LE1

• Pipette


  A lab device used to measure out or dispense small amounts of liquid in volumes of milliliters (mL) or microliters (µL)
• Pipette


  French word: "small pipe"
• Types of pipettes

  • Glass (borosicilate)
  • Plastic (polyethylene terephthalate)
  • Electronic (microprocessors)
• Most commonly used to measure volumes under 1 mL
• The smallest volume measured with an electronic pipette is 0.1 µL
• Air displacement method


  Telescoping movement of the spring enables the piston to suction and discharge liquids
• Positive displacement method


  1. Direct contact with the liquid is made by a disposable piston that moves inside the tip

  2. In response to the piston's push, some air is let out, the liquid is drawn in by atmospheric pressure, and the air is subsequently forced out to release the liquid
• Parts of a pipette

  • Plunger
  • Tip ejector button
  • Volume adjustment knob
  • Volume window or volumeter
  • Shaft
  • Tip cone
  • Pipette tip
• Pasteur pipettes


  • Also known as eye droppers or simply droppers
  • Conventionally made from glass, although plastic Pasteur pipettes have superseded them
  • Specifically intended to mediate the transfer of small amounts of liquids
  • Joined at the upper end by a plastic or rubber bulb and taper down to a small orifice at the bottom end
• Volumetric pipettes


  • Also known as bulby or belly pipette
  • Commonly used in analytical chemistry in making laboratory solutions from stock and preparing solutions for titration
  • Its bulb is sizable, and its part is long and thin
  • Can be used for quick measurements
• Graduated pipettes


  • Have indicated volume increments alongside the tube
  • Looks like a graduated cylinder because with volume increments on the side
  • Comes in various shapes and are frequently employed for straightforward solution transfers
  • Frequently have a tapered tip and are constructed of glass or strong plastic
• Types of graduated pipettes

  • Type 1: partially deliverable solutions
  • Type 2: 0 at the bottom and the nominal value at the top
  • Type 3: exclusively supply the solution at the nominal value
• Serological pipettes


  • Utilized in the laboratory for gentle mixing of cell suspensions, reagents, and chemical solutions, creating gradients in reagent layering, transferring liquid (1ml to 50ml), and volumetric measurements
  • Make it possible for cells to spread equitably throughout a solution, which is essential for cell culture
• Mohr's pipettes


  • The scale is divided into units of one and one-tenth of a milliliter
  • Less precise than a volumetric pipette due to its wide neck
  • Used when taking a large number of solutions where precision is not a high priority
  • Can release liquid gradually and are filled similarly to volumetric ones
• Transfer pipettes


  • Disposable transfer pipettes, one of the graduated pipettes that serve as a great alternative to Pasteur pipettes
  • Employed in blood banking, urinalysis, wet chemistry, microbiology, hematology, and serology
  • The low affinity of the unbreakable low-density polyethylene plastic surface reduces the loss of cells and desired proteins due to binding as they are inert to biological fluids and acids
• Vacuum-assisted pipettes


  • Both graded and volumetric vacuum-assisted pipettes are available
  • Volumetric vacuum-assisted pipettes only measure a single volume and hence only have one graduation mark
  • Graduated vacuum-assisted pipettes use multiple graduation marks
  • Polystyrene, glass, or borosilicate are used to create vacuum-assisted pipettes
  • They lack pistons but need a suction device
• Repeater pipette


  • Perfect for dispensing the same quantities repeatedly into several receptacles without pausing in between each dispensing process, enhancing speed and efficiency
  • Lightweight and only require one hand to operate, enabling a single operator to work at a throughout capacity
• Pipette types


