Problem 169 - Objective Biology for NEET

Question

Assertion: Eukaryotic cells have more DNA than prokaryotic cells. Reason: Eukaryotes are genetically more complex than prokaryotes.

Step-by-Step Solution

Answer

The assertion and reason are correct. Eukaryotic cells do contain more DNA than prokaryotic cells, and its presence in the nucleus along with certain organelles, contributes to the genetic complexity of eukaryotic cells as compared to prokaryotes.

Step 1: Understand the terms

The first step requires understanding the difference between prokaryotes and eukaryotes. Eukaryotic cells have a nucleus, while prokaryotic cells do not. Both contain DNA, however, the amount and complexity vary between the two types of cells.

Step 2: Correlate the assertion with the reason

The assertion states that Eukaryotic cells have more DNA than prokaryotic cells while the reason suggests that Eukaryotes are genetically more complex. It is important to note that because eukaryotic cells have a nucleus which contains multiple, linear DNA molecules, they indeed have more DNA as compared to prokaryotic cells which contain a single, circular DNA molecule. This correlates with the assertion provided.

Step 3: Referencing genetic complexity

Eukaryotes are structurally more complex and carry additional layers of genetic regulation. In addition to the main DNA stored within the nucleus, eukaryotic cells also contain DNA within certain cell organelles like the mitochondria and chloroplasts (in plants). This, along with other factors, contributes to their genetic complexity when compared to prokaryotes. Thus, the reason provided correctly supports the assertion.

Key Concepts

Genetic complexity of eukaryotes

When we talk about the genetic complexity of eukaryotes, we're discussing various factors that contribute to the intricate nature of their genetic makeup. Eukaryotic cells, unlike their prokaryotic counterparts, boast a nucleus that houses their genetic material in the form of multiple linear chromosomes. This not only allows for a greater volume of DNA but also introduces multiple levels of genetic regulation.

For example, eukaryotic DNA is wrapped around proteins called histones, forming structures known as chromatin. This configuration enables sophisticated mechanisms for gene expression and regulation that do not occur in prokaryotes. Additionally, eukaryotic cells undergo complex processes like mitosis and meiosis that ensure proper division and genetic variation, also contributing to their genetic complexity.

DNA content comparison

Comparing the DNA content of prokaryotic and eukaryotic cells reveals significant differences. Prokaryotes generally have a single, circular DNA molecule that floats freely within the cell in an area called the nucleoid. On the other hand, eukaryotic cells possess a clearly defined nucleus containing multiple chromosomes.

These chromosomes are not only more in number but larger and collectively hold vastly more genetic information than the DNA found in prokaryotes. Additionally, the presence of non-coding DNA sequences, such as introns, and repetitive elements in eukaryotes also increases the total DNA content when contrasted with prokaryotic cells.

Cellular organelles and DNA

Eukaryotic cells are distinct in their possession of membrane-bound organelles, each with specialized functions. Two such organelles with their own DNA are the mitochondria and chloroplasts (in plants). This feature adds another layer to the genetic complexity of eukaryotes.

Mitochondrial DNA is involved in producing energy for the cell via the process of oxidative phosphorylation, while chloroplast DNA plays a key role in photosynthesis. The fact that these organelles contain their own genetic material suggests an evolutionary past where they were once free-living prokaryotes that formed a symbiotic relationship with early eukaryotic cells, leading to the powerhouse cells we learn about today.

Structural differences between cell types

When examining structural differences between prokaryotic and eukaryotic cells, it is evident that eukaryotic cells are far more complex. Eukaryotes not only have a nucleus which safeguards their genetic material, but also possess a variety of organelles such as endoplasmic reticulum, Golgi apparatus, lysosomes, and peroxisomes, all contributing to their intricate physiology.

Each organelle has specific duties that support the cell, from protein synthesis and modification to waste breakdown and energy metabolism. In contrast, prokaryotic cells have a simpler organization, lacking organelles and thus these compartmentalized functions, which translates into different capabilities and limitations of the cells.