Chapter 3—The Molecules of Life

Compare a dehydration reaction to hydrolysis:

A dehydration reaction involves removing a molecule of water—putting monomers together in the process—creating polymers, while a hydrolysis (to break [lyse] with water [hydro]) reaction adds water—breaking the monomer's bonds—dehydration and hydrolysis are reverse processes

Describe the special bonding properties of carbon that allow it to form an endless variety of organic molecules:

Carbon is very versatile when it comes to molecular ingredients A carbon atom has four valence electrons and can complete its shell by sharing electrons with other atoms in four covalent bonds that can branch off Carbon can bond with other carbon atoms Molecules with multiple carbon "intersections" can form elaborate shapes Carbon atoms of organic compounds can also partner with other common elements such as: hydrogen, oxygen, and nitrogen

Describe the unique properties of lipids:

Lipids are hydrophobic Lipids are a diverse group of molecules made from different "building blocks" (they are not macromolecules or polymers) There are two types of lipids: fat and steroids

Compare the structures and roles of monosaccharides, disaccharides, and polysaccharides in living organisms. Give examples of each:

MONOSACCHARIDES: simple sugars, monomers of carbohydrates that cannot be broken into smaller sugars i.e. glucose (C6H12O6) and fructose (has the same molecular formula as glucose but a different arrangement—isomer) monosaccharides tend to provide the energy for cellular work DISACCHARIDES: double sugar, constructed from two monosaccharides by a dehydration reaction i.e. lactose ("milk-sugar"), maltose, or sucrose (table sugar) POLYSACCHARIDES: complex carbohydrates, polymers of monosaccharides i.e. starch (linear), glycogen (branched), cellulose (cross-linked) These are all carbohydrates by the way Monosaccharides and disaccharides dissolve readily in water, forming sugary solutions, while cellulose does not, but water adheres to the surface (a fluffy bath towel being water absorbent because of the cellulose) Almost all carbohydrates are hydrophilic molecules

Describe and compare the structures of DNA and RNA:

Nucleic acids are made up of monomers called nucleotides. Each nucleotide consists of a sugar (deoxyribose/ribose), phosphate group, and nitrogenous base (G,C,A,T/U) Dehydration reactions link nucleotide monomers into long polynucleotide chains—DNA strands DNA: (deoxyribose nucleic acid) RNA: (ribonucleic acid) Both are polymers of nucleotides RNA has the base "uracil" instead of DNA's "thymine" and RNA is single stranded, DNA exists in a double helix

Define organic chemistry:

Organic chemistry is the branch of chemistry dealing with organic molecules/compounds—they contain carbon

Describe the structure of proteins and how temperature and pH can affect their shape and function. Distinguish between the primary structure and the final three-dimensional shape:

PROTEINS: polymers of amino acid (20 different kinds) monomers—most diverse/elaborate molecules—thousands of proteins that have a unique three-dimensional shape corresponding to its specific function AMINO ACIDS: consists of a central carbon atom bonded to four covalent partners (remember carbon always forms four covalent bonds *wink*) Peptide bonds exist between adjacent amino acids through dehydration reactions—resulting in a polypeptide chain PRIMARY STRUCTURE: the specific amino acid sequence, the "spelling" of the polypeptide The polypeptide chain(s) fold(s) into an intricate 3-D shape to be a functioning protein, enabling it for a specific function in a cell; "function follows form" There are primary, secondary, tertiary, and quaternary levels of structure in a protein depending on how many polypeptide chains form it DENATURATION: an unfavorable change in temperature, pH, or some other quality of the environment causes the protein to unravel and lose its normal shape (egg white become opaque when you cook it because the protein denatures) Fevers are dangerous because they can eventually lead up to the denaturation of proteins in the body

Explain why lactose intolerance has evolved differently in humans spread throughout the world:

The availability of milk in the area affects how lactose intolerance has evolved differently in humans. The domestication of cattle in Northern Europe allowed for milk and dairy products to be available year-round—natural selection would've favored anyone with the lactase gene on. Other cultures where dairy isn't a staple would result in natural selection not favoring such a mutation because there is no need to drink milk. Ability to drink milk has been a result of thousands of years in the practice.

Compare the structure and properties of saturated and unsaturated fatty acids:

Three fatty acids attach to a glycerol molecule joined together by a dehydration reaction to create a typical fat—triglyceride SATURATED FATTY ACIDS: have the maximum number of hydrogen atoms, thus they have a straight shape—a saturated fat has all of its three fatty acid tails full of hydrogen atoms (tend to be solid at room temperature) UNSATURATED FATTY ACIDS: don't have the maximum amount of hydrogen atoms, thus, the tail bends at the double bond—if one or more of the fatty acids are unsaturated, it's an unsaturated fat (most are liquid at room temperature) Polyunsaturated fat has several double bonds within its fatty acids

Explain why we think that lactose intolerance has a genetic basis:

Why else? We thought that there must have been a defect in their lactase gene, but most lactose-intolerant people have a normal version of the lactase gene. They actually found out that there is a regulatory protein that interacts with the nucleotides near the lactase gene—approximately 14,000 nucleotides nearby. The regulatory protein prevents that part of the gene from being expressed, it only lets go of its "bear-hug" when lactose is present and goes back on when it's all gone.