Nucleic Acids Flashcards
Outline the functions of nucleic acids
- Gene expression
- Storage and transmission of genetic information
How are phosphodiester bonds formed?
- Between 5’ phosphate and 3’- OH of sugar
Describe the double helix.
- Two strands coil to form right handed double helix - antiparallel
- Sugar phosphate backbone on outside - hydrophilic
- Nitrogenous bases on inside - hydrophobic
The double strands of DNA are not exactly opposite each other. Why?
- Helix contains major and minor grooves (22 and 12 amino acids apart respectively)
- Bases exposed in grooves interact with proteins/drugs
Describe DNA melting and annealing.
- 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.
When do negative and positive supercoiling of DNA occur?
- NEGATIVE - usually how DNA is coiled
- POSITIVE - DNA replication/transcription
- SUPERCOILING - important for DNA packaging
DNA coils around histone proteins. Why are histones rich in lysine and arginine residues?
- Give a positive charge to them
- Aids in winding of negatively charged DNA around the histone core.
Describe nucleosomes.
- DNA complexed with 8 histones
- Nucleosomes linked by H1 histone
Describe DNA replication
- Semiconservative
- Occurs in 5’ and 3’ direction
- DNA polymerase catalyse synthesis by joining of dNTPs
Describe initation in the DNA replication fork.
- RNA primers synthesized in 5’- 3’ by DNA polymerase that copies the DNA template.
Describe elongation in the DNA replication fork. PART 1
- DNA Polymerase alpha adds dNTP to the 3’-OH group of the RNA primer
- DNA Polymerase gamma extends the growing strand.
Describe elongation in the DNA replication fork. PART 2
- Leading strand - synthesized continuously toward replication fork
- Lagging strand - synthesized discontinuously away from replication for using short Okazaki fragments
Describe termination in DNA replication fork.
- 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)
Describe the enzymes involved in DNA replication
- Topoisomerase and helicase
- Primase - synthesise RNA primers
- Ligase - joins adjacent DNA - form phosphodiester bonds
Compare and contrast DNA and RNA.
- Sugar in RNA is ribose
- Base with RNA is uracil
- RNA is single stranded
Describe mRNA.
- Synthesised in 5’ to 3’ direction by polymerase
- Start codon is AUG/ Stop codon is UAA/UAG/UGA
Describe rRNA.
- Non-coding RNA - primary component of ribosomes
- In humans, form 18S, 28S, 5S and 5.8S subunits
- S - Sedimentation value
Describe tRNA.
- Cloverleaf structure - 3’ terminus attaches to corresponding amino acid
- Anticodon recognises specific mRNA codon
- Upon recognition of corresponding codon, tRNA transfers amino acid to end of growing polypeptide chain.
TRUE OF FALSE: Transcription occurs in nucleus of prokaryotes and translation occurs in cytoplasm.
FALSE
- Both happen in same compartment
Describe ATP
- Ribonucleotide
- Energy source for cellular activity
Describe NAD and FAD.
- NAD - electron carrier for oxidation reactions in TCA cycle and ETC
- FAD - assist dehydrogenase enzymes in catabolism of fat/carbohydrates and fat synthesis
Describe CoA
- Necessary for metabolism of carbohydrates and other biomolecules
Describe cAMP.
- Behave as a secondary cellular messenger
- Involved in glycogen/fatty acid metabolism and gluconeogenesis
Describe sickle cell anaemia.
- Autosomal recessive
- Single base substitution from adenine base to thymine base - glutamine(hydophilic) substituted for valine (hydrophobic)
- Causes distinct sickle shape of RBC
