Biology Flash Cards

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Biology Definitions

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Rabies VirusA negative stranded RNA virus with a protein capsid and an envelope. Like Tobacco Mosaic Virus (TMV), it has a helical structure, but unlike TMV, it also has an envelope.Virus, Tobacco Mosaic Virus
Rational Drug DesignThe process of inventing new drugs based on knowledge of the biochemical and genetic components of a disease. Historically, drugs have been discovered and tested through empirical methods, often using statistical studies with little or no knowledge of how the drug performs its function. With new breakthroughs in biology, scientists now have the tools to study the biochemical pathways and genetic causes of disease, and design drugs that disrupt the disease by disrupting its known biochemical pathways.Cancer, PCR
Reading FrameSince each codon is comprised of 3 bases, a messenger RNA can be read in three different ways, starting from the first, second, or third base. Some viruses cleverly use all three reading frames to translate proteins, allowing them to efficiently use a very small genome.mRNA
ReceptorA protein embedded in the plasma membrane (liped bilayer) of the cell. A cell has many of these receptor proteins, and different cell types (e.g. liver cells, skin cells, etc.) have different types of receptors. Receptors bind to specific molecules they encounter in the extra-cellular space. Different receptors bind to different ligands; (e.g. some bind to other peptides, some bind to hormones, some bind to antigens or toxins, etc.) Once bound, the chemical properties of the receptor change (e.g. the shape), initiating or preventing a biochemical pathway inside the cell. Most viruses hijack a receptor, tricking the receptor into giving the virus safe passage into the cell.Ligand, Virus, Cell, Peptides
RecessiveAn allele's phenotype is recessive if it is not expressed when a dominant allele is present. For example, in peas, when both the round and wrinkled alleles are present, peas will appear as round and not wrinkled because the round allele is dominant over the wrinkled allele. If two copies of the wrinkled allele are present (homozygous), the pea will appear as wrinkled.Gene, Allele, Recessive, Homozygous, Heterozygous, Mendel
Recombinant DNADNA which contains genes from different sources. DNA which has been altered in the laboratory by adding or replacing a gene, usually from another species.. DNA Cloning, DNA, Gene
Recombination RateAn individual receives a copy of a particular homologous chromosome from each parent. The individual will pass only one of these two homologous chromosomes on to a given offspring. Generally, these chromosomes are passed on unchanged to the children. Sometimes, the two homologous chromosomes will exchange genetic material in a "crossover", resulting in a child which has a non-Parental Type (one of the child's chromosome is not an exact copy of one of its parent's chromosome, but is instead a combination of two of its parent's homologous chromosomes). The rate at which these crossovers occur is called the Recombination Rate. Recombination Rates are used to calculate Genetic Maps. Specifically, the Frequency of Non-Parental types are used as the Recombination Rate when calculating Genetic Maps.Genetic Map, Chromosomal Theory of Inheritance, Chromosome, Gene
ReplicationThe process by which DNA makes a copy of itself. DNA separates sections of its two strands. Starting with a primer, it creates a contiguous new complementary strand of DNA from its leading strand (which runs 3' to 5') using DNA Polymerase. The new strand starts at the 5' end and has nucelotides added to its 3' end. Because the original DNA's lagging strand is oriented from 5' to 3', causing its complementary strand to be oriented from 3' to 5' (the wrong way for adding nucleotides -- nucleotides must be added to the 3' end), it uses many primers to create small DNA fragments (Okazaki fragments), oriented in a backward direction, which are then ligated together to form the full, complementary DNA strand. In Eukaryotes, Replication takes place in the Nucleus. In Prokaryotes, Replication takes place in the Cytoplasm.Central Dogma of Molecular Biology, Transcription, Translation, Okazaki Fragments, Ligase, Primer, DNA Polymerase
Restriction EnzymesSpecial enzymes which can cut DNA at particular sequences. Very often, these sequences are palindromes. Used in DNA cloning to cut up a genome into fragments. Some bacteria use restriction enzymes to cut the DNA of invading bacteriophage (viruses). These bacteria may mark matching sections of their own DNA with methyl groups (using another specialized protein), which blocks the restriction enzyme from destroying the cell's own DNA.DNA Cloning, Recombinant DNA, EcoR1
Restriction MappingA technique used by biochemists to analyze a clone. A biochemist make take a gene sequence which she wishes to analyze, cuts it with a certain restriction enzyme, and then uses gel electrophoresis to analyze the sizes of the cut pieces. She then uses a second restriction enzyme to cut the gene, and again uses gel electrophoresis. She then cuts the gene with both restriction enzymes, and again performs gel electrophoresis. Entering the observed results from the many gel electrophoresis procedures into a computer program, she can determine the locations of the restriction sites. This is called Restriction Mapping.Gel Electrophoresis, Cloning
