A&P - Lecture 2 (Cell, Transport) Flashcards
What are the three main parts of the cell?
Plasma membrane; nucleus; and Cytoplasm
What are the general functions of the plasma membrane?
- barrier separates the inside and outside of the cell 2. Controls the flow of substances into and out of the cell 3. Helps identify the cell to other cells (immune cells) 4. Participates in intracellular signaling 5. Cytoplasm
What are the two compontents of cytoplasm?
Cytosol and Organelles
Cytosol
the fluid portion (aka: intracellular fluid) Contains: water; dissolved solutes; suspended particles
Organelles
little organ: structures suspended in the cytosol; all with characteristic shape and function
Examples of Organelles
Examples: golgi complex; mitochondrion; ribosomes; lysosomes; peroxisomes
What is the function of the nucleus?
- Houses the cell’s DNA; which controls most aspects of cellular structure and function.
Chromosome
a single molecule of DNA associated with several proteins and contains thousands of hereditary units called genes.
What is the plasma membrane?
flexible; yet sturdy barrier that surrounds and contains the cytoplasm of a cell
Fluid-Mosaic Model
model used to describe the plasma membrane
What are the features of the fluid-mosaic model
- Molecular arrangement resembles a continually moving sea of fluid lipids containing a mosaic of many different proteins. 2. Some proteins float freely like icebergs in the lipid sea 3. Membrane lipids allow passage of several lipid-soluble type proteins, but restrict charged or polar substances 4. Some proteins allow movement of polar molecules and ions; in and out of the cell 5. Some proteins act as signal receptors 6. Some proteins can link the plasma membrane to intracellular and extracellular proteins
What are the three types of molecules in the plasma membrane?
Phospholipids (75%) Cholesterol (20%) Glycolipids (5%)
Three molecules - largest to smallest
Phospholipids; Cholesterol; Glycolipids
What molecule give rigidity?
Glycolipids
What makes a bilayer?
Amphipathic nature of the lipids. Lipids have both polar and nonpolar regions; specifically phospholipids.
Integral protein
Goes from one side of the bilayer to the other
Preferal protien
On both sides of the bilayer but does not go all the way through
What are the parts an Amphipathic Phospholipid?
Head and two fatty acid tails
Is the head polar or non-polar?
Polar: head (hydrophilic-loves water)
Is the tail polar or non-polar?
Non-polar: two long fatty acid tails (hydrophobic-hates water)
What are the characteristics of a choelesterol molecule?
- Weakly amphipathic 2. Dispersed among the other lipids 3. Found in both layers of the bilayer 4. There is a tiny ?OH region on the cholesterol. This is the only region that is polar. This forms hydrogen bonds with the polar heads phospholipids and glycolipids. 5. Steroid ring and hydrocarbon tail of cholesterol is stiff and nonpolar and associates with the nonpolar; hydrophobic tails
What are the characteristics of glycolipids?
- Carbohydrate groups form a polar ?head? 2. Fatty acid tails are nonpolar 3. Appear only in the membrane layer that faces the extracellular fluid (one reason the bilayer is considered asymmetric)
Types of Membrane Proteins
Integral Proteins and Peripheral Proteins
Integral Proteins
extend into or through the lipid bilayer and are firmly imbedded in it
Peripheral Proteins
not as firmly embedded in the membrane; attached to the polar heads of membrane lipids or to integral proteins at the inner or outer surface of the membrane
Intergral Proteins Characterisitics
- Transmembrane (most) [span the entire lipid bilayer and protrude into both the cytosol and the extracellular fluid] 2. Other (few) [tightly attached to one side of the bilayer by covalent bonding to the fatty acids] 3. Amphipathic (hydrophilic regions protrude into cytosol/extracellular fluid; hydrophobic regions reside among the fatty acid tails.
Peripheral Proteins Characterisitics
- Glycoproteins (most) [proteins with carbohydrate groups attached to the head] 2. Glycoproteins are oligosaccharides (chains of 2-60 monosaccharides; both straight or branched) 3. Glycocalyx: sugary coat formed by the glycolipids and glycoproteins. Functions 1. important in cell recognition; 2. cell adherence and 3. protection from digestion by enzymes in the extracellular fluid. 4. Pattern of carbohydrates in the glycocalyx will vary from cell type to cell type. This means the pattern acts as a signature that allows cells to recognize each other. Ex: White blood cells can recognize a ?foreign? signature or glycocalyx and mount an immune response to destroy the cell.
Ion Channel (Integral)
Forms a pore through which ions can flow to cross the membrane Found in most plasma membranes; specific channels for several ions
Carrier (Integral) [aka. Transporters]
Transports a specific substance across membrane by undergoing a change in shape
Examples of Carrier function
Amino acids needed to synthesis new proteins enter via ?carrier proteins?
