Structure and Function of the Nucleus in Animal Cells

Lia Kim, Amanda Robb

Author
Lia Kim
Lia Kim has a B.S. in Earth Systems from Stanford University. She also has certifications in Phytobiotechnology and Ethnopharmacognosy from University of Hawai'i of Manoa.
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Instructor
Amanda Robb
Amanda has taught high school science for over 10 years. She has a Master's Degree in Cellular and Molecular Physiology from Tufts Medical School and a Master's of Teaching from Simmons College. She is also certified in secondary special education, biology, and physics in Massachusetts.
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Do animal cells have a nucleus? Yes! Learn the structure of the nucleus and understand its functions within the cell. Updated: 12/01/2021

The Nucleus
The Animal Nucleus Structure
Nucleus Function in an Animal Cell
Lesson Summary

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The Nucleus

A nucleus is an organelle within a cell that encloses DNA. DNA stands for deoxyribonucleic acid, a molecule that contains genetic information. The nucleus not only stores DNA but directs the synthesis of ribosomes, acting like the boss of a cell.

Do animal cells have a nucleus? Yes! All animals are eukaryotes, meaning they are made up of many cells with a true nucleus. The animal nucleus is membrane-bound, which is one of the many structural components that differentiates them from prokaryotic organisms like bacteria.

The dark brown circle is the nucleus of a living onion skin cell. All eukaryotic cells have a membrane-bound nucleus.

Animal Cells vs. Plant Cells

Both animals and plants are eukaryotes, meaning they both have a nucleus, plasma membrane, ribosomes, mitochondria, peroxisomes, and cytoplasm. However, animal cells and plant cells have important structural differences.

Animal cells have centrosomes and lysosomes, while plant cells do not.

The centrosome is a cellular structure, or an organelle, involved in animal cell division that is found near the nucleus. It is also where all microtubules originate. Microtubules are major components involved in cell division and maintenance of cell shape. The microtubules help separate the chromosomes into the daughter cells. It is important to note that while plant cells do not have centrosomes, they are still capable of cell division.

The lysosome is an organelle that contains digestive enzymes. Plant cells do not have lysosomes, but instead, have vacuoles. Both lysosomes and vacuoles break down waste products, excess or worn-out cell parts, or destroy viruses and bacteria.

Animal cells have both lysosomes and vacuoles, while plant cells only have vacuoles. Plant cells also have a large central vacuole, which stores water to maintain pressure in the cell.

Plant cells have a rigid cell wall, plasmodesmata, chloroplasts, and plastids, which are all lacking in animal cells.

The cell wall in plant cells helps maintain the shape of the cell and protects it. The main component within the plant cell wall is cellulose, a polysaccharide. The crunchiness in raw vegetables is due to cell walls breaking! Plant cells also contain plasmodesmata, which are membrane-lined channels that connect different plant cells together and enable cell-to-cell communication. Animal cells have gap junctions, which have a similar function to plasmodesmata but are structurally different.

Another unique organelle within a plant cell is a chloroplast. Chloroplasts allow plant cells to conduct photosynthesis, an important series of reactions that convert carbon dioxide, water, and energy from light into sugar and oxygen. The greenness of plants is due to the pigment called chlorophyll that is found in chloroplasts. Plant cells also have plastids, which stores pigments, unlike animal cells.

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0:00 The Nucleus
1:17 Structure
2:27 Storing DNA
3:39 Making Ribosomes
3:58 Copying DNA
5:20 Lesson Summary

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The Animal Nucleus Structure

In a eukaryotic cell, the nucleus is one of the largest organelles. It is not just a rigid, solid ball-like structure; it has pores, a nuclear membrane, nucleoli, and is filled with nucleoplasm.

