1 - Cell structure

• The nucleus contains DNA, which controls the metabolic activity of the cell.
• DNA is contained within a double membrane known as a nuclear envelope.
• The nuclear envelope contains nuclear pores which allow molecules to move in and out of the nucleus. DNA is too large to leave.
• The nucleolus produces ribosomes. It is made of proteins and RNA.
• DNA associates with proteins called histones to form chromatin. This coils and condenses to form chromosomes.
• Mitochondria are the final site of cellular respiration in the cell.
• Very active cells have lots of mitochondria.
• Mitochondria make energy available by producing a molecule called ATP.
• Mitochondria have a double membrane. The inner membrane folds to form structures called cristae.
• The fluid interior of mitochondria is called the matrix.
• The membrane that forms cristae contains enzymes used in aerobic respiration.
• Mitochondria contain a small amount of DNA, called mtDNA.
• Mitochondria can produce their own enzymes and reproduce themselves.
• Vesicles are sacs that have a single membrane with fluid inside.
• Vesicles are used to transport materials around the cell.
• Lysosomes are special forms of vesicles that break down waste materials in the cell, including old organelles.
• Lysosomes break down the pathogens ingested by phagocytic cells. They also play an important role in programmed cell death (apoptosis).
• The cytoskeleton holds organelles in place and helps the cell keep its structure. It is responsible for any movement of the cell.
• The cytoskeleton has three component:

  • Microfilaments
  • Microtubules
  • Intermediate fibres
• Microfilaments are responsible for cell movement and contraction during cytokinesis.
• Microtubules determine the shape of the cell and act as tracks for the movement for organelles like vesicles.
• Spindle fibres are made of microtubules.
• Centrioles are found in most eukaryotic cells except flowering plants and most fungi.
• Centrioles are made up of microtubules. Two combine to form a centrosome.
• Flagella are used for cell motility, while cilia can be mobile or stationary.
• Cilia are comprised of two central microtubules surrounded by nine pairs of microtubules in the 9+2 arrangment.