Struture and Functions of Enzymes

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Cells are the structural and functional units of all living organisms; each specialised to perform dedicated duties throughout their life span. All living organisms can be sorted into one of two groups depending on the fundamental structure of their cells. These two groups are the prokaryotes and the eukaryotes. A Prokaryote cell is the first form of cells for many millions of years until the eukaryote cell evolved from the prokaryote cell, which created life. Prokaryote cells are organisms made up of cells which lack a cell nucleus or any membrane encased organelles, which means the DNA in prokaryotes is not bound with a nucleus. In the eukaryotes, DNA is organized into chromosomes, which is surrounded by a membrane. According to Dr Lynn Margulis (2005), she states that the origins of mitochondria and chloroplasts which are organelles of eukaryotic cells. This means that the mitochondria and chloroplasts were prokaryotic cells, which entered the eukaryotic cells and co-existed through endosymbiosis.

There are many organelles inside a eukaryote cell, each performing dedicated functions. For example, the nucleus, this is a membrane bound structure containing DNA and other genetic information. The mitochondria reserve and convert energy into form usable by the cell. They are known as the power houses of cells. The plasma membrane is also another important structure in a cell.

The plasma membrane is the structure of the cells which define and enclose the cell. The membrane forms a barrier between the inside and the outside of the cell, enabling different chemical environments to exist on each side of it. The cell membrane is made up of phospholipid bilayers, carbohydrates and proteins arranged in a fluid mosaic structure. There are five main methods by which substances can move across a cell membrane; these are lipid diffusion, osmosis, passive transport, active transport and vesicles. (BiologyMad, 2004)

See Appendix 1 (Eukaryote Cell)

The egg cell (ovum) is produced in the ovaries and can be seen to the naked eye, making it the largest cell in the human body. It is 0.1mm in diameter, and is enclosed within the egg follicles of the ovaries. The female human is born with all the egg cells she will ever have, these will remain in her ovaries until puberty, where each month, with the stimulation of oestrogen and FSH, an egg is released, and waits to be fertilised.

It is the cytoplasm in this cell which is what specialises it. The cytoplasm contains yolk, glycogen and proteins, which provides a large food store needed for the developing young organism once it is fertilised. The cytoplasm in the egg cell is differentiated into outer transparent exoplasm and inner opaque endoplasm.

See Appendix 2 (Ovum Cell)

The sperm cell is specialised by the organelles it contains. These are the nucleus, mitochondria, cytoplasm and acrosome. The sperm cell has a long tail and a cone shaped head, this specialised structure allows the sperm to swim at a fast pace and the cone shaped head full of acrosome breaks down the barrier which protects the egg cell.

This cell is produced outside the body called the testes and is the smallest and straightest cell in the body. As well as the sperm cell having a specialised structure, the organelle sperm cells rely on the most is mitochondria. The mitochondria are needed to allow the tiny sperm swim to an egg cell, break down its barrier and fertilise it.

See Appendix 3 (Sperm Cell)

Nerve cells are the basic structural units of the nervous system. They have specialised structures which allow them to send and transmit electrical and chemical impulses via a synapse. Each nerve cell has a cell body, containing the nucleus, from which trail processes called dendrites; these are responsible for receiving incoming signals. The cells longest structure is the axon; this carries impulses away from the cell body. (TalkTalk, 2012)

When a neuron receives a nerve impulse, its job is...
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