CHAPTER 11 Organic
Nucleic Acids and Protein Synthesis
Section 1 Section 2 Section 3 Section 4 Section 5
Section 6 Section 7 Section 8 Section 9 Section 10
SECTION 11.1 Components of Nucleic Acids |
1. Nucleic acids are classified into two categories: ribonucleic acid (RNA), found mainly in the cytoplasm of living cells, and deoxyribonucleic acid (DNA), found primarily in the nuclei of cells.
__________________ is the nucleic acid found primarily in the cytoplasm of living cells.
2. Both DNA and RNA are polymers, consisting of long, linear molecules. The repeating structural units, or monomers, of the nucleic acids are called nucleotides.
The repeating units, or monomers, found in DNA and RNA are called _____________.
3. Nucleotides are composed of three components: a heterocyclic base, a sugar, and a phosphate (see Figure 11.2).
Three components: a heterocylic base, a __________, and a phosphate comprise all nucleotides.
4. Heterocyclic bases commonly found in nucleic acids can be classified as either a pyrimidine or a purine.
The heterocyclic base portions of nucleic acids are either _______________ or purines.
5. The three pyrimidine bases are uracil, thymine, and cytosine, usually abbreviated U, T, and C. Adenine (A) and guanine (G) are the two purine bases (see Figures 11.3).
A and G are __________ bases.
6. Adenine, guanine, and cytosine are found in both DNA and RNA, but uracil is ordinarily found only in RNA, and thymine only in DNA.
The base ___________ is a pyrimidine base found only in ribonucleic acids.
7. The sugar component of RNA is ribose, as the name ribonucleic acid implies. In deoxyribonucleic acid (DNA), the sugar is deoxyribose. The deoxy- prefix denotes the absence of a hydroxy group which is present in ribose.
The sugar component of DNA is called _______________.
SECTION 11.2 The Structure of DNA |
8. The nucleotides are joined together in nucleic acids by phosphate groups that connect the 5' carbon of one nucleotide to the 3' carbon of the next. These linkages are referred to as phosphodiester bonds (see Figure 11.5).
Nucleotides are joined together by ___________________ bonds.
9. The sugar-phosphate chain is referred to as the nucleic acid backbone (see Figure 11.4).
The nucleic acid backbone encompasses the ______________ chain.
10. Watson and Crick, from various experimental data, theorized that DNA is composed of two strands entwined around each other in a double helix, as shown in Figure 11.7.
The secondary structure of DNA contains two strands of DNA that form a _____________ helix.
11. The two intertwined polynucleotide chains of the DNA double helix run in opposite (antiparallel) directions. Thus, each end of the double helix contains the 5' end of one chain and the 3' end of the other.
Two polynucleotide chains running in opposite directions are said to be ________.
12. The DNA structure is stabilized by hydrogen bonding between the bases that extend inward from the sugar-phosphate backbone.
____________________ interactions between atoms in the base portion of nucleotides provide the stabilizing force to the double helix.
13. Complementary DNA strands are two strands of a DNA in a double helix with matching bases forming hydrogen bonds. The most common complimentary base pairs in double-helical DNA are the thymine-adenine pair and the guanine-cytosine base pair (see Figure 11.8).
The two most common base pairs in DNA double helixes are the thymine- adenine pair and the guanine-_____________ base pair.
14. One strand of a DNA molecule has the base sequence of CCATTG (written in the 5' to 3' direction).
What is the base sequence for the complementary strand in the 5' to 3' direction?
SECTION 11.3 DNA Replication |
15. A human cell normally contains 46 structural units called chromosomes (see Figure 11.9).
A human cell contains _________________ chromosomes.
16. Each chromosome contains one molecule of DNA coiled tightly about a group of small, basic proteins called histones.
_____________ are the small basic proteins that form the core around which DNA coils in chromosomes.
17. Individual sections of DNA molecules make up genes, the fundamental units of heredity. Each gene directs the synthesis of a specific protein or, in some cases, a series of proteins.
___________________ are sections of DNA that are the fundamental units of heredity.
18. A bacterial cell may contain 1000 genes, whereas a human cell contains approximately 30,000 genes.
A human cell contains an estimated ____________ genes.
