Organelle Research Task

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Organelle Research Task Dylan Adlard Mitochondrion: Mitochondria are 1μm in diameter and are ‘cigar’ shaped. One, therefore, requires an electron microscope to view them. The number of mitochondria per cell varies greatly depending on the cell. For example a liver cell would consist of more mitochondria than a lymphocyte. Two membranes surround mitochondria, the inner one being folded to form cristae, which project into the matrix. There is a gap in between these two membranes known as the inter-membrane space. The outer membrane contains a transport protein called porin, which forms aqueous channels, thus making it permeable to oxygen, pyruvate, ADP etc. The main function of mitochondria is to carry out aerobic respiration. It is also involved in the synthesis of lipids. Energy is released from energy-rich molecules (sugars & fats) in a series of reactions during Diagram of a Mitochondrion

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Biology A level research task. Great for extra information on the cell's organelles.

Transcript of Organelle Research Task

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Organelle Research TaskDylan Adlard

Mitochondrion:

Mitochondria are 1μm in diameter and are ‘cigar’ shaped. One, therefore, requires an electron microscope to view them. The number of mitochondria per cell varies greatly depending on the cell. For example a liver cell would consist of more mitochondria than a lymphocyte. Two membranes surround mitochondria, the inner one being folded to form cristae, which project into the matrix. There is a gap in between these two membranes known as the inter-membrane space. The outer membrane contains a transport protein called porin, which forms aqueous channels, thus making it permeable to oxygen, pyruvate, ADP etc.

The main function of mitochondria is to carry out aerobic respiration. It is also involved in the synthesis of lipids. Energy is released from energy-rich molecules (sugars & fats) in a series of reactions during respiration. This energy is transferred to molecules of adenosine triphosphate, the universal energy carrier. Respiration specifically takes place in solution in the matrix and the cristae. The matrix contains enzymes including those of the Krebs cycle (not sure if I should have included the cycle?), which supply the hydrogen and electrons to the reactions inside the cristae. The folding of the cristae increases the efficiency of respiration due to the increase of surface area.

Diagram of a Mitochondrion

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Mitochondria also contain small circular DNA molecules (maternal only), as well as 70S ribosomes (protein synthesis), as in bacteria. They thus have the facilities to produce their own ribonucleic acid. It is interesting to note that this is because mitochondria and chloroplast are, in effect, ancient bacteria, which now live inside the larger cells typical of animals and plants. This is known as the endosymbiont theory. Mitochondria and chloroplasts cannot, however, live independently.

Lysosomes:

Lysosomes are spherical sacs surrounded by a single with minimal internal structure. They are usually 0.1-0.5μm in diameter. They contain around fifty different hydrolytic enzymes, which digest unwanted structures such as old organelles or even whole cells (mammary cells after lactation). The medium in which these enzymes are contained is acidic with a PH of around five. The membrane (phospholipid bilayer) contains proton pumps, which allow the entrance of H+ ions. The enzymes have to be kept separate from the cell itself, as so it doesn’t damage the cell’s contents. Even if the enzymes did escape, however, they would dissociate due to the neutral PH of the cytoplasm. Lysosomes are also used to digest bacteria (endocytosis), as in white blood cells. Lysosomes, known as acrosomes in this case, are also found in the heads of sperm cells, in order to digest a path to the ovum.

Molecules enter the lysosome via phagocytosis and pinocytosis. Pinocytosis is the ingestion of fluids and small macromolecules, whereas phagocytosis is defined as the bulk ingestion of large particles. Phagocytic engulf the particles by forming a vesicle around the substance, which later fuses with the lysosome

Diagram of a Lysosome

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followed by the enzymes going to work.

Golgi Complex:

The Golgi complex is a stack of flattened cells. Vesicles constantly bud off from the endoplasmic reticulum at one end (cis face) and the stack is broken down again at the other end (trans face) to form Golgi vesicles. The stack of sacks together with the associated vesicles is referred to as the Golgi complex (or Golgi apparatus). The Golgi complex sorts and processes molecules (mostly from the ER) in preparation for transport in Golgi vesicles either to other parts of the cell (mostly lysosomes), the plasma membrane or to outside of the cell (secretion). An example of protein processing in the Golgi complex is the addition of sugars to proteins to make glycoproteins. Lysosomes are also made in the Golgi vesicles.

Diagram of a Golgi apparatus Electron micrograph of a Golgi apparatus

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Simply put, the Golgi apparatus is a critical member of the biochemical manufacturing and supply chain inside a cell.

Endoplasmic Reticulum:

Endoplasmic reticulum is made of membranes, which form an extended system of flattened compartments, which spread throughout the cell. The sacs can form a complete system called a reticulum, which is continuous with the outer membrane of the nuclear membrane. There are two types of ER: smooth ER and rough ER. Rough ER is covered with many ribosomes (site of protein synthesis). The proteins made in these ribosomes enter and move through the sacs, and are often modified along the way. The sacs/vesicles can break off from the ER and join together to form the Golgi body. They thus form part of the secretory pathway, and the proteins can, therefore, be exported from the cell via the Golgi vesicles. Smooth ER, however, lacks ribosomes and instead of producing proteins, it contains enzymes that catalyse reactions involved with lipid metabolism (synthesis of cholesterol, oestrogen and testosterone for example).

Centrioles:Centrioles are hollow cylinders about 500nm long, formed from a ring of nine triplets of short microtubules (tubulin protein subunits). There are two centrioles positioned just outside the nucleus of animal cells. They lie close together and at right angles to each other in the centrosome. The main function of centrioles lies within cell division. Before a cell divides, spindles made of threads of tubulin form from the centrioles. Chromosomes then attach to the middle of the spindle, whilst motor proteins walk along the tubulin threads,

Simple diagram of ERElectron micrograph of SER and RER

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pulling the chromosomes to opposite ends of the cell. Centrioles are also involved in the formation of cilia and undulipodia.

Diagram of a centriole Computer generated image of a centriole