I have learned that materials can go in and out the cell in the process of endocytosis. Endocytosis takes the material in by forming an infolding. Exocytosis is when waste materials move out the cell.
I've learned that not all the resources needed by the cell comes from their inside enviroment, they also need the resources outside like the oxgen, protien, they need it for their production.
Mateials can go in and out of the cell by the different process like diffusion and osmosis have similarities but they also have differences like osmosis happens on water. Facilitated diffusion and active transport use a carrier or chanel proteien.
I've learned about Passive and Active transport is that passive transport occurs when there is a difference in concentration between substnaces either side of the membranr of cellular tranport wherein substance move against the concentration gradient.
Passive transport includes diffusion, and osmosis (hypotonic, isotonic, hypertonic).
I've learned a lot. This helps me to give more information about the movement of molecules.
Thursday, August 9, 2007
In active transport, molecules again move through a transport protein, but now energy must be expended to move them against their concentration gradient. The cell's solution to moving solutes against their concentration gradients is pumps. Many kinds of pumps are in operation in active transport, but each is specific for one or perhaps two substances. The energy source for such transport is ATP (adenosine triphosphate).
Sunday, August 5, 2007
+ is the process by which a cell directs secretory vesicles to the cell membrane. These membrane-bound vesicles contain soluble proteins to be secreted to the extracellular environment, as well as membrane proteins and lipids that are sent to become components of the cell membrane.
In multicellular organisms there are two types of exocytosis: 1) Ca2+ triggered non-constitutive and 2) non Ca2+ triggered constitutive. Exocytosis in neuronal chemical synapses is Ca2+ triggered and serves interneuronal signalling. Constitutive exocytosis is performed by all cells and serves the release of components of the extracellular matrix, or just delivery of newly-synthesized membrane proteins that are incorporated in the plasma membrane after the fusion of the transport vesicle
Exocytosis is needed by cells for secretion of proteins like enzymes, peptide hormones and antibodies from cells, turnover of plasma membrane, release of neurotransmitter from presynaptic neurons, placement of integral membrane proteins, acrosome reaction during fertilization, antigen presentation during the immune response and recycling of plasma membrane bound receptors.
Exocytosis is important in cellular signaling. In neuronal communication both chemical and electrical information needs to be sent throughout the cell. Exocytosis sends and converts the electrical information into chemical information. Within the neural cells, the information is electrical. In the synapse, after exocytosis has occurred, the neurotransmitters are released, and the information is chemical. The release of the neurotransmitter can either be excitatory (causing activity from the target cell) or inhibitory (preventing activity by the target cell).
Membrane-bound vesicles move to the cell surface where they fuse with the plasma membrane. This accomplishes three things:
It restores the normal amount of plasma membrane.
Any molecules dissolved in the fluid contents of these vesicles are discharged into the extracellular fluid - this is called secretion.Example: the various components of the extracellular matrix are secreted by exocytosis.
Any integral membrane proteins exposed to the interior surface of the vesicles will now be displayed at the cell surface because the vesicles turn inside out as they fuse with the plasma membrane. Thus exocytosis does not simply replace plasma membrane but ensures that the plasma membrane will display its characteristic cell-surface proteins.
Exocytic vesicles are created from several sources:
Some are simply endosomes traversing the cell.
Others are pinched off from endosomes before they fuse with lysosomes.
Others bud off from the endoplasmic reticulum and Golgi apparatus taking their products to the surface of the cell.
The exocytosis of lysosomes supplies the membrane needed to repair wounds in the plasma membrane.
>>> is a process whereby cells absorb material (molecules such as proteins) from the outside by engulfing it with their cell membrane. It is used by all cells of the body because most substances important to them are polar and consist of big molecules, and thus cannot pass through the hydrophobic plasma membrane. The function of endocytosis is the opposite of exocytosis
TYPES OF ENDOCYTOSIS
1. Phagocytosis- (literally, cell-eating) the process by which cells ingest large objects, such as cells which have undergone apoptosis, bacteria, or viruses. The membrane folds around the object, and the object is sealed off into a large vacuole known as a phagosome
2. Pinocytosis- (literally, cell-drinking) is a synonym for endocytosis. This process is concerned with the uptake of solutes and single molecules such as proteins.
