Skin cells are made of proteins, water, and fat. But brain cells are only made up of amino acids, which ca make protein.<span />
Mutations acquired by somatic cells are generally only retained by the individual they acquire in as there is no vector by which to transmit the mutation.
<span>Between generations, the only mutations that may be transmitted are those already acquired from a parent, and those that occur within the individuals own germ cells. If mutations in the germ cells result in sperm or eggs that contain that mutation, then they may be transmitted to their offspring. </span>
<span>Red blood cells in all humans and other mammals, though, don't contain nuclear DNA and as such cannot acquire mutations.</span>
If a lot of tryptophan is present, the operon will be repressed.
Under intermediate amounts of tryptophan, the change to stop codons would cause the ribosome to stall and therefore would mimic as if there were no tryptophan present.
If no tryptophan present, the operon would be maximally expressed.
a - True. The ribosome would always be stalled in the leader sequence - so this wouldn't matter. However, the operon would still be transcribed because the repressor would be active (remember Trp operon is controlled both by attenuation and repression). True as long as there's not much tryptophan to activate the repressor!
b- True - With no tryptophan the repressor isn't engaged and the ribosome is stalled in the leader sequence.
c- Matters about how much tryptophan is available. So True if there's lots of tryptophan available.
d- I would choose this one as all of the above could be true depending on the levels of tryptophan.
