TheCentralDogmaofMolecularBiologyLandofMayo：分子生物学的中心教条地梅奥课件

1、The Central Dogma of Molecular BiologyMark MayoCypress CollegeLast update 10/6/131第1页，共52页。The Central Dogma of Molecular BiologyReverseTranscription2第2页，共52页。Importance of Proteins There are three main kinds:structural - make up most body partshormone - chemical that controls the bodyenzyme - catal

2、yst - speeds up chemical reactionsInsulin, a protein3第3页，共52页。Importance of Proteins Without proteins there would be no lifeAll cells make proteinsProteins in your body make up your:HairNailsMusclesSkinCartilage4第4页，共52页。Discovery of DNA (deoxyribonucleic acid) 1953 Watson, Crick and Wilkins determi

3、ned the structure of DNA to be a double helixThey won a Nobel Prize for their work 5第5页，共52页。Structure of the DNA molecule DNA is shaped like a double helixIt is like a spiral staircaseAnother way to think of it is a twisted ladder6第6页，共52页。Connecting the DNA moleculeRails* of the DNA ladder are alt

4、ernating sugar & phosphatesRungs* are composed of pairs of basesA bonds with T*G bonds with C*7第7页，共52页。Connecting the DNA MoleculeThe DNA Ladder*PS APS TPS GPS - C PT - S PA - S PC - S PG - SPS APS TP? GPS - C PT - ? P? - S PC - S PG - S* * *8第8页，共52页。Connecting the DNA moleculeThe two strands of D

5、NA are differentOne is called the sense strand and it is the plan to make a proteinThe other strand is the antisense strand and it is only used for protection of the sense strand9第9页，共52页。Connecting the DNA moleculeThe two strands of DNA are said to be antiparallel*One strand is oriented in a 5 to 3

6、 direction*The other strand is oriented in the opposite 3 to 5 direction*5 33 5senseantisense10第10页，共52页。Connecting the DNA moleculeNucleotides are units composed of abase, phosphate and a sugar 11第11页，共52页。Connecting the DNA moleculeThe two strands of DNA bases are connected by weak forces called h

7、ydrogen bonds* 2 hydrogen bonds3 hydrogen bonds*12第12页，共52页。Components of DNA Phosphate 13第13页，共52页。Components of DNADeoxyribose (sugar) 14第14页，共52页。Components of DNADNA bases (4 different types)AdenineThymine*GuanineCytosine 15第15页，共52页。Components of DNAProteins are attached to the DNA helix in cel

8、lsThese proteins are known as histones They assist in DNA storage16第16页，共52页。DNA and RNA Compared DNA Found only in nucleus*Double stranded helixBases = ATGC*Sugar = Deoxyribose RNAFound in ribosomes, nucleolus*Single stranded helix *Bases = AUGC (URACIL) *Sugar = Ribose* DNA is also found in a sele

9、ct number of other organelles17第17页，共52页。Replication of DNA Replication - the making of an exact copy of the DNA moleculeReplication occurs whenever a cell dividesThe copy must be 100% accurate (errors = death possibly)Replication practice (find the complimentary bases or base sequence)*A pairs with

10、 ?T pairs with ?G pairs with ?C pairs with ?18第18页，共52页。Replication of DNA19第19页，共52页。Stages in replication (basic)DNA molecule is split in two at the end by the work of enzymes *DNA unzips slightly and the two strands unwind *new nucleotides attach to the free ends * ( A-T, G-C)more DNA unzipsmore

11、nucleotides attach *process continues until completedresult is two (2) double strands of DNAeach strand is 50% new and 50% old DNA20第20页，共52页。Stages in replicationDNA replication is different on the leading and lagging strands *Lagging strand has Okazaki fragments*21第21页，共52页。Stages in replicationDN

12、A replication is different on the leading and lagging strands *22第22页，共52页。Enzymes * Involved in DNA ReplicationDNA polymerase adds nucleotides in a 5 to 3 directionTopoisomeraseGyraseRNA primaseDNA ligase connects the gaps in the lagging strand23第23页，共52页。DNA Replicationin Motion24第24页，共52页。Introns

