Bio Chapter 4

Receptor Proteins (integral)

have a shape that allows a specific molecule to bind to it. The binding of this molecule causes the protein to change its shape and thereby bring about a cellular response. The coordination of the body's organs is totally dependent on such signal molecules. For example, the liver stores glucose after it is signaled to do so by insulin.

glycolipids

lipid in plasma membrane that contain an attached carbohydrate chain (assembled in golgi apparatus)

Desmosomes

one form of adhesion junction. In a desmosome, internal cytoplasmic plaques, firmly attached to the intermediate filament cytoskeleton within each cell, are joined by integral membrane proteins called cadherins between cells. The result is a sturdy but flexible sheet of cells. Adhesion is most common type between skin cells

fluid-mosaic model

the combination of proteins, steroids, and phospholipids in the plasma membrane

Osmotic pressure

the pressure that develops in a system due to osmosis.2 In other words, the greater the possible osmotic pressure, the more likely it is that water will diffuse in that direction. Due to osmotic pressure, water is absorbed by the kidneys and taken up by capillaries in the tissues. Osmosis also occurs across the plasma membrane.

isotonic solutions

the solute concentration and the water concentration both inside and outside the cell are equal, and therefore there is no net gain or loss of water For example, a 0.9% solution of the salt sodium chloride (NaCl) is known to be isotonic to red blood cells

Adhesion junctions

Adjacent plasma membranes held together by intercellular filaments attached to buttonlike thickenings

cytolysis vs hemolysis vs turger pressure

All involve hypotonic solutions: disrupted cells=cytolysis when talking about red blood cells= hemolysis (lysis=burst of cell) turger pressure: The swelling of a plant cell in a hypotonic solution. the cytoplasm expands because the large central vacuole gains water and the plasma membrane pushes against the rigid cell wall. The plant cell does not burst because the cell wall does not give way

Gap junction

Allows communication between cells by joining plasma membrane channels between the cells The channel of each cell is lined by six plasma membrane proteins. A gap junction lends strength to the cells, but it also allows small molecules and ions to pass between them. Gap junctions are important in heart muscle and smooth muscle because they permit a flow of ions that is required for the cells to contract as a unit.

proteoglycans

Amino sugars in the ECM form multiple polysaccharides that attach to a protein and are, therefore, called proteoglycans. Proteoglycans, in turn, attach to a very long, centrally placed polysaccharide. The entire structure, which looks like an enormous bottle brush, resists compression of the extracellular matrix. Proteoglycans assist cell signaling when they regulate the passage of molecules through the ECM to the plasma membrane, where receptors are located. Thus, the ECM has a dynamic role in all aspects of a cell's behavior.

Osmosis

The diffusion of water across a selectively permeable membrane due to concentration differences.

Endocytosis

Energy required Macromolecules move inside the cell Vesicle formation

Exocytosis

Energy required Macromolecules move toward outside of cell (Hormones, neurotransmitters, and digestive enzymes) Vesicle fuses with plasma membrane and secretion occurs

Active Transport

Energy required Towards higher concentration Needs carrier protein plus energy Ex: Sugars, amino acids, and ions

How permeable is the plasma membrane?

Selectively permeable: meaning that certain substances can move across the membrane while others cannot

Cell recognition protein (integral)

Glycoproteins in the membrane that identify self and help the body defend itself from pathogens so an immune response can occur

plasmodesmata

In plant cell walls, they are cytoplasmic connections that connect two adjacent cells numerous narrow, membrane-lined channels that pass through the cell wall. Cytoplasmic strands within these channels allow direct exchange of some materials between adjacent plant cells and eventually connect all the cells within a plant. The plasmodesmata allow only water and small solutes to pass freely from cell to cell.

Examples of organs where desmosomes are found

In some organs such as the heart, stomach, and bladder, where tissues get stretched, desmosomes hold the cells together

Integrins

Integrins are integral membrane proteins that connect to fibronectin externally and to the actin cytoskeleton internally. Through its connections with both the ECM and the cytoskeleton, integrin plays a role in cell signaling, permitting the ECM to influence the activities of the cytoskeleton and, therefore, the shape and activities of the cell.

Facilitated Transport

No energy required Toward lower concentration Needs channels or carrier protein and concentration gradient Ex: Glucose and some amino acids and aquaporins

Diffusion

No energy required toward lower concentration (down gradient) until equilibrium is achieved and they are distributed equally. Diffusion is a physical process that can be observed with any type of molecule. Ex: Lipid-soluble molecules and gases Ex: Oxygen (O2) diffuses into the capillaries of the lungs because there is a higher concentration of oxygen in the alveoli (air sacs) than in the capillaries Ex. Both dye (solute) and water (solvent) move to low concentration until the dye dissolves

hypertonic solutions

Solutions that cause cells to shrink or shrivel due to loss of water. A higher percentage of solute (lower concentration of water) than the cell. If a cell is placed in a hypertonic solution, water leaves the cell. Salt solution higher than 0.9%

What is in a plant cell wall

The primary cell wall contains cellulose fibrils (very fine fibers) in which microfibrils are held together by noncellulose substances. Pectins allow the wall to stretch when the cell is growing (Pectins are especially abundant in the middle lamella, which is a layer of adhesive substances that holds the cells together.) Noncellulose polysaccharides harden the wall when the cell is mature.

