nucleic acids (DNA + RNA)

structure

DNA replication (semi-conservative)

transcription

genetic code

pentose monosaccharide, phosphate group, nitrogenous base

phosphodiester bonds

carbon, hydrogen, oxygen, nitrogen, phosphorus

pyrimidines: T/U + C (smaller + single ringed)

monomer: nucleotides

DNA

large polymer: nucleic acid

covalent bond between phosphate group (at carbon 5) and hydroxyl group at carbon 3

sugar phosphate backbone

condensation reactions between two different monosaccharides

purines: A + G (larger + double ringed)

RNA

deoxyribose sugar (1 less sugar)

two antiparallel strands in a helix shape

hydrogen bonds between bases

binds to DNA to makes copies

small enough to enter and exit the nuclear pores + travel to ribosomes

ribose sugar

single stranded + smaller

A + T/U have 2 hydrogen bonds

G + C have 3 hydrogen bonds

sense strand: the strand that is needed to be replicated antisense strand: the strand that is used as a template

free nucleotides bind to complimentary base pairs on the antisense strand

DNA helicase unzips the double helix as far as a gene from the start codon, breaking the hydrogen bonds

phosphodiester bonds are formed between new nucleotides catalysed by RNA polymerase

the process of making mRNA so that a copy of the DNA strand can leave the nucleus to the ribosomes

occurs when cells divide so another copy of DNA needs to be made

double helix has to unwind (using DNA helicase) which breaks hydrogen bonds between bases

then free nucleotides find their complimentary base pairs and form hydrogen bonds

then DNA polymerase forms phosphodiester bonds between the free nucleotides on the new strand

so two new identical double helixes have formed with one new and one old strand each

the code is universal - all organisms use it

the code is degenerate - more than one codon can code for an amino acid

each gene is the amount of code needed for 1 protein

triplet code (codons) - each 3 bases code for an amino acid

there are 64 possible codons and 20 amino acids

DNAs code for a sequence of amino acids

there are three stop codons which signal the end of a sequence

thymine is replaced with uracil

mRNA detaches from the template and then leaves via the nuclear pore and the helix reforms

translation

anticodons will bind to codons, tRNA carries a corresponding amino acid

a maximum of two tRNA can be bound at time

mRNA binds to a specific site on the small subunit of a ribosome

peptidyl transferase catalyses the formation of peptide bonds between the amino acids

mRNA is coded into a sequence of amino acids

protein may undergo further modifications at the Golgi apparatus

tRNA - a strand of RNA folded so that the anticodon (three bases) are at one end of the molecule