NR548: ADVANCED PATHOPHYSIOLOGY
Functions of the cellular organelles Organelles, according to Norris (2019), are small organs inside the cell. (p.12) These “small organs” are very much like the organs in the animal body that they make up. Each organelles has a different purpose. In this discussion there were be an overview of the following organelles: nucleus, protoplasm, ribosomes, endoplasmic reticulum, Golgi apparatus, lysosomes and proteasomes, mitochondria, and cytoskeleton. There is minor mention of the cell membrane, but that is not listed in the organelles category. The nucleus is the “control center,” each cell usually only has one but there are some cells that have more. (Norris, 2019 p. 12) The organelles are surrounded by protoplasm. This is where the supplements that are needed for the cells metabolism are found, it is important to have theses supplements or the cell can not create energy. The cell membrane are not considered part of the organelles according but it does have a primary role in helping the protoplasm balanced with the appropriate supplements for the cell.
The next organelles is the ribosomes, which are responsible for protein synthesis. (Norris, 2019 p. 13) The proteins that are produced may attached to the endoplasmic reticulum, which is responsible for different functions depending if it is rough or smooth. Rough endoplasmic reticulum has ribosomes attached to it and this produces produces parts for organelles or the cell membrane but can also be changed into secreted proteins. (Norris, 2019 p.13) With smooth endoplasmic reticulum it does not produce proteins, but lipids. The endoplasmic reticulum is very sensitive if one or more by products is produced and can called endoplasmic reticulum stress, which can cause inflammation and cell death. (Norris, 2019 p. 14) The Golgi apparatus or Golgi complex is used to make these products from both rough and smooth endoplasmic reticulum and package in the products so the body can use them. The Golgi apparatus can also make carbohydrates and pair them with proteins for the bodies use. (Norris, 2019 p. 14) There is the digestive organelles in the cell called the lysosomes. There are many different types and they all have different jobs. The primary lysosomes get their enzymes from the Golgi apparatus and do not do anything until they fuse with something that can be digested. Primary lysosomes become secondary when they enter heterophagy, taking in substances from outside the cell, and take in phagosomes which is produced when the cell membrane forms a barrier around the external substance. The primary lysosomes become secondary when they go to digest the phagosomes. (Norris, 2019 p. 14) Proteasomes are the organelles that are make of complexes in the cytoplasm (the protoplasm inside the cell) and they recognize misinformed and misfolded proteins and get rid of them. (Norris, 2019 p. 14) The mitochondria is where energy is made. Often referred to as the “power plants” (Norris, 2019) of the cell. (p. 15) They has their own DNA and ribosomes, which they use to self replicate. Mitochondria are also responsible for programmed cell death and has been linked to the growth of cancers. (Norris, 2019 p. 15) The cytoskeleton is part of the list of organelles and it affects the cells shape and movement. There are microtubules and microfilaments in this organelles. The microtubules are able to relocate and reassemble in locations when needed. (Norris, 2019 p. 15) They are also responsible for transporting things within and outside the cell. They also help with cell division. (Norris, 2019 p. 15) Microfilaments are responsible for movement within cells. There are different classes and they work together for the movement off the organ depending on where it may be in the body. (Norris, 2019 p. 15-16) When looking at all the structures and what the do it may be hard to understand how they connect to each other and how it may work, but what if one part of the cell fails? Are there things we can learn about the disease processes of some genetic disorders by looking closer at the relationships between organelles themselves? Norris, T. L. (2019). Porth’s essentials of pathophysiology: Concepts of altered health states (5th ed.).
Adenosine Triphosphate (ATP) is basically a molecule that transports energy within cells. ATP is used by the cell for muscle contraction and active transport of molecules across cellular membranes. So, ATP’s function is to store energy and transfer that energy from one molecule to another. Energy is stored by molecules of carbohydrate, lipid, and protein, which when catabolized, transfer energy to ATP. “ATP is an end product of processes such as, photophosphorylation, cellular respiration, and fermentation” (BD Editors, 2017).
ATP is produced through phosphorylation (specific for plants and bacteria) occurring during photosynthesis when ATP is created from ADP (adenosine diphosphate) using energy from sunlight. ATP is also formed from cellular respiration in the mitochondria of the cell through aerobic respiration (requiring oxygen), or anaerobic respiration (does not require oxygen). Aerobic respiration produces ATP along with CO2 and water from glucose and oxygen. While anaerobic respiration uses other chemicals (not O2) and it’s used by archaea and bacteria that live in anaerobic environments and occurs in the cytoplasm through the glycolytic pathway. The other way of ATP production is through fermentation and does not require oxygen, but it is different from anaerobic respiration as it does not use an electron transport chain, yeast and bacteria are examples of organisms that use fermentation to produce ATP (BD Editors, 2017).