3. Receptor- mediated endocytosis is a more specific active event where the cytoplasm membrane folds inward to form coated pits. These inward budding vesicles bud to form cytoplasmic vesicles.
+(sometimes called active uptake) is the mediated transport of biochemicals, and other atomic/molecular substances, across membranes. Unlike passive transport, this process requires the expenditure of cellular energy to move molecules "uphill" against a gradient.
+involves the use of proteins that don't just passively facilitate the transport of substances across the cell membrane, but require the use of cellular energy(usually ATP) to actively pump substances into or out of the cell. The animation represents the action of a sodium-potassium pump found in the cell membrane of neurons. This protein pumps sodium ions(red squares) from the inside to the outside of the neuron and pumps potassium ions(green squares)in the opposite direction. Notice the cell must use ATP(purple) for this process. As the sodium fits onto a site on the protein, a phosphate is transferred to the protein providing energy to kick the sodium ion to the outside and the potassium ion to the inside. This process sets up a high concentration of sodium ions outside the cell and a high concentration of potassim ions inside the cell. This concentration difference across the membrane is important for the generation of thenerve impulses by which neurons transmit information from on end of the neuron to the other. So even if you're zoned out in front of the tube your neurons are actively working to maintain this concentration difference...just in case they nave to send any information.
Active transport is used to:
1. Generate charge gradients. For example in the mitochondrion, hydrogen ion pumps pump hydrogen ions into the intermembrane space of the organelle as part of making ATP.
2. Concentrate ions, minerals and nutrients inside the cell that are in low concentration outside.
3. Keep unwanted ions or other molecules out of the cell that are able to diffuse through the cell membrane.
In all these cases the key is that active transport uses energy to send substances against the direction they would travel by simple diffusion: that is from a region of low concentration to a region of high concentration
~In this form of transport, molecules move against either an electrical or concentration gradient (collectively termed an electrochemical gradient).
The active transport of small molecules or ions across a cell membrane is generally carried out by transport proteins that are found in the membrane.
Larger molecules such as starch can also be actively transported across the cell membrane by processes known as endocytosis and exocytosis.
Particles that are moved through a membrane from a region of low concentration to high is known as active transport.
In primary transport, energy from hydrolysis of ATP is directly coupled to the movement of a specific substance across a membrane independent of any other species.
In secondary active transport, the required energy is derived from energy stored in the form of concentration differences in a second solute. Typically, the concentration gradient of the second solute was created by primary active transport, and the diffusion of the second solute across the membrane drives secondary active transport of the first solute.
~Facilitated diffusion (or facilitated transport) is a process of diffusion, a form of passive transport, where molecules diffuse across membranes, with the assistance of transport proteins.
Charged ions dissolve in water and diffuse through water channel proteins. These ion channels are gated so they can open and close, thus regulating the ion flow. Larger molecules diffuse through carrier proteins that change shape as the molecules are carried through, for example glucose and amino acids.
Small uncharged molecules can easily diffuse across cell membranes. However, due to the hydrophobic nature of the lipids that make up cell membranes, water-soluble molecules and ions cannot do so; instead, they are helped across by transport proteins. The transport protein involved is intrinsic(transmembranal), that is, it completely spans the membrane. It also has a binding site for the specific molecule such as glucose, or ion to be transported. After binding to the molecule, the protein changes shape and carries the molecule across the membrane, where it is released. The protein then returns to its original shape, to wait for more molecules to transport.
In contrast to active transport, facilitated diffusion does not require metabolic energy (ATP) and carries molecules or ions down a concentration gradient.
Facilitated diffusion can take place in pores and gated channels. Pores never close, but gated channels open and close in response to stimuli.
The transport proteins participating in facilitated diffusion resemble enzymes. Just as enzymes are substrate specific and only catalyse certain substrates, transport proteins are solute specific and only transport certain solutes. Transport proteins also have a limit of how many solutes they can transport. Finally, molecules can inhibit the protein in a way similar to competitive inhibition in enzymes.
