proteins Flashcards
Proteins are the most complex and most diverse group of biological compounds. They have an astonishing range of different functions. Give some examples. Say 5.
1.structure e.g. collagen (bone, cartilage)keratin (hair), actin (muscle)2.enzymes e.g. amylase, pepsin, catalase, 3. transport e.g. haemoglobin (oxygen), transferrin (iron)4.pumps e.g. Na+K+ pump in cell membranes5. motors e.g. myosin (muscle), kinesin (cilia)6.hormones e.g. insulin, glucagon7.receptors e.g. rhodopsin (light receptor in retina)
and another 5
antibodies e.g. immunoglobulinsstorage e.g. albumins in eggs and blood, caesin in milkblood clotting e.g. thrombin, fibrinlubrication e.g. glycoproteins in synovial fluidtoxins e.g. diphtheria toxinantifreeze e.g. glycoproteins in arctic flea
Proteins are made of ____________which are made of the five elements
amino acidsC H O N and sometimes S
There is a central carbon atom called
the “alpha carbon”
what four different chemical groups are attached to it?
a hydrogen atoma basic amino groupan acidic carboxyl groupa variable “R” group (or side chain)There are 20 different R groups, and so 20 different amino acids
Amino acids are so-called because they have both amino groups and acid groups, which have opposite charges. At neutral pH (found in most living organisms), the groups are ionized as shown above, so there is a positive charge at one end of the molecule and a negative charge at the other end. The overall net charge on the molecule is therefore zero. A molecule like this, with both positive and negative charges is called a
zwitterion
When two amino acids join together a __________ is formed.
dipeptideThe reaction involves the formation of a molecule of water in a condensation polymerisation reaction.Three amino acids form a tripeptide. Many amino acids form a polypeptide
In a polypeptide there is always one end with a free amino (NH2) (NH3 in solution) group, called theand one end with a free carboxyl (COOH) (COO in solution) group, called the
N terminusC terminus
What are the 4 levels of protein structure?
Primary StructureSecondary StructureTertiary StructureQuaternary Structure
what makes up the amino group?
NH2
what makes up the carboxylic acid group?
COOH
What does the R group do?
It gives the amino acid its specific characteristics
What is a dipeptide?
Two amino acids joined together in a condensation reaction
What bond is formed in a condensation reaction to form a dipeptide?
A peptide bond
What is the primiary structure of a protein?
A chain of amino acids
What is the secondary structure of a protein?
When the chain of amino acids is folded or twisted to form either an alpha helix or a beta pleated sheet held together with hydrogen bonds
What is the tertiary structure of a protein?
The alpha and beta secondary structures are folded into random shapes by folding once more
What bonds are used to keep the tertiary structure together?
Disulfide bonds - covalent and strong, Ionic bonds - weaker than disulfide and affected by changes in pH, Hydrgen bonds which are weak but many
What is the quaternary structure of a protein?
lots of tertiary structures joined together using similar typed of bonds
Example of a molecule which has quaternary structure
Haemoglobin
what the difference between globular and fibrous proteins?
Globular proteins are used a lot in the metabolism whereas fibrous proteins are structural and they hold things together e.g. cartilage and keratin and collagen
How do you test for proteins
Biuret Test
How do you carry out the biuret test?
Add an equal volume of solution and biuret solution - if positive then it changes to a lilac colour
What does the biuret solution detect?
Peptide bonds
