Biology: Human Body Composition, Water, pH, and Biomolecular Bonds

What percentage of a standard 75-kg adult is water?

About 60%.

What percentage of body weight is protein?

About 16%.

What percentage of body weight is triglyceride (fat)?

About 13%.

What is the primary function of water in the body?

It is the primary solvent of life.

What is a major function of protein in the body?

Structural support, enzymatic catalysis, membrane transport, and motility.

What is the main storage form of metabolic energy?

Triglycerides (fat).

What do insoluble inorganic salts primarily provide?

Strength to bones; they are mostly calcium phosphate.

What is the main role of nucleic acids?

Storage and transmission of genetic information.

Which major ion is high in extracellular fluid?

Na+ (sodium).

Which major ions are high in cytoplasm?

K+ and Mg2+.

What is the approximate pH of extracellular fluid?

About 7.4.

What is the approximate pH range of cytoplasm?

About 6.5-7.5.

Why is water an electrical dipole?

Electrons are displaced toward oxygen, giving O a partial negative charge and H atoms partial positive charges.

What is the approximate angle between the H-O bonds in water?

105°.

What is a hydrogen bond?

A weak attraction involving a hydrogen attached to an electronegative atom, such as O or N, and another electronegative atom.

How strong is a water hydrogen bond compared with an O-H covalent bond?

A water hydrogen bond is about 29 kJ/mol; breaking an O-H covalent bond requires about 450 kJ/mol.

How does water dissolve salts?

Through ion-dipole interactions.

Which end of water attracts cations?

The oxygen/partial-negative end.

Which end of water attracts anions?

The hydrogen/partial-positive end.

What is pH?

The negative logarithm of hydrogen ion concentration: pH = −log[H+].

What happens to [H+] when pH changes by 1 unit?

It changes by a factor of 10.

What is the relationship between [H+] and [OH−] at 25°C?

[H+][OH−] = 10^−14 mol/L.

What is a Brønsted acid?

A proton donor.

What is a Brønsted base?

A proton acceptor.

What happens to a carboxyl group at physiological pH?

It is mainly deprotonated and negatively charged.

What happens to an amino group at physiological pH?

It is mainly protonated and positively charged.

What is an ionizable group?

A group capable of dissociating to yield H+ or gain/lose charge.

What is pK?

The pH at which an ionizable group is 50% protonated and 50% deprotonated.

At pH below pK, is an ionizable group mostly protonated or deprotonated?

Mostly protonated.

At pH above pK, is an ionizable group mostly protonated or deprotonated?

Mostly deprotonated.

What is the Henderson-Hasselbalch equation?

pH = pK + log([base]/[acid]).

What is normal arterial blood pH?

About 7.40.

What is normal venous blood pH?

About 7.35.

Why is venous blood slightly more acidic than arterial blood?

It contains more CO2, which forms carbonic acid.

What is a buffer?

A mixture of a weak acid and its conjugate base that resists changes in pH.

What is the most important physiological buffer system?

The bicarbonate/carbonic acid system.

Which organ primarily regulates CO2 in the bicarbonate buffer system?

The lungs.

Which organ primarily regulates HCO3−?

The kidneys.

Why is phosphate an especially important intracellular buffer?

Phosphate concentrations are relatively high inside cells.

What is acidemia?

Arterial blood pH below 7.35.

What is alkalemia?

Arterial blood pH above 7.45.

What is respiratory acidosis?

A disorder caused primarily by CO2 retention, usually from hypoventilation.

What is respiratory alkalosis?

A disorder caused primarily by excessive CO2 loss, usually from hyperventilation.

What is metabolic acidosis?

A disorder caused by excess acid production or failure to excrete acid.

What is metabolic alkalosis?

A disorder caused by abnormal loss of acid, such as excessive vomiting.

What brain region is the primary respiratory control center?

The medulla oblongata.

What are the six major elements of biomolecules emphasized in the guide?

Carbon, hydrogen, oxygen, nitrogen, sulfur, and phosphorus.

What is a condensation reaction?

A reaction that joins molecules while releasing water.

What is hydrolysis?

Cleavage of a chemical bond by addition of water.

What is an ionic bond?

Attraction between oppositely charged ions, typically involving a metal and nonmetal.

