PROTEINS

Front

what are proteins

Back

protiens are

1. 1. organic compounds of large molecular mass

2. 2. account for more than 50 percent of dry mass of most cells

3. 3. contain carbon hydrogen oxygen and nitrogen at all times bUT sulfur sometimes

Front

geeral structure of amino acids

Back

amino acids are the basic building blcks of proteins, and 20 amino acids occur commonly in protein, the geneal strcture, has each amino acid has

1. 1. one amino group (-nh2) and one carboxyl group (-cooh) the carbon next to carboxyl group is the alpha carbon

2. 2. each aloha carbon has one hydorgen, one r group, one carboxyl and one amino group bonded to it,

3. 3. all amino acids differ only due to r group--> r group gives each amino acid its uniqueness

Front

formation of polypeptides

Back

1. 1. amino acids join together to form a polypeptide chain. they are joined via peptide bonds

2. 2. a condensation reaction occurs between amino group of one amino acid and carboxyl group of another to form a dipeptide and a peptide bond joins them together. this happens with the elimination of one water molecule

3. 3. dipeptide can be joined to other amino acids via same reaction to form a polypeptide

4. 4. a polypeptide chain is folded into a unique three- dimensional shape this shape is due to the chemical bonds (peptide bonds) that occur between various amino acid residues in the polypeptide chain

5. 5. a polypeptide has an amino end (n terminal) and a carboxyl end (c terminal)

6. 6. n terminal is beginnging, so write sequence n order from there NAD SEQUENCE CHANGEs MOLEUCLE

Front

types of structure of protein

Back

1. 1. a protein moleucle can either be made up of one polypeptide chain folded into a unique 3-d shape which is held by chemical bonds

2. 2. or several polypeptide chains held together by chemical bonds into a unique 3-d shape

Front

primary stage of protein

Back

1. 1. defn: it is the variety, number and sequence of amino acids in a polypeptide chain

2. 2. only chmeical bond involved is the peptide bond

3. 3. the priamry strcutre of a protein is unique- differ from each other in variety, number and sequence of constituent amino acids,

4. 4.the primary structure is cruicial t its properties and functions - a slight change in primary strcuture alters properties drastically

5. 5. for living cells, sequence of amino acids is specified by DNA cond

Front

secondary stage of proteins

Back

defn: it is the localised repetitive folding of the polypeptide chain

1. 1. the secondary structure is stabilised by intramolecula forces ofrattraction, hydrogen bonds, between peptide linkages and polypeptide back bone R groups not involved in bonding

2. 2. three main types :

3. 1. alpha helix: takes form of extended spiral spring, stabilised by hydrogen bonds ocurring between -c=o and - NH group within polypeptide chain

4. 2. beta pleated sheets:

5. two or more regions of the polypeptide chain lie parallel to each other occuring in flat zig zag sheets, intramolecular forces pf attraction between - c=o and -nh groups of one part of the back bone and another on the adjacent part in parallel regions to hold structure together

6. - polypeptide chains may run in same direction (parallel) or opposite direction ( anti parallel)

7. --> fibroin --> high tensile strenth

Front

tertiary structure of protien

Back

defn : tje polypeptide chain folds and bends into a precise, compact globlar three - dimensional shape unique to the protein

1. 1. the shape is held together by FOUR types of intramolecular forces of attraction that occur between the R groups of amino acids at diff regions in the polypeptide chain

2. bonds are: Disulfide, hydrogen, ionic, bonds hydrohphobic interaction

Front

quarternary strcutrue

Back

defn: it is the combination of a number of polypeptide chains and may involve associated non protein groups into a large, complex and functional protein moleucule. each polypeptide chain in such a protein is called a subunit.

1. 1. many complex protein consitis of more than one polypeptide chain, these chains from the quartenray strcuture, the subunits are held together by THE FOUR INTTER MOLECULAR FOA, hydrpgen bonds ipnic bonds hydrophobic interactions and disulfide bonds

Front

functions of preotin

Back

1. 1. homeostatic : soluble proteins in blood plasma act as buffers, stabilising pH

2. 2. enzymatic: All chemical reactions occuring in the cell are catalysed by eznymes(proteins) that speed up rate of reaction

3. 3. hormonal : some prtoteins function as hormones in the body like insulin and glucagons

4. 4. transport : poteins in plasma membreane functino to transport certain substeances in and out of the cell or membreane bound organelle

5. eg lipoproteins transport of cholesterol in blood, haemoglobin transports oxygen in vertebrates

6. 5. storage : ferritin functions to store iron in the liver and myoglobin in skeletal muscle tissues function to store oxygen

7. 6. protection : antibodies fuction as part of immune system and lood clotting actors

8. 7. support/strcutrual : collagen in connective tissues, cartilage, tendons and ligaments, keratin in hair hoofs and feathers

9. 8. soruce f energy : source of energy during extreme starvation when carbs and fats reserves depleted

Front

test for protein

Back

principle: biuret test detects proteins by testing for the presence of peptide bonds. in the presence of dilute copper sulfate in alkaline solution, nitrogen atoms in the peptide chain from a purple compelx with copper 2+ ions

methof: to 2 cm 3 of test sample add equal volume of 5% sodiumhydroxide slution, add two drops of % copper sulfate solution and mix

observe colour chnages:

+: light blue to violet

-ve : remains light blue