Membrane bound organelles in a cell and Functions

Membrane bound organelles in a cell are a type of organelles in eukaryotes that help in carrying out the necessary cellular functions. Before we proceed, let’s refresh our understanding of what organelles are.

All creatures have a cell that serves as their structural, functional, and biological unit. In these cells, it is the membrane-bound structure that contains cytoplasmic compartments and structures.

What are membrane bound organelles?

Organelles that are membrane-bound are cellular structures that are enclosed or covered by a biological membrane. The membrane is normally made up of a single or double layer of lipids with interspersed proteins.

A eukaryotic cell showing membrane bound organelles.
A eukaryote cell diagram showing membrane bound organelles.

List of membrane bound organelles

The above listed are the membrane bound organelles in a cell, some of these organelles are either double or single bounded membrane organelles.

Endoplasmic reticulum

The endoplasmic reticulum (ER) is a double-membrane organelle that is important for protein and lipid synthesis, glucose metabolism, drug detoxification, and intracellular transport, among other things.

The endoplasmic reticulum is one of the eukaryotic cell’s most visible organelles and it is a cytoplasmic organelle that appears as a network of flattened sacs or tubules (called cisternae).

The rough endoplasmic reticulum (rER) and the smooth endoplasmic reticulum (sER) are the two types of ER. The rER’s outer surface is covered in ribosomes, giving it a rough appearance; hence its name. The sER, on the other hand, does not have ribosomes connected to its outer surface, making it smoother.

Because rER has ribosomes attached to its surface, it is involved in protein synthesis and folding, as well as protein shuttling to the Golgi apparatus, where the nascent protein is matured. It produces serum proteins (such as albumin) and hormones (such as insulin) as well as other compounds (such as milk) in the liver and glands.

Golgi apparatus

The Golgi apparatus is a double-membraned organelle that is involved in glycosylation, secretion packing, lipid transit inside the cell, and the formation of lysosomes.

The Golgi apparatus appears as a stack of pancake-like flattened membrane sacs, or cisternae, right off the rough endoplasmic reticulum. It gets vesicles containing proteins that the rER has just generated. For freshly produced proteins, the Golgi apparatus can be compared to a warehouse or post office. The proteins are then further changed, packed, and transported to their final destinations within the cell or body.

The Golgi apparatus is polar, meaning it has a directional structure because it receives and sends vesicles from opposite sides of its stack of cisternae. The cis-face accepts vesicles and is positioned near the rER. The trans-face is located on the organelle’s opposing side and releases vesicles by budding the plasma membrane. The number of stacks is determined by the cell’s purpose.

Plastids

A plastid is a cytoplasmic organelle that plays a role in food synthesis and storage. Plant cells contain plastids, which are double-membrane-bound organelles found in photosynthetic cells. Plastids, like mitochondria, have their own DNA and ribosomes.

The presence of pigments is critical to its function and these pigments are also responsible for the color of a plant structure, for example, green leaf, red flower, and yellow fruit to mention a few.

A chloroplast is a plastid that contains green pigment (chlorophyll), whereas a chromoplast is a plastid that contains pigments other than green. A leucoplast is a plastid that lacks pigments and is used mostly for food storage. An amyloplast, which stores starch, an elaioplast, which stores fat, or a proteinoplast, which stores proteins, are all examples of leucoplasts. A proplastid is an undifferentiated plastid and it has the potential to grow into any of the types of plastids listed above.

Nucleus

The nucleus is one of the most significant differences between bacterial and eukaryotic cells. Prokaryotic cells lack a structured nucleus, whereas eukaryotic cells have membrane-bound nuclei (and organelles) that house the cell’s DNA and regulate the creation of ribosomes and proteins. The nucleus stores chromatin (DNA and proteins) in the nucleoplasm, a gel-like substance.

The nucleus regulates gene expression and is crucial for maintaining DNA integrity as well as controlling cellular processes such as metabolism, growth, and reproduction. Because of its relatively large size and generally round form, the nucleus is one of the most visible structures in a cell.

A nuclear envelope, which is a lipid bilayer perforated with nuclear pores, holds the nucleus together, however, some cells do not have a nucleus. In adulthood, red blood cells, for example, shed their nucleus to increase their affinity for respiratory gases like oxygen. Multiple linear DNA molecules are arranged into structures called chromosomes inside the nucleus.

Mitochondria

The mitochondrion (plural mitochondria) is a double-membrane-bound organelle. Mitochondria are the cell’s powerhouses and these organelles are where cellular respiration, or the production of energy from carbohydrates and fats, takes place.

Peroxisomes

Peroxisomes are small membrane compartments containing enzymes that extract hydrogen atoms from food. Hydrogen peroxide is formed when free hydrogen atoms bind to oxygen.

