Chapter summary
Biomolecules: structure explains function, at a glance
Scan the key ideas, or hide the answers and try to recall them.
01
Alpha-glucose and beta-glucose
How can moving one group change the polymer?
Key idea and reminders
Alpha- and beta-glucose have the same molecular formula but differ in the orientation of the hydroxyl group at carbon 1 in the ring form.
- Glucose is a soluble monosaccharide.
- The orientation at carbon 1 distinguishes the forms.
Keep in mind: Both have formula C6H12O6. They differ in arrangement at carbon 1, not their numbers of carbon, hydrogen and oxygen atoms.
02
Starch stores; cellulose supports
How do glycosidic bonds change the chain?
Key idea and reminders
Starch has alpha-glucose chains suited to storage. Cellulose has beta-glucose chains that form strong fibres through many hydrogen bonds.
- Amylose is unbranched; amylopectin is branched.
- Cellulose has beta-1,4 bonds and interchain hydrogen bonds.
Keep in mind: Hydrolysis uses water. Condensation forms the bond and releases water.
03
One glycerol, two different lipid designs
Why does a phospholipid form a bilayer?
Key idea and reminders
A triglyceride has three fatty acids joined to glycerol. A phospholipid has two fatty-acid tails and a phosphate-containing head, giving it both hydrophobic and hydrophilic regions.
- Condensation forms ester bonds; hydrolysis breaks them.
- Phospholipids are amphipathic; triglycerides are largely hydrophobic.
Keep in mind: In the standard model, a phosphate-containing head replaces one fatty-acid position, leaving two hydrophobic tails.
04
Join amino acids in a particular order
Which part varies and which part forms the link?
Key idea and reminders
An amino acid has an amino group, a carboxyl group, hydrogen and an R group around its central carbon. Peptide bonds join the amino and carboxyl groups of adjacent units.
- The R group is the variable side chain.
- A linear chain of n amino acids has n - 1 peptide bonds.
Keep in mind: Peptide bonds join amino and carboxyl groups to form the backbone. R-group interactions contribute to higher levels of structure.
05
Four levels of protein structure
Which bonds hold each level together?
Key idea and reminders
Sequence constrains folding. Hydrogen bonds stabilise local structures, while interactions among side chains help create the overall three-dimensional shape.
- Secondary structure uses hydrogen bonds between backbone groups.
- Tertiary shape includes ionic, hydrogen, disulfide and hydrophobic interactions.
Keep in mind: Quaternary structure requires more than one polypeptide subunit. A functional single-chain protein lacks this level.
06
When protein shape changes
Why can heat or pH alter function without cutting the chain?
Key idea and reminders
High temperature and extreme pH can disrupt interactions maintaining a protein's shape. Denaturation usually alters higher-order structure while leaving peptide bonds intact.
- pH can change side-chain charges.
- Loss of function does not prove peptide bonds were broken.
Keep in mind: Denaturation concerns loss of normal folding. Hydrolysis breaks peptide bonds and is a different process.
07
Haemoglobin carries oxygen reversibly
How does a four-subunit protein serve transport?
Key idea and reminders
Adult haemoglobin has four polypeptide subunits, each with an iron-containing haem group that can bind one oxygen molecule reversibly.
- Four subunits, four haem groups, up to four O2 molecules.
- Quaternary structure and reversible binding both matter for transport.
Keep in mind: It can bind up to four oxygen molecules, one at each haem group, and binding must be reversible for transport.