1 - Cells and Cell Structures Flashcards
Resolution
Minimum distance between two objects for them to appear as separate objects
Magnification
The degree to which the size of an image is larger than the image itself
magnification = image size / real size
Optical / Light Microscope
Light travels through different lenses
Max magnification around x1500
No vacuum necessary
Sample can be living
Images are coloured
Low resolution compared to electron microscopes
Specimen has to be thin
Portable
Cheap
Scanning Electron Microscope (SEMs)
Electron gun (electromagnets) used to produce beam of electrons
Electrons bounce off of surface
Deflected electrons detected
Can produce 3D images
Specimens don’t need to be thin
Lower resolving power compared to TEMs so can’t see internal structures
Transmission Electron Microscope (TEMs)
Electron gun (electromagnets) produce beam that passes. through a thin section of the specimen
Denser parts absorb more electrons so appear darker
High resolution
Specimen needs to be really thin
Electron Microscope (TEMs and SEMs)
Shorter wavelengths so higher resolution
Cannot observe live specimens
Do not produce colour images
Artefacts present
Complex staining process
Cell Fractionation
Process by which cells are broken up and their organelles separated
Conditions needed for Cell Fractionation
Cold:
Reduces kinetic energy
Reduces rate of enzyme activity which could lead to the breakdown of organelles
Isotonic:
Prevents water from moving in and out of cells through osmosis which could lead to cells bursting or swelling
Buffered:
Maintains a constant pH so the enzymes don’t denature (prevents damage to enzymes)
Stages of Cell Fractionation
1) Homogenation and Filtration
Cells broken up by a homogeniser which breaks the cell membrane
Homogenate is produced (fluid that contains organelles and cell debris)
Homogenate is filtered using a gauze to remove complete cells and unwanted debris
2) Ultracentrifugation
Filtrate placed in an ultra centrifuge and spun at low speed
Heaviest organelles forced to bottom and form a thin pellet
Fluid at top removed and transferred to another tube
Repeated at higher speeds until each organelle is separated
Order by which Cell Organelles are collected during centrifugation
Nuclei
Chloroplasts
Mitochondria
Lysosomes
Endoplasmic Reticulum
Ribosomes
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Nucleus
Surrounded by double membrane called the nuclear envelope which has nuclear pores on it
Nucleoplasma which contains chromatin (what chromosomes are made of)
Nuceloulus:
Dense, darker part
Produces ribosomes and RNA
Ribosomes
Made of ribosomal RNA and protein
In eukaryotic, 80s and in prokaryotic 70s
Used in protein synthesis to assemble the polypeptide
Rough Endoplasmic Reticulum
Flattened sacs of membrane called cisternae
Contains ribosomes
Protein synthesis / Forming polypeptides
Normally found near nucleus
Smooth Endoplasmic Reticulum
Manufactures lipids and steroids such as certain hormones
Flattened sacs of membrane called cisternae
No ribosomes
Golgi Apparatus
Stacks of membrane bound sheets
Small membrane bound transport sacks called vesicles fuse with it and can get pinched off
Receives proteins from RER and modifies them and then releases them in vesicles for transportation
Lysosomes
Dark spherical organelles
Contain digestive enzymes
Break down old organelles or foreign material
Can fuse with cell membrane and release its enzymes out of the cell
Used in cell self-destruction (apoptosis)
Mitochondria
Capsule shaped made from double membrane filled with a fluid called matrix
Inner membrane folded into cristae to provide a large surface area
Self-replicating
Cell Wall
Freely permeable
Strength and support
Made up of middle lamella, which contains pectin, and the cellulose microfibrils
Plant cells can be linked together by gaps in the cell walls called plasmodesmata
Chloroplast
Double membrane bound capsule organelle
Inner membrane folded into thylakoids which are stacked up to form a granum
-Provides large surface area
Granna linked by lamella and surrounded by liquid called stroma
Vacuole
Temporary, small in animals but large, permanent in plants
Filled with cell sap which is dissolved substances in water
Used to maintain cell shape and for storage
Prokaryotic Cells
Any organism whose DNA is suspended freely in the cytoplasm
Lack membrane-bound organelles
Cell wall is made of the glycoprotein murein
Capsule (Prokaryotic)
Only present in some cells
Protects bacterium from drying out in certain condition and by being discovered by the immune system
Mesosome (Prokaryotic)
Same function as mitochondria
Plasmids (Prokaryotic)
Small circular loops of DNA
Can be transferred between bacteria
