Lecture 1-2: DNA structure and replication Flashcards
RNA and DNA are polymers, each repeating unit has a (3)
sugar, phosphate and base
The base in DNA all contain
nitrogen
Purines:
includes+shape
- Guanine and adenine
- double ring structure
Pyrimidines
include+shape
- thymine and cytosine, uracil
- single ring structure
nucleotide has at least
1 phosphate
Nucleoside
- Base bonded to a sugar
General feature of DNA structure: (4)
- Two strands in opposite directions from a right handed helix (one strand 3’-5’ and one is 5’-3’)
- The sugar phosphate backbone is on the outside of the helix and the purine and pyrimidine bases face the middle
Bases are perpendicular to the helical axis, with bases seperated by 3.4 A (consitent spacing in helical ladder) - Helix is approx. 20 A wide
Lot more —– are more stable then —–
- C-G
A-T
Deoxyadenosine contains:
Sugar+adenine
In the deoxyribose sugar, a base attaches on the—– carbon and the phosphate attach on the —- carbon. The —- carbon has a —-
- 1’
- 5’
- 3’
- OH group
DNA Base pairing (3):
- Same amount of purine nucleotides as pyrimidine nucleotides (in dsDNA)
- Same amount of A and T; Same amount of G and C
- A+T isnt necessarily equal to G+C
There are — base pair in a full twist of DNA and
adjacent bases are separated by approximately —-
- 10
- 3.4 A
The melting temperature is defined as the —
The melting temperature of DNA refers to the temperature at which 50% of DNA in a sample has denatured from double-stranded DNA (dsDNA) to single-stranded DNA
What are the chemical forces that stabilize the double helix?
Hydrogen bonds between base pairs and van der Waals interactions among the bases. The van der Waals interactions come into play because of the hydrophobic effect, which forces the bases to the interior of the helix.
Nucleotides contain….. and are
- phosphate
- sugar
- base
- are the repeating unit in nucleic acids
Nucleotides form DNA strands by
phosphodiester linkages
Phosphodiester linkages (2)
what it does+what it includes
- Phosphate/sugar backbone
- links the 3’ carbon of one sugar to the 5’ carbon of aother via a phosphate
The 2 sugar phosphate backbones are
antiparallel
one is 5’-3’ nd other is 3’-5’
DNA strands are held together by — hydrogen bonds. AT has — and CG has—-
2 or 3
2
3
Semi conservative replication (3)
what happens+ results in
- 2 DNA strands unwinds from eachother
- Each DNA strand acts as a template for the synthesis of a new complementary strand
- Results in 2 double helices that are identical to the original
Replication is catalyzed by—- which is—-
DNA polymerase which is an enzyme that adds nucleotides into a growing DNA chain
What drives DNA synthesis or DNA polymerase?
Cleaving off pyrophohphate produces energy to help drie DNA synthesis
In DNA replication, what does the OH hydroxyl group on the 3’ carbon of growing strand do?
Forms a nucleophillic attack on alpha phosphorus. Cleaves off the 2 pyrophosphate which provides energy to drive the rxn.
New nucleotides can only be added on the —- because it has to ——
- 3’ end
- have a free OH group to form the nucleophillic attack for new nucleotides
DNA is synthesized in the
5’-3’ direction
Replication is catalyzed by
DNA polymerase
What drives the DNA synthesis?
Cleaving off the pyrophosphate (2) on the triphosphate base by 3’oh produces energy to help drive DNA synthesis
New nucleotides can only be added on the
3’ end
Where is the base attached in dna
1’ carbon of the deoxyribose sugar
—– in purines
and —– in pyrimidines form a bond with the sugar.
N-9
N-1