81⟩ What is meant by cellular secretion?
Cell secretion is the elimination to the exterior of substances produced by the cell (for example, hormones, mucous, sweat, etc.)
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111 Cell Biology Questions And Answers
82⟩ What are some examples of secretory cells?
Endocrine and exocrine pancreatic cells, thyroid and parathyroid endocrine cells, adenohypophysis, adrenal and pineal endocrine cells, the many types of gastric exocrine and endocrine cells, the mucous secretory cells of the lungs and of the bowels, the salivary gland cells, the lacrimal gland cells, the sebaceous gland cells, the secretory cells of the ovaries and testicles, etc., are all examples of secretory cells.
83⟩ Which cell organelles are well-developed in secretory cells?
In secretory cells, like the secretory cells of endocrine glands, organelles related to production, processing and “exportation” of substances are widely present and well-developed. These organelles are the rough endoplasmic reticulum and the Golgi apparatus.
The nuclear membrane of the secretory cells generally has more pores to allow the intense traffic of molecules related to protein synthesis between the cytoplasm and the nucleus.
Rough endoplasmic reticulum Golgi apparatus
84⟩ How do the amoeboid movements occur? What are examples of beings and cells that use such movements for locomotion?
Amoeboid movements are created by cytoplasmic movements and plasma membrane projections called pseudopods. Their formation actively changes the external shape of some portions of the cell surface making it to move along a substratum. Pseudopods appear from differences of viscosity among neighboring regions of cytoplasm near the plasma membrane and from the contractile action of microfilaments.
Amoeboid movements occur, for example, in amoebas (a protozoan), organisms that use their movement to find food. The leukocytes, cells of the immune system, when attracted by chemical substances (immune mediators) use amoeboid movements to get out from capillaries in regions of tissue damage to participate in the inflammatory process.
Cytoskeleton and Cell Movement - Image Diversity: pseudopods
85⟩ What is cyclosis?
Cyclosis is a type of internal cell movement in which an oriented flow of circulating material is created and maintained in the cytoplasm by the action of microfilaments. Cyclosis is more easily observed in plant cells.
Cytoskeleton and Cell Movement - Image Diversity: cyclosis
86⟩ What are some examples of movement created by the contraction of sarcomeres of the muscle cells?
The handling of a cup of coffee, the peristaltic movements of the bowels, the cardiac beats and even a smile are examples of movement created by contraction of the sarcomeres of the muscle cells. This contraction is a type of cell movement.
87⟩ What is extracellular digestion?
Extracellular digestion is that in which food breaking into utile molecules that can be internalized by the cell is done in the extracellular space, i.e., outside the cell. In extracellular digestion the cells secret substances that break big molecules into smaller ones in the external environment. Later the cell can benefit from these products of the digestion.
88⟩ What is intracellular digestion?
Intracellular digestion, or cellular digestion, is the breaking in the interior of the cell of big molecules coming from outside or even from the own cell metabolism into smaller molecules. Products and residues of the intracellular digestion are used by the cell or excreted.
Intracellular digestion is classified into two types: heterophagic intracellular digestion and autophagic intracellular digestion.
89⟩ What is the main cell organelle involved in cell digestion? What are the properties of that organelle that enable it to the task?
The organelles responsible for intracellular digestion are the lysosomes. Lysosomes are vesicles that contain digestive enzymes capable of breaking big molecules into smaller ones. These vesicles fuse with others that carry the material to be digested and then digestion takes place.
Cell Digestion Review - Image Diversity: lysosomes
90⟩ What is heterophagic intracellular digestion? How is this process accomplished?
Heterophagic intracellular digestion is the breaking into smaller substances of external substances engulfed in the cell by pinocytosis or phagocytosis. Phagosomes or pinosomes fuse with lysosomes making the digestive vacuoles. Within the digestive vacuoles the molecules to be digested are hydrolyzed and the products of the digestion cross through the membrane and reach the cytoplasm or they are kept inside the vacuoles. The vacuole with residues from digestion is called residual body and by exocytosis it fuses with the plasma membrane and liberates its “waste” in the exterior space.
91⟩ What is autophagic intracellular digestion? Why is this type of intracellular digestion intensified in an organism undergoing starvation?
Autophagic intracellular digestion is the cellular internal digestion of waste and residual materials. In general it is done by lysosomes.
Autophagic intracellular digestion is intensified in situations of starvation because in such condition the cell tries to obtain from its own constituent materials the nutrients necessary to stay alive.
92⟩ What are some biological examples in which lysosomic enzymes play fundamental role?
