The chemical structure of DNA and RNA. Genes are heritable units of expression that determine the physical characteristics of a cell. Correct! Genes were defined by observing passage of physical characteristics from parents to progeny. things into which one can peek to determine the sex of an individual. Correct! All physical traits of an organism, including the sex, are determined by the genes of that organism. always present in a cell in two similar copies that may be slightly different, often called alleles. False! Diploid cells do have two copies, often slightly different, gene versions called alleles. Some cells (bacteria and sex cells) are haploid and contain only a single copy of each gene, while other cells (plants and amphibians) can be polyploid and contain many copies of each gene.. present only in very simple organisms like viruses. False! Genes seem to be crucial to the function of all life forms. Gene function is a mathematical equation that predicts the physical traits of offspring. False! Mathematics can be used to examine the role of gene function in distribution of traits in a population or in the passage of traits to offspring. is immutable and cannot be changed. False! Gene function is subject to the occurrence of changes called mutations. can be demonstrated only for simple organisms like bacteria. False! All known life forms utilize similar principles of gene structure and function. describes the mechanism by which parents pass physical traits to offspring. Correct! Physical traits are passed to progeny by means of cellular components called genes. The general cellular genetic information is stored in structures known as chromosomes. Correct! The majority of information for physical traits is present in the cellular chromosomes. mitochondria. False! Mitochondria, as well as chloroplasts, do contain DNA that carries very specialized genetic information. vacuoles. False! These are membrane-bounded bags of proteins required for specialized cellular metabolic functions. endoplasmic reticulum. False! These structures are involved in the synthesis of proteins. Cellular components that play an important role in the structure and function of chromosomes include protein. Correct! Proteins play important structural and functional roles in the chromosome. deoxyribonucleic acid or DNA. Correct! DNA is generally the information storage molecule in the chromosome. ribonucleic acid or RNA. Correct! RNA can play an important role in chromosome structure and is required for conversion of stored information to physical traits. membrane. Correct! Membranes can be involved in chromosomal attachment sites or in compartmentalizing chromosomes within the cell. The most important molecule involved in long-term storage of genetic information is protein. False! Proteins are the catalytic or structural components of the living cell. lipid. False! Lipids are a crucial component of membranes, which form individual compartments within cells. deoxyribonucleic acid or DNA. Correct! DNA is the chemical that most frequently is used for long-term storage of genetic information. ribonucleic acid or RNA. False! RNA plays a key role in conversion of stored information into physical traits, although it is used for information storage by some viruses. The role of proteins in chromosomal function can involve maintaining chromosome structure. Correct! Proteins like histones help maintain chromosome structure. converting the stored infomation to a more readily accessible format. Correct! Protein complexes called RNA polymerases express the stored information in a more usable form, while regulatory proteins modulate levels of expression. reproducing the genetic information. Correct! Proteins called DNA polymerases or replicases make new copies of the genetic information for transmission during cell division. correcting damage to the genetic information. Correct! Damage to the genetic information is monitored and repaired by DNA recombination and repair proteins. The association of the molecule RNA with the cellular chromosome is of minor genetic importance. False! RNA is synthesized from the chromosomal DNA as an integral step gene function. of key structural significance to maintaining chromosome structure. False! Although RNA may contribute somewhat to maintaining chromosome structure, the primary role of RNA is in converting stored genetic information to an acessible form. a consequence of control of levels of gene expression. Correct! The RNA synthesized from the DNA gene template present in the chromosome is then used as the template for the synthesis of proteins, which then determine the physical cellular traits. caused by the presence of viruses that insert themselves into the chromosome structure. False! Viruses can be found associated with the cellular chromosome, but the synthesis of RNA at a chromosomal site is a normal cellular function. The chemical structure of DNA is of minor importance to chromosomal function. False! Gene function is made possible by DNA chemical structure. is controversial and poorly understood. False! X-ray diffraction studies revealed the basic structure of DNA more than 40 years ago. of crucial importance to gene function. Correct! DNA