Polynucleotide strands are formed from condensationreactions between nucleotides to form strong phosphodiester bonds and make the sugar phosphate backbone.
DNA is a double helix of 2 deoxyribose polynucleotide strands (2 sugar phosphate backbones)
hydrogenbonds form between complementarybasepairs on strnds that run antiparallel.
The two purine bases are adenine and guanine which are tworinged molecules.
The three pyrimidine bases are thymine, cytosine and uracil and they are onering molecules.
DNA replication is semiconservative because strands from original DNA molecules act as templates.
New DNA molecule contains 1oldstrand and 1newstrand. Specific base pairing enables genetic material to be conserved accurately.
New strands are formed during semi-conservative replication.
free nucleotides attach to exposed bases by complementarybasepairing
dna polymerase joins adjacent nucleotides on new strand in 5’ to 3’ direction through condensation reactions to form phosphodiester bonds
hydrogen bonds re form
Genetic code is degenerate - more than one triplet codes for the same amino acid (64 possible triplets for 20 amino acids)
Genetic code is universal - same bases and sequences used by all species
A gene determines the sequence of amino acids as it consists of base triplets that code for specific amino acids
DNA can be purified by precipitation by adding ethanol and a salt to an aqueous solution. Nucleic acids precipitate out of solution. Centrifuge to obtain pellet of nucleic acid. Wash pellet with ethanol and centrifuge again.
Transcription produces mrna and it occurs in the nucleus
The process of transcription
RNApolymerase binds to start region on a gene
section of DNA uncoils into 2 strands with exposed bases.Antisense strand acts as a template
freenucleotides are attracted to their complementary bases
rnapolymerase joins adjacent nucleotides by phosphodiester bonds
Translation produces an aminoacid chain and it occurs in cytoplasm or on ribosomes
Translation :
ribosome moves along mrna until ’start’ codon
trna anticodon attaches to complementary bases on mrna
condensation reactions between amino acids on trna form peptide bonds
process continues to form polypeptide chain until ’stop’ codon is reached
Adenosine triphosphate has threeinorganic phosphate groups attached to a ribose sugar which is attached to an adenine base
A mutation Is an alteration to the DNAbasesequence. Mutations often arise spontaneously during DNA replication.
Genetic code is non overlapping - each triplet is only read once
In DNA, two antiparallel DNA strands twist round eachother to form a double helix
DNA forms a right handed helix, with about 10. Nucleotide pairs for each turn
In the condensation reaction between nucleotides H is lost from either C3 or C5 on sugar and the OH is lost from the phosphate group
ATP is used for energy as small amounts of energy are used to break off the end phosphaste but it releases lots of energy
Complementary bases occur in equalproportions
so if 33% of the dna bases is A; then 33% of the bases are T
DNA replicates during interphase - the S phase
In the meselson and stahl experiment:
it showed DNA replication as semiconservative because the percentage of DNA that had N15 base decreased and the percentage of dna that had the N14 base increased (semi) but there were always 2 strands of N15 DNA (showing its ‘conservative’ nature)
A gene is a section of DNAthatcodesforthesequenceofamino acids in a polypeptide
Alleles are differentversions of the samegene
Shape and behaviour of proteins depends on the sequence of aminoacids.
Genetic code is always read from the template strand - antisense strand
Practical investigation to purify dna:
crush piece of fruit using pestle and mortar
add detergent (washing up liquid)
add protease enzyme - found in pineapple
filter to remove solids
add salt to help dna clump together
pour cold alcohol into mixture - dna is insoluble in alcohol so will float to top
Crushing fruit in DNA practical helps to break down the cellulosecellwall
Adding detergent in DNA practical helps dissolve the cell surface / plasma membrane
Adding protease enzyme in DNA investigation breaks down histone proteins associated with DNA.
In transcription:
the gene coding for a protein is exposed by DNA helicase catalysing the splitting of hydrogenbonds holding bases together.
Free rna nucleotides form a complementarystrand by lining up base pairs of antisense strand
rnapolymerase helps form phosphodiester bonds in between RNA nucleotides
After mRNA leaves the nucleus through a nuclear pore and the DNA reforms,translation occurs
Adenosine diphosphate has two inorganic phosphate groups attached to a ribose sugar which is attached to an adenine base