3.4 eukaryotic cell structure

• the nucleus contains the organism's hereditary material and controls the cell's activities
• components of the nucleus:

  1. nuclear envelope
  2. nuclear pores
  3. nucleoplasm
  4. chromosomes
  5. nucleolus
• mitochondrion structure:

  1. double membrane which controls entry and exit of the cell
  2. the inner membrane folds to form a cristae which increases surface area
  3. the matrix
• mitochondria are the site of aerobic respiration
• mitochondria produce ATP
• chloroplasts are the organelles that carry out photosynthesis
• thylakoid stacks are called grana
• chloroplasts have an outer membrane with internal thylakoids (flattened sacs) containing chlorophyll
• chloroplasts contain chlorophyll, which absorbs light energy from sunlight
• structure of chloroplast:

  1. the chloroplast envelope
  2. the grana which are stacks of thylakoids
  3. thylakoids contain the pigment chlorophyll which is where the first stage occurs
  4. the stroma which is where the second stage of photosynthesis occurs
• chloroplasts are adapted by:

  1. the granal membranes provide a large surface area
  2. the fluid in the stroma contain enzymes needed to make sugar
  3. contains both DNA and ribosomes for proteinsynthesis
• inner mitochondrial membrane has folds called cristae
• mitochondria are the site of aerobic respiration
• In the endoplasmic reticulum, the membranes enclose a network of tubules and flattened sacs called cisternae
• smooth ER does not have ribosomes on its outer surface
• rough ER contains ribosomes on its outer surface
• there are two types of ER:

  1. smooth
  2. rough
• RER functions:

  1. provide a large surface area for the synthesis of proteins and glycoproteins
  2. provide a pathway for the transport of materials, especially proteins, throughout the cell
• SER functions:

  1. synthesise, store and transport lipids
  2. synthesise, store and transport carbohydrats
• The Golgi apparatus is made up of stacks of flat membrane-bound sacs called cisternae with small rounded hollow structures called vesicles
• The proteins and lipids produced by the ER are passed through the golgi apparatus in strict sequence
• the golgi apparatus modifies and packages these molecules into vesicles that bud off from it
• the functions of the golgi apparatus:

  1. add carbohydrates to proteins to form glycoproteins
  2. produce secretary enzymes
  3. secrete carbohydrates
  4. transport, modify and store lipids
  5. form lysosomes
• lysosomes are formed when the vesicles produced by the golgi apparatus contain enzymes such as proteases and lipases
• lysosomes contain lysozymes which hydrolyse the cell walls of certain bacteria
• lysosomes isolate enzymes from the rest of the cell before releasing them, either to the outside or into a phagocytic vesicle within the cell
• functions of lysosomes:

  1. hydrolyse materials ingested by phagocytic cells
  2. release enzymes to the outside of the cell (exocytosis)
  3. digest worn out organelles
  4. completely break down cells after they have died (autolysis)
• ribosomes are the site of protein synthesis
• cell walls are made out of microfibrils of the polysaccharide cellulose
• the functions of the cellulose cell wall are:

  1. tot provide mechanical strength
  2. prevent the cell from bursting under osmotic pressure
  3. contribute to the movement of water through the plant
• the cell walls of algae contain either cellulose, or glycoproteins or a mixture of both
• the cell walls of fungi are made up of a mixture of nitrogen-containing polysaccharides
• a fluid-filled sac bounded by a single membrane may be termed a vacuole
• the single membrane around the vacuole is called the tonoplast
• a plant vacuole contains a solution of mineral salts, sugars, amino acids, waste, pigments
• functions of vacuole:

  1. provide a turgid structure
  2. temporary food storage
  3. pigment may attract pollinating insects