BCHEM 393 Midterm 1 - UofC

BCHEM 393 Winter 2025

TOPIC 1: INTRO & LIPIDS

Classes of Lipids (5)

• Free fatty acids

• Triacylglycerols

• Phospholipids

• Glycolipids

• Steroids

Lipids are

water insoluble molecules that are soluble in organic solvents

Fatty Acid Structure (2)

• Hydrocarbons with a terminal carboxylic acid group

• Fuel and building blocks for membranes

Which form of a molecule is found predominantly at pH 7?

Ionized

• Negatively charged, which is more basic than regularly charged carboxylic acids

Fatty Acid: Naming Conventions Ratio

Number of carbons : number of unsaturated bonds (double bonds)

Carbon 1 (in a fatty acid) is at the

carboxyl terminus

Carbon 2 (in a fatty acid) is called

⍺ (alpha)

Carbon 3 (in a fatty acid) is called

β (beta)

The last carbon (in a fatty acid) is called

ω (omega)

𝚫 marks the position of a ______

double bond

Fatty Acid Suffix in Protonated Form

-oic acid

Fatty Acid Suffix in Ionized (-) Form

-oate

In Fatty Acid Naming Conventions, how does naming change when there is 1 or more unsaturated bond(s)?

The ‘a’ changes to an ‘e’

enoate

dienoate

trienoate

tetraenoate

Melting Point in Fatty Acids is dependent on _______

degree of saturation and chain length (# of C)

Unsaturated fatty acids and shorter carbon chains have a ______

lower melting temperature

Unsaturated fatty acids have a lower melting point than saturated fatty acids because of _______________

Van der Waals interactions between the hydrocarbon chains are disrupted by gaps created by the cis double bonds

Fatty acids with fewer carbons have a lower melting point because ________________

fewer atoms are available to form Van der Waals interactions

Generally, ___ double bonds are more unstable (more unsaturated) than ___ double bonds

cis, trans

Fatty Acids in Animals (4)

• Typically, an even number of carbon atoms (between 12-20 carbons)

• 16- and 18-carbon fatty acids are most common

• The configuration at double bonds is usually cis

• Double bonds in polyunsaturated fatty acids are separated by at least one methylene group

Triacyclglycerols are basically

The storage form of fatty acids (glycerol connected to fatty acids via ester linkage)

Triacyclglycerols are efficient forms for stored energy because: (2)

• They are hydrophobic molecules that pack tightly

• Fatty acids are highly reduced molecules

TOPIC 2: WATER / BUFFERS / WEAK INTERACTIONS

Hydrogen bond is ___________ (3)

• Between H-bond donor and H-bond acceptor (~3 Å long)

• Strongest when the angle at H is 180°

• Non-covalent

Charge distribution around atoms in van der Waals interactions is not _______

symmetric

What charges interact in van der Waals interactions?

Positive and negative partial charges

Why does water shield charges (high dielectric constant)?

So water can dissolve salts

What is D (dielectric constant) in water in relation to Coulombs Law?

~ 80

Second Law of Thermodynamics

Total entropy increases in a spontaneous process

Why does entropy increase when there are free water molecules?

Free molecules make more interactions (water is more ‘random’)

Hydrophobic Effect (2)

• The hydrophobic effect is the tendency of nonpolar molecules to avoid water and aggregate

• In membranes, hydrophobic tails group inward, and hydrophilic heads face water, forming a bilayer

In terms of stability, covalent bonds are ______ and ______

more stable, harder to break

A high bond energy (i.e. 100-500 kJ/mol) means ______

It takes more energy to break the bond

The general bonds from strongest to weakest are

Covalent bonds —> Ionic interactions —> Hydrogen bonds —> van der Waals interactions

How many hydrogen bonds on average does a water
molecule form in liquid water?

3.4

Why can’t liquid water form all 4 hydrogen bonds per molecule?

The molecules are constantly moving and breaking/reforming bonds due to thermal energy, so all possible bonds (4) are not viable

Buffer pH is equal to

pKa

Biological systems are generally buffered because _______

Buffers help maintain a stable pH (for proper enzyme function and cellular processes)

Buffers and Components (2)

• A buffer resists changes in pH by neutralizing acids or bases

• Consists of a weak acid and its conjugate base (or vice versa)

Lungs breathe out _______ to _______ pH

CO2, raise

Kidneys remove _______ to_______ pH

bicarbonate, lower

Equation to Calculate: pKa given Ka

pKa = -log(Ka)

Henderson-Hasslebalch Equation (2)

• pH = pKa + log([base]/[acid])

• Used to calculate the pH of a buffer based on the ratio of the conjugate base to the weak acid

TOPIC 3: AMINO ACIDS

Amino Acid Groups (5)

• Amino group (NH3+ is exception)

• Carboxylate group (COO-)

• Carbon atom

• Hydrogen atom

• R group

Glycine (2)

• Gly, G

• R group: H

Alanine (2)

• Ala, A

• R group: CH3

Valine (2)

• Val, V

• V shape

Leucine (2)

• Leu, L

• L shape, add CH2 to Valine

Isoleucine (2)

• Ile, I

• Constitutional isomer of leucine

Proline (2)

• Pro, P

• Secondary amine: 5-membered ring

Methionine (2)

• Met, M

• Methionine, has sulfur, but not at end, therefore less reactive

Phenylalanine (2)

• Phe, F

• Phenyl group attached to alanine

Tryptophan (2)

• Trp, W

• Two rings (indole)

Serine (2)

• Ser, S

• Alanine with a OH added

Threonine (2)

• Thr, T

• Valine but with OH instead of CH3

Tyrosine (2)

• Tyr, Y

• Phenylalanine with an OH added

Cysteine (2)

• Cys, C

• Sulfur group at the end, reactive

Asparagine (2)

• Asn, N

• Terminal carboxamide group

Glutamine (2)

• Gln, Q

• Terminal carboxamide group and extra CH2 in backbone

Aspartate (2)

• Asp, D

• R group is usually negatively charged (-)

Glutamate (2)

• Glu, E

• R group is usually negatively charged (-)

Lysine (2)

• Lys, K

• Second amino group, generally protonated

Arginine (2)

• Arg, R

• Guanidinium group, generally protonated

Histidine (2)

• His, H

• Imidazole group, can be protonated