“Cell Biology Interview Questions and Answers will teach us now that The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. Some organisms, such as most bacteria, are unicellular. So learn every thing about the Cell Biology with this Cell Biology Interview Questions with Answers guide”
Cells can be classified as eukaryotic or prokaryotic.
Prokaryotic cell is that without a delimited nucleus. Eukaryotic cells are those with nucleus delimited by membrane.
Cell Structure Review - Image Diversity: eukaryotic cell prokaryotic cell
Animal cells (cells of living beings of the kingdom Animalia) have an interior membrane that delimits a cell nucleus and thus they are eukaryotic cells; in these cells the genetic material is located within the nucleus. Bacterial cells (cells of living beings of the kingdom Monera) do not have organized cellular nucleus and so they are prokaryotic cells and their genetic material is found dispersed in the cytosol.
Cell theory is a theory that asserts that the cell is the constituent unit of the living beings.
Before the discovery of the cell, it was not recognized that the living beings were made of building blocks like cells.
The cell theory is one of the basic theories of Biology.
What is being observed is the Golgi complex, or Golgi apparatus. This cytoplasmic organelle is associated with chemical processing and modification of proteins made by the cell and with storage and branding of these proteins for posterior use or secretion. Vesicles seen in the electronic microscope contain material already processed, ready to be exported (secreted) by the cell. The vesicles detach from the Golgi apparatus, travel across the cytoplasm and fuse with the plasma membrane then secreting their substances to the exterior.
Cell Structure Review - Image Diversity: Golgi apparatus
Intracellular digestion occurs by the action of lysosomes. Lysosomes have digestive enzymes (hydrolases) that are made in the rough endoplasmic reticulum and stored in the Golgi apparatus. Lysosomes are hydrolase-containing vesicles that detach from the Golgi apparatus.
Lysosomes make autophagic and heterophagic digestion: autophagic digestion by digesting residual substances from the cellular metabolism; heterophagic digestion by digesting substances that enter the cell. Lysosomes enfold the substances to be degraded forming digestive vacuoles, or residual vacuoles, that later migrate toward the plasma membrane fusing with it and liberating (exocytosis) the digested material to the exterior.
Cell Structure Review - Image Diversity: lysosomes
The organelles that participate in the cell division and in the formation of cilia and flagella of some eukaryotic cells are the centrioles. Some cells have cillia (paramecium, the bronchial ciliated epithelium, etc.) or flagella (flagellate protists, sperm cells, etc.); these cell structures are composed by microtubules originated from the centrioles. Centrioles also make the aster microtubules that are very important for cell division.
Cell Structure Review - Image Diversity: centrioles
Similarities: lysosomes and peroxisomes are small membranous vesicles that contain enzymes and enclose residual substances from internal or external origin degrading them. Differences: lysosomes have digestive enzymes (hydrolases) that break substances to be digested into small molecules; peroxisomes contain enzymes that degrade mainly long-chained fatty acids and amino acids and that inactivate toxic agents including ethanol; within peroxisomes there is the enzyme catalase, responsible for the oxidation of organic compounds by hydrogen peroxide (H2O2) and, when this substance is in excess, by the degradation of the peroxide into water and molecular oxygen.
Mitochondria are the organelles in which the most important part of the cellular respiration occurs: the ATP production.
Mitochondria are organelles delimited by two lipid membranes. The inner membrane invaginates to the interior of the organelle forming cristae that delimitate the internal space known as mitochondrial matrix and where mitochondrial DNA (mtDNA), mitochondrial RNA (mt RNA), mitochondrial ribosomes and respiratory enzymes can be found. Mitochondria are numerous in eukaryotic cells and they are even more abundant in those cells that use more energy, like muscle cells. Because they have their own DNA, RNA and ribosomes, mitochondria can self-replicate.
Cell Structure Review - Image Diversity: mitochondria
Mitochondria are the “power plants” of aerobic cells because within them the final stages of the cellular respiration process occurs. Cellular respiration is the process of using organic molecule (mainly glucose) and oxygen to produce carbon dioxide and energy. The energy is stored in the form of ATP (adenosine triphosphate) molecules and later used in other cellular metabolic reactions. In mitochondria the two last steps of the cellular respiration take place: the Krebs cycle and the respiratory chain.
