proteins Flashcards
what are amino acids?
monomers that make up a polymer called a polypeptide which can combine to make proteins
what is the central carbon atom on an amino acid attached to?
-amino group (-NH2)
-carboxyl group (-COOH)
-hydrogen (-H)
-R group - a variety of different chemical groups which cause amino acids to differ
how many types of naturally occurring amino acids are there?
20
what element do amino acids have which differs them from carbohydrates and lipids?
nitrogen
which additional element do some amino acids have?
sulfur
what is a polypeptide?
many amino acids chemically joined by peptide bonds
what is a dipeptide?
two amino acids chemically joined together by a peptide bond
describe a condensation reaction to join two amino acids to form a dipeptide?
reaction is between the carboxyl group of one amino acid and the amine group of the second amino acid. Water is removed and a peptide bond is formed
what do polypeptide bonds have?
they always have an amine group on one side and a carboxyl group on the other
what is the primary structure of proteins?
the sequence of amino acids in the polypeptide chain, held together by peptide bonds
what is the secondary structure of proteins?
folding/ coiling of the polypeptide chain into an alpha helix or beta pleated sheet held by hydrogen bonds
which part of the amino acids do hydrogen bonds form in the secondary structure?
between the hydrogen on the amine group and the oxygen on the carboxyl group
what is the tertiary structure of proteins?
further folding of the secondary structure to form a 3D shape, held by disulphide bridges, ionic bonds and hydrogen bonds
where do disulphide bridges form on cysteine amino acids and what kind of bonds are they?
between two sulphurs from two different R groups
covalent
list the bonds that hold the tertiary structure in place in order of strength?
- disulphide bridges
- ionic bonds
- hydrogen bonds
what determines where bonds form on the tertiary structure?
DNA code determines sequence of amino acids
what is a quaternary structure of proteins?
the 3D shape that forms when there’s more than one polypeptide chain
what are the two types of proteins?
globular and fibrous
what are some examples of globular proteins?
enzymes, plasma proteins, haemoglobin, antibodies
why are globular proteins soluble?
they carry out metabolic reactions
the parts of the polypeptide chain with hydrophobic R groups are in the centre of the molecule and the hydrophilic R groups are on the outside
why are globular proteins being soluble an advantage for enzymes and plasma proteins?
enzymes are in solution so they can catalyse chemical reactions
plasma proteins are dissolved in water of the blood plasma, and they lower water potential of the blood
what are fibrous proteins?
structural molecules
what are examples of fibrous proteins?
keratin
collagen
describe the structure of collagen?
-primary structure is an unbranched polypeptide chain
-secondary structure the polypeptide chain is coiled and held together by hydrogen bonds
-lots of the amino acid glycine helps close packing
-in the tertiary structure, the helix is twisted into a second helix held together by disulphide brides, ionic bonds and hydrogen bonds
-its quaternary structure is made of three such polypeptide chains wound together like a rope (fibre)
how is collagen insoluble?
-external R groups on the molecule are non polar
-it is large
-straight tertiary structure
how are collagen molecules in the fibre arranged?
so that the end of one fibre is not in line with the end of another- means there isn’t a weak spot in the structure which would lead to a tendon breaking under force of muscle contraction
