Biology

• There are two main types of microscopes: light microscopes which use a pair of convex glass lenses that can resolve images that are 0.2um apart, and electron microscopes which can distinguish between items 0.1nm apart.
• HIV is treated with antiretroviral drugs which keep the levels of HIV in the blood stream very low, reducing the impact on the host's immune system.
• The magnification of an image as seen through a microscope can be calculated using the equation: Magnification = size of image/size of real object.
• Viruses don't have a cell wall and are reproduced within a host cell, making them unaffected by antibiotics.
• Resolution is defined as the minimum distance apart that two objects can be distinguished as separate objects in an image.
• The limitation of light microscopes only resolving to a resolution of 0.2um means that electron microscopes can be used to look at objects that are closer than 0.2um apart.
• There are two main types of electron microscope, transmission electron microscopes (TEM) and scanning electron microscopes (SEM).
• Electron microscopes work in a similar way to light microscopes, but instead use a beam of electrons that are focused by electromagnets inside a vacuum environment.
• Transmission Electron Microscope - a beam of electrons passes through a thin section of a specimen, areas that absorb the electrons appear darker on the electron micrograph that is produced.
• Scanning Electron Microscope - in a scanning electron microscope a beam of electrons passes across the surface and scatter, the pattern of scattering builds up a 3D image depending on the contours of the specimen.
• There are some limitations when using electron microscopes, the limitations for SEM and TEM are: The whole system must be in a vacuum so living specimens cannot be observed, a complex staining process is required which may introduce artefacts into the image, specimens have to be very thin, particularly for TEM so that the electrons can pass through, SEM has a lower resolving power than TEM, but both have greater resolving power than a light microscope.
• Cell fractionation is the process in which different parts and organelles of a cell are separated so that they can be studied in detail.
• The most common method of cell fractionation is differential centrifugation.
• The ultrastructure of eukaryotic cells can be obtained by using a microscope.
• The rough endoplasmic reticulum folds and processes proteins made on the ribosomes.
• Ribosomes are composed of two subunits and are the site of protein production.
• The nucleus of a eukaryotic cell is a double membrane called the envelope containing ~3000 nuclear pores that enables molecules to enter and leave.
• A granular jelly-like material called nucleoplasm makes up the bulk of the nucleus.
• The role of mitosis and the cell cycle is to produce identical daughter cells for growth and asexual reproduction.
• Cells of multicellular organisms are organised into tissues, tissues into organs and organs into systems.
• Centrioles are hollow cylinders containing a ring of microtubules arranged at right angles to each other.
• The Golgi apparatus is a series of fluid-filled, flattened & curved sacs with vesicles surrounding the edges.
• Mitosis is important for repair as all cells produced are identical so organisms can replace dead tissues using mitosis.
• All living organisms are made of cells, which can be of different types, some sharing common features.
• The inner membrane of mitochondria is folded to form projections called cristae with a matrix on the inside containing all the enzymes needed for respiration.
• Centrioles are involved in producing spindle fibres for cell division.
• All eukaryotic cells contain a nucleus and membrane-bound organelles.
• Viruses are non-living structures which consist of nucleic acid (either DNA or RNA) enclosed in a protective protein coat called the capsid, sometimes covered with a lipid layer called the envelope.
• Prokaryotic cells such as bacteria contain a cell wall, capsule, plasmid, flagellum, pili, ribosomes, and mesosomes.
• The nucleus of a eukaryotic cell contains chromatin and a nucleolus which is the site of ribosome production.
• Mitosis is important for growth as all cells produced are identical so organisms can grow using mitosis.
• Humans are made up of eukaryotic cells.
• The smooth endoplasmic reticulum is a system of membrane-bound sacs that produces and processes lipids.
• The Golgi apparatus processes and packages proteins and lipids and also produces lysosomes.
• Lysosomes are vesicles containing digestive enzymes bound by a single membrane.
• The rough endoplasmic reticulum is a series of flattened sacs enclosed by a membrane with ribosomes on the surface.
• Mitochondria are oval-shaped, bound by a double membrane called the envelope.
• The process of homogenation involves blending the cells in an homogeniser forming the resultant fluid called the homogenate, placing the homogenate in a centrifuge and spinning at a slow speed, forcing the heaviest organelles, the nuclei, to the bottom of the tube where a thin sediment or pellet forms, removing the fluid at the top, called the supernatant, which leaves just the sediment of the nuclei, transferring the supernatant to another tube and spinning at a slightly faster speed, this time the pellet that forms contains the next heaviest organelle, the mitochondria, repeating the proces
• HIV binds to the protein CD4, which is most frequently found on T-Helper cells, and the capsid then fuses with the cell surface membrane and the RNA and reverse transcriptase enter the cell.
• Monoclonal antibodies are useful due to their ability to produce many clones of a single type of antibody, and have many different uses including direct therapy, indirect therapy, diagnosis, and pregnancy testing.