Nucleic Acids and their functions

2 polynucleotide strands in a double helix shape

Pentose sugar is Deoxyribose

4 nitrogenous/organic bases :

Purines : Adenine and Guanine

Pyrimidines: Cytosine and Thymine

Complementary base pairing [Hyrdogen bonds] A--T C---G

Antiparallel strands

very stable molecule, info is passed relatively unchanged from gen to gen

very large and carries a large amount of genetic info

2 strands are able to separate due to hydrogen bonding

base pairs on the inside within the deoxyribose sugar phosphate backbone = genetic info is protected

single stranded polynucleotide

Pentose sugar Ribose

Purines: Adenine and Guanine

Pyrimidines: Cytosine and Uracil

these 3 types of RNA are involved in the process of protein synthesis

Messenger RNA (mRNA) - synthesised in the nucleus and carries genetic info from nucleus to the ribosomes in the cytoplasm

Ribosomal RNA (rRNA) - ribosomes are made from rRNA and protein. they are the site of translation of the genetic code into the protein

Transfer RNA (tRNA) - cloverleaf shape. carries a sequence of 3 bases called an anticodon. transport specific amino acids to the ribosomes in proteins synthesis

takes place during interphase in the nucleus

Conservative: parental double helix remains and a whole new double helix is made

Semi-conservative: parental double helix is separated into 2 strands each of which acts as a template for synthesis of a new strand

Dispersive: 2 new double helices contain fragments from both strands of the parental double helix

bacteria was grown in N15, they found that this made the DNA fully incorporate the N15 into its nucleotides. they centrifuged it and it was low as it was heavier than the normal N14.

the heavy N15 bacteria was then grown in a new sample of N14

after 1st generation, half of the DNA was heavy and half was light (intermediate)

after 2nd generation, half of the DNA was light and half was intermediate

after 3rd generation, a quater of the DNA was intermediate and the other 3 quarters was light

1 1   1 1    1st gen    1/1 intermediate = 1 middle band

1 1   1 1   1 1   1 1  2nd gen 1/2 intermediate (2/4) = 1 middle band and 1 light band

1 1   1 1   1 1   1 1   1 1   1 1   1 1   1 1  3rd gen 1/4 intermediate (2/8)  = 1 middle band and thick light band

1=N15   1= N14     this proves it was semi-conservative as not 1 that was entirely heavy (conservative) and not N15 and N14 in all strands

triplet code- always had 3 times the number of bases than amino acid chain it coded for

if 3 bases where removed from a polypeptide chain it would lose 1 less amino acid and if gained 2 extra it would gain an amino acid

- 64 possible codes but only 20 amino aicds are found in proteins so more than 1 triplet can code for each amino acid - code is degenerate / redundant

- code is punctuated = stop codons mark the end of a portion to be translated

- universal

-non-overlapping - each base occurs in only 1 triplet

DNA triplet can also be referred to as an RNA codon and are complimentary to each other

pre-mRNA contains both exons and introns but introns need to be removed as they are non coding, they are not translated into proteins

the introns are cut out using endonucleases

the exons are the pieces which are left which are then spliced (joined together) with ligases which forms the mature mRNA

DNA helicase breaks the hydrogen bonds between the bases on the DNA strands causing them to unzipand expose nucleotide bases

RNA polymerase binds to the template strand, this results in complimentary base pairing between the free RNA nucleotides A--U and C---G.

mRNA is synthesised as RNA polymerase moves along the DNA forming bonds between base pairs

RNA polymerase detaches from the template strand when it reaches a stop codon

each ribsome has 2 sites for attachment of tRNA molecules. it moves along the mRNA holding the codon-anticodon complex together until the animo acids attached to the tRNA bind

Initiation- mRNA leaves the nucleus through the nuclear pores and binds to the ribsome at the start codon, first tRNA within a complimentary anticodon binds to the mRNA strand with its specific amino acid and then the next tRNA binds aswell

Elongation-the 2 amino acids are close enough to form a peptide bond catalysed by ribosomal enzymes as well as ATP being used to create this bond, the first tRNA leaves and the next one binds

Termination- the sequence is repeated until it reaches a stop codon, the ribosome detaches from the mRNA and a polypeptide chain is formed

-once a tRNA is released from the ribosome, it can collect another amino acid from the AA pool in the cytoplasm. energy from ATP is needed to attach the amino acid to the tRNA = amino acid activation

polypeptides made on ribosomes are transported to the golgi body

the golgi body usually folds them and changes their structure to secondary, tertiary or quaternary and may be chemically modified

can be modified with:

carbohydrates -glycoproteins

lipids -lipoproteins

phosphates -phospho-proteins

ie haemoglobin, quaternary structure, each polypeptide has alpha helix(secondary) and is folded(tertiary), four polypeptides are combined (quaternary). the protein is modified with 4 non-protein haem groups