Eukaryotic cell: structure and organelles (2023)

Author: Lorenzo Crumbie MBBS, BSc•Advisor: Francesca Salvador MSc
Last revision: 07.09.2022
Reading time: 20 minutes

Eukaryotic cell: structure and organelles (1)

plasma membrane



Synonym:Cell membrane, cell membrane

The cell is thesmallest functional unitwithin a living organism that can function independently. It consists of different types ofOrganellesthat allow the cell to function and reproduce. There are two general classes of cells: the simple self-sustaining cells known asprokaryotic(Bacteria and Archaea) and the more complex dependent cells known asmieukaryotes. IT IStypes of eukaryotic cellsThey are usually found in animals, plants, algae and fungi. For the purposes of this article, the focus is on the structure andHistologythe animal cell. Key differences between animal and plant cells are also explored.

As mentioned above, the basic components of a cell are its organelles. it isOrganellesThey are made from different combinations of atoms and molecules. Organelles direct many cell functions, from metabolism to energy production and replication. Cells with specific functions come togetherorgans(Which means.lung parenchyma). Organs with related functions work together within aSystem(Which means.respiratory system). These systems, although they have different functions, work in synergy tobody(i.e. human) to survive. Every aspect of a cell is important to its survival.

Key facts about eukaryotic cells
definition of cellsmallest functional unit within a living organism that can function independently
Cell typesProkaryotes (bacteria and archaea) and eukaryotes (in animals, plants, algae and fungi)
plasma membranePhospholipid bilayer (amphipathic, selective permeability), cholesterol, proteins (channels, transporters, receptors)
EndozitosePhagocytosis (solid uptake), pinocytosis (liquid uptake), receptor-mediated endocytosis (uptake controlled by cell surface receptors)
CytoplasmSemi-solid medium that maintains suspended organelles and dissolved nutrients in the internal cellular environment
ZitoskeletonResponsible for shape and support, composed of microtubules, microfilaments, intermediate filaments, cilia, flagella
ribosomesProtein synthesis, consisting of a small and a large subunit
Endoplasmatisches RetikulumrudeIt has ribosomes on its surface, stores proteins and is the extension of the nuclear membrane.
TogetherIt lacks ribosomes, is a collection of independent sacs or a continuation of the rough ER, and synthesizes lipids, steroids, and phospholipids.
Golgi ApparatProtein storage center divided into cis and trans components
gallbladderExocytic (for excretion of contents), Lysosomal (digestion and defense of proteins), Secretory (for regulated excretion of contents in response to a stimulus)
mitochondriaEnergy production (ATP) consisting of an outer membrane, an inner membrane, and an intermembrane space
KernIt is composed of chromatin (heterochromatin, euchromatin), which consists of DNA wrapped around histone proteins.
KernmembraneNameLipid bilayer surrounding the nucleus with nuclear pores.
Animal cells vs. vegetablesThe image- Animal cells are irregular, plant cells are rectangular
cellulose- absent in animal cells, surrounds the plasma membrane in plant cells
ATP production- Mitochondria in animal cells, chloroplasts in plant cells
eyelashes- Present in animal cells, absent in plant cells
ClinicalApoptose, hyperplasia, hypertrophy, metaplasia, dysplasia


  1. plasma membrane (cell)
    1. Phospholipid-Component
    2. protein component
    3. material entrance
  2. Cytoplasm
  3. ribosomes
  4. Endoplasmatisches Retikulum
  5. Golgi Apparat
  6. vesicles and lysosomes
  7. mitochondria
  8. Kern
  9. KernmembraneName
  10. Differences between animal and plant cells.
  11. clinical importance
    1. Cell death
    2. cellular changes
  12. Fuentes

+ see all

plasma membrane (cell)


The plasma membrane is the outermost layer of the cell. The main function of the plasma membrane is to protect the cell from its environment. It is often referred to as liquid mosaic.Fosfolipídeo bilayerthat is hydrophilic outside and inside, but hydrophobic at its core. HimhydrophilicThe property derives from the charged phosphate molecule that forms the head of the phospholipid and thehydrophobenature is in the two lipid tails that make up the nucleus. This feature allows thedirected permeabilityFor example, hydrophilic particles (eg ions) cannot pass through the hydrophobic core and hydrophobic particles (eg fats) are repelled by the outer surface. This allows the cell to isolate its internal environment from the external environment.

