TOPIC 5 PROTEINS

What are proteins?

1. Proteins are macromolecules made up of many small monomer units called amino acids,

2. Joined by condensation reactions.

What groups are contained in the general formula of amino acids?

1. An amino group (-NH2)

2. A carboxyl group (-COOH)

3. Attached to a carbon atom (-C-H)

4. And to an R group that varies between amino acids

What role do the R groups play in the structure of the amino acid?

1. The R group is not involved in the reactions which join the amino acids together,

2. But the structure of the R group does affect the way the amino acids interact with others within the protein molecule.

3. This will mainly depend on whether the R group is polar or not. This will affect the tertiary structure of the protein.

How do amino acids join and what bond is formed?

1. Amino acids join by a condensation reaction. An OH from the carboxyl group and an H from the amino group of another amino acid form an H2O molecule,

2. A peptide bond is formed there and a dipeptide is the result.

3. The R group is not involved in this reaction.

What other bonds are there in proteins asides from the peptide bond?

1. Hydrogen bond, disulfide bond and ionic bonds.

2. These bonds are dependent on the atoms in the R groups.

How are there hydrogen bonds present in amino acids?

1. There is a small partial negative charge on the present on the Oxygen of the carboxyl group and a tiny partial positive charge on the Hydrogen of the amino groups.

2. When these charged groups are close to each other, the opposite charges attract, forming a hydrogen bonds.

How do the hydrogen bonds between polypeptide chains affect the protein structure?

1. The hydrogen bonds may be weak, but they can be made between any two amino acids in the correct position.

2. There are many of them holding the protein together very firmly. They are very important in the folding and coiling of polypeptide chains.

3. Hydrogen bonds break easily and reform if pH or temperature change.

How does a disulphide bond form ?

1. Disulfide bonds form when two cysteine (CH2-SH) molecules are close together in the structure of polypeptid.

2. An oxidation reaction occurs between the two sulfur-containing groups.

3. Resulting in a strong bond called disulfide bonds.

What is the role of disulfide bonds between polypeptide chains?

1. These disulfide bonds are much stronger than hydrogen bonds but they happen much less often.

2. They are important for holding the folded polypeptide chains in place.

How do ionic bonds in proteins form?

1. Ionic bonds are formed between some of the strongly positive and strongly negative amino acid side chains which are sometimes found deep inside the protein molecules.

2. They are strong bonds, but they are not as common as other structural bonds.

Describe what happens to the bonds in your hair when they are restyled.

1. Hair is made of keratin.

2. Blow drying or straightening hair breaks the hydrogen bonds and temporarily reforms the

3. With the hair curling a different way until the hydrogen bonds reform.

How does perming change hair for a long period?

1. Perming breaks the disulfide bonds between the polypeptide chains and reforms them at a different place.

What is the primary structure of proteins?

1. It is the sequence of amino acids that make up the polypeptide chains, held together by peptide bonds.

What is the secondary structure of proteins?

1. The secondary structure of protein is the arrangement of the polypeptide chains and into a regular 3D structure, held together by hydrogen bonds.

2. Alpha-helix, a spiral coil with peptide bonds forming the backbone and the R groups protruding in all directions.

3. Beta-pleated sheet, in which the polypeptide chain folds into regular pleats led together by hydrogen bonds between the amino and carboxyl ends of the amino acids.

4. Most fibrous proteins have this type of structure.

What is a tertiary structure of a protein?

1. It is another level of 3D organization in addition to the secondary structure.

2. How alpha-helixes and beta-pleated sheets interact with each other.

3. The amino acid is folded into more complex shapes.

4. Hydrogen bonds, disulphide bonds and ionic bonds help hold it together.

What is the quaternary structure of proteins?

1. Is the 3D arrangement of more than on polypeptide chain.

What is denaturation?

1. It is when the bonds in the proteins break, resulting in a change in protein shape.

2. It could be caused by a change in temperature or pH.

What characteristics do fibrous proteins have?

1. Little to no tertiary structure.

2. Long, parallel polypeptide chains with occasional cross-linkages that form into fibers.

3. Insoluble in water and very tough.

Where in the body do fibrous proteins appear?

1. Tendons, matrix of bones, keratin in hair.

Collagen is a fibrous protein, why is it strong?

1. It’s quarternary structure has 3 polypeptide chains, each up to 1000 amino acids long.

2. The primary structure of these chains is repeating sequences of glycine with two other amino acids—- often proline and hydroxyproline.

3. The 3 polypeptide chains are arranged in a unique triple helix, held together by a very large number of hydrogen bonds..

What traits do globular proteins have ?

1. They have complex tertiary and sometimes quarternary structures.

2. They fold into globular shapes.

3. Some R groups on globular proteins are hydrophobic, they are usually found on the inside of globular proteins.

4. Some R groups on globular proteins are hydrophilic, they are usually found on the outside of globular proteins.

What is a colloid?

1. A colloid is when the microscopic particles of one substance are suspended throughout another substance.

2. They do not settle, and they cannot be separated easily.

Why do globular proteins form colloids?

1. Even though the carboxyl and amino ends give them ionic properties,

2. The globular proteins are so big, that they form colloids instead.

What are examples of globular proteins forming colloids?

1. Globular proteins are important as they hold molecules in position in the cytoplasm.

2. Antibodies are globular proteins, enzymes and some horomones are globular proteins and help maintain the structure of the cytoplasm.

Haemoglobin?

1. Very large molecule with 574 amino acids arranged in four polypeptide chains,

2. Which are connected by disulphide bonds.

3. Each polypeptide chain surrounds an iron-containing haem group.

4. The iron enables haemoglobin to bind and release oxygen molecules,

5. And the arrangement of the polypeptide chains determines how easily the oxygen is bind or release.

What are conjugated proteins?

1. Protein molecules that are joined with another molecule called a prosthetic group.

List some examples of conjugated proteins.

1. Haemoglobin is a conjugated protein, the iron is the prosthetic group.

2. Lipoproteins are formed when proteins are conjugated with lipids.

What are glycoproteins?

1. Are proteins with carbohydrate prosthetic group.

2. The carbohydrate part of the molecule helps them to hold a lot of water.

3. It makes it hard for protein digesting enzymes to break them down.

What are the two main lipoproteins in your blood?

1. Low-density lipoproteins

2. High-density lipoproteins

How do the sequence of amino acids affect the protein formed?

1. The structure of a protein is determined by a variety of bonds between amino acids within polypeptide chains.

2. Different amino acids can form different weaker bonds with other amino acids.

3. These bonds determine the secondary, tertiary and quarternary structure of the protein.

Hydrogen bonds are weaker than disulphide bonds and ionic bonds, but they are more important in maintaining protein structure. Why?

1. There are many more hydrogen bonds because they can form between any two amino acid.

With reference to proteins, explain the importance of constant internal conditions.

1. The 3-dimensional shape of proteins is important for there function,

2. Weak bonds in between amino acids create the shape of the protein.

3. These bonds may be affected by a change in the internal environment of the body.