In this video, we're going to begin our introduction to biological membranes. Now, it's important to recall from way back in our previous lesson videos, we said that in aqueous solutions, amphipathic lipids can spontaneously aggregate or clump together via the hydrophobic effect. And so if you don't remember anything about the hydrophobic effect and the ability for amphipathic lipids to spontaneously aggregate via the hydrophobic effect, then make sure to go back and check out those older lesson videos before you continue here. Now, the ability for amphipathic lipids to spontaneously aggregate via the hydrophobic effect will actually lead to the formation of 3 different types of membranes. The first are the micelles, the second are the liposomes or the vesicles, Here in the middle, we're showing you the liposome or the vesicle. Here in the middle, we're showing you the liposome or the vesicle. And then over here on the far right, we're showing you the lipid bilayer. And so starting over here on the far left with the micelle, what you'll notice is that it is a monolayer of lipids, and this is what allows it to have a hydrophobic core at its center. And so if you were to zoom in on one of these lipid molecules in the micelle, you would see that it's likely going to be a free fatty acid. And that's because free fatty acids have this triangular-shaped geometry, if you will, that makes them so suitable for the formation of micelles upon their aggregation via the hydrophobic effect. Now liposomes or vesicles, as you can see over here, they actually have a bilayer of lipids. So you can see that there's a layer of lipids here on the outside, but also here on the inside, there's a second layer. And so this is what allows liposomes or vesicles to have an aqueous core at its center instead of having a hydrophobic core at its center like micelles do. Now, liposomes or vesicles, they're generally very small and only contain a handful of dissolved molecules in the aqueous core. And if we were to zoom in on one of these lipid molecules in the liposome, you would see that it's likely going to be a free phospholipid like this one, which upon aggregation with other ones allow them to form a vesicle or bilayer because of their proper square shaped geometry that's suitable for the formation of vesicles and bilayers. And then last but not least, over here on the far right, we have the lipid bilayer, which you'll notice also has a bilayer of lipids here. And, the real difference between the lipid bilayer and the liposome or the vesicle is again that the liposome or vesicle are generally much smaller with only a handful of molecules in the aqueous core, whereas lipid bilayers are going to be much, much, much larger and they can encapsulate an entire cell and create, entire organelles. Now, notice that this lipid bilayer here has 2 different sheets or leaflets. There's this sheet or this leaflet right here, that we can call the extracellular leaflet or sheet and that's because it's on the outside of the cell and notice that this other leaflet over here, we can call the intracellular leaflet or sheet. Again, because it's on the inside here of our cell. And so, it's important to be able to distinguish between these two different leaflets. Now, one thing that I want to let you guys know here is that both glycerophospholipids and sphingophospholipids have optimal shapes or geometries that allow them to form lipid bilayers and liposomes or vesicles. And so, as we already mentioned, the micelle here is generally formed from free fatty acids which have this triangular shaped geometry. And free phospholipids, they have a square shaped geometry. And so down below here, what we're showing you is that the free fatty acids with their triangular shaped geometry, they are not suitable for forming vesicles or bilayers because they are not able to close these gaps that form, here and here and that makes them unstable as a vesicle or a lipid bilayer. And the same goes for free triacylglycerols. They tend to have a trapezoid-shaped geometry like what you see here and again, that geometry or shape will create these gaps that make it make them very unstable as they try to form vesicles or bilayers. And so really, the only, lipids that are capable of forming these, liposomes or lipid bilayers are the free phospholipids, either the glycerol phospholipids or the Sphingophospholipids. And so this here really concludes our introduction to biological membranes and as we move forward through our course, we're going to learn more and more about these biological membranes. So, I'll see you guys in our next video.
