IB Unit 5: Cell Membrane
Describe the function of enzyme proteins.
Promote chemical reactions that synthesize or break apart biological molecules. (Integral or peripheral) Eg. ATP synthase produces ATP from ADP phosphate on membrane of mitochondria and chloroplasts.
Explain what happens to cell when placed in solutions of the same osmolarity, higher osmolarity and lower osmolarity.
Higher solution: Water would move out of the cells, thus the cells are HYPOTONIC and the solution is HYPERTONIC Lower solution: Water would move iNTO the cells, thus the cells are hypertonic to the hypotonic solutions. Same osmolarity: Water would be moving out and into the cell.
Describe simple diffusion
Simple diffusion is when small particles move from higher to lower concentration. It's passive and doesn't require energy -Often just passes through the cell membrane.
State examples of molecules for simple diffusion, osmosis, facilitated and active transport
Simple: CO2, O2 Osmosis: H2O Facilitated: Cl-, Na+, carbohydrates etc. Active: anything that's against the gradient, glucose, amino acids etc.
Explain what models are and their purposes in science
• Models are conceptual representations used to explain and predict a phenomena. -> Physical Models -> Computer Models -> Mathematic models.
Draw a simplified diagram of the structure of the phospholipid, including the phosphate-glycerol head and 2 fatty acid tails.
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Describe why the understanding of cell membrane and structure has changed over time?
- Better tools and equipment; improving our observations and understanding of the cell membrane. - Better techniques; Freeze-fractured, cell fusion, fluorescent antibody tagging and protein extractions. (Thus allowing scientists to gain a better understanding of the structure of cell membrane proteins.
Describe the observation and conclusion drawn by Davson and Danielli in discovering the structure of the cell membranes.
-1935 Davson and Danielli proposed the "protein-lipid sandwich." -Under the microscope, they saw 2 dark parallel lines with a lighter region in between. -Proteins would appear black and lipids would appear light. -Thus they came up with the conclusion that the phospholipid bilayer was between 2 layers of proteins. *They discovered existence of proteins on the bilayers *
Explain the need for repeated measurements (multiple trials) in experimental design.
-Allows us to see if the results are consistent for accuracy. -Consistent measurements allows us to reinforce a stronger conclusion.
Explain the need to controlled variables in an experimental design.
-By the controlled variables we can be more confident that the any affects on the responding variable is due to the manipulated variable, and not other factors.
Describe conclusions about cell membrane strucutre drawn from freeze-etched electron micrograph images of the cell membrane.
-Cells are first frozen, then fractured in the center of the cell membrane. -Globular structure throughout the membranes were interpreted as transmembrane proteins. -Transmembrane proteins were not accounted for by Davson and Danielli's model of the cell membrane. *Meaning they saw little bumps inside the cell membrane*
Describe the function of cholesterol in molecular diagrams.
-Cholesterol acts as a regulator for the cell membrane, keeping them from falling apart or packing too close together (viscosity of the cell membrane) -lower temperatures: prevents the phospholipids from packing too close which could lead to stiffening. -High temperatures: prevents the phospholipids from falling by raising the melting point and stabilises it.
Describe the relationship between the cell size and the SA:V ratio
-If the cell size increases, the SA:V ratio decreases. Larger cells = smaller surface area in relation to volume. •Smaller ratio = harder for cells to meet metabolic demands.
Describe conclusions about cell membrane structure drawn from the improvements in techniques and determining the structure of the membrane proteins.
-Improved tools allows scientists to extract membrane protein (determine chemical properties). -Membrane proteins are varied in shape and sizes (some proteins hydrophobic, thus didn't match Davson and Danielli; relative uniformed shape and hydrophilic.
Determine osmolarity of a sample given changes in mass when placed in solutions of various tonicites
-Osmolarity of the sample is the position where the percent change in mass is at 0%. • Can be determined by graphing!
Compare the Davson-Danielli model of membrane structure with the Singer-Nicolson model
-Proposed a model which incoporated evidence about membrane. -Didn't comply with Davson and Danielli. -Rather than the proteins on the surface of the phospholipid, the proteins are embedded within and throught the cell membrane --> "Fluid-Mosaic Model."
Outline 2 examples of materials released from a cell via exocytosis
-Secretion of neurotransmitters at synaptic terminus. -Secretion of digestive juices from exocrine cells.
Explain the release of materials from cells via exocytosis
-Secretory vesicles. -Wastes moves towards the plasma membrane. Fuses with the membrane, releasing contents to extracellular space.
