L4 eukaryotic cells

• endomembrane system

  nuclear membrane, endoplasmic reticulum, golgi apparatus and lysosomes
• smooth endoplasmic reticulum -> relatively small amount in cells
• functions of smooth endoplasmic reticulum

  • making phospholipids, fats and steroids
  • break down stored glycogen to release glucose (in hepatocytes)
  • detoxify lipid soluble drugs e.g. barbiturates
  • carbohydrate metabolism
• sarcoplasmic reticulum is a type of

  smooth endoplasmic reticulum
• role of sarcoplasmic reticulum

  • store calcium ions from the cytosol
  • involved in muscle contractions
• sarcoplasmic reticulum is found in _ cells

  muscle
• sarcomere is a repetitive section of sarcoplasmic reticulum
• muscle contraction:

  1. action potential triggers SR to release calcium into cytosol
  2. calcium ions bind to tropomyosin and troponin
  3. causes conformational change exposing myosin binding head
  4. myosin interacts with actin and causes muscle contraction through slding filament theory
• myosin is a _ filament

  thick
• actin is a _ filament

  thin
• rough endoplasmic reticulum is the site of _

  protein synthesis
• what are the 4 classes of protein synthesis?

  secreted

  glycosylated

  lysosomal enzymes

  membrane bound proteins
• RER only attach to proteins with specific _

  signal peptide sequence
• signal recognition particle attaches to signal peptide and stops translation in the cytosol
• signal recognition protein (SRP) binds to signal recognition protein _ on the ER which restarts translation


  receptor
• signal peptide passes into the membrane of the ER
• polyribosomes

  a cluster of ribosomes simultaneously translating an mRNA molecule
• glycosylation means

  addition of sugars
• where does glycosylation happen?

  in the rough endoplasmic reticulum and the golgi apparatus
• golgi role:

  modify and sort proteins
• cis face of golgi is for

  receiving side
• trans face of golgi is for

  shipping side
• lysosomes contain

  hydrolytic enzymes
• lysosomes role:

  • autophagy (recycle worn out organelles)
  • phagocytosis
  • autolysis (during apoptosis)
• where does the addition of mannose on the peptide send the protein?

  lysosome
• rough endoplasmic reticulum has _ on its surface

  ribosomes