As an example of facilitated diffusion, glucose molecules diffuse by simple diffusion only very slowly across a cell membrane since glucose is not readily soluble in the phospholipid bilayer. However, glucose diffuses very quickly across a cell membrane by facilitated diffusion because the carrier proteins help the glucose molecule cross into the cell. Specific examples: GLUT1 in erythrocytes, a passive transporter involved in importing glucose molecules and GLUT2 in liver cells, involved in importing glucose molecules.
=> transfer of a liquid solvent through a semipermeable membrane that does not allow dissolved solids (solutes) to pass. Osmosis refers only to transfer of solvent; transfer of solute is called dialysis. In either case the direction of transfer is from the area of higher concentration of the material transferred to the area of lower concentration. This spontaneous migration of a material from a region of higher concentration to a region of lower concentration is called diffusion
PRINCIPLES OF OSMOSIS
=>Osmosis will occur if a vessel is separated into two compartments by a semipermeable membrane, both compartments are filled to the same level with a solvent, and solute is added to one side. The level of the liquid on the side containing the solute will rise as the solvent flows from the side of its higher concentration to the side of lower concentration. If an external pressure is exerted on the side containing the solute, the transfer of solvent can be stopped and even reversed (reverse osmosis). Two solutions separated by a semipermeable membrane are said to be isotonic if no osmosis occurs. If osmosis occurs, transfer of solvent is from the hypotonic solution to the hypertonic solution, which has the higher osmotic pressure.
The minimum pressure necessary to stop solvent transfer is called the osmotic pressure. Since the osmotic pressure is related to the concentration of solute particles, there is a mathematical relationship between osmotic pressure, freezing-point depression, and boiling-point elevation. Properties such as osmotic pressure, freezing point, and boiling point, which depend on the number of particles present rather than on their size or chemical nature, are called colligative properties. For dilute solutions the mathematical relationship between the osmotic pressure, temperature, and concentration of solute is much like the relation between pressure, temperature, and volume in an ideal gas (see gas laws). A number of theories explaining osmotic pressure by analogy to gases have been devised, but most have been discarded in favor of thermodynamic interpretations using such concepts as the entropy of dilution.
BIOLOGICAL IMPORTANCE OF OSMOSIS
=>Osmosis and dialysis are of prime importance in living organisms, where they influence the distribution of nutrients and the release of metabolic waste products. Living cells of both plants and animals are enclosed by a semipermeable membrane called the cell membrane, which regulates the flow of liquids and of dissolved solids and gases into and out of the cell. The membrane forms a selective barrier between the cell and its environment; not all substances can pass through the membrane with equal facility. Without this selectivity, the substances necessary to the life of the cell would diffuse uniformly into the cell's surroundings, and toxic materials from the surroundings would enter the cell.
If blood cells (or other cells) are placed in contact with an isotonic solution, they will neither shrink nor swell. If the solution is hypertonic, the cells will lose water and shrink (plasmolyze). If the solution is hypotonic (or if pure solvent is used) the cells will swell; the osmotic pressure that is developed may even be great enough to rupture the cell membrane. Saltwater from the ocean is hypertonic to the cells of the human body; the drinking of ocean water dehydrates body tissues instead of quenching thirst.
In plants osmosis is at least partially responsible for the absorption of soil water by root hairs and for the elevation of the liquid to the leaves of the plant. However, plants wilt when watered with saltwater or treated with too much fertilizer, since the soil around their roots then becomes hypertonic.
=>contain a high concentration of solute relative to another solution (e.g. the cell's cytoplasm). When a cell is placed in a hypertonic solution, the water diffuses out of the cell, causing the cell to shrivel.
=>contain a low concentration of solute relative to another solution (e.g. the cell's cytoplasm). When a cell is placed in a hypotonic solution, the water diffuses into the cell, causing the cell to swell and possibly explode
=>contain the same concentration of solute as an another solution (e.g. the cell's cytoplasm). When a cell is placed in an isotonic solution, the water diffuses into and out of the cell at the same rate. The fluid that surrounds the body cells is isotonic.