Biochemistry: Introductory Principles (lecture 1) Flashcards
Describe C-C and C-H bonds
- Electrons shared equally
- Non-polar
- Unreactive
Describe C-O and C-N bonds
- Electrons shared unequally
- Polar
- Reactive
Describe Oxidation
- Is a loss of electrons
- Generally energy releasing (exergonic)
- Examples: direct loss of electrons, loss of hydrogen, gain of oxygen
Describe Reduction
- Gain of electrons
- Generally energy absorbing (endergonic)
- Examples: direct gain of electrons, gain of hydrogen, loss of oxygen
C=C vs C-C
C=C is more oxidized (and less reduced) than C-C
In RedOx reactions, electrons are transferred from molecules with…
…Lower affinity for electrons to molecules with higher affinity for electrons
Reducing agent (reductant)
- The electron donor
- Lower electron affinity
Oxidizing agent (oxidant)
- The electron acceptor
- Higher electron affinity
Standard Reduction Potential (SRP)
- Is a quantitative measure of the tendency of redox pairs to lose electrons
The lower the SRP, _____
The greater the tendency to LOSE electrons
The higher the SRP, _____
The greater the tendency to ACCEPT electrons
Naming for undisassociated acid?
“…ic acid,” like “acetic acid”
Naming for disassociated acid?
“ate,” like “acetate”
Nitrogen-containing groups are usually ____ and can acquire a proton, becoming ____
Basic, positively charged cations
Unequal sharing of electrons between atoms generates…
Polarity
Nucleophile
- Nucleus / positive-charge loving
- Provides an electron pair to form a covalent bond
Electrophile
- Electron / negative-charge loving
- Accepts an electron pair to form a covalent bond
T/F: Conjugate acids are usually protonated.
True!
Equilibrium Constant (Keq)
[B] / [A]; the rate of the forward and reverse reactions are equal
What is the pKa?
It is the pH at which [acid] = [base]; 50% dissociated. The lower the pKa, the stronger the acid!
Dissociation of a weak acid
HA ⇌ H+ + A-
Henderson-Hasselbach equation
pH = pKa + log([A-]/[HA])
If pH > pKa…
A- > HA, and is strongly dissociated
If pH < pKa…
HA > A-, and is not dissociated (or weakly)
Know logs!
Log 1 = 0
Log 10 = 1
Log 100 = 2
Log 1000 = 3
Antilog 1 = 10
Antilog 2 =100
Antilog 3 = 1000
Antilog -1 = 1/10
Antilog -2 = 1/100
Antilog -3 = 1/1000
If Lactic acid has a pKa of ~3.7, at which pH would it be present as an acid?
Present at pH 2, compared to a pH of 5, 7 and 9.
What is a buffer?
Buffers are solutions of weak acids and their conjugate bases
Function of buffers?
To resist pH changes when an acid or base is added to the solution
Maximum buffering capacity is when…
pH = pKa
What is the main acid produced by the body?
Carbon dioxide! CO2 is also its own buffer.
Bicarb and RBCs
Large amounts of carbonic anhydrase are found in RBC. As carbonic acid dissociates, the H+ is taken up by Hb because an unbound His residue has a pKa of 6.7. RBC exchanges HCO3- with Cl- in plasma so high [HCO3-] is in plasma. In the lung, CO2 released from RBC into blood, Hb-H loses proton to facilitate O2 binding.
Concentration of chloride in the peripheral tissues vs lungs
[Cl] is lower in the blood plasma of peripheral tissues because Cl is being taken up by the RBCs
Near the lungs, this is reversed; Cl leaves the cell and enters teh blood, so the level of Cl in the blood plasma is higher
Diabetic Ketoacidosis
Fatty acids circulating in the blood leads to ketoacidosis, a lowering of blood pH
DKA, continued
As pH increases, breathing increases and becomes rapid; this results in a loss of CO2, so pH increases, as well.
Anxious breathing
As breathing increases, CO2 decreases (is exhaled out)
Can treat with paper bag, so not as much CO2 is breathed out.
How to calculate pI
- Choose the species that is at zero overall charge
- Take the average of the 2 pKa values that flank it
Other important buffer systems
- H2PO4 -> HPO4
- NH3 + H -> NH4
- Serum and intracellular proteins containing Histidine
pH and drug absorption
- Aspirin is more likely to cross membranes if uncharged (protonated); it will only be protonated if its pH is below the pKa of 3.5.
- Absorption is more efficient in the stomach than in the intestine
