intracellular digestion

Examples of intracellular digestion in the following topics:

• Invertebrate Digestive Systems

  • Invertebrates can be classified as those that use intracellular digestion and those with extracellular digestion.
  • The simplest example of digestion intracellular digestion, which takes place in a gastrovascular cavity with only one opening.
  • The food particles are engulfed by the cells lining the gastrovascular cavity and the molecular are broken down within the cytoplasm of the cells (intracellular).
  • Because the food has been broken down exterior to the cells, this type of digestion is called extracellular digestion.
  • Their food is broken down in their digestive tract (extracellular digestion), rather than inside their individual cells (intracellular digestion).

• Natural Killer Cells

  • T cells are lymphocytes that mature in the thymus gland and identify intracellular infections, especially from viruses, by the altered expression of major histocompatibility class (MHC) I molecules on the surface of infected cells.
  • A granzyme, a protease that digests cellular proteins, induces the target cell to undergo programmed cell death, or apoptosis.
  • Phagocytic cells then digest the cell debris left behind.

• Cell-Mediated Immunity

  • First, an antigen-presenting cell (APC, such as a dendritic cell or a macrophage) detects, engulfs (via phagocytosis in the case of macrophages or by entry of the pathogen of its own accord in the case of dendritic cells), and digests pathogens into hundreds or thousands of antigen fragments.
  • TC cells attempt to identify and destroy infected cells by triggering apoptosis (programmed cell death) before the pathogen can replicate and escape, thereby halting the progression of intracellular infections.
  • MHC I complexes display a current readout of intracellular proteins inside a cell and will present pathogen antigens if the pathogen is present in the cell.
  • An antigen-presenting cell (APC), such as a macrophage, engulfs a foreign antigen, partially digests it in a lysosome, and then embeds it in an MHC class II molecule for presentation at the cell surface.

• The lac Operon: An Inducer Operon

  • The lac operon encodes the genes necessary to acquire and process the lactose from the local environment, which includes the structural genes lacZ, lacY, and lacA. lacZ encodes β-galactosidase (LacZ), an intracellular enzyme that cleaves the disaccharide lactose into glucose and galactose. lacY encodes β-galactoside permease (LacY), a membrane-bound transport protein that pumps lactose into the cell. lacA encodes β-galactoside transacetylase (LacA), an enzyme that transfers an acetyl group from acetyl-CoA to β-galactosides.
  • The cell can use lactose as an energy source by producing the enzyme b-galactosidase to digest that lactose into glucose and galactose.

• Cell Structure, Metabolism, and Motility

  • Amoebas and some other heterotrophic protist species ingest particles by a process called phagocytosis in which the cell membrane engulfs a food particle and brings it inward, pinching off an intracellular membranous sac, or vesicle, called a food vacuole .
  • The stages of phagocytosis include the engulfment of a food particle, the digestion of the particle using enzymes contained within a lysosome, and the expulsion of undigested materials from the cell.

• Digestion and Absorption

  • Mechanical digestion refers to the physical breakdown of large pieces of food into smaller pieces which can subsequently be accessed by digestive enzymes.
  • Different organs play specific roles in the digestive process.
  • Digestive enzymes are found in the digestive tracts of animals.
  • The digestion of carbohydrates begins in the mouth.
  • Digestion of carbohydrates is performed by several enzymes.

• Digestive Systems

  • Animals use the organs of their digestive systems to extract important nutrients from food they consume, which can later be absorbed.
  • During digestion, food particles are broken down to smaller components which will later be absorbed by the body.
  • The digestive system is one of the largest organ systems in the human body.
  • The functions of the digestive system can be summarized as follows: ingestion (eat food), digestion (breakdown of food), absorption (extraction of nutrients from the food), and defecation (removal of waste products).
  • This diagram shows a generalized animal digestive system, detailing the different organs and their functions.

• Vertebrate Digestive Systems

  • Vertebrates have evolved more complex digestive systems to adapt to their dietary needs.
  • Humans and many animals have a monogastric digestive system .
  • The process of digestion begins with the mouth and the intake of food.
  • The digestive enzymes of these animals cannot break down cellulose, but microorganisms present in the digestive system can.
  • This is the site where the roughage is fermented and digested.

• Programmed Cell Death

  • Programmed cell-death (or PCD) is death of a cell in any form, mediated by an intracellular program.
  • Macroautophagy, often referred to as autophagy, is a type of programmed cell death accomplished through self-digestion.

• Types of Receptors

  • Receptors, either intracellular or cell-surface, bind to specific ligands, which activate numerous cellular processes.
  • Enzyme-linked receptors are cell-surface receptors with intracellular domains that are associated with an enzyme.
  • In some cases, the intracellular domain of the receptor itself is an enzyme or the enzyme-linked receptor has an intracellular domain that interacts directly with an enzyme.
  • Hydrophobic signaling molecules typically diffuse across the plasma membrane and interact with intracellular receptors in the cytoplasm.
  • Many intracellular receptors are transcription factors that interact with DNA in the nucleus and regulate gene expression.