Option C1

C.1.1: Proteins: Four levels of structure

Proteins are the most abundant organic molecules in the living cell. All proteins are made up of amino acids and it is the linear arrangement of these amino acids into chains which composes the primary (or first level) structure. The primary structure determines the three-dimensional shape of a protein, which may consist of one to or several polypeptide chainseither covalently linked or held together by weak bonds. Secondary (or second level) structure refers to the regular patterns of coils or folds of a polypeptide chain demonstrated in Figure 2 below. Tertiary (or third level) structure refers from the folding of the chain to produce globular or fibrous-like molecules while quaternary (or fourth level) structure results from the joining of two or more polypeptide chains.

Figure 1 - Four levels of proteins

Protein Structure

C.1.2: Globular or Fibrous?

Figure 2 - Globular and fibrous protein structure

Plasma Membrane Structure

Compare the structures of the globular and fibrous proteins

Use Figure 2 above to compare the structure of a globular protein to a fibrous protein. Click on "Show comparison of globular and fibrous proteins" for answer.

Show comparison of globular and fibrous proteins | Hide comparison of globular and fibrous proteins
Globular and Fibrous Comparison

C.1.3: Polar vs Non-polar ammino acids

Amino acids are grouped according to the R-groups (sidechains) present. The presence of charge, polarity and hydrophobicity help in the formation of bonds and the and the stabilization of the protein core. Figure 1 explains the significance of polar and nonpolar amino acids in protein structure.

Figure 3 - Significance of polar and non-polar amino acids

Polar and Non-polar amino acids

C.1.4: Four functions of proteins

Type Example Function
Enzymes Pepsin Help break down proteins.
Storage Myoglobin Oxygen storage in muscles.
Hormones Insulin Regulates glucose metabolism.
Protective Antibodies Forms complexes with foreign proteins.
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