- 1. Introduction to Biochemistry4h 34m
- What is Biochemistry?5m
- Characteristics of Life12m
- Abiogenesis13m
- Nucleic Acids16m
- Proteins12m
- Carbohydrates8m
- Lipids10m
- Taxonomy10m
- Cell Organelles12m
- Endosymbiotic Theory11m
- Central Dogma22m
- Functional Groups15m
- Chemical Bonds13m
- Organic Chemistry31m
- Entropy17m
- Second Law of Thermodynamics11m
- Equilibrium Constant10m
- Gibbs Free Energy37m
- 2. Water3h 23m
- 3. Amino Acids8h 10m
- Amino Acid Groups8m
- Amino Acid Three Letter Code13m
- Amino Acid One Letter Code37m
- Amino Acid Configuration20m
- Essential Amino Acids14m
- Nonpolar Amino Acids21m
- Aromatic Amino Acids14m
- Polar Amino Acids16m
- Charged Amino Acids40m
- How to Memorize Amino Acids1h 7m
- Zwitterion33m
- Non-Ionizable Vs. Ionizable R-Groups11m
- Isoelectric Point10m
- Isoelectric Point of Amino Acids with Ionizable R-Groups51m
- Titrations of Amino Acids with Non-Ionizable R-Groups44m
- Titrations of Amino Acids with Ionizable R-Groups38m
- Amino Acids and Henderson-Hasselbalch44m
- 4. Protein Structure10h 4m
- Peptide Bond18m
- Primary Structure of Protein31m
- Altering Primary Protein Structure15m
- Drawing a Peptide44m
- Determining Net Charge of a Peptide42m
- Isoelectric Point of a Peptide37m
- Approximating Protein Mass7m
- Peptide Group22m
- Ramachandran Plot26m
- Atypical Ramachandran Plots12m
- Alpha Helix15m
- Alpha Helix Pitch and Rise20m
- Alpha Helix Hydrogen Bonding24m
- Alpha Helix Disruption23m
- Beta Strand12m
- Beta Sheet12m
- Antiparallel and Parallel Beta Sheets39m
- Beta Turns26m
- Tertiary Structure of Protein16m
- Protein Motifs and Domains23m
- Denaturation14m
- Anfinsen Experiment20m
- Protein Folding34m
- Chaperone Proteins19m
- Prions4m
- Quaternary Structure15m
- Simple Vs. Conjugated Proteins10m
- Fibrous and Globular Proteins11m
- 5. Protein Techniques14h 5m
- Protein Purification7m
- Protein Extraction5m
- Differential Centrifugation15m
- Salting Out18m
- Dialysis9m
- Column Chromatography11m
- Ion-Exchange Chromatography35m
- Anion-Exchange Chromatography38m
- Size Exclusion Chromatography28m
- Affinity Chromatography16m
- Specific Activity16m
- HPLC29m
- Spectrophotometry51m
- Native Gel Electrophoresis23m
- SDS-PAGE34m
- SDS-PAGE Strategies16m
- Isoelectric Focusing17m
- 2D-Electrophoresis23m
- Diagonal Electrophoresis29m
- Mass Spectrometry12m
- Mass Spectrum47m
- Tandem Mass Spectrometry16m
- Peptide Mass Fingerprinting16m
- Overview of Direct Protein Sequencing30m
- Amino Acid Hydrolysis10m
- FDNB26m
- Chemical Cleavage of Bonds29m
- Peptidases1h 6m
- Edman Degradation30m
- Edman Degradation Sequenator and Sequencing Data Analysis4m
- Edman Degradation Reaction Efficiency20m
- Ordering Cleaved Fragments21m
- Strategy for Ordering Cleaved Fragments58m
- Indirect Protein Sequencing Via Geneomic Analyses24m
- 6. Enzymes and Enzyme Kinetics13h 38m
- Enzymes24m
- Enzyme-Substrate Complex17m
- Lock and Key Vs. Induced Fit Models23m
- Optimal Enzyme Conditions9m
- Activation Energy24m
- Types of Enzymes41m
- Cofactor15m
- Catalysis19m
- Electrostatic and Metal Ion Catalysis11m
- Covalent Catalysis18m
- Reaction Rate10m
- Enzyme Kinetics24m
- Rate Constants and Rate Law35m
- Reaction Orders52m
- Rate Constant Units11m
- Initial Velocity31m
- Vmax Enzyme27m
- Km Enzyme42m
- Steady-State Conditions25m
- Michaelis-Menten Assumptions18m
- Michaelis-Menten Equation52m
- Lineweaver-Burk Plot43m
- Michaelis-Menten vs. Lineweaver-Burk Plots20m
- Shifting Lineweaver-Burk Plots37m
- Calculating Vmax40m
- Calculating Km31m
- Kcat46m
