Lecture 3 Phys 2130 PDF

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Hey kids 2 things 1. I don’t put images on the word doc so you might wanna go through the lectures to get the diagrams and such 2. I didn’t include info I already knew, so you also might want to go through the notes and add in any info I might’ve skimmed/ skipped overBasic cell organelles  The Golg...

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Hey kids 2 things 1. I don’t put images on the word doc so you might wanna go through the lectures to get the diagrams and such 2. I didn’t include info I already knew, so you also might want to go through the notes and add in any info I might’ve skimmed/ skipped over Basic cell organelles  The Golgi apparatus o Responsible got packaging proteins from the rough endoplasmic reticulum to the membrane bound vesicles o Two vesicles are produced: secretary vesicles that transport proteins to the cell membrane for release into the extracellular environment, and storage vesicles like the lysosome whose contents are stored within the cell  Secretory vesicle o Produced by the Golgi apparatus and are used to transport various types of proteins out of the cell for use in other parts of the body o Secretion: process that the cells release proteins through the membrane into the extracellular environment  Free ribosome o Dense granules of rna and protein o Manufacture proteins from amino acids under the control of the cells dna o Fixed ribosomes are attached to the rt o Free ribosomes float in the cytoplasm and form polyribosome groups of 10-20 ribosomes  Lysosome o Storage vesicle produced by Golgi o Act as the digestive system of the cell o Contain several kinds of enzymes that are used by the cell to destroy damaged organelles, kill bacteria, and break down other kinds of biomolecules  Mitochondria o Membranous organelle where the atp is produced o Can replicate when increased energy is needed ie in muscle cells  Endoplasmic reticulum o Continuation of the cells nuclear membrane and the site for the synthesis, storage, and transport of proteins and lipid molecules o Rough ER: covered with rows of ribosomes, site of protein synthesis, proteins manufactured then are packaged into vesicles that transport them to the Golgi body o Smooth ER: lacks ribosomes, responsible for the synthesis or lipids and fatty acids  Cell membrane o Regulate the passage of substances into and out of the cell o Detects chemical signals from other cells and in forming physical links with adjacent  Centriole o Cylindrical bundles of microtubules that are responsible for directing the movement of dna strands during cell division  Nucleolus o Dense body within the cell nucleus which contains the specific dna that produce the rna found in ribosomes The cell membrane  Separates the intracellular environment from the extracellular environment  Proteins, nucleotides, and large molecules needed for structure and function of the cell can’t penetrate the pm

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Selectively permeable- two way traffic for nutrients and waste needed to sustain metabolism while prevents the passage of other substances between intra and extracellular components Made up of proteins that form channels and pores, carbohydrate molecules for cell recognition, and cholesterol for stability Phospholipid molecules are most abundant in the pm Phospholipid molecule o Hydrophilic head is composed of a phosphate head  Faces into the water base solutions inside and outside of the cell o Hydrophobic tail is oriented away from the aqueous surrounding Cholesterol molecules: inserted into the non-polar lipid layer of the membrane o Helps with membrane impermeability to some water soluble molecules o Helps keep the membrane flexible over a wider temperature range Associated enzyme proteins can be attached to either the intra or extracellular surface of the membrane o Enzymes are a form of associated protein which act as a catalyst for certain reactions immediately inside or outside the membrane Carbohydrate molecules are found associated with extracellular membrane proteins or lipids o Form a protective later called the glycocalyx which plays a role in immune response of the cell and in recognition of other cells in the body Membrane spanning protein is a protein embedded in the phospholipid bilayer such that the protein spans the entire width of the PM o Act as gates or channels that control the movement of certain substances into and out of the cell Associated structural proteins are generally attached to the inside surface of the cell membrane o Can support and strengthen the membrane while others may anchor some cells organs to the intracellular side of the membrane

Phospholipids  Phosphate head o hydrophilic  Fatty acid/ lipid tail o Hydrophobic  These molecules form a phospholipid bilayer where the head groups face outwards and tail groups face inwards  Hydrophobic tails are the major barrier to water and water soluble substances like ions, glucose, urea  Fat soluble substances like oxygen, co2, and steroid hormones can penetrate this portion of the membrane easily by dissolving through the lipid region of the membrane Membrane proteins  Receptors for the attachment of chemical hormones and neurotransmitters  Enzymes that help with chemical reactions or breakdown molecules  Ion channels or pores that allow water soluble substances like ions into the cell  Membrane transport carriers that transport molecules across the membrane  Cell identity markers, like antigens or glycoproteins o Antigens are foreign particles that stimulate the immune system  Proteins function to transport substances across the membrane o Endocytosis/ exocytosis/ pinocytosis for small molecules o Diffusion throughout the lipid bilayer in the case of fat soluble molecules o Diffusion through protein channels in the case of water, and water soluble molecules o Facilitated diffusion o Active transport Diffusion

