the present invention relates to novel expression cassettes and expression vectors , comprising three nucleic acid sequences for araa , arab and arad , each coding for a polypeptide of an l - arabinose metabolic pathway , in particular , a bacterial l - arabinose metabolic pathway . the invention particularly relates to expression cassettes and expression vectors , comprising codon - optimized nucleic acid sequences for araa , arab and arad . the invention further relates to host cells , in particular modified yeast strains containing the expression cassettes or expression vectors and expressing the polypeptides for the l - arabinose metabolic pathway , in particular , for the bacterial l - arabinose metabolic pathway . when using these modified host cells , arabinose is more effectively fermented by these cells , in particular into ethanol . the present invention is therefore relevant , inter alia , in connection with the production of biochemicals from biomass , such as bioethanol for example .