They are found in the thylakoid membranes of plants, algae and cyanobacteria (in plants and algae these are located in the chloroplasts), or in the cytoplasmic membrane of photosynthetic bacteria. Plasmid – An extrachromosomal DNA molecule separate from the chromosomal DNA and capable of sexual replication, it is typically ring shaped and found in bacteria. Spindle fiber – The structure that separates the chromosomes into the daughter cells during cell division.