Cell Structure Flashcards
Outline how a student could prepare a temporary mount of tissue for a light microscope
- Obtain a thin section of tissue
- Place tissue in a drop of water
- Stain tissue on a slide
- Add cover slip using mounted needle at 45 degree angle to avoid trapping air bubbles
Describe how light microscopes work
- Lenses focus rays of light and magnify the view of a thin slice of specimen
- Different structures absorb different amount and wavelengths of light
- Reflected light is transmitted to the observer via the objective lens and eyepiece
Describe how TEM’s work
- Pass a high energy beam of electrons through a thin slice of specimen
- More dense structures appear darker since they absorb more electrons
- Focus image onto florescent screen or photographic plate using magnetic lenses
Describe how a SEM works
- Focus a beam of electrons onto a specimens surface using electromagnetic lenses
- ## Reflected electrons hit a collecting device and are ampilfied to produce an image on a photographic plate
Describe how a laser scanning confocal microscope works
- Focus a laser beam onto a small area of a sample’s surface using objective lenses
- This causes flourescence from the components labelled with a dye
- The specimens emitted light is filtered through a pinhole aperture
- Only light radiated from very close to the focal plane is detected
Why do samples need to be stained for light microscopes?
- Coloured dye binds to the structures
- Facilitates absorption of wavelengths of light to produce image
What is differential staining?
Contrast between heavily and lightly stained areas distinguishes structures
What is the magnification and resolution of a light microscope and SEM ?
Light - x200, 200nm
SEM - x500 000, 0.5nm
Describe the structure of the nucleus
- Surrounded by a nuclear envelope, a semipermeable double membrane
- Nuclear pores allow substances to enter/leave
- Dense nucleolus made up of RNA and proteins assemble ribosomes
Describe the structure and function of the golgi apparatus
- Stack of membrane bound, flattened sacs aligning with rER
- Modifies and packages proteins for export
- Synthesises glycoproteins
Describe the structure and function of ribosomes
- Formed of protein and rRNA
- Have large subunit which joins amino acids
- Small subunit with mRNA binding site
Describe the relationship between the organelles involved in the production and secretion of proteins
- Ribosomes synthesis proteins and are attached to rER
- Golgi apparatus modifies proteins for secretion and is aligned with rER
Describe the function of a lysosome
- Digests contents of phagosome
- Exocytosis/carrying of digestive enzymes
Describe the structure and function of a plant cell wall
- Made of cellulose microfibrils for mechanical support
- Plasmodesmata form part of apoplast pathway to allow molecules to pass between cells
- Middle lamella separates adjacent cell walls
What are bacterial and fungal cell walls made of?
Bacteria - Peptidoglycan
Fungi - Chitin
Describe the structure and function of centrioles
- Spherical group of 9 microtubules arranged in triplets
- Located in centrosomes
- Migrate to opposite poles of a cell during prophase and spindle fibres form between them
Describe the structure and function of the plasma membrane
- Fluid mosaic phospholipid bilayer with extrinsic and intrinsic proteins embedded
- Isolates ctyoplasm from extracellular environment
- Selectively permeable to regulate transport of substances
- Involved in cell signalling/recognition
Explain the role of cholesterol, glycoproteins and glycolipids in the plasma mebrane
Cholesterol - Connects phospholipids and reduces fluidity
Glycoproteins - Cell signalling, cell recognition (antigens) and binding cells together
Glycolipids - Cell signalling and cell recognition
Describe the structure and function of the flagella
- Hollow helical tube made of the protein flagellin
- Rotates to propel organism
Why is the cytoskeleton important?
- Provides mechanical strength
- Aids transport within cells
- Enables cell movement
Describe microfilaments
- Formed from actin
- Responsible for cell movement and cell contraction during cytokineses
Describe microtubules
- Act as tracks for movement of organelles, including vesicles
- Spindle fibres are composed of microtubules
Describe intermediate fibres
- Give mechanical strength to cells and help maintain their integrity
