Cell Structure And Function

The cell structure is defined by the cell membrane, the cytoplasm, and the nucleus. A cell is the smallest unit of life and its structure helps it to work as the basic building block of biology.

The cell function is to keep all of the functions of the body performing as intended. This includes keeping toxins out of the body, help to break down waste, make nutrients and act as barriers within organelles.

Cells are the basic building blocks of life. Yet what are all the components of a cell that enable them to carry out their basic functions? Cells are made up of a wide variety of structures and components, and each component plays a necessary and important role.

“The body is a community made up of its innumerable cells or inhabitants.” — Thomas A. Edison

Different types of cells have different structures, depending on the function of the cell. Certain cells like algae cells, for instance, have a tail that helps them propel themselves through the water. While other cells like pollen have little spikes on them so they can stick to insects.

Despite their differences, most cells have structures in common. These common structures include a cell membrane, DNA, ribosomes, and cytoplasm.

Four Key Parts of a Cell: Cell Membrane, Cytoplasm, DNA and Ribosomes

Cells have a plasma membrane, cell membrane, or cell wall that surrounds the cell and acts as their skin. It makes up the boundary between the cell and their environment and controls what can move in and out of the cell. The cell membrane is constructed out of a phospholipid bilayer, two layers of lipids facing opposite directions. The lipid layers are made out of building blocks of fatty acids and consist of a head and body. The body of the lipid is hydrophobic, meaning it repels water while the heads of the lipids are hydrophilic, meaning that it likes water.

In addition to the cell membrane found in animal cells, plant cells also have a cell wall. The cell wall is made out of cellulose and it helps give the cell extra protection and support. A crucial difference is that unlike cell membranes, cell walls do not allow for the passage of materials through them. To get around this problem, cell walls have unique structures called plasmodesmata, special holes that allow the material to move in and out.

Photo: By LadyofHats (Mariana Ruiz) – Own work using Adobe Illustrator. Image renamed from Image: Animal cell structure.svg, Public Domain, https://commons.wikimedia.org/w/index.php?curid=4266142

The cell membrane holds in a cell’s cytoplasm. The cytoplasm is a jelly-like substance, made up of mostly water, that keeps the various organelles within the cell separate from each other. Many of the cell’s biochemical reactions, like metabolic processes, occur within the cytoplasm.

There are gaps in a cell’s plasma membrane referred to as pores or channels. These pores or channels are made out of proteins and they control what chemicals, like water and food, are able to move into the cell.

Deoxyribonucleic Acid, or DNA, is frequently referred to as “the blueprints for life” and it contains the generic information that allows cells to reproduce and perform their respective functions. The DNA of a cell is held within the nucleus of the cells, specifically within the nucleolus.

The cell’s nucleus is often referred to as the “brain” of the cell, or the control center. It is the largest part of the cell within the cytoplasm. Cells that have nuclei are found in plants, animals, algae, protozoa, and fungi. Bacterial cells do not have a nucleus. The nucleus is home to a smaller structure within it called the nucleolus. The nucleolus is an organelle that creates ribosomes. The nucleus has nuclear pores that allow the ribosomes to exit the nucleus and for other materials to move in.

The nucleus has pores that allow the ribosomes to move in and out. Photo: Mariana Ruiz, LadyofHats via Wikimedia Commons, Public Domain

The ribosomes themselves are organelles which assist in the creation of proteins. Proteins are necessary for the cell to carry out its essential functions. Ribosomes are made out of one large piece and one smaller unit. Both of the subunits in the ribosomes assist in the creation of proteins when they come together with messenger RNA. Though some ribosomes can be found in the cytoplasm itself, most of the ribosomes are found in the endoplasmic reticulum. The proteins that ribosomes create while attached to the endoplasmic reticulum will move from the cell to do work within the body or will remain within the cell to synthesize the proteins that the cell needs.

Other Important Parts of a Cell

The endoplasmic reticulum (ER) is made out of various membranes, and it synthesizes proteins and for the cell. The endoplasmic reticulum is referred to as “rough ER” when it has the ribosomes attached to it, and it is called “smooth ER” when there are no ribosomes attached to it. The rough endoplasmic reticulum synthesizes the proteins, while the smooth endoplasmic reticulum performs two functions. The smooth ER synthesizes lipids for use in the cell, but it also detoxifies harmful substances.

After the proteins of the cell have been synthesized by the ribosomes on the endoplasmic reticulum, they are distributed by an organelle called the “Golgi complex”. The Golgi complex sorts the proteins out and then sends them to the area that they are needed in. In this respect the Golgi complex is like a post office, distributing packages to their destinations.

The mitochondria are organelles that are responsible for converting the food eaten by an organism into energy. Food is converted into units of energy called ATP by the mitochondria and every cell has differing amounts of mitochondria depending on the cell’s function and needs. Cells that do more work, like heart cells, need more mitochondria than other cells.

Photo: By BruceBlaus. When using this image in external sources it can be cited as:Blausen.com staff (2014). “Medical gallery of Blausen Medical 2014”. WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436. – Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=28223972

Plant cells have chloroplasts, while animal cells don’t. The chloroplasts in a plant cell are where photosynthesis happens, converting the energy from the sun into chemical energy that the plant cells can use. Plant cells also have a vacuole or seemingly large empty space in the middle of the cell. However, the vacuole of a plant cell actually contains important chemicals like sugar and water.

Tiny organelles called vesicles can also be found floating around within the cytoplasm. The vesicles are responsible for carrying materials in, out, and around the cell. The vesicles carry material from one part of the cell to another, but they also transport waste products outside the cell in a process called exocytosis.

There are also some small structures found in the cytoplasm that carry out various functions depending on the type of cell. Peroxisomes are responsible for collecting toxic chemicals and breaking them down into harmless byproducts, while centrioles are unique to animal cells and they guide the division and organization of chromosomes as cells divide. Finally, lysosomes are structures secreted by the Golgi apparatus which can take large molecules and break them apart into smaller chunks the cell can utilize.

Cells are complex systems with many moving parts that work together to form the diverse abundance of life we all around us.