Cell Structure and Function PDF

Cell structure and function The cell: can be divided into four [principal parts: 1) Plasma cell membrane: - Phospholipids – arranged in two parallel rows forming a lipid bilayer (consisting of a hydrophilic head-group and two long hydrophobic hydrocarbon chains). In water,...

Cell structure and function The cell: can be divided into four [principal parts: 1) Plasma cell membrane: - Phospholipids – arranged in two parallel rows forming a lipid bilayer (consisting of a hydrophilic head-group and two long hydrophobic hydrocarbon chains). In water, these lipids form a two-layered film with the hydrophilic heads of each layer pointing out towards the water and the hydrophobic tails packed next to one another. - Glycolipids – these are located on the outer surface of the plasma membrane. - Proteins – embedded in the lipid matrix (some proteins extend through the whole membrane and others are only anchored in the outer or inner layer). Some other proteins provide channels through which water and ions can diffuse in and out of the cell. Some proteins are glycoproteins (provide receptor sites that enable a cell to recognise other cells, hormones, nutrients, and other chemicals). - Cholesterol (carbohydrates) – stabilises the cell membrane. Functions of the plasma cell membrane: - Flexible boundary – encloses the cellular contents and separates them from external environment. - Facilitates contact – with other body cells or with foreign cells or substances. - Receptors for chemicals such as hormones, neurotransmitters, enzymes, nutrients, and antibodies. - Selective permeability meaning that permits some substances to pass more readily than others. Some factors: size of the molecules (small molecules like water and amino acids enter and exit the cell easily while large molecules do not enter the cell), solubility in lipids (oxygen, carbon dioxide, and steroid hormones), charge on ions, presence of carrier molecules. - Cytoplasm consists of water, proteins, carbohydrates, lipids, and inorganic substances. Some chemical reactions occur, example: synthesis of new  substances and where chemicals are packaged for transport to other parts of the cells. It also facilitates the excretion of waste materials. Organelles: these have roles in growth, maintenance, repair, and control. - Nucleus – contains the genetic material DNA and RNA that controls protein synthesis. - Ribosomes – consist of rRNA and are found on the rough endoplasmic reticulum. These are the sites of protein synthesis. - Endoplasmic reticulum – provides a surface area for chemical reactions to occur. Also acts as a transport channel through which various substances may pass from one part of the cell to another. Serves as a storage site for synthesised molecules. Lastly. It plays a role in the packaging of molecules together with the Golgi Complex. - Golgi Complex – processes, sorts and delivers proteins to various parts of the cell and helps lipids package and secrete. - Mitochondria – provides energy of the cell by producing ATP.  - Lysosomes – contain powerful digestive enzymes and their function is to remove the debris from within the cell. - Centrosome – a dense area of the cytoplasm located near the nucleus. Centrioles – a pair of cylindrical structures. These play a part in spindle formation during cell division. Cell inclusions: - Melanin – a pigment stored in cells of the skin, hair and eyes and protects the body by screening out harmful ultraviolet rays from the sun. - Glycogen – polysaccharide stored in the liver, skeletal muscle cells and the vaginal mucosa. It is broken down by the liver into glucose. - Lipids – stored in adipocytes and it may be decomposed producing energy. - Mucus – provides lubrication and protection. Cytoskeleton (collection of protein filaments and cylinders): - Determines the shape of the cell. - It lends it structural support. - Organizes its contents. - Moves substances through the cell.