BIO:F211

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• Light microscope: Res: 200nm Mag: x 1,500
• Transmission electron microscope: Res:0.1nm Mag: x 500,000
• Scanning electron microscope: Res:0.1nm Mag:100,000
• SEM gives a 3D picture and cell surface structures can be seen. TEM gives 2D picture and allows details of organelles to be seen

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• Magnification is the number of times larger the image is compared to the object. Resolution is the degree to which it is possible to distinguish between two objects that are very close together. It allows the viewer to see detail

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• A lot of biological material inside a cell isn’t colored, so it might be difficult to distinguish between different features.
• Coloured stains are used to stain specimens for use with the light microscope
• Chemicals which bind to other chemicals on, or in, the specimen allows for specimen be to seen. Some chemicals bind to specific structures, such as Acetic orcein staining DNA red.

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• Image size = Actual size x Magnification

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• Nucleus: Largest organelle Houses all of the cell’s genetic material in the form of DNA, which contains the instructions for protein synthesis.
• Nucleolus: Dense, spherical structure inside nucleus Makes ribosomes and RNA which pass into the cytoplasm and are used in protein synthesis
• Nuclear envelope: Surrounds the nucleus A double membrane with nuclear pores to allow mRNA out to go to the ribosomes for use in protein synthesis
• Rough and smooth endoplasmic reticulum (RER/SER):Continuous with the nuclear envelope. RER is studded with ribosomes, SER is not. RER: transports proteins made by the attached ribosomes
• Golgi apparatus: sack of membrane-bound flattened sacs Modifies proteins received from the Rough ER and then packages them into vesicles so they can be transported. Produces lysosomes
• Ribosomes: Tiny. Some are in the cytoplasm and some are bound to the RER Site of protein synthesis
• Lysosomes: Spherical sacs. Single membrane. Contain lysins which are digestive enzymes whichbreak down organelles, pathogens and cells. When a cells dies it undergoes autolysisunder the direction of lysosomes
• Chloroplasts: Only in plant cells. Two membranes. Contain Thylakoids. Site of photosynthesis in plant cells.
• Plasma (cell surface) membrane: Phospholipid bilayer Controls the entry and exit of substances into and out of the cell
• Centrioles: Small tubes of protein fibers. Pair of them next to Nucleus in Animal cells. Form the spindle which moves chromosomes during cell division.
• Flagella and cilia: Hair-like extensions projecting from the surface of a cell. Move by using ATP (sperm, cilia in lungs)
• Mitochondria: spherical or sausage shaped. Double membrane. Where ATP is made

1. Animal Cell

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• 1.The gene containing the instructions for the production of the hormones is copied onto a piece of mRNA
• 2.mRNA leaves the nucleus through the nuclear pore.
• 3.mRNA attaches to a ribosome
• 4.Ribosome reads the instruction to assemble the protein
• 5.Molecules are ‘pinched off’ in vesicles and travel towards the golgi apparatus
• 6.Vesicle fuses with golgi apparatus
• 7.Golgi apparatus processes and packages the molecules, ready for release
• 8.The molecules are ‘pinched off’ in vesicles from the golgi apparatus and move towards the cell surface membrane
• 9.Vesicles fuse with the cell surface membrane
• 10.Cell surface membrane opens to release molecules outside this is exocytosis

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• Prokaryotic cells do not have a nucleus. They are bacteria and are much smaller than Eukaryotic cells. They have: One membrane No membrane-bound organelles Cell wall made of peptidoglycan not cellulose Their ribosomes are smaller Circular DNA DNA is not surrounded by a membrane. ATP production takes place in specialized infolded regions of the cell surface membrane called mesosomes Some have Flagella

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• Increasing the temperature means that the molecules have more kinetic energy. This increased movement makes the membrane leaky, so molecules which would not normally do so can move into and out of the cell. The membrane structure is disrupted as the phospholipid bilayer melts. Membrane proteins and  carrier proteins are denatured and unable to function. The membrane becomes more permeable

