All eukaryotic mRNA molecules have a cap structure at the 5' ends which plays a crucial role in the scanning model of their translation initiation. In an alternative way of translation, the active ribosome is formed in a cap-independent mode due to the presence of IRES, internal ribosome entry site, in the 5' untranslated region of certain mRNAs. This region folds into a distinct secondary and tertiary structure, which binds the 40S ribosomal subunit and some protein factors, and subsequently forms the initiation complex and the translationally active 80S ribosome. This enables the synthesis of specific proteins under the conditions when cap-dependent translation is inhibited or strongly reduced. The cap-independent mode of translation initiation concerns proteins that play very important roles during cell cycle, apoptosis, response to stress stimuli and cancer development.