Biomolecule structure: bonds, polarity and function
הוצג| English | משמעות |
|---|---|
| peptide bond/ˈpeptaɪd bɒnd/ | קשר פפטידי |
| hydrolysis/haɪˈdrɒləsɪs/ | הידרוליזה |
What would explain this observation?
- Starch, a triglyceride and a protein can all contain carbon, hydrogen and oxygen, yet their structures and functions differ. An element list alone does not identify a biomolecule.
Build the model
- Carbohydrates include monosaccharides and polymers joined by glycosidic bonds.
- A triglyceride has glycerol joined to three fatty acids by ester bonds.
- Proteins contain amino-acid residues joined by peptide bonds 肽键; side chains and folding contribute to their properties.
- These structures support storage, membrane or functional roles depending on the molecule.
- peptide bond: A covalent linkage between amino-acid residues.
- hydrolysis 水解: Breaking a linkage using water.
What distinguishes a triglyceride in this model?
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
A triglyceride is one glycerol joined to three fatty acids by ester bonds formed in condensation reactions. Peptide bonds belong to proteins, and thymine marks DNA - neither describes a lipid.
Match each technical term to its precise meaning.
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- Condensation forms a linkage with a small molecule such as water released in the simplified model; hydrolysis uses water to break such a linkage.
- Polymer sequence, branching, polarity and three-dimensional shape matter.
- Saturated fatty acids have no carbon-carbon double bond, while unsaturated fatty acids have at least one; this difference can influence packing under stated conditions.
In the lab: Use labelled molecular models and identify the actual linkage rather than memorizing shapes alone. Compare an attributed structure with the proposed function, mark polar and non-polar regions where justified, and distinguish a monomer from a residue within a polymer. Food tests provide evidence of chemical groups under specific conditions, not complete molecular structures.
Which two habits make the investigation or model in this case more defensible?
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
Stating the conditions and assumptions lets others repeat the work exactly, and recording the supporting evidence lets them check the conclusion. Hiding disagreeing results removes the evidence that could challenge a wrong conclusion, and one measurement can never establish a wider claim.
Work from known quantities
- Known: a single unbranched peptide formed from 20 amino acids contains 19 peptide linkages.
- In a simplified condensation accounting model, forming these links releases 19 water molecules.
- A triglyceride formed from one glycerol and three fatty acids has three ester linkages and releases three waters in the corresponding model.
- These are linkage counts, not complete pathways in living cells.
Your turn: A single unbranched peptide contains 35 amino-acid residues. How many peptide bonds join them?
A single unbranched peptide contains 35 amino-acid residues. How many peptide bonds join them?
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
The result is 34 bonds. Known: 35 amino-acid residues in one unbranched chain. Each bond joins two neighbours, so peptide bonds = residues - 1 = 35 - 1 = 34. Forming them by condensation releases the same count of water molecules in this model.
Check the conclusion and its limits
- Not every protein is an enzyme, and not every catalyst is a protein.
- Lipids are not all polymers of repeating monomers.
- A protein can lose function when its folding changes without every peptide bond being broken.
Not true: Every protein is an enzyme and every lipid is a repeating-monomer polymer. Enzymes are one functional class of protein; structural and transport proteins are not enzymes. And lipids such as triglycerides are built from unlike parts, not repeating monomers, so they are not polymers.
- Carbohydrates include monosaccharides and polymers joined by glycosidic bonds.
- Condensation forms a linkage with a small molecule such as water released in the simplified model; hydrolysis uses water to break such a linkage.
- Watch for: not every protein is an enzyme, and not every catalyst is a protein.
Write from 27 peptide bonds
- A single unbranched peptide has 28 amino-acid residues.
- Find the number of peptide bonds. Condensation releases water in the simplified model.
Enzymes are one functional class of protein; structural and transport proteins are not enzymes.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
True. Enzymes are one functional class of protein; structural and transport proteins are not enzymes. And lipids such as triglycerides are built from unlike parts, not repeating monomers, so they are not polymers.
A covalent linkage between amino-acid residues: write the technical term.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
peptide bond means A covalent linkage between amino-acid residues.
A single unbranched peptide has 28 amino-acid residues. How many peptide bonds join them, and what does condensation release in the simplified model?
28 residues in one chain have 27 links. A branched chain would need its own count.
How many peptide bonds are in this chain?
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
28 minus 1 is 27 peptide bonds. Other options — 34 peptide bonds (the earlier calculation's result for 35 residues); 19 peptide bonds (the lesson example's result for 20 amino acids).