19. The process by which an exact copy of DNA is produced is called replication.
DNA molecules are copied by a process called _______________.
20. Semiconservative replication is a replication process that produces DNA molecules containing one strand from the parent and a new strand that is complementary to the strand from the parent (see Figure 11.10).
The type of replication process that produces a DNA copy with a new strand and one from the parent is known as _________________ replication.
21. Step one in the replication process is the unwinding of the double helix catalyzed by the enzyme helicase.
___________ is the enzyme that catalyzes the unwinding of the double helix in the first step of DNA replication.
22. The point at which the unwinding of the double helix takes place is called the replication fork (see Figure 11.11).
Helix unwinding is initiated at the ______________________.
23. Step two of DNA replication involves synthesis of DNA segments. New daughter strands form as nucleotides, complementary to those on the exposed strands, are linked together under the influence of the enzyme DNA polymerase.
The enzyme __________________ is responsible for the synthesis of DNA.
24. DNA polymerase synthesizes the daughter chains in the 5' to the 3' direction.
The direction of growth of the DNA daughter chain is from the _________ end.
25. Okazaki fragments are DNA fragments produced during replication as a result of strand growth in a direction away from the replication fork.
Because growth of one strand proceeds away from the replication fork, ______________ fragments are formed
26. Step 3 of DNA replication involves closing the nicks between the Okazaki fragments on one strand of the newly synthesized DNA. The other daughter strand contains a continuous chain of nucleotides and does not require this process.
The final step of DNA replication involves closing nicks between ________ fragments on one strand.
27. An enzyme called DNA ligase is responsible for catalyzing the joining of the Okazaki fragments.
Okazaki fragments are joined by the enzyme _________________.
28. Through detailed understanding of DNA replication, a revolutionary laboratory technique called the polymerase chain reaction (PCR) was born. PCR mimics the natural DNA replication process in a controlled laboratory environment.
The __________ technique is a process through which scientists duplicate natural DNA replication outside living cells.
29. The primary structure of RNA differs from that of DNA in two ways. As we learned in Section 11.1, the sugar unit in RNA is ribose rather than deoxyribose. The other difference is that RNA contains the base uracil (U) instead of thymine (T).
The base ____________ is found in RNA in place of thymine.
30. The secondary structure of RNA is also different from that of DNA. RNA molecules are single-stranded, except in some viruses.
RNA molecules exist primarily as ____________ strands.
31. Cells contain three types of RNA: messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA). Each of these kinds of RNA performs an important function in protein synthesis.
RNA molecules are involved in the synthesis of _______________.
32. Messenger RNA (mRNA) functions as a carrier of genetic information from the DNA of the cell nucleus directly to the cytoplasm.
Genetic information is carried from the cell nucleus to the cytoplasm via _____________________.
33. Molecules of mRNA have a short lifetime, usually less than 1 hour.
In general terms, the turnover rates for mRNA are __________.
34. A ribosome is a subcellular particle that serves as the site of protein synthesis in all organisms.
________ function as the site of protein synthesis.
35. Ribosomal RNA (rRNA) constitutes 80-85% of the total RNA of the cell. It is located in the cytoplasm in organelles called ribosomes.
_____________ RNA makes up the majority of a cell's RNA.
36. Transfer RNA (tRNA) molecules deliver amino acids, the building blocks of proteins, to the site of protein synthesis.
Amino acids are delivered to ribosomes via ____________________.
37. The tRNA are the smallest of all the nucleic acids, containing 73-93 nucleotides per chain.
The smallest of the nucleic acids are the ________.
38. Two regions of tRNA molecules have important functions during protein synthesis. The anticodon enables the tRNA to bind to mRNA during protein synthesis (see Figure 11.14).
The ____________portion of tRNA molecule is the binding site for mRNA during protein synthesis.
39. The second important site is the 3' end of the molecule, which binds to an amino acid and transports it to the site of protein synthesis.
The _____________ end of the tRNA molecule is the binding site for the amino acid it carries.
SECTION 11.5 The Flow of Genetic Information |
40. The central dogma of molecular biology is the well-established process by which genetic information stored in DNA molecules is expressed in the structure of synthesized proteins.
The process by which genetic information is expressed in ______________ structure constitutes the central dogma of molecular biology.
