Molecular and Cellular Bases- Pt 1.docx

Eukaryotes Have 2 major parts: Cytoplasm: separated from external environment via the plasma membrane. Nucleus: separated from the cytoplasm via the nuclear membrane. Cells contain: Water Water is a polar molecule which is the major component of most cells. Except for fat cells (adipocytes) which on...

Eukaryotes Have 2 major parts: Cytoplasm: separated from external environment via the plasma membrane. Nucleus: separated from the cytoplasm via the nuclear membrane. Cells contain: Water Water is a polar molecule which is the major component of most cells. Except for fat cells (adipocytes) which only contain 5% water, and have 95% lipid composition. Water chemical reactions can take place: at the surface of particles inside the membrane amongst dissolved chemicals Carbohydrates Carbohydrates do not typically have a structural function unless they are combined with lipids or proteins. Carbohydrates are typically used as a major energy source. In the ECF (extracellular fluid), glucose is readily used as an energy source. Carbohydrates are stored in small quantities within cells as glycogen. Proteins After water, proteins are the 2nd most abundant substance within cells. The 3D shape of proteins impacts it’s function, and allow for specificity when binding, like within “lock and key”. Proteins can alter their shape to adjust their function or binding properties. Proteins are essential for the mediation of physiological changes. Proteins can be: Structural Example: cytoskeleton Functional Examples: signaling protein, enzyme, transport protein Ions Ions are polar, hydrophilic molecules that provide inorganic chemicals for cellular reactions, making them necessary for cellular mechanisms. Cellular mechanism example: Ions transmitting electrochemical impulses in nerve and muscle cells. Ions with high quantities inside of the cell include: Phosphate Magnesium Sulfate Bicarbonate Potassium Ions with small quantities inside of the cell include: Sodium Chloride Calcium Positive ions will bind to the negative charge on water, while negative ions will do the opposite. This means that water positioning will vary based on ion charge. A membrane potential is the voltage difference caused by the uneven distribution of ions on opposite sides of the cell membrane (interior vs exterior). The ECF (extracellular fluid- outside of the cell) has more sodium. The ICF (intracellular fluid- inside of the cell) has more potassium. Lipids Lipids are non-polar molecules that play a key role in the cell’s membrane bound organelles, and are insoluble in water. Lipids are as diverse as proteins, yet lipids have been researched less than proteins, so their function is not fully understood. Phospholipids and cholesterol They make up the cell membrane, and intracellular membrane barriers which separate the cell’s compartments. Phospholipids will spontaneously form when exposed to an aqueous solution. When cholesterol is mixed with phospholipids, it stabilizes the lipid bilayer by enhancing its barrier properties. Triglycerides Adipocytes are the major source of lipid (energy-giving nutrients) storage for the body and are 95% composed of triglycerides. Triglycerides are composed of 1 glycerol and 3 fatty acids. Most cells store excess lipids in lipid droplets. Cell Membrane Cell membrane composition The plasma (cell) membrane is mostly composed of lipids and proteins and is impermeable to water-soluble substances. The intrinsic membrane proteins are imbedded within the lipid bilayer. The outer surface of the plasma membrane is composed of carbohydrates that have been combined with lipids or proteins. Lipids found within the cell membrane include: Phospholipids Phospholipids are found in high quantities within the cell membrane. Phospholipids attach to one another at the middle of the membrane. Sphingolipids Sphingolipids are found in small quantities within the membrane but are prevalent in nerve cells. Cholesterol Cholesterol aids in controlling membrane fluidity and permeability. Proteins found within the cell membrane include: Integral proteins Integral proteins are typically transmembrane proteins which are permanently attached to the cell membrane and can play a structural or functional role within the membrane. Integral proteins typically act as transporters, receptors, or channels. Peripheral proteins Peripheral proteins are attached to only one surface of the membrane without penetrating all the way through it. Peripheral proteins are typically attached to integral proteins and tend to act as an enzyme or channel controller. Cell membrane functions include: Compartmentalization via organizing biochemical reactions. Selective transport Processes and transmits information Membrane Potential Membrane potential generates an electrical charge that can influence the activity of proteins embedded in the cell membrane. In excitable cells, the membrane potential can help transmit signals between different parts of the cell. Cytosol vs. Cytoplasm The cytosol is the fluid composition of the cell in which the cells organelles reside. The cytosol is composed of water, dissolved proteins, electrolytes, and glucose. The cytoplasm is the space between the cell membrane and the nucleus. The cytoplasm contains the organelles and cytosol. Membrane Bound Organelles Endoplasmic Reticulum (ER) The ER is a network of netlike branching tubules and flattened sacs with a membrane that is continuous with the nuclear membrane. The smooth ER (sER or “agranular ER”) synthesizes lipids, and is therefore larger in cells with high lipid production. The sER lacks ribosomal attachment. The rough ER (rER or “granular ER”) synthesizes proteins. The rER has ribosomes attached to it, and is composed of RNA and proteins. The ER also serves as a reservoir for intracellular calcium storage, which will be (later) used signaling pathways. Golgi Apparatus The golgi apparatus is composed of a collection of flattened cisternae. Cisternae are membrane enclosed compartments. Due to the golgi being closely related to the ER, the vesicles that pinch off from the ER will fuse to the golgi apparatus. The functions of the golgi apparatus are to process and form: Lysosomes Secretory vesicles Other cytoplasmic components Lysosomes Lysosomes are vesicular organelles composed of the digestive enzyme “hydrolase” which is used to digest the following: Unwanted matter (such as bacteria) Food particles (via phagocytosis) Damaged cell structures Lysosomes are the major site of intracellular digestion. Peroxisomes Peroxisomes are vesicular organelles which can be formed via self-replication or be formed by the ER. Peroxisomes contain at least 50 different enzymes, of which most are oxidases, and some are catalases. Oxidases will combine oxygen and hydrogen together to form “H2O2”. Catalases will break down hydrogen peroxide. Peroxisomes also contain oxidated compounds such as amino acids and fatty acids. Peroxisomes are involved in lipid biosynthesis. For example, in hepatocytes, peroxisomes aid in bile acid synthesis. Mitochondria The mitochondria uses oxidative phosphorylation to burn down food into ATP which is then used as an energy source for the cell. Tissues that use more energy tend to have more mitochondria present. The mitochondria is capable of self-replication. Cytoskeleton The cytoskeleton is a network of fibrillar proteins organized into either tubules or filaments such as: Microtubules Intermediate filaments Microfilaments Actin is an example of a microfilament. The cytoskeleton functions include aiding the cell’s: Shape (ex: actin helps maintain cell shape) Movement Division Mechanical strength Track-line system to the movement of organelles/molecules Nucleus The nuclear membrane (AKA: nuclear envelope) continues with the ER and it can be penetrated via several pores. The nucleolus is a combination of large amounts of RNA and proteins. The nucleolus helps with protein synthesis. The nucleus also contains genetic information, such as DNA (chromosomes and chromatin). This genetic information is used to regulate cell death, cell growth, maturation, and division.