DNA and RNA Flashcards
DNA and RNA is made up of …
Base>Scaffold>connector
Differences between DNA and RNA is
- 2-deoxyribose (H instead of OH in position 2) vs ribose
- Thymine vs Uracil
- double stranded vs single stranded
Nitrogenous bases bind to sugar at carbon position ____
1
AT bp has __ bonds and GC bp has __ bonds
AT bp has 2 bonds and GC bp has 3 bonds (stronger)
Bonds between sugar molecule and phosphodiester are ____while the bonds between nucleic acid pairs are ___.
Bonds between sugar molecule and phosphodiester are flexible while the bonds between nucleic acid pairs are fixed.
Bases choose their position according to :
- Formation of optimal hydrophobic interaction between neighboured bp
- Avoiding contact with functional groups of the vincity bp
Right-handed double helix
A-Form DNA and B-Form DNA
Left handed double helix
Z- From DNA
A- form DNA (Rare)
- right handed
- flexible but rigid DNA structure due to dehydration
- major and minor grooves can be observed in each turn
- 11 bp/helix turn
- angle between two bases: 33.1 D
- angle between bases and helix axis: 71-77 D
B- Form DNA (common)
- right handed
- major and minor grooves present alternatively
- 10.4 - 10.5 bp/helix
- angle between two bases: 35.9 D
- angle between bases and helix axis: 90 D
- narrower than A DNA
Z- Form DNA
- left handed
- zigzag appearance
- recognition for binding of regulator proteins
- 12 bp/ helix turn
- angle between two bases: 60 D
What is positive supercoiling?
Positive supercoiling is over- wounded DNA.
- more than 10.4 bp/turn (increase in linking number)
- More difficult to separate the DNA
What is negative supercoiling?
Negative supercoiling is under-wounded DNA
- less than 10.4bp/turn (decrease in linking number)
- easier to separate DNA
Topoisomerase I
- break one DNA strand, pass other strand though gap and reseal the nick
- ATP not required
Topoisomerase II
- break both DNA strands
- energy required (ATP or NADH)
- Gyrase (in bacteria)
Gyrase
Gyrase is Top II in bacteria which introduce negative supercoil
What is hyperchromicity?
Hyperchromicity is increase in UV light absorption (260nm) in single stranded DNA than double stranded DNA
- H-bond limits the resonance of the aromatic ring and limit the absorbance
- hypochromic effect depends on GC content of DNA
What is Tm?
Tm is temp at which 50% of the DNA strand is separated
How is DNA denatured?
- separate H-bond by heating or base addition
How is DNA renatured?
- Nucleation: paired nucleotide sequence sequence meet each other
- fast reestablishment of double strand
Velocity of DNA renaturation/ reassociation depends on. __
- concentration of cations to mask the negative charges of the phosphorus-group
- temp (optimal ~25 D celcius)
- size and concentration of DNA
How many bp in human genome?
3000 million bp
3* 10^9
Louis Pasteur
Life only develops only out of life
Gregor Mendel
the law of heredity
Ernst Haeckel
the nucleus is responsible for heredity
Friedrich Miescher
discover that DNA is nucleus
Griffith Avery, MaCarty and MacLeod
DNA could transform one type of bacteria into another type of bacteria
Chargaff
Analyzed the relative amount of A,C,G, T in cells
- found A=T, C=G
Hershey and Chase
DNA, not protein is the infectious agent in viruses
- T2 phage , DNA is labeled with 32P and Protein is labeled with 35S
Watson and Chase
X-ray diffraction photo of DNA, double helix discovery
Meselson and Stahl
Semi-conservative model of DNA replication (one new strand pair with one old strand)
- bacteria cultured in heavy nitrogen (15N) medium then transferred to light nitrogen (14N)
then centrifuged DNA sample
What are 3 possible DNA replication mechanism?
Conservative model
Dispersive model
Semiconservative model
Conservative model
the parental strand remain intact and a second new double strand is made
Dispersive model
daughter strand contains segments of parental strand and segments of newly synthesised strand
Semiconservative model
daughter strand consist of one new strand and one parental strand (each parental strand is used as template)
What are two ways to prove semi-conservative model?
- culturing bacteria in heavy nitrogen medium and then transferring to light nitrogen medium and centrifuging the DNA sample
- sister chromatid staining (sister chromatid exchange and BrdU)
Sister chromatid exchange
the exchange of genetic material between two identical sister chromatids
