2.1.1 cell structure Flashcards
Outline how a student could prepare a temporary mount of tissue for a light microscope
- Obtain thin section of tissue
- Place tissue in a drop of water
- Stain tissue on a slide to make structures visible
- Add a coverslip using a mounted needle at 45° 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 amounts and wavelengths of light
- Reflected light is transmitted to the observer via the objective lens and eyepiece
Describe how a transmission electron microscope works
- Pass a high energy beam of electrons through a thin slice of specimen
- More dense structures appear darker since they absorb more electrons
- Image is focused onto a fluorescent screen or photographic plate using magnetic lenses
Describe how a scanning electron microscope works
- Focus a beam of electrons onto a specimens surface using electromagnetic lenses
- Reflected electrons hit a collection device and are amplified to produce an image on a photographic plate
Define resolution and magnification
Magnification: factor by which the image is larger than the actual specimen
Resolution: smallest separation distance at which 2 separate structures can be distinguished from one another
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
- Differential staining: contrast between heavily and lightly stained areas distinguishes structures
State the magnification and resolution of an optical microscope
Magnification: x200
Resolution: 200nm
State the magnification and resolution of TEM
Magnification: x500,000
Resolution: 0.5nm
State the magnification and resolution of a SEM
Magnification: x500,000
Resolution: 3-10nm
Explain how to use an eyepiece graticule and stage micrometer to measure the size of a structure
- Place micrometer on stage to calibrate eyepiece graticule
- Line up scales on graticule and micrometer. Count how many graticule divisions are in 100um on the micrometer
- Length of 1 eyepiece division = 100um/ number of divisions
- Use calibrated values to calculate actual length of structures
Describe the structure of the nucleus
- Surrounded by a nuclear envelope, a partially permeable double membrane
- Nuclear pores allow substances to enter/exit
Dense nucleolus made of RNA and proteins assemble into ribosomes
Describe the function of the nucleus
- Contains DNA coiled around chromatin into chromosomes
- Contains cellular processes: gene expression determines specialisation and site of mRNA transcription, mitosis, semi conservative replication
Describe the structure and function of the endoplasmic reticulum
- Rough endoplasmic reticulum: many ribosomes attached for protein synthesis and transport
- Smooth endoplasmic reticulum: lipid synthesis
- Cisternae: network of tubules and flattened sacs extends from cell membrane and connects to nuclear envelope
Describe the structure and function of the golgi apparatus
- Planar stack of membrane bound flattened sacs
- Molecules are processed in cisternae
- Vesicles bud off via exocytosis
- 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 and small subunits with mRNA binding site
Describe the relationship between the organelles involved in the production and secretion of proteins
- The ribosomes that synthesise proteins are attached to the rER
- The golgi apparatus, which modifies proteins for secretion, alligns with rER
Describe the structure of a mitochondrion
- Surrounded by double membrane
- Folded inner membrane forms cristae: site of electron transport chain
- Fluid matrix: contains mitochondrial DNA, respiratory enzymes, lipids, proteins
Describe the structure of a chloroplast
- Vesicular plastid with double membrane
Thylakoids: flattened discs stack to form grana. Contains photosystems with chlorophyll - Intergranal lamellae: tubes attach thylakoids in adjacent grana
- Stroma: fluid filled matrix
State the function of mitochondria and chloroplasts
- Mitochondria: site of aerobic respiration to produce ATP
- Chloroplasts: site of photosynthesis to convert solar energy to chemical energy
Describe the structure and function of a lysosome
- Sac surrounded by single membrane
- Embedded H+ pump maintains acidic conditions
- Contains digestive enzymes hydrolase enzymes
- Glycoprotein coat protects cell interior: digests contents of phagosome, exocytosis 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 cells 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 cell during prophase and spindle fibers form between them
Describe the structure and function of the plasma membrane
- Fluid mosaic phospholipid bilayer with extrinsic and intrinsic proteins embedded
- Isolated cytoplasm from extracellular environment
- Selectively permeable to regulate transport of substances
- Involved in cell signalling/ cell recognition
