Question

Which of the following characteristics is (are) not shared by bacteria, archaea, and eukaryotes? a. DNA is the genetic material. b. Messenger RNA encodes the information to produce proteins. c. All cells are surrounded by a plasma membrane. d. The cytoplasm is compartmentalized into organelles. e. Both a and d are not shared by bacteria, archaea, and eukaryotes.

Short answer

The correct answer is option D. The cytoplasm, in bacteria and archaea, is not compartmentalized into organelles, which is different from eukaryotes.

Step-by-step solution

Evaluating Option A

Option A suggests that DNA is the genetic material. For bacteria, archaea, and eukaryotes, this is indeed true. All three of these organisms utilize DNA as their genetic material. Therefore, option A is incorrect, because it is a shared feature not a unique one.

Evaluating Option B

Option B suggests that Messenger RNA (mRNA) encodes the information to produce proteins. This is also a shared feature among bacteria, archaea, and eukaryotes. These organisms use mRNA to transport genetic information from the DNA to the ribosome where proteins are synthesized. Therefore, option B is also incorrect because it is again a shared feature.

Evaluating Option C

Option C suggests that all cells are surrounded by a plasma membrane. This is indeed true for bacteria, archaea, and eukaryotes. Hence, option C is incorrect as it is a shared feature.

Evaluating Option D

Option D suggests that the cytoplasm is compartmentalized into organelles. This is not true for all bacteria, archaea, and eukaryotes. While eukaryotic cells do contain compartmentalized organelles within the cytoplasm, bacterial cells and archaea do not. Therefore, option D is the correct answer.

Evaluating Option E

Option E suggests that both options A and D are not shared by bacteria, archaea, and eukaryotes. However, we have already established that option A is a shared feature, which makes option E incorrect.

Key concepts

Genetic Material in Cells

In the world of cellular organization, understanding the concept of genetic material is fundamental. All living organisms, from the tiniest bacteria to humans, store their genetic information using DNA (deoxyribonucleic acid). Imagine DNA as a biological blueprint; it contains instructions for building and maintaining an organism.

In all cells, DNA is organized in chromosomes, and the sequence of DNA determines the genetic codes, which are translated into proteins. These proteins are crucial for various cellular processes. In eukaryotic cells, such as those in plants and animals, the DNA is primarily found within the nucleus. In contrast, prokaryotic cells, including bacteria and archaea, do not have a nucleus, and their DNA floats freely within the cell in a region called the nucleoid.

This highlight helps reconcile why option A in the exercise was incorrect, since DNA as genetic material is indeed shared across bacteria, archaea, and eukaryotes, serving as the universal code of life.

Messenger RNA Function

The role of messenger RNA (mRNA) is pivotal in the central dogma of molecular biology, which describes the flow of genetic information in a cell. Messenger RNA is like the courier in the cellular world, carrying the genetic message from DNA to the ribosomes, where the information is used to synthesize proteins.

mRNA is produced during transcription, where a segment of DNA is copied into RNA by the enzyme RNA polymerase. Once mRNA is synthesized, it exits the nucleus in eukaryotic cells or remains in the cytoplasm in prokaryotic cells. Then, the ribosome reads the mRNA sequence and translates it into a specific sequence of amino acids, creating a protein during a process known as translation.

The function of mRNA is thus a shared characteristic among all cell types, reflecting why option B was also incorrect in the textbook exercise.

Plasma Membrane

The plasma membrane is an essential cellular barrier that defines the limits of a cell and is crucial to its survival and function. Think of the plasma membrane as the gatekeeper controlling what enters and exits the cell. It is composed of a lipid bilayer with proteins embedded within it. These proteins are responsible for various functions such as transport, signal transduction, and cell recognition.

All cells, regardless of being bacteria, archaea, or eukaryotic, possess a plasma membrane. This membrane maintains the integrity of the cell, as well as establishing a controlled environment for cellular processes to occur. This common feature underscores the universal nature of the plasma membrane in cellular organization and explains why option C does not distinguish amongst these organisms.

Cytoplasmic Compartmentalization

Cytoplasmic compartmentalization refers to the presence of specialized structures, or organelles, within the cell's cytoplasm, which carry out different functions. This is characteristic of eukaryotic cells, such as those from animals and plants, that have a complicated internal architecture. Organelles such as the nucleus, endoplasmic reticulum, and mitochondria are bounded by membranes and perform specific roles contributing to cell efficiency and specialization.

In sharp contrast, the cytoplasm of bacteria and archaea, the prokaryotes, is not compartmentalized by membrane-bound organelles. Their cellular components are distributed throughout the cytoplasm without being sectioned off into separate compartments. This lack of compartmentalization in bacteria and archaea is what made option D the correct answer in the exercise, highlighting a significant difference in the cellular organization of eukaryotes compared to prokaryotes.