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
Describe the structure of fibrous proteins
Collagen is made up of 3 alpha helix polypeptide chains twisted into rope-like strands
Held together by hydrogen bonds
What are the properties of fibrous proteins?
Tough
Non-specific
Insoluble (held by hydrogen bonds)
What are globular proteins?
Can be tertiary proteins
Can be quaternary proteins
What are some examples of globular proteins?
Enzymes
Antibodies
Plasma
Proteins
Hormones
Haemoglobin
What are the properties of globular proteins?
Compact and folded into spherical molecules
Have a specific shape
Soluble in water
