Structure of cell components and functions

For information purpose only.

1. Sri Ramya Vaddiparthy V/VI Pharm.D Structure of CELL- Components & Functions

2. Introduction The  cell  (from Latin  cella , meaning "small room ") is the basic structural, functional, and biological unit of all known organisms. A cell is the smallest unit of life. Cells are often called the "building blocks of life". The study of cells is called cell biology, cellular biology, or cytology . The number of cells in plants and animals varies from species to species; it has been estimated that humans contain somewhere around 40 trillion (4×10 13 ) cells .  The human brain accounts for around 80 billion of these cells.

3. History 1595  – Jansen credited with 1st compound microscope 1655  – Hooke described ‘cells’ in cork. 1674  – Leeuwenhoek discovered protozoa. He saw bacteria some 9 years later. 1833  – Brown descibed the cell nucleus in cells of the orchid. 1838  – Schleiden and Schwann proposed cell theory. 1840  – Albrecht von Roelliker realized that sperm cells and egg cells are also cells. 1856  – N. Pringsheim observed how a sperm cell penetrated an egg cell. 1858  – Rudolf Virchow (physician, pathologist and anthropologist) expounds his famous conclusion:  omnis cellula e cellula , that is cells develop only from existing cells [cells come from preexisting cells]

4. 1857  – Kolliker described mitochondria. 1879  – Flemming described chromosome behavior during mitosis. 1883  – Germ cells are haploid, chromosome theory of heredity. 1898  – Golgi described the golgi apparatus. 1938  – Behrens used differential centrifugation to separate nuclei from cytoplasm. 1939  – Siemens produced the first commercial transmission electron microscope. 1952  – Gey and coworkers established a continuous human cell line. 1955  – Eagle systematically defined the nutritional needs of animal cells in culture. 1957  – Meselson , Stahl and Vinograd developed density gradient centrifugation in cesium chloride solutions for separating nucleic acids. .

5. 1965  – Ham introduced a defined serum-free medium. Cambridge Instruments produced the first commercial scanning electron microscope. 1976  – Sato and colleagues publish papers showing that different cell lines require different mixtures of hormones and growth factors in serum-free media. 1981  – Transgenic mice and fruit flies are produced. Mouse embryonic stem cell line established 1995  – Tsien identifies mutant of GFP with enhanced spectral properties 1998  – Mice are cloned from somatic cells. 1999  – Hamilton and Baulcombe discover siRNA as part of post-transcriptional gene silencing (PTGS) in plants

6. Cells were discovered by  Robert Hooke  in 1665, who named them for their resemblance to cells inhabited by  Christian monks  in a monastery .  Cell theory, first developed in 1839 by  Matthias Jakob Schleiden   &  Theodor Schwann , states that all organisms are composed of one or more cells, that cells are the fundamental unit of structure and function in all living organisms , and that all cells come from pre-existing cells .  Cells emerged on Earth at least 3.5 billion years ago.

7. Cell Theory The cell theory developed in 1839 by microbiologists Schleiden and Schwann describes the properties of cells. It is an explanation of the relationship between cells and living things. The theory states that: all living things are made of cells and their products. new cells are created by old cells dividing into two. cells are the basic building blocks of life. The cell theory applies to all living things, however big or small. The modern understanding of cell theory extends the concepts of the original cell theory to include the following : The activity of an organism depends on the total activity of independent cells. Energy flow occurs in cells through the breakdown of carbohydrates by respiration. Cells contain the information necessary for the creation of new cells. This information is known as 'hereditary information' and is contained within DNA. The contents of cells from similar species are basically the same.

8. The Cell Structure

9. Cell types

10. CELL Animals are a large group of diverse living organisms that make up to three-quarters of all species on earth. With their ability to move, to respond to stimuli, respond to environmental changes and adapt to different modes of feeding defense mechanisms and reproduction, all these mechanisms are enhanced by their constituent elements in the body .  Some of these living things are single-celled ( unicellular ) and other organisms are made up of more than one cell ( Multicellular ).

11. Most cells are covered by a protective membrane known as the  cell wall  which gives the cells their shape and rigidity. An animal cell is a eukaryotic cell that lacks a cell wall, and it is enclosed by the  plasma membrane . The cell organelles are enclosed by the plasma membrane including the cell nucleus.

12. Size & Shape Animal cells come in all kinds of shapes and sizes, with their size ranging from a few millimeters to micrometers. The largest animal cell is the ostrich egg which has a 5-inch diameter, weighing about 1.2-1.4 kg and the smallest animal cells are the neurons of about 100 microns in diameter.