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• Passive transport the transport of a molecule without using energy Diffusion: is the net movement of molecules from a region of high concentration of the molecule to an area of lower concentration of the molecule down a concentration gradient. Small, non-polar substances diffuse through the phospholipid bilayer in between the phospholipid molecules. Water can do this because although it is polar it is small
• Facilitated diffusion: Large and charged molecules need to be transported across the phospholipid bilayer, they can’t just diffuse across.Channel proteins form pores in the bilayer which are shaped to allow only one type of ion through. Aquaporins are channel proteins allowing water through. Channel proteins are often gated (can be opened and closed) Carrier proteins are shaped to fit a specific molecule (like glucose). Once this fits in the carrier changes shape to allow the molecule through to the other side of the membrane.
• Active transport The movement of molecules or ions across membranes, using ATP to drive ‘protein pumps’ within the membrane. Moves molecules and ions against a concentration gradient. Examples include: mineral ions being moved into root hair cells hydrogen ions being moved out of companion cells mineral ions being moved across the endodermis movement of sucrose out of sieve tube at sink  

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• Hormones are used in cell signalling. The Target Cells have a receptor which is complementary to the hormone, meaning that it can bind to the receptor cells, triggering the desired internal response. Drugs have also been developed which bind to the receptor molecules on cells. Beta-blockers are used to prevent a muscle from increasing the heart rate to a dangerous level, and some drugs used to treat schizophrenia mimic a natural neurotransmitter which some individuals cannot produce.

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• Process that leads to communication and coordination between cells, e.g. hormones binding to their receptors on the cell surface membrane to trigger a response or reaction inside the cell. It allows for cell recognition and the coordination of the action of different cells

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• The movement of water molecules from a region of higher water potential to a region of lower water                potential across a partially permeable membrane

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• Animals placed in high WP; Water moves in. Cell bursts- haemolysed Placed in -ve WP; Water moves out. Cell Is crenated
• Plants placed in high WP;Water moves in. Cell is turgid Placed in -ve WP; Water moves out. Cell is plamolysed

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• A bilayer of phosopholipid molecules forms the main structure. Various proteins are studded in the bilayer. Some are partially embedded (extrinsic) whereas some completely span the membrane (intrinsic)

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• At the surface of cell: Separate cell contents from the outside environment Cell recognition and signalling Regulating the transport of materials into or out of cells

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• Phospholipids Have a hydrophobic head and a fatty acid tail. They form a bilayer separating the cell from the outside.   They are fluid so components can move around freely. They act as a barrier, selecting what goes in/out of the cell. They are permeable to small and/or non-polar molecules, but impermeable to large molecules and ions.
• Cholesterol Gives the membranes stability by sitting between fatty acid tails and therefore making the barrier more complete, preventing molecules like water and ions from passing through the membrane.
• Glycolipids Phosopholipid molecules that have a carbohydrate part attached. They are used for cell signalling, cell surface antigens and cell adhesion.
• Proteins Channel proteins allow the movement ofsome substances, such as the large molecule sugar, into and out of the cell as theycan’t travel directly through the cell surface membrane. Carrier proteins activelymove substances across the cell surface membrane.
• GlycoproteinsProtein molecules with a carbohydrate attached. Act as antigens Enable the identification of cells as self or non-self Used in cell signallingAct as receptors or binding sites for hormones. They have a specific shape that is complementary to shape of the communicating moleculewhich binds to the receptorAct as receptors on transport proteinsto trigger movementAllow cell adhesion to hold cellstogether in a tissueAttach to water molecules to stabilisethe membrane

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• Interphase (pre-Mitosis) The DNA replicates
• Prophase The chromosomes supercoil & become visible under a light microscope. The nuclear envelope breaks down. The centriole divides in two and move to opposite ends of the cell to form a spindle.