1. What is the function of a chromosome?
2. Name the two types of molecules that are present in chromosomes. What is the function of each of these types of molecules?
3. Name two major functions of proteins in living cells.
4. Name the "building blocks" of proteins.
5. How many different kinds of amino acids are used by humans for constructing proteins?
6. How many different kinds of proteins are present in human cells?
7. Name the “building blocks” of nucleic acids (ie., DNA and RNA).
8. Name the three components of a nucleotide.
9. How many different kinds of nucleotides are used to build molecules of DNA?
10. How many different kinds of nucleotides are used to build molecules of RNA?
11. Name a nucleotide that is present in DNA but not in RNA.
12. Name a nucleotide that is present in RNA but not in DNA.
12a. Name the nucleotide that is complementary to a nucleotide containing adenine.
12b. Name the nucleotide that is complementary to a nucleotide containing cytosine.
12c. Name the nucleotide that is complementary to a nucleotide containing uracil.
13. Name three nucleotides that are present in both DNA and RNA.
14. How does the shape and structure of a DNA molecule differ from a RNA molecule?
15. Name three kinds of RNA molecules.
16. Where in a cell are RNA molecules manufactured?
17. What is the function of mRNA molecules?
18. What is the function of tRNA molecules?
19. What is the function of rRNA molecules?
20. How many nucleotides are present in a tRNA molecule?
21. How many amino acids can one tRNA transport at a time?
22. How many different kinds of amino acids can one tRNA transport?
23. Can a tRNA transport 50 molecules of an amino acid?
24. How many nucleotides are present in the tRNA at the point where tRNA connects to an amino acid?
25. Name the three nucleotides that are used to connect tRNA to an amino acid.
26. How many nucleotides are present in an anticodon?
27. Name the molecule in which an anticodon is present.
28. What is the function of an anticodon?
29. How many different kinds of anticodons are present in a cell?
30. How many different kinds of tRNA molecules are present in a cell?
31. How do tRNA molecules differ from each other?
32. Were in a cell are tRNA molecules manufactured?
33. Name the cell organelle on which protein molecules are manufactured.
34. Name the primary component of ribosomes.
35. Where in a cell are ribosomes normally found?
36. Where in a cell are molecules of rRNA manufactured?
37. Define the term “transcription” as used when describing protein synthesis.
38. Where in a cell does transcription occur?
39. Define the term “translation” as used when describing protein synthesis.
40. Where in a cell does translation occur?
EXAMPLE OF A PROTEIN SYNTHESIS PROBLEM
Strand "A" of a DNA molecule has the following sequence of nucleotides:
A-A-T-C-C-C-G-C-T-T-T-T
The following tRNA molecules are present. Each tRNA is identified by its anticodon. The amino acid transported by each tRNA is named.
tRNA ANTICODON AMINO ACID TRANSPORTED
AAU 1. ASPARAGINE
UUA 2. LEUCINE
CCC 3. PROLINE
GGG 4. GLYCINE
GCU 5. ALANINE
CGA 6. ARGININE
UUU 7. PHENYLALANINE
AAA 8. LYSINE
ACU 9. THREONINE
41. How many nucleotides are present in strand "A" of the DNA molecule?
42. How many nucleotides will be present in strand "B" of the DNA molecule?
43. Name the first three nucleotides in strand "B" of the DNA molecule.
44. How many amino acids will be present in a protein formed using the information in strand "A" of the DNA molecule?
45. How many amino acids will be present in a protein formed using the information in strand "B" of the DNA molecule?
46. How many nucleotides will be present in a mRNA molecule that is formed from strand "A" of DNA?
47. How many codons will be present in a mRNA molecule that is formed from strand "A" of DNA?
48. The mRNA molecule will move from its point of formation in the nucleus to an organelle called the _?_ which is located in the cytoplasm.
49. Name the three nucleotides present in the first codon of the mRNA that was formed from strand "A" of DNA.
50. Name the three nucleotides in the anti-codon of tRNA that complements the first codon of the mRNA that was formed from strand "A" of DNA.
51. Name, in proper sequence, the amino acids of a protein that is formed using the information in strand "A" of DNA.
52. Name, in proper sequence, the amino acids of a protein that is formed using the information in strand "B" of DNA.
53. Define the term “mutation.”
54. Assume that a mutation occurs in strand "A" of DNA; the mutation is a substitution in which a nucleotide containing cytosine replaces the second nucleotide in the DNA strand "A."
54a. What are now the first three nucleotides in the mutated strand "A" of DNA?
54b. Name the first three nucleotides in the mRNA formed from the mutated DNA strand "A."
54c. Name, in proper sequence, the amino acids in a protein that is formed using the information in mutated strand "A" of DNA.
54d. Will the protein formed from the mutated strand "A" of DNA have the same enzymatic properties as the protein formed from the original (not mutated) strand "A" of DNA?
55. Can the change of one nucleotide (either a gain, a loss, or a substitution) in a DNA molecule significantly affect the structure and functioning of a protein formed from that DNA molecule?
56. Can the information in a mRNA be used to manufacture more than one protein molecule?
57. How many times can a tRNA molecule be used?
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 uracil-uracil-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: adenine-cytosine-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.