nucleic acid Flashcards
describe nucleic acids
large molecules discovered in cell nuclei
two types:
DNA
RNA
large polymers formed from nucleotides (monomers) linked together in a chain by condensation to form polynucleotides
describe the structure of a nucleotide
phosphate group
inorganic and negatively charged
bonded covalently to a
pentose monosaccharide (5 carbon atoms)
nitrogenous base
organic
one-two carbon rings
describe the formation of phosphodiester bonds
occurs by the removal of a water molecule when 2 hydroxyl groups from 2 different nucleotides bond with a phosphate group in a condensation reaction
what do phosphodiester bonds between the phosphate and the deoxyribose (pentose) sugar form
long, strong sugar phosphate backbone
what are the two types of bases?
pyrimidines
contain single C ring structures – thymine (T) and cytosine (C)
purine
contain double C ring structures – adenine (A) and guanine (G)
describe the formation of a double helix
DNA molecule made of 2 strands (held by hydrogen bonds between bases) of polynucleotides coiled into a helix
two parallel strands arranged to run in opposite directions (anti parallel)
describe complementary base pairing
A + T form 2 hydrogen bonds and join with each other
C + G form 3 hydrogen bonds and only bind to each other
this means there will always be an equal amount of A&T and C&G
what does this base pairing mean?
arrangement between pyrimidine and purine bases mean there’s a constant distance between he DNA backbone forming parallel polynucleotide chains
describe the structure of RNA
short section of DNA molecule (corresponding to a single gene) that gets transcribed into
mRNA
polymer
short than a chromosome
describe two differences between RNA and DNA nucleotides
RNA contains a ribose, whereas a DNA contains a deoxyribose
if the base was a T, this will be replaced by a uracil (U) base in RNA
uracil is a pyrimidine base which forms 2 hydrogen bonds between adenine
describe the function of RNA
RNA polymers leave nucleus and travel to ribosomes for protein synthesis
after protein synthesis, RNA molecules are degraded in cytoplasm
phosphodiester bonds are hydrolysed
RNA nucleotides released and reused
how is the structure of DNA ideally fit to its function?
polymer - contains a lot of information
base sequence is used as a code
doubled stranded - molecule is stable and allows for accurate replication
a sample of DNA was tested and 21% of total bases present were adenine
calculate the percentage of the other three bases present in the sample
21% - adenine
21% - thymine
29% - cytosine
29% - guanine
genes are
sequences of nucelotides
what is a nucleotide
nitrogen-containing organic substance forming the basis of DNA & RNA
what is the function of ATP?
produced in respiration
provides energy for cellular reactions
what does ATP stand for and what does this suggest about its structure?
adenosine triphosphate
adenine base
binded to a ribose sugar
which binds to three inorganic phosphate groups
how is ADP formed?
hydrolysis of ATP –>
forms ADP + an inorganic phosphate group
releases 30.5 kJ
how is DNA packaged
as chromosomes
eukaryotic DNA associates with histones to form chromatin
chromatin coils and condenses to form chromosomes
what does ADP stand for
Adenosine diphosphate
what’s a codon
sequence of three nucleotides
codes for an amino acid
describe the steps of semi conservative replication
double helix structure unwinds and separates into 2 strands
each strands acts as a template for creation of new DNA molecules
hydrogen bonds holding comp bases break
free nucleotides pair up with exposed bases and form hydrogen bonds
new nucleotides join adjacent nucleotides with phosphodiester bonds
leads to formation of 2 new DNA molecules
each molecule has the old (template) strand and the new strand
name the enzyme used to cause the strands of DNA to separate
DNA helicase
describe the function of DNA polymerase
enzyme
catalyses the synthesis of DNA strands from free nucleotides
what can DNA polymerase only do?
bind to the 3’ (OH) end
They always need a template
They proofread
removing the vast majority of “wrong” nucleotides that are accidentally added to the chain
describe the leading strand
strand unzipped from the 3’ end which can be continually replicated as DNA molecule unzips
(continuous replication)
describe the lagging strand
other strand unzipped from the 5’ end
so DNA polymerase has to wait for a section of strand to unzip and then work back along the strand
DNA is produced in Okazaki fragments
(which then have to be joined by DNA ligase to remove nicks)
(discontinuous replication)
what is the replication fork?
point at which two DNA strands separate
how does the DNA polymerase at the lagging strand initiate DNA synthesis
from an RNA primer (made by primase complex)
polymerase elongates strand opposite to the fork
newly synthesised lagging strand fragment loops out between the polymerase and the fork
once polymerase completes an okazaki fragment
it dissociates from the DNA template
a new primer produces at the fork
the polymerase reassociates with the template at this position
describe a gene
section of DNA containing the complete sequence of bases to code for an entire protein
