Structure And Function Of Cells Essaytyper

The Theme of Structure and Function in Cells

Up until now, we have spent some time (OK, maybe lots of time…stop looking at us like that) describing the junk, er, different components you might expect to find in different kinds of cells. We have also spent a lit—lots of time talking about what each of these unique components do for the cell. That is, we have talked about their functions. Hopefully, by now, you have begun to notice that, in almost every case, the structure of a given cellular component has a lot to do with its function. In fact, one mantra of biology encapsulates this idea perfectly: "Structure dictates function" (you should probably memorize this phrase now). The name for these relationships are, uh, structure-function relationships. To really appreciate how true this idea is, let’s look at a few examples in detail.

Let's zip back to mitochondria and chloroplasts. These organelles are really nothing more than membranes within membranes, with a little space between said membranes. The main function of mitochondria is to convert the energy in glucose to ATP, a usable form of energy for the cell, through the process of cellular respiration. This exceedingly important function is only possible because of the unique structure of the mitochondrial membranes, which allow for an intermembrane space to form where protons can accumulate, and for a matrix to which the protons can flow.

Without the inner mitochondrial membrane, or IMM, there would be no "Hoover Dam" to hold back protons and force them to flow through the ATP synthase rotor. Moreover, the IMM is folded into structures called cristae, which pave the way for millions of ATP synthase complexes to jam into a single mitochondrion. Sounds a little crowded. Without the unique folded structure of cristae, cells would need millions of mitochondria in order to produce the same amount of energy produced by just a few with cristae. Structure dictates function.

As for chloroplasts, without the thylakoid membranes separating the stroma from the lumen, there would be no space for protons to accumulate and flow back into. Without the products produced by the thylakoid membrane proteins, including ATP (we know; he's everywhere), and without a space for glucose to be made, or the stroma, photosynthesis would not occur, and life on Earth as we know it would cease to exist. Are you ready to acknowledge the vital relationship between structure and function yet, or what? Do you want the world to end? DO you?!

In the end, only the structures of the mitochondria and chloroplasts allow the processes of cellular respiration and photosynthesis to take place. In both cases, the presence of a membrane allows for compartments to form. Those compartments can have different concentrations of hydrogen ions, and it is those differences in concentration that drive formation of important substances.

Ribosomes provide another good example of structure determining function. These small cellular components are made of protein and ribosomal RNA (rRNA). Their main function is to translate messenger RNA, or mRNA, into strings of amino acids called proteins.

Ribosomes are composed of two main parts:

  1. A large subunit
     
  2. A small subunit.

Let's go back to our picture of a complete ribosome:

The small subunit has a special groove that allows for mRNA to bind to it. Once the mRNA is bound, the large subunit attaches on top, and a complete ribosome is formed. mRNA is pulled through the space between the two subunits as another molecule, transfer RNA (tRNA), binds to a second groove in the ribosome and to the mRNA, leaving behind an amino acid in yet a third groove.

For every three base pairs of mRNA, tRNA leaves behind one specific amino acid. When the end of the mRNA strand is reached, the ribosome subunits detach and let both the mRNA and the newly formed string of amino acids, aka the protein, run free into the big wide world. The grooves of the ribosome allow for mRNA to be held in place while tRNA reads the "code" that determines which amino acid is next in the sequence. It is the very structure of ribosomes that completes the Central Dogma of Biology, or DNA to RNA to Protein.

See?

Without proteins, a big, fat nothing would get done in the cell. N.O.T.H.I.N.G.

A cell is the smallest working unit of all living organisms on our planet earth, which is capable of performing life functioning. Hence it can also be defined as a fundamental unit of life. The term cell was first observed and identified by an English physicist Robert Hook in the year 1665.There were many theories developed for cell. Later in the year 1839 a two German scientist – Schwann and Schleiden provided few basic principles of cell.

