UNIT 2 FRQs / Last minute cram

Winter wheat (Triticum aestivum) survives freezing temperatures by altering the lipid composition of its plasma membranes through the action of fatty acid desaturase enzymes, which convert saturated fatty acid tails into unsaturated fatty acid tails. Researchers isolate wild-type winter wheat cells and a mutant strain lacking functional desaturase enzymes. Both cell cultures are grown at a moderate temperature of  before being transferred to a cold chamber maintained at . The researchers then measure the rate of passive glucose entry into the cells via transmembrane carrier proteins down a concentration gradient

(a) State the null hypothesis regarding the effect of the desaturase mutation on the rate of passive glucose transport across the plasma membrane at 4 degrees celcius

The desaturase mutation on the rate of passive glucose transport across the plasma membrane at 4 degrees celcius will have no effect.

Winter wheat (Triticum aestivum) survives freezing temperatures by altering the lipid composition of its plasma membranes through the action of fatty acid desaturase enzymes, which convert saturated fatty acid tails into unsaturated fatty acid tails. Researchers isolate wild-type winter wheat cells and a mutant strain lacking functional desaturase enzymes. Both cell cultures are grown at a moderate temperature of  before being transferred to a cold chamber maintained at . The researchers then measure the rate of passive glucose entry into the cells via transmembrane carrier proteins down a concentration gradient

(b) State an alternative hypothesis predicting how exposing wild-type winter wheat cells to  will alter the structural composition of their plasma membrane lipids over time

Exposing wild-type winter wheat cells to 4 degrees celcius temperature will alter the structural composition of the plasma membrane lipids by creating an increase of unsaturated fatty acid tails to prevent tight packing and increase fluidity to survive in such cold temperatures.

Winter wheat (Triticum aestivum) survives freezing temperatures by altering the lipid composition of its plasma membranes through the action of fatty acid desaturase enzymes, which convert saturated fatty acid tails into unsaturated fatty acid tails. Researchers isolate wild-type winter wheat cells and a mutant strain lacking functional desaturase enzymes. Both cell cultures are grown at a moderate temperature of  before being transferred to a cold chamber maintained at . The researchers then measure the rate of passive glucose entry into the cells via transmembrane carrier proteins down a concentration gradient

(c) Predict the relative rate of passive glucose transport in the desaturase-mutant cells compared to the wild-type cells after 24 hours at , and justify your prediction referencing hydrocarbon tail structure, membrane packing, and protein function

The relative rate or passive glucose transport will significantly decrease in the desaturase-mutant cells compared to the wild-type cells after 24 hours at 4 degrees celcius. This is because the desaturase-mutant cells lack functional desaturase enzymes which allow fluidity in the cell. because Glucose is a large molecule, it needs a transmembrsne protein to assist with its diffusion.

Because carrier proteins must undergo conformational (shape) changes to shuttle polar glucose molecules across the membrane, the rigid, solidified lipid environment restricts protein mobility and halts facilitated diffusion

Winter wheat (Triticum aestivum) survives freezing temperatures by altering the lipid composition of its plasma membranes through the action of fatty acid desaturase enzymes, which convert saturated fatty acid tails into unsaturated fatty acid tails. Researchers isolate wild-type winter wheat cells and a mutant strain lacking functional desaturase enzymes. Both cell cultures are grown at a moderate temperature of  before being transferred to a cold chamber maintained at . The researchers then measure the rate of passive glucose entry into the cells via transmembrane carrier proteins down a concentration gradient

(d) Describe a control experiment or treatment researchers should perform to confirm that any observed reduction in glucose uptake at low temperatures is caused by altered membrane lipid fluidity rather than the irreversible denaturation or structural destruction of the glucose carrier proteins

Researchers should rewarm the cold-treated cells back to moderate temperatures and remeasure the rate of glucose transport. If the carrier proteins were permanently denatured by cold, returning to 25 degrees would not restore glucose transport. However, if the carrier proteins remain functional and the transport reduction was purely due to membrane solidification, returning to 25 degrees restores membrane fluidity, allowing carrier proteins to immediately resume normal transport rates