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-optimised 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.