section 2: biological molecules - topic 5: proteins Flashcards
what are proteins?
polymers.
what are the monomers of proteins?
amino acids.
what is formed when 2 amino acids join together?
a dipeptide.
what is formed when more than 2 amino acids join together?
a polypeptide.
what are proteins made up of?
one or more polypeptides.
what is the general structure of all amino acids?
a carboxyl group (-COOH) and an amino group (-NH2) attached to a carbon atom.
what is the difference between different amino acids?
the variable group they contain.
what chemical elements do all amino acids contain?
carbon.
oxygen.
hydrogen.
nitrogen.
some also contain sulphur.
what are amino acids linked together by?
peptide bonds - to form dipeptides and polypeptides.
what type of reaction is it to form dipeptides and polypeptides?
a condensation reaction.
^ a molecule of water is released during the reaction.
the reverse of this adds a molecule of water to break the peptide bond.
- hydrolysis reaction.
what are the 4 structural levels of a protein?
primary.
secondary.
tertiary.
quaternary.
describe the primary structure.
- this is the sequence of amino acids in the polypeptide chain.
- different proteins have different sequences of amino acids in their primary structure.
- a change in just 1 amino acid may change the structure of the whole protein.
- it’s held together by the peptide bonds between the amino acids.
describe the secondary structure.
- the polypeptide chain doesn’t remain flat and straight.
- hydrogen bonds form between the -NH and -CO groups of the amino acids in the chain.
- this makes it automatically coil into an alpha helix or fold into a beta pleated sheet.
describe the tertiary structure.
- the coiled or folded chain of amino acids is often coiled and folded more.
- more bonds form between different parts of the polypeptide chain.
what are the bonds involved in the tertiary structure?
ionic bonds.
disulphide bonds.
hydrophobic & hydrophilic interactions.
hydrogen bonds.
describe the ionic bonds in the tertiary structure.
these are attractions between negatively-charged R groups and positively-charged R groups on different parts of the molecule.
describe the disulphide bonds in the tertiary structure.
whenever 2 molecules of the amino acid cysteine come close together, the sulphur atom in 1 cysteine bonds to the sulfur in the other cysteine, forming a disulphide bond.
describe the hydrophobic & hydrophilic interactions in the tertiary structure.
when hydrophobic R groups are close together in the protein, they tend to clump together.
this means that hydrophilic R groups are more likely to be pushed to the outside.
^ affects how the protein folds up into its final structure.
describe the hydrogen bonds in the tertiary structure.
these weak bonds form between slightly positively-charged hydrogen atoms in some R groups and slightly negatively-charged atoms in other R groups on the polypeptide chain.
what is the quaternary structure?
some proteins are made of several different polypeptide chains held together by bonds.
the quaternary structure is the way these polypeptide chains are assembled together.
what is the quaternary structure determined by?
the tertiary structure of the individual polypeptide chains being bonded together.
- because of this, it can be influenced by all those bonds (ionic, disulphide, hydrophobic + hydrophilic, hydrogen).
for proteins made from more than 1 polypeptide chain, the quaternary structure is the proteins final 3D structure.
what are the 2 types of proteins?
globular.
fibrous.
what do globular proteins look like?
they are round and compact.
what is the structure of a globular protein?
the hydrophilic R groups on the amino acids tend to be pushed to the outside of the molecule.
- this is caused by the hydrophobic and hydrophilic interactions in the proteins tertiary structure.
this makes globular proteins soluble, so they’re easily transported in fluids.
what are examples of globular proteins?
haemoglobin.
insulin.
amylase.
describe heamoglobin.
haemoglobin is a globular protein that carries oxygen around the body in red blood cells.
it’s a conjugated protein - means it’s a protein with a non-protein group attached.
the non-protein part = a prosthetic group.
each of the 4 polypeptide chains in haemoglobin has a prosthetic group called haem.
- it’s the iron-containing haem groups that bind to oxygen.
describe insulin.
insulin is a hormone secreted by the pancreas - helps to regulate the blood glucose level.
its solubility is important - means it can be transported in the blood to the tissues where it acts.
an insulin molecule consists of 2 polypeptide chains - held together by disulphide bonds.
- when they’re in the pancreas, 6 of these molecules bind together to form a large, globular structure.
describe amylase.
amylase is an enzyme that catalyses the breakdown of starch in the digestive system.
it’s made of a single chain of amino acids.
its secondary structure contains both alpha-helix and beta-pleated sheet sections.
most enzymes are globular proteins.
what do fibrous proteins look like?
they are tough and rope-shaped.
what are the 2 properties of fibrous proteins?
insoluble.
strong.
what kind of protein are fibrous proteins?
structural.
- fairly unreactive (unlike many globular proteins)
what are examples of fibrous proteins?
collagen.
keratin.
elastin.
describe collagen.
collagen is found in animal connective tissues - bone, skin, muscle.
it’s a very strong molecule.
minerals can bind to the protein to increase its rigidity i.e. in bone.
describe keratin.
keratin is found in many of the external structures of animals - skin, hair, nails, feathers, horns.
it can either be flexible (as in skin) or hard and tough (as in nails).
describe elastin.
elastin is found in elastic connective tissue - skin, large blood vessels, some ligaments.
it’s elastic - allows tissues to return to their original shape after they’ve been stretched.
