Cell Biology and Genetics

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Unit1 – Cell Biology & Genetics

By Kendra Pinder

The Nucleus (Fig 1) is the largest organelle in a single cell. As you can clearly see from the cell in fig 3, under an electron microscope this cell is spherical in shape and the darker stained area is the Nucleolus.  

The nucleus quite literally is the control centre of each cell and initiates the directives for the other organelles within the cell. As well as initiating directives it also controls the growth and duplication of the other organelles within the cell. If a cell was seen as a company an organisation the nucleus would be comparable to a manager/director of that company. The Cell has one or more nucleoli and it is here that ribosome’s are manufactured for protein synthesis, providing ATP etc for the cell. This is made possible as the Nucleolus contains all the information that the cell will need to function.

The nucleus itself is surrounded by a thin membrane that protects it from other parts of the cell. Though this membrane does surround the nucleolus it is a double semi permeable membrane (also known as the nuclear envelope) and within the membrane layer’s there are nuclear pores. These pores allow the exchange between the nucleus and the cytoplasm of molecules for example the aforementioned ribosomes.

Inside the membrane where the nucleolus resides you will also find a smaller organelle, a nucleoli which is called chromatin. Chromatin is the complex basis of DNA and proteins that make up chromosomes, these chromosomes are loosely coiled but condensed in structure enabling it to fit within the nucleolus. In other words allowing what would be very long DNA molecules to fit into the cell’s nucleous tiny space.

These chromosomes provide a very important function for the cell. They carry the strands of DNA and proteins for the cells functionality. DNA’s function to the cell is that it carries the code for the proteins controlling which proteins are made therefore controlling the cells activity.

Ribosome’s are very small organelles found in the cytoplasm and on the endoplasmic reticulum. They are structured into two parts, a large and small subunit which fit together and work as one. Their job is to synthesise proteins needed for the cell to function. The instructions for what proteins are needed for the cell are carried within messenger RNA that attach to these ribosomes. The ribosome’s themselves are made up of proteins and ribosomal RNA and so are able to connect/gel as such to the Messenger RNA and translate the information held within it like a molecular translation machine. The Messenger RNA would have been loaded originally with its information in the following way and as you will see the original source for this information is the nucleolus.

From Nucleolus >>Chromatin >>DNA >>Messenger RNA >>Ribosome’s >>Proteins

The nucleolus also makes the ribosome’s sending them out to work and to carry out there specific functions. They are made to function in two forms, one type as free and the other type as bound. Free ribosome’s move around freely within the cytoplasm and the bound ribosome’s can be found attached to the surface of the rough endoplasmic reticulum. Though they are different in the way they move or are bound within the cell, ribosome’s are identical in there structure and there function.

The Proteins from the ribosomes are transported throughout the cell by endoplasmic reticulum.

        

The Mitochondria (Fig 4) are the power plants of a cell, as in processing and producing ATP (the energy carrier in cells). The way that this is enabled is via a special respiratory system which allows the transfer of enzymes etc into and out through the cell membrane. The more active an organism is the more mitochondria it will have in its cells. It actually is the part that turns food into energy. They each have two membranes, usually they are elongated (like corn on the cob) however they can sometimes be round. The outer membrane limits the organelle from expanding any further or changing its shape, whilst the inner membrane is layered into folds see fig 5. Meaning the area inside of the organelle is greater than the surface area. These are called “Cristae Mitochondrial” This also allows more production of ATP. As well as ATP the inner membrane has other proteins which have different functions, for example there will be certain proteins that carry out oxidation reactions and others that regulate the passage in and out of the matrix.

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This matrix contains a variety of enzymes and mitochondria ribosome’s to aid ATP synthesis and transportation.

Endoplasmic Reticulum (see fig 6) – Is easier to understand if you were to see it as a conveyor belt of a cell, taking proteins etc to and from other organelles within the cell and out of it. Smooth ER looks different to rough ER as it has no ribosome’s attached so quite simply it is called smooth ER because it has a smooth and not rough appearance. Smooth ER looks like layered sacs (fig 26) that have been flattened and it will ...

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*** This report appears to be a set of revision notes that has been well presented with good clear diagrams but there are a number of errors in key facts that should be corrected. References have listed but not cited in the text. To improve The student needs to ensure that key terms are spelt correctly throughout. The nucleus and the nucleolus are not the same thing and the student has mixed these terms up in a number of sentences. It is important not to talk about animal cells having a cell wall. The description of active transport is erroneous in a number of key facts. The student would need to review this section in particular.