1.5 Structure of RNA and DNA

describe the structure of a nucleotide

phosphate joined to a pentose sugar which is joined to a organic, nitrogen-containing base

what is the pentose sugar in DNA and RNA

* in DNA: deoxyribose
* in RNA: ribose

how do polynucleotides form

through the condensation of many mononucleotides to form a phosphodiester bonds

what is the role of DNA in living cells

base sequence of genes code for functional RNA and the amino acid sequence of polypeptide. DNA forms genes which determines inherited characteristics that influences structure and function of organisms.

what is the role of various types of functional RNA in living cells

mRNA: complementary sequence to one gene from DNA with introns splices out. codons are translated into polypeptides by ribosomes.

rRNA: component of ribosomes

tRNA: supplies complementary amino acid to mRNA codons during translation

describe the structure of DNA

* double helix made of 2 polynucleotide strands
* base pairing: adenine to thymine by 2 H-bonds and guanine to cytosine joined by 3 H-bonds
* purine bonds to pyrimidine to keep the 2 strands the same distance apart

which bases are purine and which are pyrimidine

* A and G are purine (2-ring)
* C, T and U are pyrimidine (1-ring)

how is the structure of DNA related to its function

* sugar-phosphate back bone protect the bases, and numerous H-bonds provide stability
* helix is compact for storage in nucleus
* double strand allows it to unzip for semi-conservative replication
* long molecule stores lots of information

describe structure of mRNA

long ribose polynucleotide with uracil instead of thymine. single stranded and contains a codon sequence that’s complementary to the exons of a gene from a DNA strand.

how is the structure of mRNA adapted to its function

* breaks down quickly so there’s no excess polypeptides.
* can be translated into a specific polypeptide by ribosomes

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