Final answer:
The presence and activity of an enzyme in a cell are affected by pH level, temperature, and substrate concentration, but not by the nucleotide sequence. The nucleotide sequence determines the enzyme's synthesis, not its post-synthesis activity.
Step-by-step explanation:
The presence and activity of an enzyme within a cell are influenced by various environmental factors, which include but are not limited to pH level, temperature, and substrate concentration. Regarding the question about what does not affect whether an enzyme is active and present within a cell, the answer is D. Nucleotide Sequence. While factors like pH level, temperature, and substrate concentration play significant roles in enzyme activity, the nucleotide sequence is related to the genetic code that determines the amino acid sequence of the enzyme during its synthesis, rather than its activity post-synthesis.
Enzymes have an optimal pH and temperature range in which they function most efficiently. High or low temperatures can lead to denaturation, whereas pH levels can affect the chemical bonds within the enzyme's active site. Moreover, substrate concentration will impact enzyme activity up to a certain saturation point where no additional substrate can be bound. These parameters are crucial for enzyme functionality and can greatly enhance or inhibit the catalytic processes enzymes are meant to carry out.