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Movement of molecules from an area of high concentration to low concentration due to the molecules random thermal motion Molecules move down a chemical concentration gradient from a high concentration to a low concentration until a uniform concentration is achieved Charged molecules tend to move towards areas of opposite charge, positive moves to negative down their electrical gradient o Charged ions can move down both their chemical concentration gradient and electrical gradient to achieve an electrochemical equilibrium (when the electrical force is equal to and in opposite direction to the chemical force) Substances that are lipid soluble can pass right through the cell membrane, while those that are water soluble will have difficulty Lipid soluble substances include oxygen, co2, fatty acids, and some steroid hormones o These molecules can diffuse right through the membranes lipid bilayer and are not stopped by the hydrophobic fatty acid chains Substances that are water soluble cannot diffuse directly through the fatty acid region of the cell membrane but may still cross the membrane o Water, sodium ions, potassium ions, etc. appear to cross cell membrane through channel proteins Each pore or channel is specific and will generally only allow one type of ion through

Diffusion Factors: there are limits to diffusion through protein channels  The size of the protein channels o Molecules larger than 0.8nm cannot pass  The charge of the molecule will affect the rate of movement through channels bc proteins making up channels also have charges on them o +ve ion won’t go through a +ve channel  The greater the electrochemical gradient of a molecule, the greater its rate of movement through the channels o Substances move down both their electrical and chemical gradients  The number of channels in the membrane o Large concentration gradient for an ion, an ion won’t move across unless there are enough channels o The more channels that exist, the more ions that will diffuse Facilitated diffusion  Other water soluble substances like sugars cannot diffuse through the lipid bilayer and are too large to pass through protein channels still cross the membranes at a relatively fast rate  These molecules attach to specific protein carriers on the membrane and cause a conformational change in the protein, resulting in an opening of the protein channel  Doesn’t require energy and its powered by the concentration gradient of the molecule  Rate of transport is limited by the number of available proteins o If the carriers are all occupied, the system is saturated and rate plateaus  Facilitated diffusion shows chemical specificity and may be competitively inhibited by molecules of similar shape Active transport  Active transport requires protein carriers that span the membrane  This mechanism can be saturated, shows chemical specificity, and shows competitive inhibition  Active transport requires ATP or energy bc active transport moves molecules up their concentration gradients from low to high  Sodium potassium pump is an example of active transport

Osmosis  Diffusing water requires special pores since it cannot diffuse through the hydrophobic portion of the lipid membrane  Water in = water out so that cell volume remains constant  Osmosis is the net movement of water down a concentration gradient, producing a concentration difference  Solute is substance that’s being dissolved in a liquid (solvent) to produce a solution  A solution with a high concentration of solute will have a lower water concentration, if a cell with a high intracellular concentration of glucose was placed in water, the water would move down the concentration gradient from high to low into the cell, causing the cell to swell  Osmosis is affected by o The permeability of the membrane to the solutes in the intracellular and interstitial fluids o The concentration gradients of solutes in the intracellular and interstitial fluids o The pressure gradient across the cell membrane Units of osmosis  A solution with a high concentration will have a low water concentration, therefore, to know which way osmosis takes place, we have to be able to describe the concentration of a solution in terms of the number of solute particles in a solvent  A particle that causes osmosis is called an osmotically active particle, and the unit to describe the number of osmotically active particles in a solution is called an osmole  Two units describing the concentration of a solution o Osmolality is equal to the number of osmoles per kg of water o Osmolarity is equal to the number of osmoles per liter of solution Tonicity  Tonicity is a term used to describe the ability of a solution to cause osmosis across a biological cell membrane  The fluid in a typical human cell has a concentration of 300 mOsm/kg of water  Isotonic: same concentration as body fluids  Hypotonic solution: lower concentration compared to cellular fluids and would cause osmosis into the cell and result in swelling  Hypertonic solution: higher concentration compared to the cell and would cause osmosis out of the cell, causing the cell to shrink Concentration gradient and membrane permeabilities  Na+ ca++ and Cl- have a higher concentration outside the cell compared to the inside o Their concentration gradient will try to move them into the cell  K+ has a higher concentration inside the cell compared to the outside o Its concentration gradient will try to move it outside the cell  This does not mean that they will diffuse in those direction- the cell membrane will determine how many ions can move  The membrane therefore is permeable to a particular ion but the permeability will vary on the ion and cell type  In general most cells aren’t very permeable to na, cl, and ca o They have large concentration gradients but few channels to actually move them  The membrane is more permeable to potassium ions so they tend to leak down their concentration gradients Key Concepts  The relative ion concentrations and the permeability of the membrane to each ion

