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The Nucleus | Location & Function Within a Cell

Hilma Gallegos, Wendy McDougal
  • Author
    Hilma Gallegos

    Hilma has a Bachelor of Science in the Biological Sciences and has a second major in Natural and Applied Sciences from Florida International University. She has spent several years as a tutor and learning assistant in subjects ranging from elementary English and college Genetics courses.

  • Instructor
    Wendy McDougal

    Wendy has taught high school Biology and has a master's degree in education.

In this lesson, learn what the nucleus is and where it is located inside plant and animal cells. Understand the anatomy of a nucleus and its functions. Updated: 12/22/2021

What is a nucleus?

The nucleus is a membrane-bound structure contained in eukaryotic cells. A eukaryotic cell, in fact, is demarcated by its possession of a clearly defined nucleus. Prokaryotic cells do not store their genetic information within a membrane-protected structure like a nucleus; instead, they contain a region referred to as a nucleoid, an area in the center of a cell's cytoplasm.

The nucleus contains the genetic information of a cell stored in deoxyribonucleic acid, or DNA. It is also responsible for replicating the DNA and transcribing it into messenger ribonucleic acid or mRNA for protein synthesis. It also regulates cell metabolism, growth, and replication through the creation of these proteins. For these reasons, the nucleus is often referred to as the control center of the cell.

Cells as Building Blocks

When you walk outside and take a look around, chances are you will see other life forms. People walking by, birds flapping through the trees, and animals roaming about. Although appearances may tell you otherwise, you have a vast amount in common with all of those living things. Of course, you and a tree do not look alike, but you, the tree, and every living thing on Earth are made of the same building blocks: cells.

Cells come in two types: prokaryotic and eukaryotic. Prokaryotes are simple, single-celled organisms such as bacteria. In this lesson, we will focus on eukaryotic cells, like those that make up plants and animals. These cells have their own tiny organs called organelles. At the heart of each eukaryotic cell is an organelle that holds an organism's genetic information, the all-important nucleus. Prokaryotes have no nucleus.

Like a safe that keeps important papers tucked away, the nucleus holds tight its genetic information (DNA). Where, exactly, is the nucleus located within a cell? Let's take a look.

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Where is the nucleus located?

Figure 1. Animal Cell

Animal Cell

The nucleus is suspended in the cytoplasm in the middle of the cell. This is true both in animal cells and plant cells. Plant cells, however, contain vacuoles. Vacuoles are membrane bound sacs that reside in the center of plant cells. These vacuoles help with waste management and water balance of the cell. Often, they can make up a large portion of a cell.

Figure 2. Plant cell

Plant Cell

Consequently, the nucleus of a plant cell might not always reside in the exact center of the cell - as seen in figure 2. Additionally, while the nucleus is generally spherical, it might flatten out as the vacuole expands around it.

Nucleus Anatomy

Figure 3. Structure of a nucleus

Nucleus

The makeup of a nucleus includes the following components:

  • nuclear envelope
  • nucleolus
  • nucleoplasm
  • chromatin and
  • nuclear pores.

Additionally, there is the rough endoplasmic reticulum (RER), an extension of the nuclear envelope, that has ribosomes attached to it. The nuclear envelope is a double membrane made up of an outer membrane and an inner membrane. In this way, it can separate the important contents of the nucleus from the rest of the cell. Throughout the nuclear membrane exist nuclear pores that serve to regulate communication between the nucleus and the cytoplasm beyond it. These pores only allow small molecules and ions to pass through diffusion. Other molecules, such as mRNA, are allowed in or out through the pores if they contain nuclear tags. These nuclear tags signal to the pore that whichever molecule that is attempting to pass through is indeed allowed to do so.

Inside, the nucleus is filled with nucleoplasm - a colorless protoplasm similar to the cytoplasm of a cell. The nucleoplasm helps the nucleus maintain its spherical shape and suspend its contents. Molecules, for example DNA, are suspended in the nucleoplasm. Within the nucleosome lays the nucleolus - a form in which DNA is stored. Whenever cells are not undergoing mitosis or meiosis, DNA molecules are not condensed into the tightly packaged structure known as chromosomes. Instead, they are present in their nucleosome form. A nucleosome is sequence of DNA wrapped tightly around eight histones - a type of protein. Nucleosomes in turn come together to form chromatin (as seen in figure 4). Chromatin is then further packaged together to make chromosomes.

Figure 4. From left to right: DNA - Nucleosomes - Chromatin.

DNA Structures

Outside of the nuclear envelope lay the ribosomes on the rough endoplastic reticulum (RER). It is in the ribosomes that proteins are synthesized through the use of an mRNA template provided by the nucleus. These mRNA molecules are allowed to exit through the nuclear pores of the nucleus, because they contain nuclear export tags (NES).

The Nucleus in Animal Cells

Let's talk about animal cells. You are probably aware that cells are too small to see with the naked eye. We must turn to our trusty light microscope in order to examine these miniscule entities. Examining a cell under a microscope allows us to locate and study the various organelles, including the nucleus.

Cells are not exact replicas of each other. They do, however, have similar general characteristics that can be found under a microscope. In an animal cell, the nucleus is located in the central region. This does not mean that it's always right smack in the middle of the cell like the pit in the center of a fruit. Rather, it sits in the center of the cell in a general sense.

Bound by its own membrane, the nucleus is suspended in a jelly-like substance called cytoplasm. The nucleus is truly the area of central command in the cell, like the cockpit of an airplane. There's a great deal of work happening in the nucleus, as it sends directions for growth and reproduction.

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Video Transcript

Cells as Building Blocks

When you walk outside and take a look around, chances are you will see other life forms. People walking by, birds flapping through the trees, and animals roaming about. Although appearances may tell you otherwise, you have a vast amount in common with all of those living things. Of course, you and a tree do not look alike, but you, the tree, and every living thing on Earth are made of the same building blocks: cells.

Cells come in two types: prokaryotic and eukaryotic. Prokaryotes are simple, single-celled organisms such as bacteria. In this lesson, we will focus on eukaryotic cells, like those that make up plants and animals. These cells have their own tiny organs called organelles. At the heart of each eukaryotic cell is an organelle that holds an organism's genetic information, the all-important nucleus. Prokaryotes have no nucleus.

Like a safe that keeps important papers tucked away, the nucleus holds tight its genetic information (DNA). Where, exactly, is the nucleus located within a cell? Let's take a look.

The Nucleus in Animal Cells

Let's talk about animal cells. You are probably aware that cells are too small to see with the naked eye. We must turn to our trusty light microscope in order to examine these miniscule entities. Examining a cell under a microscope allows us to locate and study the various organelles, including the nucleus.

Cells are not exact replicas of each other. They do, however, have similar general characteristics that can be found under a microscope. In an animal cell, the nucleus is located in the central region. This does not mean that it's always right smack in the middle of the cell like the pit in the center of a fruit. Rather, it sits in the center of the cell in a general sense.

Bound by its own membrane, the nucleus is suspended in a jelly-like substance called cytoplasm. The nucleus is truly the area of central command in the cell, like the cockpit of an airplane. There's a great deal of work happening in the nucleus, as it sends directions for growth and reproduction.

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Frequently Asked Questions

What is the location and function of the nucleus?

The nucleus is suspended in the cytoplasm in the middle of cell. This is true both in animal and plant cells. Plant cells, however, contain vacuoles in the center of the cell, so the nucleus might not be in the exact center in these cases.

What is in the nucleus of a cell?

The nucleus is the control center of the cell. It is a membrane-bound structure in eukaryotic cells that contains the genetic information of a cell stored in DNA.

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