Role of Plasma Membrane in Cell with its Environment
It regulates materials moving into and out of the cell. It secretes user substances such as enzymes, hormones, etc. It removes waste and toxic substances such as ammonia, urea, and uric acid.
It keeps a constant favorable ionic concentration within the cell for enzymatic nervous and muscular activities. The transport of substances across the plasma membrane occurs by endocytosis, exocytosis, osmosis, diffusion, etc.
1.3 Cytoplasm and Organelles
The living contents of the eukaryotic cells are divided into the nucleus and cytoplasm, these two together are known as protoplasm. The word "cytoplasm" literally means "living gel of cell". It is a liquid substance lying inside the cell membrane and outside the nucleus.
The cytoplasm is a mixture of organic and inorganic materials and forms a solution having all fundamental molecules of life i.e., amino acids, sugars, fatty acids, nucleotides, vitamins, salts, and dissolved gases.
The soluble part of the cytoplasm is called cytosol which is about 90% water, the small molecules and ions form a true solution and large molecules form colloidal
solution (Such as starch particles in plant cells and glycogen granules of animal cells). The colloidal solution may be in the form of a sol (nonviscous) or gel
(viscous) parts.
Cytoplasmic Organelles:
These are highly organized cellular bodies that perform specific functions. Such as endoplasmic reticulum, ribosome, Golgi bodies mitochondria, plastid, centrioles, lysosomes etc.
Functions: Store House:
The cytoplasm serves as a storehouse of vital materials, and chemicals e.g., glycogen in liver cells. Site for metabolic activities:
Maintain the cell shape:
The cytoskeleton present in the cytoplasm, not only maintains the shape of the cell but also helps in the movement of organelles.
1.3.1 Endoplasmic Reticulum (ER)
The endoplasmic reticulum is a network of channels or tubules in contact and extending between the nuclear membrane and the cell membrane of all eukaryotic cells. The components of the endoplasmic reticulum are:
Cisternae: These are long flattened and unbranched units arranged in stack Vesicles: These are oval membrane-bound structures.
Tubules: These are irregular often branched tubes bounded by membrane. Tubules may be free or connected with cisternae.
The endoplasmic reticulum divides the intracellular space into two distinct compartments, i.e., luminal (inside) and extraluminal (cytoplasm).
Types: There are two types of endoplasmic reticulum, Rough ER and Smooth ER.
Modification of Endoplasmic Recle cells SER is known as sarcoplasmic reti in skeletal and cardiac muscle cellsculum (SR). These store calcium ions in their lumen. If many ribosomes are attached to the small parallel cisternae of RER, then it is called ergastoplasm. In nerve cells, the ergastoplasm is known as Nissl's body.
Functions of ER:
Mechanical Support: Along with microfilaments and microtubules, ER gives mechanical support to the cell.
Intracellular Exchange: The ER forms an intracellular connecting system and transports material of the cell from one part to another part of the cell.
Connection: The ER also helps in connecting nuclear material with the plasma membrane.
Protein synthesis: Rough ER helps in protein synthesis as ribosomes are
attached with their outer surface.
Lipid Synthesis: Cholesterol and phospholipid are synthesized by smooth
ER.
Cellular Metabolism: The membranes of ER increase surface area for metabolic activities and also contain some enzymes like sucrases, glucose 6 phosphatases, NAD diphosphatase, etc.
Formation of Nuclear membrane: Fragmented elements of the disintegrated nuclear membrane and E.R. elements arrange around the chromosomes to form a nuclear membrane during cell division.
Formation of Organdles: All membranous organelles and chloroplast are formed by ER.
Detoxification: Smooth ER is concerned with pollutants, steroids, and other toxins.
mitochondria toxification of drugs,
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