Peroxisomes are particularly important in the liver because they detoxify toxic substances by converting hydrogen from toxins or alcohol to oxygen atoms.

Lysosomes

Lysosomes are membranous sacs that hydrolyze macromolecules in order to perform intracellular digestion and are used to digest food by single-celled organisms such as amoebas. Lysosomes are also used to recycle the materials within the cell and damaged organelles and organic monomers are returned to the cell cytosol for reuse after being broken down in the lysosome.

Transport vesicles

Transport vesicles are membrane-bound sacs that function by moving materials through the cytoplasm of a cell. These vesicles are formed by the budding of other organelles’ plasma membranes. They are also responsible for moving proteins throughout the cell and releasing neurotransmitters into the synaptic space.

Vacuoles

Vacuoles are commonly defined as irregularly shaped storage bubbles found in cells. They are fluid-filled organelles that are surrounded by a membrane. The vacuole stores food or a variety of nutrients that a cell may require in order to survive. It also serves as a repository for waste and eventually disposes of the waste products resulting in the safety of the rest of the cell from contamination. The size and number of vacuoles in animal and plant cells differ and plant cells have larger vacuoles than animal cells.

Endosomes

Endosomes are membrane-bound cytoplasmic structures that transport endocytosed molecules to the lysosome.

What type of cell has membrane bound organelles?

A eukaryotic cell is the type of cell that has membrane bound organelles because it is defined by the presence of membrane-bound organelles, whereas a prokaryotic cell is defined by the absence of such organelles.

Function of membrane bound organelles

The functions of membrane bound organelles are categorized as either single or double membrane-bound organelles. The functions will be in a tabular form for easy understanding.

Double membrane organelles functions

Double membrane organelles
Functions of double membrane bound organelles
Nucleus
By regulating gene expression, it is responsible for maintaining the integrity of DNA and controlling cellular activities such as metabolism, growth, and reproduction.
Endoplasmic reticulum
Involved in protein and lipid synthesis, carbohydrate and calcium concentration metabolism, drug detoxification, receptor attachment to cell membrane proteins, and intracellular transport.
Plastids
In charge of food storage and photosynthesis.
Mitochondria
Through the process of cellular respiration, it generates the majority of the cell’s supply of adenosine triphosphate.
Golgi apparatus
Involved in glycosylation, molecule packaging for secretion, lipid transport within the cell, and the formation of lysosomes.
A table showing the functions of double membrane organelles

Single membrane organelles functions

Single membrane organelles
Functions of single membrane bound organelles
Vacuoles
Involved in structural support, intracellular secretion, excretion, storage, and digestion.
Lysosomes
Specifically for digestion and removal of excess or worn-out organelles, food particles, and engulfed viruses or bacteria.
A table showing the functions of single membrane organelles

FAQ on membrane bound organelles

Do prokaryotes have membrane bound organelles?

Prokaryotic cells have a plasma membrane surrounding them, but no internal membrane-bound organelles within their cytoplasm.

Which type of cell has membrane bound organelles?

Eukaryotic cells have a “true” nucleus, membrane-bound organelles, and rod-shaped chromosomes, whereas prokaryotic cells do not.

Do viruses have membrane bound organelles?

Viruses are acellular biological entities, which means they lack a cellular structure. As a result, they lack the majority of cell components, such as organelles, ribosomes, and the plasma membrane.

Do bacteria have membrane bound organelles?

Bacteria are prokaryotic creatures without membrane-bound organelles. They do, however, have a cell wall and a plasma membrane as outer coverings for confinement.

Do both prokaryotes and eukaryotes have membrane bound organelles?

Only eukaryotes have cells with organelles that are membrane bound.

Do plant cells have membrane bound organelles?

Plant cells have membrane-bound organelles like the nucleus and mitochondria.

What type of cell has no membrane bound organelles?

Although prokaryotic cells have a plasma membrane around them, they lack internal membrane-bound organelles in their cytoplasm.

How did membrane bound organelles originate in eukaryotic cells?

Endosymbiotic events gave rise to the energy-producing organelles within eukaryotic cells, such as mitochondria and chloroplasts, which gave rise to eukaryotic cells. Because eukaryotes’ nuclear genome is most closely connected to the Archaea, it’s possible that an early archaean absorbed a bacterial cell that evolved into a mitochondrion.

Mitochondria are thought to have come from an alpha-proteobacterium, whereas chloroplasts are thought to have come from a cyanobacterium. Secondary endosymbiotic occurrences have also been seen. Endosymbiotic processes may have also produced other cell components.

Do animal cells have membrane bound organelles?

Animal cells have membrane-bound organelles like the nucleus and mitochondria.

A video explaining membrane bound organelles.

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