To understand the cell metabolism, it is important to know that ATP is formed through three pathways: glycolytic, the citric acid cycle, and the electron transport chain. So, the cell starts the energy metabolism process with the anaerobic glycolytic pathway in the cytoplasm. If oxygen is present the pathway moves to the mitochondria to the aerobic pathway. Both pathways involve oxidation-reduction reactions.
Glycolysis (glycolytic pathway) is where energy is released from glucose (important energy provider in cells that lack mitochondria). It involves the splitting of the six-carbon glucose molecule into two three-carbon molecules of pyruvic acid. So, because the reaction of splitting glucose requires two ATP molecules, there is a gain of only two molecules of ATP from each metabolized glucose molecule. When oxygen appears in the equation, pyruvic acid moves into the mitochondria, and it enters the aerobic citric acid cycle.
When oxygen is present, under aerobic conditions, both of the pyruvate molecules (formed during glycolysis) enter the mitochondria where pyruvate combines with acetyl-coenzyme to form acetyl-coenzyme A (acetyl-CoA). The formation of acetyl-CoA begins the reactions in the citric acid cycle, also known as the tricarboxylic acid TCA or Krebs Cycle. Then reactions release CO2, and some other reactions transfer electrons from the hydrogen atom to NADH (Nicotinamide Adenine Dinucleotide) or FADH (Flavin Adenine Dinucleotide). Fatty acid and amino acid breakdown products in addition to pyruvate also enter the citric acid cycle. Fatty acids are oxidized to acetyl-CoA in order to enter the citric acid cycle. The oxidative metabolism takes place in the electron transport chain in the mitochondria. At the end of the citric acid cycle, each glucose molecule has yielded four ATP molecules (two from glycolysis and the other two from the citric acid cycle). Oxidation of the electrons carried by NADH and FADH2 is accomplished through a series of enzyme reactions in the mitochondrial electron transport chain. During those reactions protons (H+) combine with O2 to form water, and a lot of energy is released and used to add a high-energy phosphate bond to ADP, converting it to ATP. Due to the fact that the formation of ATP involves the addition of a high energy phosphate bond to ADP, the process is also called oxidative phosphorylation. So basically, 2 molecules from glycolysis, 2 molecules from the citric acid cycle, and 32 from the electron transport chain, the end result is of 36 molecules of ATP from one glucose molecule (Norris, 2019, pp. 24–26).
In which conditions would pyruvate be converted into lactic acid, allowing glycolysis to be the mean that supplies cells with ATP when there is no oxygen?
BD Editors. (2017). Adenosine Triphosphate (ATP) – Definition, Structure and Functions | Biology Dictionary. Biology Dictionary. https://biologydictionary.net/atp/
Norris, T. L. (2019). Porth’s pathophysiology: Concepts of altered health states (10th ed., pp. 24–26). Wolters Kluwer.
The membrane has a variety of roles to maintain cell homeostasis one of which includes the transportation of important materials. My particular discussion looks at how the membrane executes this transportation responsibility through a process called diffusion.
The term diffusion means “the movement of particles down their gradient” (Khan Academy). The gradient refers to difference of concentration in a particular area. For example, the outside of the cell and inside of the cell with the cell membrane in between. By understanding this term, the associated processes of simple diffusion and facilitated diffusion follow this concept.
With simple diffusion, there is movement across some gradient without the need for energy. The molecules that travel through this method must be “small and non-polar” (Khan Academy). The facilitated diffusion version has a “membrane transport channel”(Khan Academy) that allow specific molecules to move across the gradient. The molecules still move based on concentration differences between two areas, but it is more picky about which molecules enter and which do not like a bouncer at a club. These processes are passive in nature and do not require energy for it to occur.
There are instances where molecules must move against the natural gradient. To move against this gradient, there must be energy inputted also referred to as active transport. Can you think of examples showcasing this type of mechanism?
1. Khan Academy. (n.d.). Passive Transport and active transport across a cell membrane article (article). Khan Academy. Retrieved June 7, 2022, from https://www.khanacademy.org/test-prep/mcat/cells/transport-across-a-cell-membrane/a/passive-transport-and-active-transport-across-a-cell-membrane-article#:~:text=Facilitated%20diffusion%20is%20diffusion%20that,to%20pass%20through%20the%20membrane .