Cell Structure and Function Notes PDF

- Structure and function of Cytoplasm and Cell membrane. - Study mechanisms of cell transport through membrane. - Types of intercellular Junctions Lecture 3 Dr. Zainab Almansour  Cytoplasm Cytoplasm is a thick solution...

- Structure and function of Cytoplasm and Cell membrane. - Study mechanisms of cell transport through membrane. - Types of intercellular Junctions Lecture 3 Dr. Zainab Almansour  Cytoplasm Cytoplasm is a thick solution that fills each cell and is enclosed by the cell membrane. - It is mainly composed of water, salts, and proteins. - a majority of cell organelles (ribosome, Golgi apparatus, Endoplasmic Reticulum, etc) are located in the cytoplasm.  Function of Cytoplasm Functions of the Cytoplasm: Functions of the cytoplasm can be attributed to its components. Some of these functions include: 1- Transport 2- Maintain the shape and structure of a cell 3- Protection 4- Storage 5- Site of metabolic activities 6- Cell movement 7- Cell Division 8- Cell growth  Cytosol Cytosol The cytosol is the intracellular fluid of the cytoplasm. It is largely composed of water (over 70 percent) and surrounds all organelles located/suspended in the cytoplasm. Cytosol Functions - It involved in signal transduction originating from the cell membrane. - It contributes to the transduction signaling from the plasma membrane to the nucleus - The cytosol is also involved in the transportation of metabolites (e.g. amino acids in eukaryotic cells) in addition to being the site of metabolic chemical reactions in prokaryotes. The difference between cytoplasm and cytosol lies in the fact that cytosol is the fluid (intracellular fluid) of the cell while cytoplasm consists of all cell components within the cell membrane (excluding the nucleus).  Protoplasm Protoplasm: The term protoplasm is used to refer to the cytoplasm and the internal components of a cell in general. It consists of proteins, lipids, sugars, and starches (carbohydrates), phosphates, potassium, and sodium (inorganic salts) and water. The difference between cytoplasm and protoplasm: Whereas cytoplasm includes cell components within the cell (excluding the nucleus) the term protoplasm is sometimes used to refer to all components within the cell including the nucleus. The difference between cytoplasm and protoplasm  Cell Membrane The cell membrane, also known as the plasma membrane, is a double layer of lipids and proteins that surrounds a cell. - It separates the cytoplasm (the contents of the cell) from the external environment. - It is a feature of all cells, both prokaryotic and eukaryotic.  Function of Cell Membrane Function of the Cell Membrane - The cell membrane gives the cell its structure and regulates the materials that enter and leave the cell. - It is a selectively permeable barrier, meaning it allows some substances to cross, but not others. - The cell membrane also plays an important role in cell signalling and communication.  Structure of Cell Membrane - The cell membrane is made up of a phospholipid bilayer. - Phospholipids are lipid molecules made up of a phosphate group head and two fatty acid tails. - The phosphate group head of a phospholipid is hydrophilic, whereas the phospholipid tail is hydrophobic. This means that the phosphate group is attracted to water, whereas the tail is repelled by water.  Structure of Cell Membrane - The cell membrane also contains many different proteins. - Proteins make up about half of the cell membrane. - Many of these proteins are transmembrane proteins, which are embedded in the membrane. - Membrane proteins perform a variety of functions vital to the survival of organisms.  Mechanisms of cell transport through membrane -All cells are enclosed by a cell membrane, which is selectively permeable. -Molecules can move into or out of cells by diffusion and active transport. -Cells can gain or lose water by osmosis. There are two major ways that molecules can be moved across a membrane: Passive mechanisms like diffusion use no energy, while active transport requires energy to get done.  Diffusion Diffusion is the movement of a substance from an area of high concentration to an area of low concentration. Factors Affecting Diffusion 1- Temperature 2- Area of Interaction 3- Size of the Particle. 4- The steepness of the concentration gradient. Significance of Diffusion During the process of respiration, this process helps in diffusing the carbon dioxide gas out through the cell membrane into the blood. Diffusion also occurs in plant cells. In all green plants, water present in the soil diffuses into plants through their root hair cells. The movement of ions across the neurons that generates electrical charge is due to diffusion.  Diffusion - Diffusion is one form of passive transport that doesn’t require the expenditure of cellular energy. - A molecule can diffuse passively through the cell membrane if it’s lipid-soluble, uncharged, and very small. - The unassisted diffusion of very small or lipid-soluble particles is called simple diffusion. The assisted process is known as facilitated diffusion. - Embedded in the membrane are transmembrane protein molecules called channel proteins that create diffusion- friendly openings for molecules to move through during the facilitated diffusion  Osmosis Osmosis is a form of passive transport that’s similar to diffusion and involves a solvent moving through a selectively permeable or semipermeable membrane from an area of higher concentration to an area of lower concentration. - Solutions are composed of two parts: a solvent and a solute. The solvent is the liquid in which a substance is dissolved. A solute is the substance dissolved in the solvent.  Osmosis Osmolarity is the term used to describe the concentration of solute particles per litre. An isotonic solution has the same concentration of solute and solvent as found inside a cell. A hypotonic solution has less solute and higher water potential than inside the cell. A hypertonic solution has more solute and lower water potential than inside the cell. Diffusion Vs Osmosis Diffusion  Active Transport Active Transport is a process that involves the movement of molecules from a region of lower concentration to a region of higher concentration against a gradient or an obstacle with the use of external energy. There are two types of active transport : 1- Primary active transport that uses adenosine triphosphate (ATP). 2- Secondary active transport that uses an electrochemical gradient. An example of active transport in human physiology is the uptake of glucose in the intestines. Active Transport Passive Vs Active Transport  Endocytosis Endocytosis is the process of actively transporting molecules into the cell by engulfing it with its membrane. The material to be internalized is surrounded by an area of cell membrane, which then buds off inside the cell to form a vesicle containing the ingested material. Endocytosis includes 1- pinocytosis (cell drinking) 2- phagocytosis (cell eating) 3- receptor- mediated endocytosis  Exocytosis Exocytosis is a form of active transport in which a cell transports molecules from within a cell to the exterior of the cell by secreting them through an energy- dependent process. During exocytosis vesicles form in the cytoplasm and move to the surface of the cell membrane.Then they merge with the membrane and release their contents to the outside of the cell. Exocytosis removes the cell’s waste products, which are the parts of molecules that are not used by the cell.  Intercellular Junctions Cell junctions (or intercellular bridges) are specialized regions of contact between the plasma membranes of adjacent cells, consisting of multiprotein complexes that provide contact between neighbouring cells or between a cell and the extracellular matrix. Three different types of intercellular junctions can be distinguished according to their function: 1- Tight or occluding junctions. 2- Adherent or anchoring junctions, including desmosomes and hemidesmosomes. 3- Gap junctions.