41. Genetic information contained in DNA molecules is transferred to RNA molecules, followed by expression of this information in the structure of synthesized proteins.
__________________molecules provide the link between genetic information stored in DNA and the structure of proteins.
42. Before proteins can be synthesized, the stored information must be carried out of the nucleus. This is accomplished by transcription, or transferring the necessary information from the DNA molecule onto a molecule of messenger RNA (see Figure 11.16).
_____________________ refers to the transfer of genetic information from DNA to mRNAs.
43. The mRNA serves as a template on which amino acids are assembled in the proper sequence necessary to produce the specified protein. This process, called translation, takes place when the code or message carried by mRNA is converted into an amino acid sequence.
______________________ refers to the synthesis of a protein according to the code on the corresponding mRNA molecule.
SECTION 11.6 Transcription: RNA synthesis |
44. An enzyme called RNA polymerase catalyzes the synthesis of RNA.
The synthesis of RNA is catalyzed by ______________________.
45. The sequence of DNA is as follows: 5'-G-C-A-A-C-T-T-G-3'.
Write the sequence for the mRNA, in the 5' to 3' direction, that could be synthesized from this sequence.
46. Genes of eukaryotic cells are segments of DNA that are "interrupted" by segments that do not code for amino acids. These DNA segments that carry no amino acid code are called introns, and the coded DNA segments are called exons.
Segments of DNA within coding DNA regions that do not code for amino acids are called ________.
47. When transcription occurs in the nuclei of eukaryotic cells, both introns and exons are transcribed. This produces what is called heterogeneous nuclear RNA or hnRNA (see Figure 11.18).
The RNA produced in the nuclei of eukaryotic cells containing RNA transcribed from both introns and exons is called ________ nuclear RNA.
48. The long hnRNA molecule undergoes a series of enzyme-catalyzed reactions that cut and splice the hnRNA to produce mRNA.
In order to form ________ from hnRNA, the noncoding regions must first be cut and then the coding regions joined together.
SECTION 11.7 The Genetic Code |
49. Nature uses three-letter code words to store and express genetic information. Each sequence of three nucleotide bases that represents code words on mRNA molecules is called a codon (see Table 11.2).
The three letter codes that store and express genetic information are called ________.
50. A three base code has 43 or 64 possible combinations.
There are ______ possible codons.
51. One important characteristic of the genetic code is that it applies to every organism (see Table 11.3). The code is almost universal from species to species.
The genetic code is almost ________, differing only rarely from species to species.
52. A second feature of the genetic code is that most of the amino acids are represented by more than one codon, a characteristic known as degenerate.
The genetic code is said to be ________ when an amino acid is represented by more than one codon.
53. Only 61 of the possible 64 base triplets represent amino acids. The remaining three (UAA, UAG, UGA) are signals for chain termination.
Codons that do not code for amino acids are signals for _______________________.
54. There is only one initiation (start) codon, and it is AUG, the codon for the amino acid methionine.
AUG, the chain initiation signal, codes for the amino acid _______.
SECTION 11.8 Translation and Protein Synthesis |
55. There are three major stages in protein synthesis: initiation of the polypeptide chain, elongation of the chain, and termination of the completed polypeptide chain (see Figure 11.19).
The three steps of protein synthesis are initiation, ____________ and termination.
56. The initiation process begins when mRNA is aligned on the surface of a small ribosomal subunit in such a way that the initiating codon, AUG, occupies a specific site on the ribosome called the P site (peptidyl site).
The initiating codon of the mRNA must occupy the _________ site of the ribosome for the initiation process to begin.
57. A tRNA molecule with its attached f-Met binds to the codon through hydrogen bonds. The resulting complex binds to the large ribosomal subunit to form a unit called an initiation complex.
Upon binding of the large ribosomal subunit to the mRNA, followed by binding of the small ribosomal subunit and the f-Met tRNA molecule, the ________ complex is complete, enabling the next step of protein synthesis to commence.
58. A second site, called the A site (aminoacyl site), is located on the mRNA-ribosome complex next to the P-site. The A site is occupied by an incoming tRNA carrying the next amino acid.
The binding site for incoming tRNA molecules adjacent to the P site is called the _______________.
