Cell physiology is the biological study about the activities that take place in a cell to keep it alive. This includes, among animal cells, plant cells and microorganisms. The term "physiology" refers to all the normal functions that take place in a living organism. All of these activities in the cell could be counted as following ; nutrition, environmental response, cell growth, cell division, reproduction and differentiation. The differences among the animal cell, plant cell and microorganisms show the essential functional similarity even though those cells have different structures.
General characteristics of cell physiology
Prokaryotes first came into existence and contain no self-contained nucleus, therefore making their mechanisms much simpler compared to the later-evolved Eukaryotes, which do contain a nucleus enveloping the cell's DNA and nuclear organelles.
Prokaryotes have DNA located in an area called the nucleoid, which is not membrane-bound. There are 2 domains of prokaryotes, which are bacteria and archaea. Unlike eukaryotes, prokaryotes do not have as much organelles. Some similarities between prokaryotic and eukaryotic structures is that both have plasma membranes and ribosomes. Some unique differences in prokaryotic structure is the presence of fimbriae and flagella. Fimbriae are finger-like projections that are on the surface of the cell and flagella are threadlike structures that aid in locomotion.
Eukaryotes have a nucleus where DNA is contained. They are usually larger than prokaryotes and contain much more organelles. For example, the nucleus contains the nuclear envelope, nucleolus, and chromatin. In the cytoplasm, is the endoplasmic reticulum (ER), which is where membrane synthesis and other metabolic activities. There are two types, rough ER and smooth ER. Rough ER contains ribosomes and smooth ER lack ribosomes. Ribosomes are structures that synthesize proteins that float free in the cytoplasm or attach to the rough ER. The Golgi Apparatus consists of multiple membraneous sacs that is responsible for manufacturing and shipping out materials such as proteins. Lysosomes are structures that consists of enzymes that are used to break down substances. It is carried out through the process of phagocytosis, which consists of endocytosis and exocytosis. The mitochondria is the site where metabolic processes such as cellular respiration occurs. The cytoskeleton is made up of fibers that support the structure of the cell and plays an important role in the movement of the cell.
There are different ways cells are able to transport substances across the cell membrane. The two main pathways are known as Passive Transport and Active Transport. Passive transport is more direct and doesn’t require the use of the cell’s energy to proceed. It relies on an area that maintains high-to-low concentration gradient. Active transport on the other hand utilizes ATP in order to transport a substance that moves in opposition to its concentration gradient.
Movement of proteins
Pathway of proteins in cells start at endoplasmic reticulum (ER). Lipids and proteins are synthesized in the ER and carbohydrates are added in order to make glycoproteins. Glycoproteins undergo further synthesis in the Golgi apparatus which become glycolipids. Both glycoproteins and glycol lipids are then transported into the vesicles to the plasma membrane. The cell released secretory proteins known as exocytosis.
Transport of Ions
Ions travel across cell membranes through either channels, pumps, and transporters. Ions in channels move down an electrochemical gradient to produce electrical signals, while transporter use more than one gradient to produce these electrical signals. Pumps help maintain electrochemical gradients. The main type of pump is the Na/K pump. The pump helps move 3 sodium ion out of the cell and two potassium ions into the cell. The entire process converts one ATP molecule to ADP and Pi.
Endocytosis in Animal Cells
Endocytosis is a form of active transport where a cell takes in molecules through the use of the plasma membrane and packages them into vesicles.
A cell surrounds particles, including food particles via extension of the pseudopods which are located on the plasma membrane. These pseudopods then package these particles in a food vacuole. An organelle known as the lysosome which contains hydrolytic enzymes will then fuse with the food vacuole. The hydrolytic enzymes also known as digestive enzymes will then digest the particles within the food vacuole.
A cell takes in or “gulps” extracellular fluid into vesicles which are formed when the plasma membrane surrounds the fluid. The cell takes in the molecules which are found in the droplets. The cell can take in any molecules or solutes through this process.
A form of pinocytosis where the cell takes in more specific molecules or solutes. There are proteins with receptor sites located on the plasma membrane which bind to specific solutes. The receptor proteins that are attached to the specific solutes go inside coated pits which then forms a vesicle. The vesicles now surrounds the receptors that are attached to the specific solutes. The molecules are then released from the vesicles and receptor proteins are recycled back to the plasma membrane by the same vesicle.
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