Nucleic Acids, RNA and DNA: Lectures 7 and 8 Flashcards
(23 cards)
Nucleoside Vs Nucleotide
Nucleoside refers to the sugar and the phosphate
Nucleotide refers to the sugar, phosphate and the base
Purines Vs Pyrimidines
Purines (2 rings) - Adenine and Guanine
Pyrimidines (1 ring) - Cytosine, Thymine and Uracil
Silver is pure (Ag are purines)
Why are purines and pyrimidines categorised as such?
Since they have different biosynthetic and catabolic pathways due to their different ring structures.
H bonds: A-T Vs C-G
A and T form 2 H-bonds
C and G form 3 H-bonds
What does primary secondary and tertiary structure of DNA refer to?
Primary - The sequence of bases, held together by the sugar phosphate backbone
Secondary - The shape formed by the two strands (double helix) with antiparallel strands
Tertiary - The chromosomal packing of DNA onto chromatin
Describe how the tertiary structure of DNA is formed
DNA double helix wraps around histones (“beads on a string”) forming a nucleosome
Nucleosomes combine to form a chromatin fibre
Chromatin fibre is supported by chromosome scaffolding
Condenses to form the chromosome
Why can RNA have a helical secondary structure? Provide an example
It can self-bind to form a helix such as in t-RNA
What are the two pathways by which nucleic acids can be synthesised?
De novo and Salvage
What are the main features of de novo purine synthesis?
The sugar phosphate is further phosphorylated to increase reactivity
Purine ring is formed off of the ribose ring
Small elements from another molecule are removed to contribute to the formation of the nucleotide (minimises energy expenditure)
The purine pathway has a common precursor for adenosine and guanosine
Why is tetrahydrofolate important in biology and pharmacology?
It is often used in biology to add a single carbon to a molecule (think like an electron carrier)
What are the main features of de novo pyrimidine synthesis?
The nucleic acid isn’t built off of the ribose ring, the nucleic acid ring is assembled first then attached afterwards.
What do kinase enzymes do
They add phosphate groups to a molecule
How are nucleotide monophosphates converted to triphosphates?
Monophosphate kinases add a phosphate to their specific nucleotide. A nonspecific diphosphate kinase adds a phosphate to any of the DNPs
How are ribonucleotides reduced to deoxyribonucleotides?
A multitude of thiol reducing agents react with the ribonucleotides reducing them and removing oxygen from OH groups
Why can nucleotide catabolism abnormalities be problematic? Give an example
Abnormal catabolism of nucleotides can lead to a build up in byproducts such as uric acid. The accumulation of uric acid in particular causes gout
Steps to DNA Replication
- Helices action (like A Level)
- Single-strand binding proteins keep DNA strands separated and unwound
- Topoisomerase attaches further down the strand to RELEASE TENSION
- RNA primers produced to initiate the addition of new nucleotides
How and why do Okazaki fragments form?
They form when DNA Polymerase binds together multiple nucleotides on the lagging strand in sections as the bubble moves since it can only work in the 5’ to 3’ direction
How are Okazaki fragments joined together?
By DNA Ligase
How is DNA proofread?
Enzymes go over the complete DNA molecule and check for base pairing errors
Explain the benefits of proofreading DNA
By proofreading DNA, the base pairing error rate decreases from 1 in 10,000 to 1 in 1 billion. In doing so the likelihood of incorrect protein synthesis is drastically reduced
Prokaryotic Vs eukaryotic DNA replication
Prokaryotes only have one replication bubble whereas eukaryotes have multiple
Describe the structure of a stop sequence and explain how it functions
Often a T-rich sequence followed by GC rich self-complementary sequence. Since it is self-complementary it forms a hairpin loop in the RNA strand which blocks further replication.
