Proteins

Is proteins present in protoplasm???

Proteins are always present in protoplasm. Their molecules are the largest and most complicated of all the food substances.

Why is Amino acids the building block of protein???Every protein molecules is built up from simpler

compounds known as amino acid. A amino acid is made up of an amino group (-NH2), an acidic group (-COOH) and a side chain (donated by R). the general formula for an amino acid can be written as:

Links• Amino acids link up to form

polypeptides.• Two amino acid may link up in

condensation reaction. The bond formed between the two amino acids is strong and is called a peptide bond.

• Many amino acids linked up by peptide bonds form a polypeptide or peptone.

TAKE NOTE OF THIS!!!• In most proteins, the chains are coiled

or folded, giving the protein a more complex, three- dimensional shape. The coils are held in place by weak bonds. These weak bonds are easily broken by heat and chemicals such as acids, and alkalis. When these bonds are broken, the protein loses its three-dimensional shape. We say the protein has been denatured. Denaturation usually involves a loss of function of the protein.

Why must protein be broken down???• Animals cannot directly absorb the

proteins it takes in, because protein molecules are too large to pass through living cell surface membranes.

• These protein molecules must be broken down by enzymes during digestion.

AMINO ACIDS IN ANIMALS!

• Amino acids are simpler and much smaller molecules than proteins. They are soluble in water and are small enough to diffuse through living membrane. Hence, they can easily be absorbed into an animal’s body.

• When amino acids enter the body cells, they are linked up again to form the protein need by the animal.

WHERE CAN WE FOUND PROTEINS??

• Proteins can be found in both animals and plants foods. Milk, eggs, seafood and meat such as chicken and lean beef are some animal foods rich in proteins. Plant foods rich in proteins include soya. Beans, nuts, grains, and vegetables such as French beans.

What are the functions of proteins??

• Proteins are used: In the synthesis of new

protoplasm, for growth and repair of worn-out body cell;

In the synthesis of enzymes and some hormones; and

In the formation of antibodies to combat disease.

Effects of protein deficiency!

• The average adult human being needs 50-100g of proteins a day. Children who do not get enough protein may end up with a protein deficiency disease (disease caused by lack of proteins) called KWASHIORKOR. Such children usually have:

Swollen stomachs. Their skins crack and become scaly.

BIURET EXPERIMENT

Introduction:

• Biuret solution is a blue solution made up of sodium hydroxide and copper (II) sulphate. It turns violent (deep purple) when the proteins are present and turns pink when short-chain polypeptides are present.

•To detect the presence of peptide bonds in molecule.

MATERIALS• Test tubes• Test tube rack• Egg white• Beaker• 10% Sodium

Hydroxide(NaOH)• 0.5% Copper

Sulfate(CuSO4)

Procedure:

• Add 1 cm3 of sodium hydroxide solution ( 40% or bench solution) to 2cm3 of egg white solution in a test tube and shake it thoroughly.

• Add 1% copper (II) sulphate solution, drop by drop, shaking after every drop. (Alternatively, to 20cm3 of egg white solution add an equal volume of biuret solution. Shake well and allow the mixture to stand for 5 minutes). What color do you observed?