Exam 2 Review - Nucleic Acids, Carbohydrates, Lipids & Cell Biology

Practice flashcards designed for Exam 2 review covering Chapters 4, 5, 6, and 7 on nucleic acids, carbohydrates, lipids, cell membranes, transport, and eukaryotic organelles.

What primary biological function do nucleic acids fulfill in living organisms?

Nucleic acids store the information that encodes life.

How do DNA and RNA differ in their primary specialization regarding biological function?

DNA is specialized for stability and long-term information storage, whereas RNA is specialized for structural versatility and catalysis.

What key structural difference between ribose and deoxyribose is identified at the $2'$ carbon position?

Ribose contains a hydroxyl group ($-OH$) attached to the $2'$ carbon, whereas deoxyribose contains a hydrogen atom ($-H$) attached to the $2'$ carbon.

Which nitrogenous bases belong to the pyrimidine class and which belong to the purine class?

Cytosine, uracil, and thymine are single-ring pyrimidines, while guanine and adenine are double-ring purines.

What reaction polymerizes nucleotides into nucleic acids, and which functional groups form the phosphodiester linkage?

A condensation reaction forms a phosphodiester linkage between the $3'\text{-OH}$ group of one nucleotide sugar and the $5'\text{-phosphate}$ group of an adjacent nucleotide, producing a molecule of water ($H_2O$).

What hydrogen-bonding rule governs complementary base pairing between nitrogenous bases in DNA?

Guanine ($G$) pairs with cytosine ($C$) forming three hydrogen bonds, and adenine ($A$) pairs with thymine ($T$) forming two hydrogen bonds.

What secondary structure is formed when a single strand of RNA folds back on itself via complementary base pairing?

RNA folds into a hairpin (stem-loop) secondary structure, where complementary bases on the same strand form hydrogen bonds.

What are the three major functional roles played by carbohydrates in biological systems?

Carbohydrates function in cell structure, cell identity, and energy storage.

How are aldose and ketose monosaccharides distinguished structurally by the location of their carbonyl group ($C=O$)?

An aldose has its carbonyl group ($C=O$) at the end of the carbon chain (carbon-1), whereas a ketose has its carbonyl group inside the carbon chain (carbon-2).

What structural variation differentiates glucose from galactose?

Glucose and galactose are stereoisomers that differ in the spatial orientation of the hydroxyl group ($-OH$) attached to carbon-4 ($C\text{-}4$).

What determines whether a cyclic monosaccharide forms an $\beta$ or $\text{anomer}$ upon ring closure?

The orientation of the newly formed hydroxyl group ($-OH$) at carbon-1 ($C\text{-}1$) determines the anomer: pointing down relative to C-6 produces $\text{alpha}(\frac{}{})\text{-glucose}$, whereas pointing up produces $\beta\text{-glucose}$.

How do $\text{alpha-}1,4\text{-glycosidic}$ linkages and $\beta\text{-}1,4\text{-glycosidic}$ linkages differ in structural geometry?

In $\text{alpha-}1,4\text{-glycosidic}$ linkages, the bridging oxygen atom points downward between both C-1 and C-4 monomer units, while in $\beta\text{-}1,4\text{-glycosidic}$ linkages, the oxygen bridge points upward and alternates orientation.

How do cell-surface carbohydrates contribute to cell identity?

Carbohydrates covalently bonded to proteins (glycoproteins) and lipids (glycolipids) extend outside the plasma membrane to serve as molecular recognition tags for cell identity.

What are the structural components of steroids and fats (triacylglycerols)?

Steroids consist of a bulky four-ring carbon backbone, whereas fats consist of a glycerol molecule linked to three fatty acid chains through ester linkages.

What structural feature makes phospholipids amphipathic?

Phospholipids possess a polar, hydrophilic head (a charged phosphate group linked to glycerol) and nonpolar, hydrophobic tails composed of two hydrocarbon/fatty acid chains.

What distinguishes active transport from passive transport across cell membranes?

Passive transport moves substances down their concentration gradient without energy input, whereas active transport uses energy (such as ATP) to pump molecules against their concentration gradient (e.g., the $Na^+/K^+$ pump).

What process occurs when solute molecules move across a membrane until equilibrium is achieved?

Dynamic diffusion, where solutes move net down a concentration gradient until equal concentrations are established on both sides of the membrane.

What happens to a membrane vesicle when placed in hypertonic, hypotonic, and isotonic solutions?

In a hypertonic solution, water flows out and the vesicle shrinks; in a hypotonic solution, water flows in causing the vesicle to swell or burst; in an isotonic solution, net water movement is zero and volume remains unchanged.

How does relative permeability of a phospholipid bilayer vary among different classes of chemical species?

Phospholipid bilayers exhibit high permeability to small nonpolar molecules, moderate permeability to small uncharged polar molecules, low permeability to large uncharged polar molecules, and extremely low permeability (impermeability) to small ions.

What structural features visually distinguish a eukaryotic animal cell from a prokaryotic cell?

A eukaryotic animal cell contains membrane-bound organelles including a prominent nucleus, endoplasmic reticulum, Golgi apparatus, and mitochondria, which are absent in prokaryotic cells.

Which cellular organelles shown in a eukaryotic plant cell are absent in an animal cell?

Chloroplasts, a large central vacuole, and a rigid outer cell wall surrounding the plasma membrane.