【正文】 Molecular Biology 大連理工大學(xué) What we learned last class ? Teaching arrangement of this course ? Definition of Molecular Biology ? Goals of Molecular Biology ? Major events in the history of MB ? Preview of some concepts and processes of Molecular Biology Molecular Biology 大連理工大學(xué) Translation ? Process of generating a protein or polypeptide from an mRNA molecule is known as translation. ? Protein: a polymer or chain of amino acids, whose sequence is determined by the mRNA template – 3 nulceotides code for 20 naturally occurring amino acids – 43 = 64。 thus several trinucleotide sequences (codons) correspond to a single amino acid. – There is no nucleotide between codons, and a few codons represent start and stop. Molecular Biology 大連理工大學(xué) 3 Ribosomes ? Ribosomes 。 Factory for protein synthesis。 are posed of ribosomal RNA and ribosomal proteins (known as a Ribonucleoprotein or RNP). They translate messenger RNA (mRNA) to build polypeptide chains using amino acids delivered by transfer RNA (tRNA). Molecular Biology 大連理工大學(xué) 4 Ribosomes ? Eukaryotic ribosomes are larger. They consist of two subunits。 a 60S subunit holds three rRNAs(5S, , 28S) and about 40 proteins, and a 40S subunit contains an18S rRNA and about 30 proteins , which e together to form an 80S particle pared with prokaryotic 70S ribosome. Molecular Biology 大連理工大學(xué) 5 ? Most mRNA are translated by more than one ribosome at a time。 the result, a structure in which many ribosomes translate an mRNA in tandem, is called a polysomes. Polysomes Molecular Biology 大連理工大學(xué) 6 The Protein ? Proteins are the basic building materials of a cell, made by cell itself。 the final product of most genes. ? Proteins are chain like polymers of a few or many thousands of amino acids. Amino acids are represented by codons, which are 3nucleotide RNA sequences. Amino acids joined together by peptide bonds (polypeptide). Proteins can be posed of one or more polypeptide chains. ? Proteins have many functions: provide structure that help cells integrity and shape (. collagen in bone)。 serve as enzymes and hormones。 bind and carry substance and control activities of genes…. Molecular Biology 大連理工大學(xué) 7 Four levels of a protein39。s structure: ? Primary structure: Formed by joining the amino acid sequence into a polypeptide. ? Secondary structure: Different conformation that can be taken by the polypeptide: alpha helix and strands of beta sheet. ? Tertiary structure : Result from folding the secondary structure ponents of the polypeptide into threedimensional configuration. ? Quaternary structure : plex of several protein molecules or polypeptide chains, usually called protein subunits, which function as part of the larger assembly or protein plex. Molecular Biology 大連理工大學(xué) 8 Protein Structure Molecular Biology 大連理工大學(xué) Biological function of proteins ? Enzyme catalysis: DNA polymerases, lactate dehydrogenase, trypsin ? Transport: hemoglobin, membrane transporters, serum albumin ? Storage: ovalbumin, eggwhite protein, ferritin ? Motion: myosin, actin, tubulin, flagellar proteins ? Structural and mechanical support: collagen, elastin, keratin, viral coat proteins ? Defense: antibodies, plement factors, blood clotting factors, protease inhibitors ? Signal transduction: receptors, ion channels, rhodopsin, G proteins, signalling cascade proteins ? Control of growth, differentiation and metabolism: repressor proteins, growth factors, cytokines, bone morphogenic proteins, peptide hormones, cell adhesion proteins ? Toxins: snake venoms, cholera toxin Molecular Biology 大連理工大學(xué) 10 Types of control in Eukaryotes ? Transcriptional, regulate transcription, prevent mRNA from being synthesized. ? Posttranscriptional, control mRNA after it has been produced. ? Translational, prevent translation。 involve protein factors needed for translation. ? Posttranslational, after the protein has been produced: modify proteins to regulate its halflife, localization, etc. Molecular Biology 大連理工大學(xué) Mutation ? Mutation includes both gross alteration of chromosome and more subtle alteration to specific gene sequence. ? Gross chromosomal aberrations include: large deletions。 addition and translocation (reciprocal and nonreciprocal). ? Mutation in a gene39。s DNA sequence can alter the amino acid sequence of the protein encoded by the gene. Point mutations are the result of the substitution of a single base. Frameshift mutations occur when the reading frame of the gene is shifted by addition or deletion of one or more bases. Molecular Biology 大連理工大學(xué) 12 Mutation Mutations can have harmful, beneficial, neutral, or uncertain effects on health and may be inherited as autosomal dominant, autosomal recessive, or Xlinked traits. Mutations that cause serious disability early in life are usually rare because of their adverse effect on life expectancy and reproduction. Molecular Biology 大連理工大學(xué) 13 Common Tools in Molecular Biology ? Nucleic acid fractionation ? Polymerase chain reaction ? Probes, Hybridization ? Vector, Molecular cloning ? Nucleic acid enzymes ? Microarray ? DNA sequencing ? Electrophoretic separation of nucleic acid ? Detection of genes: ? *DNA: Southern blotting。 inSitu hybridization。 FISH Technique ? *RNA: Northern blotting ? *Protein: Western blotting, immunohistochemistry Molecular Biology 大連理工大學(xué) Molecular Biology 大連理工大學(xué) 15 Molecular Biology : Uses The Most Recent Applied Technologies ? Geic engineering in agriculture ? Application in research ?