Receptor (Integral)
Recognize specific ligand; then alters the cell?s function In some way
Receptor Example
Antidiuretic hormone binds to receptors in the kidneys and changes the water permeability of certain plasma membranes
Enzyme (Integral and peripheral)
Catalyzes reactions inside or outside the cell (depends on the direction the active site faces) - speeds up
Example of Enzymes
Lactase protruding from epithelial cells lining the small intestine splits the disaccharide lactose (found in milk)
Linker (Integral and Peripheral)
Anchors filaments inside and outside the plasma membrane to provide structural stability and shape for the cell - think of scafuling; sit inside of cell and hold. May also participate in movement of the cell or link two cells together.
Cell Identity Marker (glycoprotein)
Distinguishes your cells from anyone else?s (unless you are an identical twin)
Cell Identity Marker (glycoprotein) Example
MHC (major histocompatibility Complexes)
Permeable
structure permits passage of substances
Impermeable
structure does not permit the passage of substances through it
Selective permeability
variation of the permeability of the plasma membrane to certain substances; where some pass more readily than others.
Lipid bilayer highly permeable to
Nonpolar molecules: Oxygen (O2); Carbon dioxide (CO2); steroids
Lipid bilayer impermeable to
Ions & large uncharged polar molecules: glucose
Permeability characteristics of plasma membrane are due to
Lipid bilayer?s nonpolar; hydrophobic interior; Exceptions: permeability to water and urea (unexpected) because these are ?polar? molecules; and Transmembrane proteins
More hydrophobic and lipid-soluble: greater the membrane is to be permeable to that substance
Hydrophobic interior of plasma membrane allows nonpolar molecule to pass through rapidly; Ions and large; uncharged polar molecules are restricted
Mechanism in which they are thought to pass through
Fatty acid tails of membrane phospholipids and glycolipids randomly move about; Small gaps appear in the hydrophobic interior of the membrane; ? Water and urea are small molecules with no charge; they can move from gap to gap until they have crossed the membrane.
Transmembrane proteins
Act as channels and carriers and make membranes permeability to ions and uncharged molecules it would normally be permeable to; if the environmental conditions are right.
Gradients across the plasma membrane
Concentration Gradient; Electrical Gradient; and Electrochemical gradient
Concentration Gradient
difference in the concentration of a chemical from one place to another
Concentration Gradient Characteristics
Ions and molecules from cytoplasm to extracellular fluid; Flow is from high concentration to low concentration; most cases (?down its concentration gradient?) to reach equilibrium Example: ECF (more concentrated O2 and Na+) than in cytosol; cytosol is more concentrated in K+ and CO2)
Electrical Gradient
Difference in the distribution of positively and negatively charged ions between two sides of the plasma membrane
Electrical Gradient Chracteristics
Difference creates an ?electrical gradient.? Typically the inner surface of the membrane is more negatively charged; outer is more positively Occurs across the plasma membrane The charge difference that exists across the membrane is aka: membrane potential. Movement is ?opposites attract? o Positive moves toward negative o Negative moves toward positive
Electrochemical gradient
influence of concentration gradient and electrical gradient on movement of a particular ion
What are the two classifications of transport across a membrane?
Active Transpot and Passive Transport
Active Transport
cellular energy-usually ATP or vesicles are required to transport substances ?uphill?
Passive Transport
a substance moves down its concentration or electric gradient using its own kinetic energy
Examples of Active Transport
endocytosis; exocytosis
Examples of Passive Transport
Diffusion; osmosis
What are the factors in which influence the diffusion rate of substances across a membrane
Steepness; Temperature; Mass of diffusing substance; Diffusion distance; and Surface Area
Steepness of the concentration gradient
greater the distance in the concentration between the two sides; the faster the diffusion
Temperature
the higher the temperature; the faster the diffusion
Mass of the diffusing substance
the mass of the diffusing particle; the slower the diffusion rate
Diffusion Distance
the greater the distance over which diffusion must occur the longer it takes
Surface Area
the larger the membrane surface area available; the longer it takes
Diffusion
a passive process in which there is a random mixing of particles in a solution due to the particles? kinetic energy. BOTH solutes and solvents undergo diffusion. Solute in high concentration to solute low concentration
Solutes
Dissolved substances
Solvent
Liquid that does the dissolving
Simple Diffusion
a passive process in which substances must move through the lipid bilayer of the plasma membrane without the help of membrane transport proteins
What is the physiological significance of simple diffusion?
movement of oxygen and carbon dioxide between the blood and body cells and between the blood and air within the lungs and breathing.
Facilitated Diffusion
a passive process of transport in which and integral protein assists a specific substance across the membrane) Molecules: Solutes; too polar or highly charged
What are the two types of facilitated diffusion?
