Chapter 3: Chemical Level of Organization: Cells And Homeostasis Flashcards
What is a plasma membrane?
Cell’s outer surface surrounding the cell internal’s and external organs
What is the cytoplasm?
Consists of all the cell’s cellular contents between the plasma membrane and nucleus. Contains 2 parts: Cytosol (fluid portion of cytoplasm, contains water, dissolved solvents, suspended particles), and organelles (Characteristic shape and function).
What is the nucleus?
Contains most of cell’s DNA. Each chromasome within has thousands of genes that control most aspects of a cell’s structure and function.
What is the fluid-mosaic model?
The molecular arrangement of the plasma membrane resembles a continually moving sea of fluid lipids that contain a mosaic of different proteins
What are the 4 functions of the plasma membrane?
1) Acts as a barrier separating inside or outside of cell. 2) Controls the flow of substances into and out of cell. 3) Helps identify the cell to other cells (eg immune cells) and 4) Participates in intercellular signalling
Describe the basic structure of the lipid bilayer
2 back-to-back layers made up of 3 types of lipid molecules: Phospholipids (75%… contains phosphorus), cholesterol (20%… steriod with attached OH group) and glycolipids (5%… attahched carbohydrate group)
How do phospholipids orient themselves in the lipid bilayer?
Their hydrophilic heads face outward… the heads face a watery fluid on either side (cytosol on the inside and EC fluid on the outside). Hydrophobic fatty acid tails in each half of the bilayer point toward one another forming a nonpolar hydrophobic region in the membrane’s interior
What are integral proteins?
Extended into or through the lipid bilayer and firmly embedded in it. Most are transmembrane proteins so extend the entire width of the bilayer and portrude into both the cytosol and the EC fluid. Example are glycoproteins (proteins with carbohydrate groups attached to the ends that protrude into the EC fluid. The carbohydrates are oligosaccharides)
What is peripheral proteins?
Not as firmly embedded in the membrane. Attached to the polar heads of membrane lipids or integral proteins at the inner or outer surface of the membrane.
What is Glycocalyx?
Carbohydrate portions of glycolipids and glycoproteins that form an extensive sugary glyccalyx. Enables cells to recognize one another (ie WBCs ability to detect a foreign glycocalyx).
What are the 5 functions of integral proteins?
1) ion channels (pores/holes that specific ions can flow through to can into/out of cell). 2) Carriers (Selectively moving a polar substance or ion from one side of the memebrane to the other). 3) Receptors (Recognizes and binds a specific types of molecules. Insulin receptors bind insulin. A molecule that binds to a receptor is called a LIGAND). 4) Enzymes (catalyze specific chemical reactions). 5) Linkers (Anchor proteins in plasma membranes of nearby cells to one another or to protein filaments inside and outside of cell)
What’s a main function of glycoproteins and glycolipids?
Serve as identity markers. May enable a cell to 1) recognize other cells of the same kind during tissue formation and 2) Recognize and respond to foreign dangerous cells. Eg blood cells must be compatible or RBCs will clump together.
Functions of peripheral proteins?
1) Support plasma membrane. 2) Anchor integral proteins. 3)Move materials and organelles within cells. 4) Attach cells to one another.
What does membrane fluidity depend on?
The number of double bonds in the fatty acid tails of the lipids in the bilayer. Each double bond puts a kink in the fatty acid tail which increases membrane fluidity by preventing lipid molecules from packing together
Why is membrane fluidity important?
Enables movement of membrane materials responsible for important cell processes like cell movement, growth, division, and secretion. It also allows it to self-seal when punctured or torn (ie intracytoplasmic sperm injection).
How does cholesterol’s affect on the lipid bilayer vary based on temperature?
Makes lipid bilayer stronger (and less fluidity) at normal temperature and weaker (and more fluidity) at lower temperature
What is selective permeability?
The plasma membrane allows some substances t pass more readily than others. Nonpolar molecules (CO2, O2, steriods) are highly permeable, moderately permeable to small uncharged polar molecules (water and urea) and impermeable to large uncharged polar molecules (like glucose). Transmembrane proteins that act as channels and carriers can increase the plasma membrane’s permeability to a variety of selective ions and uncharged polar molecules.
