proteins Flashcards
what elements do proteins contain
- carbon
- oxygen
- hydrogen
- nitrogen
what makes amino acids different from each other
‘R’ groups
(side chains)
how many different amino acids?
20
- 5 non essential as our body is able to make them from others
- 9 essential and can only be obtained from eating
- 6 conditionally essential as only needed by children
how do amino acids join
- condensation reaction
- hydroxyl in the carboxyl group and hydrogen in amine group
- forms peptide bond
- water is produced
what catalyses a condensation reaction for peptide bonds
enzyme called peptidyl transferase
(found in ribosomes-site of protein synthesis)
what is the primary structure of a protein
the sequence in which amino acids are joined
peptide bonds only
what influences the function of a protein
the particular amino acids in the sequence will influence how the polypeptide folds to the protein’s final shape
secondary structure of a protein
- hydrogen bonds form within the chain
- pulling it into a coil shape (alpha helix)
or - forming sheet like structures by polypeptides lying parallel to each other (beta pleated sheet)
tertiary structure of a protein
the folding of a protein into its final shape
- the coiling/folding of polypeptides into their secondary structure brings out R groups of different amino acids closer enough to interact and further folding occurs
interactions in a protein’s tertiary structure
-hydrophobic/ hydrophilic interactions between polar and non-polar groups
- hydrogen bonds (weakest)
- ionic bonds (between oppositely charged R groups
- disulfide bonds (strongest covalent)
quaternary structure of a protein
- association of 2 or more individual proteins called subunits
- interactions between subunits are the same as in tertiary structure except they are between protein molecules rather than within 1 molecule
what subunits do enzymes often consist of
2 identical subunits
where are proteins assembled
the aqueous environment of the cytoplasm
where are hydrophobic/hydrophilic groups on a protein?
hydrophilic groups are on the outside of the protein
hydrophobic groups are on the inside of the protein, shielded from water in cytoplasm
what catalyses a hydrolysis reaction for peptides
enzyme proteases
what are features of globular proteins
compact
water soluble
roughly spherical
when do globular proteins form
when proteins fold into their tertiary structures in such a way that they hydrophobic R groups are kept away from the aqueous environment, and hydrophilic R groups are on the outside of the protein
what type of protein is insulin
globular
why is insulin a globular protein
- hormones are transported in the bloodstream so need to be soluble
- hormones have to fit into specific receptors on membranes to have their effect so they need to have precise shapes
what are conjugated proteins
globular proteins that contain a non-protein component called a prosthetic group
(proteins without prosthetic groups are called simple proteins)
examples of types of prosthetic groups
- lipids/carbohydrates can combine with proteins to form lipoproteins or glycoproteins
- metal ions/molecules from vitamins (called co-factors if they are necessary for the protein’s function)
- Haem groups contain an iron 2+ ion (catalase, haemoglobin)
structure of haemoglobin
- conjugated protein
- quaternary protein
- 4 polypeptides
- 2 alpha, 2 beta subunits
- each subunit has a prosthetic haem group
- iron ion is able to combine reversibly with an oxygen molecule
structure of catalase
- enzyme
- conjugated protein
- quaternary protein
- 4 haem prosthetic groups
- iron ion allows catalse to interact with hydrogen peroxide and speed up its breakdown
- hydrogen peroxide is a byproduct of metabolism but damages cells
structure of fibrous proteins
- long, insoluble molecules which aren’t folded into complex 3d shapes
- due to high proportion of amino acids with hydrophobic R groups in their primary structures
- limited range of amino acids with small R groups
- primary structure sequence is quite repetitive
- leads to very organised structures
(keratin, elastin, collagen)
what is keratin
fibrous protein
where is keratin present
hair
skin
nails
structure of keratin
- fibrous
- high proportion of cysteine (contains sulfur)
- many strong disulfide bonds forms strong, inflexible, insoluble materials
- degree of disulfide bonds determines flexibility
- hair contains fewer, nails contains more bonds
what is elastin
fibrous protein
structure of elastin
- found in elastic fibres
- present in walls of blood vessels, alveoli (gives flexibility to expand)
- quaternary protein
- made from tropoelastin
what is collagen
fibrous protein
structure of collagen
- connective tissue found in skin, tendons, ligaments, nervous system
- 3 polypeptides wound together in a long, strong rope-like structure
- flexible
- fibrous
test for proteins and why
Biuret test
peptide bonds form violet complexes with copper ions in alkaline solutions
how to carry out a test for proteins
- 3cm^3 of sample mixed with equal volume of 10% sodium hydroxide solution
- 1% copper sulfate solution added a few drops at a time until solution turned blue
- solution mixed and left for 5 minutes
- should turn lilac (positive test)
