Cell Structure and Function

• Robert Hooke - published Micrographia, first used the term "Cell"


  1665
• A. van Leeuwenhoek - developed the first microscope able to observe micro-organisms "animalcules"


  1674
• Robert Brown, Botanist at Kew Gardens observed cells in all the plants he studied and noticed a feature common to all cells - the nucleus


  1830
• Theodor Schwann and Mathias Schleiden - brought together plant and animal studies and realised cells are the smallest, self-sustaining unit of all organisms - cell theory was born


  1837
• Many still thought cells arose spontaneously
• Bacterial growth


  No bacterial growth
• Pasteur showed cells must give rise to other cells - spontaneous generation is rubbish!!
• Robert Remak showed cell division for the first time and postulated that multi-cellular organisms arise through the division of cells


  1840s
• Cell Theory


  • The cell is the smallest unit to retain the properties of life
  • All organisms are made up of 1 or more cells
  • New cells arise by the division of existing cells
  • Many basic structures are shared by all cells
  • Functions performed by the cells are fundamental to life
  • All organisms have evolved from a primordial ancestral cell
• Advances in Microscopy
• Electron Microscopy


  • Uses beams of electrons rather than light
  • Focused using magnets
  • x 500,000 possible
  • 0.5 nm resolution
  • Complex sample preparation
• Scanning Electron Microscopy


  Shows the structure of the cell surface
• Transmission Electron Microscopy


  Shows the internal details of a preserved cell
• Light Microscopy


  • Shows the cell and its interior
  • Uses light 400-750 nm
  • x 1000 magnification
  • Resolution ~200 nm
  • Can observe living cells - features can be highlighted by staining
• Uses of Light Microscopes


  • Best for stained or naturally pigmented specimens
  • prepared slides of tissue sections
  • living photosynthetic organisms
  • stained bacteria
  • stained organelles
  • Good for viewing morphology, tissue structure, sizing cells
• Magnification


  1. The eyepiece graticule measures...

  2. 1 eyepiece unit measures...

  3. The stage micrometer is split into 10 µM divisions, by comparing the eye-piece graticule (ocular scale) and stage micrometer you can determine what 1 division of the eyepiece scale measures at each magnification
• Cells at 40x magnification


  • Cell
  • Nucleus
• E. coli


  are about 2 µM in length. In this micrograph they appear 2 mm in length What magnification is this image taken at.
• Prokaryotes


  Single-celled organisms, no membrane bound organelles, e.g. bacteria and archaea
• The Cell Wall - Plants


  • In addition to a cell (plasma) membrane plants have a cell wall made of polysaccarides cellulose linked together by hemicellulose and embedded in pectin
  • Provides shape to the many different cell types needed to form the tissues and organs of a plant
  • Plays an important role in intercellular communication
  • Important in plant-microbe interactions e.g. defense responses against potential pathogens
• The Cell Wall - Bacteria


  • In addition to a cell membrane bacteria have cell walls made of peptidoglycan, the arrangement determines whether the wall retains a gram stain
  • Forms a protective layer and is responsible for the organism's shape and are essential for viability
  • Provide immunological distinction among strains of bacteria
  • Often a target for antibiotic treatments e.g. penicillins block the enzymes that cross-link the sugar in peptidoglycan resulting in the death of the bacterium
• The Cell Wall - Bacteria


  • Gram +ve
  • Gram -ve
• The plasma membrane


  • Maintains the structural integrity of the cell
  • Controls transport of molecules in and out of the cell - permeable to water and small uncharged molecules (e.g. O2 and CO2), impermeable to charged ions (e.g. Ca2+, Na+, Cl-) hydrophillic molecules and macromolecules (e.g. RNA, protein)
  • Recognises and responds to chemical signals
• Cell Transport


  • Passive diffusion
  • Facilitated diffusion
  • Active transport
• Passive Diffusion


  Movement of molecules from areas of high concentration to areas of low concentration, Passive process requires no energy, Hydrophobic, small, uncharged molecules pass easily across the membrane, e.g. water moves in and out of cells by osmosis, Small hydrophilic molecules pass through the membrane, Pores can be opened or closed - known as "gated" channels, Pores can be activated by ligand binding (e.g. ACh), voltage (e.g. nerve cells), light (cGMP) or mechanical triggers (e.g. movement of cilia), Molecules move from areas of high concentration to low concentration (requires no energy)
• Active Transport


  Movement of molecules from areas of low concentration to areas of high concentration, Active process requires energy (ATP), Involves carrier (transporter) proteins in the cell membrane e.g. proton pumps, Involves membrane bound vesicles e.g. Macromolecules are imported by endocytosis
• Cell Communication (Local) - Paracrine signalling


  e.g. Cytokines: Chemokines - attract white blood cells (leukocytes), Interleukins - a secreted protein produced by leukocytes that regulate cell growth, differentiation, and motility and stimulate immune responses such as inflammation
• Cell Communication (Local) - Synaptic signalling


  e.g. Neurotransmittors: Acetylcholine - controls muscle contraction, heart rate, digestion and memory, Serotonin - regulates sleep, mood and eating, Dopamine - regulates movement and experiencing pleasure, Endorphin - moderates pain
• Long-distance communication - Hormonal (endocrine) signalling


  Hormones are molecules produced by glands that are transported by the circulatory system e.g. Proteins (Prolactin, Insulin), Peptides (Vasopressin, Gastrin), Modified amino acids (Adrenalin), Steroids (Estrogen, Progesterone)
• Internal structures of Eukaryotic Cells


  • Nucleus
  • Endoplasmic reticulum (ER)
  • Golgi apparatus
  • Vesicles
  • Mitochondria
  • Chloroplasts
  • Nucleolus
  • Ribosomes
  • Cytoskeleton
  • Centrosome
  • Centrioles
• Cytoplasm


  Semi-fluid (basic) substance held within the boundary of the cell membrane, Made of water, salts and organic molecules, Holds the cytoskeleton and organelles, Cytosol - cytoplasm not within the organelles
• The Nucleus


  • Nuclear membrane
  • Nucleolus
  • Nucleoplasm
  • Chromatin
• The Nucleus - Nuclear membrane


  • A double plasma membrane with many pores to allow transport in/out of the nucleus
• The Nucleus - Nucleolus


  • Dense mass of proteins where the genes for ribosomal RNA are transcribed, and ribosomes are assembled
• The Nucleus - Chromosome


  A single DNA molecule plus associated proteins, this complex is known as Chromatin, DNA is the molecule of inheritance (formed from a chain of -vely charged nucleotides, exact copies are passed on to daughter cells during cell division), DNA holds the genetic code (the instructions for making proteins), DNA transcribed to RNA within the nucleus
• Endoplasmic Reticulum


  • Smooth ER
  • Rough ER
• Smooth Endoplasmic Reticulum


  • Interconnected tubes, No ribosomes, Synthesises lipids, processes sugars and detoxifies drugs and metabolic waste products
• Rough Endoplasmic Reticulum


  • Arranged a series of flattened sacs, Covered in ribosomes, Synthesises proteins
• Ribosomes


  • Prokaryotes
  • Eukaryotes
  • Mitochondria
• Ribosomes


  Protein synthesising machines: holds mRNA molecules in place to allowed tRNAs to translate the code and assemble the protein