Primary structure
Jan 18, 2016
Proteins• Proteins contain Carbon (C), Hydrogen (H), Oxygen,
Nitrogen (N) and sometimes Sulphur (S)
• The monomer units of proteins are called Amino Acids
• Single Amino Acids can be joined together by a Peptide bond to form a Dipeptide
• Long chains of amino acids are called Polypeptides
• Proteins are formed by one or more polypeptides.
Secondary structure
• Hydrogen bonds form because O has a weak negative charge and H has a weak positive charge……if they get close then a Hydrogen bond (a H bond) forms.
• Individually hydrogen bonds are weak, but because the molecule has A LOT of them, collectively they are strong
Tertiary structure The Tertiary structure of a protein is held
together by 3 different types of bonding:
1) Hydrogen bonding between R groups.
2) Ionic bonding (between positively and negatively charged R groups).
3) Disulphide bonds (between R groups containing sulphur)
GLOBULAR PROTEINS
• Their overall tertiary structure (3d shape) is important for their function
• They may contain more than one type of secondary structure
Characteristics of Globular Proteins:
• They are soluble
• Their function depends on their overall shape – the protein will fit other molecules with a specific complementary shape.
Good Examples of Globular Proteins:
• Enzymes, Receptor proteins on membranes, Channel proteins and Carrier proteins in membranes, Cell recognition proteins.
REMEMBER
• THE FUNCTION OF ALL PROTEINS DEPENDS ON THEIR SHAPE.
• THIS IS DETERMINED BY THE ORDER OF AMINO ACIDS IN THE PRIMARY STRUCTURE.
Write this & don’t forget it!• It is the primary structure of a protein (the
sequence of amino acids) that determines what its overall shape will be.
• Any change in the sequence of these amino acids may change the position of the hydrogen/ionic/disulphide bonds that hold the tertiary structure together.
• This may then have the effect of changing the tertiary shape of the protein, so that…..
• …..now the protein can no longer function!
FIBROUS PROTEINS
• Secondary structure can be α helix or β pleated sheet
• There may be several polypeptide strands associated together and with H bonding between them.
CHARACTERISTICS
• Insoluble.
• Tough fibres and strong, flexible sheets.
• eg Keratin (in hair and nails), Collagen (in skin, tendons, bones, teeth), spider web silk.
Collagen - A fibrous protein
• ¼ of all of the protein in the human body is collagen
• Collagen is a major structural protein, that strengthens tendons and supports the skin and internal organs
• Bones and teeth are formed from collagen bonded to other minerals
Collagen - A fibrous protein• Collagen is composed of three chains,
wound together in a tight triple helix
• Each chain is 1000+ amino acids long (only 20 are shown on the next slide)
• A repeated sequence of three amino acids forms this sturdy structure (every third amino acid is glycine