Study Pals - Micro Lecture Test # 3

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Adenine

Back 1

Portrayed as “A”. One of the nitrogen bases found in DNA and RNA, with a purine form.

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Ames test

Back 2

A method for detecting mutagenic and potentially carcinogenic agents based upon the genetic alteration of nutritionally defective bacteria.

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Anticodon

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The trinucleotide sequence of transfer RNA that is complementary to the trinucleotide sequence of messenger RNA (the codon).

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Antiparallel strands

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One strand of DNA runs from 5’ to 3’ and the other runs from 3’ to 5’. Native double stranded DNA always has the anitparallel configuration.

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Back-mutation

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A mutation that counteracts an earlier mutation, resulting in the restoration of the original DNA sequence.

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Base Substitution Mutation

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The substitution of one base pair for another in DNA. Three kinds are: Missense, Nonsense and Silent.

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Chargaff’s Rules

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Basically that adenine (A) binds to thymine (T) with 2 hydrogen bonds. And guanine (G) binds to cytosine (C) with 3 hydrogen bonds. (It then follows that when the original two strands split, each is able to make an exact copy of the part that just split away.)

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Chromosomes

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The tightly coiled bodies in cells that are the primary sites of genes. (Most bacteria have only one and it is circular because they have trouble copying the ends of DNA.)

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Conjugation

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In bacteria, the contact between donor and recipient cells associated with the transfer of genetic material such as plasmids. Can involve special (sex) pili. Also a form of sexual recombination in ciliated protozoans. Transfer of a plasmid or chromosomal fragment from a donor cell to a recipient cell via a direct connection.

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Cytosine

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Portrayed as “C”. One of the nitrogen bases found in DNA and RNA, with a pyrimidine form.

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Central Dogma

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A basic tenet of biology. Genetic information flows from DNA to RNA to protein. Master code of DNA is first used to synthesize RNA via transcription. Then info in RNA is used to produce proteins via translation.

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Deoxyribose Sugar

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A 5-carbon sugar that is an important component of DNA.

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DNA – deoxyribonucleic acid (DNA)

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The nucleic acid often referred to as the “double helix.” It carries the master plan for an organism's heredity.

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DNA polymerase

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A class of enzymes that all synthesize DNA from a preexisting template. All synthesize only in the 5’ to 3’ direction and require a primer to extend. Proofreads nucleotides during DNA replication.

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Fertility Factor

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Donor plasmid that allows synthesis of a pilus in bacterial conjugation. Presence of the factor is indicated by F+, and lack of the factor is indicated by F−.

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Frameshift

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An insertion or deletion mutation that changes the codon reading frame from the point of the mutation to the final codon. Almost always leads to a nonfunctional protein.

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Gene

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A site on a chromosome that provides information for a certain cell function. A specific segment of DNA that contains the necessary code to make a protein or RNA molecule. The fundamental unit of heredity responsible for a given trait.

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Genome

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The complete set of chromosomes and genes in an organism.

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Genotype

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The genetic makeup of an organism. It is ultimately responsible for an organism's phenotype, or expressed characteristics. All the types of genes that constitute the genetic makeup.

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Guanine

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Portrayed as “G”. One of the nitrogen bases found in DNA and RNA in the purine form.

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Helicase

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Any of a group of enzymes that unwind the two strands in the double helix to facilitate DNA replication.

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Induced mutations

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Any alteration in DNA that occurs as a consequence of exposure to chemical or physical mutagens. Result from exposure to known mutagens, physical (primarily radiation) or chemical agents that interact with DNA in a disruptive manner.

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Inducible operon

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Operon is turned ON by substrate: enzymes needed to metabolize a nutrient are produced when needed.

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Introns

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The segments of split genes of eukaryotes that do not code for a polypeptide. They can have regulatory functions. Eukaryote DNA contains these intervening sequences of noncoding DNA which have to be splices out of the final mRNA transcript.

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Lactose

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One of the carbohydrates commonly referred to as sugars. Commonly found in milk.

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Lactose (lac) operon

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Control system that manages the regulation of lactose metabolism. It is composed of three DNA segments, including a regulator, a control locus, and a structural locus.

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Ligase

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When replication forks meet, it links together the DNA fragments in the lagging strand to complete synthesis

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Messenger RNA – (MRNA)

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A single-stranded transcript that is a copy of the DNA template that corresponds to a gene. Carries DNA message through complementary copy; message is in triplets called codons.