Carrier Protein (integral)

They combine with a substance and help it move across the membrane. For example, a carrier protein transports sodium and potassium ions across a nerve cell membrane. Without this carrier protein, nerve conduction would be impossible. Carrier proteins are specific for the substances they transport across the plasma membrane

Channel proteins (integral)

They have a channel that allows a substance to simply move across the membrane. For example, a channel protein allows hydrogen ions to flow across the inner mitochondrial membrane. Without this movement of hydrogen ions, ATP would never be produced. Channel proteins may contain a gate that must be opened by the binding of a specific molecule to the channel. A channel protein forms a pore through the membrane that allows molecules of a certain size and/or charge to pass.

Sodium-potassium pump

a carrier protein active in all animal cells, but is especially associated with nerve and muscle cells moves sodium ions (Na+) to the outside of the cell and potassium ions (K+) to the inside of the cell using active transport A change in carrier shape after the attachment of a phosphate group, and again after its detachment, allows the carrier to combine alternately with sodium ions and potassium ions. The phosphate group is donated by ATP when it is broken down enzymatically by the carrier. The sodium-potassium pump results in both a solute concentration gradient and an electrical gradient for these ions across the plasma membrane. it undergoes an ATP-dependent change in shape. Three sodium ions are carried outward for every two potassium ions carried inward. Therefore, the inside of the cell is negatively charged compared to the outside.

extracellular matrix (ECM)

a meshwork of proteins and polysaccharides in close association with the cell that produced them. Collagen and elastin fibers are two well-known structural proteins in the ECM; collagen resists stretching and elastin gives the ECM resilience.

Fibronectin

adhesive protein that binds to a protein in the plasma membrane called integrin.

Receptor-mediated endocytosis

form of pinocytosis (selective and more efficient) Molecules first bind to specific receptor proteins, which migrate to, or are already in, a coated pit. The vesicle that forms contains the molecules and their receptors and can fuse with a lysosome. vitamin, peptide hormone, lipoprotein, LDL

Peripheral proteins

associated with only one side of the plasma membrane. Peripheral proteins on the inside of the membrane are often held in place by cytoskeletal filaments. structural role in that they help stabilize and shape the plasma membrane. They may also function in signaling pathways

Tight junctions

bring cells even closer than desmosomes. Tight junction proteins actually connect plasma membranes between adjacent cells together, producing a zipperlike fastening. Tissues that serve as barriers are held together by tight junctions; in the intestine, the digestive juices stay out of the rest of the body, and in the kidneys, the urine stays within kidney tubules, because the cells are joined by tight junctions.

Enzymatic Proteins

carry out metabolic reactions directly (catalyzes reaction). The integral membrane proteins of the electron transport chain carry out the final steps of aerobic respiration. Without the presence of enzymes, some of which are attached to the various membranes of the cell, a cell would never be able to perform the metabolic reactions necessary to its proper function.

aquaporins

channel proteins that allow water to quickly cross the membrane

hydrophobic (water-fearing) nonpolar tails

facing each other

hydrophilic (water-loving) polar heads

facing the outside and inside of the cell (where water is found)

glycoproteins

protein in plasma membrane that contain an attached carbohydrate chain (assembled in golgi apparatus)

hypotonic solutions

refers to a solution with a lower concentration of solute (higher concentration of water) than inside the cell. If a cell is placed in a hypotonic solution, water enters the cell. The net movement of water is from the outside to the inside of the cell.

crenation vs plasmolysis

shriveling of red blood cells in hypertonic solution: crenation plasmolysis: shrinking of the cytoplasm due to osmosis

What can freely pass through the membrane?

small, noncharged molecules, such as carbon dioxide, oxygen, glycerol, and alcohol These molecules go "down" their concentration gradient as they move from an area where their concentration is high to an area where their concentration is low

integral proteins

span the membrane, and can protrude from one or both sides. The integral proteins largely determine a membrane's specific functions

The fluidity of the membrane is regulated by

steroids such as cholesterol, which serve to stiffen and strengthen the membrane

Factors that influence rate of diffusion

temperature, pressure, electrical currents, and molecular size. For example, as temperature increases, the movement of molecules increases, which in turn increases the rate of diffusion.

Phagocytosis (type of endocytosis)

transports large substances, such as viruses, food particles Phagocytosis is common in single-celled organisms such as amoeba (human white blood cells act the same way)

pinocytosis (type of endocytosis)

transports small substances or liquid, such as macromolecules, into cells (polypeptide, blood cells, plant root cells, kidney cells)