Glaucophyte algal chloroplasts have a peptidoglycan layer between the chloroplast membranes. Some chloroplasts contain a structure called the chloroplast peripheral reticulum. Commonly used organelles include lysosome, chloroplast and mitochondria. In plants, ATP is synthesized in the thylakoid membrane of the chloroplast. Plants depend critically on photosynthesis by chloroplast thylakoid membranes which are exposed cold environmental temperatures. As in prokaryotes, genes in chloroplast DNA are organized into operons. It is also present in some chloroplast and mitochondrial transcripts. It was based on molecular phylogenetic analysis of chloroplast and nuclear DNA sequences. Thylakoids are membrane-bound structures embedded in the chloroplast stroma. These rare biparental zygotes allowed mapping of chloroplast genes by recombination. The mesophyll contains most of the chloroplast where photosynthesis can occur. This phylogeny was based on 6000 basepairs of chloroplast DNA. These are concentrated in the chloroplast, cytosol, and in some cases the extracellular space. Double membrane of chloroplast envelope surrounds the chloroplast. Starch granules vary in composition and location across different chloroplast lineages.