1.4 PROTEINS Flashcards
Describe
amino acid general structure
- central C
- -COOH carboxyl group
- -NH₂ amine group
- -R variable side group
- -H hydrogen
Describe
test of proteins
Biuret test
1. add equal volume of sodium hydroxide at room temp
2. add dropos of dilute copper (II) sulfate solution
3. +ive result: colour changes from blue to purple
State and explain
number of amino acids and how they differ
20
differ only by side ‘R’ group
Describe
dipeptide and polypeptide formation
- condensation reaction forms peptide bond (-CONH-) & eliminates molecule of water
- dipeptide: 2 amino acids
- polypeptide: 3 or more
State
number of levels in protein structure
4
Define
primary structure of proteins
- sequence, number & type of amino acids in the polypeptide
- determined by sequence of codons on mRNA
Define
secondary structure of proteins
Hydrogen bonds form between O δ- attached to -C=O & H δ+ attached to -NH
Describe
2 types of secondary protein structures
α-helix:
* all N-H bonds on same side of protein chain
* spiral shape
* H-bonds parallel to helical axis
β-pleated sheet:
* N-H & C=O groups alternate from one side to the other
Define and name
tertiary structure of proteins
3D structure formed by firther folding of polypeptide
* disulfide bridges
* ionic bonds
* hydrogen bonds
Describe
type of bonds in tertiary structures of proteins
- disulfide bridges: strong covalent S-S bonds
- ionic bonds: relatively strong bonds between charged R groups (changed by pH)
- hydrogen bonds: numerous & easily broken
Define
quaternary structure of proteins
- functional proteins with more than one polypeptide
- precise 3D structure held together by the same types of bond as tertiary structure
- may involve addition of prosthetic groups
Describe
globular protein structure and functions
- spherical & compact
- hydrophilic R groups face outwards & hydrophobic R groups face inwards = usually water-soluble
- involved in metabolic processes e.g. enzymes
Describe
fibrous proteins structure and function
- can form long chains or fibres
- insoluble in water
- useful for structure and support e.g. collagen
Outline
use of chromatography in identifying amino acids
- use capillary tube to spot mixture onto pencil origin line & place chromatography paper in solven
- allow solvent to run until it almost touches other end of paper. Amino acids move different distances based on relative attraction to paper & solubility in solvent
- use revealing agent or UV llight to see spots
- calculate Rf values & match to database
Define
enzyme
- biological catalysts for intra & extrecellular reactions
- specific tertiary structure determines shape of active site, complementary to a specific subestrate
- formations of ES complexes lowers activation energy of metabolic reactions
Explain
induced fit model of enzyme action
- shape of active site is not directly complementary to substrate & is flexible
- conformational change enables ES complexes to form
- strains substrate bonds, lowering the activation energy
Describe
change in models of enzyme action
- lock & key model: rigid shape of active site complementary to only 1 substrate
- induced fit model: explains binding at allosteric sites changing active site shape
Describe
process to identify activation energy from an energy level diagram
difference between free energy of substrate & peak of curve
Name
5 factors that affect rate oof enzyme-controlled reactions
- enzyme conc.
- substrate conc.
- inhibitor conc.
- pH
- temp
Explain
effect of substrate conc on enzyme controlled reactions
given that enzyme is in excess, rate increases proportionally to substrate conc.
rate levels when max no. ES complexes form
Explain
effect of enzyme conc on enzyme controlled reactions
given that substrate is in excess, rate increases proportionally to enzyme conc.
rate levels when max no. ES complexes form
Explain
effect of temp on enzyme controlled reactions
rate increases as kinetic energy increases & peaks at optimum temp
above optimum, ionic & H-bonds in 3⁰ structure break = changes in active site shape so no longer complementary (denaturation)
Explain
effect of pH on enzyme controlled reactions
enzymes have a narrow optimum pH range
outside range, H⁺/OH⁻ ions interact with H-bonds & ionic bonds in 3⁰ structure = denaturation
Contrast
competitive and non-competitive inhibitors
competitive:
* similar shape to substrate = bind to active site
* don’t stop reactions; ES complex forms when inhibitor releases
* increasing substrate conc, decreases effect
non-competitve:
* bind at allosteric binding site
* may permanently stop reactions; triggers active site to change shape
* increasing substrate conc, has no impact
