Sophie.cerys
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Are the extrinsic or intrinsic proteins?

My textbook says they're intrinsic, but then the glossary in the same textbook says they're extrinsic, so I'm very confused!!
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macpatgh-Sheldon
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Sophie.cerys
Good morning Sophie! Sorry no-one has helped you out for so long on this Q, and that you are confused.com ($), and also sorry to wake you up so early on Mon morning [although not many students go clubbing on a Sun night! ].

It might be expected that glycoproteins are mostly extrinsic because this is what their functions suggest e.g. they act as receptor sites for hormones and neurotransmitters, which inherently need to be on the exterior surface of the cell. However, in fact they are mostly integral, the hydrophobic parts of them being embedded in the lipid bilayer, and the polar [hydrophilic] carbohydrate chain extrudes outwards into the extracellular fluid e.g. glycophorin, a human red blood cell protein, has a single transmembrane alpha-helix [the glyco part of glycophorin tells us that it indeed has a carbohydrate moiety as part of its structure i.e. it is a glycoprotein]; mammalian spermatozoa recognize galactose residues on the glycoproteins of the ovum leading to fertilization [presumably, the polypeptide chain of this gycoprotein of the ovum, being hydrophobic, is embedded in the lipid bilayer of its cell membrane [ need to check with an obs & gynae specialist].

For A level, just remember, glycoproteins are integral [although the above would be useful if you are aiming for A*].

M
PS Watch this space as I upload a pic showing integral glycoprotein.
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macpatgh-Sheldon
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Note that the labelled glycoprotein soans the thickness of the cell membrane ie it is integral.
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macpatgh-Sheldon
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Sorry pic is sideways so put your laptop on your bed and lie on your side to read it - you probs will not complain as it will give you a chance to go back to bed after I woke you in the early hours!! Just DO NOT FALL ASLEEP WITH LAPTOP ON RE: risk of fire!
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Sophie.cerys
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(Original post by macpatgh-Sheldon)
Sophie.cerys
Good morning Sophie! Sorry no-one has helped you out for so long on this Q, and that you are confused.com ($), and also sorry to wake you up so early on Mon morning [although not many students go clubbing on a Sun night! ].

It might be expected that glycoproteins are mostly extrinsic because this is what their functions suggest e.g. they act as receptor sites for hormones and neurotransmitters, which inherently need to be on the exterior surface of the cell. However, in fact they are mostly integral, the hydrophobic parts of them being embedded in the lipid bilayer, and the polar [hydrophilic] carbohydrate chain extrudes outwards into the extracellular fluid e.g. glycophorin, a human red blood cell protein, has a single transmembrane alpha-helix [the glyco part of glycophorin tells us that it indeed has a carbohydrate moiety as part of its structure i.e. it is a glycoprotein]; mammalian spermatozoa recognize galactose residues on the glycoproteins of the ovum leading to fertilization [presumably, the polypeptide chain of this gycoprotein of the ovum, being hydrophobic, is embedded in the lipid bilayer of its cell membrane [ need to check with an obs & gynae specialist].

For A level, just remember, glycoproteins are integral [although the above would be useful if you are aiming for A*].

M
PS Watch this space as I upload a pic showing integral glycoprotein.
Thank you so much! That's really helpful😊
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macpatgh-Sheldon
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My pleasure!
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