b1.2 proteins Flashcards
(20 cards)
what are proteins?
proteins are composed of long chains of recurring monomers called amino acids. each amino acid contains a central alpha carbon linked to an amine group, carboxyl group, variable group, and hydrogen atom.
there are 20 different amino acids which are universal to all living organisms. each type of amino acid differs in the composition of their variable side chain.
how are peptide bonds formed and what are polypeptides?
amino acids can be covalently joined together via condensation reactions to form a dipeptide and water. the bond that is created is called a peptide bond and forms between the amine and carboxyl groups of adjacent amino acids.
long chains of covalently bonded amino acids are called polypeptides and these chains can be broken down via hydrolysis.
what are the different types of amino acid?
amino acids can either be essential, non-essential or conditional according to dietary requirements. essential amino acids cannot be produced by the body and must be present in the diet. non-essential amino acids can be produced by the body and are therefore not required as part of the diet. conditional amino acids can be produced by the body, but at rates lower than certain conditional requirements (ie. they’re essential at certain times only).
how does diet relate to amino acids?
a shortage of one or more essential amino acids in the diet will prevent the production of specific proteins. this is known as protein deficiency malnutrition and health effects will vary depending on the amino acid. certain diets (like vegan) require particular attention to ensure essential amino acids are consumed.
how do r groups in amino acids affect a proteins function?
amino acids in polypeptides will each have a specific side chain. these side chains will have distinct chemical properties and hence cause the protein to fold differently according to its specific position within the polypeptide chain. the way a protein folds plays a critical role in determining its eventual function and level of biological activity.
what functions do proteins have?
structure, hormones, immunity, transport, sensations, movement, enzymes
what is denaturation?
denaturation is a structural change in a protein that results in the loss of its biological properties. because the way a protein folds determines its function, any change of the three dimensional structure will alter its activity.
how does temperature affect denaturation?
high levels of thermal energy may disrupt the hydrogen bonds that hold the protein together. as these bonds are broken, the protein will begin to unfold and lose its capacity to function as intended. temperatures at which proteins denature may vary, but most human proteins function optimally at body temperature.
how does pH affect denaturation?
changing the pH will alter the shape of the protein, which in turn will alter protein solubility and overall shape. all proteins have an optimal pH which is dependent on the environment in which it functions.
what is an r group?
an r group is how each amino acid differs and why amino acid properties differ. the r group gives the basis of diversity in protein function and form. the r group is either hydrophobic or hydrophilic.
what is the primary structure of a protein?
the sequence of amino acids makes up the primary structure of a protein. the precise position of each amino acid within the structure determines the eventual three dimensional shape. the same sequence will always give rise to the same three dimensional shape, meaning that proteins have precise, predictable and repeatable structures.
what is the secondary structure of a protein?
the secondary structure of a protein forms due to pleating and coiling of the amino acid chain. secondary structure is held together by weak hydrogen bonds. the pleating and coiling within a proteins secondary structure can give rise to alpha helices and beta pleated sheets.
what is the tertiary structure of a protein?
a proteins tertiary structure is the complex three dimensional shape that gives proteins a very specific shape that is important for function. folding of the tertiary structure occurs due to interactions between r groups of the amino acids, and interactions between r groups and the surrounding environment.
what interactions between r groups affect tertiary structure?
hydrogen bonds between polar r groups; hydrophobic interactions between non-polar r groups and water (r group faces inwards); covalent bonds between r groups to form disulfide bridges; ionic bonds between positively and negatively charged r groups
what proteins are soluble in water?
proteins with polar amino acids can form structures that are soluble in water. these proteins develop a globular structure.
non-polar amino acids can be found in regions of proteins that do not interact with aqueous solutions.
what is the quaternary structure of a protein?
some proteins have a quaternary structure, meaning that they contain multiple polypeptide chains functioning together as a single protein. the quaternary structure of a protein can be either conjugated (containing non-protein prosthetic groups) or non-conjugated.
what is haemoglobin’s quaternary structure?
haemoglobin has a quaternary structure and is a conjugated protein (4 polypeptide subunits, has a prosthetic haem group).
what are insulin and collagen’s quaternary structures?
insulin and collagen have quaternary structure and are non-conjugated proteins. insulin consists of 2 polypeptide subunits joined by disulfide bridges and collagen is a fibrous protein consisting of 3 polypeptide subunits in a helix shape
what are globular proteins?
roughly circular; irregular and wide range of r groups; physiological function; soluble in water; haemoglobin, enzymes, insulin, immunoglobin
what are fibrous proteins?
long strands; repetitive sequence with a limited range of r groups; structural function; generally insoluble in water; collagen, keratin, myosin, actin, fibrin
