Cytology: Study of cell

Dr. Pallavi

J.N.L. College

Khagaul, Patna

Cell

• Cell is the basic functional unit of life and allthe living things are made up of theseindividual units.

• Antony van leeuwonhoek (Father ofmicrobiology) first used crude lense to seemicrobes in pond water

• Robert Hooke (Father of cytology) gave theterm “cell” to the microscopic compartmentsof cork.

Cell theory

• Schleiden and Schwann proposed cell theory (1838)

– Cell is the basic unit of life

– All organism are made up of cell

– Rudolf Virchow (1855) added an important point to this theory that all the cells arise from preexisting cells.

What are the exception to this theory?

Plant cell

Hierarchy of plant organization

Cellular Processes

• Nutrition– Digestion: enzymatic breakdown of substances– Absorption: transport of dissolved substances into cells

• Internal functions– Biosynthesis: assembling of organic compounds for growth,

replacement, or secretion– Respiration: breakdown of food to release energy

• Releasing materials– Excretion: removal of soluble waste (urine)– Egestion: removal of non-soluble, non-digestible waste (feces)– Secretion: releasing a substance synthesized in the cell

• Continuing existence– Homeostasis: maintaining a steady environment– Reproduction: formation of new cells

Types of cells

• Prokaryotic

– No true nucleus (nuclear area: clumps or rings of DNA)

– No membrane-bound organelles

– Mesosomes: indentations of the plasma membrane that contain enzymes used in the function of the cell

• Eucaryotic

– True nucleus

– Membrane-bound organelles

– Complex organization

Cell organelles and their functions• Cell Wall - The cell wall surrounds the cell membrane and serves to strengthen and

protect the cell. The cell wall also serves as a filter that controls the movement ofmolecules in and out of the cell.

• The plasma membrane (cell membrane) is the organelle that encapsulates the contentsof the cell. Apart from encapsulating cell contents, the plasma membrane also plays avital role in regulating the movement of substances in and out of the cell. The plasmamembrane is made up of two layers of phospholipids (phospholipids bilayer).

• The nucleus houses DNA (the hereditary material) as well as variousproteins and the nucleolus. In eukaryotic cells, the nucleus isenclosed in a nuclear membrane. It is the organelle that controlsthe hereditary traits of an organism by directing such processes asprotein synthesis and cell division among others. For prokaryotes,the DNA lacks a nuclear membrane. The genetic material istherefore bound in the nucleotide region. The nucleolus plays animportant role in ribosome production.

• Ribosomes are tiny organelles that contain RNA and specificproteins within the cytoplasm. Within the cell, ribosomes aredirectly involved in the manufacture of proteins by using their RNAand amino acids. This process involves decoding the informationcontained in the mRNA and using amino acids to produce therequired proteins.

Mitochondria are some of thelargest organelles within a cell.Compared to some of the otherorganelles, mitochondria containDNA which makes themsemiautonomous. Mitochondriaalso contain a double-membranewith the inner membrane foldingto form cristae. Also known asthe powerhouse, mitochondriaplay an important role inrespiration where they generateATP (Adenosine Tri Phosphate)from substrates in the presenceof oxygen. Using their DNA,mitochondria are able to encodefor some of the components theyrequire to perform theirfunctions. ATP stores energy inthe form of chemical bonds and isreleased whenever it is neededfor various cell functions.

• A vacuole may be described as a space inside thecell that does not contain cytoplasm. It issurrounded by a membrane and filled with afluid. Vacuoles store various molecules includingenzymes, waste products of the cell, water, andeven food material depending on the type of cell.In cases were vacuoles contain waste products ofthe cell, they are also involved in the exportationof waste from the cell thus protecting the cellfrom toxicity. Some vacuoles also play a role inmaintaining the internal hydrostatic pressure ofthe cell as well as regulating pH.

• Plastids are a type of organelle found in plant cells and algae. Like mitochondria, plastids are membrane-bound organelles and have their own genetic material. As such, they are also semi-autonomous organelles.

Based on the function they are of following different types:

• Chloroplast - Chloroplasts contain the pigment chlorophyll that captures energy from sunlight forphotosynthesis. Therefore, the chloroplast is the site of photosynthesis (the process through whichplants produce food)

• Chromoplasts - Chromoplasts are present in certain photosynthetic eukaryotes. They are primarilyinvolved in the production and storage of pigments (carotenoid pigments). These pigments are involvedin absorbing light energy as well as protecting chlorophyll in some plants.

• Leucoplast - Compared to the other plastids, leucoplasts are unpigmented organelles. Leucoplast is specialized for such functions as the storage of starch (amyloplasts), lipids (elaioplasts) and proteins (proteinoplasts).

• Endoplasmic reticulum (ER) is the organelle that forms an interconnected networkof flattened sacs (cisternae). Like some of the other organelles found ineukaryotes, ER is enclosed in a membrane. The ER is divided into two regions thatvary in structure and function.

• Smooth endoplasmic reticulum - The smooth ER is named so because it lacks aribosome on its surface. As a result, it is more smooth in appearance as comparedto the rough ER. It is involved in the synthesis of lipids (e.g. phospholipids) andcarbohydrates that are used to build the cell membrane.

• Some of the other functions of the smooth ER include:• Transportation of vesicles• Enzyme production in the liver• Contraction of muscle cells in the muscles• Synthesis of hormones in the brain cells• Rough endoplasmic reticulum- Unlike the smooth ER, rough ER has ribosome

attached to its surface. It is involved in the manufacture of various proteins in thecell. On the other hand, the rough ER is involved in the production of antibodies,insulin as well as transportation of proteins into the smooth ER.

• Centrioles are cylindrical organelles found in mosteukaryotic cells. They contain tube-shaped moleculesknown as microtubules that help separate chromosomesand move them during cell division.

• Lysosome is a ball shaped organelle which stores enzymes.They are membranous organelles that contain acidicenzymes (hydrolase enzymes) that serve to digest variousmacromolecules (e.g. lipids and nucleic acids) in the cell.

• Golgi apparatus are found in eukaryotic and are highlyfolded into cisternae (flattened sacs). They are enclosed ina membrane that varies in thickness from different regions.In the cell, Golgi apparatus are actively involved in themanufacturing, storage as well as transportation ofproducts from the ER.

Sources

• https://www.britannica.com/science/cell-biology

• http://www.goldiesroom.org/Note%20Packets/03%20Cytology/00%20Cytology--WHOLE.htm

• https://home.apu.edu/~jsimons/Bio101/cytology.htm

• https://www.microscopemaster.com/organelles.html