Biomolecules
A runner eats pasta before a race. Which biomolecule in pasta provides glucose for cellular respiration? Explain the connection
Carbohydrates. Cells break starch into sugars, including glucose, that can fuel cellular respiration
An enzyme speeds a reaction at body temperature. What does an enzyme do to speed the reaction?
The enzyme lowers activation energy.
A cell releases large quantities of digestive proteins. Why would abundant rough ER support this function?
Ribosomes associated with rough ER synthesize proteins entering the secretion pathway. Rough ER also supports their folding and initial processing.
A gland cell makes a protein hormone. Which structure assembles its amino acids, and what molecule provides the immediate instructions?
A ribosome assembles amino acids using the sequence iin RNA,
Lysosomal enzymes stop working. What material is likely to accumulate, and which cell process becomes less effective?
Undigested large molecules and damaged cell components accumulate. Intracellular digestion and recycling become less effective.
A seed stores energy for germination. Why would lipids be useful for storing a large energy reserve in a small mass?
Lipids store more energy per gram than carbohydrates. Their many energy-rich bonds make them effective long-term energy reserves.
An enzyme breaks down starch but does not break down a protein. What feature best explains this difference?
The active site has a shape and chemical properties suited to particular substrates. Starch and proteins have different structures and bonds.
Muscle mitochondria have extensively folded inner membranes. How does this structure support repeated contraction?
The folds increase surface area for electron transport and ATP synthase. ATP production supplies energy for muscle contraction.
A newly made secreted protein enters the rough ER. Name the next major processing organelle and explain how the protein gets there.
The Golgi apparatus. Transport vesicles carry the protein from the rough ER to the Golgi for further modification and sorting.
Airway cells produce normal mucus, but their cilia cannot move. Predict how this affects respiratory defense.
Mucus and trapped microbes are cleared less effectively. Their retention increases the opportunity for infection even though mucus production continues.
Cellulose and starch both contain glucose. Why can humans digest starch for energy but cannot digest cellulose?
Their glucose units have different bond arrangements. Human digestive enzymes break starch bonds but lack the enzymes needed to break cellulose bonds.
An enzyme works slowly at 5°C and rapidly at 35°C. Activity returns when a chilled sample warms to 35°C. Why is permanent denaturation a poor explanation?
Recovery shows that the enzyme retained a functional structure. Cooling usually slows molecular motion and productive collisions rather than permanently changing the active site.
A leaf cell contains many Chloroplasts Predict how extensive damage to these membranes affects sugar production. Explain why.
Sugar production decreases.
Protein synthesis is normal, but a cell cannot sort proteins to their correct destinations. Which organelle is the leading suspect, and why?
The Golgi apparatus. It modifies and sorts proteins into routes that deliver them to specific destinations. The evidence suggests a sorting problem rather than a synthesis problem.
A chemical sharply reduces mitochondrial ATP (energy) production. Predict the effect on membrane pumps that are powered by ATP.
Pump activity decreases as ATP becomes limited. This may prevent some material from getting across the cell membrane
A drug blocks RNA production but leaves DNA intact. Existing proteins work briefly, then enzyme activity declines. Explain how nucleic acids and proteins connect these observations.
DNA contains instructions that cells transcribe into RNA. Without new RNA, protein synthesis eventually declines as existing RNA and proteins break down. Cells cannot adequately replace enzymes.
With enzyme amount held constant, reaction rate rises as substrate increases, then levels off. Explain the plateau and predict the effect of adding more enzyme.
At the plateau, enzyme active sites are occupied much of the time. Adding enzyme supplies more active sites and can increase the rate if enough substrate remains available.
A plant cell loses water and becomes limp while its cell wall stays intact. Explain how the vacuole and cell wall normally work together to support the plant.
Water in the central vacuole helps generate turgor pressure. The cell contents press against the resisting cell wall. Water loss lowers this pressure and reduces support.
A cell has normal hormone RNA and normal total hormone protein, but hormone accumulates in the rough ER. The Golgi works normally on other cargo. Identify the likely disrupted step.
Export from the rough ER or delivery to the Golgi. A transport-vesicle or cargo-selection defect could prevent this hormone from reaching the Golgi despite normal synthesis.
A treated plant cell produces less sugar in light. Supplied sugar restores much of its ATP production. Does the evidence more strongly suggest chloroplast damage or complete mitochondrial failure? Explain.
Chloroplast damage is better supported. Reduced photosynthesis limits sugar production, while ATP recovery after sugar addition indicates that cellular respiration remains functional. This evidence does not identify the exact damaged component.
A mutation changes the amino acid sequence of a membrane transport protein. Predict how this could change transport even if the cell produces the normal amount of protein.
A changed amino acid sequence can alter folding and the shape of a binding site or channel. The protein may transport less material even when its amount is unchanged.
A digestive enzyme works best in acidic conditions. At neutral pH, activity drops even though enzyme and substrate amounts stay constant. Explain the cause.
pH can change charges and interactions that maintain the active site, reducing function.
A cell can make phospholipids but cannot make functional membrane transport proteins. Predict how its membrane could form yet fail to maintain normal internal conditions.
Phospholipids can still form a bilayer. Without working channels, carriers, or pumps, transport of selected substances becomes impaired. Ion gradients and nutrient balance can be disrupted.
Secretory vesicles reach the cell surface but cannot fuse with the plasma membrane. Predict hormone levels inside and outside the cell, then explain whether extra ribosomes would solve the problem.
Hormone accumulates inside vesicles and release outside decreases. Extra ribosomes would not repair membrane fusion. More synthesis could increase the internal buildup.
Two cells release little protein. Cell A has normal RNA but makes little protein. Cell B makes normal protein that accumulates in the Golgi. Propose a different failure for each and one test for B.
A may have impaired translation. B may have impaired Golgi export or later secretion.