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Missense mutation

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A mutation in which a change in the DNA sequence results in a different amino acid being incorporated into a protein, with varying results.

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Mutagens

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Any agent that induces genetic mutation. Examples: certain chemical substances, ultraviolet light, radioactivity.

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Mutant strain

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A subspecies of microorganism that has undergone a mutation, causing expression of a trait that differs from other members of that species. Often shows variance in morphology, nutritional characteristics, genetic control mechanisms, resistance to chemicals, etc.

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Mutation

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A permanent inheritable alteration in the DNA sequence or content of a cell. A change in phenotype due to a change in genotype (nitrogen base sequence of DNA).

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Nitrogenous base

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A nitrogen-containing molecule found in DNA and RNA that provides the basis for the genetic code. Adenine, guanine, and cytosine are found in both DNA and RNA, whereas thymine is found exclusively in DNA and uracil is found exclusively in RNA.

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Nonsense codons

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A triplet of mRNA bases that does not specify an amino acid but signals the end of a polypeptide chain. Also called stop codon.

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Nonsense mutation

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A mutation that changes an amino acid-producing codon into a stop codon, leading to premature termination of a protein. Changes a normal codon into a stop codon.

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Nucleotide

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The basic structural unit of DNA and RNA; each nucleotide consists of a phosphate, a sugar (ribose in RNA, deoxyribose in DNA), and a nitrogenous base such as adenine, guanine, cytosine, thymine (DNA only) or uracil (RNA only).

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Okazaki Fragment

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In replication of DNA, a segment formed on the lagging strand in which biosynthesis is conducted in a discontinuous manner dictated by the 5’ to 3’ DNA polymerase orientation.

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Operator

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In an operon sequence, the DNA segment where transcription of structural genes is initiated.

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Operon

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A genetic operational unit that regulates metabolism by controlling mRNA production. In sequence, the unit consists of a regulatory gene, inducer or repressor control sites, and structural genes.

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Phenotype

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The observable characteristics of an organism produced by the interaction between its genetic potential (genotype) and the environment. The expression of the genotype that produces observable traits.

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Phosphate

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An acidic salt containing phosphorus and oxygen that is an essential inorganic component of DNA, RNA, and ATP.

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Pilus

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Small, stiff filamentous appendages in gram-negative bacteria that function in DNA exchange during bacterial conjugation.

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Point Mutations

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A change that involves the loss, substitution, or addition of one or a few nucleotides.

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Primase

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The enzyme that synthesizes the RNA primers required by DNA polymerases

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Primers

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Synthetic oligonucleotides of known sequence that serve as landmarks to indicate where DNA amplification begin.

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Promoter

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Part of an operon sequence. The DNA segment that is recognized by RNA polymerase as the starting site for transcription.

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Promoter region

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The site composed of a short signaling DNA sequence that RNA polymerase recognizes and binds to commence transcription.

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Protein

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Predominant organic molecule in cells, formed by long chains of amino acids

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Purines

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A nitrogen base that is an important encoding component of DNA and RNA. The two most common are adenine and guanine.

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Pyrimidines

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Nitrogen bases that help form the genetic code on DNA and RNA. Uracil, thymine, and cytosine are the most important.

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Pyrimidine dimer

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The union of two adjacent pyrimidines on the same DNA strand, brought about by exposure to ultraviolet light. It is a form of mutation

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Recombinant

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A type of genetic transfer in which DNA from one organism is donated to another.

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Recombinant DNA

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A technology, associated with genetic engineering that deliberately modifies the genetic structure of an organism to create novel products, microbes, animals, plants, and viruses.

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Recombination

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A type of genetic transfer in which DNA from one organism is donated to another.

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Redundancy

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The concept that the 64 combinations of 3-letter codons means that some amino acids can be generated by up to six different codons. Most have at least two different codons. Two only have one codon: Methionine and Tryptophan

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Regulatory Genes

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Genes that control gene expression. (can be a protein or functional RNA

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Replication

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In DNA synthesis, the semiconservative mechanisms that ensure precise duplication of the parent DNA strands.

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Replication fork

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The Y-shaped point on a replicating DNA molecule where the DNA polymerase is synthesizing new strands of DNA.

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Replicon

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A piece of DNA capable of replicating. Contains an origin of replication.