Cell Structures

There are many cells in an individual, which performs several functions throughout the life. The different types of cell include- prokaryotic cell, plant and animal cell.  The size and the shape of the cell range from millimeter to microns, which are generally based on the type of function that it performs. A cell generally varies in their shapes. A few cells are in spherical, rod, flat, concave, curved, rectangular, oval and etc. These cells can only be seen under microscope.

Cell Theory

  • Every living organism is made up of a single cell (unicellular) (or) many cells (multicellular) and all types of cells have certain structures in common like: genetic material and plasma membrane.
  • Cell is the smallest living thing.
  • Each cell arises only from pre-existing cells.

Cell Structure and Function

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Cell wall: It helps in protecting the plasma membrane and plays a vital role in supporting and protecting the cells.    It is a thick outer layer made of cellulose. 

Cell membrane: It is a double layered, thin barrier, surrounding the cell to control the entry and exit of certain substances.

Cytoplasm: It is a membrane, which protects the cell by keeping the cell organelles separate from each other. This helps to keep a cell in stable. Cytoplasm is the site, where many vital biochemical reactions take place.

Nucleus: They are the membrane bound organelles, which are found in all eukaryotic cells. It is the very important organelle of a cell as it controls the complete activity of a cell and also plays a vital role in reproduction.

Nuclear membrane: The bilayer membrane, which protects the nucleus by surrounding around it and acts as a barrier between the cell nucleus and other organs of a cell.

Nucleolus: It is an important membrane found inside the nucleus. It plays a vital role in the production of cell's ribosome.

Chromosomes: It is made up of DNA and stored in the nucleus, which contains the instructions for traits and characteristics. 

Endoplasmic reticulum: It helps in the movement of materials around the cell. It contains an enzyme that helps in building molecules and in manufacturing of proteins. The main function of this organelle is storage and secretion. 

Ribosome: It plays a vital role in protein synthesis.

 

Mitochondria: They are double membrane, filamentous organelles, which play a vital role in generating and transforming the energy. Mitochondria play a vital role in various functions of the cell metabolisms including oxidative phosphorylation.

Golgi Bodies: It helps in the movement of materials within the cell.

Lysosomes: It is also called as suicidal bags as it helps in cell renewal and break down old cell parts.

Vacuoles: It helps plants in maintaining its shape and it also stores water, food, wastes, etc.

Chloroplast: They are the site of photosynthesis, which are present in chlorophyll bacteria, blue-green algae, etc.

Prokaryotic Cell Structure

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They are the first organisms to be present on our planet earth. Organisms, with this cell type are known by the term prokaryotic organisms (or) prokaryotes. Bacteria, blue green algae and E.coli are few examples of this category. Prokaryotic cells are single-celled organisms, with the absence of nucleus and comprises of capsule, cell wall, cell membrane, cytoplasm, nucleiod, ribosome, plasmids, pili and flagella.



Prokaryotic Cell General Features

  • The size of a cell ranges from 1-10 microns. Few prokaryotic cells vary in their size.
  • They are single-celled (unicellular), which forms a colony or filamentous.
  • The shape of the cell includes spherical, rod and flat shaped organisms.
  • Mode of nutrients-- few organisms are photosynthetic (performing food with the help of sunlight), feed on living things and dead things.
  • They reproduce asexually by the process called binary fission, transformation, conjugation, transduction.

Structure and Functions of a Prokaryotic Cell

Capsule: It is the slimy outer coating of the cell wall. It is composed of the polypeptide. The main function of the capsule is to protect the cell from getting dry and also helps in protecting cells from external pressures.

Cell wall: It is the tougher and a rigid structure, which provides the shape and protects the internal organelles of a cell. It is the middle layer, which is present in between the capsule and cell membrane.

Cell membrane: It is the inner delicate structure, which plays a vital role in regulating the entry and exits of materials in the cell. It acts a permeable membrane and separates the cell from its environment. It is of about 5-10nm in thickness, which helps in the secretion of proteins and elimination of waste products. It is also called by a name plasma membrane.

Cytoplasm: It is the liquid membrane, which is present in between the cell membrane and nucleiod. It plays a vital role in storing all types of materials, which are required for an organism to sustain the life.

