Proteins - Structure and Function (PDF)

Proteins/water -- structure and function   **MLO5.    **Explain the importance of water in biological systems and explain how the polar nature of water molecules influences the structure of cells and molecules.\      **MLO6.    **Describe the structure of the principle biological molecules containe...

Proteins/water -- structure and function   **MLO5.    **Explain the importance of water in biological systems and explain how the polar nature of water molecules influences the structure of cells and molecules.\      **MLO6.    **Describe the structure of the principle biological molecules contained within cells, i.e. DNA, RNA, carbohydrates, proteins, and lipids. Cytosol, or intracellular fluid is made of water, as it is the main solvent in the body. Extracellular fluid is made of interstitial fluid, which is formed of plasma. Structure of water molecules: - Oxygen is more electronegative than hydrogen, so electrons are pulled towards oxygen molecules - Hydrogen bonds formed between H and O atoms - Only a small fraction of water is ionized, which is the decomposition of water to form H+ and OH- Protein are polymers made of many amino acids that performs functions for our cells. Between the amino acids are peptide bonds. All naturally occurring amino acids are L-amino acids Amino acid structure: - Alpha amino acids are formed of carbon, hydrogen, oxygen and nitrogen - All amino acids except for proline have an acidic carboxyl group and a basic amino group, where there is an alpha hydrogen connected to the alpha carbon - Each amino acid also has an R group which determines what amino acid it is, and there are 20 amino acids in the human body - Aspartic acid and glutamic acid are acidic amino acids - Histidine and lysine are basic amino acids - Glutamine, glycine and serine are uncharged hydrophilic amino acids - Alanine, phenylalanine and valine are hydrophobic amino acids - Cysteine and methionine are sulphur containing amino acids Protein structure: - Primary structure: the sequence of amino acids forming a polypeptide - Secondary structure: two major forms, the alpha helix and beta pleated sheet - \- Alpha helix: quite stable, side chain faces the outside, tend to be globular - \- Beta pleated sheet: chains are linked by hydrogen bonds, small amino acids are involved therefore can pack very tightly, hence very strong - Tertiary structure: folding over of secondary structure, stabilized by salt bridges, hydrogen bonds and disulphide bonds - Quaternary structure: 3D structure of multiple tertiary structured proteins coming together Structural proteins: - Globular proteins: roughly spherical, partially soluble in water - Fibrous proteins: provide structural support, ie. Proteoglycans which are in the bones for elastic strength - Fibrous globular proteins: responsible for things such as contractions Collagen: - Found in the connective tissue for tensile strength - Secreted by specialised cells called fibroblasts - Collagen tripeptides form microfibrils, which come together to form fibres - When collagen becomes disorganised, tissue starts to atrophy, causing skin to deflate Moodle recap quiz Q: Aspartic acid is an -? A: acidic amino acid Q: Glycine is an -? A: hydrophilic amino acid Q: Histidine is a -? A: basic amino acid Q: Methionine is a -? A: sulphur containing amino acid Q: Alanine is a -? A: hydrophobic amino acid Q: The sequence Glu-Lys-Pro-Ser-Asp represents a -? A: Polypeptide Q: There is a natural limit to the number of amino acids that can be linked together. True or false? A: False Q: All naturally occurring alpha amino acids are -? A: L-amino acids Q: How many different alpha-amino acids are available to make a protein A: 20