2.3-the only calm one (DNA) Flashcards
(38 cards)
what is a nucleotide?
phosphate esters of pentose sugars
what are the functions of nucleotides?
1) form monomers of nucleic acids
2) become ADP and ADP, and through this help regulate many metabolic pathways.
3) may be components of many coenzymes
what are the purines?
adenine or guanine: two rings
what are the pyramidines?
thymine or cytosine: one rings
what is the bond between the sugar residue and the phosphate group ?
covalent bond formed by condensation reaction- phosphodiester bond.
how many h-bonds between adenine and thymine?
2
how many h-bonds between guanine and cytosine?
3
how is dna organised in eukaryotic cells?
- majority of DNA content in nucleus
- histone proteins and chromatin
- loop of dna, without histones, inside mitochondria and chloroplasts.
how is dna organised in prokaryotic cells?
- DNA in a loop within cytoplasm
- no histones-“naked”
how is dna organised in viruses?
loop of naked DNA
what does dna polymerase do in dna replication?
catalyses addition of new nucleotide bases using DNA strands as templates
what direction does dna polymerase work?
moves 3’ to 5’
forms 5’ to 3’
what supplies energy to make phosphodiester bonds in dna replication?
hydrolysis of activated nucleotides to release the extra phosphate groups
how does DNA in prokaryotes, mitochondria, and chloroplasts replicate?
semi-conservatively:
bubble sprouts from the loop and unwinds and unzips, the complementary nucleotides join to the exposed nucleotides.
what does gyrase do?
untwists the double helix
what does dna helicase do?
breaks h-bonds between nucleotide bases
how is rna structurally different from dna?
- sugar molecule is ribose not deoxyribose
- U instead of T
- single stranded
- shorter than dna
- 3 forms
what are the three forms of rna?
mRNA
tRNA
rRNA
what are 4 examples of protein shape allowing them to carry out their function?
1) shape of active site of enzyme
2) shape of antibody complementary to antigen
3) receptor on cell membrane complementary to shape of cell-signalling molecule
4) ion-channel protein must be hydrophyllic on the inside and lipophyllic on the outside
what is the nature of the genetic code?
universal
degenerate
non-overlapping
why is the genetic code universal?
in almost all living organisms the same triplet of DNA codes for the same amino acid.
why is the genetic code degenerate?
for almost all amino acids there is more than one base triplet
what is the effect of the genetic code being degenerate?
reduces the effect of point mutations, as a change in one base of the triplet could produce another base for the same amino acid.
why is the genetic code non-overlapping?
read starting from a fixed point in groups of threes- if a base is added or deleted it causes a frame shift, as every base triplet after that, and hence every amino acid coded for, is changed.
