Difference Between Bacterial Cell and Animal Cell

Main Difference – Bacterial Cell vs Animal Cell

Bacterial and animal cell are two kinds of living cells found in nature. Bacterial cells belong to the kingdom: Monera and animal cells belong to the kingdom: animalia. Since bacterial cells are prokaryotic cells, they do not membrane-bound organelles. All the cellular contents are openly accessible within the cytoplasm in prokaryotes. Animal cells consist of membrane-bound organelles such as nucleus and mitochondria. This is the main difference between bacterial cell and animal cell.

This article looks at, 

1. What is a Bacterial Cell
      – Cellular Structure, Classification, Metabolism
2. What is an Animal Cell
      – Characteristics, Cellular Structure
3. What is the difference between Bacterial Cell and Animal Cell

What is a Bacterial Cell

Bacterial cells are prokaryotes, which can be considered as simple, unicellular microorganisms. They are lacking membrane-bound organelles like nucleus and mitochondria. Bacteria are found in habitats such as soil, water, acidic hot springs, deep portions of Earth’s crust and radioactive waste. They live in either symbiotic or parasitic relationships with plants and animals. By attaching to surfaces, bacteria form dense aggregations like a mat. These bacterial mats are called biofilms.

Cellular Structure of Bacterial Cell

Bacterial cells are 0.2 to 2 µm in size. The cell is surrounded by a cell membrane. The membrane-enclosed cytoplasm contains nutrients, proteins, DNA and other essential components of the cell. Small 70S ribosomes are present for the protein synthesis. Protein localization is carried out by their primitive cytoskeleton. A single, circular chromosome is found in the nucleoid. This simple arrangement of bacteria is referred to as ‘bacterial hyperstructures’.

Murein forms a cell wall outside the bacterial cell membrane. The cell wall provides protection to the cell, maintains the shape and prevents the cell from dehydration. The thicker cell wall is classified as gram-positive and the thinner cell wall is classified as gram-negative in the gram staining of bacteria. Flagella are used for the mobility of the cell. The entire cell is covered by glycocalyx which forms the capsule.

Some genera of gram-positive bacteria form a resistant, dormant structures called endospores. Endospores contain some parts of the cytoplasm, DNA and ribosomes covered by a cortex. They are resistant to radiation, detergents, disinfectants, heat, freezing, pressure and desiccation. Bacterial cells reproduce asexually by binary fission and sexually by conjugation. A generalized structure of a gram-positive bacterial cell is shown in figure 1.

Figure 1: Generalized gram-positive bacterial cell

Classification of Bacterial Cell

Bacteria can be categorized depending on their morphology:

• Cocci are the spherical-shaped bacteria.
• Bacillus are the rod-shaped bacteria.
• Vibrio are the comma-shaped bacteria
• Spirilla are the spiral-shaped bacteria
• Spirochaetes are tightly coiled bacteria

Some bacteria live as single cells. But, some of them live in pairs called diploids. Streptococcus are the bacterial chains. Staphylococcus form ‘bunch of grapes’ like clusters. Filaments are the elongated bacteria like Actinobacteria. Some are branched filaments such as Nocardia.

Metabolism

Depending on the carbon source, bacteria can be divided into two groups: heterotrophs and autotrophs. The carbon source is organic compounds in heterotrophps whereas the carbon source is carbon dioxide in autotrophs. Depending on the energy source, bacteria can be divided into three groups: phototrophs, lithotrophs or organotrophs. In the phototrophs, the energy source is sunlight. Organic compounds are used as the energy source in organotrophs. In lithotrophs, the energy source is inorganic compounds.

What is an Animal Cell

Animal cell can form either unicellular or multicellular eukaryotic organisms, containing membrane-enclosed organelles such as nucleus, mitochondria and Golgi apparatus. Multicellular eukaryotes contain specialized tissues made by different types of cells.  Approximately 210 distinct animal cell types can be found in the adult human body.  They have various functions like the production of enzymes, hormones and energy. Animal cells are heterotrophs.

Cellular Structure of Animal Cell

Animal cells are larger in size compared to bacterial cells and are about 10 to 100 µm in size. They are irregular in shape due to the lack of a cell wall. The outer boundary of an animal cell is the plasma membrane, which is considered as semi-permeable. Semi-permeable membranes only allow selected molecules to move across it. Plasma membrane is composed of phospholipids containing polor heads and non-polor tails. It is described by the lipid bi-layer model.