chemical structure allows storage of information and minimizes errors during passage of information to progeny. very different from all other naturally occcuring molecules. False! The structure is very similar to that of RNA, another molecule involved in genetic function. The primary chemical structure of DNA includes a phosphorylated sugar backbone. Correct! A series of deoxyribose sugar molecules polymerized through a 5' to 3' phosphate linkage forms the DNA backbone. individual components called amino acids. False! Amino acids are the constituents of proteins. individual components called nucleotide bases. Correct! The nucleotide bases attached at the 1' carbon of the sugar molecules form the central core of the DNA molecule. complete structural symmetry. False! The overall chemical structure of DNA is asymmetric, although regions within a DNA molecule may possess two-fold rotational symmtery. The nucleotide bases present in DNA include only adenine (A) and thymine (T). False! Guanine (G) and cytosine (C) also occur in DNA. only guanine (G) and cytosine (C). False! Adenine (A) and thymine (T) also occur in DNA. both uracil (U) and thymine (T). False! Uracil (U) is normally found in RNA, while thymine (T) is normally found in DNA. adenine (A), thymine (T), guanine (G), and cytosine (C) Correct. adenine (A), uracil (U), guanine (G), and cytosine (C) False! This more accurately describes the nucleotide bases present in RNA. DNA is most commonly single-stranded with little, if any internal base pairing. False! Most DNA is double-stranded, although some viruses like M13 contain single-stranded DNA. double-stranded. Correct! DNA is most commonly described as like a ladder, where the sides of the ladder are two sugar phosphate backbones in the opposite orientations with the rungs of the ladder composed of pairs of nucleotide bases. single-stranded with extensive internal base pairing. False! While this description may apply to certain DNA molecules, it is more commonly reserved to describe RNA. polar. Correct! The polarity of a DNA molecule is established by the assymetric nature of the sugar-phosphate backbone, which has a 5'-phosphate at one end and a 3'-hydroxyl group at the other. Double-stranded DNA, when it occurs, is antiparallel. Correct! The two sugar-phosphate backbones are aligned with each other in opposite orientations. parallel. False! The two sugar-phosphate backbones are aligned with each other in opposite, rather than the same, orientations. complementary. Correct! The opposing nucleotide bases align in pairs of the same dimensions to maintain the distance between the opposing sugar-phosphate backbones. anti-complementary False! Complemetarity of base pairs is fundamental to DNA structure. The base pairing arrangements that occur in double-stranded DNA as determined by hydrogen bonding include A with C and G with T. False! Although each pair consists of a purine (A or G) with a pyrimidine (C or T), the optimum hydrogen bonding scheme is not maintained (2 hydrogen bonds for A and T and 3 hydrogen bonds for G and C). A with U and G with C. False! This describes the base pairing observed in double- stranded RNA. A with T and G with C. Correct! This arrangment involves a purine (A or G) paired with the appropriate pyrimidine (T or C), with 2 hydrogen bonds in the AT pair and 3 in the GC pair. C with T and A with G. False! This involves pyrimidine-pyrimidine and purine- purine pairing, which changes the dimensions of the base pair, distorting the base-paired core of the DNA helix. The base pairing ability of DNA is critical to the function of DNA as a genetic molecule in that it facilitates easy introduction of base changes to allow rapid evolution of gene function. False! Base pairing is a key feature of high-fidelity replication, which ensures that daughter cells each receive a corret set of all cellular genes. it allows production of an accurate RNA copy for use by the protein assemby machinery of a cell. Correct! Base pairing allows the synthesis of an RNA copy of one strand of a DNA molecule for use as a template in protein assembly. the pairing of the bases with each other generates a chemical stability that completely protects them from interaction with other cellular components. False! The chemical stability of DNA in comparison to RNA is caused by the presence of 2' deoxyribose rather than ribose in the sugar-phospate backbone. changes that do occur in one strand of a double-stranded DNA molecule can be passed on to progeny. Correct! The ability to transmit information to offspring is the fundamental requirement of any genetic system. Cellular RNA is most commonly single-stranded with little, if any internal base pairing. False! RNA is a much more instable molecule than DNA, and many studies indicate that extensive internal base pairing plays a role in determining overall RNA stability in a cell. double-stranded. False! RNA is more accurately described as a single- stranded molecule that folds back on itself and has extensive internal base pairing. single-stranded with extensive internal base pairing. Correct! This is probably the best description of the overall structure of RNA in a cell. polar. Correct! Like DNA, the polarity of an RNA