Channel Mediated Facilitated Diffusion and Carrier Mediated Facilitated Diffusion
Channel Mediated Facilitated Diffusion
solute moves down its concentration gradient across the lipid bilayer via the selective membrane channel). These can be gated. Examples: ion channels
Carrier Mediated Facilitated Diffusion
movement of a solute down its concentration gradient requiring no cellular energy) solute binds to a specific carrier on one side of the membrane and is release on the other side; following a change in the shape of the protein Examples: glucose; fructose; galactose; some vitamins Example in Physiology: Transport of glucose across a membrane 1. Glucose binds to a specific type of carrier protein on the outside surface of the membrane; AKA GLUT transporter. 2. As the transporter undergoes change in shape; the glucose passes through the membrane. 3. Transporter release glucose on the other side of the membrane
Transport Maximum
maximum rate at which facilitated diffusion can occur. There can be no further increase in concentration. This is determined by the number of carrier proteins in a membrane.
Saturation
this occurs when all of the carriers are occupied and the transport maximum has been reached; where the concentration gradient is no longer able to increase the rate of facilitated diffusion.
Osmosis
A type of passive diffusion in which there is net movement of a solvent through a selectively permeable membrane.
Osmosis: Selectively permeable membrane
membrane is permeable to water (solvent); impermeable to certain solutes
Osmosis Diffusion Properties
Water moves through the semipermeable membrane; from high concentration to low concentration OR Water moves through the semipermeable membrane from an area of lower solute concentration to area of higher solute concentration
Mechanisms by which water moves through the plasma membrane in osmosis:
- by moving between neighboring phospholipid molecules in the lipid bilayer via simple diffusion 2. via aquaporins (integral membrane proteins that function as water channels)
Aquaporins
integral membrane proteins that function as water channels
What are the two types of “pressure” in osmosis that helps to maintain equilibrium?
Hydrostatic pressure and osmotic pressure
Tonicity
a measure of solution?s ability to change the volume of cells by altering their water content
Isotonic solution
Any solution in which a cell (ex: RBC) maintains its normal shape and volume
Hypertonic Solution
place RBC in a solution has higher concentration of solutes; than the cytosol of the RBC; there will be a net movement of water out of the cells. The cells will shrink or ?crenate?
Hypotonic solution
place a RBC in a solution with a lower concentration of solutes than the cytosol of the RBC; there will be a net movement of water into the cells. The cell will swell and eventually burst; also called hemolysis. Pure water is hypotonic and would cause rapid hemolysis
Hypertonic solutions can be useful is certain medical situations
Example: Cerebral edema (excess interstitial fluid in the brain) Infusion of a hypertonic solution (mannitol) will relieve the fluid overload by causing osmosis of fluid into the blood. The kidneys are then able to excrete the excess water from the blood into the urine
Hypotonic solutions
Dehydration; water in the hypotonic solution will move from the blood into the cells and rehydrate
Active Transport
This is the movement of molecules (polar or charged solutes) ?uphill? or against their concentration gradients. This is considered active transport because energy is required for carrier proteins to move solutes across the membrane.
Types of Active Transport
Primary active transport and secondary active tranport
Primary active transport
energy derived from hydrolysis of ATP leads to a conformation change in the shape of the protein; ?pumping? a substance across the membrane Most prevalent: Na+/K+ ATPase
Operation of the Na+/K+ pump
- 3 Na+ in the cytosol bind to the pump inside 2. Binding of Na+ triggers the hydrolysis of ATP into ADP; a reaction that also attaches a phosphate group to the pump protein. This chemical reaction changes the shape of the protein; expelling the 3 Na+ into the ECF. Now the shape of the pump protein favors the binding of 2 K+ ions. 3. K+ binding triggers release of the phosphate group from the pump protein; causes the shape of the pump protein to change. 4. Pump reverts back to original shape and in the process releases K+ into the cytosol. The pump is ready again to bind 3 Na+ and the cycle will repeat.
Secondary Active Transport
energy stored in a Na+ or H+ concentration gradient is used to drive other substances across the membrane against their concentration gradients
Types of Secondary Active transporters transporting more than two solutes
Symporters and Anitporters
Symporters
transport of two substances in the SAME direction (Na+-glucose & Na+ Amino acid symporters
Antiporters
Transport of two substances in the OPPOSITE direction (Na+-Ca+)
Sources of cellular energy used in active transport
- Energy obtained from hydrolysis of ATP (primary active transport) 2. Energy stored in ionic concentration gradient (secondary active transport) Note: these will also have a saturation and a transport maximum.
Vesicles
?little blister or little bladder.? A small spherical sac that can transport a variety of substances from one structure to another.
Transport in vesicles types?
endocytosis; exocytosis
Endocytosis
moved into a cell; in a vesicle formed from the plasma membrane
Exocytosis
materials move out of a cell by the fusion with the plasma membrane of vesicles formed inside the cell Both of these processes require energy supplied by ATP; therefore making this ?active transport.?
Three types of endocytosis:
Receptor-mediated endocytosis; phagocytosis; bulk-phase endocytosis (Pinocytosis)
Describe the characteristics and the role of cholesterol in the plasma membrane.
Weakly amphipathic
Dispersed among the other lipids
Found in both layers of the bilayer
There is a tiny –OH region on the cholesterol. This is the only region that is polar. This forms hydrogen bonds with the polar heads phospholipids and glycolipids.
