2.1 Cell Structure Flashcards
Why do light microscopes use glass lenses to resolve images that are
0.2 um apart
0.2 um is the wavelength of light and therefore restricts resolution of light microscopes
What’s the magnification equation
Magnification = image/ real
What’s the definition of resolution
Minimum distance apart that 2 objects can be distinguished as separate objects in an image
The greater the resolution, the more clear the image will be
How far can an electron microscope distinguish separate objects apart
0.1 nm
2 main types of Electron Microscopes
TEM and SEM
What do electron microscopes use instead of the wavelength of light
A beam of electrons that are focused by electromagnets inside a vacuum environment
Why is a vacuum environment needed
So that air particles don’t deflect electrons out of beam alignment
How does TEM work
Beam of electrons passes through thin section of specimen.
Areas that absorb the electrons appear darker on micrograph that’s produced
How does SEM work
Beam of electrons pass across surface and scatter
Pattern of scattering builds up a 3D image depending on contours of specimen
Limitations of TEM and SEM
- whole system must be in a vacuum so living organisms cannot be observed
- complex staining process which may introduce artefacts in final images
- specimens have to be thin so electrons can pass through
- SEM has resolving power less than TEM but higher than Light
- both are crazy expensive AF
Define cell fractionation
Where different parts and organelles of cells are separated so that they can be studied in detail
What’s the method of cell fractionation
Centrifugation
Describe process of homogenisation
- Cells are blended in homogeniser to create fluid homogenate
- Heaviest organelles are forced into bottom of tube forming a pellet (nuclei)
- Fluid on top of pellet is called supernatant and must be removed leaving sediment of pellet
- Supernatant is transferred to another tube and this time a new heavy pellet is formed (mitochondria)
- Process continues with increasing speeds to produce next heaviest organelles that are sedimented and supernatant is separated
Why is the homogenate placed in a cold, buffered solution of the same water potential as cells
Prevent organelles from bursting under osmotic pressure
To prevent enzymes from breaking down organelles
So pH doesn’t fluctuate
What’s the Nucleus
Double membrane called nuclear envelope containing ~3000 pores to enable molecules entering and leaving
Contains chromatin and nucleolus which is site of ribosome production
Granular jelly (nucleoplasm) makes up the bulk of it
What’s RER
Series of flattened sacs that are enclosed by a membrane with ribosomes on surface
Folds and processes proteins made on ribosomes
What’s SER
System of membrane bound sacs
Produces and processes lipids
What’s Golgi apparatus
Series of fluid filled flattened and curved sacs with vesicles surrounding its edges
Processes and packages proteins and lipids
Also produces lysosomes
What’s Mitochondria
Site of aerobic respiration to produce ATP
Oval shaped, bound by double membrane (envelope)
Inner membrane is folded to form Cristae with Matrix on inside containing enzymes needed for respiration
What’s Cristae
Site of electron transport chains
What’s Matrix
Contains mitochondrial DNA, respiratory enzymes, lipids and proteins
What’s chloroplasts
Site of photosynthesis to convert solar energy into chemical energy
A vesicular plastid with double membrane
- Thylakoids are flattened discs stacked to form grana; contains photosystems with chlorophyll
- Integranal lamellae are tubes attached to thylakoids in adjacent grana
- Stroma is a fluid filled matrix
What’s Lysosomes
Sac surrounded by single membrane embedded H+ pump maintains acidic conditions containing hydrolase enzymes
Glycoproteins coat protects cell interior
Digest contents of phagosome
Exocytosis of digestive enzymes
What’s ribosomes
Formed of proteins and rRNA free in cytoplasm or attached to ER
Site of protein synthesis via translation:
- Large subunit: joins amino acids
- Small subunit: contains mRNA binding site
What’s cisternae
Network of tubules and flattened sacs extends from cell membrane through cytoplasm and connects to nuclear envelope
Also linked to RER and SER
What’s cell wall
In bacteria it’s made up of polysaccharide murein
In plants it’s made up of cellulose microfibrils which allow molecules to pass through in between cells
Middle lamella acts as a boundary between adjacent cell walls
Keeps cell rigid, acts as a physical barrier against pathogens, part of apoplast pathway (plants) to enable easy diffusion of water
What’s cell vacuole
Surrounded by single membrane (tonoplast), contains cell sap (mineral ions, water, enzymes, soluble pigments)
Controls turgor pressure
Absorbs and hydrolyses potentially harmful substances to detoxify cytoplasm
Explain some common cell adaptations
Microvilli increases SA e.g. diffusion
Lots of Mitochondria is suitable for large amounts of ATP to be released for active transport
Walls one cell thick to reduce distance of diffusion pathway
What’s plasmids
Circular piece of DNA carrying non- essential genes
What’s capsule
Protective slimy layer which helps cell to retain moisture and adhere to surfaces
What’s flagellum
A tail like structure which rotates to move the cell
What’s pili
Hair like structure which attaches to other bacterial cells
What’s mesosomes
Artefacts when cells are prepared for electron microscopy
What are viruses
Non living structures which consist of nucleic acid enclosed in a protective protein coat called capsid sometimes covered with a lipid layer (envelope)
What’s the organisation for multicellular organisms
Cells
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Tissues
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Organs
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Organ Systems
