Animation of a flight through a human cell, showing the nucleus and other organelles. The cell is bounded by its cell membrane. Within this, there is a variety of organelles, each with a specific purpose. The nucleus (red) contains the cell's genetic material, and is the site of gene expression, where the cell's DNA is transcribed to RNA so that it can be used to produce proteins. Also seen is the Golgi apparatus (pink layers), which is responsible for sorting and preparing proteins made by the nucleus for their ultimate function. The orange bodies are mitochondria, which provide energy for the cell in the form of the molecule ATP. Seen next is the endoplasmic reticulum, which is covered in small bodies called ribosomes. Ribosomes are the site of the manufacture of proteins, where mRNA from the nucleus is translated into proteins. HD supplied with alpha, or for a flat version on a black background see image number K003/3803.