Cell structure

• Magnification means how much an image is enlarged.
• Resolution means the detail seen on an image.
• Transmission electron microscope (TEM) uses a beam of high-energy electrons that pass through thin sections of cells or tissues to form an image.
• Electron microscopes use electrons instead of light waves to produce images with higher magnifications and resolutions compared to light microscopes.
• The maximum magnification of a light microscope is 1500 and resolution is 200nm.
• The maximum magnification of a TEM is 1000,000 and resolution is 0.2nm.
• The maximum magnification of an SEM is 500,000 and resolution is 2nm.
• Cellular staining is used to visualise cells and their components under a microscope.
• Staining can highlight metabolic processes and differentiate between living and dead cells.
• Permeabilization involves the treatment of cells with a mild surfactant, which dissolves cell membranes in order to allow larger dye molecules to enter the cell.
• Fixation serves to preserve cells through the preparation of process. This involves adding a chemical fixative which creates chemical bonds between proteins to increase their rigidity.
• Mounting involves takin samples to a glass microscope slide for observation and analysis.
• Staining involves immersing the sample in a dye solution and then rinsing and observing the sample. Methylene blue and eosin require a mordant to react with the stain to form a precipitate. This will remain in the sample when the dye is washed away.
• At 4x magnification, 1 eye piece unit is 25 micro meters.
• At 10x magnification, 1 eye piece unit is 10 micro meters.
• At 40x magnification, 1 eye piece unit is 3.3 micro meters.
• Eukaryotic cells are complex, nucleated cells, containing internal organelles- specialised compartments that often contain their own DNA.
• The nucleus is a membrane bound organelle containing genetic material. It contains the chromatin and nucleolus (contains ribosomes). It manages cell's genetic material, controls cell growth and division, and produces proteins.
• The endoplasmic reticulum is a network of membranes that extends in all cytoplasm. It is attached to the nuclear envelope. It modifies proteins and synthesises lipids. The SEM metabolises glycogen and processes lipids whilst the RER is covered in ribosomes and folds and packages proteins.
• Golgi apparatus gathers simple molecules and combines them to make more complex molecules (glycoproteins). It makes lysosomes and sorts modifies proteins and lipids from the ER.
• Lysosome breaks down waste materials using enzymes. They digest food particles and remove worn out or damaged parts of the cell.
• Mitochondrion produce energy through cellular respiration. They also store calcium which maintains homeostasis of levels in cell. They also regulate the cell's metabolism and play roles in apoptosis and cell signalling. They have a double membrane that folds in cristae which contain matrix containing enzymes for respiration.
• Ribosome is where protein synthesis occurs. They are made up of rRNA and proteins. Free floating ones are found in cytosol and those attached to rough ER are called bound ribosomes.
• Centrioles are cylindrical structures composed of microtubules. They form part of centrosome which helps organise spindle fibres during mitosis. They are involved in formation of cilia and flagella.
• The cell surface membrane is made up of phospholipids, lipids and proteins. It is selectively permeable and controls the passage of substances. It also has receptor molecules on it allowing response to chemicals as hormonals.
• Nuclear envelope surrounds nucleus and consists of two layers of phospholipid bilayer. Nuclear pores allow movement between cytoplasm and nucleoplasm. The nuclear lamina provides structural support to the envelope.
• Cilia are hair-like structures that beat to keep internal passages clear of mucus. They have a 9+2 microtubule formation structure.
• Flagellum is similar to cilium but longer and stronger. They move by bending back and forth due to dynein arms moving along microtubules.
• Chloroplasts are responsible for photosynthesis and contain chlorophyll and carotenoids as photosynthetic pigments to absorb sunlight. They contain grana formed by thylakoid membranes, linked by lamella as well as a double membrane.
• The cell wall is a strong structure that surrounds the cell and provides support and protection. It is made of chitin in fungi and cellulose in plants.
• Vesicles are small membrane bound sacs that contain lipids and proteins. They transport materials around the cell. Some are formed at the golgi or the ER and others on the cell surface.
• The cytoskeleton is made up of microfilaments and microtubules, made of actin.
• Microfilaments form bundles called stress fibres which give cells shape and strength. Actin filaments slide past one another allowing muscle contraction.
• Microtubules are hollow tubes with walls made from protein subunits. They are involved in movement within the cytoplasm and also make up centrioles.
• Microtubules have a hollow tube with walls made from tubulin protein. They are involved in movement within the cytoplasm such as chromosome separation during mitosis.
• In prokaryotic cells, DNA is naked whilst it is wrapped around histones in eukaryotic cells, therefore not naked.
• Eukaryotic cells are larger than prokaryotic cells. They are 10-100 micro metres and contains 80s ribosomes. Prokaryotic cells are less than 2 micro metres and have 70s ribosomes.
• The flagellum in a euk. is made of microtubules in a 9+2 formation whilst in pro. they are made of flagellin.
• Eukaryotic cells have membrane bound organelles, whilst pro. have few/none.
• DNA in a euk. is linear whilst in pro. it is circular.