Cytoskeleton of the animal cell is composed of microfilaments, microtubules and intermediate filaments. Cytoskeleton plays a vital role in cellular organization and its shape. Animmal cells are composed of a variety of membrane-bound organelles. The nucleus is enclosed by two membranes called nuclear membrane or nuclear envelop. Nuclear membrane forms the endoplasmic reticulum (ER) which is involved in protein maturation and transportation. Ribosomes are large, 80S in size and are bound to the ER. Ribosome-bound ER is referred to as rough ER. Vesicles are present for the transformation of various molecules within the cell such as golgi bodies, lysosomes and peroxizomes. Lysosomes store digestive enzymes. Mitochondria is also surrounded by two phospholipid bilayers. They covert sugar into ATPs in order to use it as energy. Animal cells contain structures like cilia, centrioles, flagella and lysosomes. A generalized animal cell is shown in figure 2.

Figure 2: Generalized animal cell

Usually, animal cells are composed of more than one chromosomes in the nucleus. These chromosomes are linear and often exist in multiple copies called homologous. Animal cells reproduce asexually by mitosis and sexually by meiosis, followed by the fusion of gametes.

Difference Between Bacterial Cell and Animal Cell

Type

Bacterial cell: Bacterial cell is a prokaryotic cell.

Animal cell: Animal cell is a eukaryotic cell.

Size

Bacterial Cell: Bacterial cells are 0.2 to 2 µm in size.

Animal Cell: Animal cells are larger in size compared to bacterial cells and 10 to 100 µm in size.

Cell wall

Bacterial Cell: The bacterial cell wall is made up of murein.

Animal Cell: Animal cells do not have a cell wall. The plasma membrane is the outer boundary.

Shape

Bacterial Cell: Bacterial cells consist of several shapes like coccui, bacillus, vibrio, spirilla.

Animal Cell: Animal cells are irregular in shape due to the lack of a cell wall.

Cell Nucleus

Bacterial Cell: Bacterial cells do not possess a nucleus.

Animal Cell: Animal cells are composed of a membrane-bound nucleus.

Plasmids

Bacterial Cell: Bacterial cytoplasm has plasmids.

Animal Cell: Animal cells do not have plasmids.

Mitochondria

Bacterial Cell: Bacterial cells do not contain  mitochondria.

Animal Cell: Animal cells contain mitochondria in the cytoplasm.

Ribosomes

Bacterial Cell: Bacterial cells contain 70S, small ribosomes.

Animal Cell: Animal cells contains 80S, larger ribosomes.

Centrioles

Bacterial Cell: Bacterial cells do not contain centrioles.

Animal Cell: Animal cells contain centrioles.

Lysosomes

Bacterial Cell: Bacterial cells do not contain lysosomes.

Animal Cell: Animal cells contain lysosomes.

Metabolism

Bacterial Cell: Bacterial cells can be either heterotrophs or autotrophs.

Animal Cell: Animal cells are heterotrophs.

Reproduction

Bacterial Cell: Bacterial cells reproduce asexually by binary fission and sexually by conjugation.

Animal Cell: Animal cells reproduce asexually by mitosis and sexually by meiosis, followed by the fusion of gametes.

Conclusion

Bacterial cells and animal cells can be considered as independent units, carrying out cellular metabolism and reproduction without the aid of other cells. Bacterial cells contain a primitive origin compared to animal cells. Bacterial ribosomes are smaller than the animals’ ribosomes. Also, animal cells contain membrane-bound organelles like nucleus, mitochondria, Golgi apparatus and ER. On the contrary, bacterial cells lack membrane-bound organelles. Bacterial chromosomes are localized to an area in the cytoplasm called as nucleoid. The main difference between bacterial cell and animal cell is their cellular organization.  

Reference:
1. “Bacterial cell structure”. Wikipedia, the free encyclopedia, 2017. Accessed 01 March 2017
2.“What’s in a cell?”. BBC, 2014. Accessed 01 March 2017
3.“Eukaryote”. Wikipedia, the free encyclopedia, 2017. Accessed 01 March 2017

Image Courtesy:
1. “Prokaryote cell”By  Ali Zifan – Own work; used information from Biology 10e Textbook (chapter 4, Pg: 63) by: Peter Raven, Kenneth Mason, Jonathan Losos, Susan Singer · McGraw-Hill Education. (CC BY-SA 4.0) via Commons Wikimedia
2.”Animal cell structure en” By LadyofHats (Mariana Ruiz) – Own work . Image renamed from Image: Animal cell structure.svg (Public Domain) via Commons Wikimedia