What is a covalent bond?

A bond in which atoms share electrons.

What is an endergonic process?

A process requiring an input of free energy; ΔG is positive.

What is an exergonic process?

A process that releases free energy; ΔG is negative.

What types of bonds are considered energy-rich in the guide?

Anhydride, phosphoanhydride, and thioester bonds.

What is an isomer?

A compound with the same molecular formula as another compound but a different structure.

What are constitutional isomers?

Compounds with the same molecular formula but different atomic connectivity.

What are positional isomers?

Compounds with the same composition but different positions of functional groups.

What are enantiomers?

Non-superimposable mirror-image optical isomers.

What are diastereomers?

Stereoisomers that are not mirror images; epimers are a type.

What are geometric isomers?

Isomers differing in arrangement around a rigid bond or ring, such as cis/trans forms.

Why are noncovalent interactions important?

They determine solubility, macromolecular shape, and molecular binding/communication.

What is a hydrogen bond in biomolecules?

A dipole-dipole interaction involving H bound to O or N.

What is an electrostatic/salt interaction?

Attraction between oppositely charged groups, such as NH3+ and COO−.

What is an ion-dipole interaction?

Attraction between a charged ion and a polar bond.

What is a hydrophobic interaction?

Clustering of nonpolar groups to minimize their contact with water.

What are van der Waals forces?

Weak attractions from induced dipoles at optimal distances; excessive closeness causes repulsion.

What is the basic structure of a triglyceride?

One glycerol esterified to three fatty acids.

What is a saturated fatty acid?

A fatty acid containing only single carbon-carbon bonds.

What is an unsaturated fatty acid?

A fatty acid containing one or more carbon-carbon double bonds.

What is a monosaccharide?

The simplest type of sugar, such as glucose, fructose, or galactose.

Why is D-glucose especially important?

It is a major metabolic fuel for cellular respiration.

What bond links monosaccharides?

A glycosidic bond.

What is a disaccharide?

A carbohydrate containing two monosaccharides.

What is an oligosaccharide?

A carbohydrate containing about 3-6 monosaccharides.

What is a polysaccharide?

A carbohydrate containing 7 or more monosaccharides.

What is an epimer?

A diastereomer differing in configuration at only one chiral carbon.

What is an anomer?

An isomer differing at the anomeric carbon, producing α and β forms.

What is mutarotation?

Spontaneous interconversion between α and β anomers in solution.

What is the difference between furanose and pyranose?

Furanose has a five-membered ring; pyranose has a six-membered ring.

What is the anomeric carbon?

The carbon that becomes asymmetric during ring formation and is attached to the ring oxygen and the anomeric OH/group.

What are the approximate α- and β-D-glucose proportions in aqueous solution?

β-D-glucose ~66%; α-D-glucose ~34%.

What are the three major polysaccharides listed?

Amylose, glycogen, and cellulose.

What is glycogen?

A branched animal storage polysaccharide.

What is cellulose?

A structural plant polysaccharide.

What is amylose?

An unbranched component of starch.

What are the monomers of proteins?

20 different L-amino acids.

What bond links amino acids in proteins?

Peptide bonds.

Which amino acid lacks a chiral center?

Glycine.

What is the basic structure of an amino acid?

An α-carbon attached to an α-carboxyl group, α-amino group, H, and variable R group.

What is a zwitterion?

A molecule carrying both positive and negative charges with a net charge of zero.

What is the approximate pK of the α-carboxyl group?

About 2.0.

What is the approximate pK of the α-amino group?

About 9-10.

What is the isoelectric point (pI)?

The pH at which a molecule has a net charge of zero.

What is the difference between pK and pI?

pK describes an ionizable functional group; pI describes the entire molecule's net-zero-charge pH.

Which amino acids are acidic at physiological pH?

Aspartate and glutamate.

Which amino acids are basic at physiological pH?

Lysine and arginine; histidine is weakly basic.

Which amino acids have branched hydrophobic side chains?

Valine, leucine, and isoleucine.

Which amino acids have hydroxyl side chains?

Serine and threonine.

Which amino acids contain sulfur?

Cysteine and methionine.

Which amino acids are aromatic?

Phenylalanine, tyrosine, and tryptophan.