Nucleiod: It is the cytoplasm region containing genetic material. The DNA of a prokaryotic organism is one big loop or a circular, which is located inside the nucleiod. It plays a vital role in cell division.

Ribosome: It  comprises of both RNA and proteins. It helps in protein synthesis in the cell. They are smallest membrane present inside the cytoplasm.

Plasmids: They are smallest membrane of a cell with double stranded DNA. Plasmids are rarely present in prokaryotic organisms. The main role of plasmids is it helps in DNA exchanging between the bacterial cells.

Pilli: It is the thinnest membrane of a prokaryotic cell. They are composed of protein complex called pilin and are mainly involved in sticking to the objects especially during sexual reproduction.

Flagella: It is the helical shaped membrane, whose sizes ranges from 19-20nm in diameter and plays a vital role in motility of an organism from one place to another place. It also helps in swimming, gliding, spinning and rotating both in clockwise and anti clockwise directions.


Eukaryotic Cell Structure

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They are the cells with the presence of true nucleus. Organisms, with this cell type are known by the term eukaryotic organisms (or) eukaryotes. Animals, plants and other organisms excluding bacteria, blue green algae and E.coli have been grouped into this category. Eukaryotic cells are more complex than prokaryotic cells. These organisms have membrane bound nucleus with many cell organelles to perform several cellular functions within the system. 


Eukaryotic Cell General Features

  • The size of a eukaryotic cell ranges from 10-100 microns. Few eukaryotic cells vary in their size.
  • They are large, advanced, multicellular and have membrane bound organelles.
  • They reproduce both by sexually and by asexually.
  • Mode of nutrients - Autotrophic and heterotrophic.
  • Kingdom protozoa, algae, fungi, Plantae and Animalia are organisms with eukaryotic cell.

Structure and Functions of a Eukaryotic Cell

Plasma membrane: They are semi permeable membrane that acts as a boundary of a cell, which protects and separates the cell from the external environment.

Nucleus: It is surrounded by double layered of Phospho lipid bilayer called as nuclear envelope.  

They are the storehouse for the cell’s genetic materials in the form of DNA and store all the necessary information, which are required for a cell to control all types of activities. 

Nuclear membrane: It is the double membrane layer that surrounds the nucleus and it plays a role of entry and exits of materials within the nucleus.

Nucleolus: It is the non membrane bound organelles, which is present within the nucleus and is mainly involved in controlling all types of cellular activities including cellular reproduction.

Mitochondria: They are the double smooth membrane, which are present in all eukaryotic cells. They are the powerhouse of the cell. It plays a vital role in the synthesis of ATP and converts glucose to ATP.

Endoplasmic reticulum: They are the double membrane organelle, which divides the cell into compartments. It is connected to the nuclear membrane of the cell. It plays a vital role in protein synthesis, biosynthesis of lipids and steroids, stores and regulates calcium and metabolism of carbohydrates.  Endoplasmic reticulum is of two types – rough and smooth Endoplasmic reticulum.

Ribosome: It is present in the cytoplasm. They are the site for cell’s protein synthesis, which are composed of ribosomal RNA and proteins.

Golgi Bodies: It is the flattened membrane, which are mainly used to store the substances made by the cell. This membrane also helps in preserving, transporting materials within the cell. Hence it is also called as the post office of a cell.

Lysosomes: They are the membrane bound organelles, which contains digestive enzymes to break down macromolecules. Lysosome plays a vital role in protecting cell by engulfing or destroying foreign bodies entering the cell.

Cytoplasm: They are the jelly types of organelles, which are present in the inner region of a cell. It plays a vital role in keeping a cell in a stable and keeps the cell organelles separate from each other.

Chromosomes: The rod shaped structures, which are composed of proteins and DNA. Chromosomes also play a vital role in determining a sex of an individual. All human cells contain 46 numbers of chromosomes.

