proteins Flashcards
kms kms kms
what elements always and sometimes make up a protein?
always: carbon, hydrogen, oxygen, nitrogen
sometimes: sulfur
what are amino acids? describe and draw their structure
amino acids are the basic building blocks of proteins
- each amino acid has one animo group (-NH2) and one carboxyl group (-COOH)
- the carbon atom next to the carboxyl group is called the α carbon
- each α carbon has a hydrogen atom, a carboxyl group, an animo group and a R group bonded to it
- all amino acids only differ in the R group
what do amino acids join together to form?
describe the condensation reaction
they join together to form a polypeptide chain, joined by peptide bonds
the condensation reaction occurs between the animo group of one amino acid and the carboxyl group of another, to form a dipeptide, which is accompanied by the elimination of one water molecule.
briefly describe the polypeptide chains
- folded into three-dimensional shape, due to chemical bonds between various amino acid residues in polypeptide chains
- has an amino end (N-terminal) and carboxyl end (C-terminal)
what is the characteristic three-dimensional shape and structure of protein know as?
conformation
define primary structure
variety, number, and sequence of amino acids in a polypeptide chain
what bonds are present in primary structure?
peptide bond
describe the primary structure
- unique - proteins differ from each other with the variety, number and sequence of their consistuent amino acids
- slight change in primary structure of a protein can alter is properties drastically
define secondary structure
localised, repetitive folding of the polypeptide chain
what bonds are present in secondary structure?
it is stabilised by hydrogen bonds between peptide linkages of polypeptide backbone (R groups of amino acids are NOT involved)
a) describe:
- the shape of α-helix
- the bonding in α-helix
b) provide an example of a protein which mainly has α-helix
a)
- extended spiral spring
- stabilised by hydrogen bonds between -C=O and N-H groups within polypeptide chain
b) keratin
hydrogen bonds are between -C=O and N-H groups for both secondary structures
a) describe:
- the shape of β-pleated sheet
- the bonding in β-pleated sheet
b) provide an example of a protein which mainly has β-pleated sheet
a)
- two or more regions of polypeptide chain lie parallel to each other in flat, zig zag sheets. the polypeptide chains may run in the same direction (parallel β-pleated sheets) or in opposite direction (anti-parallel β-pleated sheet)
- stabilised by hydrogen bonds between the -C=O and N-H groups of one part of the backbone and the -C=O and N-H groups of an adjacent part in the parallel regions
b) fibroin (protein in silk) -> hence it has high tensile strength
hydrogen bonds are between -C=O and N-H groups for both secondary structures
define tertiary structure
the polypeptide chain folds and bends into a precise, compact, globular three-dimensional shape, unique to the protein
what are all the bonds present in tertiary structure?
stabilised by intermolecular R group interactions / (disulfide bonds, hydrogen bonds, ionic bonds and hydrophobic interactions) between R groups of amino acids at different regions of polypeptide chain
define quaternary structure
combination of a number of polypeptide chains and may involve associated non-protein groups into a large, complex and functional protein molecule. each polypeptide chain in the protein is called a subunit
what are the bonds present in quaternary structure?
subunits are held together by intermolecular R group interactions / (disulfide bonds, hydrogen bonds, ionic bonds and hydrophobic interactions)
name a protein in RBC with a quaternary structure. briefly describe it.
haemoglobin
it has 4 subunits (4 polypeptide chains), with 2 α-chains and 2 β-chains each containing a heme group (non-protein group). the heme group has a Fe2+ ion.
describe the functions of 8 types of proteins (in living organisms)
1) homeostatic: soluble proteins in blood plasma act as buffers to stabilise pH
2) enzymatic: catalyses and speed up the rate of chemical reactions in the cell
3) hormonal: hormones in the body like insulin and glucagon
4) transport:
- proteins in plasma membrane function in transport of certain substances into and out of cell or membrane-bound organelle
- haemoglobin functions in transport of oxygen in vertebrates
- lipoproteins function in transport of cholesterol in blood
5) storage:
- ferritin functions to store iron in liver
- myoglobin in skeletal muscle cells functions to store oxygen
6) protection:
- antibodies function as part of immune system
- blood clotting factors are important in blood clotting mechanism
7) support / structural:
- collagen as a component of connective tissue, cartilage, tendons and ligaments
- keratin in hair, hoofs and feathers
8) source of energy: during extreme starvation when carbohydrates and fat reserves are depleted
the examples or not very very important, but at least remember what named proteins function as.
describe the test for proteins
1) to 2cm3 of test sample, add an equal volume of 5% sodium hydroxide solution
2) add two drops of 1% copper sulfate solution and mix
3) (observe any colour change)
expected results:
positive result: contents turned from light blue to violet
negative result: contents remained light blue
NOTE: this test tests for presence of peptide bonds, and individual amino acids won’t yield a positive result
draw the condensation reaction between 2 amino acids
