Unit 2 Biology - 3

• Common features of cells of all living organisms

  • Cell surface membrane
  • Cytoplasm
  • DNA
  • Ribosomes
• Prokaryotic cells


  Have no internal membranes and smaller ribosomes
• Eukaryotic cells


  Have several internal membrane-bound organelles and larger ribosomes
• Cell ultrastructure


  The internal structures of the cell
• Multicellular cell organisation


  Cells can become specialised for specific functions and group together to form tissues, organs, and organ systems
• Levels of organisation


  • Cells
  • Tissues
  • Organs
  • Organ systems
• Examples of specialised cells and their associated tissues, organs and organ systems

  • Epithelial cells in small intestine - epithelial tissue - digestive system
  • Red blood cells - blood tissue - circulatory system
  • Xylem cells in plants - vascular tissue - transport system
• Eukaryotic cells


  Have a more complex ultrastructure than prokaryotic cells, are larger, and have membrane-bound organelles
• Animal cells


  Contain centrioles and some have microvilli, but do not have a cellulose cell wall, large permanent vacuoles, or chloroplasts
• Plant cells


  Have a cellulose cell wall, large permanent vacuoles, and chloroplasts, but do not contain centrioles
• Cell surface membrane


  Controls the exchange of materials between the internal cell environment and the external environment, is partially permeable
• Nucleus


  Separated from the cytoplasm by a double membrane called the nuclear envelope, contains chromatin and nucleoli
• Mitochondria


  The site of aerobic respiration, surrounded by a double membrane with an inner membrane folded to form cristae, contain enzymes, DNA, and ribosomes
• Ribosomes


  Complexes of rRNA and proteins, the site of translation, 80S ribosomes in eukaryotes and 70S ribosomes in prokaryotes, mitochondria, and chloroplasts
• Rough endoplasmic reticulum (RER)


  Formed from folds of membrane continuous with the nuclear envelope, covered in ribosomes, processes proteins made on the ribosomes
• Smooth endoplasmic reticulum (SER)

  Formed from folds of membrane, involved in the production, processing and storage of lipids, carbohydrates and steroids, does not have ribosomes on its surface
• Golgi apparatus


  Consists of flattened sacs of membrane, modifies proteins and lipids before packaging them into Golgi vesicles which transport them to their required destination
• Lysosomes


  Specialist vesicles containing hydrolytic enzymes, break down waste materials such as worn-out organelles
• Centrioles


  Made of hollow fibres known as microtubules, organise the spindle fibres during cell division, not found in plants and fungi
• Lysosomes


  Contain digestive enzymes
• Centrioles


  Made of hollow fibres known as microtubules
• Microtubules


  • Filaments of protein that can be used to move substances around inside a cell, as well as to support the shape of a cell from the inside
• Formation of centrosome


  Two centrioles at right angles to each other form a centrosome which organises the spindle fibres during cell division
• Centrioles are not found in plants and fungi
• Centrioles


  Structures formed from microtubules; they are involved with the process of nuclear division in animal cells
• Organelles involved in protein synthesis

  • Nucleus
  • Ribosomes
  • Rough endoplasmic reticulum (RER)
  • Golgi apparatus
  • Cell surface membrane
• Nucleus


  Transcription of the DNA code occurs here
• Ribosomes


  Free ribosomes and those on the RER produce proteins in the process of translation
• Rough endoplasmic reticulum (RER)


  • Ribosomes on the RER produce proteins that can be secreted out of the cell or become attached to the cell surface membrane
  • Proteins that have been passed into the lumen of the rough endoplasmic reticulum are folded and processed here
• Golgi apparatus


  • Processed proteins from the RER are transported to the Golgi apparatus in vesicles which fuse with the Golgi apparatus, releasing the proteins into the Golgi
  • The Golgi apparatus modifies the proteins, preparing them for secretion
  • Proteins that go through the Golgi apparatus are usually exported, e.g. extracellular enzymes, put into lysosomes, e.g. hydrolytic enzymes, or delivered to other membrane-bound organelles
• The RER and Golgi apparatus are involved with producing, packaging and transporting proteins in a cell. This process can be used to produce and export extracellular enzymes.
• Prokaryotic cells


  • Lack membrane-bound organelles
  • Have ribosomes that are smaller (70 S) than those found in eukaryotic cells (80 S)
  • Have a single circular bacterial chromosome that is free in the cytoplasm and is not associated with proteins
  • Have a cell wall that contains the glycoprotein murein
• Additional prokaryotic structures


  • Loops of DNA known as plasmids
  • Capsules
  • Flagella (singular flagellum)
  • Pili (singular pilus)
  • Cell membrane that contains folds known as mesosomes
• Bacteria are prokaryotic cells
• Differences between prokaryotic and eukaryotic cells

  • Presence/absence of membrane-bound organelles
  • Size of ribosomes
  • Structure of DNA
  • Presence/absence of cell wall
• Not all of the structures mentioned are present in all prokaryotic cells
• Plasmids


  Loops of DNA found in prokaryotic cells
• Capsule


  Structure found in some prokaryotic cells
• Flagella


  Structure found in some prokaryotic cells
• Pili


  Structure found in some prokaryotic cells