AMINO ACIDS AND PROTEINS 1
What are Proteins?
Proteins are macromolecules or large biological molecules that are made up of a single or a number of chains of amino acids.
It’s has a number of important functions in living organisms:
. As Receptors, receptor proteins are basically used for the intercommunication between cells carrying messages to cells around the entire body, some examples are cytokine receptors and guanine nucleotide binding protein receptors.
. Channels – channel proteins or ion channels forms pores that help in establishing and controlling a small voltage gradient across the plasma membrane of cells .These pores allows ions and small molecules to pass though via the process of diffusion.
. Storage – an example of this is ferritin which is a protein that stores iron in the liver as well as release it in a controlled fashion..
.Enzymes – there are many different enzymes which are responsible for catalyzing many major biological reactions.
. Structural Function – these are fibrous and provide support, examples are collagen and elastin in skin and provide support in connective tissue and keratin in hair.
. Immune Response – there are specalised proteins which are called antibodies and help the body defend against antigens.
. For Transport – a well known organic molecule called hemoglobin which is the taxi or transport vessel for oxygen as well as carbon dioxide around the body.
Now let’s talk about the stuff that make up the proteins.
What are amino acids?
Amino acids are very important organic compounds which are made up of an amine (-NH2) and carboxylic acid (-COOH) functional groups, a hydrogen H and an R group which is specific to each amino acid.
example of an amino acid basic structure
Ok now these R groups which make each different type of protein different from each other.
The R Groups
NON POLAR ALIPHATIC R GROUPS
This group is also hydrophobic and that increases as the number of C in the hydrocarbon chain increases. The name of the amino acids in the groups are glycine, alanine, proline, valine, leucin, methionine and isoleucine, amino acids prefer to remain inside the protein molecule but glycine and and alanine are like rebels and are ambivalent which means they can be inside and outside.
POLAR, UNCHARGED R GROUPS
This group consists of five amino acids serine, threonine, cysteine, asparagine and glutamine. These are polar because of the oxygen O which is much more electronegative than the carbon C and hydrogen H thus polar bonds form.
AROMATIC R GROUPS
This group of amino acids are relatively non polar to a degree and all absorbs ultraviolet light. The amino acids in this group are tyrosine, tryptophan, phenylalanine.
POSITIVELY CHARGED R GROUPS
This group includes lysine, arginine and histidine. They have pH values pKa‘s and are very hydrophilic. They are positively charged because of the positive charge from the group ammonia.
NEGATIVELY CHARGED R GROUPS
This groups consists of aspartate and glutamate and there is an acidic group.
Amino acids have nonionic form and a zwitterionic form. This happen when the proton which is the hydrogen H on the carboxylic group is lost and the amino group NH2 will accept it.
Essential Amino Acids
There are 20 amino acids essential for the human body and 10 of the 20 the human body cannot produce and must rely on a proper diet to obtain them.
Complete proteins are protein food source that contain all the essential amino acids that we can’t produce on our own. Proteins from animals alone with the exception of beans have all the essential proteins.
These are proteins that do not contain all the essential amino acids and are found in vegetables with the exception of beans.
This is a reaction that tests for amino acids. Amino acids are mostly colourless but if you conduct the ninhydrin test and it is positive it give a purple colour which says that amino acids are present. is a white or yellow toxic, crystalline or powdery compound that reddens when heated above 100°C and is soluble in water and alcohol.
Amino Acids and Proteins 2
Proteins can have four levels of structure.
The level of the structure is based on the level of folding due to;
Bonding between hydrogen and an electronegative atom like nitrogen or oxygen in protein folding. Bonds range from .27 to .31 nm. Hydrogen bonding is stronger than van der Waal forces but weaker than covalent bonds.
Interactions between groups of opposite charge. The bond is referred to as a salt bridge.
Formed by the oxidation of two cysteine residues to form a cystine residue. Also called a disulphide bridge
Interactions between non-polar molecules in order to avoid contact with water.
This level of structure has no folding. It is a linear sequence of amino acids joined by peptide bonds. The primary structure tells you what amino acids are present and what sequence they are in.
This level of structure has regular folding of the polypeptide chain. This folding can either be helices and beta pleated sheets. Both are held together by hydrogen bonding. Alpha helix is a conformation where the amino acids are arranged helical. Hydrogen bonding occurs between the carbonyl oxygen in each peptide bond to the hydrogen on the amino group. In the alpha helix there are 3.6 amino acids per turn. This conformation is more common because there is optimal use of internal hydrogen bonding which gives the helix stability. Beta pleated sheeting is formed by hydrogen bonding between peptide bonds of the polypeptide chain or between different polypeptide chains. The polypeptide is pleated with the amino acids above and below the sheet. Beta pleated sheets can be parallel or anti-parallel. The parallel beta pleated sheet has both C-terminal ends running along the same side while the anti-parallel beta pleated sheet has the C-terminals alternating.
This level of structure has irregular folding of the polypeptide chain. Hydrophobic forces are the main cause for such folding. The chain folds itself in way that the hydrophobic side chains are in the interior with the polar molecules on the outside. Besides hydrophobic forces there are electrostatic forces, hydrogen bonding and covalent disulphide bonds.
This is a level of structure containing more than one polypeptide chain eg. Haemoglobin. Theses chains are held together by hydrogen bonding, electrostatic forces, hydrophobic forces and disulphide bonds.
Denaturation of Proteins
The disruption and or destruction of the quaternary, tertiary and secondary structures of proteins. The primary structure is not changed. When a protein is denatured the bonds are broken and can return natural structures under good conditions. Under extreme conditions, however, the protein cannot return to its natural state. Proteins can be denatured by heat, UV radiation, some organic solvents (ethanol and acetone), strong acids or bases, urea and agitation.
Now that you know about proteins, go forth into the world and share the good news about proteins!!!
References for pictures