13. Animal cells are eukaryotic cells with a membrane-bound nucleus. therefore they have their genetic material in the form of DNA enclosed in the nucleus. They also have several structural organelles within the plasma membrane which perform various specific functions for proper cell function and generally to maintain the body normal mechanisms.

14. Plasma membrane (Definition, structure, functions) It is a thin semi-permeable protein membrane layer that surrounds animal cell. Structure of Plasma membrane (Cell membrane) Thin semi-permeable membrane It contains a percentage of lipids making a semi-permeable barrier between the cell and its physical environment. It has some protein components a It is very consistent around the cell All living cells have a plasma membrane.

15. Functions of Plasma membrane (Cell membrane) To enclose and protect the cell content To also regulate the molecules that pass into and out of the cell, through the plasma membrane. Therefore it controls homeostasis. The proteins are actively involved in transporting materials across the membrane The proteins and lipids allow cell communication, and carbohydrates (sugars and sugar chains), which decorate both the proteins and lipids and help cells recognize each other.

16. Nucleus ( Definition,structure , Functions) This is a spherical structured organelle found majorly at the center of a cell surrounded by a double-layered nuclear membrane separating it from the cytoplasm. It is held together to the cytoplasm with the help of the filaments and microtubules. It holds other cells organelles including the nucleolus, nucleosomes , and chromatins. A cell has one nucleus which divides producing multinucleated cells e.g. the skeletal muscle cell fibers. Some cells lose their nuclei after maturations e.g. the red blood cells .

17. Structure of Nucleus The double-layered membrane is a continuous channel of membranous from the endoplasmic reticulum network. The membrane has pores which allow entry of large molecule Nucleoli (Singular; nucleolus) are tiny/small bodies found in the nucleus The nucleus and its component organelles are suspended in the  nucleoplasm ( House of the chromosomal DNA and genetic materials)

18. Functions of Nucleus The primary role of the nucleus is to control and regulate cell activities of growth and maintain cell metabolisms. It also carries the genes that have hereditary information of the cell. The chromosomal DNA and genetic materials, which are made up of genetic coded ultimately make up their proteins’ amino acid sequences for use by the cell. Therefore, the nucleus is the information center. It is the site for Transcription (formation of mRNA from DNA) and the mRNA is transported to the nuclear envelope.

19. Cytoplasm A jelly-like material which contains all the cell organelles, enclosed within the cell membrane. The substance found within the cell nucleus, contained by the nuclear membrane is called the nucleoplasm .

20. Mitochondria(Definition, Structure, Function) These are membrane-bound organelles located in the cytoplasm of all eukaryotic cells The number of mitochondria found in each cell varies widely depending on the function of the cell it performs. For example, erythrocytes do not have mitochondria while the liver and muscle cells have thousands of mitochondria.

21. Structure A mitochondrion contains outer and inner membranes composed of  phospholipid bilayers  and  proteins.The two membranes have different properties. Because of this double- membraned organization, there are five distinct parts to a mitochondrion. They are: the outer mitochondrial membrane, the intermembrane space (the space between the outer and inner membranes), the inner mitochondrial membrane, the  cristae  space (formed by infoldings of the inner membrane), and the  matrix (space within the inner membrane). Mitochondria stripped of their outer membrane are called  mitoplasts .

22. Functions Energy conversion A dominant role for the mitochondria is the production of ATP, as reflected by the large number of proteins in the inner membrane for this task. This is done by oxidizing the major products of glucose:  pyruvate , and NADH, which are produced in the cytosol .  This type of  cellular respiration known as aerobic respiration, is dependent on the presence of oxygen, which provides most of the energy released. When oxygen is limited, the glycolytic products will be metabolized by anaerobic fermentation, a process that is independent of the mitochondria .  The production of ATP from glucose and oxygen has an approximately 13-times higher yield during aerobic respiration compared to fermentation .

23. Heat production Under certain conditions, protons can re-enter the mitochondrial matrix without contributing to ATP synthesis. This process is known as  proton leak  or mitochondrial uncoupling and is due to the facilitated diffusion of protons into the matrix. The process results in the unharnessed potential energy of the proton  electrochemical  gradient being released as heat .  The process is mediated by a proton channel called  thermogenin , or UCP1 .   Thermogenin  is a 33 kDa  protein first discovered in 1973 .   Thermogenin is primarily found in brown adipose tissue, or brown fat, and is responsible for non-shivering thermogenesis .

24. Storage of calcium ions Transmission electron micrograph of a  chondrocyte , stained for calcium, showing its nucleus (N) and mitochondria (M). The concentrations of free calcium in the cell can regulate an array of reactions and is important for signal transduction in the cell. Mitochondria can transiently store calcium, a contributing process for the cell's homeostasis of calcium .  In fact, their ability to rapidly take in calcium for later release makes them very good " cytosolic buffers" for calcium .  The endoplasmic reticulum (ER) is the most significant storage site of calcium,and there is a significant interplay between the mitochondrion and ER with regard to calcium .