Explain why cells are often limited in size by the SA:V ratio.
-Surface area decreases in relation to the volume; cell won't have enough surface area to move nutrients or wastes out. -Larger cells would require more nutrients and create more waste in the cytoplasm. *If it un unfavourable to the cell (too big) it would just divide! *
Define the measurement uncertainly of a measuring tool.
-Take the smallest marking of the tool (mm, ml etc) -Take that and divide it by 2. -Round the divided number to 1 significant figure.
Describe the observations and conclusions drawn by Gorter and Grendel in discovering the structure of the cell membrane
-They took a look at the surface area of the cell membrane. -Took a red blood cell and extract its cell membrane. -Noticed how when the membrane was intact on a cell, it's surface area was only half of the surface area when it was extracted. -Thus concluding that the cell membrane must be a BILAYER if the surface area doubles. -Heads facing out, tails facing inwards.
Outline 2 examples of endocytosis
1) White blood cells eating bacteria to kill it. 2) Amoeba eating bacteria as a food source.
Outline the factors that regulate the rate of diffusion
1) concentration of diffusing molecules. -> Increase in concentration = increase in diffusion rate. 2) temperature. -> increase in temperature = increase in diffucion rate. 3) Pressure. -> increase in pressure = increase in diffusion rate.
List three ways or adaptions of cell that maximizes the SA:V ratio.
1) extensions of the cell membrane (microvilli in small intestine cells). 2)Flattened/thin shaped to increase surface area. 3) Long cellular extensions (increases in SA without too much increase of volume).
Explain two examples of simple diffusion of molecules into and out of the cell
1. Gas exchange by diffusion through the capillaries and alveoli in your lungs. It's thin enough to let gas molecuels pass/diffuse through. CO2 to alveoli and O2 into capillary. 2. Gas exchange by diffusion through the eye cornea. The cornea allows small gas particles to pass. O2 into cornea, CO2 out of cornea.
Compare active transport to passive transpot
Active: requires energy, goes against the gradient. (L->H) Passive: does not require energy, goes with concentration gradient (H-L)
Explain one example of active transport of molecules into and out of the cell through protein pump.
Actively transports other molecules using ATP. Eg. protein pumps. Sodium-potassium pumps: transports (3 sodium out, 2 potassium in) actively
Define amphipathic and outline the amphipatic properties of phospholipids.
Amphipathic is to show 2 properties, both ways. • Phospholipids has two properties: hydrophobic tails and hydrophilic heads.
Describe the function of adhesion proteins.
Anchor the cell membrane to inner cytoplasm to outside proteins and to other cells (integral or peripheral). Eg. Desmosome proteins found in muscles to bind one muscle to another.
Explain the benefits and limitations of using cubes to model the surface area of the cell.
BENEFITS: easily measured, manipulated and visualised. LIMITATIONS: Cells aren't cubes, they harder to manipulate or to visualise or to measure due to microscopic sizes. •Relationship of SA:V is same for cubes and cells.
Describe one example of facilitated diffusion through a channel protein
CTFR channels moves chloride ions from higher concentration to lower concentration. • Higher concentration from inside to outside of the cell.
Explain the vesicle formation via endocytosis.
Cells actively transport molecules into the cell. -Engulfs molecules into a vesicle form through the cell membrane capture and fusion. it includes the cell membrane
Contrast the two types of transport proteins: pumps and channels
Channels: they are passive, goes with the concentration gradient and is shaped like pores/tunnels. Pumps: they are active, required ATP, goes against the concentration gradient. *Note that the ATP changes the shape of the pump allowing things to pass.*
Define osmosis
Diffusion of water through the cell membrane. PASSIVE.
Explain why the cell membrane is fluid.
Fluidity allows cell membranes makes it possible for endo/exocytosis. 1) weak to no bond in the phospholipid tails. 2) kinds in the tails prevent close packageing. 3) cholesterol keeps phospholipids from packing too close or drifting too far.
Describe the fluid properties of the cell membrane and vesicles.
Fluidity: viscosity flow of phospholipids in cell membrane and organelles of the endomembrane system (including vesicles). Fluidity is impacted by: temperature, fatty acid length, fatty acid fluidity, presence of chloresterol
Describe the function of the receptor protein and an example.
Gets a message and passes it on to inside of the cell. It binds to specific molecules found outside of the cell and triggers changes in cell action (integral or peripheral) Eg. insulin receptor on body cells receive insulin and respond by opening to the cell to glucose from the blood.
Define hydrophobic and hydrophilic.