Restriction PointAfter a cell finishes Mitosis, and enters the G1 resting phase, it is at the "restriction" point, where it then "decides" whether or not it should continue the cell cycle, and enter the S Phase, beginning another growth and division cycle. or else exit the cell cycle, and go to G0. The cell makes this decision based on the presence or absense of extra-cellular Growth Factors. Also called the "R" point. If mutations cause the cell to misinterpret or ignore mitogens or growth inhibitory factors, and the cell continues to grow and divide even if extra-cellular signals tell it otherwise, the cell is said to be cancerous.Cell Cycle, G1, Mitosis
RetinoblastomaA rare eye tumor of children. A point mutation in a tumor suppressor gene deactivates the gene, and the eye cells grow and divide unregulated, forming a tumor. Retinoblastoma is a recessive phenotype, requiring a copy of the defective gene from both parents, or a defective gene from one parent and a (deletion) mutation in the other allele. Without the correct gene to regulate it at the Restriction Point, the cell grows and divides constitutively.Tumor Suppressor Genes, Restriction Point
RetrovirusA virus that can install DNA into a cell that it infects. Typically, a retrovirus contains RNA within its capsid. Once it has infected the cell, it uses reverse transcripase to convert its RNA into DNA, which is then inserted into the host cell's DNA (via Integrase), so that it can produce more virus proteins, and thus more virus particles (virions). Note that there is no known mechanism to remove retroviral DNA from a cell. HIV is a retrovirus.Reverse Transcriptase, Integrase, Provirus, Virus
Reverse TranscriptaseA protein that can create DNA from RNA. Note that normally, RNA is created from DNA. Some viruses that carry RNA genomes in their capsid use Reverse Transcriptase in the infected cell to convert their RNA into DNA which can then be used to create more virus particles in the cell. Plus Strand RNA viruses typically encode reverse transcriptase in their RNA, whereas minus strand RNA viruses usually include reverse transcriptase inside the capsid along with the RNA. Many of the drugs used to combat AIDs are reverse transcriptase inhibitors.Virus, Transcription
Rheumatoid ArthritisA type of autoimmune disease in which the immune system recoginzes (attacks) antigens in the cartilage of joints.Autoimmune Disease
RibosomeAn organelle in the cell that uses a messenger RNA (mRNA) and many transfer RNAs (tRNA) to translate a messenger RNA into a protein. It reads codons (3-letter nucleotide sequences) from the mRNA, finds a tRNA with the complementary sequence (anti-codon), removes the amino acid from the tRNA, and adds it to the growing polypeptide, eventually producing a protein.mRNA, tRNA
RNALike DNA, RNA is also a macromolecule which contains the instructions which tell the cell how to produce proteins. There are differnt classes of RNA, including Messenger RNA (mRNA), transfer RNA (tRNA), and RNA intereference (RNAi). An RNA monomer is comprised of a sugar (Ribose, not 2' Deoxyribose as in DNA), a base (Adenine, Guanine, Cytosine, and Uracil), and a Triphosphate. The energy of the Triphosphate is used to add the RNA monomer to the 3' end of the RNA polymer. Because RNA has a Ribose (with an additional Oxygen) instead of a Deoxyribose, it cannot form double helixes, and is less stable than DNA. Similarly, the Uracil that RNA uses differs from the Thymine DNA uses by a single Methyl group. DNA, Transcription, Protein, mRNA, tRNA, RNAi
RNA PolymeraseThe enzyme responsible for transcibing an RNA molecule from a DNA gene. RNA Polymerize transcribes a DNA Adenine (A) to an RNA Uracil (U, not Thymine as in DNA), Thymine (T) to Adenine (A), Guanine (G) to Cytosine (C), and Cytosine (C) to Guanine. RNA Polymerase begins transcribing right after a Promoter Site on the DNA gene, and stops transcribing when it detects a stop signal.DNA Polymerase, Polymer, Promoter
RNA SplicingThe process by which an immature mRNA is turned into a mature mRNA by removal of some of the base pairs, and splicing together of the remaining segments. This process occurs in Eukaryotes, and is also called post-transcriptional processing. For example, a typical human gene may be 30,000 base pairs long, but its mature RNA may only be 1500 base pairs long.Transcription, Alternative Splicing, Eukaryote
RNA StabilityA type of Gene Regulation which takes place at the Transcriptional level. The cell can control the production of that gene's protein by either rapidly degrading the mRNA (preventing the production of the protein), or by protecting the mRNA from degradation (allowing it to be used to create many copies of the protein).DNA Regulation
Rous Sarcoma Virus (RSV)The first discovered (1911) oncovirus (cancer-causing virus). Peyton Rous discovered the virus in a tumor of a chicken. After grinding up the tumor, and passing it through a filter, Rous discovered that the filtrate (the material that passed through the filter) could cause a tumor when injected into another chicken. This led to the discovery of small particles we now call viruses. Rous Sarcoma Virus (RSV) is a single-stranded RNA virus. The RNA is reverse-transcribed (copied into a double-stranded DNA molecule which is called a "provirus"), The provirus is then integrated into the host chromosome, where it hijacks the cell's machinery to produce mRNA (for virus proteins) as well as progeny genomic RNA (more virus RNA) which are then used to create more virus particles. Rous Saroma Virus is about 9-10 Kilobases in length. RSV contains genes for both replication and transformation (the cancer-causing gene is called SRC).Virus, Replication, Transformation, SRC

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