Nucleosides and Nucleotides Flashcards
What is the difference between nucleosides and nucleotides?
Nucleotides have a phosphate group
What is the structure of a nucleoside?
A pentose sugar linked by N-glycosidic bond to a nitrogenous base
How is a phosphate added to a nucleoside to become a nucleotide?
Via a condensation reaction
What are the 2 options for pentose sugar?
Ribose or Deoxyribose
What is the difference between a deoxyribose and a ribose sugar?
Deoxyribose has one less - OH group
What bases are purine?
Adenine and Guanine
What bases are pyrimidine?
Uracil, Thymine and Cytosine
How are base sequences labelled?
From 5’ to 3’
How many bonds are between G-C bonds?
3 Hydrogen bonds
How many bonds are between A-T bonds?
2 Hydrogen bonds
What is Chargaff’s Rule?
%A=%T and %G=%C
How do the 2 strands of DNA run?
Anti-parallel
Why does 1 purine match with 1 pyrimidine?
There is only space for one of each in the double helix
What are the stabilising forces of the DNA double helix?
H bonding - Large number of weak H bond
Electrostatic interactions - phospho-diester group of the DNA backbone and cation
Hydrophobic effect - nitrogen base rings move away from aqueous solvents to the interior of the helix
Stacking interaction - stacked base pairs from weak Van der Waals attractions. These forces are additive so more bases=more stable
What is ribosomal RNA?
Combines with series of proteins to form complex structures called ribosomes
What is mRNA?
Messenger RNA which carries genetic instructions for protein synthesis from DNA to ribosomes
What is tRNA?
Transfer DNA delivers specific individual amino acids to the ribosomes for protein synthesis
What is the process of polymerisation?
Addition to free nucleoside triphosphate, strands unwind and separate, each strand acts as a template for a complementary strand to be built
How is DNA replication controlled?
DNA polymerase builds new double helices, polymerase lines up nucleotides in the right order, polymerase bonds to the double helix to the double bond by wrapping round it, enzyme pulls helix apart and nucleotides brought in to build new DNA strand
What does PCR do?
Mimics rapid production of multiple copies of DNA nucleotide sequences.
How many PCR cycles does it take for DNA to be amplified a billion fold?
30 cycles
What are the applications of PCR?
Detection of infectious organisms, detection of genetic variation, and amplification of DNA in crime scenes
How is DNA affected by anticancer drugs?
They inhibit cell division
