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Hello!
So I'm confused as to how I got this question wrong:
Which of the following would be allowed to cross the cell membrane without the aid of an accessory protein?
a.) Glucose
b.) Glycine
c.) Ketone Bodies
d.) Triglycerides
My thoughts:
a.) No. Glucose is obviously not the answer because it is a larger molecule and a lot of the time it uses Na+ to get into cells or other forms of transport.
b.) Best answer. Small amino acid, but polar and may not be able to cross the biphospholipid membrane.
c.) Eh. Can range from small (acetone) to larger molecules and also polar.
d.) No. Large molecules that you could describe as amphipathic if you use the term loosely. Not the best answer.
Examkrackers Answer:
c.) "Small, non polar molecules are most easily able to cross the cell membrane through simple diffusion because of the hydrophobic interior of the membrane. Oxygen is a small non polar molecule. Therefore, it can diffuse across the cell membrane without the assistance of an accessory protein. Glucose and Glycine are too polar to cross the cell membrane without the assistance of an accessory protein. Triglycerides, while non polar, are too large to cross the cell membrane without being broken down first."
I thought amphipathic molecules were best for crossing the bilayer of cell membranes and also... Why isn't the answer talking about "ketone bodies" instead of "oxygen?" Last time I checked... ketones are definitely polar. Am I going crazy or is there an error in this book?
Thanks!
-NF
So I'm confused as to how I got this question wrong:
Which of the following would be allowed to cross the cell membrane without the aid of an accessory protein?
a.) Glucose
b.) Glycine
c.) Ketone Bodies
d.) Triglycerides
My thoughts:
a.) No. Glucose is obviously not the answer because it is a larger molecule and a lot of the time it uses Na+ to get into cells or other forms of transport.
b.) Best answer. Small amino acid, but polar and may not be able to cross the biphospholipid membrane.
c.) Eh. Can range from small (acetone) to larger molecules and also polar.
d.) No. Large molecules that you could describe as amphipathic if you use the term loosely. Not the best answer.
Examkrackers Answer:
c.) "Small, non polar molecules are most easily able to cross the cell membrane through simple diffusion because of the hydrophobic interior of the membrane. Oxygen is a small non polar molecule. Therefore, it can diffuse across the cell membrane without the assistance of an accessory protein. Glucose and Glycine are too polar to cross the cell membrane without the assistance of an accessory protein. Triglycerides, while non polar, are too large to cross the cell membrane without being broken down first."
I thought amphipathic molecules were best for crossing the bilayer of cell membranes and also... Why isn't the answer talking about "ketone bodies" instead of "oxygen?" Last time I checked... ketones are definitely polar. Am I going crazy or is there an error in this book?
Thanks!
-NF
