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Video Source: www.youtube.com/watch?v=1Fl_rSgQ5_8
Proteins: Tertiary and Quaternary Structure in a Snap! Unlock the full A-level Biology course at http://bit.ly/2tjNTmw created by Adam Tildesley, Biology expert at SnapRevise and graduate of Cambridge University. • SnapRevise is the UK’s leading A-level and GCSE revision exam preparation resource offering comprehensive video courses created by A* Oxbridge tutors. Our courses are designed around the OCR, AQA, SNAB, Edexcel B, WJEC, CIE and IAL exam boards, concisely covering all the important concepts required by each specification. In addition to all the content videos, our courses include hundreds of exam question videos, where we show you how to tackle questions and walk you through step by step how to score full marks. • Sign up today and together, let’s make A-level Biology a walk in the park! • The key points covered in this video include: • • 1. Tertiary Structure • 2. Quaternary Structure • 3. The Importance of Protein Structure • • Tertiary Structure of Proteins • • The α-helices and β-pleated sheets also twist and turn to form a protein with a unique 3-D structure. This structure is held in place by bonds formed between the R groups of amino acids. Hydrogen bonds form between polar R groups, Ionic bonds form between positive and negatively charged R groups, Disulphide links form between sulphur atoms in R groups. The specific 3-D structure is also determined by hydrophilic and hydrophobic R groups. Amino acids with hydrophobic R groups tend to be found in the centre of the protein, Amino acids with hydrophilic R groups tend to be found on the outside of the protein. The overall 3-D structure is therefore a result of R group properties and interactions - the primary structure determines the tertiary structure. The tertiary structure of a protein is the overall specific 3-D shape of a protein. This is determined by interactions between R groups and properties of R groups. • • Quaternary Structure of Proteins • • Some proteins are only composed of one polypeptide chain. However, many proteins are made up of multiple polypeptide chains. Just like tertiary structure bonding, the polypeptide chains are held together by hydrogen bonds, ionic bonds and disulphide links. Non-protein groups (prosthetic groups) may also be associated with the polypeptide chains forming conjugated proteins. The bonding of different chains and prosthetic groups results in the formation of proteins with a unique quaternary structure. The quaternary structure of a protein is the specific 3-D shape of a protein that is determined by the multiple polypeptide chains and/or prosthetic groups bonded together. • • The Importance of Protein Structure • • Overall, the primary structure determines the secondary, tertiary and quaternary structures which gives proteins their unique shapes. This allows every protein to carry out a specific function. However, the bonds that maintain the structure of proteins can be broken by changes in temperature and pH. This results in a change of shape, preventing the protein from being able to carry out its function - we say that the protein is denatured. • • Summary • • The primary structure of a protein is the sequence of amino acids • The secondary structure of a protein is the curling or folding of the polypeptide chain into α- helices and β-pleated sheets • The secondary structure of a protein is stabilised by hydrogen bonds • The tertiary structure of a protein is the overall specific 3-D shape of a protein • The quaternary structure of a protein is the specific 3-D shape of a protein that is determined by multiple polypeptide chains and/or prosthetic groups bonded together • Both the tertiary and quaternary structure are held in shape by hydrogen bonds, ionic bonds and disulphide links • These bonds can be broken by changes in temperature or pH resulting in the protein becoming denatured
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