Proteins Flashcards
(16 cards)
What is a gene
-A gene is a specific sequence of bases on a DNA molecule that codes for a sequence of amino acids in a polypeptide chain
Structure of amino acids
-Amino acids contain an amine group and a carboxyl group, both of which stay the same in every different type of amino acid
-Amino acids also contain an “R” group, which changes in every type of amino acid
Amino acids contain these elements
-Oxygen
-Hydrogen
-Nitrogen
-Carbon
-Some amino acid’s contain sulfur
Peptide bond
-When two amino acids chemically react together, they form a peptide bond
-This is a condensation reaction, as a molecule of water is produced
-Two molecules of amino acids joined by a peptide bond is called a dipeptide, and this reaction happens in the ribosome during translation
-In order to break the peptide bond, we can add water, using a hydrolysis reaction which is carried out by the enzyme protease in the digestive system
Polypeptide
-When three or more amino acids are chemically joined by peptide bonds, we call this a polypeptide
-Polypeptides are often made up of hundreds of amino acids
Difference between polypeptide and protein
-In order to be considered a protein, a polypeptide must fold into a specific 3D shape
-Once the polypeptide has folded into the correct shape, it can then carry out its function
-Then it will be considered a protein
Primary structure
-Primary structure of a protein is the sequence of amino acids in a polypeptide chain
-This sequence is determined by the gene (specific sequence of bases in DNA)
-the primary structure is held together by peptide bonds between amino acids
WHY THE PRIMARY STRUCTURE IS IMPORTANT
-Primary structure is important as the order of amino acids in a polypeptide chain determines how the protein will fold and therefore it’s final 3D shape and function
Bonds in 3D structure of proteins
-As the polypeptide folds, there are different types of bonds that form between R groups of amino acids:
-Hydrogen bonds form between polar R groups
-Ionic bonds form between oppositely charged R groups
-Disulfide bridges are strong covalent bonds that form between two cysteine amino acids (contain sulfur)
-These interactions give the protein it’s secondary, tertiary, and sometimes quaternary structure
Secondary structure
-Secondary structure is the local folding of the polypeptide chain
-It can form alpha helices and beta pleated sheets
-Secondary structures are held together by hydrogen bonds and can help to determine the overall shape and function of a protein
Tertiary structure
-Tertiary structure is the final 3D shape of the protein
-Tertiary structures are a result of further folding of secondary structures
-Tertiary structures determine the overall function of the protein
-Tertiary structure is stabilised by hydrogen bonds, ionic bonds , disulfide bridges (with amino acids contain sulfur) and hydrophobic interactions
Quaternary structure
-Quaternary structure (some proteins) are more than one polypeptide chain joined together
Fibrous proteins function and structure
-Fibrous proteins often have structural roles due to it’s stable and strong structure
-It’s insolubility also means that it will not dissolve in tissue fluids
STRUCTURE
-Fibrous proteins are long polypeptide chains that intertwine to form a rope or fiber
-Fibrous proteins mostly form secondary structure (often alpha helices or triple helix)
-Fibrous proteins have a large number of hydrophobic R groups, which makes them insoluble in water
-Repeating amino acid sequences allow tight packing
-The chains are held together my multiple hydrogen bonds and covalent cross linkages, making their structure very strong
Collagen as a fibrous protein
-Collage is an example of a fibrous protein and is found in skin, bones, ligaments and tendons
-Collagen is comprised of three polypeptide chains intertwined to form a triple helix shape
-Many hydrogen bonds and covalent cross-linkages hold the chains together, which maintains it’s strong structure
-Additionally, repeating amino acid sequences allow tight packing
-Collagen has structural roles due to its stable and strong structure
-Collagen is also insoluble, which means that it does not dissolve in tissue fluid, making it ideal for structural roles
Globular proteins function and structure
-Globular proteins are involved in metabolic roles e.g oxygen transport
STRUCTURE
-Globular proteins are spherical
-Globular proteins have hydrophilic R groups on their surface, and has hydrophobic R groups in their centre to stabilise structure
-These hydrophilic R groups means that globular proteins are soluble in water
-Globular proteins often have prosthetic groups
Haemoglobin as a globular protein
-Haemoglobin is a globular protein (quaternary structure) with four subunits (2x alpha subunits and 2x beta subunits)
-Haemoglobin reversibly binds to oxygen in the lungs and releases the oxygen to body tissues
-Each subunit has a prosthetic “haem” group and each “haem” group has an FE2+ ion
-This is where the oxygen molecule attaches, meaning that four oxygen molecules can bind to one haemoglobin molecule at one time
Basic differences between globular and fibrous proteins
SHAPE
-Fibrous proteins have a long and rope-like shape
-Globular proteins have a spherical and compact shape
SOLUBILITY
-Fibrous proteins are insoluble (large number of hydrophobic R groups)
-Globular proteins are soluble (hydrophillic R groups on the surface of the protein)
BONDING
-Fibrous proteins have hydrogen bonds and covalent cross-links
-Globular proteins have hydrogen bonds, ionic bonds, and disulfide bonds
STABILITY
-Fibrous proteins are very stable
-Globular proteins are less stable
