Question

Which of the following structures of a eukaryotic cell is not likely derived from endosymbiotic bacterium? a. mitochondrial DNA b. mitochondrial ribosomes c. inner membrane d. outer membrane

Short answer

d. outer membrane

Step-by-step solution

Understand the Endosymbiotic Theory

The endosymbiotic theory suggests that some of the organelles in today’s eukaryotic cells were once prokaryotic microbes. This theory applies to organelles such as mitochondria and chloroplasts.

Identify Structures Derived From Bacteria

According to the endosymbiotic theory, mitochondria were once free-living bacteria that became engulfed by a cell. Therefore, structures within or directly related to mitochondria are likely of bacterial origin.

Analyze the Options

Examine each option to determine if it could have been derived from an endosymbiotic bacterium: a. Mitochondrial DNA – Bacteria have their own DNA, which supports this origin. b. Mitochondrial ribosomes – Similar to bacterial ribosomes, supporting this origin. c. Inner membrane – Similar to bacterial membranes. d. Outer membrane – More likely derived from the host cell's membrane.

Draw a Conclusion

Most structures within the mitochondria are bacterial in origin. However, the outer membrane likely originated from the engulfing eukaryotic cell during the endosymbiotic event.

Key concepts

mitochondria

Mitochondria are often called the powerhouses of the cell because they generate most of the cell's supply of adenosine triphosphate (ATP), used as a source of chemical energy. According to the endosymbiotic theory, mitochondria originated from specialized bacteria that were incorporated into early eukaryotic cells. This happened through a process called endosymbiosis, where one cell engulfs another and both benefit from the arrangement.

Mitochondria have their own DNA, which is separate from the nuclear DNA found in the cell's nucleus. This mitochondrial DNA is circular, similar to bacterial DNA.

In addition to DNA, mitochondria have their own ribosomes and reproduce independently within the cell. These traits strongly suggest a bacterial origin.

eukaryotic cell structures

Eukaryotic cells are distinguished by having membrane-bound organelles, such as the nucleus, mitochondria, and chloroplasts. These structures allow the cell to compartmentalize functions, resulting in more efficient and complex biological processes compared to prokaryotic cells, which lack these compartments.

The nucleus, which houses the cell's genetic material, is a signature feature. Yet, organelles like mitochondria and chloroplasts are unique because they have features reminiscent of bacteria. This supports their endosymbiotic origins.

Other structures in eukaryotic cells that are not believed to have originated from bacteria include:

• Endoplasmic Reticulum - involved in protein and lipid synthesis
• Golgi Apparatus - processes and packages proteins
• Lysosomes - carry out digestive functions

These structures evolved within the eukaryotic cell, differentiating them from the endosymbiotic origin of mitochondria.

bacterial origin

The concept of bacterial origin for certain eukaryotic cell structures primarily focuses on mitochondria and chloroplasts. These organelles have striking similarities to bacteria, supporting the idea that they were once independent prokaryotic organisms.

Mitochondria share several features with bacteria:

• Circular DNA - similar to bacterial DNA
• Ribosomes - more closely related to bacterial ribosomes
• Binary fission - similar to bacterial reproduction

These features indicate that mitochondria likely originated from a symbiotic relationship where a proto-eukaryote engulfed an aerobic bacterium.

The outer membrane of the mitochondria is an exception. It likely comes from the host cell, contrasting with other mitochondrial structures.

This bacterial origin hypothesis is crucial because it not only explains the similarities but also provides insights into the evolution of complex life forms. By understanding these roots, we can better appreciate the intricate symbiosis that enabled the diversification of eukaryotic life.