13、 and ExonsIntrons sequences in the DNA that are NOT used to make mRNA or to make a protein. They are NOT transcribed *Exons sequences in the DNA that are expressed or used to make mRNA and ultimately are used to make a protein25第25页，共52页。Introns and Exons26第26页，共52页。Restriction EnzymesRestriction en

14、zymes (also known as restriction endonucleases) recognize specific DNA sequences and CLEAVE or cut the DNA into pieces *Generally these cuts occur in a manner which leaves a sticky end of single strand DNAThese pieces can be separated by using gel electrophoresis (this is like electronic chromatogra

15、phy)We use restriction enzymes for cutting bacterial, viral or even human DNA and later insertion of the desired DNA fragments called gene splicing *27第27页，共52页。Restriction Enzymessticky endssticky endsblunt endsblunt ends28第28页，共52页。Restriction Enzymes29第29页，共52页。Ribonucleic Acid (RNA)Three types o

16、f RNA:rRNA = ribosomal RNA - makes up the ribosomemRNA = messenger RNA - is the message from DNA for the construction of the new protein molecule *tRNA = transfer RNA - carries amino acids to ribosomes 30第30页，共52页。Ribonucleic Acid (RNA)Ribosomal RNA is used to make a ribosomeThe ribosome “reads” the

17、 mRNA plan for the new proteinmRNA is the set of directions for a new protein*Ribosome31第31页，共52页。Ribonucleic Acid (RNA)Messenger RNASenseAntisense32第32页，共52页。Ribonucleic Acid (RNA)Transfer RNAEach tRNA holds one amino acidEvery tRNA has a special region called the anti-codon (3 bases) An tRNA anti-

18、codon mates with codon on the mRNA moleculeThere are 61 different tRNA molecules, yet only about 20 amino acids (hint: 3 stop codons)33第33页，共52页。Ribonucleic Acid (RNA)Transfer RNA34第34页，共52页。Transcription Transcription is the special copying of one side of the DNA molecule (the sense strand) that re

19、sults in the production of a single strand of RNA *The original DNA is not changedThis process can be repeatedThe amount of DNA that is transcribed is usually one geneThe r in the title is red to remind you that transcription makes RNA35第35页，共52页。TranscriptionProcess of TranscriptionDNA is unzipped

20、by an enzymeOnly one side fills with RNA nucleotides by the action of another enzyme RNA polymerase A-U, G-C (NO THYMINE = T) As the RNA strand separates the DNA strands reattach as before the process started4. The result is the original DNA plus a new RNA strand36第36页，共52页。Transcription37第37页，共52页。

21、TranscriptionUracil a base only found in RNA38第38页，共52页。TranscriptionTranscription Practice *A (in DNA) pairs with _ in RNA T (in DNA) pairs with _ in RNA G (in DNA) pairs with _ in RNAC (in DNA) pairs with _ in RNA39第39页，共52页。Transcription40第40页，共52页。TranscriptionSometimes two or more ribosomes att

22、ach to the mRNA transcript at the same time and this is called a polysome *41第41页，共52页。TranslationTranslation * is the reading of the RNA code, by ribosomes, to make proteins * or polypeptides Translation is often called protein synthesis*42第42页，共52页。TranslationmRNA is the message (the plan for the

23、protein)rRNA reads the mRNA (the ribosome) *tRNA molecules carry amino acids to the ribosome for assembly into proteinsThe ribosome allows only the correct tRNA to add its amino acid others are rejected43第43页，共52页。Translation *Anticodons *Codons *44第44页，共52页。Translation45第45页，共52页。TranslationTriplet codons -groups of three bases on mRNA that code for specific amino acids * 46第46页，共52页。TranslationThe function of special stop codons is to terminate* or end the translation process*The stop codons are: UAA, UAG and UGAThe function of the start codon is to serve a