Cell Organelles and their Functions

Introduction

Cell organelles are specialised structures within cells that come in various shapes and sizes. They serve a crucial purpose because we must compartmentalize all of the operations within the cell. As a result, a membrane must surround the systems within a cell that produce a different product; organelles are entirely membrane-bound. They also distinguish one function from another. We will look in detail at the cell organelles and their function chart.

Types of Cell Organelles

The cytoplasm and the nucleus are the two major sections of a cell. A nuclear envelope surrounds the nucleus, which contains The genetic code in the format of a chromosome. The cytoplasm is a liquid network surrounding the nucleus, separated by the cell’s outer membrane. Organelles are tiny structures in the cytoplasm that perform functions that keep the cell in a state of homeostasis. They are involved in various functions, including energy synthesis, protein and secretion formation, toxin destruction and reacting to external signals.

Cell organelles can be divided into three categories:

1. General cell organelles: Cell membrane, mitochondrion, rough endoplasmic reticulum, smooth endoplasmic reticulum, lysosome, plastid ,ribosomes, golgi bodies, nucleus and cytoskeleton are a few examples present in both animal and plant cells at all times.
2. Temporal cell organelles: Chromosome, centrosome , endosome and autophagosome are only found at specific stages of the cell’s life cycle.
3. Cell organelles specific to cell type: Chloroplast, central vacuole and cell wall are only found in plant cells.

Cell Organelles and their Functions

Plasma membrane

The plasma membrane is a barrier between the cytosol and the cell’s extracellular matrix. Some cell organelles have lumens encased by plasma membranes. It includes phospholipids, cholesterol and membrane proteins and it resembles a fluid mosaic.

Functions of plasma membrane

• The plasma membrane surrounds most cells and physically separates the cytoplasm (the cell’s substance) from the extracellular fluid (the fluid outside the cell). It protects the cell’s components from the outside world while allowing independent operations within and outside the cell
• The rate at which specific molecules can enter and leave the cell is controlled by the membrane
• In both endocytosis and exocytosis, the cell membrane plays a vital role. To allow molecules to enter or exit the cell, the shape of the membrane changes. It also creates vacuoles – tiny membrane bubbles capable of transporting many molecules at once – to transfer materials to different cell parts

Endoplasmic reticulum

The endoplasmic reticulum (ER) is a vast network of membranes involved in protein synthesis, lipid metabolism and transportation and toxin detoxification. The endoplasmic reticulum function is divided into two categories, each with its own set of functions:

Smooth endoplasmic reticulum

The smooth endoplasmic reticulum (SER) is an endoplasmic reticulum that lacks ribosomes, due to which it appears smooth underneath a microscope. Every function of the smooth endoplasmic reticulum is different, depending on the cell type:

• It is essential for the production of steroid hormones from cholesterol
• The SER enzymes in the liver catalyse reactions that make medicines, metabolic wastes and toxic substances water-soluble, allowing them to be removed from the body during detoxification
• Glycogen-6-phosphatase, an enzyme found in SER, catalyses the liver’s final step in glucose synthesis
• When nerve impulses stimulate a muscle cell, calcium ions are released, causing muscular contraction

Rough endoplasmic reticulum

The outer plasma membrane of RER is covered with ribosomes, giving it a spotty appearance under a microscope; this is where protein is made. The functions of the rough endoplasmic reticulum are –

• It is vital in controlling the cell’s response to stress and quality control for proper protein folding
• It contains enzymes that bind to and alter RNA and are involved in RNA metabolism
• It also contains proteins that identify and assist in translocating various signal sequences inside a developing polypeptide

Golgi apparatus

The Golgi apparatus appears as a stack of pancake-like flattened membrane sacs or cisternae, right off the rough endoplasmic reticulum

Functions of Golgi apparatus

• The Golgi’s many sacs act as distinct chambers for chemical processes
• Functions include transporting molecules from the endoplasmic reticulum to their end destination and altering products along the way
• Protein and lipid  moves from the ER to the Golgi for modification in glycolipids, glycoproteins and  then sent to various destinations in the cell, including the lysosomes and the cell surface

Mitochondria

The mitochondrion (plural mitochondria) is a double-membrane-bound organelle. Cristae have many infoldings in the inner membrane. The intermembrane space is the space between the outer and inner membranes; the matrix is the space inside the inner membrane.

Functions of mitochondria

• Oxidation: They use oxygen to convert water and carbon dioxide from carbohydrates and lipids in the cell. A part of the energy released by oxidation is used to make ATP
• The mitochondria are the cell’s powerhouse because it produces the energy-rich chemical ATP
• Mitochondria are considered semi-autonomous organelles since they may produce some of their own proteins

Chloroplast-  It is double membrane bound cell organelle and is the largest organelle of plant cells

Grana- It constitutes of the lamellar system.These are found in layers on top of each other, these stacks are called as grana    Each lamella is made up of unit membrane.Each granum of the chloroplast is formed by superimposed, closed compartments called thylakoid.

Function :  Site of light reaction.

Different grana are connected with the help of tubular connections, called stroma lamellae or Fret channels or intergranum.

Stroma:- It is a granular transparent substance filled in the cavity of chloroplast. It is also called a matrix. Grana are embedded in it. It contains enzymes of the calvin cycle or dark reaction. Rubisco is the most abundant enzyme on the earth. It made 16% protein of the chloroplast.

Chloroplasts have their own genetic system & complete protein synthesis machinery (ds-DNA, RNA, 70 s type of Ribosome enzymes. Amino Acids), thus chloroplasts are called as semi autonomous organelle of the cell. DNA of chloroplast is called plastidome.

Function:- Site of dark reaction.

Conclusion

Each organelle has a specific function, and if you don’t know what cell or organelle you’re talking about, the cell will most likely stop working. Although, as an organism evolves, some organelles may become obsolete or be replaced by others, in which case the organelle may naturally disappear. The function of cells will be impacted, but if mitochondria or other critical organelles such as the nucleus are missing, the cell would not be able to survive.