proteins Flashcards
describe the formation of a peptide bond
condensation reaction
between amine group on one AA
and carboxylic acid group of another AA
forming a water molecule
describe how hydrogen bonds form within secondary structure of proteins
oxygen is relatively negative and hydrogen is relatively positive
oxygen and hydrogen are attracted to each other
alpha keratin is composed of alpha helices
explain why alpha keratin has a more regular structure than the quaternary protein haemoglobin
secondary structures are simple repeating structures
globular protein haemoglobin has a tertiary structure formed from complex folding of a secondary structure
compare and contrast the role of R-Group interactions in the formation of tertiary and quaternary structures of proteins
R-groups on AA interact
tertiary – interact within the protein molecule determines its shape
quaternary – interact between protein molecules holds molecules together
both involve the same interactions
what’s a peptide bond
formed between amino acids
covalent
carboxylic group of one AA interacts with amine group of another AA in a condensation reaction
what’s a protein
polypeptides (and macromolecules) made up of amino acids (monomers)
sequence, type and number of amino acids determines the protein’s shape (and its function)
what determines a different amino acid?
the R-group
how many different AA are commonly found in cells?
how many of these are essential?
20
9 and can only be obtained from what we eat
how is protein synthesised?
peptide bond between amino acids
condensation reaction:
amine group interacts with carboxylic group of another AA
forming a dipeptide/polypeptide
what is the production of polypeptides catalysed by?
enzyme peptidyl transferase (present in ribosomes)
describe the formation of a primary structure of a protein
sequence of amino acids bonded by covalent peptide bonds
DNA of a cell determines the primary structure of a protein by instructing the cell to add certain amino acids in specific quantities in a certain sequence
this affects the shape and function of the protein
describe the formation of a secondary structure of a protein
occurs when (weak) negatively charged nitrogen and oxygen atoms
interact with the weak positively charged hydrogen atoms
forming hydrogen bonds between polypeptide chains
describe the formation of alpha helic
hydrogen bonds form within AA chain
pulling the chain into a coiled shape
describe the formation of a beta pleated sheet
formed by parallel polypeptide chains that form hydrogen bonds
describe tertiary structure of a protein
folding of a protein into its final shape
coiling/folding of sections into a protein’s secondary structure brings r-groups of different AAs closer together to interact
what interactions are seen in tertiary structure
weak hydrophilic/hydrophobic interactions
between polar and non-polar r-groups
hydrogen bonds (weakest)
ionic bonds
formed between oppositely charged r-groups
disulfide bonds
covalently forms between AAs that contain sulfur
describe a quaternary structure
results from association of more than 1 polypeptide chain (subunit) working as a functional macromolecule
protein subunits can be identical or different
what’s the difference between hydrophobic and hydrophilic proteins?
proteins are assembled in the aqueous environment of the cytoplasm
so the way a protein folds depends on whether the r-groups are hydrophilic or hydrophobic
philic groups – outside the protein
phobic groups – inside of molecule shielded from water in cytoplasm
what enzyme catalyses the break down peptide bonds?
protease – catalyses break down of peptides into their constituent AA
a conjugated protein is held together by many different types of bond
which bond is not formed when a conjugated protein folds into its quaternary structure?
peptide
what are the properties of globular proteins?
compact
water soluble
usually roughly spherical
how are globular proteins formed?
found where proteins fold into their tertiary structure
where the hydrophobic r-groups are kept away from aqueous environment
hydrophobic r-groups on the outside of the protein
this is essential for regulating many of the processes necessary to life
what’s an example of a globular protein
insulin
involved in blood glucose regulation
hormone, therefore has to fit into specific receptors on membrane
water soluble, so it’s able to be transported in the blood
what’s a conjugated protein?
a globular protein which contains a non-protein, prosthetic group
what’s a cofactor?
metal ions and molecules derived from vitamins that form prosthetic groups
what’s an example of a conjugated protein?
haemoglobin
quaternary protein made from 4 polypeptides, consisting of
2 alpha, and 2 beta subunits
each subunit contains a prosthetic haem group
the haem group consists of iron (II) ions which combine reversibly with oxygen
describe the formation and function of catalase
enzyme
quaternary protein containing 4 haem prosthetic groups
iron (II) ions allows catalase to react with hydrogen peroxide to increase the rate of reaction
(hydrogen peroxide is a common byproduct of metabolism and causes damage to cells when it accumulates)
what’s a fibrous protein?
formed from long, insoluble molecules
which is due to high proportion of amino acids with hydrophobic r-groups in their primary structure
the amino acid sequence in primary structure is usually repetitive
which makes the structures of fibrous proteins more organised and stronger
describe the formation and function of keratin
fibrous protein
has large proportion of cysteine
(sulfur-containing amino acid)
many strong disulfide bonds (disulfide bridges)
results in forming strong, inflexible, insoluble materials
having a high degree of disulfide bonds leads to what
flexibility
describe the formation and function of elastin
fibrous quaternary protein found in elastic fibres
made from tropoelastin (stretchy molecule)
gives blood vessels the elasticity to expand when needed, or go back to their normal size
describe the formation and function of collagen
fibrous protein
connective tissue found in skin, tendons, ligaments and nervous system
most are made up of 3 polypeptides wound together in long and strong rope-like structure (gives flexibility)
describe the secondary structure of a protein
secondary structure of a protein is held together by hydrogen bonds
that form between the amine group of one amino acid and the carboxyl group of another
These hydrogen bonds cause the polypeptide chain to coil
into an alpha helix/beta pleated sheet
how are amino acids made in:
plants
and animals
made in autotrophic green plants as products of photosynthesis which are assembled into proteins
heterotrophic organisms gain amino acids from plants through food chains
describe the difference between simple and conjugated proteins?
simple contain amino acids in their structure
conjugated contain amino acids plus a prosthetic group
what are the three ways the charges on a protein resulting from the pH effect may influence its behaviour
charges on active site affects capability of enzyme to join with its specific substrate
at iso-electric point (IEP) the protein carries equal numbers of opposite charges
which attract, making the protein clump together and ppt.
at other pHs the proteins carry like charges which repel molecules
which increase the solubility
at extreme pHs the protein molecules may carry huge numbers of like charges
which may exert a large repulsive force which breaks apart the hydrogen and ionic bonds holding the 3D structure together
leads to denaturation since structure and functional ability is lost
state three properties of a fibrous protein different from a globular protein
insoluble
strong
unreactive
