分子生物学名词解释

TermsDNA denaturation: When DNA is exposed to some destabilizing factors such as heat, acid, alkali, urea or amide, double strand DNA is separated to single strand DNA and lost its’native conformation. Also, DNA lost its biological functions. When high temperature is used to denature DNA, the DNA is said to be melted.Hyperchromic effect: The absorbance at 260 nm of a DNA solution increases when the double helix is melted into single strands.Hybridization: When heterogeneous DNA or RNA are put together, they will become to heteroduplex via the base-pairing rules during renaturation if they are complementary in parts (not complete). This is called molecular hybridization.Ribozyme: They are the RNA molecules with catalytic activity. The activity of these ribozymes often involves the cleavage of a nucleic acid.The Central Dogma:It described that the flow of genetic information is from DNA to RNA and then to protein. DNA directs the synthesis of RNA, and RNA then directs the synthesis of proteins. Semiconservative replication: The two strands of DNA double helix are separated, each strand serves as a template for the synthesis of a new complementary strand, producing two daughter molecules. Each daughter molecule has one parental strand and one newly synthesized strand. Reverse transcription: Synthesis of a double-strand DNA from an RNA template.Reverse transcriptase: A DNA polymerase that uses RNA as its template.Asymmetric transcription: Transcription generally involves only short segments of a DNA molecule, and within those segments only one of the two DNA strands serves as a template. The template strand of different genes is not always on the same strand of DNA. That is, in any chromosome, different genes may use different strands as template.Split gene: It is the eukaryotic structural gene on which the coding regions (exons) are often interrupted by the noncoding regions (introns). After splicing of introns and connecting exons again, it become mature RNA. For example, protein coding gene.Exon: Exons are the sequences that are presented in split genes and mature RNA molecules, and they encompass not only protein-coding genes but also the genes for various RNA (such as tRNAs or rRNAs).Intron: Introns are the intervening nucleotide sequences in the structural gene and its pre-RNA that are removed from the primary transcript when it is processed into a mature RNA.Open reading frame (ORF): The nucleotide acid sequence in mRNA from 5’AUG to 3’stop codon, which consists of a group of contiguous genetic codons edcoding a whole protein. Usually, it includes more than 500 genetic codes.Poly(ribo)some: Ribosomes(10~100) are tandemly arranged on one mRNA and move in the direction of 5’-3’. Such a complex of one mRNA and a number of ribosomes is called polyribosone. Increasing the efficiency of protein synthesis.Signal peptide: A short amino-terminal sequence that directs a newly synthesized protein to a specific location (ER), which is subsequently cleaved away by signal peptidase. It consists of several basic amino acids, 10 to 15 hydrophobic amino acids and lytic site for signal peptidase. Housekeeping gene: It is the genes coding for proteins that are needed for basic life processes in all kinds of cells(such as enzymes for citric acid cycle).Constitutive gene expression:Operon: The operon consists of more than 2 coding sequences, promoter, operator and other regulatory sequences clustered in the genome.Enhancer: Apart from transcription start site(1~30kb); Determining the temporal and spatial specificity of gene expression; Functions in different direction and distance on upstream or downstream; Enhancing the activity of promoter; Consisting of several functional elements→core sequence for specific TF binding; Require promoter to exert its function.Cis-acting element:It is the specific DNA sequences regulating gene expression (control gene expression only on the same chromosome). It is the site to bind RNA-pol and transcription factors. Trans-acting factor (TF): They are the protein factors that can interact with the cis-acting element of other gene, and control the transcription of other gene.DNA cloning: To clone a piece of DNA, DNA is cut into fragments using restriction enzymes. The fragments are pasted into vectors that have been cut by the same restriction enzymes to form recombinant DNA. Then, the recombinant DNA was transferred into a host cell where it replicate. This process and related technique are called DNA cloning, also called gene cloning.Genomic library: The collection of bacteria clones that contain all the DNA in the organism’s genome on vector of plasmids or bacteriophage.cDNA library: The collection of bacteria clones that contains only complementary DNA molecules synthesized from mRNA molecules in a cell. The advantage of cDNA library is that it contains only the coding region of a genome.Secondary messenger: They are some small signal molecules that are generated in the cell in response to extracellular signals. They can activate many other downstream components. The most important second messengers are: Ca2+, cAMP, cGMP, DAG, IP3, Cer, AA and its derivatives, etc. Oncogene: A gene whose product is involved either in transforming cells in culture or in inducing cancer in animals including virus oncogene (v-onc) and cellular-oncogene (c-onc). Most oncogene are mutant forms of normal genes (proto- oncogene) involved in the control of cell growth or division.Tumor Suppressor Genes: A kind of negative regulatory gene which can check cell-cycle progression, and hold cells in quiescence or even lead cells to commit suicide unless conditions are appropriate for cell-cycle progression, means that they can prevent cells from becoming cancerous. (Rb genep53 gene).Blotting: Transfer (blot) biological macromolecules separated in the gel and fix them to nitrocellulose/nylon membrane by diffusion, electro-transferring or vacuum absorption, then detect it.Probe: DNA or RNA fragment labeled with radioisotope, biotin or fluorescent, is used to detect specific nucleic acid sequences by hybridization. Including DNA probe, RNA probe, Antibody. Polymerase Chain Reaction (PCR): PCR is a technique for amplifying a specific DNA segment in vitro by multiple cycles of DNA synthesis. The reaction system include DNA template, Taq DNA-pol, dNTPs, short oligonucleotide primers, buffer containing Mg2+. The process including 3 steps: denaturation, annealing, extension.Southern blotting: Genomic DNA (from tissues or cells) are cut by RE, separated by gel electrophoresis and denatured in solution, then transferred to a nitrocellulose membrane for detecting specific DNA sequence by hybridization to a labeled probe. It can be used to quantitative and qualitative analyze genomic DNA, or analyze the recombinant plasmid and bacteriophage (screening DNA library).Northern blotting: RNA samples (from tissues or cells) are separated by gel electrophoresis and denatured in solution, then transferred to a nitrocellulose membrane for detecting specific sequence by hybridization to a labeled probe. It can be used to detect the level of specific mRNA in some tissues (cells) and to compare the level of same gene expression in different tissues (cells) or at different development period.Western blotting: Protein samples are separated by PAGE electrophoresis, then electro-transferred to NC membrane. The proteins on NC membrane hybridize with a specific antibody (1st antibody ), then the target protein binding with antibody is detected with a labeled secondary antibody (2nd antibody). Also called immunoblotting. It can be used to detect the specific protein, semi-quantify specific protein, etc.De novo synthesis of nucleotide begins with their metabolic precursors: amino acid, ribose-5-phosphate, CO2, and one carbon unit.Salvage pathways recycle the free bases and nucleosides released from nucleic acid breakdown.。