Cell Structure & Organisation

• 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
• Eukaryotic cells have a more complex ultrastructure than prokaryotic cells
• Cytoplasm of eukaryotic cells


  Divided up into membrane-bound compartments called organelles
• Key structures shared by animal and plant cells


  • Membrane-bound organelles, including a nucleus
  • Larger ribosomes known as 80S ribosomes
• Key differences between animal and plant cells


  • Animal cells contain centrioles and some have microvilli while plant cells do not
  • Plant cells have a cellulose cell wall, large permanent vacuoles, and chloroplasts while animal cells do not

  
• Cell surface membrane


  Controls the exchange of materials between the internal cell environment and the external environment
• Cell membrane


  Partially permeable, formed from a phospholipid bilayer spanning a diameter of around 10 nm
• Cell surface membrane


  Also referred to as the plasma membrane
• Nucleus


  Relatively large and separated from the cytoplasm by a double membrane called the nuclear envelope, which has many pores
• Nuclear pores


  Important channels for allowing mRNA and ribosomes to travel out of the nucleus, as well as allowing enzymes and signalling molecules to travel in
• Chromatin


  The material from which chromosomes are made
• Nucleolus


  Darkly stained regions of the nucleus where ribosome production occurs
• Mitochondria


  The site of aerobic respiration within eukaryotic cells, surrounded by a double-membrane with the inner membrane folded to form structures called cristae
• Mitochondrial DNA


  Small circular pieces of DNA found in the matrix of mitochondria, needed for replication of mitochondria before cell division
• Ribosomes


  Complex of ribosomal RNA (rRNA) and proteins, the site of translation
• 80S ribosomes


  Found in eukaryotic cells
• 70S ribosomes


  Found in prokaryotes, mitochondria, and chloroplasts
• Rough Endoplasmic Reticulum (RER)


  Formed from folds of membrane continuous with the nuclear envelope, with ribosomes on its surface to process proteins
• Smooth Endoplasmic Reticulum (SER)


  Formed from folds of membrane, involved in the production, processing and storage of lipids, carbohydrates and steroids, without ribosomes on its surface
• Golgi apparatus


  Consists of flattened sacs of membrane, modifies proteins and lipids before packaging them into Golgi vesicles for transport
• Lysosomes


  Specialist forms of vesicle which contain hydrolytic enzymes to break down waste materials
• Centrioles


  Made of hollow fibres known as microtubules, involved with the process of nuclear division in animal cells
• Protein synthesis and secretion in cells


  1. Nucleus - transcription of DNA code

  2. Ribosomes - translation to produce proteins

  3. Rough endoplasmic reticulum - folding and processing of proteins

  4. Golgi apparatus - modification and packaging of proteins into vesicles

  5. Cell surface membrane - secretion of proteins
• Prokaryotic cells are much smaller than eukaryotic cells
• Protein transport from RER to Golgi apparatus

  1. Proteins from the RER are transported to the Golgi apparatus in vesicles

  2. Vesicles fuse with the Golgi apparatus, releasing the proteins into the Golgi
• Protein modification in the Golgi apparatus

  The Golgi apparatus modifies the proteins, preparing them for secretion
• Destinations of proteins that go through the Golgi apparatus


  • Exported, e.g. hormones such as insulin
  • Put into lysosomes, e.g. hydrolytic enzymes
  • Delivered to other membrane-bound organelles
• Protein transport from Golgi apparatus

  The modified proteins then leave the Golgi apparatus in vesicles
• RER and Golgi apparatus


  Involved with producing, packaging and transporting proteins in a cell
• 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
• Differences between prokaryotic and eukaryotic cells


  • Presence/absence of membrane-bound organelles
  • Size of ribosomes
  • Structure of genetic material
  • Presence/absence of cell wall
• Cell theory states that cells are the basic functional unit of all living organisms
• Specialised cells


  Cells that are specialised for specific functions
• Tissue


  A group of cells that work together to perform a particular function
• Organ


  A group of tissues working together to perform a particular function
• Organ system


  A group of organs working together to perform a particular function