactured from DNA in the nucleus of
a cell.
17. Messenger RNA (mRNA) is an "information" molecule that provides
instructions for the construction of a protein.
18. Transfer RNA (tRNA) is a "delivery" molecule that transports amino acids,
one at a time, to the mRNA where a protein is being built.
19. Ribosomal RNA (rRNA) is a major component, along with protein, of
ribosomes. Think of the rRNA as part of an assembly machine. However,
without mRNA (the instructions) or tRNA (to deliver materials, the amino
acids) the rRNA can not build a protein.
20. A molecule of tRNA contains approximately 75-95 nucleotides.
21. A molecule of tRNA can transport only one amino acid per trip (but
remember that the rRNA, like any delivery truck, can make many trips).
22. Each molecule of tRNA can transport only one kind of amino acid.
23. Yes. Since a tRNA can transport only one amino acid at a time, the tRNA
would have to make 50 trips in order to transport 50 amino acids. (Remember
that all 50 of the amino acids would be identical if they are carried by the same
tRNA.)
24-25. The universal "hitch" or connecting point between tRNA and an amino
acid consists of the same three nucleotides on all tRNA molecules. These three
nucleotides are adenine, cytosine , and cytosine (CAA).
26-27. An anticodon consists of three nucleotides, located on the middle loop
of a tRNA molecule.
28. The anticodon of a tRNA will complement the codon of a mRNA and, thus,
determine the position of one amino acid in a protein molecule that is being
constructed.
29-30. Each cell will contain at least twenty different kinds of tRNA; each of
these differs from the others in the sequence of nucleotides in the anticodon.
31. Molecules of tRNA differ from each other in the sequence of nucleotides in
their anticodons.
32. Molecules of tRNA (like all molecules of RNA) are manufactured from
DNA in the nucleus.
33. Protein molecules are manufactured on cell organelles called ribosomes.
34. The primary component of ribosomes is rRNA; ribosomes also contain
some protein.
35. Ribosomes are normally found in the cytoplasm of a cell; most of the
ribosomes are attached to endoplasmic reticulum.
36. Molecules of rRNA are manufactured from DNA in the nucleus of a cell.
37. The term transcription refers to the manufacturing of mRNA from DNA;
both RNA and DNA are composed of building blocks called nucleotides, so the
production of RNA from DNA involves only one "language" (the language of
nucleotides).
38. Transcription occurs in the nucleus of a cell.
39. The term translation refers to the use of information in mRNA (which was
copied from DNA) to manufacture molecules of protein. Since the RNA is
composed of nucleotides and proteins are composed of amino acids, one
"language" (that of nucleotides) is being translated into another "language"
(that of amino acids).
40. Translation occurs in the cytoplasm as the mRNA attached to a ribosome is
used to manufacture a protein.
41. Strand "A" of DNA contains 12 nucleotides. Remember that each
nucleotide contains one nitrogen base; by counting the number of nitrogen
bases we can determine how many nucleotides are present.
42. Strand "B" of DNA will contain the same number of nucleotides (= 12) as
strand “A” of the DNA.
43. The nitrogen bases in strand "B" are complementary to the nitrogen bases in
strand "A"; the first nucleotide in strand "A" contains adenine, so the first
nucleotide in strand "B" will contain thymine. The second nucleotide in strand
"A" also contains adenine so the second nucleotide in strand "B" will contain
thymine; the third nucleotide in strand "A" contains thymine so the third
nucleotide in strand "B" will contain adenine. A-A-T in strand "A" is
complemented by T-T-A in strand "B."
44. Recall the "triplet code:" three nucleotides in a strand of DNA (or in a
strand of mRNA) determine the position of one amino acid in a protein.” Since
strand "A" of DNA contains 12 nucleotides, the protein formed using this
information will contain 12/3 = 4 amino acids.
45. Since strand "B" of the DNA molecule will contain the same number of
nucleotides as strand "A" of the DNA molecule, the protein formed using the
information will contain the same number of amino acids (4) as the protein
formed using the information in strand "A." This answer could be determined
by counting the number of nucleotides in strand "B" and dividing by 3. (12/3
=4)
46. The mRNA that forms from strand "A" of DNA contains the same number
of nucleotides as DNA strand “A.” The answer is 12.
47. A codon contains three nucleotides. The mRNA that forms from DNA
strand "A" contains 12 nucleotides which will equal four codons.
48. The mRNA that forms from DNA strand "A" in the nucleus of the cell will
move (with the expenditure of much ATP) through the nuclear envelope to a
ribosome in the cytoplasm.
49. The mRNA that forms from DNA strand "A" will be complementary to
DNA strand "A"; however, since RNA is being formed, no thymine will be
used. The adenine-adenine-thymine of DNA will be complemented by uraciluracil-adenine of mRNA.
50. After the mRNA attaches to a ribosome, a tRNA with the anticodon of
adenine-adenine-uracil will complement the codon of uracil-uracil-adenine of
the first codon of the mRNA. Referring to the table of tRNA anticodons and the
amino acids they transport, we learn that the tRNA with an anticodon of
adenine-adenine-uracil is carrying the amino acid asparagine. This amino acid
will be the first amino acid in the protein formed using the information in DNA
strand "A."
51. The protein formed using the information in DNA strand "A" will contain
four amino acids in the sequence: asparagine-proline-alanine-phenylalanine.
52. The protein formed using the information in DNA strand "B" will contain
four amino acids in the sequence: leucine-glycine-arginine-lysine. To arrive at
this answer: (1) form the DNA strand "B", which will be complementary to
strand "A"; (2) form the mRNA complementary to DNA strand "B"; (3) divide
the mRNA into codons (each of 3 nucleotides) and complement each codon
with an anticodon from tRNA; (4) determine from the table which amino acid
is carried by each tRNA that was used to complement the mRNA.
53. A mutation results in a change in the genetic information in a gene (= a
section of DNA); this change may occur in several ways, such as the loss of a
nucleotide, the insertion of an extra nucleotide, the substitution of one
nucleotide for another, or reversing the positions of two adjacent nucleotides.
54a. The first three nucleotides in the mutated strand "A" of DNA are: adeninecytosine-thymine.
(Note that a nucleotide containing cytosine has replaced the second nucleotide
which contained adenine.)
54b. The first three nucleotides in the mRNA that forms from the mutated DNA
strand “A” are: uracil-guanine-adenine.
54c. The amino acids in a protein formed using the information in the mutated
DNA strand “A” are: threonine-proline-alanine-phenylalanine. Note that the
only difference between this protein and the protein formed using the original
DNA strand “A” is in the first amino acid.
54d. The protein formed from the mutated DNA strand "A" will probably not
have the same enzymatic properties as the protein formed from the original
DNA strand "A." Remember that the active sites of an enzyme have a specific
shape; changing the amino acid sequence of a protein will probably result in a
change in the shape of the active sites. This means that the original substrates
will not be able to attach to the active sites (and, consequently, the enzyme will
no longer affect the same reaction.)
55. Yes, changing one nucleotide in a DNA molecule can affect the structure
and functioning of a protein formed from that DNA.
56. The information in a mRNA can be used to produce only one kind of
protein molecule, but the mRNA can be used many times to make multiple
copies of that protein.
57. A tRNA molecule can carry only one molecule of one kind of amino acid;
however, like any "delivery truck," a tRNA can be used many times.