It is presumed that mitochondria were primitive aerobic prokaryotes that were engulfed in mutualism by primitive anaerobic eukaryotes, receiving protection from these beings and offering energy to them. This hypothesis is called the endosymbiotic hypothesis on the origin of mitochondria.
The hypothesis is strengthened by some molecular evidences as the facts that mitochondria have own and independent DNA and protein synthesis machinery, with own RNA and ribosomes, and that they can self-replicate.
The endosymbiotic theory can be applied for chloroplasts too. It is supposed that these organelles were primitive photosynthetic prokaryotes because they have own DNA, RNA and ribosomes and they can self-replicate too.
The cytoskeleton is a network of very small tubules and filaments distributed throughout the cytoplasm of eukaryotic cells. It is made of microtubules, microfilaments and intermediate filaments.
Microtubules are formed by molecules of a protein called tubulin. Microfilaments are made of actin, the same protein that participates in the contraction of muscle cells. Intermediate filaments are made of protein too.
Cell Structure Review - Image Diversity: cytoskeleton
As the name indicates, the cytoskeleton is responsible for the supporting of the normal shape of the cell; it also acts as a facilitator for substance transport across the cell and for the movement of cellular organelles. For example, the sliding between actin-containing filaments and the protein myosin creates pseudopods. In cells of the phagocytic defense system, like macrophages, cytoskeleton is responsible for the plasma membrane projections that engulf the external material to be interiorized and attacked by the cell.
Chloroplasts are organelles present in the cytoplasm of plant and algae cells. Likewise mitochondria, chloroplasts have two boundary membranes and many internal membranous sacs. Within the organelle there are own DNA, RNA and ribosomes and also the pigment chlorophyll, responsible for absorption of photic energy that is used in photosynthesis.
The main function of chloroplasts is photosynthesis: the production of highly energetic organic molecules (glucose) from carbon dioxide, water and light.
Cell Structure Review - Image Diversity: chloroplasts
The chlorophyll molecules are the responsible for the absorption of the light energy for photosynthesis. These molecules are found on the internal membranes of chloroplasts.
Chlorophyll absorbs all other colors of the electromagnetic spectrum but it practically does not absorb the green. The green color is reflected and such reflection provides the characteristic color of plants. If the green light that reaches a plant is blocked and the exposition of the plant to other colours is maintained there would be no harm for photosynthesis. Apparent paradox: the green light is not important for photosynthesis.
There is difference between the optimun color frequency for the two main types of chlorophyll, the chlorophyll A and the chlorophyll B. Chlorophyll A has an absorption peak in approximately 420 nm wavelenght (anil) and chlorophyll B has its major absorption in 450 nm wavelenght (blue).
Cell Structure Review - Image Diversity: electromagnetic spectrum
The energy source of photosynthesis is the sun, the unique and central star of our planetary system. In photosynthesis the solar energy is transformed into chemical energy, the energy of the chemical bonds of the produced glucose molecules (and of the released molecular oxygen). The energy of glucose then is stored as starch (a glucose polymer) or it is used in the cellular respiration process and transfered to ATP molecules. ATP is consumed in metabolic processes that spend energy (for example, in active transport across membranes).
The plant cell wall has structural and protective functions. It plays important role in the constraint of the cell size, preventing the cell to break when it absorbs much water.
The plant cell wall is made of cellulose. Cellulose is a polymer whose monomer is glucose. There are other polymers of glucose, like glycogen and starch.
Cell Structure Review - Image Diversity: plant cell wall
Plant cell vacuoles are cell structures delimited by membranes within which there is an aqueous solution made of several substances like carbohydrates and proteins. In young plant cells many small vacuoles can be seen; within adult cells the most part of the internal area of the cell is occupied by a central vacuole.
The main function of the vacuoles is the osmotic balance of the intracellular space. They act as “an external space” inside the cell. Vacuoles absorb or release water in response to the cellular metabolic necessities by increasing or lowering the concentration of osmotic particles dissolved in the cytosol. Vacuoles also serve as storage place for some substances.
The membrane that delimits the vacuoles is called tonoplast, named after the osmotic function of the structure.
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