DNA Replication Flashcards
Describe the structure of DNA
Double helix
Composed of two strands
- Sugar-phosphate backbone on the outside
- Nucleotide bases on the inside
Nucleotide bases formed complementary pairs (Chargaff’s rule)
the complementary strand is antiparallel to the main strand
Pyrimidine
Cytosine, Thymine, Uracil (RNA), have 1 ring structures
Nucleotide
DNA building blocks composed of five carbon deoxyribose sugar, a nitrogenous base, and one or more phosphate groups.
What is each strand of dna composed of?
Nucleotides
Sugar-phosphate backbone
Purine
Adenine, Guanine, have 2 ring structures
What is semiconservative replication?
In 1958, Meselson and Stah
Replication generates two identical duplexes (double -stranded helices) of DNA
The two complementary strands of the original DNA separate from one another and become templates for the synthesis of new complementary strands
Each new DNA duplex now has one parental strand and one daughter strand
-*Parent strand serves as template strand for new strand
Nucleosides
5-carbon sugar + nitrogenous base (hydrophobic)
Describe the Sugar-phosphate backbone
Deoxyribose sugars alternate with phosphate groups due to phosphodiester bonding (covalent bond)
Sugar phosphate backbone is hydrophilic
Are the nitrogenous bases hydrophilic or hydrophobic explain?
Bases are hydrophobic and turn towards the interior of the double helix- Bases are inside because they are hydrophobic
Sugar phosphate backbone is hydrophilic
phosphodiester bond
a type of covalent bond formed between 2 nucleotides in a nucleic acid strain
formed between the 5’ phosphate group of one nucleotide and the 3’ OH of the adjacent molecule
parental strand
the DNA strand acting as a template to direct the synthesis of a new “daughter” strand
describe strand polarity
5’ end = phosphate group 3’ end = hydroxyl group
Phosphate group and hydroxyl group allow the formation of the phosphoditer bond and formation of sugar phosphate backbone
What type of bond forms between the complementary base pairs?How many?
hydrogen bonds joining the 2 strands into a helix
Complementary nucleotides form hydrogen bonds by the attraction of + and – charges
2 hydrogen bonds between A-T
3 hydrogen bonds between G-C
- Takes more energy to break g- c bonds because they have more bonds
antiparallel
opposite 5’ and 3’ orientations of 2 complementary nucleic acid strands- one is 5’ to 3’ and the complementary strand is 3’ to 5’
daughter strand
a newly synthesized strand of DNA that is complementary to a template strand
Describe the configuration of the nucleotide bases
The nitrogenous base is attached to the deoxyribose sugar to the 1’ carbon by a covalent bond
The hydroxyl group is attached to the 3’ carbon
Forms the phosphodiester bond with the phosphate group
The phosphate group is attached to the 5’ carbon
dNMPs
Monophosphate forms of deoxynucleotides
dNTPs
Triphosphate configurations- forms of deoxynucleotides
Used as energy because they have more phosphates so more energy to release
what is the difference between RNA and DNA?
2 hydroxyl groups instead of one in RNA
uradine instead of thymines
ribose is used instead of deoxyribose
enzyme
specialized protein that has a special function in metabolic pathway
Describe the function of DNA polymerase?
(make polymers) catalyses the formation of the phosphodiester bonds between the 3’ hydroxyl group of one nucleotide and the 5’ triphosphate group on the other
- catalyses complementary base pairing during strand elongation
-Two of the phosphate groups are removed, leaving the nitrogenous bases in their monophosphate form in the sugar-phosphate backbone
What does it mean that two strands are complementary and antiparallell?
Two strands are complementary to each other (ie A pairs with T, G pairs with C)
- A purine always pairs with a pyrimidine via hydrogen bonds
- If it didn’t, there would be bulges and kinks in the helix
The two strands are antiparallel (because of complementary base pairing)
One strand is 5’- ATCG-3’, the other strand is 3’-TAGC-5’
The proportion of base pairs equals:
A=T, C=G
A+T) + (G+C) = 1.0 (or 100%
what is the bp turn for the helix?
Helix has a right-hand twist of ~10 bp(base pairs)/turn
Twist creates a major and minor groove for protein interactions