Some of the phospholipid structures are linkedcholesterolmolecules. The latter maintain the consistency of the plasma membrane and more recent studies are examining their role in supporting the immune system.

protein component

Like any living organism, the cell is not completely self-sufficient and therefore needs nutrients from the external environment and also to export its products to the external environment. Controlled fabric movement is thus accomplishedProtein channelsjConveyor Proteinanchored in the plasma membrane, which allow certain particles to enter and exit the cell selectively or generally.

(Video) Eukaryotic Cell Structure & Organelles | A-level Biology | OCR, AQA, Edexcel

Some protein molecules are tagged with glycogen chains (i.e., glycoproteins) and function asreception channelsthat initiate cellular processes. Other proteins are restricted to the cytosol(intracellular protein)the extracellular type(extracellular protein)of the membrane, while others span the entire membrane(transmembrane protein). This is the reason for the term "fluid mosaic", as it refers to the fact that proteins located in or on the membrane move freely along the phospholipid bilayer.

material entrance

For substances that cannot pass through the membrane or use membrane channels, the plasma membrane has the ability to engulf foreign materials in a process known asEndozitose. In this process, foreign microorganisms or native substances are recognized by receptors on the cell membrane and the area of ​​membrane that has been transported into the cytoplasm is then folded around the desired structure. Endocytosis can be divided into three types.

PhagozitoseIn this way, nonspecific substances (usually solid) enter the pinositesIt involves the entry of certain substances (usually extracellular fluid) into the cell.receptor-mediated endocytoseinvolves the specific uptake of certain macromolecules that is controlled by cell surface receptors.


The semi-solid medium that keeps organelles suspended and nutrients dissolved in the internal cell medium is the cytoplasm. In addition to organelles, the cytoplasm also contains microfilaments, microtubules, and secretory granules. HimmicrofilamentsjmicrotubulesThey are part of the cellular architecture that gives the cell its structure (Zitoskeleton) and play a role in cell replication. They also contribute to the formation ofeyelashesjflagellain some cell lines that require motility.





In order for cells to grow and replicate, they must produce the necessary building blocks for this feat. In addition, some cells, such as the β cells of thepancreas– Produce protein-based hormones to maintain homeostasis. This process is carried out by ribosomes. Ribosomes are complex molecules based on ribonucleic acid (i.e., ribosomal ribonucleic acid; rRNA) responsible for translating messenger RNA (mRNA) encoded sequences into proteins. They consist of akleinit is alarge subunitthey coordinate with each other to translate the mRNA strand. Some ribosomes are membrane-bound while others float freely in the cytoplasm. while free ribosomessynthesize proteinsUsed within the cell, the proteins synthesized by the attached ribosomes are destined for export.

Endoplasmatisches Retikulum

Clusters of sacs and vesicles formcisterns(tubules) in the cytoplasm. These structures form the endoplasmic reticulum. There are two types of endoplasmic reticulum: one with ribosomes attached to its surface -rough endoplasmic reticulum (RER), while the other lacks ribosomes -smooth endoplasmic reticulum (SER).

Another distinguishing feature between rough and smooth endoplasmic reticulum is that the rough endoplasmic reticulum is an extension of the nuclear membrane whereas the smooth endoplasmic reticulum can be an independent collection of sacs or a continuation of the rough endoplasmic reticulum. As mentioned above, the rough endoplasmic reticulum stores proteins synthesized by ribosomes on its surface. In contrast, the smooth endoplasmic reticulum synthesizes phospholipids, steroids and lipids, which are subsequently used in the synthesis of steroid-based hormones.

smooth endoplasmic reticulum

non-granular endoplasmic reticulum


Synonym:It's smooth, SEE

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Golgi Apparat

Named after the Italian scientist who discovered it in 1898, Camillo Golgi, this organelle exists in the cytoplasm asstorage centerfor proteins that are distributed to other sites. The Golgi apparatus (also known as the Golgi complex or Golgi body) is structurally divided intocisjtransThe first represents flattened vesicles arriving from the endoplasmic reticulum that fuse into a formcisterns. The trans aspect of the structure is the region from which vesicles bud to attach to other vesicles, lysosomes, or the cell surface (for exocytosis).

