AP Biology Unit 1 Topic 1.5: How Structure Determines Function in Biological Macromolecules

Question 1

What does it mean that structure determines function?

Accepted Answer

Structure determines function means that the shape and chemical properties of a molecule determine what it can do biologically. A protein cannot bind a substrate it does not fit, an enzyme cannot catalyze a reaction without the right active site, and DNA cannot be read without the correct base pairing. Form precedes function in biology.

Question 2

How does enzyme structure relate to function?

Accepted Answer

An enzyme has a specific three-dimensional shape with an active site that fits its substrate like a lock fits a key, or more accurately like a hand fits a glove that flexes around it. This shape complementarity allows the enzyme to bind specific molecules and catalyze a particular reaction.

Question 3

How do membrane proteins illustrate structure-function relationships?

Accepted Answer

Membrane proteins have hydrophobic regions that span the lipid bilayer and hydrophilic regions that face the watery environment inside and outside the cell. This dual nature allows them to bridge the membrane and serve as channels, pumps, receptors, and enzymes. Their structure perfectly fits their environment.

Question 4

How does the structure of phospholipids enable membrane formation?

Accepted Answer

Phospholipids are amphipathic, meaning they have both hydrophilic phosphate heads and hydrophobic fatty acid tails. In water, this dual nature drives them to spontaneously form a bilayer where tails point inward and heads point outward. The structure literally forces the function of forming a barrier.

Question 5

How does cellulose structure relate to its function in plants?

Accepted Answer

Cellulose has straight, unbranched chains of glucose connected by beta bonds that pack into tight bundles called microfibrils through hydrogen bonding. This straight, tightly packed structure makes cellulose strong enough to support plant cell walls against turgor pressure, perfectly matching its structural function.

Question 6

How does DNA structure enable its function?

Accepted Answer

DNA is a double helix with two complementary strands held together by hydrogen bonds between base pairs. The complementary base pairing means each strand contains all the information needed to reconstruct the other, which is essential for accurate replication. The structure directly enables the function of information storage and transmission.

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