Biochemistry Study Guide: Lipids, Membranes, & Chemical Bonds

Vocabulary practice flashcards generated from the biochemistry lecture notes on chemical bonds, functional groups, lipids, membrane transport, and intermolecular interactions.

Electronegativity

An atom's ability to attract shared electrons within a chemical bond.

Electronegativity Values of Common Biological Elements

Hydrogen ($H$) is $2.2$, Carbon ($C$) is $2.55$, Nitrogen ($N$) is $3.04$, and Oxygen ($O$) is $3.44$. The relative electronegativity order is $O > N > C > H$.

Nonpolar Covalent Bond

A covalent bond where electrons are shared approximately equally between atoms, characterized by an electronegativity difference of $0-0.4$.

Polar Covalent Bond

A covalent bond where electrons are shared unequally, characterized by an electronegativity difference of $0.41-1.7$, giving the more electronegative atom a partial negative charge ($\delta-$) and the less electronegative atom a partial positive charge ($\delta+$).

Ionic Bond

A chemical interaction involving fully charged or ionized atoms or groups, characterized by an electronegativity difference greater than $1.7$.

Partial Charge vs. Full Charge

Partial charges ($\delta+ / \delta-$) occur in polar covalent bonds due to unequal electron sharing, whereas full charges ($+ / -$) occur in ionic interactions between ionized atoms or groups.

Intramolecular Interactions

Strong chemical bonds or interactions occurring inside a single molecule, such as $C-C$, $C-H$, and $O-H$ covalent bonds.

Intermolecular Interactions

Generally noncovalent interactions that occur between separate molecules or groups on different molecules, including hydrogen bonds, ionic interactions, Van der Waals interactions, and hydrophobic interactions.

Hydroxyl Group

A polar functional group ($-OH$) that can form hydrogen bonds and makes molecules more hydrophilic.

Methyl Group

A nonpolar and hydrophobic functional group ($-CH_3$) consisting mostly of $C-C$ and $C-H$ bonds.

Carbonyl Group

A polar functional group ($C=O$) found in aldehydes, ketones, and carboxyl groups, where oxygen carries a $\delta-$ charge and carbon carries a $\delta+$ charge.

Carboxyl Group

A polar functional group ($-COOH$) containing carbonyl and hydroxyl groups that can form hydrogen bonds and ionize to $-COO^-$.

Amino Group

A polar functional group ($-NH_2$) capable of forming hydrogen bonds and ionizing to $-NH_3^+$.

Phosphate Group

A highly polar, ionizable functional group containing phosphorus surrounded by oxygen that often carries a negative charge and makes phospholipid heads hydrophilic.

Sulfhydryl Group

A polar functional group ($-SH$) found in some proteins that forms hydrogen bonds and can form disulfide bonds when oxidized.

Hydrophilic

Water-loving property of polar or charged molecules containing atoms like $O$, $N$, or $P$ that interact favorably with water.

Hydrophobic

Water-fearing property of nonpolar molecules rich in hydrocarbons ($C-C$ and $C-H$ bonds) that do not interact favorably with water.

Phospholipids

Amphipathic lipids consisting of a hydrophilic, phosphate-containing head group and two hydrophobic hydrocarbon fatty acid tails.

Fatty Acids

Lipid molecules consisting of a polar carboxyl group attached to a long hydrophobic hydrocarbon chain.

Steroids

Lipids characterized by a core structure of four fused carbon rings with a large hydrophobic region, such as cholesterol.

Fats (Triglycerides)

Lipids composed of a glycerol backbone esterified to three fatty acid chains, dominated by hydrocarbon regions.

Amphipathic

Describing a molecule that possesses both hydrophilic (polar/charged) and hydrophobic (nonpolar) chemical regions.

Phospholipid Bilayer

A two-layered membrane structure formed in water where hydrophilic heads orient outward toward water and hydrophobic tails face inward toward each other.

Selective Permeability

The property of cellular membranes that allows small nonpolar molecules to cross directly while preventing ions and large polar molecules from passing unassisted.

Passive Transport

The movement of substances across a membrane down their concentration gradient without requiring cellular energy ($ATP$).

Active Transport

The movement of substances across a membrane against their concentration gradient requiring energy expenditure.

Primary Active Transport

Active transport that directly hydrolyzes $ATP$ to move substances against their concentration gradient, such as the $Na^+/K^+$ pump.

Secondary Active Transport

Active transport driven by the potential energy stored in an electrochemical ion gradient rather than direct $ATP$ usage at the transporter.

Symport

A co-transport mechanism in secondary active transport where two different substances are moved across the membrane in the same direction.

Antiport

A co-transport mechanism in secondary active transport where two different substances are moved across the membrane in opposite directions.

Channel Protein

A transmembrane transport protein that acts like a tunnel or pore, allowing specific substances to pass rapidly through the membrane.

Carrier Protein

A transmembrane transport protein that binds a specific solute and changes shape to move it across the membrane.

Ion Filter

A structural region within an ion channel that determines ion selectivity and controls which specific ions can pass through.

Gate (Ion Channel)

A structural control mechanism in an ion channel that dictates whether the passage pore is open or closed.

Detergents

Amphipathic molecules whose hydrophobic region interacts with fats/oils and hydrophilic region interacts with water, forming micelles to disperse nonpolar substances.

Hydrogen Bonding

An intermolecular attraction between a partially positive hydrogen atom bound to an electronegative atom and another partially negative electronegative atom.

Van der Waals Interactions

Weak, short-range intermolecular attractions between atoms or nonpolar molecules caused by temporary fluctuations in electron distribution.

Hydrophobic Interactions

The noncovalent aggregation of nonpolar groups together in water, driven by water molecules maximizing favorable hydrogen bonding with each other.

Saturated Fatty Acid

A fatty acid chain with no carbon-carbon double bonds ($C=C$), allowing straight hydrocarbon chains to pack tightly together.

Unsaturated Fatty Acid

A fatty acid chain containing one or more double bonds ($C=C$) that introduce kinks or bends, reducing packing density and increasing membrane fluidity.

Integral Membrane Proteins

Proteins embedded within the phospholipid bilayer that contain hydrophobic amino acid regions to interact with lipid tails and hydrophilic regions exposed to water.