Cells

• Cell-surface membrane

  Phospholipid bilayer with embedded proteins etc.
• Cell-surface membrane

  • Selectively permeable – enables control of passage of substances in and out of cell
  • Barrier between internal and external environment of cell
• Nucleus

  Nuclear envelope, nuclear pores, nucleolus, DNA / chromatin

  
• Nucleus

  • Controls the cells activity though transcription on mRNA
  • Nuclear pores allow substances e.g. mRNA to move between the nucleus and cytoplasm
  • Nucleolus makes ribosomes which are made up of proteins and ribosomal RNA
• Mitochondria

  Double membrane – inner membrane folded to form cristae. Matrix containing small 70S ribosomes, small circular DNA and enzymes involved in aerobic respiration (glycolysis).

  
• Mitochondria

  • Site of aerobic respiration producing ATP for energy release
• Golgi apparatus

  3 or more fluid filled membrane bound sacs with vesicles at edge
• Golgi apparatus


  • Receives protein from rough endoplasmic reticulum
  • Modifies/processes protein e.g. add carbohydrates/sugars
  • Packages into vesicles e.g. for transport to cell surface membrane for exocytosis
  • Also makes lysosomes
• Lysosomes

  Type of Golgi vesicle containing lysozymes – hydrolytic enzymes
• Lysosomes

  • Release of lysozymes to break down / hydrolyse pathogens or worn out cell components
• Ribosomes

  Float free in cytoplasm or bound to rER. Not membrane bound. Made from 1 large and 1 small subunit.

  
• Ribosomes

  • Site of protein synthesis, specifically, translation
• Rough endoplasmic reticulum

  Ribosomes bound by a system of membranes

  
• Rough endoplasmic reticulum

  • Folds polypeptides to secondary / tertiary structure
  • Packages to vesicles, transport to the Golgi apparatus etc.
• Smooth endoplasmic reticulum


  Similar to rER but without ribosomes – system of membranes
• Smooth endoplasmic reticulum


  • Synthesises and processes lipids
• Chloroplasts

  Thylakoid membranes are stacked up in some parts to form grana, which are linked by lamellae. These sit in the stroma (fluid) and are surrounded by a double membrane. Also contains starch granules and circular DNA.
• Chloroplasts

  • (Chlorophyll) absorbs light for photosynthesis to produce organic substances

  
• Cell wall

  Made mainly of cellulose in plants and algae, and of chitin in fungi
• Cell wall

  • Rigid structure surrounding cells in plants, algae and fungi. Prevents the cell changing shape and bursting (lysis)
• Cell vacuole

  Contains cell sap – a weak solution of sugars and salts. Surrounding membrane is called the tonoplast.
• Cell vacuole


  • Maintains pressure in the cell (stop wilting)
  • Stores/isolates unwanted chemicals in the cell
• Organisation of specialised cells in complex multicellular organisms

  • Specialised cell
  • Tissue
  • Organ
  • Organ system

  
• Specialised cell

  The most basic structural/functional subunit in all living organisms; specialised for a particular function

  
• Tissue

  Group of organised specialised cells; joined and working together to perform a particular function; often with the same origin
• Epithelial cells in the small intestine

  • Specialised for efficient absorption. Villi and microvilli increase surface area. Lots of mitochondria to provide energy e.g. for active transport
• Prokaryotic cell


  Cytoplasm contains no membrane bound organelles e.g. mitochondria

  
• How prokaryotic cells differ from eukaryotic cells

  • Prokaryotic cell has no nucleus / contains free floating DNA
  • Prokaryotic DNA is circular and isn't associated with proteins
  • Prokaryotic cell wall contains murein and peptidoglycan
  • Prokaryotic cells have smaller 70s ribosomes
  • Prokaryotic cells may have one or more plasmid, a capsule, and/or one or more flagella

  
• Viruses

  • Acellular → not made of or able to be divided into cells
  • Non-living → unable to exist/reproduce without a host cell
• Three types of microscopes

  • Optical microscope
  • Scanning electron microscope
  • Transmission electron microscope
• Optical microscope

  • Use light to form a 2D image
  • Visible light longer wavelength so lower resolution 200nm
  • Low magnification x1500
• Scanning electron microscope

  • Use electrons to form a 2D image
  • Beams of electrons scan surface, knocking off electrons from the specimen, which are gathered in a cathode ray tube to form an image
  • Electrons shorter wavelength (so higher resolution 0.2nm)
  • High magnification x1500000

  
• Transmission electron microscope

  • Use electrons to form a 3D image
  • Electromagnets focus beam of electrons onto specimen, transmitted, more dense = more absorbed = darker appearance
  • Electrons shorter wavelength (so higher resolution 0.2nm)
  • High magnification x1500000
• Magnification

  How much bigger the image of a sample is compared to the real size, measured by. I (size of image) = A(actual size)M (magnification)
• Resolution

  How well distinguished an image is between 2 points; shows amount of detail; limited by wavelength of radiation used e.g. light
• Measuring the size of an object viewed with an optical microscope

  1. Line up eyepiece graticule with stage micrometer

  2. Use stage micrometer to calculate the size of divisions on eyepiece graticule at a particular magnification

  3. Take the micrometer away and use the graticule to measure how many divisions make up the object

  4. Calculate the size of the object by multiplying the number of divisions by the size of division

  5. Recalibrate eyepiece graticule at different magnifications

  
• Preparing a 'temporary mount' of a specimen on a slide

  1. Use tweezers to place a thin section of specimen e.g. tissue on a water drop on a microscope slide

  2. Add a drop of a stain e.g. iodine in potassium iodide solution used to stain starch grains in plant cells

  3. Add a cover slip by carefully tilting and lowering it, trying not to get any air bubbles
• Principles of cell fractionation and ultracentrifugation as used to separate cell components

  1. Homogenise tissue using a blender

  2. Place in a cold, isotonic, buffered solution

  3. Filter homogenate

  4. Ultracentrifugation
• Cell fractionation and ultracentrifugation


  • Disrupts cell membrane / break open cell
  • Release contents / organelles
  • Cold reduces enzyme activity so organelles aren't broken down
  • Isotonic so water doesn't move in/out of organelles by osmosis so they don't burst / shrivel
  • Buffered keeps pH constant so enzymes don't denature
  • Remove large, unwanted debris e.g. whole cells, connective tissue
  • Centrifuge homogenate in a tube at a low speed
  • Remove pellet of heaviest organelle and spin supernatant at a higher speed
  • Repeated at higher and higher speeds until organelles separated out, each time pellet is made of lighter organelles
  • Separated in order of mass/density: nuclei → chloroplasts → mitochondria → lysosomes → endoplasmic reticulum → ribosomes
• Mitosis

  Parent cell divides = two genetically identical daughter cells, containing identical/exact copies of DNA of the parent cell.