Question

select all that apply choose all functions typically carried out by membrane proteins. receive external chemical messages transport oxygen into the cell code for the production of new polynucleotides attach the membrane to the cytoskeleton connect adjacent cells and hold them together

Explanation:

1. Receive external chemical messages: Membrane proteins (like receptor proteins) can bind to signaling molecules (e.g., hormones, neurotransmitters) to receive external chemical messages, so this is a function of membrane proteins.
2. Transport oxygen into the cell: Oxygen is a small non - polar molecule that diffuses across the cell membrane directly, and membrane proteins are not involved in transporting oxygen into the cell. Hemoglobin (an intracellular protein in red blood cells) transports oxygen in the blood, not membrane proteins in general cells.
3. Code for the production of new polynucleotides: DNA (a polynucleotide) contains the code for the production of new polynucleotides, and membrane proteins do not have this coding function.
4. Attach the membrane to the cytoskeleton: Some membrane proteins (like anchor proteins) can attach the cell membrane to the cytoskeleton, helping to maintain cell shape and structure.
5. Connect adjacent cells and hold them together: Membrane proteins (like cell - adhesion molecules) can connect adjacent cells and hold them together, for example, in tight junctions, desmosomes, etc.

Answer:

A. Receive external chemical messages
D. Attach the membrane to the cytoskeleton
E. Connect adjacent cells and hold them together