\documentclass[12pt,border=0pt,tikz,class=scrartcl]{standalone} \usepackage[T1]{fontenc} \usepackage[latin1]{inputenc} \usepackage{lmodern} \usepackage{mathtools,amssymb} \usepackage{pgfplots} \pgfplotsset{compat=1.10} \usetikzlibrary{positioning,calc,arrows,fit,backgrounds,decorations.text,shapes}  \usepackage{chemfig,chemmacros} \renewcommand*{\familydefault}{\sfdefault} \renewcommand*\printatom[1]{\ensuremath{\mathsf{#1}}} \setatomsep{1.5em} \setdoublesep{.6ex} \setarrowdefault{,1,ultra thick} \setbondstyle{thick,cap=round}  \pagestyle{empty} \begin{document} \begin{tikzpicture} 	\node (n1) { 		\chemfig{*6(--(-)=( 		-=_[::-60]-[::60](-[2]) 		=_[::-60]-[::60]=_[::-60]-[::60](-[2]) 		=_[::-60]-[::60]=^[::-60]N(-[6,.6,,1,draw=none]H|^{\scriptstyle+})-[::60,,,1]R|hodopsin 		)-(-[::-30])(-[::-90])--)} 	}; 	\node at ($(n1)-(25em,0)$) (n2) { 		\chemfig{*6(--(-)=( 		-=_[::-60]-[::60](-[2]) 		=_[::-60]-[::60]=_[::-60]-[::60](-[2]) 		=_[::-60]-[::60]=_[::-60]O 		)-(-[::-30])(-[::-90])--)} 	}; 	\node at ($(n2)-(2,4.8)$) (n3) { 		\chemfig{*6(--(-)=( 		-=_[::-60]-[::60](-[2]) 		=_[::-60]-[::60]=_[::-60]-[::60](-[2]) 		=_[::-60]-[::60]-[::-60]OH 		)-(-[::-30])(-[::-90])--)} 	}; 	\node at ($(n3)-(0,3.8)$) (n4) { 		\chemfig{*6(--(-)=( 		-=_[::-60]-[::60](-[2]) 		=_[::-60]-[::60]=_[::-60]-[::60](-[2]) 		=_[::-60]-[::60]-[::-60]OH 		)-(-[:120])(-[:60])--)} 	}; 	\node at ($(n4.west)-(0,4)$) (n5) [anchor=west] { 		\chemfig{*6(--(-)=( 		-=_[::-60]-[::60](-[2]) 		=_[::-60]-[::60]=_[::-60]-[::60](-[2]) 		=_[::-60]-[::60]-[::-60]O-[::60](=[2]O)-[::-60]R 		)-(-[:120])(-[:60])--)} 	}; 	\node at ($(n5)+(34em,0)$) (n6) { 		\chemfig{*6(--(-)=( 		-=_[::-60]-[::60](-[2]) 		=_[::-60]-[::60]=_[::-60]-[6](-[::-60])=^[::60]-[::-60]-[::60]OH 		)-(-[:120])(-[:60])--)} 	}; 	\node at ($(n6)+(0,4)$) (n7) { 		\chemfig{*6(--(-)=( 		-=_[::-60]-[::60](-[2]) 		=_[::-60]-[::60]=_[::-60]-[6](-[::-60])=^[::60]-[::-60]=^[::60]O 		)-(-[:120])(-[:60])--)} 	}; 	\node at ($(n7.east)+(.1,2.9)$) (n8) [anchor=south east] { 		\chemfig{*6(--(-)=( 			-=_[::-60]-[::60](-[2]) 			=_[::-60]-[::60]=_[::-60]-[6](-[::-60])=^[::60]-[::-60]=^[::60] 			N(-[6,.6,,1,draw=none]H|^{\scriptstyle+})-[::60,,,1]R|hodopsin 			)-(-[:120])(-[:60])--)} 	}; 	\node at ($(n5.east)!.5!(n6.west)-(3.7,4)$) (n9) { 		\chemfig{*6(--(-)=( 			-=_[::-60]-[::60](-[2]) 			=_[::-60]-[::60]=_[::-60]-[6](-[::-60])=^[::60]-[::-60]-[::60]OH 			)-(-[:120])(-[:60])--)} 	}; 	\node at ($(n5.east)!.5!(n6.west)+(3.7,-4.5)$) (n10) { 		\chemfig{*6(--(-)=( 			-=_[::-60]-[::60](-[2]) 			=_[::-60]-[::60]=_[::-60]-[6](-[::-60])=^[::60]-[::-60]-[::60]O-[::-60] (-[::60]R)=[::-60]O 			)-(-[:120])(-[:60])--)} 	}; 	\begin{pgfonlayer}{background}  		\node [rounded corners=2em,draw=green,fill=yellow!30,line width=6pt,fit=(n1) (n2) (n3) (n8),inner sep=8pt] (big1) {}; 		\node [rounded corners=2em,draw=green,fill=cyan!30,line width=6pt,fit=(n4) (n5) (n6) (n7) (n9) (n10),inner sep=8pt] (big2) {}; 	\end{pgfonlayer} 	\draw [-latex,ultra thick]  		(n1.west) -- (n2.east)  		node [pos=.5,above] {\large\chemfig[green!50!black]{H_2O}}; 	\draw [-latex,ultra thick]  		(n2.south) node [above right] {\large all-trans retinal}  		-- (n3.north)  		node [pos=.5,left] {\large\color{green!50!black}all-trans RDH}; 	\draw [-latex,ultra thick]  		(n3.south) node [above right] {\large all-trans retinol}  		-- (n4.north); 	\draw [-latex,ultra thick]  		(n4.south) node [above right] {\large all-trans retinol}  		-- (n4.north |- n5.north)  		node [pos=.5,right] {\large\color{green!50!black}LRAT}; 	\draw [-latex,ultra thick]  		node at ($(n5)+(1,-1)$) {\large all-trans retinyl ester}  		(n5.east) -- (n6.west)  		node [pos=.5,above] {\large\color{green!50!black}RPE65}; 	\draw [very thick]  		(n9.north) .. controls ++(0,1.5) and ++(-1.5,0) .. ($(n5.east)!.5!(n6.west)$); 	\draw [-latex,very thick]  		($(n5.east)!.5!(n6.west)$) .. controls ++(1.5,0) and ++(0,1.5) .. (n10.north); 	\draw [-latex,ultra thick]  		node at ($(n6)+(0,-1)$) {\large 11-cis retinol}  		(n6.north) -- ($(n7.south)+(0,.45)$)  		node [pos=.5,left] {\large\color{green!50!black}11-cis RDH}  		node [pos=1,above] {\large 11-cis retinal}; 	\draw [-latex,ultra thick] 		(n7.north) -- (n7.north |- n8.south) 		node [pos=1,left] {\large 11-cis retinilidene}; 	\draw [-latex,ultra thick] 		(n8.north) -- ($(n1.south)-(0,.1)$) 		node [pos=1,above] {\large all-trans retinilidene} 		node [pos=.5,right,inner xsep=8pt] {\large\color{green!50!black}h$\nu$}; 	\draw [decorate, decoration={brace,amplitude=2em}, ultra thick] 		(big1.south west) -- (big1.north west) 		node [pos=.5,anchor=south,xshift=-20pt,rotate=90] {\Large Rod outer segment}; 	\draw [decorate, decoration={brace,amplitude=2em}, ultra thick] 		(big2.south west) -- (big2.north west) 		node [pos=.5,anchor=south,xshift=-20pt,rotate=90] {\Large Retinal pigment epithelium}; \end{tikzpicture} \end{document}