Problem 3 - Campbell Biology

Question

Which of the following is present in a prokaryotic cell? \(\begin{array}{ll}{\text { (A) mitochondrion }} & {\text { (C) nuclear envelope }} \\ {\text { (B) ribosome }} & {\text { (D) chloroplast }}\end{array}\)

Step-by-Step Solution

Answer

B: ribosome

Step 1: Identify Key Characteristics of Prokaryotic Cells

Prokaryotic cells are simple, unicellular organisms without a defined nucleus or membrane-bound organelles.

Step 2: Analyze the Given Options

Review the list of options considering the characteristics of prokaryotic cells: (A) mitochondrion, (B) ribosome, (C) nuclear envelope, (D) chloroplast.

Step 3: Eliminate Options with Membrane-Bound Organelles

Prokaryotic cells do not have membrane-bound organelles such as mitochondria (A) or chloroplasts (D).

Step 4: Eliminate Option with Nuclear Envelope

Prokaryotic cells lack a defined nucleus and thus do not have a nuclear envelope (C).

Step 5: Select the Correct Option

Ribosomes (B) are present in prokaryotic cells, as they are not membrane-bound and are necessary for protein synthesis.

Key Concepts

cell structure

Prokaryotic cells are often described as simple because they lack many of the structures found in eukaryotic cells. Prokaryotes include bacteria and archaea. Key characteristics of prokaryotic cells include:

• No membrane-bound nucleus: Their genetic material is not enclosed within a nuclear envelope, unlike eukaryotic cells.
• Lack of membrane-bound organelles: They do not have mitochondria, chloroplasts, or other organelles that are enclosed by membranes.
• Small size: They are generally much smaller than eukaryotic cells, typically measuring between 0.5 and 5 micrometers.

Understanding these basic features helps to differentiate prokaryotic cells from eukaryotic cells, which have a more complex structure with multiple distinct organelles.

ribosomes

Ribosomes are essential to both prokaryotic and eukaryotic cells because they are the sites of protein synthesis. However, the ribosomes in prokaryotic cells have unique characteristics:

• Smaller size: Prokaryotic ribosomes are smaller than those found in eukaryotic cells, often referred to as 70S ribosomes.
• Structure: Despite their small size, they perform the same fundamental function — translating genetic information into proteins.
• Location: In prokaryotic cells, ribosomes are free-floating in the cytoplasm rather than being attached to a specific organelle, like the rough endoplasmic reticulum in eukaryotes.

Ribosomes are not membrane-bound, which is why they fit perfectly into the simple architecture of prokaryotic cells. They are a crucial component, enabling these cells to produce the proteins necessary for their function and survival.

membrane-bound organelles

One of the defining features of prokaryotic cells is the absence of membrane-bound organelles. Common examples of membrane-bound organelles found in eukaryotic cells, but not in prokaryotic cells, include:

• Mitochondria: Often referred to as the powerhouses of the cell, mitochondria generate the energy that eukaryotic cells need. Prokaryotic cells generate energy directly from their cell membrane.
• Chloroplasts: Found in plant cells and some protists, chloroplasts capture light energy for photosynthesis. Prokaryotic cells like cyanobacteria carry out photosynthesis but do not contain chloroplasts.
• Nucleus: Unlike eukaryotic cells, which have a clearly defined nucleus encased in a nuclear envelope, prokaryotic cells have a nucleoid region where their DNA is located.

Without these complex structures, prokaryotic cells rely on simpler methods to perform similar functions, such as energy production and genetic regulation, illustrating their adaptability and efficiency in various environments.