Nucleic Acids Flashcards
1
Q
Outline the functions of nucleic acids
A
- Gene expression
- Storage and transmission of genetic information
2
Q
How are phosphodiester bonds formed?
A
- Between 5’ phosphate and 3’- OH of sugar
3
Q
Describe the double helix.
A
- Two strands coil to form right handed double helix - antiparallel
- Sugar phosphate backbone on outside - hydrophilic
- Nitrogenous bases on inside - hydrophobic
4
Q
The double strands of DNA are not exactly opposite each other. Why?
A
- Helix contains major and minor grooves (22 and 12 amino acids apart respectively)
- Bases exposed in grooves interact with proteins/drugs
5
Q
Describe DNA melting and annealing.
A
- MELTING - Separation of double helix DNA into ssDNA at high temperatures
- ANNEALING - single strands anneal to form dsDNA upon cooling. Longer strand - greater annealing temp.
6
Q
When do negative and positive supercoiling of DNA occur?
A
- NEGATIVE - usually how DNA is coiled
- POSITIVE - DNA replication/transcription
- SUPERCOILING - important for DNA packaging
7
Q
DNA coils around histone proteins. Why are histones rich in lysine and arginine residues?
A
- Give a positive charge to them
- Aids in winding of negatively charged DNA around the histone core.
7
Q
Describe nucleosomes.
A
- DNA complexed with 8 histones
- Nucleosomes linked by H1 histone
8
Q
Describe DNA replication
A
- Semiconservative
- Occurs in 5’ and 3’ direction
- DNA polymerase catalyse synthesis by joining of dNTPs
9
Q
Describe initation in the DNA replication fork.
A
- RNA primers synthesized in 5’- 3’ by DNA polymerase that copies the DNA template.
10
Q
Describe elongation in the DNA replication fork. PART 1
A
- DNA Polymerase alpha adds dNTP to the 3’-OH group of the RNA primer
- DNA Polymerase gamma extends the growing strand.
11
Q
Describe elongation in the DNA replication fork. PART 2
A
- Leading strand - synthesized continuously toward replication fork
- Lagging strand - synthesized discontinuously away from replication for using short Okazaki fragments
12
Q
Describe termination in DNA replication fork.
A
- RNA primers are removed by RNAase
- Polymerase gamma fills in the gaps and DNA ligase joins the polynucleotides by ligation (3’- OH to 5’-phosphate)
13
Q
Describe the enzymes involved in DNA replication
A
- Topoisomerase and helicase
- Primase - synthesise RNA primers
- Ligase - joins adjacent DNA - form phosphodiester bonds
14
Q
Compare and contrast DNA and RNA.
A
- Sugar in RNA is ribose
- Base with RNA is uracil
- RNA is single stranded
