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.
each nucleotide is made
from a deoxyribose sugar,
a phosphate group and a
nitrogen containing base
each nucleotide has the same
sugar and phosphate. the
bases can vary. there are four possible bases
Adenine
Thymine
Guanine
Cytosine
two DNA polynucleotide chains join together
by hydrogen bonding between the bases. each
base can only join with one particular partner.
(complementary base pairing)
Adenine always pairs with
Thymine
Guanine always pairs with Cytosine
A purine always pairs with a pyrimidine
two hydrogen bonds form between A and T and
three hydrogen bonds form between G and C.
two antiparallel polynucleotide strands,
twist to form the DNA double-helix
nucleotides are the monomers of nucleic acids
DNA replication
DNA replicates semi-conservatively
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.
RNA (ribonucleic acid)
the structure of RNA differs from DNA in 3 main ways
the sugar is a ribose sugar
the nucleotides form a single polynucleotide strand
Uracil (a pyrimidine) replaces Thmyine as a base. Uracil always pairs with Adenine
there are 3 forms of RNA
messenger RNA (mRNA)
made as a strand complementary to one strand of DNA
(template strand). it is a copy of the coding strand of DNA.
ribosomal RNA (rRNA)
is found in ribosomes
transfer RNA (tRNA)
carries amino acids to the ribosomes where
they are bonded together to form polypeptides.
protein synthesis
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.
Genes
a gene is a sequence of DNA nucleotides that codes for a protein. (a polypeptide)
its the order of nuleotide bases in a gene that determines
the order of amino acids in a particular protein
each amino acid is coded for by a sequence of three bases in a gene
too much nucleic acid causes gout
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.