The remodelation of the osseous tissue, the function of acrosomes in sperm cells and the elimination of the tadpole tail are examples of biological processes in which lysosomic enzymes are key factors.
The bone is a tissue made of osteoblast-containing matrix (osteoblasts are the secretory cells of the osseous matrix), osteocytes (mature bone cells) and osteoclasts (the remodeling cells). Osteoclasts are responsible for the the continual renovation of the osseous tissue since their lysosomic enzymes digest the osseous matrix.
The sperm acrosome, for carrying digestive enzymes within, is responsible for the perfuration of the egg cell membrane in the fertilization process. The acrosome, located in the anterior end of the sperm cell, is a specialized region of the Golgi apparatus that accumulates great amount of digestive enzymes.
In tadpoles the tail regresses while the organism develops into an adult frog. This tissue destruction is a digestion of the tail own cells and extracellular materials and it is made by lysosomes and their enzymes. The complete digestion of a cell by its own mechanisms is called autolysis, a type of apoptosis (celll suicide).
93⟩ Of which substances is chromatin made?
Chromatin is made of DNA molecules associated to proteins called histones.
Cell Nucleus Review - Image Diversity: chromatin
94⟩ How are cells with delimited nucleus called? What are the main elements of the nucleus?
Cells with delimited nucleus are called eukaryotic cells. Organisms composed of one or more eukaryotic cells are called eukaryotes.
The mains elements of the nucleus are the chromatin (made of DNA molecules), the nucleolus, the karyolymph, or nucleoplasm, and the nuclear membrane (or karyotheca).
95⟩ Do all eukaryotic cells have nucleus and only one nucleus?
There are eukaryotic cells without nucleus and others with more than one nucleus. Osteoclasts, the cells responsible for resorption of the osseous matrix, for example, are multinucleate cells; striated muscle fibers are multinucleate too. Red blood cells are example of enucleated specialized cells.
Cell Nucleus Review - Image Diversity: cell nucleus miltinucleate cells enucleated cells
96⟩ What are heterochromatin and euchromatin?
Chromatin is uncondensed nuclear DNA, the typical DNA morphology in interphase (the phase of the cell cycle in which the cells is not dividing itself). In this phase of the cell cycle chromatin can be found as heterochromatin, more condensed and dark (in electronic microscopy) portions of DNA molecules, and as euchromatin, less condensed and lighter portions of DNA molecules.
Since it is uncondensed the euchromatin is the biologically active portion of the DNA, i.e, the region that has active genes to be transcripted into RNA. The heterochromatin represents the inactive portions of the DNA molecule.
Cell Nucleus Review - Image Diversity: heterochromatin euchromatin
97⟩ What is the relation between the concepts of chromatin and chromosome? Are euchromatin and heterochromatin part of chromosomes?
Every filament of chromatin is a complete DNA molecule (a complete double helix), i.e., a complete chromosome. A DNA molecule may form euchromatin and heterochromatin portions thus both are part of chromosomes.
Cell Nucleus Review - Image Diversity: chromosome structure
98⟩ In the phase when the cell is not dividing (interphase) is there activity within the cell nucleus?
In the interphase there is intense metabolic activity in the cell nucleus: DNA is duplicating, euchromatin is being transcript and RNA is produced.
99⟩ How are the concepts of chromosome, chromatin and chromatids related? In which phase of the cell cycle does DNA duplicate?
Chromatin is a set of filamentous DNA molecules dispersed in the karyoplasm forming euchromatin and heterochromatin portions. Each chromatin filament is a complete chromosome (a DNA molecule, or double helix). The chromatin of the human somatic cell is formed by 46 DNA molecules (22 homologous chromosomes and 1 pair of sex chromosomes).
In interphase the cell prepares itself for division and duplication of DNA molecules occurs. The duplication of every DNA molecule forms two identical DNA double helix bound by a structure called centromere. In this phase each identical chromosome of these pairs is called chromatid. It is also during the interphase that the chromatids begin to condensate assuming the thicker and shorter shape typical of chromosome illustrations. So the phase of the cell cycle in which DNA duplicates is the interphase.
Some Biology textbooks call chromosome an unique filament of chromatin as well as the condensed structure made of two identical chromatids after the DNA duplication. Rigorously the pair of identical chromatids bound in the centromere are two copies of the same chromosome and therefore they are two identical chromosomes (and not only one).
Cell Nucleus Review - Image Diversity: chromatids
100⟩ What is the structure that maintains identical chromatids bound?
The structure that maintains identical chromatids bound is the centromere.
Cell Nucleus Review - Image Diversity: centromere
