Question

extension questions

1. the image below is a transmembrane protein that cl - ions move through via diffusion. four amino acids at sites 1 - 4 are indicated in the image. site 1 is exposed to the fluid surrounding a cell, which is mostly water. site 2 is exposed to the fatty acid tails in the lipid bilayer of the cell. site 3 is oriented towards the interior of the protein and helps make up the channel that allows cl - ions to move through the channel (in essence, site 3 interacts with cl - ions. site 4 is exposed to the fluid in the interior of the cell, which is mostly water.

given this information, determine the properties of the amino acids at each site that would produce a properly designed channel that would allow cl - ions to move across a membrane via diffusion.

1. consider your answers to the previous question (27). imagine a mutation in the dna of an organism causes the replacement of the amino acid at site 3 with a negatively (-) charged amino acid. how, if at all, would this impact the movement of cl - ions through this transmembrane protein? explain your answer.

Explanation:

Step1: Analyze site 1

Site 1 is in water - based fluid, so amino acids should be hydrophilic to interact well with water.

Step2: Analyze site 2

Site 2 is in the lipid - bilayer fatty acid tails, so amino acids should be hydrophobic to be compatible with the non - polar lipid environment.

Step3: Analyze site 3

Site 3 interacts with Cl - ions. Amino acids should be charged or polar to interact with the negatively charged Cl - ions, likely positively charged to attract them.

Step4: Analyze site 4

Site 4 is in water - based fluid inside the cell, so amino acids should be hydrophilic to interact with water.

Step5: Analyze the mutation in site 3 for question 28

The original amino acid at site 3 likely interacted with Cl - ions. A negatively charged amino acid at site 3 would repel the negatively charged Cl - ions. This would likely impede or completely block the movement of Cl - ions through the channel as like charges repel.

Answer:

For question 27:

• Site 1: Hydrophilic amino acids
• Site 2: Hydrophobic amino acids
• Site 3: Positively charged or polar amino acids
• Site 4: Hydrophilic amino acids

For question 28: The movement of Cl - ions through the transmembrane protein would likely be impeded or blocked because the negatively charged amino acid at site 3 would repel the negatively charged Cl - ions.