What’s a concentration gradient?
A difference in the concentration of a chemical from one place to another. Like from outside the cell to inside.
What is ELECTRICAL GRADIENT and MEMBRANE POTENTIAL?
The inner surface of the plasma membrane is more negatively charged and the outer surface is more positively charged. This difference in electrical charges is called an electrical gradient. The charge difference is termed membrane potential.
What’s the electrochemical gradient?
A substance will move downhill from where it’s more concentrated to where it’s less concentrated to reach equilibrium. A positively charged substance will move towards a negatively charged substance and vice versa. The combined influence of the concentration gradient and electrical gradient is the electrochemical gradient.
WHat are passive processes?
A substance moves down its concentration / electrical. Gradient to cross the membrane using only its own kinetic energy (energy of motion) no input from cell’s energy. Example is simple diffusion
What are active processes?
Cellular energy is used to drive the substance uphill against its concentration or electrical gradient. ATP is used. Example is active transport.
What are endocytosis and exocytosis?
They are active processes using the vesicles. In endocytosis, vesicles detach from the plasma membrane while bringing materials into a cell0. In exocytosis vesicles merge with the plasma membrane to release materials from the cell.
WHat is diffusion?
A passive process. Random mixing of particles occurs in a solution because of the particles’ kinetic energy. Both solutes and solvents undergo diffusion. Solute molecules will diffuse towards an area of low concetration (think about the dye example)… eventually they become evenly distributed and reach equilibrium
Factors that influence the diffusion rate of substances across a membrane
1) Steepness of concentration gradient (greater the difference in concentration between tthe 2 sides of the membrane the higher the rate of diffusion). 2) Temperature (the higher the temp the faster the rate of diffusion). 3) Mass of the diffusing substance (the larger the mass of the diffusing particle the slower the diffusion rate). 4) Surface area (The larger the membrane SA available for diffusion the faster the rate of diffusion… air sacs of lungs). 5) Diffusion distance (The greater the distance over which diffusion must occur the longer it takes… pneumonia).
What is simple diffusion?
Passive process. Substances move freely through the lipid bilayer of the plasma membrane of cells without the help of membrane transport proteins. Like nonpolar hydrophobic molecules. O, CO2, N gases, steriods, fatty acids, fat soluble vitamins, small uncharged polar molecules like water and urea
What is facilitated diffusion?
An integral membrane protein (either a membrane channel or carrier) assists a specific substance across a membrane. Usually solutes that are too polar or highly charged
What’s channel-mediated facilitated diffusion?
A solute moves down its concentration gradient across the lipid bilayer through a membrane channel (likely an ion channel)… passage of small inorganic molecules too hydrophilic to penetrate the nonpolar interior of the lipid bilayer
What’s a gated channel?
When a part of the channel acts as a gate or a plug, changing shape in one way to open to pore and another to close
What’s carrier-mediated facilitated diffusion?
A carrier moves a solute down its concentration gradient across the plasma membrane. Passive so no cell energy required. Solute binds to specific carrier on one side of membrane and is released on other side. The rate of carrier mediated fac diffusion is determined by the steepness of the concentration gradient across the membrane.
What is the transport maximum?
The upper limit on the rate that facilitated diffusion occurs. Once all carriers are occupies the transport maximum is reached… this is called saturation when this happens. A
Describe how glucose diffuses
1) Glucose binds to a specific protein called glucose transporter on the outside of the membrane. 2) As the transporter uundergoes changes in shape glucose passes through the membrane. 3) The transporter releases glucose on the other side of the membrane
What is osmosis?
Water molecules moving through a plasma membrane from an area of higher concentration to an area of lower concentration. NET MOVEMENT OF WATER MOLECULES
What are the 2 ways in which water passes through a plasma membrane?
1) By moving between neighbouring phospholipids in the lipid bilayer via simple diffusion or 2) by moving through aquaporins (integral membrane proteins that function as water channels)
What is hydrostatic pressure?