59. After a tRNA molecule binds to the A-site, the whole ribosome moves one codon along the mRNA toward the 3' end. This movement of the ribosome along the mRNA is called translocation, during which the A site becomes available to the next tRNA with the proper anticodon (see Figure 11.21).
___________________ is the process by which the ribosome moves along the mRNA molecule.
60. The chain elongation process and polypeptide synthesis continue until the ribosome complex reaches a stop codon (UAA, UAG, UGA) on the mRNA.
The presence of a _____________ codon results in termination of polypeptide synthesis.
61. Several ribosomes can move along a single strand of mRNA one after another. Complexes of several ribosomes and mRNA are called polyribosomes or polysomes (see Figure 11.22).
Polyribosomes contain several ______________ on a single mRNA strand.
Guide for Figure 11.1
#1. tRNA and rRNA transcription - tRNA and rRNA are transcribed from a DNA template and then pass through the nuclear membrane to the cytoplasm. In the cytoplasm, the tRNA molecules bind with specific amino acids that they code for from the amino acid pool. Some rRNA forms the large ribosomal subunits and some form the small ribosomal subunits to be used for protein synthesis.
#2. nRNA transcription - initially the RNA transcribed from the DNA template contains information from the introns and exons of the DNA segment. This first RNA formed is called "heteronuclear RNA" (hnRNA). The hnRNA then has the information from the introns cut out of it, producing nRNA that has information only from the exons of the DNA. The mRNA then passes through the nuclear membrane into the cytoplasm, where it can be used for protein synthesis.
#3. Protein synthesis:
a. In the cytoplasm, the mRNA strand binds with a small ribosome so the initiating codon is at the ribosomal P site. A tRNA with an attached fMet amino acid then hydrogen bonds with the codon on the mRNA.
b. A large ribosomal subunit completes the initiation complex.
c. A tRNA carrying the next amino acid that is coded for hydrogen bonds at the A site of the small ribosome. A peptide bond is then formed between the two amino acids.
d. The ribosomal unit then translocates (moves along on the mRNA) to the next codon, releasing the first tRNA and moving the P site to the second codon. The third tRNA carrying the next amino acid then binds at the A site and a peptide bond is formed between the amino acids. This process is repeated until a termination codon is reached and the polypeptide is released from the ribosome complex.
SECTION 11.9 Mutations |
62. Any change resulting in an incorrect sequence of bases on DNA is called a mutation.
A _____________________ is a change resulting in an incorrect sequence of DNA bases.
63. Some mutations occur naturally during DNA replication; others can be induced by environmental factors such as ionizing radiation (X rays, ultraviolet light, gamma rays, etc.). A large number of chemicals (e.g. nitrous acid and dimethyl sulfate) can also induce mutations by reacting with DNA. Such chemicals are called mutagens.
DNA mutations can occur naturally during DNA replication, or by environmental factors such as _____________ radiation, or as the result of exposure to chemicals called __________________.
SECTION 11.10 Recombinant DNA |
64. Remarkable technology is available that allows segments of DNA from one organism to be introduced into the genetic material of another organism. The resulting new DNA (containing the foreign segment) is referred to as recombinant DNA.
DNA of an organism that contains genetic material from another organism is called ________ DNA.
65. The discovery of restriction enzymes in the 1960s and 1970s made genetic engineering possible. Restriction enzymes are protective enzymes found in a wide variety of bacteria catalyzing the cleaving of foreign DNA at specific sequences.
Enzymes that catalyze the cleavage of foreign DNA in specific sequences are called ________ enzymes.
66. Another set of enzymes important in genetic engineering, called DNA ligases, has been known since 1967. These enzymes normally function to connect DNA fragments during replication, and they are used in genetic engineering to put together pieces of DNA produced by restriction enzymes.
In genetic engineering, pieces that are cleaved by restriction enzymes are connected through the use of ________________.
67. The introduction of a new DNA segment (gene) into a bacterial cell requires the assistance of a DNA carrier called a vector.
_____________ are DNA carriers used in genetic engineering to introduce foreign DNA into the desired cell.
68. Vectors are often circular units of double-stranded DNA called plasmids, which are isolated from the cytoplasm of bacterial cells.
Circular units of DNA often used as vectors are called ________.