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Repressible operon

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An operon that under normal circumstances is transcribed. The buildup of the operon's amino acid product causes transcription of the operon to stop. Genes in a series are turned OFF by the product synthesized; anabolic operon – enzymes used to synthesize an amino acid stop being produced when they are not needed.

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Repressor

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The protein product of a repressor gene that combines with the operator and arrests the transcription and translation of structural genes.

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Resistance plasmids

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Plasmids, typically shared among bacteria by conjugation, that provide resistance to the effects of antibiotics.

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Ribonucleic acid (RNA)

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The nucleic acid responsible for carrying out the hereditary program transmitted by an organism's DNA.

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Ribose

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A 5-carbon monosaccharide found in RNA.

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Ribosome

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A bilobed macromolecular complex of ribonucleoprotein that coordinates the codons of mRNA with tRNA anticodons and, in so doing, constitutes the peptide assembly site.

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Ribozyme

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A part of an RNA-containing enzyme in eukaryotes that removes intervening sequences of RNA called introns and splices together the true coding sequences (exons) to form a mature messenger RNA.

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Ribosomal RNA - rRNA

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A class of RNA molecules found, together with characteristic proteins, in Ribosomes; transcribed from the DNA of the nucleolus

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RNA polymerase

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Enzyme process that translates the code of DNA to RNA.

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Semiconservative replication

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In DNA replication, the synthesis of paired daughter strands, each retaining a parent strand template.

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Sense Strand

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The strand of DNA which is used during transcription to make mRNA. The mRNA made thus has the sequence of the antisense strand (template strand) of DNA, and it codes for a sense strand of polypeptide (which eventually becomes a protein or part of a protein) during translation.

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Silent mutation

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A mutation that, because of the degeneracy of the genetic code, results in a nucleotide change in both the DNA and mRNA but not the resultant amino acid and thus, not the protein.

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Specialized transduction

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a highly specific part of the host genome is regularly incorporated into the virus.

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Spontaneous mutation

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A mutation in DNA caused by random mistakes in replication and not known to be influenced by any mutagenic agent. These mutations give rise to an organism's natural, or background, rate of mutation.

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Start codon

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The nucleotide triplet AUG that codes for the first amino acid in protein sequences.

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Structural Genes

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Genes that code for proteins

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Termination codons

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Three codons, UAA, UAG, UGA, for which there is no corresponding tRNA. When these codons are reached, the ribosome falls off and the last tRNA is removed from the polypeptide

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Thymine

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Portrayed as “T”. One of the nitrogen bases found in DNA but not in RNA. Thymine is in a pyrimidine form

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Transcript

Back 78

A newly transcribed RNA molecule.

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Transcription

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mRNA synthesis; the process by which a strand of RNA is produced against a DNA template. Information stored on the DNA molecule is conveyed to RNA molecules through this process.

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Transduction

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The transfer of genetic material from one bacterium to another by means of a bacteriophage vector. Bacteriophage serves as a carrier of DNA from a donor cell to a recipient cell. Two types: generalized and specialized.

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Transfection

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Introduction of genetic material into an animal or plant cell using a viral or bacterial vector.

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Transfer RNA – (tRNA)

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A transcript of DNA that specializes in converting RNA language into protein language. Made from DNA; secondary structure creates loops; bottom loop exposes a triplet of nucleotides and anticodon with designates specificity and complements mRNA; carries specific amino acids to ribosomes.

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Transformation

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In microbial genetics, the transfer of genetic material contained in “naked” DNA fragments from a donor cell to a competent recipient cell. Chromosome fragments (free or naked DNA) from a lysed cell are accepted by recipient cell; the genetic code of the DNA fragment is acquired by the recipient.

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Translation

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Protein synthesis; the process of decoding the messenger RNA code into a polypeptide. (After transcription) Information contained in the RNA molecule is then used to produce proteins in this process.

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Transposon

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A DNA segment with an insertion sequence at each end, enabling it to migrate to another plasmid, to the bacterial chromosome, or to a bacteriophage.

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Uracil

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One of the nitrogen bases in RNA but not in DNA. It is in a pyrimidine form.

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Wild type

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The natural, nonmutated form of a genetic trait.

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Wobble

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Referring to three letter mRNA codons. Only the first two nucleotides are required to encode the correct amino acid. The third does not change its sense and is thought to permit some variation or mutation without changing the message.