2.1 -> 2.2 structure and replication of DNA

Question 1

structure of nucleotide structure

Answer 1

pentose sugar + phosphate group + nitrogenous base

joined by condensation reactions

Question 2

5 Nitrogenous bases

Answer 2

Adenine
Thymine
Cytosine
Guanine
Uracil

Question 3

Dinucleotide

Answer 3

phosphodiester bond- condensation reaction between deoxyribose sugar of one mononucleotide and the phosphate in the other

Question 4

DNA

Answer 4

deoxyribonucleic acid
two polynucleotides joined by hydrogen bonds between certain bases
pentose sugar is deoxyribose
bases are A,T,C,G
double helix

Question 5

RNA

Answer 5

ribonucleic acid
single, relatively short polynucleotide chain
pentose sugar always ribose
organic bases always A,G,C,U
forms a ribosome- along with a protein

Question 6

Complementary bases

Answer 6

Adenine is complementary to Thymine
Guanine is complementary to Cytosine

quantities of A+T in DNA are always the same, and so is G+C
ratio of AT:CG varies from species to species

Question 7

stability of DNA

Answer 7

phosphodiester backbone protects chemically reactive bases inside double helix

hydrogen bonds link base pairs forming bridges between phosphodiester uprights
- 3 hydrogen bonds between C-G
- higher proportion of C-G pairings, more stable molecule

base stacking holds molecule together

Question 8

5 ways DNA is adapted to function

Answer 8

1. stable structure carried through generations - most mutations repaired
2. 2 strands joined by hydrogen bonds- can separate during replication and protein synthesis
3. large molecules- carries large genetic info
4. base pairs within helical cylinder of backbone- genetic info is protected form being corrupted by chemical and physical forces
5. base pairings lead to DNA being able to replicate and transfer info as mRNA

Question 9

4 requirements for semi-conserve replication

Answer 9

1. 4 types of nucleotide, each with base A,T,C or G
2. both strands of DNA molecules act as template for attachment of these nucleotides
3. enzyme DNA polymerase
4. source of chemical energy to drive process

Question 10

Process of semi-conservative replication

Answer 10

1) the enzyme DNA helicase breaks the hydrogen bonds linking base pairs

2) double helix separates into 2 strands unwinds

3) each exposed polynucleotide strand acts as template to which complementary free nucleotides bind by specific base pairing

4) nucleotides are joined together in condensation reaction by enzyme DNA polymerase(forms phosphodiester bonds) to form missing polynucleotide strand on each of two OG polynucleotides

5) each new identical DNA molecules contains one strand of old DNA and one of new DNA material

Question 11

watson-crick model

Answer 11

worked out structure of DNA in 1953
had two theories of replication- conservative and semi-conservative

Question 12

conservative model

Answer 12

OG DNA molecules remained intact
separate daughter DNA copy was built up from new molecules of deoxyribose, phosphate and organic bases(new material)

Question 13

Meselson and Stahl experiment

Answer 13

1. they grew bacteria in a lighter 14N medium
2. they also grew bacteria in 15N medium
3. they extracted DNA and centrifuged it, and it settled near the bottom of the tube
4. They transferred the bacteria to 14N medium for a single generation to allow it to replicate once
5. they then centrifuged the extracted DNA from the bacteria in a special solution
6. the DNA had undergone semi-conservative replication as it settled in the middle of the tube as it contained one strand of 14N and one of 15N