Cell Structure

• Prokaryotic organisms are prokaryotic cells and eukaryotic organisms are made up of eukaryotic cells.
• Eukaryotic cells are complex and include all animal and plant cells.
• Prokaryotic cells are smaller and simpler (eg, bacteria)
• Plant cells have an additional cell wall with plasmodesmata, a vacuole and chloroplasts
• The plasma membrane is the membrane found on the surface of animal cells and inside the cell wall of plant cells and prokaryotic cells. Made of mainly lipids and protein
• The cell wall is a rigid structure that surrounds plant cells and mainly made of the carbohydrate cellulose
• The nucleus is a large organelle surrounded by a nuclear envelope (double membrane) which contains many pores. The nucleus contains chromatin (made from DNA and proteins) and a structure called the nucleolus.
• The nucleus controls the cells activities (controls the the transcription of DNA) DNA contains instructions to make proteins. The pores allow substances to move between the nucleus and the cytoplasm. The nucleolus makes ribosomes.
• Lysosome is a round organelle surrounded by a membrane with no clear internal structure. It contains digestive enzymes that are kept separate from the cytoplasm by the surrounding membrane, and can be used to digest invading cells or to break down worn out components of the cell
• A ribosome is a very small organelle that either floats free in the cytoplasm or is attached to the RER. It is made up of proteins and RNA and not surrounded by a membrane. It is the site where proteins are made.
• The rough endoplasmic reticulum is a system of membranes enclosing a fluid-filled space and the surface is covered with ribosomes. It folds and processes proteins that have been made at the ribosomes
• The smooth endoplasmic reticulum is similar to the RER but has no ribosomes and it synthesises and processes lipids.
• A vesicle is a small fluid-filled sac in the cytoplasm, surrounded by the membrane and it transports substances in and out of the cell and between organelles.
• The golgi apparatus is a group of fluid-filled membrane-bound, flattened sacs and vesicles are often seen at the edge of the sacs. It processes and packages new lipids and proteins and makes lysosmes.
• Mitochondrion are oval shaped and have a double membrane, the inner one is folded to form structures called cristae. Inside is the matrix which contains enzymes involves in respiration. It is the site of aerobic respiration where ATP is produced and is found in large numbers in cells that are very active and require alot of energy
• Chloroplasts is a small flattened structure found in plant cells and surrounded by a double membrane and has membranes inside called thylakoid membranes. These stack up to create gana and they are linked together by lamelle. They are the site of photosynthesis (some parts happen in the grana and some parts happen in the stroma)
• The centriole are small hollow cylinders made of microtubules. They are found in animal cells but only some plants cells. They are involved with the separation of chromosomes during cell division
• Cilia are small, hair-like structures found on the surface membrane of some animal cells. In cross-section, they have an outer membrane and a ring of nine pairs of protein microtubules inside with two mircotubules in the middle. The microtubules allow the cilia to move.
• The flagellum are like cilia but longer and stick out from the cell surface and are surrounded by the plasma membrane, they also contain two microtubules in the centre and nine pairs around the edge. The microtubules contract and the flagellum move.
• Proteins are made at the ribosomes and the ribosomes are on the RER and they make proteins which are excreted or attached to the cell membrane. New proteins that are produced at the ER are folded and processed in the rough ER. They are then transported from the ER to the golgi apparatus in vesicles. At the golgi apparatus the proteins may undergo further processing and the proteins enter more vesicles
• The cytoskeleton is a network of protein fibers that provide structure and support to the cell.
• In eukaryotic cells the protein threads are arranged as microfilaments (small solid strands) and microtubules (tiny protein cylidners)
• The cytoskeleton has four main functions, the microtubules and microfilaments support the cells organelles keeping them in position. They help strengthen the cell and maintain its shape. They are responsible for the movement of materials within the cell. The proteins of the cytoskeleton can also cause the cell to move.
• Prokaryotes are very small, have circular DNA, no nucleus, few organelles and no membrane bound organelles and has small ribosomes
• Eukaryotes are larger cells, have linear DNA, present nucleus, no cell wall, many organelles and large ribosomes
• Magnification is calculated by image size / object size
• Light microscopes use light, lower resolution (max resolution 0.2 um), usually used to look at whole cells or tissues and the maximum magnification is about x 1500
• Laser Scanning Confocal Microscopes use laser beams to scan the specimen which is tagged with fluorescent dye and lights up when it passes through the specimen.
• Electron microscopes use electrons instead of light and have higher resolution to give more detailed images.
• The two types of electron microscopes are Transmission electron microscope (TEM) and Scanning electron microscope (SEM)
• Transmission electron microscope uses electromagnets to focus a beam of electrons which gets transmitted through the specimen. Denser parts of the specimen absorb more electrons, making them look darker on the image. TEMs are good because they provide high resolution images but can only be used on thin specimens.
• Scanning electron microscope scans a beam of electrons across the specimen and this knocks off electrons from the specimen and they are then gathered in a cathode ray tube to form an image The images show the surface of the specimen and can be 3D. But they have lower resolution images than the TEMs