molecule is established by the assymetric nature of the sugar-phosphate backbone, which has a 5'-phosphate at one end and a 3'-hydroxyl group at the other. The nucleotide bases present in RNA include only adenine (A) and thymine (T). False! RNA contains adenine (A), uracil (U), guanine (G), and cytosine (C) in large amounts, while bases like thymine and pseudouracil occur in small amounts. only guanine (G) and cytosine (C). False! RNA contains adenine (A), uracil (U), guanine (G), and cytosine (C) in large amounts, while bases like thymine and pseudouracil occur in small amounts. both uracil (U) and thymine (T). False! Uracil (U) is normally found in RNA, while thymine (T) is normally found in DNA. adenine (A), thymine (T), guanine (G), and cytosine (C) False This more accurately describes the nucleotide bases present in DNA. adenine (A), uracil (U), guanine (G), and cytosine (C) Correct! There are also additional rare bases like thymine and pseudouracil in RNA. The most common base pairing arrangements that occur in double-stranded RNA as determined by hydrogen bonding include A with C and G with U. False! Although each pair consists of a purine (A or G) with a pyrimidine (C or U), the optimum hydrogen bonding scheme is not maintained (2 hydrogen bonds for A and T and 3 hydrogen bonds for G and C). A with U and G with C. Correct! This describes the most common base pairing observed in double-stranded RNA, although other base pair schemes are believed to contribute to RNA secondary structure. A with T and G with C. False! This is the base pairing arrangement observed in DNA. C with U, A, or G. False! This scheme is too non-specific to contribute stability to secondary structure. The key feature that allows the DNA molecule to store genetic information is the structure of the sugar-phosphate backbone. False! The backbone contributes by establishing the polarity, or direction, of the molecule, but information is stored by means of the order of the nucleotide bases. the order of the nucleotide bases on the sugar-phosphate backbone. Correct! the specificity with which chromosomal proteins can interact with specific DNA sequences. False! These proteins and their interactions are critical to regulation of gene expression, but the actual stored information is present as the sequence of the nucleotide bases in the DNA molecule. the ability of the DNA molecule to be directly used to produce a protein by attachment of the protein-assembly machinery to the DNA template. False! The DNA cannot be directly used as a template for the assembly of protein. A key feature that facilitates the involvement of RNA in the expression of genetic information is the instable chemical nature of RNA. Correct! This features facilitates the modulation of levels of gene expression by degrading the RNA when it is no longer needed. the ability of RNA to be recognized by the protein assembly machinery of the cell. Correct! Unlike DNA, RNA is efficiently recognized by the protein assembly machinery. the ability of amino acids to correctly align along the RNA molecule to assemble the desired gene product. False! Amino acids do not directly align along an RNA molecule, but are attached to other RNA molecules that can align along the RNA template. the resistance of the RNA molecule to rearrangemnt within a cell. False! The labile chemical nature of RNA actually facilitates genetic function by allowing rearrangements that include processing, alternative splicing, and degradation. The conversion of a double-stranded DNA molecule to single strands (denaturation) and the reversal of that process (renaturation) are strongly dependent on the temperature of the DNA solution. Correct! Increasing temperature tends to favor DNA denaturation. the amount of salt in the DNA solution. Correct! High salt concentrations favor maintaining double-stranded conformation, while low salt concentrations favor maintaining single-stranded conformation. the pH of the DNA solution. Correct! A neutral pH (7.0) favors maintaining double-stranded conformation, while alkaline pH (>10.0) favors maintaining single-stranded conformation. the size and base composition of the DNA molecule. Correct! Increasing GC content increases stability of double-stranded DNA and increasing the size of the double-stranded region improves the overall stability. Two single-stranded DNA molecules will only anneal to form a double-stranded region if the two molecules have exactly the same sequence. False! Annealing requires complementarity that conforms to the AT/GC base pairing rules. the two molecules have exactly complementary sequences. False! Sequence complementarity need not be exact, and mismatched gaps are allowed as determined by the stringency of the annealing conditions. the two molecules have sufficient sequence identity to allow extensive double-stranded regions with some mismatched bases. False! Annealing requires complementarity that conforms to the AT/GC base pairing rules. the two molecules have sufficient sequence complementarity to allow extensive double-stranded regions with some mismatched bases. Correct! The amount of mismatching allowed is determined by the stringency of the reaction (primarily salt, temperature, and pH).