Cell Structure Flashcards
Outline how a student could prepare a temporary mount of tissue for a light microscope
- Obtain thin section of tissue e.g. using ultra tome or by maceration
- Place plant tissue in a drop of water
- Stain tissue on a slide to make structures visible
- Add coverslip using 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 TEM works
- 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 fluorescent 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 amplified to produce an image on a photographic plate
Describe how a laser scanning confocal microscope works
- Focus a laser beam onto a small area on a samples surface
- Fluorophores in the sample emit photons
- Photomultiplier tube amplifies the signal onto a detector. An image is produced pixel by pixel in the correct order
How should the field of view in microscopy be recorded
Draw a diagram with a sharp pencil. Do not use sketchy lines or shading
Include a scale bar
Annotate visible structures
State an equation to calculate the actual size of a structure from microscopy
Actual size = Image size / magnification
Define magnification and resolution
Magnification: Factor by which the image is larger than the actual specimen
Resolution: Smallest separation distance at which two 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 a compound light microscope
Magnification - x2000
Resolution - 200 nm
State the magnification and resolution of a TEM
Magnification - x500000
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 graticules 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 semipermeable double membrane
- Nuclear pores allow substances to enter / exit
- Dense nucleolus made of RNA and proteins assemble ribosomes
Describe the function of the nucleus
- Contains DNA coiled around chromatin into chromosomes
- Controls cellular processes: gene expression determines specialisation & site of mRNA transcription, mitosis, semi conservative
Describe the structure and function of the ER
Cisternae: network of tubules and flattened sacs extends from cell membranes and connects to nuclear envelope:
- Rough ER: many ribosomes attached for protein synthesis & transport
- Smooth ER: Lipid synthesis
Describe the structure and function of the Golgi apparatus
Planar stack of membrane-bound, flattened sacs, cis face aligns with rER. Molecules are processed in cisternae. Vesicles bud off trans face via exocytosis
- Modifies & 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 subunit with mRNA binding site
Describe the relationship between the organelles involved in the production and secretion of proteins
The ribosomes that synthesis proteins are attached to the rER. The Golgi apparatus, which modifies proteins for secretion, aligns with the 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 stacks to form grana which contain photosystems with chlorophyll
Intergranal lamallae: 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 hydrolase enzymes
Glycoprotein coat protects cell interior:
Digests contents of phagsome
Exocytosis of digestive enzymes
Describe the structure and function of a plant cell wall
- Made of cellulose microfibrils for mechanical support
- Plasmodesmata from part of apoplast pathway to allow molecules to pass between cells
- Middle lamella separates adjacent cell wells
What are bacterial and fungal walls made of?
Bacteria : peptidoglycan
Fungi : Chitin
Describe the structure and function of the centrioles
-Spherical group of 9 microtubules arranged in triples
- Located in centrosomes
- Migrate to opposite poles of cell during prophase & spindle fibres from between them
Describe the structure and function of the cell-surface plasma membrane
‘Fluid mosaic’ phospholipid bilayer with extrinsic and intrinsic proteins embedded
- Isolates cytoplasm from extracellular environment
- Selectively permeable to regulate transport of substances
- Involved in cell signalling / cell recognition
Explain the role of cholestrol, glycoproteins and glycolipids in the cell surface membrane
Cholesterol: Steroid molecule connects phospholipids & reduces fluidity
Glycoproteins: Cell signalling, cell recognition (antigens) & 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 (usually unicellular) organism
Describe the structure and function of cilia
Hairlike protrusions on eukaryotic cells
Move back and forth rhythmically to sweep foreign substances e.g. dust or pathogens away / to enable the to move
Why is the cytoskeleton important
Provides mechanical strength
Aids transport within cells
Enables cell movement
Compare Eukaryotic and prokaryotic cells
Both have:
Cell membrane
Cytoplasm
Ribosomes
Contrast eukaryotic and prokaryotic cells
Prokaryotic :
Small cells and always unicellular
No membrane bound organelles and no nucleus
Circular DNA not associated with proteins
Small ribosomes (70S)
Binary Fission - always asexual reproduction
Made of murein (also known as peptidoglycan
Capsule, sometimes plasmids 7 cytoskeleton
Eukaryotic :
Larger cells and often multicellular
Always have organelles and nucleus
Linear chromosomes associated with histones
Larger ribosomes (80S)
Mitosis and meiosis - sexual and/or asexual
Absent in animal cells, cellulose cell wall (plants) / chitin (Fungus)
No capsule, No plasmids, always cytoskeleton
