3.1.4.1 General Properties of Proteins Flashcards
what are proteins also referred to as?
polypeptides
what are polypeptides made from (ie. monomers?)
amino acids
how many amino acids are there and how many of these are naturally occurring?
100 identified, 20 of which are naturally occuring
describe the general structure of an amino acid and draw it
(check diagram against notes)
amine group (NH₂)
carboxyl group (COOH)
central carbon (C)
hydrogen atom (H)
R group (R)
what can 2 amino acids bond together to form and which mechanism does this involve?
two amino acids can bond together to form a dipeptide, and this happens through a condensation reaction, (molecule of H₂O removed and a bond is made.)
what sort of bond is formed when a dipeptide is made and where is it?
peptide bond forms between the C-N
if condensation reactions are repeated after a dipeptide then what is formed?
polypeptide
place in order of decreasing strength: ionic, hydrogen, covalent bonds
STRONGEST
covalent
ionic
hydrogen
WEAKEST
give 3 examples of tertiary proteins
enzymes, antibodies and hormones
give 4 examples of quaternary proteins and 2 of their prosthetic groups (PG)
chlorophyll (PG = Mg)
haemoglobin (PG = Fe)
collagen
antibodies
what is an R group?
an R group is a carbon containing side chain
it is what differs between amino acids
state the 5 functions of polypeptides within an organism and give examples
- STRUCTURE eg. collagen, keratin, actin
- ENZYMES eg. carbohydrase, protease
- TRANSPORT eg. haemoglobin
- HORMONES eg. oestrogen, testosterone
- ANTIBODIES
name and describe the chemical test for proteins
BIURET TEST:
- place sample of solution into test tube
- add equal volume of sodium hydroxide
- add few drops of copper (II) sulphate
- mix gently
+ve result = purple/mauve
-ve result = remains blue
describe the differences between globular and fibrous proteins
fibrous: elongated shape, insoluble, structural roles eg. collagen, keratin, myosin, actin
globular: spherical shape, soluble in water, metabolic roles eg. haemoglobin, enzymes, hormones
describe the primary structure of a protein (3 points)
- a singular polypeptide chain
- only contains peptide bonds
- the order and number of amino acids in the chain determines the structure and function of a protein
describe the secondary structure of a protein (3 points)
- hydrogen bonding between H⁺ and O⁻
- causes the polypeptide chain to fold and twist into a 3D structure
- results in the formation of an alpha helix or a beat pleated sheet
where do the H⁺ and O⁻ originate from when forming a secondary protein?
hydrogen in -NH is delta positive and oxygen in C=O is delta negative
give 2 examples of secondary structure proteins
keratin and collagen
describe the structure of a tertiary structure protein (3 points)
- further twisting and folding of a secondary structure
- results in a 3D SPECIFIC structure
- the number and location of ionic, covalent and hydrogen bonds determine and maintain this structure of the tertiary protein
describe the strength of hydrogen bonds and what they can be broken by?
numerous and weak so easily broken by temperature changes
describe the strength of ionic bonds and what they can be broken by?
formed between the carboxyl and amine groups that are not involved in the peptide bond. easily broken by pH and are weaker than covalent but stronger than hydrogen
describe the strength of covalent bonds and what they can be broken by? given an example
a sulphide bridge is a very strong covalent bond caused by interactions between the R group of the amino acid and cysteine. not easily broken
describe the structure of a quaternary protein (2 points)
- a protein consisting of more than one polypeptide chain linked together
- possible prosthetic group
