How DNA codes for polypeptides

RNA vs DNA

RNA's pentose sugar=ribose

In RNA thymine is replaced by uracil

RNA's polynucleotide chain=single stranded+shorter

3 forms of RNA; mRNA, tRNA, rRNA

Genes

On each chromosome there are specific lengths of DNA- these are genes

Each gene contains a code that determines the sequence of amino acids in a protein

Within each gene there is a sequence of DNA base triplets that determine the amino acid sequence

As long as this is correct then the polypeptide will fold correctly+ be held in tertiary structure

Because the instructions inside the genes on chromosomes cannot pass out of the nucleus, a copy of each gene has to be transcribed into a length of mRNA.

In this form the sequence base triplets (now called codons) can pass out of the nucleus to the ribosome- ensuring the coded instructions are translated+ protein is assembled correctly.

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