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General Flashcards

1
Q

Who invented the microscope? Who refined it?

A

Invented by Robert Hooke; refined by Antonie van Leewenhoek

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2
Q

What are Animalcules?

A

Homunculi in sperm (the little people are found in sperm not eggs).

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3
Q

Who discovered animalcules?

A

Antonie van Leewenhoek

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4
Q

Who articulated Cell theory and what are the three points of Cell theory?

A

Schleiden, Schwann, and Virchow.

  • All organisms are composed of one or more cells.
  • The cell is the structural unit of life.
  • Cells arise from pre-existing cells by division.
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5
Q

What are the 10 basic properties of cells?

A
  • Life is the most basic property of cells
  • Cells are highly complex and organized
  • Cells posses a genetic program and the means to use it.
  • Cells are capable of producing more of themselves
  • Cells acquire and utilize energy
  • Cells carry out a variety of chemical reactions
  • Cells engage in mechanical activities
  • Cells are able to respond to stimuli
  • Cells are capable of self-regulation
  • Cells evolve
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6
Q

Cell biology is characterized as reductionist. Define reductionist

A

Based on the premise that studying the parts of the whole can explain the character of the whole.

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7
Q

What are all biological systems composed of?

A

The same types of chemical compounds

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8
Q

What have all biological systems developed?

A

Similar principles of organization at the cellular level

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9
Q

What is Endosymbiotic theory?

A

The theory that organelles in eukaryotic cells (mitochondria and chloroplasts) evolved from smaller prokaryotic cells.

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10
Q

What is the point of controversy in the Endosymbiotic theory?

A

The appearance of the nuclear envelope

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11
Q

What were the features of the prokaryote that evolved into a eukaryote?

A

Anaerobic and heterotrophic

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12
Q

How did the nuclear envelope evolve in eukaryotes?

A

Invagination of the plasma membrane

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13
Q

What are 6 pieces of evidence that support the Endosymbiotic theory?

A
  • Absence of eukaryote species with organelles (M&C) in an intermediate stage of evolution.
  • Many symbiotic relations are known among different organisms.
  • Organelles (M&C) of eukaryotic cells contain their own DNA not found in any other organelle.
  • Nucleotide sequences of rRNAs from eukaryotic organelles (M&C) resemble that of prokaryotes (very close in sequence).
  • Organelles (M&C) duplicate independently of nucleus.
  • Lipid composition of organelles (M&C) resemble that of prokaryotic membranes
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14
Q

What do membranes organize cells into?

A

Compartments

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15
Q

What are 8 membrane functions?

A
  • Compartmentalization – Membranes form continuous sheets that enclose intracellular compartments.
  • Scaffold for biochemical activities – Membranes provide a framework that organizes enzymes for effective interaction.
  • Selective permeability barrier – Membranes allow regulated exchange of substances between compartments.
  • Transport of solutes – Membrane proteins facilitate the movement of substances between compartments.
  • Responding to external signals – Membrane receptors transduce signals from outside the cell in response to specific ligands.
  • Intracellular interaction – Membranes mediate recognition and interaction between adjacent cells.
  • Energy transduction – Membranes transduce photosynthetic energy, convert chemical energy to ATP, and store energy.
  • Flexibility and Deformability – Allows cells to change shape or move
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16
Q

What did the 1890 Overton study conclude?

A

The boundary of cells are composed of lipids.

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17
Q

Why are red blood cells the most studied membrane?

A
  • Inexpensive to obtain and readily available in huge numbers from whole blood
  • The cells are already present as single cells and need not be dissociated from a complex tissue
  • RBCs are simple in comparison to other cells; they have no contaminating internal cell membranes.
  • One can obtain pure, intact RBC membranes (ghosts) by osmotic shock and lysis of cell (hemolysis)
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18
Q

What was the finding from the 1925 experiment by Gorter and Grendel?

A

Membrane forms a lipid bilayer.

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19
Q

Are membranes in a living cell symmetric or asymmetric?

A

Asymmetric; asymmetry is a feature of life in cells, although some membranes are symmetric.

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20
Q

Are dead cells membranes symmetric or asymmetric?

A

Symmetric

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21
Q

What are two types of molecules that are only found on the extra cellular side of the cell.

A

Glycoproteins and Glycolipids

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22
Q

What are the major components of membranes?

