Which of the following is not a distinguishing characteristic of prokaryotic cells?
a. They usually have a single, circular chromosome.
b. They have 70S ribosomes.
c. They have cell walls containing peptidoglycan.
d. Their DNA is not associated with histones.
e. They lack a plasma membrane.

Verified step by step guidance

1. Identify the characteristics of prokaryotic cells: single, circular chromosome; 70S ribosomes; cell walls with peptidoglycan; DNA not associated with histones.
2. Recall that prokaryotic cells do have a plasma membrane, which is essential for their survival and function.
3. Compare each option with the known characteristics of prokaryotic cells.
4. Recognize that options a, b, c, and d are true characteristics of prokaryotic cells.
5. Determine that option e is not a distinguishing characteristic of prokaryotic cells, as they do have a plasma membrane.

Key Concepts

Prokaryotic Cell Structure

Prokaryotic cells are characterized by their simple structure, lacking a nucleus and membrane-bound organelles. They typically have a single, circular chromosome located in a region called the nucleoid. This structural simplicity distinguishes them from eukaryotic cells, which have multiple linear chromosomes and complex organelles.

Ribosome Composition

Prokaryotic cells contain 70S ribosomes, which are smaller than the 80S ribosomes found in eukaryotic cells. The 'S' refers to the Svedberg unit, a measure of sedimentation rate during centrifugation, indicating the size and density of the ribosomes. This difference in ribosome composition is crucial for protein synthesis and is a key feature in distinguishing prokaryotes from eukaryotes.

Cell Wall Composition

Most prokaryotic cells possess a rigid cell wall made of peptidoglycan, a polymer consisting of sugars and amino acids. This structure provides shape and protection against environmental stresses. In contrast, eukaryotic cells may have cell walls made of cellulose or chitin, but they do not contain peptidoglycan, highlighting a significant difference in cell wall composition between these two groups.