Proteins Flashcards
Proteins always contain
-nitrogen
-carbon
-hydrogen
-oxygen
Many proteins may also contain
-sulphur and phorphorus
How are proteins made
-polymers made out of monomers called amino acids
Chain of amino acids is called
polypeptides
how many different amino acids are used to make up proteins
20
basic structure of amino acids
-an amino group (-NH2) at one end
-carboxyl group at the other end (COOH)
-hydrogen atom
-R group (different in each amino acid)
at ph7 the amino acid has what
-positive and negative charge
Name for an amino acid that has a positive and negative group
Zwitterion
What are linear sequences of amino acids
proteins
How is a peptide bond formed
-amino group of one amino acid reacts with the carboxyl group of another and eliminates water (condensation)
-bond between them is the peptide bond
-resulting compound is a dipeptide
How many amino acids is a polypeptide chain made of?
-polypeptide chains can have up to 20 amino acids
Primary structure is determined by
-base sequence on one strand of the DNA molecule
Secondary structure
-shape the polypeptide chain forms as a result of hydrogen bonding
-twisted into 3d shape
-spiral shape - alpha helix
-beta pleated sheet is another form
Keratin proteins
-high proportion of alpha helix and the protein fibroin
Silk has a high proportion of
-beta pleated sheet
Tertiary structure
-the alpha helix of secondary protein folded and twisted to give complex compact 3d structure
The tertiary structure is maintained by
-hydrogen bonds
-ionic bonds
-disulphide bonds
-hydrophobic interactions
what bonds are important in giving globular proteins
-hydrogen
-disulphide
-ionic
Quaternary structure
-some polypeptides are not functional unless combined
-can be associated with non-protein groups and form large, complex molecules like haemoglobin
Fibrous proteins
-long, thin shape
-insoluble in water so they have structural functions in bones
-polypeptides are in parallel chains or sheets with many cross linkages forming long fibres (keratin-hair)
-strong, tough
Collagen is needed in
-tendons because they provide strength and the toughness needed
A single fibre is normally called a
-tropocollagen that consists of 3 identical polypeptide chains twisted around each other like a rope
-3 are linked by hydrogen bonds, stable
Globular proteins are
-compacted and folded into spherical molecules which makes them insoluble in water
Functions of globular proteins
-enzyme antibodies
-plasma, proteins and hormones
Haemoglobin consists of
-four folded polypeptide chains at the centre of each is an iron containing group - haem
Test for proteins
-few drops of biuret reagent is added
-if protein is present colour change from blue -> purple
-more concentrated the proteins the darker the colour
