2.1.1 Structure of eukaryotic cells

• What are the distinguishing features of eukaryotic cells?

  • ● Cytoplasm containing membrane-bound organelles
  • ● So DNA enclosed in a nucleus
• Describe the structure of the cell-surface membrane


  Picture:

  
• 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
• 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 (proteins)
  • ● 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 rER

  • ● Ribosomes on surface synthesise proteins
  • ● Proteins processed / folded / transported inside rER
  • ● Proteins packaged into vesicles for transport eg. to Golgi apparatus
• Describe the function of sER

  ● Synthesises and processes lipids

  ● Eg. cholesterol and steroid hormones
• Describe the function of Golgi apparatus

  ● Modifies protein, eg. adds carbohydrates to produce glycoproteins

  ● Modifies lipids, eg. adds carbohydrates to make glycolipids

  ● Packages proteins / lipids into Golgi vesicles

  ● Produces lysosomes (a type of Golgi vesicle)
• Describe the function of Golgi vesicles


  ● Transports proteins / lipids to their required destination

  ● Eg. moves to and fuses with cell-surface membrane
• Describe the function of lysosomes

  • ● Release hydrolytic enzymes (lysozymes)
  • ● To break down / hydrolyse pathogens or worn-out cell components
• Describe the structure of mitochondria

  • Outer membrane
  • Cristae - inner membrane fold
  • Matrix, containing:
  • Small (70S) ribosomes
  • Circular DNA

  
• Describe the function of mitochondria

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

  • Double membrane
  • Stroma, containing:
  • Thylakoid membrane
  • Small / 70S ribosomes
  • Circular DNA
  •  Starch granules / lipid droplets
  • Lamella - thylakoid linking grana
  • Grana - stacks of thylakoid

  
• Describe the function of chloroplasts in plants and algae

  • ● Absorbs light energy for photosynthesis
  • ● To produce organic substances eg. carbohydrates / lipids
• Describe the structure of the cell wall in plants, algae and fungi

  • ● Composed mainly of cellulose (a polysaccharide) in plants / algae
  • ● Composed of chitin (a nitrogen-containing polysaccharide) in fungi
• Describe the function of the cell wall in plants, algae and fungi

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

  • ● Maintains turgor pressure in cell (stopping plant wilting)
  • ● Contains cell sap → stores sugars, amino acids, pigments and any waste chemicals
• Describe how eukaryotic cells are organised in complex multicellular

  organisms

  In complex multicellular organisms, eukaryotic cells become specialised for specific functions.

  • Tissue - Group of specialised cells with a similar structure working together to perform a specific function, often with the same origin.
  • Organ - Aggregations of tissues performing specific functions.
  • Organ system - Group of organs working together to perform specific functions.