The double-layered membrane that encloses the nucleus (which differs eukaryotic cells from prokaryotic cells) is called the nuclear membrane, or nuclear envelope. The inner membrane is called the nuclear lamina.
The nuclear membrane has pores to allow certain molecules to pass in and out of the nucleus with the help of certain proteins.
The nucleolus (plural: nucleoli) is a small, dense structure within the nucleus that contains ribosomal DNA, RNA, and ribosomal proteins to form ribosomes. The ribosomes, after they are transported out of the nucleus to the endoplasmic reticulum, become sites of protein synthesis. The nucleus can contain up to four nucleoli.
The nucleoplasm is a semifluid, gel-like matrix where the nuclear components like chromatin (a complex of DNA and protein) are suspended.

Nucleus Function in an Animal Cell

What does the nucleus do in an animal cell? It does many important things that allow for animals to live. The function of the nucleus in an animal cell include organizing, protecting, storing, and copying DNA, as well as making ribosomes. The following sections will elucidate each of the functions of the nucleus.

Storing DNA

DNA is stored in the nucleus in tightly wrapped coils known as chromatin. The DNA is coiled up because a single cell's DNA would be nearly two meters long if it was straightened out! The chromatin consists of DNA and scaffolding proteins called histones around which DNA is wrapped. Chromatin is found in the nucleoplasm and makes up a higher-order structure called chromosomes when the cell is getting ready to divide.

Making Ribosomes

The nucleus also has nucleoli, sites where ribosomes are made. After the ribosomes are assembled, they are transported to the cytoplasm outside of the nucleus.

Ribosomes are important cellular organelles that synthesize protein. Every cell needs protein for the structure and function of nearly every cellular process!

The nucleus provides instructions to the ribosome on which protein to make by transcribing DNA into messenger RNA (mRNA). The ribosomes receive the mRNA and translate the code into specific amino acids. Proteins are made up of chains of amino acids configured into a 3-dimensional structure based on the protein's specific function.

In order for an animal cell to divide, the DNA needs to replicate inside the nucleus.

Copying DNA

In order for a eukaryotic organism to grow and develop, cells must replicate themselves in great numbers, each with the full copy of the DNA found in the original cell. The nucleus plays an important role during cell division by replicating DNA. The steps of DNA replication are summarized below into three generalized steps:

The two complementary strands of DNA are separated by special enzymes such as helicase.
An enzyme called DNA polymerase comes and brings the correct nucleic acid bases to form a new complementary strand of DNA for the two separated strands.
Once the two original strands are bound to a fully complementary strand, DNA replication is terminated. This process continues until the cell's entire DNA is replicated.

Lesson Summary

The nucleus is an important organelle within a eukaryotic cell that stores DNA and directs the synthesis of ribosomes. All animals have a nucleus in their cells because all animals are eukaryotes. Within a eukaryotic cell, the nucleus is one of the largest organelles. It has pores, a nuclear membrane, nucleoli, and is filled with nucleoplasm. The nucleus does many important things that allow for animals to live. The function of the nucleus in an animal cell includes organizing, protecting, storing, and copying DNA, as well as making ribosomes. Ribosomes are sites of protein synthesis.

There are many structural differences between eukaryotic and prokaryotic cells (e.g., bacteria is a prokaryote), but one of the greatest differences is that the eukaryotic cell has a membrane-bound nucleus with DNA.

Animal cells and plant cells are both eukaryotes, meaning they have a membrane-bound nucleus, but they have important structural differences:

Animal cells have centrosomes and lysosomes, while plant cells do not. Animal cells have both vacuoles and lysosomes, while plant cells only have vacuoles. Plant cells, unlike animal cells, also have a large central vacuole.
Plant cells have a rigid cell wall, plasmodesmata, chloroplasts, and plastids, which are all lacking in animal cells.

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Frequently Asked Questions

What are the main functions of nucleus?

The function of the nucleus in an animal cell include organizing, protecting, storing, and copying DNA. The nucleus also contains nucleoli, a site that makes ribosomes, an important organelle for protein synthesis.

Do all animal cells have a nucleus?

All animals are eukaryotes. They belong to the Domain Eukarya. All eukaryotes have a membrane-bound nucleus. Thus, animal cells have a nucleus!

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Structure and Function of the Nucleus in Animal Cells

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