25. Mitochondria play a central role in many other  metabolic tasks , such as: Signaling through mitochondrial reactive oxygen species Regulation of the membrane potential Apoptosis - programmed cell death Calcium signaling (including calcium-evoked apoptosis ) Regulation of cellular  metabolism Certain  heme  synthesis reactions   Steroid synthesis . Hormonal signaling  Mitochondria are sensitive and responsive to hormones, in part by the action of mitochondrial estrogen receptors ( mtERs ). These receptors have been found in various tissues and cell types, including brain  and heart  Immune signaling 

26. Ribosomes They are small organelles majorly made up of 60% RNA cytoplasmic - granules and 40% proteins. All living cells contain ribosomes , which may be freely circulating in the cytoplasm and some are bound to the endoplasmic reticulum. It is the site for protein synthesis.

27. Structure of Ribosomes Ribosomes are made up of ribosomal proteins and ribosomal RNA ( rRNA ). In a eukaryotic cell, ribosomes constitute half ribosomal RNA and half ribosomal proteins. Each ribosome is made up of two subunits i . e large subunit and small subunit with their own distinct shapes. These subunits are designated as the 40s and 60s in the animal cell.

28. Functions of Ribosomes Ribosomes that occur as free particles are attached to the endoplasmic reticulum membrane occurring in large numbers accounting for about a quarter of the cell organelles. A single replicated cell has about 10 million ribosomes . The ribosomal subunits are the site for genetic coding into proteins. On the ribosomes , the mRNA helps determine the coding for Transfer RNA ( tRNA ) which also determines the protein amino acid sequences. This leads to the formation of the rRNA which are involved in the catalyzation of peptidyl transferase creating the peptide bond found between the amino acid sequences that develop the proteins. The formed proteins then detach from the ribosomes , migrating to other cell parts for utilization by the cell.

29. Endoplasmic Reticulum(ER) (Structure, Function) Structure of Endoplasmic Reticulum (ER) This is a continuous folded membranous organelle found in the cytoplasm made up of a thin network of flattened interconnected compartments (sacs) that connects from the cytoplasm to the cell nucleus. Within its membranes, there are membranous spaces called the  cristae spaces  and the membrane folding are called  cristae . There are two types of ER based on their structure and the function they perform including  Rough Endoplasmic reticulum  and the  Smooth endoplasmic reticulum .

30. Functions of Endoplasmic Reticulum (ER) Manufacturing, processing and transporting proteins for cell utilization both in and out of the cell. This is because it is directly connected to the nuclear membrane providing a passage between the nucleus and the cytoplasm. The ER has more than half the membranous cell content, hence it has a large surface area where chemical reactions take place. They also contain the enzymes for almost all the cell lipid synthesis hence they are the site for lipid synthesis.

31. Types of Endoplasmic Reticulum Rough Endoplasmic Reticulum (Rough ER)  – Rough ER is called “rough” because there surface is covered with ribosomes , giving it a rough appearance.  The function of the ribosomes on rough ER is to synthesis proteins and they have a signaling sequence, directing them to the endoplasmic reticulum for processing. Rough ER transports the proteins and lipids through the cell into the cristae . They are then sent into the Golgi bodies or inserted into the cell membrane. Smooth Endoplasmic Reticulum (Smooth ER) –  Smooth ER is not associated with ribosomes and their unction is different from that of the rough endoplasmic reticulum, despite lying adjacent to the rough endoplasmic reticulum. Its function is to synthesis lipids (cholesterol and phospholipids) that are utilized for producing new cellular membranes. They are also involved in the synthesis of steroid hormones from cholesterol for certain cell types.  It also contributes to the detoxification of the liver after the intake of drugs and toxic chemicals. There is also a specialized type of smooth ER known as the  sarcoplasmic reticulum.  Its function is to regulate the concentration of Calcium ions in the muscle cell cytoplasm.

32. Golgi Apparatus Structure of Golgi apparatus (Golgi bodies) These are membrane-bound cell organelles found in the cytoplasm of a eukaryotic cell, next to the endoplasmic reticulum and near the nucleus. Golgi bodies are supported together by cytoplasmic microtubules and held by a protein matrix It is made up of flattened stacked pouches known as cisternae . These cisternae maybe 4- 10 in number for animal cell Golgi bodies though some organisms like single-celled organisms have about 60 cisternae . They have three primary compartments known as  cis   ( Cisternae Nearest the Endoplasmic Reticulum) , medial  (central layers of cisternae )  and the trans  ( cisternae farthest from the endoplasmic reticulum). Animal cells have very few (1-2) Golgi bodies while plants have a few hundred.

