扬州大学：《生物化学 Biochemistry》课程教学课件（讲稿）chapter20-DNA replication and repair

DNA Replication and Repair

DNA Replication and Repair

DNA contains cell informationCompletecellDNAsequence=genome Genome of bacteria usually circular (Can be linear)Bacterial genome = 0.6 - 9.4 million bpHumangenome=4billionbp1000xaslargeas E.coli But 8× genes: 30,000 (us) vs. 4,000 (E. coli)E.coli genes uselessDNA sequence:About 1000 bases in typical bacterial gene:3000to2.4millioninhumangene

DNA contains cell information Complete cell DNA sequence = genome  Genome of bacteria usually circular (Can be linear) Bacterial genome = 0.6 – 9.4 million bp Human genome = 4 billion bp  1000× as large as E. coli  But 8× genes: 30,000 (us) vs. 4,000 (E. coli)  E. coli genes use less DNA sequence • About 1000 bases in typical bacterial gene • 3000 to 2.4 million in human gene

deoxyriboseOHOHNucleic acidsstructure(Deoxy) Ribose (A sugar)5'end3phosphategroups on5'carbonThymin 5'phosphateof onenucleotideAdenine(A)links to 3" OH of previousnucleotide2-DeoxyriboBase attached to sugarPhosphodiestbond

Nucleic acids structure  (Deoxy) Ribose (A sugar)  3 phosphate groups on 5’ carbon  5’ phosphate of one nucleotide links to 3’ OH of previous nucleotide  Base attached to sugar

B-type DNA HelixA.Space-filledB.SurfaceDNA not a perfectly linear helix Contains major and minor grooves Gives regulatory proteins access toMajorMajorgroovegrooveinternal basesMust be able to recognize sequenceMinorMinor-groovegroove

B-type DNA Helix  DNA not a perfectly linear helix  Contains major and minor grooves  Gives regulatory proteins access to internal bases  Must be able to recognize sequence

+DNACoilingDNA double helix is a right-handed helix Thumb points from bottom to top口Strands coil in the same direction as thefingersDNATowerinPerth,Australia

 DNA double helix is a right-handed helix  Thumb points from bottom to top  Strands coil in the same direction as the fingers

Chromosomes vs GenesAchromosomeconstitutesan entireDNAmolecule+protein·Protein=histones·SupercoiledDNAinnucleosomesCHROMOSOMESconsist of?Humans contain 46 such moleculesDNA and Protein(23 pairs):44somaticchromosomesⅡn: 2 sex chromosomes (X +Y)H1L19

Chromosomes vs Genes A chromosome constitutes an entire DNA molecule + protein • Protein = histones • Supercoiled DNA in nucleosomes • Humans contain 46 such molecules (23 pairs) • 44 somatic chromosomes • 2 sex chromosomes (X +Y)

Chromosomes vs Genes·Genesconstitutedistinctregionsonthechromosome?Each gene codes for a protein product000· DNA -> RNA-> proteinGene: Differences in proteins brings about differencesbetween individuals and speciesChromosome

• Genes constitute distinct regions on the chromosome • Each gene codes for a protein product • DNA -> RNA-> protein • Differences in proteins brings about differences between individuals and species Chromosomes vs Genes

CytokinesisdivisionofDNAcytoplasmDNAMitosisDNAdivisionofDNAchromosomesmitoticphDNADNAserieulMGap2rphasecellgrowth,DNACell GpreparationG2Gap1fordivisioncyclecellgrowthSDNADNADNASynthesisDNAreplicationCopyright2005PearsonPrenticeHall,Inc

The cell cycle

DNAreplication. Transfer of genetic information from generation to generation requiresthe faithful reproduction of the parental DNA. DNA reproductionproduces two identical copies of the original DNA in a process termedDNAreplication.? DNA replication results in new DNA duplex molecules in which onestrand is from the parent duplex and the other is completely new. ThismodeofDNAreplicationisreferredtoassemi-conservative

DNA replication • Transfer of genetic information from generation to generation requires the faithful reproduction of the parental DNA. DNA reproduction produces two identical copies of the original DNA in a process termed DNA replication. • DNA replication results in new DNA duplex molecules in which one strand is from the parent duplex and the other is completely new. This mode of DNA replication is referred to as semi-conservative

DNAReplicationApril25,1953Watson and Crick "It has not escaped our notice thatthe specific (base)pairing we have postulatedimmediately suggests a possible copying mechanismforthegeneticmaterial."The mechanism: Strand separation, followed bycopying of each strand.Each separated strand acts as a template for thesynthesis of a new complementary strand

April 25, 1953 Watson and Crick: "It has not escaped our notice that the specific (base) pairing we have postulated immediately suggests a possible copying mechanism for the genetic material." The mechanism: Strand separation, followed by copying of each strand. Each separated strand acts as a template for the synthesis of a new complementary strand. DNA Replication