Choose the statement that correctly characterizes bound ribosomes.

a.  bound ribosomes are enclosed in their own membrane

b.  bound and free ribosomes are structurally different.

c.  Bound ribosomes generally synthesize membrane proteins and secretory proteins.

d.  The most common location for bound ribosomes is the cytoplasmic surface of the plasma membrane.

e.  all of the above



Expert Answers

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Ribosomes are intracellular structures involved in protein synthesis.  DNA makes RNA that is used with Ribosomes to manufacture proteins.

tRNA translates the genetic information into the RNA.  The amino acid sequence in genes is imparted to mRNA (messenger RNA).

Ribosomes consist of RNA-protein complexes of two types:

Smaller = tRNA

Larger = mRNA – protein combination

Free Ribosomes are present in the cytosol and can be found anywhere in the cell except within the cell nucleus or within other organelles.

Bound or Membrane-bound Ribosomes are Ribosomes in the process of making protein, usually found within the endoplasmic reticulum (ER).  The protein produced by the bound ribosome is bound to the cytosol side of the ER, or is ejected from the cell.

Bound Ribosomes attache to the cytosol side of the ER membrane.

Free Ribosomes attach to any membrane.

Bound and Free Ribosomes have the same structure, only are making different forms of protein.

Here are comments on your multiple-choice question:

a.  Incorrect:  Bound Ribosomes are attached to the ER membrane and do not have their own membrane.

b.  Incorrect:  Bound and Free Ribosomes have identical structure (however make different forms of protein).


d.  Incorrect.  See A.

e.  Obviously incorrect.

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