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Proteins 1

QuestionAnswer
Give an example of when proteins provide structure. Collagen is the protein of bone, skin and tendon.
Give an example of when protein acts as a transport molecule. Haemoglobin is the protein involved in oxygen transport.
What is the technical name for red blood cells? Erythrocytes.
Describe the structure of haemoglobin. 4 protein subunits per molecule. Each subunit contains a Haem group that can bind to one oxygen molecule. Haem is a prosthetic group.
What composes Low-density lipoproteins? A phospholipid shell and a single molecule of apolipoprotein B.
What regulates the uptake of LDL particles? The LDL receptor that binds to LDL and facilitates internalisation.
What causes hypercholesterolemia? A mutation in the LDL receptor gene.
What is atherosclerosis? A disease of the arteries in which fatty plaques develop on their inner walls, with eventual obstruction of blood flow.
Give an example of when proteins provide defence. Antibodies are proteins that provide defence against infection.
Describe the structure of antibodies. Two identical heavy chains and two identical light chains covalently linked by disulphide bonds.
What is the antigen recognition site? A highly specific and tightly binds to the complementary antigen allowing recognition of foreign proteins by the immune system.
Give an example of when proteins act as biological catalysts. Enzymes are proteins that regulate all biological systems.
What does a lysozyme do? Catalyses the cutting of polysaccharide chains.
How does a lysozyme carry out its function? Binds to polysaccharide chain and catalyzes the cleavage of a specific covalent bond and releases the product.
Give an example of when proteins regulate genes. The Lac repressor is a protein that helps control gene expression.
What is the function of Lac repressor? Controls production (expression) of proteins metabolising lactose in bacteria.
How does the Lac repressor carry out its function? The repressor binds to DNA and prevents expression of the gene in the absence of lactose.
How many amino acids are there? 20.
What do the chemical properties of the R group in an amino acid define? The structure and function of the protein.
What are the basic amino acids? Lysine, Arginine and Histidine.
What are the acidic amino acids? Aspartate and Glutamate.
What are the polar amino acids with uncharged R groups? Serine, Threonine, Asparagine and Glutamine.
What are the hydrophobic amino acids? Alanine, Valine, Isoleucine, Leucine, Methionine, Phenylalanine, Tyrosine and Tryptophan.
Define an acid. Any molecule that tends to release a hydrogen ion.
Define a base. A molecule that readily combines with a hydrogen ion.
What is a main cause of hypercholesterolemia? Mutations in the histidine residues of the LDL-receptor.
What is an example of receptor-mediated endocytosis? The uptake of Low-density Lipoprotein.
Describe the process of the receptor-mediated endocytosis. A reduction in the pH in the endosome causes a change in conformation of the LDL receptor due to the presence of histidine residues within the protein. LDL can no longer bind and is released into the lysosome.
What is a polypeptide? A polymer of amino acids joined by peptide bonds.
What is a peptide bond? A covalent bond formed when the carbon from the carboxylate group shares electrons with the nitrogen atom from the amino group of a second amino acid.
Does a peptide bond permit rotation? No.
What is the definition of the secondary structure? The initial folding pattern (periodic repeats) of the linear polypeptide.
What are the three main types of secondary structure? Alpha-helix, Beta-sheet and Bend/Loop.
What stabilizes the secondary structure? Hydrogen bonds.
What is the structure of the alpha-helix? Right-handed and each turn has 3.6 amino acid residues.
How is the alpha-helix stabilized? By H-bonds between amino and carboxyl groups of every 4th amino acid.
Define a beta-strand. Extended stretches of 5 or more amino acids. Beta-strands are organized next to each other to make Beta-sheets.
What is a parallel beta-sheet? If adjacent strands are orientated in the same direction (N-end to C-end).
What is an anti-parallel beta-sheet? If adjacent strands run opposite to each other.
How is the bend/loop secondary structure formed? Polypeptide chains can fold upon themselves forming a bend or a loop
How many amino acids are usually required for a turn in the bend/loop structure? 4 amino acids.
What amino acid is frequently found in bends/loops? Proline residues.
Created by: robertspedding