Write an essay on the functions of proteins in plants and animals

Proteins are polymers of monomers called amino acids. Amino acids contain hydrogen, carbon, oxygen and nitrogen. When amino acids are linked together, they form polypeptide chains and bonded together by peptide bonds. There are different structures of polypeptides primary, secondary, tertiary and quaternary. The primary structure is a straight chain of polypeptides. Secondary structure is the polypeptide chain coiling to form an α helix or the polypeptide chain linking together to form a β pleated strand. In an α helix hydrogen bonding forms in the secondary structure between the NH group of one amino acid and the CO group of another amino acid. In a β pleated strand hydrogen bonding occurs between the CO and NH groups of one amino acid residue of one chain and the NH and CO group of another chain. The further folding of the polypeptide chain is known as the tertiary structure. In this structure the folding and coiling of the chain is irregular. This causes the types of bonding between the amino acid residues to vary. The quaternary structure consists of more than one polypeptide chain this structure is found in haemoglobin. The bonding between different groups in this case can vary depending upon the functional groups present. If hydrogen and oxygen bind to another hydrogen and oxygen of another R group the hydrogen bonding is present. If not then ionic bonding occurs. If the amino acid residues contain sulphur then disulphide bridges are formed. There are two types of protein fibrous which is insoluble in water and globular which is soluble in water. Fibrous proteins are found in proteins which have structural functions such as collagen whereas globular are found enzymes and hormones.

Enzymes are tertiary proteins and globular, this because they have to be soluble so that they can be transported in the blood plasma. They have a 3D shape, which allows enzymes to have an active site to which only specific substrates will be able to attach to it. For example, digestive enzymes such as amylase which breaks down starch into maltose. Rubisco found in plants allows Ribulose Bis Phosphate to catalyse carboxylation in photosynthesis.

Some hormones are also globular proteins. These too have to be soluble so that they can be transported in the blood plasma. Insulin ...

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Some hormones are also globular proteins. These too have to be soluble so that they can be transported in the blood plasma. Insulin which is a globular protein with a quaternary structure. Its function is to stimulate the conversion of glucose into glycogen when the level of glucose in the blood plasma is higher than normal. Its counterpart glucagon stimulates the breakdown of glycogen into glucose when the level of glucose in the blood plasma is lower than normal. Adrenalin is also an hormone which vasodilates and vasoconstricts the blood supply to parts of the body which require more or less blood for example during exercise where the skin requires less blood but the skeletal muscles requires more in order to allow contraction of muscles.

Proteins are also found in membranes. There are two types intrinsic and extrinsic. The main function of intrinsic proteins is to transport globular proteins. Whereas the extrinsic consists of glycoproteins. Glycoproteins are tertiary in structure. The function of glycoproteins is to contain receptors for molecules such as hormones. An example being the liver cells which contain glycoproteins molecules that can combine with insulin molecules.

Proteins found in the blood plasma include haemoglobin, myoglobin, fibrogen and antibodies. Haemoglobin has a quaternary structure but it is a conjugated protein. It is a mix of haem group but not amino acids but is still an essential molecule as it transports oxygen around the body via the blood plasma; therefore, it has to be soluble. If the solubility decreases the individual suffers from sickle cell anaemia. Antibodies have a tertiary structure and are globular to ensure that the correct antigen attaches to it. If however, the shape of the binding site changes a mutation occurs and it no longer able to fight the same illness. Fibrogen is present in the blood plasma as part of the blood clotting mechanism of the body.

Some proteins have a structural function such as collagen, elastin and keratin. Collagen is an example of a fibrous protein which has a secondary structure. Collagen is an insoluble protein because the molecule does not curl up but instead it forms long chains. Collagen is important and found in the skin and tendons. Collagen cannot be stretched but it highly flexible. This is because the α helix chain can be stretched but recoils when relaxed. Keratin is also a fibrous protein its function is to make the skin, hair and nails waterproof.

Other functions of proteins can be contractible such as myosin and actin which are found in the skeletal muscles. They also make up some of the pigments found in plants and animals. In animals, opsin is found in both rodopsin and iodopsin which allows animals to see objects in colour or black and white and is found only in the eye. Melanin found in mammals is a pigment which gives the skin colour. Phytochrome is found in plants. This protein allows the conversion of P730 into P660 or vice versa depending on the amount of far-red or red light present. This results in the stimulation or inhibition of flowering.

Many proteins are required in plants and animals to ensure that they function efficiently. Proteins are needed for many vital processes. Every protein has its own function within plants and animals varying from structural to homeostatic control.

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Adam Roberts

5th of Sep 2013

*** The scientific content is almost all relevant to the title and most of the key types of function are covered. However, more precise use of biological language would improve the quality and accuracy.

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