Eukaryotic Cell Structure

• What is the nuclear envelope?

  A double membrane that surrounds the nucleus. Its outer membrane is continuous with the endoplasmic reticulum of the cell and often has ribosomes on its surface.

  It controls the entry and exit of materials in and out of the nucleus, and contains the reactions taking place within it.
• What are nuclear pores?

  Channels in the nuclear envelope that allow for the transport of large molecules, such as messenger RNA, in and out of the nucleus.
• What is nucleoplasm?


  Granular, jelly-like material that makes up the bulk of the nucleus.
• What do chromosomes consist of?

  Protein-bound, linear DNA
• What is the nucleolus?


  A small spherical region within the nucleoplasm. It manufactures ribosomal RNA and assembles ribosomes. There can be more than one nucleolus in a nucleus.
• What are the functions of the nucleus?

  • acts as a control centre of the cell through the production of mRNA and tRNA and hence protein synthesis.
  • retains the genetic material of the cell in the form of DNA and chromosomes.
  • manufactures ribosomal RNA and ribosomes.
• How long are mitochondria?

  1-10 um
• What surrounds mitochondria?


  A double membrane that controls the entry and exit of material. The inner of the two membranes is folded to form extensions known as cristae
• What are cristae?


  Extensions of the inner membrane of mitochondria. In some species, they extend across the whole width of the mitochondrion.

  These provide a large surface area for the attachment of enzymes and other proteins involved in respiration.
• What is a matrix in mitochondria?

  A matrix makes up the remainder of the mitochondrion, it contains proteins, lipids, ribosomes and DNA that allows mitochondria to control the production of some of their own proteins, Many enzymes involved in respiration are found in the matrix.
• Mitochondria are the site of what?

  The aerobic stages of respiration (the Krebs cycle and the oxidative phosphorylation pathway).
• What molecule do mitochondria produce?

  The energy-carrier molecule, ATP, from respiratory substrates such as glucose.
• What are examples of metabolically active cells?

  Muscle cells

  Epithelial cells- found in the intestines, require a lot of ATP in the process of absorbing substances from the intestines by active transport.
• What is the chloroplast envelope?

  A double plasma membrane that surrounds chloroplasts. It is highly selective in what it allows to enter and leave the chloroplast.
• What are the grana?

  Stacks of up to 100 disc-like structures called thylakoids, which contain the photosynthetic pigment chlorophyll. Some thylakoids have tubular extensions that join up with thylakoids in adjacent grana.

  The grana are where the first stage of photosynthesis (light absorption) takes place.
• What is the stroma?

  A fluid-filled matrix where the second stage of photosynthesis (synthesis of sugars) takes place. Within the stroma are a number of other structures such as starch grains.
• How are chloroplasts adapted to absorbing sunlight and carrying out photosynthesis?

  • Granal membranes provide a large surface area for the attachment of chlorophyll, electron carriers and enzymes that carry out the first stage of photosynthesis. These chemicals are attached to the membrane in a highly ordered fashion.
  • The fluid of the stroma possesses all enzymes needed to make sugars in the second stage of photosynthesis.
  • Chloroplasts contain both DNA and ribosomes so they can quickly and easily manufacture some of the proteins needed for photosynthesis.
• What is the endoplasmic reticulum?

  An elaborate, three-dimensional system of sheet-like membranes, spreading through the cytoplasm of the cells.

  The membranes enclose a network of tubules and flattened sacs called cisternae.
• What are the functions of the ROUGH endoplasmic reticulum?

  • Has ribosomes present on the outer surface.
  • Provides a large surface area for the synthesis of proteins and glycoproteins.
  • Provides a pathway for the transport of materials, especially proteins throughout the cell
• What are the functions of the smooth endoplasmic reticulum?

  • Lacks ribosomes on the surface and is often more tubular in appearance.
  • Synthesises, stores and transports lipids
  • Synthesises, stores and transports carbohydrates
• Cells that manufacture and store large quantities of carbohydrates, proteins and lipids have a very extensive ER.

  e.g. liver and secretory cells (such as the epithelial cells that line the intestine)
• The Golgi apparatus is similar to SER in structure except that it is more compact.
• What are the structures that make up the Golgi apparatus?

  Flattened sacs called cisternae and small rounded hollow structures called vesicles
• How does the Golgi apparatus differ from the smooth endoplasmic reticulum (SER)?

  The Golgi apparatus is more compact and consists of stacked membranes compared to the SER
• What happens to proteins and lipids as they pass through the Golgi apparatus?


  They are modified, labeled, and sorted for transport to their destinations
• What role do Golgi vesicles play in the function of the Golgi apparatus?

  They transport modified proteins and lipids to their correct destinations
• What are the main functions of the Golgi apparatus?

  • Add carbohydrate to proteins to form glycoproteins
  • Produce secretory enzymes, such as those secreted by the pancreas
  • Secrete carbohydrates for cell wall formation in plants
  • Transport, modify, and store lipids
  • Form lysosomes
• In which type of cells does the Golgi apparatus occur?

  Almost all eukaryotic cells
• What is the significance of the Golgi apparatus in protein processing?

  It modifies proteins by adding non-protein components and labels them for sorting
• How does the Golgi apparatus contribute to the secretion of enzymes?


  It produces secretory enzymes that are then transported to their destination
• Why is the Golgi apparatus particularly well developed in certain cells, such as epithelial cells?

  Because these cells are involved in secretion and require efficient processing of proteins and lipids
• Vacuoles are membranous sacs within the cell containing water and dissolved solutes such as salts and sugars. They may be permanent features of the cell or temporary storage sites formed when required.
• What are lysosomes formed from?

  Lysosomes are formed when vesicles produced by the Golgi apparatus contain enzymes.
• What types of enzymes do lysosomes contain?

  Lysosomes contain proteases, lipases, and lysozymes.
• How many enzymes can a single lysosome contain?

  A single lysosome may contain as many as 50 enzymes.
• What is the diameter of lysosomes?

  Lysosomes can be up to 1.0 μm in diameter.
• What is the primary function of lysosomes?

  The primary functions of lysosomes are to hydrolyse material, release enzymes, digest worn-out organelles, and break down dead cells.
• In which types of cells are lysosomes especially abundant?

  Lysosomes are especially abundant in secretory cells and phagocytic cells.
• What are ribosomes?


  Ribosomes are small cytoplasmic granules found in all cells.
• Where can ribosomes be found in a cell?

  Ribosomes can be found in the cytoplasm or associated with the rough endoplasmic reticulum (RER).