Consider a cell in which Cl- distributes passively across the membrane according to the membrane potential. The resting membrane potential in this cell is measured to be -60 mV. If the extracellular Cl- concentration is 100 mM, then the intracellular Cl- concentration is:

1000 mM

Explanation:

Using V = -60 mV㏒₁₀[K/K'] where V = membrane potential = -60 mV, K = intracellular concentration = unknown and K' = extracellular concentration = 100 mM

So, V = -60 mV㏒₁₀[K/K']

-60  mV = -60 mV㏒₁₀[K/K']

dividing both sides by -60mV, we have

-60  mV/-60 mV = ㏒₁₀[K/K']

㏒₁₀[K/K'] = 1

taking antilogarithm of both sides, we have

[K/K']  = 10¹

multiplying both sides by K', we have

K = 10K'

K = 10 × 100 mM

K = 1000 mM

So, the intracellular Cl- concentration is 1000 mM

the real answer is b. scintillation counter

step 1: initiation

initiation is the beginning of transcription. it occurs when the enzyme rna polymerase binds to a region of a gene called the promoter. this signals the dna to unwind so the enzyme can ‘‘read’’ the bases in one of the dna strands. the enzyme is now ready to make a strand of mrna with a complementary sequence of bases.

step 2: elongation

elongation is the addition of nucleotides to the mrna strand. rna polymerase reads the unwound dna strand and builds the mrna molecule, using complementary base pairs. there is a brief time during this process when the newly formed rna is bound to the unwound dna. during this process, an adenine (a) in the dna binds to an uracil (u) in the rna.

step 3: termination

termination is the ending of transcription, and occurs when rna polymerase crosses a stop (termination) sequence in the gene. the mrna strand is complete, and it detaches from dna.