Cell and Molecular Biology - Water, Solutions, and Carbon Chemistry

Flashcards covering key biological concepts, chemical properties of water, concentration calculations, pH and buffer dynamics, organic carbon structures, isomers, and functional groups from Chapter 2 of K. Sathasivan's Cell and Molecular Biology textbook.

What is the typical percentage of water by mass in most cells and organisms?

Many cells and organisms are approximately $60\text{--}90\text{\%}$ water by mass, with some containing more than $95\text{\%}$.

What is the molecular geometry and bond angle of a water molecule?

Water has a bent molecular shape with an H-O-H bond angle of approximately $104.5^\text{o}$.

How many hydrogen bonds can a single water molecule form with neighboring water molecules?

A water molecule can form up to four hydrogen bonds: two through its hydrogen atoms and two through the lone pairs on oxygen.

What term describes the process in which dry hydrophilic materials, such as seed coats and cell walls, take up water?

Imbibition.

What is the specific heat capacity of water expressed in both calories and joules?

About $1\text{\,cal}/(\text{g} \times ^\text{o}\text{C})$, or $4.18\text{\,J}/(\text{g} \times ^\text{o}\text{C})$.

What is the heat of vaporization of water at its boiling point?

About $540\text{\,cal/g}$.

At what temperature is liquid water at its maximum density?

Liquid water is most dense near $4^\text{o}\text{C}$.

How many specified entities are contained in exactly one mole of a substance?

Exactly $6.02214076 \times 10^{23}$ specified entities.

What is the molar mass of NaOH based on atomic masses given in the text?

Approximately $40.00\text{\,g/mol}$ ($22.99 + 16.00 + 1.008 = 40.00\text{\,g/mol}$).

What molar concentration submultiple corresponds to $1 \times 10^{-6}\text{\,M}$?

1\text{\,}\times 10^{-6}\text{\,M} = 1\text{\,}\text{\mu M} (micromolar).

What formula is used to calculate the required mass in grams of a solid solute to prepare a target molar solution?

$$\text{mass required (g)} = \text{molar mass (g/mol)} \times \text{target molarity (mol/L)} \times \text{final volume (L)}$$

What equation expresses the conservation of solute during the dilution of a stock solution?

$C_1V_1 = C_2V_2$, where $C_1$ and $V_1$ are the stock concentration and volume, and $C_2$ and $V_2$ are the target concentration and final volume.

How much 10.0% NaCl stock solution is required to prepare 100.0 mL of a 2.0% NaCl solution?

$20.0\text{\,mL}$ of stock solution ($(10.0\text{\%})(V_1) = (2.0\text{\%})(100.0\text{\,mL})$).

What are the approximate hydronium and hydroxide concentrations in pure water at $25^\text{o}\text{C}$?

Each concentration is approximately $1.0 \times 10^{-7}\text{\,M}$.

What is the ion-product constant ($K_w$) for water at $25^\text{o}\text{C}$?

$K_w = [\text{H}_3\text{O}^+][\text{OH}^-] \approx 1.0 \times 10^{-14}$.

How many times greater is the hydrogen-ion activity of a solution at pH 4 compared to a solution at pH 6?

100 times greater, because the pH scale is logarithmic.

How do Brønsted-Lowry acids and bases differ according to definition?

A Brønsted-Lowry acid donates a proton, whereas a Brønsted-Lowry base accepts a proton.

What are the approximate pH values of gastric fluid and arterial blood stated in the transcript?

Gastric fluid is near pH 1–3, and arterial blood is near pH 7.4.

How does an acid's $\text{p}K_a$ value relate to its strength?

A lower $\text{p}K_a$ indicates a stronger acid, whereas a higher $\text{p}K_a$ indicates a weaker acid.

Under what condition does an acid-conjugate base pair exhibit its greatest buffering capacity?

When the $\text{pH} = \text{p}K_a$, at which point the protonated acid and conjugate base are present at equal concentrations.

What is the effective buffering range for a buffer relative to its $\text{p}K_a$?

Approximately $\text{p}K_a \pm 1$ pH unit.

What is the $\text{p}K_a$ of acetic acid at $25^\text{o}\text{C}$?

Approximately $4.76$.

Which buffer with a $\text{p}K_a$ of 8.1 is commonly used for DNA experiments that require a pH range of 7 to 9?

Trizma buffer.

Which four elements make up most of living matter?

Carbon, hydrogen, oxygen, and nitrogen.

What defines a saturated carbon chain versus an unsaturated carbon chain?

A saturated carbon chain has no carbon-carbon double or triple bonds, whereas an unsaturated chain contains one or more double or triple bonds.

What are structural (constitutional) isomers?

Isomers that have the same molecular formula but differ in the covalent connections (connectivity) among their atoms, such as leucine and isoleucine ($\text{C}_6\text{H}_{13}\text{NO}_2$).

What is the difference between cis and trans geometric isomers?

In cis isomers, comparable substituents lie on the same side of a restricted bond (such as a double bond); in trans isomers, they lie on opposite sides.

Why is the amino acid glycine achiral?

Because its central carbon is bonded to two hydrogen atoms, meaning it lacks four different substituents.

Which enantiomers of amino acids are used almost exclusively to construct proteins?

L-amino acids.

How do aldehydes and ketones differ in terms of carbonyl group position?

An aldehyde has a terminal carbonyl group (\text{\gt C=O}) with a hydrogen attached to the carbon, whereas a ketone has an internal carbonyl group bonded to two carbons.

What state do free amino acids predominantly adopt near neutral pH?

Zwitterions, which feature a protonated amino group ($-\text{NH}_3^+$) and a deprotonated carboxyl group ($-\text{COO}^-$).

What covalent bond is formed by the oxidation of two cysteine sulfhydryl ($-\text{SH}$) groups?

A disulfide bond ($-\text{S-S-}$), creating cystine.

What forms does inorganic phosphate ($\text{P}_i$) mainly take near physiological pH?

Mainly $\text{H}_2\text{PO}_4^-$ and $\text{HPO}_4^{2-}$.

What is the typical chemical effect of adding a methyl group ($-\text{CH}_3$) to a organic molecule?

A methyl group is nonpolar and usually increases the hydrophobic character of the molecule.