7.5 proteins
TRANSCRIPT
7.5 Proteins
Topic 7 Nucleic Acids & Proteins
7.5.1 Explain the four levels of protein structure, indicating the significance of each level.
(Quaternary structure may involve the binding of a prosthetic group to form a conjugated protein)
7.5.2 Outline the difference between fibrous and globular proteins, with reference to two examples of each type.
7.5.3 Explain the significance of polar and non-polar amino acids.
(Limit this to controlling the position of proteins in membranes, creating hydrophilic channels through membranes, and the specificity of active sites in enzymes)
7.5.4 State four functions of proteins, giving a named example
of each. (Membrane proteins should not be included)
Protein Structure Proteins have a complex structure. They are built up from amino acids. The sequence of amino acids will determine its shape and
ultimately its function. We can define four levels of structure in proteins:
Primary structure Secondary structure Tertiary structure Quaternary structure
Protein Structure Primary Structure:
Is the linear sequence of amino acids in a protein.
The amino acids are held together by peptide linkages - covalent bonds.
Bonding involved Covalent bonds between amino
acids – peptide bonds (linkages).
Protein Structure Secondary Structure:
These are regularly repeating structures.
These include -helix and -pleated sheets. -helix: where the polypeptide
chain is wound into a helix. -pleated sheets:
Bonding involved: Hydrogen bonding between
different amino acids in helix or pleated sheets.
Protein Structure Tertiary Structure:
Results in the overall three-dimensional shape of the protein
Can form either globular or fibrous proteins.
3D shape determines its functions. Bonding involved includes:
Covalent bonding – disulfide bridges Hydrogen bonding Ionic bonding Hydrophobic interactions
Protein Structure Quaternary Structure:
Is when two or more polypeptide chains are linked together.
Bonding involved includes: Covalent bonding – disulfide bridges Hydrogen bonding Ionic bonding Hydrophobic interactions
Shape of Proteins Proteins can be divided into two types according to their
shape: Fibrous
Have a long and narrow shape. Are mostly insoluble in water. eg: keratin, collagen
Globular Have a rounded shape. Are mostly soluble in water. eg: enzymes, antibodies
Polar & Non-polar Groups Amino acids can be divided into two types according to
the chemical characteristics of their R groups:
Polar amino acids have hydrophilic R groups. (12) Non-polar amino acids have hydrophobic R groups. (8) The distribution of polar and non-polar amino acids in a
protein influence where the protein is located in a cell and what function it can carry out.
Amine group
Carboxyl group
Polar & Non-polar Groups
Protein Functions Proteins have a huge range
Enzymes
eg: catalase Structural.
eg: collagen Transport.
eg: haemoglobin
of functions:
Movement. eg: myosin
Hormones eg: insulin
Defence. eg: immunoglobulin
7.5.1 Explain the four levels of protein structure, indicating the significance of each level.
(Quaternary structure may involve the binding of a prosthetic group to form a conjugated protein)
7.5.2 Outline the difference between fibrous and globular proteins, with reference to two examples of each type.
7.5.3 Explain the significance of polar and non-polar amino acids.
(Limit this to controlling the position of proteins in membranes, creating hydrophilic channels through membranes, and the specificity of active sites in enzymes)
7.5.4 State four functions of proteins, giving a named example
of each. (Membrane proteins should not be included)