week 3 proteins and enzymes Flashcards
what is the structure of an amino acid
NH2 - CH,R - COOH
- amine group on left
- R is variable side chain
- carboxyl group on right
are amino acids chiral
yes all are except glycine
what do amino acids behave like
zwitterions
- cations in low pH (positive)
- anions in high pH (negative) (two hydrogens are removed)
what are the 7 classes of amino acid
aliphatic aromatic sulphur-containing acidic basic polar miscellaneous
what is an aliphatic amino acid
R group consists of hydrocarbon chain
e.g. glycine, alanine, valine
what is an aromatic amino acid
R group consists of hydrocarbon ring
e.g. phenylalanine, tyrosine, tryptophan
what is phenylketonuria (PKU)
patient is unable to metabolise phenylalanine
- build-up causes neurological damage
what are sulphur containing amino acids
e. g. cysteine, methionine
- presence of sulphur allows disulphide bridges to form (covalently bonded linkages that occur between two amino acids)
what are basic amino acids
e.g. lysine, histidine, arginine
NH2 attached
what are acidic amino acids
e. g. aspartate, glutamate
- COO attached
what are polar amino acids
e. g. serine, threonine, asparagine, glutamine
- can carry charge at end of R group i.e. -OH
what is a miscellaneous amino acid
e.g. proline
what is primary structure
sequence of amino acids
- 20^100 possible combinations
- two monomers linked is dipeptide, three is tripeptide, etc. to form polypeptide chain
- monomers linked by peptide bonds
what is secondary structure
- the 3D spatial arrangement of amino acids located near each other in the polypeptide chain
- relies on hydrogen bonding
- alpha helix or beta pleated sheet
what is tertiary structure
- results when R chain of amino acids in polypeptide interact with each other
- van der waal’s, ionic, hydrogen, disulphide bridges and hydrophobic interactions
what structure are functional proteins
- at least tertiary
- some quaternary
what is quaternary structure
more than one polypeptide comes together
- all active proteins have at least tertiary structure but they can be modified further and develop quaternary structure
- this is post-translational modification
what is denaturation of proteins
- occurs when protein’s chemical bonds are disrupted (possibly destroyed) within its secondary and tertiary structure
- biological functionality is lost
- denaturation is rarely strong enough to break primary structure so that remains the same
what are the functions of proteins
- structural e.g. collagen in cartilage
- enzymatic
- receptor proteins
- hormonal e.g. insulin
- transport proteins
- defensive proteins e.g. immunoglobulin
- storage
- contractile
what are the three types of conjugated proteins
- glycoproteins
- lipoproteins
- metalloproteins
what is a glycoprotein
- conjugated protein
- protein with one or more carbohydrate molecule attached
- co-translational/post-translational modification where oligosaccharide (carbohydrate of from 3-6 simple sugars) are attached to protein
- this is glycosylation
what are the effects of glycolysation
- stability
- solubility
- cell signalling
- orientation
what are lipoproteins
proteins combined with lipids
where are lipoproteins found and what is their function
found in cell membranes
they transport hydrophobic molecules (e.g. cholesterol transport in the blood)
what are apolipoproteins
complex of lipoproteins
- they transport fat soluble vitamins and fat soluble hormones around the body
what are metalloproteins
protein molecule with metal ion in their structure (co-factor)
- various functions (enzymatic, signal transduction, transport and storage)
what are the three types of protein
- globular
- fibrous
- membranous
what are globular proteins
functions: storage, enzymes, hormones, transporters, structural
e. g. immunoglobulin
what are fibrous proteins
- commonly found in muscle fibres and connective tissue
- elongated shape
- in tissues where tensile strength is required
what are membranous proteins
- membrane transporters
- membrane enzymes
- cell adhesion molecules
what is an enzyme
a protein molecule that catalyses chemical reactions without itself being destroyed or altered
what are the six classes of enzymes
oxireductases - transfer e-
transferases - group transfers
hydrolases - hydrolysis
lyases - form, or add groups to double bonds
isomerases - transfer groups within molecules (form isomers)
ligases - formation of c-c, c-s, c-o and c-n
what is a co-factor
non-protein component needed for the reaction
what is co-enzyme
heat-stable substance that can aid enzyme reactions
what is an isoenzyme
enzymes that catalyse the same reaction but vary in structure and other properties
how do enzymes lower activation energy
- entropy reduction (force substrate to be correctly orientated)
- desolvation (weak bonds replace hydrogen bonds)
- induced fit
what is Michaelis-menten plot and equation
relates reaction rate (V) to the concentration of the substance
what is Vmax
maximum reaction velocity
- tells us how fast a reaction is proceeding when the enzyme is saturated with susbstrate
- high value = fast enzyme
what is Km
the substrate concentration when the reaction is at 1/2 the maximum velocity
- low value = good fit
- high value = poor fit
what can affect enzyme reactions
- enzyme concentration
- substrate concentration
- temperature
- pH
- inhibitors
what happens in competitive inhibition
- an inhibitor binds to the active site
- Vmax unchanged
- Km increases because it takes more substrate to overcome inhibition
what is non-competitive inhibition
- an inhibitor binds to a secondary site on the enzyme which changes shape of active site
- Vmax decreased
- Km remains the same
why measure enzymes in a clinical setting
- detection of suspected disease
- confirmation of suspected disease and assessing severity
- localisation of disease to organs
- organ pathology
- assessing response to therapy
- organ function
- assessing genetic susceptibility to drug side effects
- inherited metabolic disease
- vitamin deficiencies
what factors determine enzyme activity in samples
age, gender, pregnancy, race, time of day, genetics, drugs, disease processes, treatments, hypoxia, cellular damage, physical damage, immune disorders, microbiological agents, genetic defects, nutritional disorders