33. Functions of Golgi apparatus (Golgi bodies) Their primary function is to transport, modify and pack proteins and lipids into the Golgi vesicles to deliver them to their target sites. Animal cells contain one or more Golgi bodies while plants have a few hundred. Cis and trans Golgi network make up the outer layer of cisternae at the cis and trans face and they are responsible for sorting proteins and lipids received at the cis face and released by the trans face, by the Golgi bodies. The cis face collects the proteins and lipids, of fused vesicles in clusters. The fused vesicles move along the microtubules through a specialized compartment known as the  vesicular-tubular cluster .  This compartment is found between the endoplasmic reticulum and the Golgi apparatus.

34. The vesicle clusters fuse with the cis Golgi network, delivering the proteins and lipids into the cis face cisternae and as they move from the cis face to the trans face, they get  modified  to functional units. These functional units get delivered to intracellular and extracellular components of the cell.Modification mechanisms include: Cleaving of oligosaccharides chains Attachment of sugar moieties of different side chains

35. Lysosomes It is also known as cell vesicles; Lysosomes were discovered by Christian Rene de Duve, a Belgian cytologist in the 1950s. Structure of Lysosomes They are round subcellular organelle found in almost all eukaryotic cells Lysosomes are very acidic organelles containing the digestive enzymes and therefore each of the lysosomes is surrounded by a membrane to protect it from the outer environment. Functions of Lysosomes This is the site for digestion of cell nutrients, excretion, and cell renewal. Lysosomes break down macromolecules components from the outside of the cell into simpler elements that are transported into the cytoplasm via a  proton pump  to build new cell material s .

36. These macromolecule components include old cells and parts, cell waste products, microorganisms, and cell debris. The digestive enzymes found in the lysosomes are called hydrolytic enzymes or acid hydrolases , breaking down large molecules into smaller molecules that can be utilized by the cell .

37. Cytoskeleton, Microtubules This is a fibrous network that’s formed from and by different proteins of long chains of amino acids. It plays a major role in the movement of the cell and some cell organelles in the cytoplasm. The tiny filaments include: Actin filaments ; also known as  microfilaments;  it’s a meshwork of fibers running parallel to each other and they play a primary role in giving the cell its shape; they change consistently, helping the cell to move and to also mediate certain cell activities such as adherence ability to substrates and cleavage mechanisms during mitotic cell division Microtubules-  these are long filaments that assist in mitosis moving daughter chromosomes to new forming daughter cells. Intermediate filaments – they are more stable filaments in comparison to the actin and microtubules. They form the true skeleton of the cell, and the hold the nucleus in its rightful position within the cell.

38. Microtubules are long, straight, hollow cylinders filaments that are constructed from 13-15 sub-filaments ( protofilament ) strand of a special globular protein called  tubulin ,  found only in eukaryotic cells . They are found throughout the cytoplasm of the animal cell .

39. Transportation of some organelles like the mitochondria and the vesicles i.e. transporting vesicles from the neuron cell body to the axon tips, and back to the cell body Structural support, they give characteristic support to the Golgi bodies, holding them within the gel-matrix of the cytoplasm. They provide the rigid and organized component of the cytoskeleton of the cell, enabling a cell to take up a particular shape.

40. Centrioles This is distinctly found in the animal cell, which has the ability to replicate or make copies by itself. It is made up of 9 microtubule bundles and their primary function is to assist in organizing the cell division process. The triplet microtubules are held together by proteins, giving the centriole its shape. They are found in the centrosome , creating and holding microtubules within the cell. The triplet microtubules are surrounded by a pericentriolar matrix containing molecules that build up the microtubules.

41. Functions The centriole microtubules allow the transportation of substances that are linked together with a glycoprotein to any cell location. the glycoprotein linkage acts as a signaling unit to move specific proteins. The centrioles anchor the microtubules that extend from it and contain the factors needed to create more tubules. Mitosis is achieved by replication of each centriole which makes duplicates of each centriole (4 centrioles ). The newly formed centrioles divide into two centrosomes , each centriole at an angle to the second centriole . 

42. References https://microbenotes.com/animal-cell-definition-structure-parts-functions-and-diagram / https:// en.wikipedia.org/wiki/Mitochondrion#Function https:// intl.siyavula.com/read/science/grade-10-lifesciences/cells-the-basic-units-of-life/02-cells-the-basic-units-of-life-03 https://bitesizebio.com/166/history-of-cell-biology /

43. Thank you