Topic 2: Nucleic acids Flashcards
What consists of a nucleotide
A pentose sugar: Has five carbon atoms
A phosphate group
A nitrogen-containing base
What are the 4 bases of DNA
- Adenine
- Thymine
- Cytosine
- Guanine
What holds together the pentose sugar, phosphate group and organic base
Sugar phosphate backbone + condensation reactions
What do you call the bond between the phosphate and sugar in DNA
Phosphodiester bond
Waht do you call the continued linking of mononucleotides
Polynucelotide
What is the pentose sugar in DNA and RNA
DNA - deoxyribose
RNA - ribose
What are the bases in RNA
- Adenine
- Uracil
- Cytosine
- Guanine
What joins the polynucleotides in DNA
Hydrogen bonds
How do the bases pair and how many bonds do they form
- Adenine + Thymine (2 bonds)
- Cytosine and Guanine (3 bonds)
Give two reasons DNA is stable
- The phosphodiester backbone sits on the outside of the molecule, protecting the reactive bases
- Hydrogen bonds link the organic bases together. One hydrogen bond alone is very weak but because there are so many it creates a very strong structure.
How is DNA adapted to its function
(4 different adaptations)
- Stable structure - rarely mutates
- Two separate strands - weak H-bonds between strands allow them to separate for protein synthesis and replication
- Extremely large - can carry alot of genetic information
- Cylindrical helix - Information is protected from chemical and physical forces
Define semi-conservative replication
each strand serves as a template, which means that each new copy of DNA has one strand from the original molecule and one new strand.
What does antiparalell mean
The strands are parallel but run in the opposite direction
Explain how DNA is antiparalell
One strand runs from the 5 prime (5’) to the 3’ and the other from the 3’ to the 5’
What direction does DNA replication occur in
From the 5’ to the 3’
What 4 things are needed for semiconservative replication in DNA to occur
- The 4 types of nucleotide bases (A,T,C,G)
- 2 complimentary strands of DNA (to act as templates)
- Enzymes (DNA polymerase and DNA helicase)
- Chemical energy (from ATP)
Explain DNA replication
5 points
- DNA helicase breaks the H-bonds between base pairs and DNA unzips
- Free nucleotides bind to their exposed complimentary base pairs (A+T & C+G)
- DNA polymerase joins the free nucleotides
- The result is two new DNA molecules, both with one new strand and one old strand
- Which is known as semi-conservative replication