vesicles and lysosomes

Some proteins synthesized within the cell are used by the cell, while others are designed to be exported to other areas of the body. To prevent these products from being involuntarily activated and interacting with the cell of origin, they are stored in membrane-enclosed pockets called vesicles. There are three general types of vesicles; exocytic, lysosomal and secretory vesicles. Himexocytic gallbladdercontain proteins that are expelled from the cell by exocytosis. This happens when the vesicles fuse with the cytoplasmic membrane and expel their contents into the extracellular space. For example, the release of antibodies is activatedB cellsduring the humoral immune response.

proteins housed in itsecretory vesiclesalso serve for extracellular release, but require a stimulus; the beginning of aneurotransmittercalled acetylcholine (ACh) from the telodendria ofneuronsinto the synaptic cleft after stimulation by aaction potential.

On the other hand, proteases are enzymes designed to digest proteins. These are special proteins that are involved in cellular degradation either apoptotic (programmed cell death) or as part of the defense mechanism against invading pathogens. In both cases, these enzymes are stored in thelysosomefor later release. When an organelle, cell or microorganism is about to be digested, a vesicle forms around the substance to be dissolved, which subsequently fuses with the lysosome. This is done to prevent unwanted damage to other cytoplasmic structures.


Often called the "powerhouses" of the cell, mitochondria (i.e., mitochondria) are an elongated double-membrane structure containing numerousKamminside its inner membrane. Aside from the membrane-bound ATP synthase proteins that enable ATP production, mitochondria are the only organelles that contain their own DNA material and are therefore capable of replication.

IT ISouter membranewhich surrounds the entire organelle, is equipped with prion proteins that allow the selective uptake of some substances. Himinner membraneit also has specific proteins such as ATP synthase (generates ATP), cytochrome C (performs oxidation-reduction reactions) and transport proteins (for selective uptake of material into the mitochondrial matrix). The components ofintermembrane space(between the inner and outer membrane) are very similar to those in the cell's cytoplasm.

IT ISheadquartersThis is where the citric acid cycle (Krebs cycle - ATP formation process) takes place. The number of mitochondria found in a given cell depends on its function. For example,myocardial cellscontains more mitochondria thanepithelial cellsdoDropped downbecause they need more ATP to be resistant to fatigue.


This is the largest structure within the cell. It is circumscribed byKernmembraneNameand contains anucleolus, uterus and mainly the hereditary genetic material known asdeoxyribonucleic acid (DNA). Each cell contains approximately two meters of microscopic genetic material. This immense volume of DNA can be kept inside the cell by wrapping it tightlyHistona(protein scaffolding) which are then stacked aschromosomes. However, DNA only exists as chromosomes during the active stages of cell division. When the cell is in the growth phase, the DNA takes the formeuchromatinÖheterocromatina. DNA that assumes the euchromatic form is usually transcribed and expressed more frequently in the cell.




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Within the nucleus is a unique region known as thenucleolus. This is an area where the DNA encoding ribosomal RNA (or tandem repeats) is found. The main function is to produce and assimilate r-RNA, which is exported to the cytoplasm to translate the RNA.


There is another selectively permeable membrane that separates the cell cytoplasm from the nucleus from the nuclear matrix. This structure is known as the nuclear envelope; Like the plasma membrane, it consists of alipid bilayer. It is a bilayer structure surrounding the nucleolus and chromatin within the nuclear matrix. The nuclear envelope is continuous with the rough endoplasmic reticulum.

Now that you've learned the structure of the cell, let's use ourCell diagrams and quizzesto consolidate your knowledge!

In some areas of the bark, the inner and outer layers merge, forming openings known asKernpore. Nuclear pores allow not only the entry of nucleotides and other materials into the nucleus, but also the exit of mRNA from the nucleus for translation in the cytoplasm.


nuclear shield


Synonym:nuclear membrane, lipid bilayer membrane of cell nucleus,Show more...

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Differences between animal and plant cells.

