Chapter 3 - Nucleic Acids Flashcards
what are nucleotides composed of
- one phosphate group
- one pentose sugar
- one organic nitrogenous base
how are the subunits joined to form a nucleotide molecule
covalent bonds
DNA vs. RNA nucleotide number of strands
DNA: 2
RNA: 1
DNA vs. RNA nucleotide pentose sugar
DNA: deoxyribose
RNA: ribose
DNA vs. RNA nucleotide bases
DNA: A, T, C, G
RNA: A, U, C, G
what is a purine, name the bases
- 2 nitrogen containing rings
adenine and guanine
what is a pyramidine, name the bases
- 1 nitrogen containing ring
cystosine, thymine, uracil
what is a nucleotide
the monomer from which nucleic acids are made
what are the complementarty base pairs
cytosine and guanine
adenine and thyamine (DNA)
adenine and uracil (RNA)
how are the complementary base pairs joined
weak hydrogen bonds
how many hydrogen bonds between complementary base pairs
A-T (2)
C-G (3)
how are polynucleotides formed
- condensation reaction
- phosphdiester bond forms between the 5’ phosphate group of one nucleotide and the 3’ hydroxyl group on the sugar of another
describe the structure of DNA
- polymer of nucleotides
- 2 antiparallel helical chains of nucleotides linked by hydrogen bonds between complementary base pairs
- coiled to form a double helix
- stable structure
what is the importance of complementary base pairing
- same distance between each pair of bases
- allows faithful DNA replication
- high fidelity of replication: bases can only pair with a specific other base
define high fidelity of replication
making an accurate copy
when is DNA replicated
interphase
why is DNA replication semi-conservative
- one original strand that acts as a template
- one newly formed strand
- 50-50
what method did meselson and stahl use to separate DNA by its density
centrifugation
what enzymes are involved in DNA replication
- DNA helicase
- DNA polymerase
role of helicase in DNA replication
- unwinds the double helix
- breaks hydrogen bonds between complementary base pairs
- separates the 2 strands
what happens once the strands of DNA have been ‘unzipped’
- both strands are used as templates
- complementary base pairing occurs between template strands and free nucleotides
role of DNA polymerase in DNA replication
joins adjacent nucleotides by phosphodiester bonds formed in condensation reactions
what is mutation
- replication errors
- incorrect sequence of nucleotides when bases arent exactly matched
what is the triplet code
3 bases code for an amino acid
why is it the triplet code, not doublet?
enough combinations to code for the 20 needed amino acids
why is the genetic code universal
same 4 DNA bases in all organisms
how is the genetic code degenerate
more than one triplet codes for the same amino acid
how is the genetic code non-overlapping
- start codon AUG
- each triplet only read once, dont share bases
significance of AUG
ensures the code is read from base 1, not 2 or 3
function of base sequence in DNA
stores genetic information
function of large size and helix of DNA
large size: can store alot of genetic info
helix: compact
what is ATP
- adenosine triphosphate
- used for energy transfer in all cells of all living things
structure of ATP
- nitrogenous base (always adenine)
- pentose sugar (ribose)
- three phosphate groups
how does ATP release energy
- more energy is released than used when the weak bond holding the last phosphate group is broken as it free phosphate undergoes other reactions involving bond formation
hydrolysis of ATP
ATP + H2O —> ADP + Pi + energy
why isnt ATP a good long-term energy store
unstable phosphate bonds mean cells dont store alot of ATP
how is ATP reformed
phosphorylation of ADP
properties of ATP
- small (in+out cells)
- bonds between phosphate have immediate energy
- easily regenerated
- releases small quant energy, none wasted as heat
- water soluble