- Specificity Constant1h 1m
- 7. Enzyme Inhibition and Regulation 8h 42m
- Enzyme Inhibition13m
- Irreversible Inhibition12m
- Reversible Inhibition9m
- Inhibition Constant26m
- Degree of Inhibition15m
- Apparent Km and Vmax29m
- Inhibition Effects on Reaction Rate10m
- Competitive Inhibition52m
- Uncompetitive Inhibition33m
- Mixed Inhibition40m
- Noncompetitive Inhibition26m
- Recap of Reversible Inhibition37m
- Allosteric Regulation7m
- Allosteric Kinetics17m
- Allosteric Enzyme Conformations33m
- Allosteric Effectors18m
- Concerted (MWC) Model25m
- Sequential (KNF) Model20m
- Negative Feedback13m
- Positive Feedback15m
- Post Translational Modification14m
- Ubiquitination19m
- Phosphorylation16m
- Zymogens13m
- 8. Protein Function 9h 41m
- Introduction to Protein-Ligand Interactions15m
- Protein-Ligand Equilibrium Constants22m
- Protein-Ligand Fractional Saturation32m
- Myoglobin vs. Hemoglobin27m
- Heme Prosthetic Group31m
- Hemoglobin Cooperativity23m
- Hill Equation21m
- Hill Plot42m
- Hemoglobin Binding in Tissues & Lungs31m
- Hemoglobin Carbonation & Protonation19m
- Bohr Effect23m
- BPG Regulation of Hemoglobin24m
- Fetal Hemoglobin6m
- Sickle Cell Anemia24m
- Chymotrypsin18m
- Chymotrypsin's Catalytic Mechanism38m
- Glycogen Phosphorylase21m
- Liver vs Muscle Glycogen Phosphorylase21m
- Antibody35m
- ELISA15m
- Motor Proteins14m
- Skeletal Muscle Anatomy22m
- Skeletal Muscle Contraction45m
- 9. Carbohydrates7h 49m
- Carbohydrates19m
- Monosaccharides15m
- Stereochemistry of Monosaccharides33m
- Monosaccharide Configurations32m
- Cyclic Monosaccharides20m
- Hemiacetal vs. Hemiketal19m
- Anomer14m
- Mutarotation13m
- Pyranose Conformations23m
- Common Monosaccharides33m
- Derivatives of Monosaccharides21m
- Reducing Sugars21m
- Reducing Sugars Tests19m
- Glycosidic Bond48m
- Disaccharides40m
- Glycoconjugates12m
- Polysaccharide7m
- Cellulose7m
- Chitin8m
- Peptidoglycan12m
- Starch13m
- Glycogen14m
- Lectins16m
- 10. Lipids5h 49m
- Lipids15m
- Fatty Acids30m
- Fatty Acid Nomenclature11m
- Omega-3 Fatty Acids12m
- Triacylglycerols11m
- Glycerophospholipids24m
- Sphingolipids13m
- Sphingophospholipids8m
- Sphingoglycolipids12m
- Sphingolipid Recap22m
- Waxes5m
- Eicosanoids19m
- Isoprenoids9m
- Steroids14m
- Steroid Hormones11m
- Lipid Vitamins19m
- Comprehensive Final Lipid Map13m
- Biological Membranes16m
- Physical Properties of Biological Membranes18m
- Types of Membrane Proteins8m
- Integral Membrane Proteins16m
- Peripheral Membrane Proteins12m
- Lipid-Linked Membrane Proteins21m
- 11. Biological Membranes and Transport 6h 37m
- Biological Membrane Transport21m
- Passive vs. Active Transport18m
- Passive Membrane Transport21m
- Facilitated Diffusion8m
- Erythrocyte Facilitated Transporter Models30m
- Membrane Transport of Ions29m
- Primary Active Membrane Transport15m
- Sodium-Potassium Ion Pump20m
- SERCA: Calcium Ion Pump10m
- ABC Transporters12m
- Secondary Active Membrane Transport12m
- Glucose Active Symporter Model19m
- Endocytosis & Exocytosis18m
- Neurotransmitter Release23m
- Summary of Membrane Transport21m
- Thermodynamics of Membrane Diffusion: Uncharged Molecule51m
- Thermodynamics of Membrane Diffusion: Charged Ion1h 1m
- 12. Biosignaling9h 45m
- Introduction to Biosignaling44m
- G protein-Coupled Receptors32m
- Stimulatory Adenylate Cyclase GPCR Signaling42m
- cAMP & PKA28m
- Inhibitory Adenylate Cyclase GPCR Signaling29m
- Drugs & Toxins Affecting GPCR Signaling20m
- Recap of Adenylate Cyclase GPCR Signaling5m
- Phosphoinositide GPCR Signaling58m
