cell structure

• Cell Wall: Made of cellulose fibres in plants, chitin in fungi, peptidoglycan in bacteria are permeable, allowing water in.
• Function of cell wall: maintaining cell shape (especially when turgid) and contributing to strength and support of both the cell and the whole plant.
• Lysosomes: Type of Golgi vesicle, with a membrane so that the cell itself is not destroyed.
• Function of lysosomes: Contains digestive enzymes to destroy damaged, dead, unwanted or foreign cells.
• Mitochondria: Double membrane, spherical (2-5 micrometres), matrix: fluid which fills the structure, cristae: highly folded inner membranes.
• Function of mitochondria: site of respiration, where ATP is released.
• Mitochondria are self-replicating. Newly formed mitochondria are smaller in size.
• Ribosomes: (no membrane), made of a small and large subunit, consist of ribosomal proteins and RNA.
• Function of ribosome: site of protein synthesis.
• Golgi Apparatus: Stack of membrane-bound flattened sacs, pinch off to form vesicles, functions in modifying and packaging proteins.
• Golgi modifies proteins: protein + sugar → glycoprotein, protein + lipid → lipoprotein, folding them into 3D shape.
• Encloses substances into a vesicle to either keep in cell or transport.
• Rough Endoplasmic Reticulum: System of membranes that is continuous with nuclear membrane, cisternae: fluid filled sacs, coated with ribosomes, functions in providing large SA for protein synthesis and transporting proteins from synthesis through cisternae to Golgi apparatus.
• Smooth Endoplasmic Reticulum: System of membranes, cisternae: fluid filled sacs, functions in synthesis, transport and absorption of lipids.
• Nucleus: Chromatin: substance containing DNA and proteins, Histones: proteins which DNA wraps around, functions in controlling function of cells through DNA transcription, controlling gene expression, controlling protein synthesis, storing DNA.
• Nucleolus: Can contain 1+ nucleoli in every cell, functions in protein synthesis and production of ribosomes.
• Nuclear Envelope: Double membrane, contains nuclear pores, allows substances to pass through nucleus and cytoplasm through pores, pores are too small for DNA to pass through, so traps DNA in nucleus.
• Magnification: A measure of how many times larger the image is than the real size of the object.
• The cytoskeleton is dynamic; the protein fibres can lengthen and shorten.
• Resolution: The degree to which it is possible to distinguish between two objects that are very close together
• Chloroplasts: (plants and protists), double membrane, thylakoids: flattened membrane sacs filled with chlorophyll, continuous with inner membrane, function in photosynthesis.
• Resolving power: The resolving power of a microscope is the minimum distance apart that 2 tiny points can be distinguished as separate points.
• Chlorophyll traps light, making ATP in grana, water is ionised, H+ ions reduce CO2, using ATP energy, producing carbs in the stroma.
• Any objects smaller than the resolving power will not be visible, or will just look blurry
• This is because a light wave/beam of electrons must pass between the two objects in order for them to be distinguished as separate.
• If the object is smaller than half the wavelength of light it cannot be seen.
• Centrioles: 2 bundles of microtubules joined together at 90 degrees, forming a cylinder, microtubules made of tubulin protein subunits, function in separation of chromosomes in cell division and formation of cilia and undulipodia.
• Light waves have a wavelength of 400 – 750nm.
• Chromosomes attach to middle of the spindle, motor proteins walk along tubulin threads, pulling the chromosomes to opposite sides of the cell.
• A beam of electron have a wavelength of 0.004nm, meaning they have a shorter wavelength can can achieve a higher resolution and smaller organelles can be seen.
• Cilia: Protrusions from the cell, surrounded by cell surface membrane, formed from centrioles, function in movement of substances and allowing cell to detect signals about intermediate environment.
• Diameter of mitochondria = 1000nm
• Diameter of ribosome = 22nm
• At this wavelength, light will hit the mitochondria and miss the ribosome.
• In a Light Microscope, the specimen is placed in a beam of light and passes through a series of lenses.
• The condenser lens focuses the light onto the specimen.
• The objective lens magnifies the image (x 4, x 10, x 40, x 100).
• Lenses in the eyepiece magnify the image again (x 10 or x 15).
• This produces a magnified image.
• In a Transmission Electron Microscope (TEM), the sample is placed in a vacuum (so that air does not interfere with the beam of electrons).