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BIOL 20A Lecture Notes - Lecture 7: Lipid Bilayer, Biological Membrane, Facilitated Diffusion

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16 Nov 2017

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Molecular, Cell, and Developmental Biology

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Document Summary

The phospholipid bilayer is 6 nanometers across. The whole membrane, including membrane proteins, is 10 nanometers across! Biological membranes contain both lipids and proteins. Proteins are islands floating in a sea of lipids. Biological membranes are semi-permeable barriers (they only let certain molecules across, and on their own conditions) Permeable to small, uncharged molecules (even if polar) Highly impermeable to ions and other molecules (the bilayer is nonpolar, so it can"t stand charged atoms and/or molecules!) Transport proteins allow regulated transport of polar and charged molecules across biological membranes. Three general classes of transport across membranes. Small, uncharged molecules diffused across bilayer membrane down the concentration gradient. Diffusion occurs until molecules are randomly distributed on both sides of the membrane. Osmosis: special form of passive diffusion involving water. Hypotonic: the solute concentration outside the cell is lower. Isotonic: solute concentrations are equal inside and outside the cell. Hypertonic: solute concentration outside the cell is higher.

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Related Questions

1) This is a thermodynamics questions

In your body, normal osmolarity of blood serum is just under 0.3 molar. Because cell membranes are permeable to water, the osmolarity of intracellular fluid is approximately equal to that of extracellular fluid (though the intracellular and extracellular composition in terms of specific ions and proteins is quite different). As an aside, measurement of osmolarity of serum is an important clinical test used to check for dehydration or other imbalances of water and electrolytes.

a) In the supplemental information, the osmosis example presented involves sucrose as a solute, but the van't Hoff equation also applies for other solutes. Using this formula (â = cRT, where â is the excess pressure), calculate the osmotic pressure associated with 0.3 molar concentration of osmolytic particles (e.g., ions, proteins, or other dissolved particles) in contact with pure water through a semi-permeable membrane at physiological temperature of 310 K. Express your results in atmospheres of pressure (1 atmosphere of pressure is 1.0x10⁵ Pascal, where 1 Pascal is a Newton/m²).

b) A biological cell membrane is a bilayer of phospholipid molecules, only a few nanometers thick, and can basically be thought of much like a soap bubble, except immersed in aqueous solution. If cells are placed in pure water, they often swell and burst in just a few minutes. Explain why this would happen.

grayporcupine495

20. All living things must maintain a constantinternal environment to function properly through the process of__. (Points : 2)

metamorphosis
alkalosis
homeostasis
cryogenesis

Question 21.21. Glucose, fructose, sucrose,starch and glycogen are all examples of ___. (Points : 2)

proteins
carbohydrates
lipids
nucleic acids

Question 22.22. Some insects can "walk onwater" because __. (Points : 2)

water has a high surfacetension
water is adhesive
water istransparent
water expands when itfreezes

Question 23.23. To overcome an energy barrierbetween reactants and products in a chemical reaction, energy mustbe provided to get the reaction started. This energy is called ___energy. (Points : 2)

potential
reaction
initiation
activation

Question 24.24. Where in the cell doesglycolysis takes place? (Points : 2)

lysosomes
cytoplasm
mitochondria
nucleus

Question 25.25. Photosynthesis uses sunlightto convert water and carbon dioxide into __. (Points : 2)

carbon dioxide andwater
oxygen and sugars
proteins and sugars
carbon dioxide andoxygen

Question 26.26. The _____ of photosynthesisare the _____ of cellular respiration. (Points : 2)

electrons, protons
pigments, products
products, reactants
elements, atoms

Question 27.27. The energy currency of thecell is __. (Points : 2)

glucose
ATP
starch
glycogen

Question 28.28. When blood glucose levelsdecrease (as between meals), what reserves are tapped first?(Points : 2)

glycogen
fats
steroids
amino acids

Question 29.29. When glucose is used as anenergy source, the largest amount of ATP is produced by the ____portion of the entire respiratory process. (Points : 2)

glycolytic
Kreb's cycle
acetyl-CoAformation
electron transportchain

Question 30.30. Pyruvic acid can be regardedas the end product of ____. (Points : 2)

glycolysis
fermentation
the Kreb cycle
the electron transportchain

Question 31.31. How can one increase the rateof a chemical reaction? (Points : 2)

Increase the activationenergy.
Cool the reactants.
Decrease the pH.
Add an enzyme(catalyst).