- PSP Secondary Messengers & PKC27m
- Recap of Phosphoinositide Signaling7m
- Receptor Tyrosine Kinases26m
- Insulin28m
- Insulin Receptor23m
- Insulin Signaling on Glucose Metabolism57m
- Recap Of Insulin Signaling in Glucose Metabolism6m
- Insulin Signaling as a Growth Factor1h 1m
- Recap of Insulin Signaling As A Growth Factor9m
- Recap of Insulin Signaling1m
- Jak-Stat Signaling25m
- Lipid Hormone Signaling15m
- Summary of Biosignaling13m
- Signaling Defects & Cancer20m
- Review 1: Nucleic Acids, Lipids, & Membranes2h 47m
- Nucleic Acids 19m
- Nucleic Acids 211m
- Nucleic Acids 34m
- Nucleic Acids 44m
- DNA Sequencing 19m
- DNA Sequencing 211m
- Lipids 111m
- Lipids 24m
- Membrane Structure 110m
- Membrane Structure 29m
- Membrane Transport 18m
- Membrane Transport 24m
- Membrane Transport 36m
- Practice - Nucleic Acids 111m
- Practice - Nucleic Acids 23m
- Practice - Nucleic Acids 39m
- Lipids11m
- Practice - Membrane Structure 17m
- Practice - Membrane Structure 25m
- Practice - Membrane Transport 16m
- Practice - Membrane Transport 26m
- Review 2: Biosignaling, Glycolysis, Gluconeogenesis, & PP-Pathway3h 12m
- Biosignaling 19m
- Biosignaling 219m
- Biosignaling 311m
- Biosignaling 49m
- Glycolysis 17m
- Glycolysis 27m
- Glycolysis 38m
- Glycolysis 410m
- Fermentation6m
- Gluconeogenesis 18m
- Gluconeogenesis 27m
- Pentose Phosphate Pathway15m
- Practice - Biosignaling13m
- Practice - Bioenergetics 110m
- Practice - Bioenergetics 216m
- Practice - Glycolysis 111m
- Practice - Glycolysis 27m
- Practice - Gluconeogenesis5m
- Practice - Pentose Phosphate Path6m
- Review 3: Pyruvate & Fatty Acid Oxidation, Citric Acid Cycle, & Glycogen Metabolism2h 26m
- Pyruvate Oxidation9m
- Citric Acid Cycle 114m
- Citric Acid Cycle 27m
- Citric Acid Cycle 37m
- Citric Acid Cycle 411m
- Metabolic Regulation 18m
- Metabolic Regulation 213m
- Glycogen Metabolism 16m
- Glycogen Metabolism 28m
- Fatty Acid Oxidation 111m
- Fatty Acid Oxidation 28m
- Citric Acid Cycle Practice 17m
- Citric Acid Cycle Practice 26m
- Citric Acid Cycle Practice 32m
- Glucose and Glycogen Regulation Practice 14m
- Glucose and Glycogen Regulation Practice 26m
- Fatty Acid Oxidation Practice 14m
- Fatty Acid Oxidation Practice 27m
- Review 4: Amino Acid Oxidation, Oxidative Phosphorylation, & Photophosphorylation1h 48m
- Amino Acid Oxidation 15m
- Amino Acid Oxidation 211m
- Oxidative Phosphorylation 18m
- Oxidative Phosphorylation 210m
- Oxidative Phosphorylation 310m
- Oxidative Phosphorylation 47m
- Photophosphorylation 15m
- Photophosphorylation 29m
- Photophosphorylation 310m
- Practice: Amino Acid Oxidation 12m
- Practice: Amino Acid Oxidation 22m
- Practice: Oxidative Phosphorylation 15m
- Practice: Oxidative Phosphorylation 24m
- Practice: Oxidative Phosphorylation 35m
- Practice: Photophosphorylation 15m
- Practice: Photophosphorylation 21m
Biological Membranes - Online Tutor, Practice Problems & Exam Prep
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Biological membranes are primarily lipid bilayers that incorporate various embedded proteins, forming a fluid mosaic model. This model illustrates the dynamic nature of membranes, where phospholipids and proteins can move freely, contributing to membrane functionality. The composition of these membranes can vary significantly across different cells and organelles, affecting their properties and roles. Understanding the structure and function of membranes is crucial for grasping cellular processes, including transport mechanisms like facilitated diffusion and active transport.