For the sake of completeness, it should be noted that animal cells are not the only type of eukaryotic cells that exist. Plant cells are also eukaryotic and have components similar to animal cells. However, there are some significant differences. While animal cells are more irregularly shaped, plant cells tend to be more irregularly shaped.solid rectangular shape. This fixed form is facilitated by the rigidityCellulose-based cell wallsurrounds the plasma membrane of the plant cell; which is also absent in animal cells.

In addition to mitochondria for ATP production, plant cells also containCloroplasteno. These structures allow plants to use ultraviolet energy in the process of photosynthesis to create their own food. Finally, while a variety of animal cells may be endowed with cilia, these structures are often absent in most types of plant cells.

clinical importance

Cell death

Cells exist throughout the body and work synergistically to carry out their respective functions. These cells undergo mitotic (and meiotic transformations in the gonads) to maintain the cell population. Normally, when a cell is exposed to a stressful stimulus, it tries to adapt to that environment until the stimulus is removed. Once the cell has no mitigating damage, it usually repairs itself and returns to its normal state. However, once the cell is significantly damaged and the damage is irreversible, the cell can undergo programmed cell death, a process known as apoptosis.Apoptosisit is a natural cell-driven process in which damaged or worn-out cells autophagy. There is another form of cell death that is unplanned and can cause more damage to neighboring cells, known as cell death.Necrosis. Here, cell death follows an external agent (e.g., trauma, infection, or toxin) that initiates premature cell death.

There are some instances where genetic material can code for a mutation when exposed to a noxious stimulus, when the wrong coding is inherited, or simply because of a replication error that "turns off" important housekeeping functions of a cell. This is one of the phenomena observed inmalignant cells. There are several characteristics of cancer cells, including the ability of these cells to spread and grow to distant sites.(Metastasis), initiate angiogenesis (creating new blood vessels to improve their blood supply) and, most importantly, cells become"immortal". Although cells can be killed (albeit with difficulty) by various pharmacological, radiological, and immunological means, the cell lineage's innate apoptotic pattern is down-regulated. Although these cells have several qualities that would induce apoptosis in a normal cell line, these cells grow and multiply at an uncontrollable rate because they are somehow able to avoid programmed cell death.

cellular changes

There are some terms specifically associated with changes at the cellular level that are common in the medical field. Thus, the following must be recognized to accompany discussions on pathological processes:

  • hyperplasiarefers to the increase in size of an organ as a result of an increase in the number of cells it contains. For example, with benign prostatic hyperplasia, the number of prostate cells has increased, leading to an increase in the overall size of the gland. However, the overall size of the cells remains the same.
  • HypertrophyOn the other hand, it refers to an increase in the size of the organ as a result of an increase in the size of the constituent cells. Consider the process of left ventricular hypertrophy, in which cardiac muscle cells increase in size after a chronic increase in total peripheral resistance. However, unlike hyperplasia, the number of cells is usually the same.
  • MetaplasiaIt is a reversible process in which one mature cell type is replaced by another mature cell type. A good example of this can be found in the distal partesophagusof patients with chronic gastroesophageal disease (i.e., Barrett's esophagus). In this case, chronic exposure of the squamous-type epithelium to corrosive gastric acids promotes cellular change to more robust columnar-type cells. When the stimulus is removed, the cell line returns to its previous state. This is not considered a direct relative of malignant lesions.
  • dysplasiaspeaks of the proliferation of immature cell lineages and a decrease in the prevalence of the mature cell lineage residing at that anatomical site. This is seen in cervical intraepithelial neoplasia, where the abnormal cell lineage has not yet invaded the basement membrane. This is considered a precursor to malignant lesions.


All content published on Kenhub is reviewed by experts in medicine and anatomy. The information we provide is based on scientific literature and peer-reviewed research.Kenhub does not provide medical advice.You can learn more about our content creation and review standards by reading ourContent quality guidelines.


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  • Hernandez-Verdun, Daniele:"Nucleolus: from structure to dynamics". Histochemistry and Cell Biology 125.1-2 (2005): 127-137. Network. October 3, 2016.
  • Kumar, Vinay and others:Robbins and Cotran Pathological basis of disease. 9th ed. Philadelphia, PA: Elsevier Saunders, 2015. Press.
  • Lowe, SW:"Apoptosis in Cancer". Carcinogenesis 21.3 (2000): 485-495. Network. October 5, 2016.
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