Question 32.32. A prokaryote has ___. (Points: 2)

membrane-boundorganelles
nucleus
mitochondria
a cell membrane

Question 33.33. Unlike animal cells, plantcells have __. (Points : 2)

cell membranes
cell walls
chromosomes
mitochondria

Question 34.34. Which of the followingrequires energy to move molecules across the cell membrane? (Points: 2)

diffusion
osmosis
active transport
passive transport

Question 35.35. The ___ is the site of proteinsynthesis. (Points : 2)

nucleus
ribosome
mitochondrion
cytoskeleton

Question 36.36. Diffusion of water through asemipermeable membrane is called __. (Points : 2)

osmosis
diffusion
active transport
passive transport

Question 37.37. Which component of a cellmembrane is likely to function as a transporter? (Points : 2)

cholesterol
lipids
proteins
carbohydrates

Question 38.38. If potato slice is placed indistilled water, the cells would most likely __. (Points : 2)

lose water and becomelimp
neither take up water orlose water
take up water andswell
transport water into thecell by active transport.

Question 39.39. The chloroplast functions in___. (Points : 2)

protein synthesis
lipid storage
DNA replication
photosynthesis

Question 40.40. The fluid mosaic modelpresents the modern view of ___. (Points : 2)

the cell membranestructure
chromosome movementduring mitosis
protein synthesis
ATP production

Question 41.41. During which stage of mitosisdo nucleoli reappear and the nuclear membrane reforms? (Points :2)

prophase
metaphase
anaphase
telophase

Question 42.42. During which stage of mitosisdo chromatids separate to form two sets of daughter chromosomes?(Points : 2)

prophase
metaphase
anaphase
telophase

Question 43.43. Which of the following is thelongest stage of mitosis? (Points : 2)

prophase
metaphase
anaphase
telophase

Question 44.44. When during the cell cycle isDNA replicated? (Points : 2)

metaphase
Synthesis phase (S)
G1
cytokinesis

Question 45.45. A cell with 10 chromosomesundergoes mitosis and cell division. How many daughter cells areproduced and what number of chromosomes do they have? (Points :2)

4 daughter cells, 20chromosomes each
4 daughter cells, 5chromosomes each
2 daughter cells, 10chromosomes each
2 daughter cells, 5chromosomes each

Question 46.46. Maize (corn) has a haploidnumber of 10. How many chromosomes are in a zygote of maize?(Points : 2)

5
10
20
Not enough informationprovided

Question 47.47. Crossing over is one of themost important events in meiosis because __. (Points : 2)

homologous chromosomesare separated into different daughter cells
the number of chromosomesallotted to each daughter cell must be halved
sister chromatids must beseparated into different daughter cells
it produces new arrays ofalleles on chromosomes and contributes to genetic diversity

Question 48.48. While viewing stained onionroot tip cells you notice that distinct chromosomes cannot beobserved in most of the cells. This is because most of the cells___. (Points : 2)

were killed whilepreparing the slide
are in Interphase
are in metaphase
are undergoingMeiosis

Question 49.49. Each offspring cell producedby binary fission contains __. (Points : 2)

half the chromosomes ofthe original cell
twice as many chromosomesas the original cell
an independent assortmentof the original cell's chromosomes
an identical copy of theoriginal cell's chromosome.

Question 50.50. A DNA strand has the sequenceA-C-A-G-C-C-G-T-A. What would be its complementary strand? (Points: 2)

G-T-G-A-T-T-A-C-G
A-C-A-G-C-C-G-T-A
T-G-T-C-G-G-C-A-T
U-G-U-C-G-G-C-A-U