Cell structure

• Microscopes are instruments that produce a magnified image of an object.
• A light microscope can only distinguish between two objects if they are 0.2 μm , or further apart. Meaning a light microscope cannot see sub cellular structures due to long-wavelengths of light
• The limitation of light microscopes can be overcome by using beams of electrons rather than beams of light. This is because beams of electrons have shorter wavelengths so they can distinguish between two objects only 0.1 nm apart. We call these types of microscope : electron microscopes
• The material put underneath a microscope is referred to as the object
• The appearance of this material when viewed under the microscope is referred to as the image
• magnification = size of image / size of real object
• What is the equation for magnification?

  size of image / size of real object
• There are 10,000,000 nm in 10 mm
• The resolution, or resolving power, of a microscope is the minimum distance apart that two objects can be in order for them to appear as separate items.
• Whatever the type of microscope, the resolving power depends on the wavelength or form of radiation used.
• In a light microscope any objects closer together than 0.2 μm will appear as a single item.
• Greater resolution means greater clarity, that is the image produced is clearer and more precise
• Increasing the magnification doesn’t necessarily increase resolution
• Cell fractionation is the process where cells are broken up and the different organelles they contain are separated out
• Before cell fractionation the tissue is placed in a cold, buffered, isotonic solution
• the solution is cold to reduce enzyme activity that might break down the organelles
• the solution is buffered so that the ph does not fluctuate. Any change in ph could alter the structure of the organelles or affect the functioning of Enzymes
• Cells are broken up by a homogeniser (blender)
• Meiosis produces 4 daughter cells, each with half the number of chromosomes of the parent cell
• Mitosis is divisions of a cell that results in each of the 2 daughter cells having an exact copy of the DNA of the parent cell
• Interphase is a period of cellular activity that involves the replication of DNA
• Where do the two copies of DNA after replication go?


  Joined at the centromere
• What are the four stages of mitosis?

  Prophase, Metaphase, Anaphase, Telophase and cytokinesis
• In Prophase the chromosomes first become visible, The nucleolus then disappears and the nuclear envelope breaks down

  These chromosomes are drawn toward the equator of the cell by the spindle fibres that are attached to the centromere
• What are centrioles in animal cells?

  Animal cells contain two cylindrical organelles called centrioles which move to opposite ends of the cell ( the poles ). From each of these, spindle fibres develop which span from pole to pole

  Collectively, these spindle fibres are called the spindle apparatus
• In Metaphase the chromosomes are shown to be made up of two chromatids, each an identical copy of DNA from the parent cell

  These chromatids are joined by the centromere

  From the centromere, microtubules from the poles are attached and the chromosomes are spread along the spindle apparatus, arranging themselves across the equator of the cell
• In Anaphase the centromeres divide in two and the spindle fibres pull the chromatids apart to their opposite poles of the cell. Energy for this process is provided by the mitochondria
• In Telophase & Cytokinesis chromosomes have reached their opposite poles and begin to get longer and thinner, finally disappearing. The spindle fibres disintegrates and the nuclear envelope and nucleolus re-form. Then, the cytoplasm divides in a process called cytokinesis
• What is the name for cell division in prokaryotic cells?

  Binary Fission
• In Binary fission the circular DNA molecule replicates and both copies attach to the cell membrane, the plasmids replicate, then the cell membrane begins to grow between the two DNA molecules and begins to pinch inward, dividing the cytoplasm in two. A new cell wall forms between the two molecules of DNA, dividing the cell into two identical daughter cells, each with a single copy of circular DNA and a variable number of plasmids
• How do Viruses replicate themselves since they cannot undergo cell division?


  They replicate by attaching to their host cell with the attachment proteins on their surface. They inject their nucleic acid into the host cell, this then provides instructions for the host cells metabolic processes to start producing nucleic acid, enzymes & structural proteins which are then assembled into new viruses
• What are the three stages of the cell cycle?

  Interphase, nuclear division & cytokinesis
• what is nuclear division?

  When the nucleus divides either in two (mitosis) or four (meiosis)
• What is cytokinesis?

  Cytokinesis is the process by which a cell divides its cytoplasm and organelles into two daughter cells
• What is interphase?

  The phase of the cell cycle where the cell grows and prepares for division
• Cancer is a group of diseases caused by a growth disorder of cells. It is the result of damage to the genes that regulate mitosis and the cell cycle leading to uncontrollable growth and division of cells, this forms a tumor which rapidly expands
• The treatment of cancer involves killing dividing cells by blocking a part of the cell cycle
• Drugs used to treat cancer (chemotherapy) disrupt the cell cycle by preventing the DNA from replicating and inhibiting the metaphase stage by interfering with spindle formation
• The drugs for chemotherapy are more effective against rapidly dividing cells, regular cells (eg hair) are also vunerable to damage