Hydrophobic: This means that the substance doesn't like being near water (tails). Hydrophilic: This means that the substance likes being near water (heads).
Contrast the structure of the integral and peripheral proteins.
Integral: Large sections inside of the cell membrane. (Inside the hydrophobic tails). Some even cross through the whole membrane. Peripheral: Smaller proteins which has small sections in the cell membrane or sits on top of the cell membrane.
Explain integral and peripheral proteins.
Integral: it goes through the cell membrane Peripheral: partially inside or is sitting ontop of the cell membrane.
Define quantitive and qualitive
Quantitive: data in the form of numbers obtained by measurements counts. Qualitative: data which is in the form of words, descriptive/subjective.
List 4 functions of the membrane bound proteins.
Receptor proteins: communicate signals between the cell's internal and external environment. Transport proteins: Move ions and molecules across the cell membrane. Enzymes catalyze reactions: ATP synthase (requires energy). Adhesion molecules: Anchor the cell to other cells -> Cadherin. Recognition proteins: Identify the cell types -> MHC proteins.
Outline the use of normal saline in medical purposes.
Saline is water and salt at 0.9 osmolarity that would be isotonic to human blood. Used as: eyewash, flushing wounds and via IV to rehydrate the patient. Scenarios: A) during transplants, organs would be stored and bath in normal saline. B) Saline solution is isotonic to body cells, cell will not shrink nor expand when exposed to saline solution.
State the primary function of the cell membrane.
Semi-permeable which controls the movement of substances in and out of the cell.
Describe the function of channel proteins
Serves as pores for large of hydrophilic molecules to be passively transported into or out of cell membrane. (All are integral) Eg.Aquaporins are channel proteins for water molecules.
Describe the function of pump proteins. Include and example
Serves as pores for large or hydrophilic molecules to be actively transported into our out of the cell. (all are integral). Eg. Sodium Potassium established the resting membrane potential at the neuron 70nm. * Carriers goes with the concentration gradient*
Explain why phospholipids form bilayers in water, with reference to hydrophilic phosphate heads and two hydrophobic hydrocarbon tails.
Since phospholipids are amphipathic, the hydrophilic heads would face the water, the hydrophobic tails away. *They try to become the most free-energy form possibly* • In a higher concentration, they phospholipids would be forced to face their tails together, leave the hydrophilic heads pointing outside to the water.
Calculate the surface area, volume and SA:V ratio of a cube.
Surface Area: length^2 Volume: length^3 SA:V : l^2/l^3 •Smaller the ratio, bigger the cell.
Describe facilitated diffusion.
The movement of molecules from higher to lower concentration through a channel proteins. PASSIVE - NO ENERGY!
Describe the function of recognition proteins *glycoproteins*
They are identification tags on the surface of the cell. Often are *glycoproteins* with a carbohydrate attached. Eg. Major histocompatibility complex [MHC] that interacts with immune system to identify which cells belong to the body.
Explain why phospholipids are amphipathic. identify which parts are hydrophobic and which are hydrophillic.
They're amphipathic because phospholipids has two properties which is hydrophobic tails and hydrophilic tails.
Describe the structural placement of cholesterol within the cell
They're small enough to fit between the phospholipids. ONLY IS ANIMAL CELLS. The hydroxyl group by the heads and the hydrophobic rings in the fatty acid tails.
Describe the conclusion about cell membrane stucture drawn from cell fusion experiments.
Two cells had their proteins dyed in two colours. -It's cell membrane then gets fused together and then waited out. Proteins aren't mixed. -After around 40 minutes we see the proteins distributed colourfully. Proteins were mixed. Conclusion: molecules can move from one place to another in the cell membrane.
What is unsaturated and saturated and what parts of it applies to the phospholipid.
Unsaturated tail has less hydrogen and the carbons are not full. The double bonds creates a bend and this increases it's fluidity. Saturated tails have as many hydrogen as carbon can hold. It is a straight chain.
Outline the activities occurring in the volume and at the surface of the cell. (Draw it to demonstrate!)
Volume: is the cytoplasm which a lot of metabolic reactions occur. It produces waste which would get secreted. Surface: the plasma membrane, which nutrients and gas moved into the cell and metabolic wastes leave the cell.
Predict the direction of water movement based upon the differences in solute concentration.
Water moves from hypotonic to hypertonic. Solution has MORE solute (hypertonic) : water moves out of the cell. Solution has LESS solute (hypotonic) : water moves in to the cell. Solution is isotonic: water moves in and out of the cell.
