Biology module 2
2.1: Microscopes
2.3: Cell membranes
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Types:
Light
Transmission Electron
Scanning electron
Up to 200nm
Cheap
Easy to use
0.1nm
Expenisve
Require training
x1500
x500,000
2D image
x100,000
50nm
3D
Magnification: the degree to which the size of an image is larger than the object itself. It is the image size divided by the actual size of the object.
Resolution: the degree to which it is possible to distinguish between two objects that are very close together. The higher the resolution, the greater the amount of detail that can be seen.
Specimen preperation:
• Staining (allows the sample to be seen/increases contrast)
• Sectioning (specimens are embedded in wax to prevent being distorted when cut)
Works by using electromagnets to focus a beam of electrons, which is transmitted through the specimen. Denser parts absorb more electrons, producing a contrast
Scan a beam of electrons across the specimen
2.1: Cells and Organelles
The organelles:
• The nucleus houses all of the cells genetic material. The chromatin consists of DNA and proteins. It has the instructions for making proteins. Some of these proteins regulate the cell’s activities. The nucleolus makes RNA and ribosomes, which pass into the cytoplasm and become the site where proteins are assembled.
• Rough endoplasmic reticulum transports proteins that were made on the attached ribosomes.
• Smooth endoplasmic reticulum is involved in making the lipids needed by the cell.
• Golgi apparatus receives proteins from the ER and modifies them. The modified proteins are then packaged into vesicles to be transported.
• Mitochondria are the site where ATP is produced during respiration. Activities that require energy in the cell are driven by the energy released from ATP.
• Chloroplasts (only in plant cells) are the site of photosynthesis.
• Lysosomes contain powerful digestive enzymes. Their role is to break down material.
• Ribosomes are the site of protein synthesis in the cell.
• Centrioles take part in cell division; they form fibres, known as a spindle, which move chromosomes during nuclear division.
Key terms:
Division of labour: refers to each organelle within the cell having a specific role which contributes to the cell’s survival.
The cytoskeleton: regards the network of protein fibres found within cells that gives structure and shape to the cell, and also moves organelles around inside.
Prokaryotic vs Eukaryotic
Prokaryotes lack an organized nucleus and other membrane-bound organelles.
Prokaryotic DNA is found in a central part of the cell called the nucleoid.
The cell wall of a prokaryote acts as an extra layer of protection, helps maintain cell shape, and prevents dehydration.
Prokaryotic cell size ranges from 0.1 to 5.0 μm in diameter.
The small size of prokaryotes allows quick entry and diffusion of ions and molecules to other parts of the cell while also allowing fast removal of waste products out of the cell.
Eukaryotic cells are larger than prokaryotic cells and have a “true” nucleus, membrane-bound organelles, and rod-shaped chromosomes.
The nucleus houses the cell’s DNA and directs the synthesis of proteins and ribosomes.
Mitochondria are responsible for ATP production; the endoplasmic reticulum modifies proteins and synthesizes lipids; and the golgi apparatus is where the sorting of lipids and proteins takes place.
Peroxisomes carry out oxidation reactions that break down fatty acids and amino acids and detoxify poisons; vesicles and vacuoles function in storage and transport.
Animal cells have a centrosome and lysosomes while plant cells do not.
Plant cells have a cell wall, a large central vacuole, chloroplasts, and other specialized plastids, whereas animal cells do not.
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The phospholipid bilayer: is the basic structural component of plasma membranes (cell surface membranes). It consists of two layers of phospholipid molecules. Proteins are embedded in this layer.
Roles of the membrane:
Separating cell contents from the outside environment
Separating cell components from cytoplasm
Cell recognition and signalling
Holding the components of some metabolic pathways in place
Regulating the transport of materials into or out of cells
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