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This is a generalization- there are exceptions as permeability of the cell can change Channels respond to a variety of stimuli and each channel is specific to a certain ion Understand the diagram showing concentration gradients Know relative permeability of the membrane to the ions There are many different types of channels in the membrane that we haven’t yet examined When channels open, ions can move

Membrane potentials  The cell membrane is semipermeable and that molecules incl water, tend to move down the concentration gradient or electrical gradient  There are various membrane potentials o Equilibrium potentials o Resting membrane potentials o Action potentials o Excitatory postsynaptic potentials and inhibitory postsynaptic potentials o Generator potentials  An electric potential is a charge difference between two points  Almost all cells in the body have a charge difference between the inside of the cell and the outside, which is separated by a membrane The resting membrane potential  The fluids inside and outside of cells are electrolytic (contain ions)  A minute excess of negative ions (anions) accumulate immediately inside the cell membrane along its inner surface, and an equal number of positive ions (cations) accumulate immediately outside the membrane o The effect of this is the establishment of an electrical potential difference across the membrane with the inside negative with respect to the outside  The potential difference across the pm is present even in resting cells, its referred to as the resting membrane potential o All cells in the body have a resting membrane potential  The resting membrane potential of cells is -70 mV in most cells o Its negative bc the negative outside is compared to the positive outside  Cell membranes are permeable to varying degrees to both cations and anions  Each diffusible ion will have an influence on the resting membrane potential depending on its degree of permeability and its concentration gradient Equilibrium potentials  Any one ion will have two forces acting on it o The chemical concentration gradient which drives the ion from an area of high to low concentration o The electrical gradient which drives the ion toward and area with the opposite charge  When these two forces are equal in magnitude but in opposite direction, there I no net movement and the ion is said to be in electrochemical equilibrium  The equilibrium potential for an ion is the electrical potential that must be applied to the inside of the cell in order to stop the movement of that ion down its concentration gradient  The equilibrium potential of an ion varies depending on the animal species and the type of cell o Even nerve cells in the same animal may have different equilibrium potentials for the same ions  E(K+) = -90mV  E(Na+)= +60mV  E(Cl-) = -70mV

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These are the voltages that would have to be applied to the inside of the cell in order to keep each ion from moving down its concentration gradient The equilibrium potential for a particular ion is the electrical charge on the inside of the cell that’s necessary to stop the ion from moving down its concentration gradient o Each ion has a particular equilibrium potential because each has a different concentration gradient

Sodium Potassium Pump  The sodium potassium pump is integral membrane protein  Pumps 3 Na+ out and 2K+ into the cell  Since it contributes to the resting membrane potential by making the inside of the cell more negative (by removing more positive Na than replacing with K), it’s called an electrogenic pump  It pumps both of these ions against their concentration gradients, so it requires ATP for energy and is therefore a form of active transport  Since sodium leaks into the cell, and potassium leaks out of the cell, the sodium potassium pump acts to maintain the concentration gradients for these two ions  Since three sodium’s are removed for two potassium’s pumped in, the pump causes the cell to become electronegative on the inside, which contributes a small amount to the resting membrane potential  Without the nak pump, most cells would swell until they burst  Cells contain large numbers of proteins and other organic compounds to which the cell membrane is impermeable o Many of these carry negative charges and hence attract large numbers of positive ions around them o This increases the number of particles inside the cell which would cause substantial osmosis of water into the cell  Since the nak pump pumps out 3 na for 2 k it pumps in, it causes a reduction in particles inside the cell o This causes osmosis of water out of the cell and offsets the osmosis into the cell, and cell volume is kept constant Significance of the resting membrane potential  excitable cells use the membrane potential to do work and then spontaneously regenerate electrical potentials at their membranes  There are two excitable cell types in the body- nerve and muscles...