dna & dna replication. history dna dna comprised of genes in non-dividing cell nucleus as...
Post on 01-Jan-2016
229 Views
Preview:
TRANSCRIPT
HistoryHistoryDNADNA
Comprised of genesComprised of genes In non-dividing cell nucleus In non-dividing cell nucleus
as chromatinas chromatinProtein/DNA complexProtein/DNA complex
Chromosomes form during Chromosomes form during cell divisioncell divisionDuplicate to yield a full set in Duplicate to yield a full set in
daughter celldaughter cell
From Chapter 3From Chapter 3Nucleic acids are polymersNucleic acids are polymers
Monomers are called nucleotidesMonomers are called nucleotidesNucleotides = base + sugar + phosphateNucleotides = base + sugar + phosphate
Base = Base = adenine, guanineadenine, guanine thymine, cytosine, uracilthymine, cytosine, uracil
Sugar = deoxyribose or riboseSugar = deoxyribose or ribosePhosphate, a single phosphate in DNAPhosphate, a single phosphate in DNA
Sugar is linked to the phosphateSugar is linked to the phosphate
DNA is a Double HelixDNA is a Double Helix NucleotidesNucleotides
A, G, T, CA, G, T, C
Sugar and phosphate Sugar and phosphate form the backboneform the backbone
Bases lie between the Bases lie between the backbonebackbone
Held together by Held together by H-bonds between the H-bonds between the basesbases A-T – 2 H bondsA-T – 2 H bonds G-C – 3 H bondsG-C – 3 H bonds
H - BondsH - Bonds Base-pairing rulesBase-pairing rulesAAT only (AT only (AU U
if DNA-RNA if DNA-RNA hybrid)hybrid)
GGC onlyC only
Nucleotides as LanguageNucleotides as Language
We must start to think of the nucleotides – We must start to think of the nucleotides – A, G, C and T as part of a special A, G, C and T as part of a special language – the language of genes that we language – the language of genes that we will see translated to the language of will see translated to the language of amino acids in proteinsamino acids in proteins
Genes as Information TransferGenes as Information Transfer
A A genegene is the sequence of nucleotides is the sequence of nucleotides within a portion of DNA that codes for a within a portion of DNA that codes for a peptide or a functional RNApeptide or a functional RNA
Sum of all genes = Sum of all genes = genomegenome
DNA ReplicationDNA Replication
SemiconservativeSemiconservative Daughter DNA is a double helix with 1 parent Daughter DNA is a double helix with 1 parent
strand and 1 new strandstrand and 1 new strand Found that 1 strand serves as the templateFound that 1 strand serves as the template for for
new strandnew strand
ReplicationReplicationForkFork
Parental DNA MoleculeParental DNA Molecule
3’
5’
3’
5’
DNA TemplateDNA Template
Each strand of the parent DNA is used as a Each strand of the parent DNA is used as a templatetemplate to make the new daughter strand to make the new daughter strand
DNA replication makes 2 new complete double DNA replication makes 2 new complete double helices each with 1 old and 1 new strandhelices each with 1 old and 1 new strand
How is DNA Synthesized?How is DNA Synthesized?
DNA is synthesized byDNA is synthesized bySimple addition of nucleotides Simple addition of nucleotides
along one strand (1/2 the double along one strand (1/2 the double helix)helix)
Mistakes during ReplicationMistakes during Replication
Base pairing rules must be maintainedBase pairing rules must be maintainedMistake = genome mutation, may have Mistake = genome mutation, may have
consequence on daughter cellsconsequence on daughter cellsOnly correct pairings fit Only correct pairings fit If wrong nucleotide is includedIf wrong nucleotide is included
Special enzyme has “Special enzyme has “proofreading”proofreading” and and can remove incorrect nucleotidecan remove incorrect nucleotide
Another enzyme then adds correct baseAnother enzyme then adds correct base
Other Necessary ProteinsOther Necessary Proteins
HelicaseHelicase opens the double helix opens the double helix and helps it uncoiland helps it uncoil
Specialized binding proteinsSpecialized binding proteins keep strands separated keep strands separated
DNA RepairDNA RepairFor the rare mutations occurring during For the rare mutations occurring during
replication that isn’t caught by DNA replication that isn’t caught by DNA proofreading enzymeproofreading enzyme
If no repairIf no repair In germ (sex) cells In germ (sex) cells inherited diseases inherited diseases In somatic (regular) cells In somatic (regular) cells cancer cancer
Repair Repair MechanismsMechanisms
Different enzymes Different enzymes correct different correct different mistakesmistakes
Other enzymes make Other enzymes make the proper strand piecethe proper strand piece
Still another enzyme Still another enzyme will join new the new will join new the new piece in its proper spot piece in its proper spot on the strandon the strand
top related