Animal Cell Parts and Functions

All animals, including you and I, are made of the same basic building block called the animal cell. Animal cells are generally smaller than plant cells and lack a cell wall and chloroplasts; these are organelles pertinent to plant cells.

In the title “Animal Cell Parts and Functions”, the word “Part” pertains to “Organelles”; these are specialized parts inside a living cell.

Organelles in an animal cell are suspended in a fluid called the cytoplasm. A cell membrane encloses the cytoplasm and all contents of the animal cell.

Think of the cell membrane like the border control of the cell, controlling what comes in and what goes out.

The cell membrane also called the plasma membrane encloses the animal cell and its contents. It separates the inside of the cell from the outside. It is a selectively permeable membrane that monitors what enters and exits the cell.

The cell membrane is mostly made up of special proteins (membrane proteins) and lipids (phospholipid).

The phospholipids are arranged is a double layer – the Phospholipid Bilayer. The top and bottom of this double layer arrangement are hydrophilic (water-loving) while the inside of the double layer arrangement is hydrophobic (water-hating).

Most cell membranes have special membrane proteins embedded in the phospholipid bilayer. These proteins help in the transportation of molecules across the cell membrane. The proteins have other functions such as giving a shape to the cell as well as adhesion to neighboring cells to form tissues.

The animal cell is filled with a solution of water and nutrients to form a fluid called the Cytoplasm. Organelles of the animal cell are suspended in the cytoplasm. The cytoplasm contains the cytoskeleton; a network of protein filaments that reinforce the cell and hold all structures together.

There are three main types of filaments namely; Microfilaments, Intermediate filaments and Microtubules.

Microfilaments and intermediate filaments are thinner than microtubules. They stretch over the whole cytoplasm helping to maintain cellular shape. Microtubules are straight hollow filaments that act like support beams. They help guide the movement of organelles as well as chromosomes.

The main microtubule organizing center is called the Centrosome. It is located close to the nucleus. Not only does it participate in the network of microtubules, it is involved in the cell cycle.

The nucleus is the command center of a cell. This is where most of the cell’s DNA is stored. It is enclosed in a double membrane. The double membrane has pores which allow the movement of molecules between the nucleus (Nucleoplasm) and the cytoplasm.

The Nucleolus is located inside the nucleus. The main function of the nucleolus is to make ribosomal RNA (rRNA). rRNA then combines with special proteins to form the basic units of ribosomes. Once these units are formed the nucleolus releases them out of the nuclear envelope where they will be fully assembled into ribosomes. The nucleus sends messages to the ribosomes through messenger RNA, (mRNA). mRNA carry out orders from the nucleus to the rest of the cell.

Long strands of DNA in the nucleus combine with special protein to form long fibers called Chromatin. Chromatin is then used to make Chromosomes.

The number of chromosomes present in a cell depends on the species of animal. The human sperm and egg cell both have 23 chromosomes. The number of chromosomes found in all of the other body cells is 46.

Here is a quick guided tour of the animal cell.

Ribosomes are tiny structures found floating around in the cytoplasm or attached to the ER. Ribosomes maybe small but are essential for the proper functioning of a cell. They are responsible for protein synthesis.

The ER is like a factory for the production of proteins and lipids. It also forms a network of tubes that carry substances around the cell. There are two types of ER; the rough ER and the smooth ER. They have slightly different structure and function.

The rough ER is called “rough” because it is studded ribosomes while the smooth ER is called “smooth” because it lacks ribosomes.

The Smooth ER contains enzymes that are involved in the creation of lipids. Other enzymes in the smooth ER help in the detoxification of drugs and alcohol.

Ribosomes attached to the Rough ER are responsible for protein synthesis. These ribosomes assemble amino acids into polypeptides. When synthesis is complete the ER packages the polypeptides in special vesicles and sends them to the Golgi apparatus where they will be packaged and “shipped”.

The Golgi apparatus is the cell’s shipping department. It processes and packages proteins and sends them out to where they are needed.

The Golgi apparatus is made up of stacks of membranous layers that are referred to as Golgi bodies. Golgi bodies create hormones from proteins. They can also combine proteins with carbohydrate to make other molecules such as snot (nasal mucus).

The golgi apparatus packages its products into sacs called vessicles. These sacs have membranes made of phospholipid just like the cell membrane. These vessicles are then shipped to other parts of the cell or out of the cell.

The mitochondrion (singular) is the power house of the cell. It is responsible for converting the food that you eat into energy that your body can use. The energy that our body uses is called Adenosine Triphosphate (ATP). ATP is a super energized molecule that gives you the energy you need to function properly.

Mitochondria generate ATP from carbohydrates and fat and other fuels. They also assist in cell growth, cell cycle and cellular death.

A mitochondrion is a smooth oblong organelles with an outer smooth membrane and an inner membrane. The inner membrane has numerous infoldings called Cristae.

Some cells such as muscle cells need to power and hence have a lot more mitochondria than other cells.

Lysosomes are digestive sacs that contain enzymes to break down cellular waste or debris from outside the cell into new building material.

Lysosomes break down big macro molecules into smaller molecules which can be used to nourish the cell. They also break down damaged organelles and destroy foreign invaders such as bacteria.

Peroxisomes are similar to Lysosomes in structure. They break down molecules by oxidative reaction and produces hydrogen peroxide – harmful compound. Peroxisomes break down the hydrogen peroxide to produce water. Or they may use the hydrogen peroxide to break down other molecules. Peroxisomes are also involved in the synthesis of lipid and bile acid (liver cells).

Vacuoles are storage sacs filled with fluid. They store food, water and waste products. The vacuoles in animal cells are generally smaller than that in plant cells. Animal cells can have multiple small vacuoles while plant cells usually have a single large vacuole.

Some animal cells have cilia or a flagellum. Cilia (singular is cilium) are hairlike processes that extend from the cell’s surface. Flagellum is a wipe-like tail that protrudes from the cell. Both cilia and flagella are made of small protein fibers known as microtubules. Some cells have neither cilia nor a flagellum. A sperm cell has a flagellum. It uses its flagellum to propel itself through the female reproductive tract. Lung cells have cilia. They use cilia to push mucus up and out of the lungs.

Here is a quick guided tour of the animal and plant cell.

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