2.1.3 nucleotides and nucleic acids Flashcards
what is a nucleotide made from
a nitrogenous base
a pentose sugar
a phosphate group
what are nucleotides
the monomers of DNA and RNA
what bases can be found in DNA
adenine, thymine, cytosine, guanine
what pentose sugar is in DNA
deoxyribose
what is a purine base
contains 2 carbon nitrogen rings joined together
what bases are purines
adenine and guanine
what is a pyramidal base
only contains 1 carbon nitrogen ring so they are smaller
what bases are pyramidal
thymine and cytosine
what is the pentose sugar in RNA
ribose
what base is different in RNA
thymine is uracil instead
how is energy released from ATP
the phosphate bond stores energy that is released when ATP is broken down into ADP and Pi
what does ATP and ADP stand for
ATP - adenine triphosphate
ADP - adenine diphosphate
what are the bonds between nucleotides
phosphodiester bonds
what is the chain of sugar and phosphates called
the sugar-phosphate backbone
what is the structure of DNA
a double stranded helix
how are the two DNA strands joined together
hydrogen bonds between complementary bases (complementary base pairs)
how many hydrogen bonds between A and T
2
how many hydrogen bonds between C and G
3
how is the helix shape formed
antiparallel strands twist the DNA
how do we purify DNA
break up cells in sample
add detergent (break down cell membranes), salt (binds to DNA and clumps it together) and distilled water to the sample
heat in a water bath at 60 degrees for 15 mins to stop enzymes working
then add to ice bath to cool then filter
add protease to break down proteins and RNAase to break down RNA
drop ethanol down the side forming a layer on top, DNA forms a white precipitate
what is semi conservative replication
half the strand in each copy are from the original piece of DNA
how does DNA copy itself
DNA helicase breaks hydrogen bonds between strands
each original strand acts as a template for a new strand. free floating nucleotides join to exposed bases by complementary base pairing
nucleotides of new strand are joined by DNA polymerase to make phosphodiester bonds between nucleotides and hydrogen bonds form between strands
what is a gene
a sequence of DNA nucleotides that codes for the sequence of amino acids in a polypeptide
how many bases codes for a single amino acid
3 it is called a triplet
what is mRNA
messenger RNA
it is made in the nucleus it carries the genetic code from DNA in the nucleus to the cytoplasm for translation
what is tRNA
transfer RNA
found in the cytoplasm it has an amino acid binding site at one end of the sequence of 3 base pairs at the other end called an anticodon
what is rRNA
ribosomal RNA
forms the two subunits in a ribosome and catalyses the formation if peptide bonds between amino acids
why is the genetic code said to be non overlapping
each base triplet is read in sequence separate from the triplet before and after it. base triplets do not share bases
why is the genetic code said to be degenerate
there are more possible combinations of triplets than there are amino acids this means that some amino acids are coded for by multiple codons.
there are also start and stop codons at the ends of the codons
why is the genetic code said to be universal
the same specific codons code for the same amino acids in all living things
what is the first stage of protein synthesis
transcription
what is the purpose in transcription
an mRNA copy of a gene is made in the nucleus
what are the steps of transcription
RNA polymerase breaks the hydrogen bonds separating the strands. one of the strands and the DNA molecule is used as a template
the RNA polymerase lines up free RNA nucleotides alongside the template using complementary base pairing (U is used instead of T)
RNA nucleotides bond to make an mRNA molecule
hydrogen bonds reform between DNA strands
what is the second stage of protein synthesis
translation
what is the purpose in translation
amino acids are joined together to make a polypeptide
what are the steps of transcription
mRNA attaches to a ribosome
tRNA carries amino acids to ribosome
a tRNA molecule with a complementary anticodon to the start codon and attaches itself by complementary base pairing
a peptide bond forms between each amino acid and tRNA moves away.
this continues until stop codon
polypeptide moves away from ribosome when done.