  • Single-channel pipette
  • Multi-channel pipette
• Pipette volume


  • Fixed-volume
  • Adjustable-volume
• Operating procedure for pipette

  1. Take a tip out of the tip box by loading it into the pipette

  2. Using the volume adjustment spinning dial, adjust the volume to be transferred

  3. While maintaining a vertical grip on the pipette, press the plunger to the first stop

  4. Place the tip inside the liquid component being sampled

  5. With the tip still submerged, slowly release the plunger to draw up the liquid

  6. Place the pipette's tip inside the tube or container where the liquid is collected

  7. Completely depress the plunger until it stops at the second stop point dispense the liquid into the appropriate tube

  8. Press the ejector button to remove the used tip and place it in the garbage can
• Common pitfalls with pipettes

  • Don't use a pipette without a tip attached
  • Don't use a pipette past its volume limits
  • Don't jam the pipette tip into the pipette
• Applications of pipettes


  • Facilitates the even distribution of cells in cell seeding and avoids foaming and bubble formation
  • Allows easy media exchange of T-flask cell cultures and maintains sterility of the cultures and prevents contamination
  • 96 well microplates, frequently used in microplate applications like ELISA, PCR, or cell culture, are compatible with multichannel pipettes of 8 or 12-channel variants
  • To aliquot, a reagent into several doses--a process known as multi dispensing--electronic pipettes are employed
  • Serological pipettes are employed in conventional laboratory for cell and tissue culture
• Advantages of pipettes


  • Comfortable to use and are more user-friendly
  • Safer to handle hazardous chemicals as compared to measuring cylinders
  • Volumetric pipettes are extremely accurate and give precise measurements while delivering solutions
  • Electronic pipettes increase productivity in the lab by saving time and reducing the likelihood of human error
  • Multichannel pipettes are ideal for high accuracy, efficiency, and reproducibility of high throughput experiments
  • Can be used with various liquids, including foamy liquids, high viscosity, pressure liquids, and liquids with high viscosity
• Limitations of pipettes


  • Volumetric pipettes are more costly, and their measurements are fixed and specific to the individual volumetric pipette
  • Graduated pipettes are not precise when delivering and measuring liquid and bear a wider margin of human-use error
• DNA replication: first step in central dogma
• DNA


  • Deoxyribonucleic acid
  • Made up of nucleic acids or nucleotides (building blocks of DNA or RNA)
  • If you cut a specific segment of DNA, you call it a gene
  • DNA is closely packed (called chromosome)
  • Can't be seen under a light microscope, only the cell, nucleus, and chromosome
• Chromosome


  Found in the nucleus of a cell
• Nucleotides


  • Adenine
  • Cytosine
  • Thymine
  • Guanine
• Characteristics of genetic material

  • Replication
  • Storage of information
  • Expression of information
  • Variation by mutation
• Central dogma


  1. DNA can be replicated through DNA replication

  2. DNA can undergo transcription to become RNA (messenger RNA, ribosomal RNA, or transfer RNA)

  3. RNA goes to the ribosome (organ of the cell which produces many proteins) for translation to produce proteins
• Replication and transcription happen in the nucleus. Translation happens in the ER or cytosol
• Griffith experiment


  • Introduced the phenomenon called "transformation"
  • Virulence: capability of the bacteria to cause death or serious illness
  • Heat-killed virulent bacteria injected into the mouse caused the avirulent bacteria to become virulent, indicating that the genetic material from the dead virulent bacteria was transferred to the avirulent bacteria
• Ribosome


  Organ of the cell which produces many proteins
• Translation


  Process to produce proteins
• Replication and transcription happen in the nucleus. Translation happens in the ER or cytosol.
• Transformation


  Phenomenon introduced by Frederick Griffith's experiment on Diplococcus pneumoniae
• Virulence


  Capability of the bacteria to cause death or serious illness
• Griffith's experiment


  1. Injected virulent bacterium (living IIIS) on mice, expecting it to die

  2. Injected avirulent (no capability to cause harm) bacteria, expecting it to live. Living IIR

  3. Heat-killed IIIS injected into the mouse. The mouse lived

  4. Living IIR and Heat-killed IIIS: the mouse died because the heat-killed IIIS have flowing genetic material which the avirulent bacteria collected and therefore making it a virulent bacterium
• Transformation principle


  The DNA of the III-S strain bacteria survived the heating process and was taken up by the II-R strain bacteria, equipping it with the genes that form the smooth protective polysaccharide capsule
• DNA


  A nucleic acid