Some proteins are Fibrous proteins. In a fibrous proteins, the polypeptides join together to form long fibres ot sheets. These proteins are strong and insoluble in water. They tend to have structual fuctions for example, which makes human hair.
Haemoglobin is a globular protein. These proteins are roughly spherical or globular shape. They are usually soluble in water and tend to have a biochemical function. For example , enzymes are globualr proteins. Globular proteins are folded so that the hydrophilic R groups are on the outside. This allows them to be soluble in water-based liquids such as blood plasma and cytoplasm.
The tertiary structure of a globular protein is held together mostly by fairly weak bonds, such as hydrogen bonds. This means when the temperature increases, the molecule vibrates more. If the protein vibrates to much, this will break some of the weak bonds and the shape of the molecule will change.when this happens we say the protein has been denatured. Different proteins denature at different temperatures, but most proteins denature at temperatures around 45 degrees.
How PH effects denaturation
Hydrogen bonds depend on very weak attraction between slightly positively charged hydrogen and a slightly negatively charged oxygen in different parts of the protein molecule. Some other bonds called ionic bonds, also depend on tiny charges like this. As a result, these bonds can also be broken if the PH changes.
Haemoglobin molecule is made of four polypeptide chains, each with a haem group attached to it. Haem is a prosthetic group. In the middle of each haem group there is an iron ion, which can be assoiciated with one oxygen molecule. Since haemoglobin has four haem groups, each haemoglobin molecule can carry four oxygen molecules. As the first haem group combines with an oxygen molecule, the shape of the haemoglobin molecule changes slightly. This exposes the next haem, making it easier for it to pick up more oxygen.