Unit 1: Chemistry of Life and Macromolecules
Why carbon builds everything, why water behaves like nothing else, and how four families of polymers get assembled from small repeating parts.
7 topics · 29 questions
Each topic is a path, not a menu: work down it in order and every question builds on the one above. Click any of them to watch the answer draw itself.
Carbon's Bonding Versatility and Functional Groups
- How it worksHow do carbon's four bonding electrons let it branch, ring, and chain in so many directions?
- How it worksWalk me through how swapping a hydrogen for a hydroxyl group changes what a carbon skeleton can do.
- Common mistakeWhy isn't a functional group just a decoration stuck onto an otherwise identical carbon skeleton?
- Going furtherWhat changes about a molecule's reactivity when a hydroxyl group is replaced by a phosphate group?
Your turn1 of 2
A biochemist takes a plain hydrocarbon skeleton and swaps one of its hydrogens for a hydroxyl group. A student argues nothing important changed since the carbon backbone is identical. What is wrong with that reasoning?Water, Hydrogen Bonding, and Life's Solvent
- How it worksHow does oxygen pulling harder on shared electrons give a water molecule a plus end and a minus end?
- Common mistakeWhy isn't a hydrogen bond just a weaker version of the covalent bonds inside the water molecule itself?
- How it worksWalk me through how billions of water molecules form and break hydrogen bonds fast enough to flow as a liquid.
- Worked exampleFind how many more calories it takes to heat 1 gram of water by 1 degree C than 1 gram of ethanol, given specific heats of 1.00 and 0.58 calories per gram per degree C.
- Going furtherWhat happens to water's hydrogen bond network the moment sodium and chloride ions dissolve into it?
Your turn1 of 2
Water's specific heat is 1.059 calories per gram per degree C; ethanol's is 0.627 calories per gram per degree C. How many more calories does it take to heat 1 gram of water by 1 degree C than 1 gram of ethanol by 1 degree C?pH, Buffers, and Biological Systems
- How it worksHow does a buffer soak up an added acid or base without letting the pH crash?
- Worked exampleFind the pH of a solution with a hydrogen ion concentration of 1 times 10 to the -4 molar.
- Worked exampleFind the ratio of bicarbonate to carbonic acid needed to hold blood at pH 7.4, given a pKa of 6.1.
- Common mistakeWhy isn't a solution at pH 3 simply twice as acidic as a solution at pH 6?
Your turn1 of 2
Find the pH of a solution with a hydrogen ion concentration of 7.16 times 10 to the -7 molar.Carbohydrates: From Monosaccharides to Polysaccharides
- How it worksHow do glucose units link together one by one to build a starch chain?
- Going furtherWhat changes about a polysaccharide's shape when its glucose units link at a slightly different carbon?
- Common mistakeWhy can't the human gut break down cellulose the same way it breaks down starch?
Your turn1 of 2
A cow can digest the cellulose in grass for energy, but a human eating the same grass gets no calories from it even though both cellulose and starch are polymers of glucose. Why can't the human gut break down cellulose the way it breaks down starch?Lipids: Fatty Acids, Triglycerides, and Phospholipids
- How it worksHow does a fatty acid's water-fearing tail and water-loving head decide how the molecules pack together?
- How it worksWalk me through why a phospholipid in water spontaneously forms a two-layered sheet instead of a single layer.
- Worked exampleFind which fatty acid has the higher melting point: stearic acid with zero double bonds or oleic acid with one double bond, both eighteen carbons long.
- Common mistakeWhy isn't a fat molecule with a kinked double bond automatically worse for a membrane than a straight one?
- Going furtherWhat happens to a fatty acid's melting point as more double bonds get added along its tail?
Your turn1 of 2
Stearic acid (18 carbons, zero double bonds) and oleic acid (18 carbons, one double bond) are compared side by side. Which has the higher melting point, and why?Nucleotides and the Building Blocks of Nucleic Acids
- How it worksHow do a sugar, a phosphate, and a base combine into a single nucleotide?
- How it worksWalk me through how nucleotides link through phosphodiester bonds to build a strand with direction.
- Common mistakeWhy doesn't ATP being a nucleotide mean every nucleotide in the cell gets used for energy?
- Ties togetherHow does this same nucleotide backbone chemistry show up in both DNA and RNA?
Your turn1 of 2
A student reasons that since ATP is a nucleotide and ATP powers the cell, every nucleotide in the cell must also function as an energy carrier. What is wrong with this reasoning?Amino Acids and the Chemistry of Side Chains
- How it worksHow does the side chain hanging off each amino acid's backbone give it a different personality?
- Going furtherWhat changes about an amino acid's behavior when its side chain goes from charged to purely oily?
- Common mistakeWhy isn't a protein's function decided by which amino acids it has rather than the order they sit in?
- Worked exampleFind the net charge on a short chain made of two glutamate residues and one lysine residue at neutral pH.
Your turn1 of 2
At neutral pH, a glutamate side chain carries a charge of -1 and a lysine side chain carries a charge of +1. Find the net charge on a short chain made of 4 glutamate residues and 4 lysine residues at neutral pH.