-
8/6/2019 Review of DNA Chemistry, Structure and Function
1/19
-
8/6/2019 Review of DNA Chemistry, Structure and Function
2/19
-
8/6/2019 Review of DNA Chemistry, Structure and Function
3/19
7/21/201
-
8/6/2019 Review of DNA Chemistry, Structure and Function
4/19
7/21/201
Structural features of the DNA(secondary structure)
Double helix; 2 topographic features majorgroove and minor grooveTwo strands antiparallelIn aqueous environment phosphate-sugarbackbone outside of the helix; purine andpyrimidine rings inside the structureStrand stabilized by :H-bonds between complement basesVan der Waals andHydrophobic interactions between stackedbases
-
8/6/2019 Review of DNA Chemistry, Structure and Function
5/19
7/21/201
Conformational varieties of thesecondary structure
B-DNA crystallized fromwater; water retained in theinner structure; predominantform under physiologicalconditions10 base pairs/turn of helixRight handedDistance bet base pairs 0.34 nmDiameter 2.0 nm or 20 A
A-DNADehydrated form of B-DNARight handed helix11 base pairs/helixDiameter = 26 A
Z-DNAFound in short stretches ofnative DNA and synthetic DNALeft handed helix12 base pairs/helix
Diameter = 18 A
-
8/6/2019 Review of DNA Chemistry, Structure and Function
6/19
-
8/6/2019 Review of DNA Chemistry, Structure and Function
7/19
7/21/201
Tertiary structure of the DNA
Circular (relaxed) in E.coli; simian virus 40;bacteriophage; certain animal species
Supercoiled DNA extra twisting in the linearduplex; allows DNA to be more compact inthe cell; regulatory role in replication
Topoisomerase change topology of the DNA
Quadruplex DNA four stranded; in protozoanDNA; occur in G-rich regions; regulating andstabilizing telomeres and regulation of geneexpression
Packaging ofeukaryotic DNAintochromosomes
-
8/6/2019 Review of DNA Chemistry, Structure and Function
8/19
7/21/201
Management of GeneticInformation
Learning objectives
Understand the mechanism of DNAreplication, RNA synthesis and proteinsynthesis
Understand the basis of genetic manipulationtechnologies
Flow of genetic information DNA replication
A requirement prior to cell divisionIn prokaryotes and eukaryotes
-
8/6/2019 Review of DNA Chemistry, Structure and Function
9/19
-
8/6/2019 Review of DNA Chemistry, Structure and Function
10/19
7/21/201
1
Replication ineukaryotes
DNA synthesis based on two template strands: leading strand andlagging strand templates; mechanism in prokaryotes is presented
DNA is synthesized from its 5 -> 3 end (fromthe 3 -> 5 direction of the template)
the leading strand is synthesized continuously inthe 5 -> 3 direction toward the replication forkthe lagging strand is synthesizedsemidiscontinuously (Okazaki fragments) also inthe 5 -> 3 direction, but away from the replicationforklagging strand fragments are joined by theenzyme DNA ligase
Replication fork Enzymes and proteins in DNA replication
-
8/6/2019 Review of DNA Chemistry, Structure and Function
11/19
7/21/201
The action of DNA polymerase Start of DNA replication
UnwindingDNA gyraseintroduces a swivelpoint in advance of the replicationforka helicase binds at the replicationfork and promotes unwinding
Replication ineukaryotes
single-stranded binding(SSB) protein protectsexposed regions of single-stranded DNA
-
8/6/2019 Review of DNA Chemistry, Structure and Function
12/19
-
8/6/2019 Review of DNA Chemistry, Structure and Function
13/19
7/21/201
1
Summary of DNA replication inprokaryotesUnwinding
DNA gyrase introduces a swivel point in advance ofthe replication forka helicase binds at the replication fork and promotesunwindingsingle-stranded binding (SSB) protein protectsexposed regions of single-stranded DNA
Primase catalyzes the synthesis of RNA primerSynthesis
catalyzed by Pol IIIprimer removed by Pol I
DNA ligase seals remaining nicks
Summary of DNA replication inprokaryotes
DNA synthesis is bidirectionalDNA synthesis is in the 5 -> 3 direction
the leading strand is formed continuouslythe lagging strand is formed as a series of Okazakifragments which are later joined
Five DNA polymerases have been found to exist inE. coli
Pol I is involved in synthesis and repairPol II, IV, and V are for repair under unique conditionsPol III is primarily responsible for synthesis
Eukaryotic DNA replication
Not as understood as prokaryotic. Due in nosmall part to higher level of complexity.
Cell growth and division divided into phases:M, G1, S, and G2
DNA replication occurs during the S phase
-
8/6/2019 Review of DNA Chemistry, Structure and Function
14/19
7/21/201
1
RNA synthesis
TranscriptionTemplate is DNAMajor enzyme: DNA directed RNA polymeraseNo need for primers5 to 3 direction
Requires a promoter region in the template DNAto which the RNA polymerse will bindPromoter several base pairs upstream awayfrom the start site (+1)Termination may be rho factor dependent rhofactor terminates synthesis or rho factorindependent formation of a stable hairpin loop
-
8/6/2019 Review of DNA Chemistry, Structure and Function
15/19
7/21/201
1
Eukarotic transcription have 3 classes of RNA polymerases
RNA pol I transcribes large ribosomal RNAgenesRNA pol II transcribes protein encoding geneRNA pol III transcribes small RNAs (includingtRNA and 50SRNA)
-
8/6/2019 Review of DNA Chemistry, Structure and Function
16/19
7/21/201
1
Post transcriptional modification of theeukaryotic mRNA
Capping methyl guanosine attachment atthe 5 end to protect the cleavage of the RNAby exonucleases as RNA moves out of thenucleusAddition of poly A at the 3 end (20-250long) helps to stabilize the mRNA structure;increases resistance to cellular nucleasesSplicing removal of non coding sequences(introns)
Summary of Post-transcriptionalmodification ineukaryotic cells
-
8/6/2019 Review of DNA Chemistry, Structure and Function
17/19
7/21/201
1
Protein synthesis
TranslationBased on the m-RNA sequence, geneticcodeStarts from 5 end of the transcriptOccurs in the ribosomesActivation of amino acids attachment to thetRNAInitiation, elongation, termination
Genetic code
Triplet nucleotide one amino acidNonoverlappingNo punctuationDegenerateAlmost universal
-
8/6/2019 Review of DNA Chemistry, Structure and Function
18/19
7/21/201
1
Initiation
Initiation factorsShine-Dalgarno sequence in mRNA30S ribosomeN-formylmet
-
8/6/2019 Review of DNA Chemistry, Structure and Function
19/19
7/21/201
Inhibitors of protein synthesis