cell structure

• Cell Fractionation is the process in which different parts and organelles of a cell are separated so that they can be studied in detail.
• Homogenisation is the first stage of Cell Fractionation, which involves the breaking up of a cell to release the organelles into a solution, known as a homogenate.
• The homogenate must be kept ice-cold to slow down the enzymes and prevent destructive enzymes from damaging organelles.
• The ph of the homogenate must be buffered to keep the ph constant, as changes in ph can damage organelles.
• The homogenate must be isotonic, meaning it should have the same concentration of water and chemicals, to prevent damage to organelles through osmosis.
• Filtration is the second stage of Cell Fractionation, where the homogenised cell solution is filtered to separate any large cell debris from the organelles.
• Ultracentrifugation is the final stage of Cell Fractionation, where the solution containing a mixture of organelles is put in a centrifuge and spun to separate the different organelles.
• Organelles have different densities, with the heaviest organelle, the nuclei, being forced to the bottom of the tube where a pallet is formed.
• The rest of the organelles stay suspended in the fluid above the sediment, this is the supernatant.
• The less dense the organelle, the faster the centrifuge must spin in order to separate it from the rest of the organelles.
• Cell surface membrane is a phospholipid bilayer.
• The surface of the membrane can interact with water but water-soluble molecules cannot diffuse through the hydrophobic core.
• The cell surface membrane is described as a fluid mosaic model as it has many protein channels embedded in it.
• The cell surface membrane acts as a physical barrier which regulates the movement of substances into and out of a cell.
• The nucleus is enclosed within a double membrane known as the nuclear envelope.
• The nuclear envelope contains many pores that allow substances such as RNA to enter and exit.
• Chromatins are substances containing DNA and proteins whereas the nucleolus is a structure consisting of DNA, RNA and proteins.
• The nucleus controls the functions of the cell by controlling DNA transcription.
• The nucleus also controls gene expression and protein synthesis.
• Ribosomes are produced in the nucleus.
• The rough endoplasmic reticulum is a network of channel-like structures filled with fluid, linked to the nuclear membrane by small tubules.
• The surface of the rough endoplasmic reticulum is covered with ribosomes.
• The rough endoplasmic reticulum is responsible for processing and producing 3D structures of protein.
• The cytoplasm contains organelles that carry out various functions within the cell, such as mitochondria (energy production), ribosomes (protein synthesis), endoplasmic reticulum (synthesizing proteins and lipids), Golgi apparatus (packaging and sorting molecules), lysosomes (digestion of waste materials).