General properties of proteins Flashcards
What are amino acids?
The monomers from which proteins are made
How are dipeptides formed?
The condensation of two amino acids
How are polypeptides formed?
By the condensation of many amino acids
What are the four stages of the structure in proteins?
- primary structure
- secondary structure
- tertiary structure
- quaternary structure
Describe the primary structure of proteins
- many amino acids join together via a condensation reaction through a process known as polymerisation
- The resulting chain of many hundreds of amino acids is called a polypeptide
- polypeptide chains form the primary structure of the protein
Describe the secondary structure of proteins
- carboxyl group from one amino acid bonds onto the amino group of the amino acids, forming peptide bonds and polypeptide
- the two groups form hydrogen bonds
- causing the polypeptide chain to be twisted into a S-D shape forming an alpha helix or folded into a beta pleated sheet
Describe the tertiary structure of a protein
- alpha helices of secondary protein structure can be twisted and folded even more to give the protein a more specific and 3-D shape
- the structure is maintained by a number of different bonds:
Disulfide bridges (strongest) , ionic bonds (strong but not as strong as disulfide bridges) and hydrogen bonds (weakest)
Describe the quaternary structure of proteins
- many polypeptide chains bonding together
- large proteins often form complex molecules
- may be non-protein (prosthetic) groups associated with molecules
Describe the structure and properties of fibrous proteins
Little or no tertiary structure
Long parallel polypeptide chains
Cross linkages at intervals forming long fibres or sheets
Usually insoluble
Many have structural roles
e.g. keratin in hair and the outer layer of skin, collagen (a connective tissue)
Describe the structure and properties of globular proteins
Have complex tertiary and sometimes quaternary structures
Folded into spherical (globular) shapes
Usually soluble as hydrophobic side chains in centre of structure
roles in metabolic reactions
e.g. enzymes, haemoglobin in blood
Is haemoglobin a fibrous or globular protein
Globular protein
Is collagen a globular or fibrous protein?
Fibrous
Describe the solubility of haemoglobin
Outward pointing hydrophilic side chains maintain solubility
Describe the solubility of collagen
Usually insoluble
Describe the prosthetic group of haemoglobin
- each polypeptide chain contains a haem group
- haem group is a prosthetic group
i.e. an important permanent part of a protein molecule - not made up of amino acids - when combined with 4 polypeptide chain it forms conjugated protein
Describe the prosthetic group of collagen
Made up of three polypeptide bonds
Describe the structure of haemoglobin including the number of chains and the way they are twisted
- made up of 4 polypeptide chains
- 2 identical alpha chains and 2 identical beta chains
- nearly spherical - hydrophilic side chains point inwards
- outward pointing hydrophilic side chains
Describing the structure of collagen and the number of chains and the way they are twisted
- each of the three chains is a coil made up of 1000 amino acids
- H bonds form between chains giving strength
- made of 3 polypeptide chains, each in shape of a helix
Describe the function of haemoglobin in the body including details about how its structure helps its function
- haem group has an iron ion at its centre
- the iron combines with oxygen at high oxygen concentrations
- and releases oxygen at low concentrations
- one haemoglobin molecule can carry 4 oxygen molecules
- colour is bright red when combined with oxygen/ purplish if not
Describe the function of collagen in the body including details about how its structure helps its function
- walls of arteries prevents arteries bursting under high pressure
- tendons connect muscle to bones
- bones formed from collagen reinforced with other materials
e.g. calcium phosphate to make them hard - cartilage
- cosmetic treatment
Describe the type of bonds in collagen which support the tertiary structure
Each collagen molecule forms covalent bonds called cross-links
State what the major amino acid is in collagen and the reason for it
- Each polypeptide chain contains 1000 amino acids - every third amino acid is glycine (the smallest amoni acid)
- glycine allows the 3 polypeptides to lie closer together to form a tight coil (any other amino acids would be too big)