1.1 DNA = a polynucleotide made up of lots of nucleotides joined together.
the nucleotides join up by a condensation reaction between the
phosphate group of one nucleotide and the sugar of another.
1.1.1 each nucleotide is made
from a deoxyribose sugar,
a phosphate group and a
nitrogen containing base
1.1.2 each nucleotide has the same
sugar and phosphate. the
bases can vary. there are four possible bases
1.1.3 two DNA polynucleotide chains join together
by hydrogen bonding between the bases. each
base can only join with one particular partner.
(complementary base pairing)
220.127.116.11 Adenine always pairs with
18.104.22.168 Guanine always pairs with Cytosine
22.214.171.124 A purine always pairs with a pyrimidine
126.96.36.199 two hydrogen bonds form between A and T and
three hydrogen bonds form between G and C.
188.8.131.52 two antiparallel polynucleotide strands,
twist to form the DNA double-helix
1.1.4 nucleotides are the monomers of nucleic acids
1.2 DNA replication
1.2.1 DNA replicates semi-conservatively
184.108.40.206 1) the hydrogen bonds between the two polynucleotide DNA
strands break. the helix unzips to form two single strands. 2)
each original single strand acts as a template for a new
strand. free floating DNA nucleotides join to the exposed bases
on each original template strand by complementary base
pairing. 3) the nucleotides on the new strand are joined
together by the enzyme polymerase. hydrogen bonds form
between the bases on the new and original strand. 4) each new
DNA molecule contains one strand from the original DNA
molecule and one new strand.
2 RNA (ribonucleic acid)
2.1 the structure of RNA differs from DNA in 3 main ways
2.1.1 the sugar is a ribose sugar
2.1.2 the nucleotides form a single polynucleotide strand
2.1.3 Uracil (a pyrimidine) replaces Thmyine as a base. Uracil always pairs with Adenine
2.2 there are 3 forms of RNA
2.2.1 messenger RNA (mRNA)
220.127.116.11 made as a strand complementary to one strand of DNA
(template strand). it is a copy of the coding strand of DNA.
2.2.2 ribosomal RNA (rRNA)
18.104.22.168 is found in ribosomes
2.2.3 transfer RNA (tRNA)
22.214.171.124 carries amino acids to the ribosomes where
they are bonded together to form polypeptides.
2.3 protein synthesis
2.3.1 the sequences of bases on DNA makes up the codes for a particular protein. these bases can be exposed by splitting
the hydrogen bonds that hold the double helix together in that region. RNA nucleotides form a complementary
strand (mRNA) which peels away and leaves the nucleus through a nuclear pore. the mRNA attaches to a ribosome.
the tRNA molecules bring bring amino acids to the ribosome in the correct order. the amino acids are joined together
by peptide bonds to give a protein with a specific primary structure.
3.1 a gene is a sequence of DNA nucleotides that codes for a protein. (a polypeptide)
3.2 its the order of nuleotide bases in a gene that determines
the order of amino acids in a particular protein
3.2.1 each amino acid is coded for by a sequence of three bases in a gene
4 too much nucleic acid causes gout
4.1 uric acid is produced when excess purines are broken down in the liver. it is secreted in the urine however
some people have too much uric acid in their blood. the uric acid is insoluble at lower temperatures and forms
crystals that are deposited in joints at the extremeties, such as the toes.