Proteins

Question 1

What are proteins made out of?

Answer 1

All proteins contain hydrogen, carbon, oxygen and nitrogen; but some (like cystine) also contain sulfur.

Question 2

What functions do proteins have?

Answer 2

1. They make up structural components.
2. They are membrane carriers and pores.
3. They make up all enzymes.
4. They make up many hormones.
5. They make up all antibodies.

Question 3

What are proteins (chemically)?

Answer 3

They are polymers; a long chemical chain created by the bonding of smaller subunits called monomers.

Question 4

What are the monomers of proteins?

Answer 4

Amino acids.

Question 5

What is the basic structure of amino acids?

Answer 5

They all have a central carbon bonded onto an amino group, a carboxyl group, and a hydrogen. The R- groups are what makes proteins different from each other.

Question 6

What are R- groups?

Answer 6

R- groups are structural parts of the protein that determine the function of the protein. They can be larger than the backbone itself and have a wide range of chemical properties.

Question 7

Amino acids in plants.

Answer 7

Plants can make their own amino acids using the nitrates in soil and products of photosynthesis.

Question 8

Amino acids in animals.

Answer 8

Animals can make about half the amino they require. The other half comes from their diet. These are called ‘essential amino acids’.

Question 9

What is deamination?

Answer 9

The process of removing the amino group from an amino acid when there is a surplus in the body since amino group buildup can be toxic.

Question 10

How are polypeptides formed?

Answer 10

A condensation reaction between the amino group of one amino acid and the carboxyl group of another joins the two amino acids together with a peptide bond. The free amino group and carboxyl group on each end of the dipeptide can then bond onto other amino acids. The process continues, forming a polypeptide chain.

Question 11

Where are proteins made?

Answer 11

In the ribosome, when mRNA molecules are threaded through and amino acids are joined together one by one in order to form the right sequence.

Question 12

What is the primary structure of a protein?

Answer 12

The unique sequence of amino acids joined together with peptide bonds to form polypeptide chains.

Question 13

How are proteins broken down and rebuilt?

Answer 13

They are broken down and rebuilt with enzymes called protease that catalyse the breaking of peptide bonds.

Question 14

What is the secondary structure of protein?

Answer 14

The initial coiling of parts of a polypeptide chain to form an alpha helix or beta pleated sheet. These structures are held together by hydrogen bonds between the peptide backbones of the amino acids. Although hydrogen bonds are relatively weak, lots of them are formed which makes the overall secondary structure strong.

Question 15

What is the tertiary structure of protein?

Answer 15

Further of the polypeptide chain into a final three dimensional structure. The specific structures are decided by the primary structures of different proteins. The tertiary structure is held in place by a range of different bonds including hydrogen bonds, ionic bonds, disulfide bonds and hydrophobic/ hydrophilic interactions.

Question 16

What is the quaternary structure of protein?

Answer 16

Some proteins are made of more than one polypeptide chain joined together, or a polypeptide chain and an inorganic compound joined together.

Question 17

Haemoglobin as a globular protein.

Answer 17

Haemoglobin is a globular protein. It’s tertiary structure consists of polypeptide chains tightly folded into a globular shape. The fact that haemoglobin in a globular protein means that it is soluble in water and thus can be carried transported easily around the body in the blood. The globular structure also means that the protein has folded in to a very specific shape. This shape is very important as it is the optimum shape for haemoglobin to carry oxygen. It’s quaternary structure consists of four polypeptide chains joined together, each bonded to a haem group. The haem group is an inorganic compound and is thus called a prosthetic group. These groups are responsible for haemoglobin’s ability to carry oxygen. The presence of prosthetic groups makes haemoglobin a conjugated protein.

Question 18

Collagen as a fibrous protein.

Answer 18

Collagen is a fibrous protein. more than 35% of it’s primary structure consists of glycine, which is the smallest and simplest amino acid. This means that a collagen polypeptide can be wound very tightly in a left handed helical structure in its secondary structure which makes one polypeptide quite strong initially. However, collagen is made stronger when three collagen polypeptides wrap around each other to form a collagen molecule. The molecule is thicker than a single polypeptide so it is stronger. However, the collagen molecules then form cross links between each other in an alternating pattern to eliminate lines of weakness in a collagen fibril. These cross links are covalent and thus are quite strong.

Question 19

Similarities between haemoglobin and collagen.

Answer 19

1. They all have a primary structure. They both have a unique sequence of amino acids.
2. They both contain helical structures.
3. They both have a quaternary structure. They’re both made of more than on amino acid.

Question 20

Differences between haemoglobin and collagen.

Answer 20

Location:
Haemoglobin is found in blood whereas collagen is found in all structural entities.
Solubility:
Haemoglobin is soluble in water whereas collagen is insoluble in water.
Primary structure:
Haemoglobin is made of a range of different amino acids whereas collagen is 35% glycine.
Secondary structure:
Haemoglobin is coiled into alpha helix regions and beta pleated sheet regions.
Tertiary structure:
Haemoglobin undergos further coiling into a globular shape. This is essential for the function of carrying oxygen.
Quaternary structure:
Haemoglobin is made out of four polypeptide chains of two types. Two alpha chains and two beta chains. Each polypeptide chain is also bonded to a prosthetic haem group which allows haemoglobin to carry oxygen.Collagen is made out of strands of one type of polypeptide chain with cross links between them, this makes it strong and tough.