分子生物学名词解释(英文)

Structure and Function of Nucleic Acid
1．The primary structure of nucleic acid is the sequence of nucleoside monophosphates from 5’ end to 3’ end in nucleic acid . (usually written as the sequence of bases).
2．DNA denaturation：A DNA has lost its’ native conformation and double strand DNA is separated to single strand DNA by exposed to a destabilizing factor such as heat, acid, alkali,urea or amide. (when high temperature is used to denature DNA, the DNA is said to be melted). 3．Tm：is melting temperature at which half (50%) of DNA molecules are denatured.
4. Annealing ：The process of renaturation of heat denatured DNA by slowly cooling is called annealing.
5．Hyperchromic effect: the absorbance at 260nm of a DNA solution increases when the double helix is melted into single strands.
6．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.
Replication
1．The Central Dogma：It described that the flow of genetic information is from DNA to RNA and then to protein. According to the central dogma of molecular biology, DNA directs the synthesis of RNA, and RNA then directs the synthesis of proteins.
2．Semiconservative replication：
* The two parental strands separate and that each then serves as a template;
* 4 kinds of dNTP as the stock;
* Catalyzed by DNA polymerase;
* Follow the usual base-pairing rules of A with T and G with C;
* Each daughter duplex has one parental strand and one newly synthesized strand.
3．Okazaki fragments ：The Short segments of DNA (1000－2000 bases in bacteria, 150-200 bases in eukaryotes) formed in the discontinuous lagging strand synthesis of DNA and are rapidly joined by DNA ligase to form a continuous DNA strand.
4．Replicon：A unit of DNA that is replicated from one replication origin. 5．Primosome：The protein complex containing DnaB, DnaC, primase (DnaG), DNA oriC sequence and other factors that initiates synthesis of DNA.
DNA synthesis proceeds in a 5'→3' direction and is semidiscontinuous. One of the new DNA strands is synthesized continuously and the other discontinuously in short pieces：
6．Leading strand ：The strand that is continuously synthesized (in the same direction as replication fork movement).
7．Lagging strand：The strand that is synthesized discontinuously in short pieces (Okazaki fragments) in a direction opposite to the direction of replication fork movement. The Okazaki fragments are then spliced together by DNA ligase.
8．Telomere：Specialized structure at the end of a linear eukaryotic chromosome, which consists of tandem repeats of a short T,G-rich sequence on the 3’ ending strand and its complementary sequence on the 5' ending strand, allows replication of 5' ends of the DNA without loss of genetic information and maintains the stability of eukaryotic chromosome.
9．Telomerase：An RNA-containing reverse transcriptase that using the RNA as a template, adds nucleotides to the 3’ ending strand and thus prevents progressive shortening of eukaryotic linear DNA molecules during replication. Human telomerase contains three parts:
Human telomerase RNA, hTR
Human telomerase associated protein 1, hTP1
Human telomerase reverse transcriptase, hTRT
10．Reverse Transcription：Synthesis of a double-strand DNA from an RNA template. 11．Reverse transcriptase：A DNA polymerase that uses RNA as its template.
RNA-dependent DNA polymerase
RNase
DNA-dependent DNA polymerase
Gene Recombination and Genetic Engineering
1. 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 restriction enzyme to form recombinant DNA. The recombinant DNA are needed to transfer and replicate DNA in a host cell.This serial process and related technique are called DNA cloning, also called gene cloning.
2. Genomic DNA library:The collection of bacteria clones that contain all the DNA in the organism’s genome on vector of plasmids or bacteriophage.
3. α-complementation:some plasmid vectors (eg,pUC19) carry lacZ gene, whose product αfragment is the N-terminal of the β-galactosidase. Whereas, the mutant E.coli strain only synthesize the ω fragment, which is the C-terminal of the enzyme. Eitherα or ω fragment alone is nonfunctional. When the vector containing lacZ is introduced into mutant E.coli, both theαand ωfragments are present. So there is an interaction and a functionally intact β-galactosidase can form. This interaction is called α- complementation.
Regulation of Gene Expression
1. 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).
2. Operon:consists of more than 2 coding sequences, promoter, operator and other regulatory sequences clustered in the genome.
3. Promoter: It is the specific DNA sequence binding to RNA-pol to initiate transcription.
4. Enhancer: consisting of several functional elements, apart from transcriptional initiation site, enhancing the activity of promoter, determining the stage and spatial specificity, functioning in different direction and distance on upstream or downstream。

5. cis-acting element:It is the specific DNA sequences regulating geneexpression (control gene expression only on the same chromosome).It is the site binding RNA-pol and transcription factors.
6. Trans-acting factor: They are the protein factors that can interact withthe cis-acting element of other gene, and control the transcription of other gene.
Cell Communication and Signal Transduction
1．G-protein: GTP-binding protein, a membrane-associated protein, consists of α, β, and γsubunits, the α subunit of the G-protein binds GTP or GDP, when the α subunit has GTP bound, the βγ-subunit leave, and the G-protein are active which can activate AC then induce biological effect.
2．Secondary messenger: are small signaling 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, etc. 3．Calmodulin: is a small cytosol protein, single polypeptide, 1 CaM can bind 4 Ca2+, binding of Ca2+ causes CaM to undergo a conformational change, then Ca2+-CaM can regulate some protein kinase including Ca2+/calmodulin-dependent protein kinase.
4．Ras protein:1 polypeptide, coding by ras gene, 21kD (P21 protein or small G protein), GTP-binding membrane protein, function as Gαof G protein, alternates between an active on state with a bound GTP and an inactive off state with a bound GDP. Ras protein has important functions in cell signal transduction and mutant Ras plays important roles in tumorigenesis.
Oncogene and Tumor suppressor gene
1．Oncogenes：genes whose products have the ability to transform eukaryotic cells in culture or to induce cancer in animals, including virus oncogene（v-onc）and cellular oncogene (c-onc). Most oncogene are mutant forms of normal genes （proto- onc）involved in the control of cell growth or division.
2．Proto-oncogenes are the normal counterparts in the eukaryotic genome to the oncogenes carried by some retroviruses. They are often directly involved in growth regulation of normal cells.
3．Tumor suppressor genes(anti-oncogene)：genes that have a negative, suppressing effect on tumor creation and thus help to prevent formation of tumors. They function cooperatively with pro-oncogenes to regulate cell growth、proliferation and differentiation. Mutant anti-oncogenes also can induce tumorigenesis.
4．Apoptosis:When cells receive some extracellular signals or are effected with pathological stimulus, they can initiate a series of gene expression and kill themselves. This kind of death is positive and have important significance in keeping balance of internal environment、development、etc.
Molecular biology techniques commonly used
1.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.I t c a n b e u s e d t o quantitative and qualitative analyze genomic DNA, or analyze the recombinant plasmid and bacteriophage(screening DNA library)
2. Northern blotting: RNA samples (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 sequence by hybridization to a labeled probe.I t c a n b e u s e d t o d etect 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.
3. 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.
4. Molecular hybridization:During renaturation, two complementary polynucleotide strands (DNA and DNA; DNA and RNA;RNA and RNA) from different sources (either DNA or RNA) can form a heteroduplex according to base complementary rule.
5.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
6. Probe:DNA or RNA fragment labeled with radioisotope, biotin or fluorescent, is used to detect specific nucleic acid sequences by hybridization.。