The higher the column of solution in the right arm becomes, the more pressure it exerts on its side of the membrane and water molecules are forced back into the left arm. Equilibrium is reached when just as much water molecules move from right to left due to hydrostatic pressure as move from left to right due to osmosis.
What is osmotic pressure?
The solution with the impermeable solute also exerts a force (osmotic pressure) which is proportional to the concentration of solute particles that can’t cross the membrane. So the higher the solute’s concentration the higher the osmotic pressure. It’s the pressure needed to stop the movement of water from left tube into right
What is Tonicity?
A measre of the solution’s ability to change the volume of cells by altering their water content. An ISOTONIC SOLUTION is any solution in which a cell maintains its normal shape and volume
Define hypotonic solution
A solution that has a LOWER concentration of solutes than the cutosol inside the RBCs… water enters faster than it leaves. RBCs swell and may burst (hemolysis)
Define Hypertonic solution
A higher concentration of solutes in solution than the cytosol inside the RBCs so cells shrink (crenation)
What is Active transport?
Against the concentration gradient. Energy required for carrier proteins to move solutes across the membrane against their concentration gradient.
WHat are the 2 sources of cellular energy to drive ACTIVE TRANSPORT?
1) energy obtained from the hydrolosys of ATMP (Primary active transport). 2) Energy stored in an ionic concentration gradient (secondary active transport)
What is Primary Active Transport?
Energy derived from hydrolysis of ATP changes the shape of a carrier protein which “pumps” a substance across a plasma membrane against its concentration gradient. Like cyanide turns off ATP production so is lethal
What’s the sodium-potassium pump?
Expels NA+ ions from cells and brings K+ ions in. Maintains low concentration of NA+ ions in cytosol by pumping these ions into the EC fluid against the Na+ concentration gradiant. Pumps K+ into cells against K+ gradient. Maintains low concentration of sodium and high concentration of potassium
What is secondary active transport?
The energy stored in Na or H concentration gradient is used to drive other substances across the membrane against their own cncentration gradient. Indirectly uses ATP because Na and H gradient is established by primary active transport. The Na-K pump maintains a steep concentration gradient of Na+ across the plasma membrane so the Na ions have stored / potential energy… like water behind a damn. . STored energy converted to kinetic and transport other substances against their concentration gradient. A carrier protein simultaneously binds to Na and other substance and then changes shape so that both substances cross the membrane at the same time.
What are symporters?
If the transporters move 2 substances in the same direction across the membrane (secondary active transport)
What are antiporters?
Opposite direction across the membrane. Na+ H+ antiporters help regulate blood pH by expelling excess H. Calcium ions low in cytosol because antiporters eject them.
What are the 3 types of endocytosis?
receptor-mediated endocytosis, phagocytosis, and bulk-phase endocytosis
What is endocytosis and what are its steps?
A vesicle forms after a receptor protein in the plasma membrane recognizes and binds to a particle in the EC fluid in the EC fluids. There are 6 steps. 1) BINDING: An LDC particle that contains cholesterol binds to a specific receptor in the plasma membrane to form a receptor-LDL complex. The receptors are integral membrane proteins concentrated in regions of the plasma membrane called clathrin-coated pits. 2) VESICLE FORMATION: The invaginated edges of the membrane around the clathrin-coated pit fuse and a small piece of membrane pinches off. 3) UNCOATING: The clathrin-coated vesicle loses its clathrin coat to become an uncoated vesicle. 4) FUSION WITH ENDOSOME: Uncoated vesicle quickly fuses with a vesicle known as the endosome (within the endosome the LDL particles separate from the receptors). 5) RECYCLING OF RECEPTORS TO PLASMA MEMBRANE: Transport vesicles return the receptors to the plasma membrane. 6) DEGRADATION IN LYSOSOMES: Other transport vesicles, which contain the LDL particles, bud off the endosome and soon fuse with a lysosome. The lysosomes contain digestive enzymes and certain enzymes break down the large protein and lipid molecules of LDL particle into amino acids, fatty acids, and cholesterol. These smaller molecules leave the lysosome.
