L7 - Introduction To Nucleic Acids Flashcards
What is DNA?
Deoxyribonucleic acids
What are the building blocks of DNA?
Nucleotides
What are nucleotides?
Phosphate + sugar + base
What are nucleosides?
Sugar + base
What are the 4 nucleotides?
Deoxy
- adenosine
- guanosine
- thymidine
- cytidine
Phosphate
What are the 4 nucleosides?
Deoxy
- adenosine
- guanosine
- thymidine
- cytidine
What are features of the sugars?
- when it points down it’s alpha, when it points up it’s beta
- pentose sugar
What does deoxyribose exist as?
The beta anomer in DNA
What are purines?
Nucleic acids with two rings
- adenine
- guanine
What are pyrimidines?
Nucleic acis with one ring
- cytosine
- thymine
What is the primary structure of DNA?
The sequence of bases, held together by the sugar phsophate backbone
(Contains the genetic information)
What is the secondary structure of DNA? (2)
Shape that the primary sequence adopts
- DNA double helix
- due to complimentary base pairings
A = T, G=-C
Features of the secondary structure of DNA (3)
- Directionality: 5’ to 3’, 3’ to 5’, anti parallel
- There are major grooves and minor grooves
- there are 10 base pairs per turn
What is the tertiary structure of DNA? (2)
How the DNA gets stores into the cell
- chromosomal packing of DNA onto chromatin
= complex of histone proteins with DNA/RNA - solenoidal supercoililng
What is the primary structure of RNA? (3)
- complimentary code to DNA (transcription)
- Ribose instead of deoxyribose
- Uracil instead of thymine
What is the secondary structure of RNA? (3)
- single stranded
- interacts with itself = helical secondary structure (tRNA)
- AU, GC
What is the tertiary structure of RNA? (3)
- mRNA: relays code for protein from DNA to protein production site
- tRNA: links triplet code on mRNA to specific a/a
- rRNA: present in ribosomes, structurally and catalytically important
What is the central dogma?
Primary sequence of DNA read to code for the primary sequence of mRNA = proteins
What are the biosynthesic pathways of nucleic acids?
Salvage - recycling pathways, takes less energy
De novo - from the basics
What are the key points for the de novo synthesis of purine nucleotides? (3)
- energy provided by dephosphorylation of ATP to ADP
- additional atoms/groups are added with a loss of another molecule (a/e)
- when a single C additon is required, tetrahydrofolate
How do conversion of nucleotide monophosphates to triphosphates happen?
NMP + ATP = NDP + ADP
NDP + ATP = NTP + ADP
What is monophosphate kinases?
Enzymes specific for each base but not sugar
Adds phosphate to NMP
What is diphosphate kinase?
Enzyme that is non-specific
Adds phosphate to NDP
How are ribonucleotides reduced to deoxyribonucleotides?
ribo - NDP + reductant - (SH)2 = deoxyribo - NDP + reductant - (S-S)
What are examples of reducing agents? (2)
- thioredoxin (SH)2 = thioredoxin (S-S)
- glutaredoxin + 2-glutathione -SH = glutaredoxin + (glutathione-S-)2
What is thimine the addition of?
5-methyl uracil + CH3
takes place at the nucleotide monophosphate stage dUMP
What enzyme joines the 5-methyl uracil with the CH3? and what products are formed?
thymidilate synthase
= dTMP and dihydrofolate
What is the inhibition of thymidilate synthase good for?
effective treatment strategy for several cancers
- it prevents the dUMP from converting into dTMP
What does the reductive catabolism of pyrimidine bases result in?
small soluble molecules that are easily excreted
- using NADPH + H+
- releases CO2 and NH4+
What are the key points for catabolism of pyrimidines? (3)
- can occur through oxidative or reductive pathways
- products of catabolism are small, water soluble compounds
- degradation products are readily excreted
What does the catabolism of purine nucleotides lead to?
production of uric acid
- using adenosine deaminase (ADA)
- and xanthine oxidase
Why is uric acid bad? what does excess lead to?
It’s excreted in urine as solid (crystallised)
- excess accumulation leads to hyperuricemia (gout) affects joints
How are clinical problems of nucleotide catabolism resolved?
there is one enzyme to target to reduce uric acid (xanthine oxidase)
Allopurinol: blocks xanthine oxidase as it’s similar to substrate Hypoxanthine/Xanthine
