Ultrastructure of eukaryotic cells

• Centrioles – every animal cell has one pair of centrioles, which are hollow cylinders made up of a ring of nine protein

  microtubules. They are involved in the formation of the spindle during nuclear division and in their transport with the cell

  cytoplasm.
• Mitochondria – the inner of its two membranes is folded to form finger-like projections called cristae. The mitochondria

  are the site of the later stages of aerobic respiration.
• Nucleus – enclosed by an envelope composed of two membranes perforated by pores, Contain chromosomes and a

  nucleolus. Chromosome are made of DNA contain genes that control the synthesis of proteins.
• Nucleolus – a dense body within the nucleus where ribosomes are made
• Rough Endoplasmic Reticulum – a system of interconnected membrane-bound flattened sacs. Ribosomes are attached

  to the outer surface. Protein made on these ribosomes are transported through the ER to other parts of the cell.
• Ribosomes – made of RNA and protein these small organelles are found free in the cytoplasm or attached to the

  endoplasmic reticulum. They are the site of protein synthesis.
• Cell Surface Membrane – phospholipid bilayer containing proteins and other molecules forming a partially permeable

  barrier.
• Smooth Endoplasmic Reticulum – like rough ER but does not have any attached ribosomes. Smooth ER makes lipids and

  steroids.
• Golgi Apparatus – stacks of flattered membrane bound sacs formed by fusion of vesicles from the ER. Modifies proteins

  and packages them in vesicles for transport.
• Lysosome – spherical sacs continuing digestive enzymes and bound by a single membrane. Involved in the breakdown of

  unwanted structures within the cell and in the destruction of the whole cells when old cells are to be replaced or during

  development. The acrosome is a specialised lysosome.