L17: Biological Reactions- Fundamentals Flashcards
Why are most biologically relevent molecules are asymmetric (chiral)?
They are based on carbon
What does molecular recognition depend on?
Presence fit of ligand to receptor
Define racemisation
Synthesis involving asymmetric carbons leading to a mixture of stereoisomers
What does Gram-positive bacteria use in their cell walls, and which antibiotic can bind & disrupt bacterial cell wall synthesis WITHOUT harming human cells?
D-alanine
- Vancomycin
Protons in acids & bases in Brønsted Lowry
Acids donate protons (H+)
Bases accepts protons (H+)
Electron pair in acids & bases in the Lewis Definition
Acid: Electron pair acceptor
Base: Electron pair donor
What does the molecule have to do to act as a base/acid?
Release OH- or H+ ions
What happens when a base accepts a proton (H+)?
Turns into acid
What happens when an acid accepts a proton (OH-)?
Turns into a base
Relationship between pKa and acid
Smaller pKa -> Stronger acid
Larger pKA -> Weaker acid
What is the strength of acids/bases determined by?
Its ability to donate/accept protons (H+)
3 main factors that influence the strength of an acid
1) Bond strength (HA bond dissociation energy)
2) Electronegativity of A
3) Stabilisation of the conjugate base
Relationship in bond strength between HA Bond
Weaker the bond between H & A, the easier it is for proton to leave, making acid stronger
Is conjugate base of STRONG ACID weak/strong?
WEAK
Is conjugate base of WEAK ACID strong/weak?
Strong
What are strong acids?
Dissociate fully in H2O to produce a max no. of H+ ions
What are strong bases?
Ability to remove a proton from an weak acid
What are weak bases?
Doesn’t fully convert into OH- ions
What are weak acids?
Partially dissociate in H2O to form H+ ions
What is a conjugate base?
Substance formed by the removal of a proton by an acid
What is an conjugate acid?
Compound formed when an acid gives a proton to a base
Effect on acidity of:
1) Bond strength
2) Electronegativity of A
3) Resonance Stabilisation
1) Weaker bond -> Stronger acid
2) Higher electronegativity -> Stronger acid
3) More resonance -> Stronger acid
What is a conjugate acid-base pair?
2 substances whose formula differ only by a H+ ion
Catalysts
Fill out these sentences:
Catalysts lower the 1____ ____ of a reaction
Catalysts do NOT change the
2___ ___
Catalysts increase reaction speed by providing an 3____ ____
1) Activation Energy
2) Reaction Energy
3) Alternative Pathway
Define oxidation in redox reactions
Molecule/atom/ion LOSES OR DONATES electrons
Define reduction in redox reactions
Molecule/atom/ion GAINS OR ACCEPTS electrons
Define radicals
Highly reactive species with unpaired electrons
O2 radical: O·
Cl radical: Cl·
What happens in homolytic bond cleavage?
2 electrons in a covalent bond are divided equally, each atom gets 1 electron
- Requires energy
What happens in recombination bond cleavage?
2 radicals combine to form a stable, non-radical molecule
