characteristics of genetic material
- can store and express information
- can replicate and transmit to progeny
- can periodically mutate to generate variation
2 reasons that DNA is more suitable for storing genetic information
- DNA is more resistant against enzymes that degrade nucleic acids
- DNA is double stranded and provides an accurate mechanism for replication
pyrimidines
thymine and cytosine (and uracil)
single-ring structures
purines
adenine and guanine
double-ring structures
adenine and thymine bond
2 hydrogen bonds
guanine and cytosine bond
3 hydrogen bonds
deoxyribose characteristics
- five-carbon sugar
- monosaccharide component of DNA
- has hydrogen atom at carbon 2 position
nucleoside definition
combination of a nitrogenous base (A, T, G, or C) and a sugar
nucleotide definition
nitrogenous base, sugar, and a phosphate group added at the position 5 carbon of the sugar
Chargaff’s first rule
amount of purines will always equal amount of pyrimidines
steps of prokaryotic DNA replication
- DNA protein bind to single origin of replication
- upstream region melts, and helicase binds and unwinds DNA
- RNA primers are added to provide a 3’ end for elongation
- 5’ to 3’ syntheis of leading strand and lagging strand is carried out by DNA polymerase
- DNA replaces RNA and lagging strands are joined
- Tus protein stops replications forks from crossing each other and ends synthesis
ribose sugar
differs from deoxyribose only in that it has an OH group at the carbon 2 position
order of events in polymerase chain reaction (PCR)
- reaction mixture contains 3 copies of a particular DNA sequence
- heated to 94 ‘C
- DNA is denatured to form single strands (denaturation)
- temp lowered to allow primers to anneal to the DNA template (annealing)
- heated to 72 ‘C
- Taq polymerase synthesizes a new DNA strand (elongation)
- now contains 6 copies of DNA
characteristics of PCR replication
- involved continuous synthesis only
- duplicates a small fragment of the genome
- catalyzed by DNA polymerase
semiconservative model of DNA replication
- supported by Meselson and Stahl Experiment
- parental DNA replicates into 2 new things of DNA, each with a parental and daughter strand
major enzymes in DNA replication
initiator proteins, helicase (unwinds DNA), primase, DNA poly III, DNA poly I, ligase (binds okizaki fragments, topoisomerase
5 DNA polymerases
- alpha for nuclear DNA replication
- beta for DNA repair
- gamma for mitochondria DNA
- theta for nuclear DNA
- epsilon for DNA repair
telomerase is used for:
- replication of DNA
2. protection of DNA
