Proteins Flashcards
What 4 elements make up amino acids?
Carbon
Oxygen
Hydrogen
Nitrogen
What are the 3 groups found in amino acids?
Carboxyl group (COOH)
R group
Amino group (NH2)
Which is a constant and variable in amino acids?
Amino group - constant
R group - variable
Carboxyl group - constant
What are dipeptides?
When 2 amino acids joined together through a condensation reaction
What bond is formed when 2 amino acids join together?
Peptide bonds
What are polypeptides?
Formed by many amino acids joined together by peptide bonds
Polypeptides = polymers
Amino acids = monomers
What do amino acids form and what do polypeptides form?
Amino acids = polypeptides (chain of amino acids)
Polypeptides = proteins (functioning)
What are the 4 structures proteins have?
Primary structure
Secondary structure
Tertiary structure
Quaternary structure
What is a primary structure?
Number and the sequence of amino acids in a polypeptide chain
What is a secondary structure?
Primary structure of the polypeptide can coil to form 2 structures
Either an alpha helix or a beta-pleated sheet
Describe the structure of the alpha helix
Most common type of secondary structure
Held in a spiral shape by hydrogen bonds
Some fibrous proteins have alpha helices linked to rope-like strands
Examples - keratin and collagen
Describe the structure of the beta pleated sheet
Less common secondary structure
A flat zig-zag structure
Stabilised by hydrogen bonds
Example - protein silk
What is a tertiary structure?
More complex proteins when complete have tertiary structure
Secondary structure folds to give complex three-dimensional shapes
Are globular proteins tertiary structures?
Yes
Examples - enzymes, hormones, plasma and cell membrane proteins
Describe the tertiary structure of a protein
Secondary structure is folded
Held in a specific 3D shape by bonds and interactions
Form between R groups of some of the amino acids in the polypeptide chain
What bonds and interactions are present in tertiary structures?
Hydrogen bonds - form between O & OH
Ionic bonds - form between oppositely charged R groups
Disulphide bridges - form between S atoms (e.g. in cysteine)
Hydrophobic R groups interactions - on the inside of the protein
Hydrophilic R groups - on the outside of the protein
What is a quaternary structure?
Occurs when more than 1 polypeptide chain, each with a tertiary structure, combine to form a larger protein complex
Describe the quaternary structure of a protein
Tertiary structures are joined together by bonds similar to those within the tertiary structures themselves
Ionic, hydrogen, disulphide and hydrophobic interactions
Quaternary proteins are sometimes associated with non-protein groups called prosthetic groups
What is an example of quaternary protein?
Haemoglobin
Protein that carries oxygen in mammalian blood
Made of 4 polypeptide chains each with a tertiary structure
What non-protein components does haemoglobin contain?
Haem group
These contain iron (Fe2+)
What bonds and interactions do quaternary structures have?
Ionic
Hydrogen
Disulphide
Peptide
What are the 2 groups proteins can be classified into?
Fibrous proteins
Globular proteins
What are fibrous proteins?
Carry out structural functions
What are some examples of fibrous proteins?
Keratin - found in hair and nails
Collagen - found in connective tissue and the skin