Biological Membranes
Video transcript
Biological Membranes
Video transcript
So in our last lesson video, we introduced 3 different membrane structures, which were the micelles, the liposomes or the vesicles, and the lipid bilayers, and so in this video, we're going to introduce the biological membranes. Biological membranes are lipid bilayers themselves. However, they're more than just a lipid bilayer. Biological membranes are lipid bilayers with other membrane-embedded molecules as well, such as proteins, for instance. Recall from your previous biology courses that the fluid mosaic model applies to biological membranes. The fluid mosaic model is basically saying that biological membranes are both fluid and a mosaic of membrane-embedded proteins.
If we take a look at our image down below, notice over here on the far left, we're showing you a scanning electron micrograph (SEM) of a biological membrane right here. Notice that we're zooming into this specific region of the biological membrane, and we're getting this image right here. Most of the membrane molecules are indeed these phospholipids, but also embedded within the biological membrane. Notice that there's a good portion of these purple structures which are proteins. Recall that the fluid mosaic model applies to membranes like this one, where the phospholipids that we see here and the proteins and really all of the membrane-embedded molecules are fluid because they're capable of shifting around and moving to different areas within the membrane. The membrane is also a mosaic because all of these different membrane components, specifically these proteins, can make the biological membrane look like a mosaic.
To put things in perspective a little, biological membranes can actually be comprised of anywhere between 20 to 80% proteins by mass, and that is quite a lot of proteins. We already knew that biological membranes were going to be composed of mostly lipid structures because they are lipid bilayers. But maybe we did not really realize how much protein could actually be embedded within the bilayer. This goes to show that when talking about biological membranes, we cannot forget about the protein aspect of it because there can be quite a lot of proteins embedded within a biological membrane.
Another important thing to note is that membrane lipid composition can vary quite a lot from cell to cell, from sheet to sheet, and between different organelles. Clearly, different cells can have different phospholipid compositions and different proteins embedded. The sheet the sheet can also differ too. This extracellular sheet could have a different membrane composition than the intracellular sheet. Also, the membrane composition can vary between different organelles, so the mitochondria can have a different membrane composition than the nuclear membrane or than the endoplasmic reticulum membrane. This is just a general idea that's important to keep in mind.
This here concludes our review and introduction to biological membranes, and we'll be able to apply the concepts that we've learned and reviewed as we move forward in our practice problem. So, I'll see you guys there.
Membranes are a fluid mosaic of what components?
a) Proteins, cholesterol, and triacyglycerols.
b) Phospholipids, proteins, and cholesterol.
c) Phospholipids, nucleic acids, and cholesterol.
d) Eicosanoids, proteins, and phospholipids.
Which of the following lipids would likely not be involved in a lipid bilayer structure?
a) Phospholipid.
b) Cholesterol.
c) Glycolipid.
d) Sphingolipid.
e) Triacylglyceride.
f) Glycerophospholipid.
Membrane components within a lipid bilayer are held together primarily by:
a) Hydrogen bonds.
b) Covalent bonds.
c) Disulfide bonds.
d) Hydrophobic interactions.
e) Electrostatic interactions.
f) All of the above.