In order to investigate the effect of structural units on the ability of grain boundaries to generate dislocations, tensile and compressive loading tests were performed on aluminum bicrystals with $⟨112⟩$ tilt grain boundaries using molecular-dynamics simulations. Five favored boundaries were found for $⟨112⟩$ boundaries in an energy minimization analysis. Each structure could be identified using only its single structural unit period: $A$ unit for $\ensuremath{\Sigma}1$ with $\ensuremath{\theta}=0\ifmmode^\circ\else\textdegree\fi{}$, $B$ unit for $\ensuremath{\Sigma}11$ with $\ensuremath{\theta}=62.96\ifmmode^\circ\else\textdegree\fi{}$, $C$ unit for $\ensuremath{\Sigma}5$ with $\ensuremath{\theta}=90\ifmmode^\circ\else\textdegree\fi{}$, $E$ unit for $\ensuremath{\Sigma}7$ with $\ensuremath{\theta}=120\ifmmode^\circ\else\textdegree\fi{}$, and $D$ unit for $\ensuremath{\Sigma}3$ with $\ensuremath{\theta}=180\ifmmode^\circ\else\textdegree\fi{}$. The favored boundaries all show an energy cusp except for the $\ensuremath{\Sigma}7$ boundary. Other boundaries could be represented by a combination of these five structural units. When $\ensuremath{\Sigma}11$ with $|B|$ period showing a minimum energy cusp was used as a reference structure, the core of $2/11[\overline{3}\text{ }1\text{ }\overline{1}]$ or $2/11[3\text{ }\overline{1}\text{ }1]$ dislocations calculated for the displacement sift complete lattice of $\ensuremath{\Sigma}11$ were introduced at interfaces having larger or smaller misorientation angles than $\ensuremath{\Sigma}11$, respectively. Each grain-boundary dislocation corresponds to $A$ and $C$ units, respectively. For example, $\ensuremath{\Sigma}21$ with $\ensuremath{\theta}=44.42\ifmmode^\circ\else\textdegree\fi{}$ and $\ensuremath{\Sigma}15$ with $\ensuremath{\theta}=78.46\ifmmode^\circ\else\textdegree\fi{}$ consists of $|BBA|$ and $|BBC|$ periods, respectively. When the $\ensuremath{\Sigma}15$ bicrystal was loaded in tension, lattice dislocations having the $1/2[1\text{ }\overline{1}\text{ }0]$ core were emitted from $C$ units and then the $C$ units change their structure to the $B$ units. Therefore, the $\ensuremath{\Sigma}15$ boundary can change its structure to the energetically stable $\ensuremath{\Sigma}11$ structure by emitting dislocations from $C$ units. For $\ensuremath{\Sigma}21$, the same structural change occurred when the $\ensuremath{\Sigma}21$ bicrystal was deformed in compression. The simulation results show that there are tilt grain boundaries having the strong anisotropic strength and that the ability of grain boundaries to generate dislocations is closely related to their structural units.