Plant Cell Structure

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A plant cells are eukaryotic cells, with the presence of true nucleus, multicellular large and advanced membrane bound organelles. These plant cells are quite different from animal cells like in shape and other few organelles which are only found in animal cells but are absent in plant cells. Based on structure and functions, plant cells comprise of:



Cell wall: It is the outer layer of a plant cell, which helps a providing the shape and strength to the entire plant. A cell wall is composed of cellulose that protects and supports the plant to grow.

Cell membrane: It is a biological membrane that separates living cell organelles from non living structures. This membrane plays a vital role in helping a cell to communicate with the external environment and also in transporting proteins and other molecules throughout the cell.

Chloroplasts: They are green coloured oval shaped double membrane organelles, which are the sites of photosynthesis. The green colour pigment (chlorophyll) present in the leaves helps plants in absorbing solar energy to prepare food.

Cytoplasm: A jelly types double membrane organelles, which are present in the inner region of a cell. It helps by keeping a cell in stable and protects the cell organelles by separating them from each other.

Lysosomes: They are single membrane round organelles, which helps in digesting proteins, fats and carbohydrates. It also helps in excretion of undigested materials from the plant cells. It also helps in cell renewal and breakdown of large cells into smaller cells, old and dead cells.

Golgi Bodies (or) Gogi complex: The sac like structures, which are present in a cell to manufacture, store, packing and shipping the materials throughout the cell.

 Endoplasmic reticulum: The network of membrane, which helps in transporting materials around the cell. It forms a connection between nuclear envelope and the cell membrane of a cell.

Mitochondria: They are rod shaped organelles, plays an important role in releasing energy and they are the powerhouse of a cell. In plant cell, they are the sites of cellular respiration.

Nucleus: They are large, oval shaped organelle that contains one or more nucleoli with DNA. The main role of nucleus in plant cell is it controls all types of cellular activities.

Nucleolus: They are the spherical membranes, present inside the nucleus. This membrane contains RNA, which is used to build proteins. They are the sites of RNA synthesis.

Vacuole: They are the fluid sacs, which are present in large numbers in plant cells. The main function is this membrane is to store food and other waste materials. Vacuoles are the largest organelles present in the plant cells.

Animal Cell Structure

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Animal cells are eukaryotic cells, with the presence of true nucleus; multicellular large and advanced membrane bound organelles. Like plant cells, animal cells have same organelles except the cell wall, chloroplasts, number of vacuoles and many more. Due to the absence of cell wall the shape of an animal cell is irregular. Based on structure and functions, animal cells comprise of:



Cell membrane: They are semi-permeable membrane surrounding the cell. It helps in holding the cell together and allows entry and exits of nutrients into the cell.

Nucleus: The largest organelle in the cell, which contains DNA and other cell's hereditary information. The main role of nucleus in animal cell is it controls all cellular activities.

Vacuole: They are the fluid sacs, which are present in less numbers in animal cells compared to plant cells. The main function is this membrane is to store food and other waste materials.

Golgi Bodies (or) Gogi complex: The sac like structures, which are present in a cell to manufacture, store, packing and shipping the selected particles throughout the cell.

Ribosome: It is present in the cytoplasm. They are the site of protein synthesis, which are composed of ribosomal RNA and proteins.

Endoplasmic reticulum: The network of membrane, which helps in transporting materials around the cell and also helps in the synthesis of lipids and proteins. It forms a connection between nuclear envelope and the cell membrane of a cell.

Mitochondria: They are rod shaped organelles, plays an important role in releasing energy and they are the powerhouse of a cell.

Cytoplasm: A jelly types double membrane organelles, which are present in the inner region of a cell. It helps by keeping a cell in stable and protects the cell organelles by separating them from each other.

Lysosomes: They are round single membrane round organelles, which helps in recycling of cell organelles. Lysosome of an animal cell contains some digestive enzymes that help in the digesting out the cell debris.

All types of cells – eukaryotic and prokaryotic cell, animal and plant cells have many similarities and also differences in them, which all depends on its structure and functions of each cell organelles.

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