Biochemistry: Introductory Principles (lecture 1)

Question 1

Describe C-C and C-H bonds

Answer 1

• Electrons shared equally
• Non-polar
• Unreactive

Question 2

Describe C-O and C-N bonds

Answer 2

• Electrons shared unequally
• Polar
• Reactive

Question 3

Describe Oxidation

Answer 3

• Is a loss of electrons
• Generally energy releasing (exergonic)
• Examples: direct loss of electrons, loss of hydrogen, gain of oxygen

Question 4

Describe Reduction

Answer 4

• Gain of electrons
• Generally energy absorbing (endergonic)
• Examples: direct gain of electrons, gain of hydrogen, loss of oxygen

Question 5

C=C vs C-C

Answer 5

C=C is more oxidized (and less reduced) than C-C

Question 6

In RedOx reactions, electrons are transferred from molecules with…

Answer 6

…Lower affinity for electrons to molecules with higher affinity for electrons

Question 7

Reducing agent (reductant)

Answer 7

• The electron donor

- Lower electron affinity

Question 8

Oxidizing agent (oxidant)

Answer 8

• The electron acceptor

- Higher electron affinity

Question 9

Standard Reduction Potential (SRP)

Answer 9

• Is a quantitative measure of the tendency of redox pairs to lose electrons

Question 10

The lower the SRP, _____

Answer 10

The greater the tendency to LOSE electrons

Question 11

The higher the SRP, _____

Answer 11

The greater the tendency to ACCEPT electrons

Question 12

Naming for undisassociated acid?

Answer 12

“…ic acid,” like “acetic acid”

Question 13

Naming for disassociated acid?

Answer 13

“ate,” like “acetate”

Question 14

Nitrogen-containing groups are usually ____ and can acquire a proton, becoming ____

Answer 14

Basic, positively charged cations

Question 15

Unequal sharing of electrons between atoms generates…

Answer 15

Polarity

Question 16

Nucleophile

Answer 16

• Nucleus / positive-charge loving

- Provides an electron pair to form a covalent bond

Question 17

Electrophile

Answer 17

• Electron / negative-charge loving

- Accepts an electron pair to form a covalent bond

Question 18

T/F: Conjugate acids are usually protonated.

Answer 18

True!

Question 19

Equilibrium Constant (Keq)

Answer 19

[B] / [A]; the rate of the forward and reverse reactions are equal

Question 20

What is the pKa?

Answer 20

It is the pH at which [acid] = [base]; 50% dissociated. The lower the pKa, the stronger the acid!

Question 21

Dissociation of a weak acid

Answer 21

HA ⇌ H+ + A-

Question 22

Henderson-Hasselbach equation

Answer 22

pH = pKa + log([A-]/[HA])

Question 23

If pH > pKa…

Answer 23

A- > HA, and is strongly dissociated

Question 24

If pH < pKa…

Answer 24

HA > A-, and is not dissociated (or weakly)

Question 25

Know logs!

Answer 25

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

Question 26

If Lactic acid has a pKa of ~3.7, at which pH would it be present as an acid?

Answer 26

Present at pH 2, compared to a pH of 5, 7 and 9.

Question 27

What is a buffer?

Answer 27

Buffers are solutions of weak acids and their conjugate bases

Question 28

Function of buffers?

Answer 28

To resist pH changes when an acid or base is added to the solution

Question 29

Maximum buffering capacity is when...

Answer 29

pH = pKa

Question 30

What is the main acid produced by the body?

Answer 30

Carbon dioxide! CO2 is also its own buffer.

Question 31

Bicarb and RBCs

Answer 31

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.

Question 32

Concentration of chloride in the peripheral tissues vs lungs

Answer 32

[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

Question 33

Diabetic Ketoacidosis

Answer 33

Fatty acids circulating in the blood leads to ketoacidosis, a lowering of blood pH

Question 34

DKA, continued

Answer 34

As pH increases, breathing increases and becomes rapid; this results in a loss of CO2, so pH increases, as well.

Question 35

Anxious breathing

Answer 35

As breathing increases, CO2 decreases (is exhaled out) Can treat with paper bag, so not as much CO2 is breathed out.

Question 36

How to calculate pI

Answer 36

- Choose the species that is at zero overall charge | - Take the average of the 2 pKa values that flank it

Question 37

Other important buffer systems

Answer 37

- H2PO4 -> HPO4 - NH3 + H -> NH4 - Serum and intracellular proteins containing Histidine

Question 38

pH and drug absorption

Answer 38

- 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