2.3 nucleic acids and enzymes Flashcards
what is the structure of nucleotides
a phosphate
5 carbon sugar
nitrogenous base
name the pentose sugars in RNA and in DNA
deoxyribose
ribose
describe how polynucleotide strands are formed and broken down
condensation reactions form strong phosphodiester and glycosidic bonds
hydrolisis reactions use a molecule of water to break these bonds
describe the structure of DNA
molecule twists to form a double helix of 2 deoxyribose polynucleotide strands that are anti parallel to each other
a-t
c-g
name the purine bases and describe their structure
adenine
guanine
two ring molecules
name the pyrimidine bases and describe their structure
thymine
cytosine
uracil
one ring molecules
why is DNA replication described as semi conservative
strands from original DNA molecule act as a template
new DNA molecule contains 1 old strand and 1 new strand
explain the role of helicase in semi conservative replication
breaks hydrogen bonds between base pairs to form 2 single strands, each of which can act as a template
how is a new strand formed during semi conservative replication
DNA gyrase unwinds and helicase unzips DNA
primase adds a primer so that DNA polymerase knows where to start adding nucleotides
ligase sticks together the fragments
what is the lagging strand
DNA polymerase only goes in the 5’3’ direction so okozaki fragments are made in the lagging strand and stuck together by ligase
identify features of genetic code
non overlapping - each triplet is only read once
degenerate - more than one triplet codes for the same amino acid (64 possible triplets for 200 amino acids)
universal - same bases and sequences used by all species
how does a gene determine the sequence of amino acids in a protein
consists of base triplets that codes for specific amino acids
describe how DNA could be purified through precipitation
add ethanol and salt to aqueous solution, nucleic acids precipitate out of solution
centrifuge to obtain a pellet of nucleic acid then wash and centrifuge again
what does transcription produce and where does it occur
produces mRNA and occurs in the nucleus
outline the process of transcription
RNA polymerase binds to the DNA strand and unwinds a short section
this then travels along the DNA strand building an RNA molecule from the template strand
splicing removes non-coding strands of mRNA (introns)
mRNA leaves through the nuclear pores and attaches to the ribosomes
what does translation produce and where doe it occur
produces proteins and occurs in the cytoplasm on ribosomes
outline the process of translation
tRNA carries specific individual amino acids
tRNA carries an anti codon that matches up to the corresponding bases on mRNA
process continues to form polypeptide chain until ‘stop’ codon is reached
what is a mutation
an alteration to the DNA base sequence
when does DNA replicate
during interphase
describe enzymes
biological catalysts used to spead up reactions
what is the difference between intra and extracellular enzymes
intracellular enzymes are inside the cell e.g DNA polymerase
whereas extracellular enzymes are outside the cells e.g. protease
define turnover number
number of reactions an enzyme can catalyse per second
define anabolic reaction
building up
define catabolic reactions
breaking down
describe the lock and key theory
substrate molecules fit into the active site and are then released
describe the induced fit hypothesis
when the substrate molecules fit into the enzymes active site, the active site changes shape slightly to mould itself around the substrate molecule
