Structure of eukaryotic cells

• Describe the structure of the cell-surface membrane

  • Phospholipid bilayer
  • Hydrophilic phosphate heads - point to/attracted to water
  • Hydrophobic fatty acid tails - point away/repelled from water
  • Protein channels/carriers
• Describe the function of the cell-surface membrane

  • Selectively permeable - enables control of passage of substances in/out of cell
  • Molecules/receptors/antigens on surface - allow cell recognition/signalling e.g. glycoproteins
• Describe the structure of the nucleus

  Nuclear envelope

  • Double membrane
  • Has nuclear pores

  Nucleoplasm

  Nucleolus (Dense region)

  Protein/histone-bound, linear DNA

  • Chromatin = condensed
  • Chromosome = Highly condensed
• Describe the function of the Nucleus

  • Holds/stores genetic information which codes for polypeptides
  • Site of DNA replication
  • Site of transcription (part of protein synthesis), producing mRNA
  • Nucleolus makes ribosomes/rRNA
• Describe the structure of a ribosome

  • Made of ribosomal RNA and protein (Two subunits)
  • Not a membrane-bound organelle
• Describe the function of a ribosome 


  Site of protein synthesis (Translation)
• Describe the function of the rough endoplasmic reticulum

  • Ribosomes on surface synthesise proteins
  • Proteins processed/folded/transported inside rER
  • Proteins packaged into vesicles for transport e.g. to Golgi apparatus
• Describe the function of the smooth endoplasmic reticulum

  • Synthesises and processes lipids
  • E.g. cholesterol and steroid hormones
• Describe the structure of Golgi apparatus and Golgi vesicles

  Golgi apparatus - flattened membrane sacs

  Golgi vesicle - small membrane sac
• Describe the function of the Golgi apparatus

  • Modifies and labels proteins with carbohydrates and phosphates to produce glycoproteins
  • Modifies and labels lipids with carbohydrates and phosphates to make glycolipids
  • Packages proteins and lipids into vesicles
  • Produces lysosomes (a type of Golgi vesicle)
• Describe the function of Golgi vesicles

  • Transports proteins/lipids to their required destination
  • E.g. moves to and fuses with cell-surface membrane
• Describe the structure of lysosomes

  Membrane containing hydrolytic enzymes (Lysozymes)
• Describe the function of lysosomes

  • Releases lysozymes
  • To hydrolyse pathogens or worn out cell components
• Describe the structure of Mitochondria

  • Double membrane
  • Cristae - inner membrane fold
  • Matrix (fluid) - containing small (70s) ribosomes and circular DNA
• Describe the function of Mitochondria

  • Site of aerobic respiration
  • To produce ATP for energy release
  • E.g. for protein synthesis/vesicle movement/active transport
• Describe the structure of chloroplasts in plants and algae

  Double membrane

  Stroma (Fluid) containing:

  • Thylakoid membrane
  • 70s ribosome
  • Circular DNA
  • Starch Granules/lipid droplets

  Lamella - thylakoid linking grana

  Grana - stacks of thylakoids
• Describe the function of chloroplast in plants and algae

  • Absorbs light energy for photosynthesis
  • To produce organic substances e.g. carbohydrates/lipids
  • Produces oxygen and glucose
• In algae what is the cell wall composed of?

  Cellulose
• In fungi what is the cell wall composed of?


  Chitin
• Describe the function of the cell wall in plants, algae and fungi

  • Provides mechanical strength to the cell
  • So prevents cell changing shape or bursting under pressure due to osmosis
• Describe the structure of the vacuole in plants

  • Surrounded by a tonoplast membrane
  • Contains cell sap
• Describe the function of the cell vacuole in plants

  • Maintains turgor pressure in cell (stops plant wilting)
  • Contains cell sap - stores sugars, amino acids, pigments and any waste chemicals
• Describe the structure of the rER and the sER

  Both are a system of folded membranes

  rER = ribosomes on surface

  sER = smooth