A

Lipids and proteins

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23
Q

What do lipids and proteins do in a membrane?

A
  • Act as the structural backbone of the membrane

- Major component that stabilizes the permeability barrier.

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24
Q

Different compositions of lipids and proteins will cause variability in what aspect of the cell membrane?

A

Thickness

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25
Q

What is the bilayer thickness of a typical membrane?

A

30 A (angstrom)

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26
Q

What determines the thickness of a bilayer?

A

The length of the fatty acid chains.

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27
Q

What are the three major classes of lipids in eukaryotic membranes?

A

Glycerolipids, Sphingolipids, and sterols.

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28
Q

How many different lipid species comprise a eukaryotic cell?

A

1300-1500

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29
Q

Where are sterols found?

A

In the hydrophobic core

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30
Q

In a glycerolipid what does position 3 on the glycerol backbone form?

A

Always forms and ester bond with a phosphate group

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31
Q

In Glycerolipids, if the R group on the phosphate is Choline what is the compound called?

A

Phospatidylcholine (lecithin)

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32
Q

What type of backbone do Glycerolipids have?

A

A glycerol backbone

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33
Q

What type of backbone do Sphingolipids have?

A

A Sphingosine backbone

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34
Q

When a Sphingolipid has an acyl tail what is the compound called?

A

Ceramide

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35
Q

When the R group on the phosphate of a Sphingolipid is choline what is the compound called?

A

Sphingomyelin

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36
Q

What are the characteristics of sterols?

A

Cyclic molecules that are smaller and less amphipathic than other membrane lipids.

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37
Q

What are the names of the sterols found in: plants, fungi, animals?

A

Plants: phytosterols
Fungi: ergosterols
Animals: cholesterol

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38
Q

What is the precursor of all phospholipids?

A

Phosphatidic acid (a phospho-mono-ester).

Can have many different combinations in lipids.

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39
Q

What is the net charge at a pH of 7 of phosphatidic acid.

A

-1

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40
Q

What 2 phospholipids have a net charge of zero?

A

Phosphatidylcholine (PC), and phosphatidylethanolamine (PE)

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41
Q

What are 2 negatively charged phospholipids

A

Phosphatidylserine (PS), and phosphatidylinositol (PI)

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42
Q

What are the two extremely negatively charged mitochondrial lipids (they are also present in prokaryotes)?

A

Phosphatidylglycerol (PG) and diphosphatidylglycerol (Cl)

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43
Q

True or false, Membrane lipids move easily within a leaflet but only rarely “flip-flop”

A

True

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44
Q

Why is the asymmetry of lipids in the membrane important?

A

Provides different physico-chemical properties appropriate for different interactions

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45
Q

What is known as the signalling lipid?

A

Phosphatidylinositol (PI); bulky lipids do not play a huge role in signalling

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46
Q

True or false, in eukaryotes only some lipids are glycerol 3-phosphate based.

A

False, all are glycerol 3-phosphate based

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47
Q

What types of Glycerolipids do bacteria have and which do they not have?

A

Predominantly PG, CL, and PE and are glycerol 3-phosphate based. There is no PC or PI (use PA for cell signalling instead of PI)

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48
Q

Do bacteria have sphingolipids or sterols?

A

No

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49
Q

Do Archaea have Glycerolipids?

A

Yes but they are very different (glycerol 1-phosphate based); very different lipids in order to survive in extreme conditions.

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50
Q

What kinds of sphingolipids and sterols are found in Archaea?

A

Not sure if they have them or not. Archaea have isoprano chains instead of fatty acid chains.

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51
Q

Lipids of biological membranes can exist in several possible phases what are they?

A

Lipid disordered (tails are bent), solid gel (tails are more straight), and liquid ordered raft (compounds inserted into the membrane).

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52
Q

What compounds can form bilayers?

A

Pure phospholipids such as phosphatidylcholine and sphingomyelin; (cholesterol can insert into the bilayer)

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53
Q

What do open bilayers do?

A

Pure phospholipid bilayers spontaneously seal to form closed structures.
ie. Liposome

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54
Q

In liposomes stained with fluorescent dye what do the liposomes look like if there is only phosphatidylcholine and sphingomyelin, or if there is both phosphatidylcholine, sphingomyelin, and cholesterol?

A

A liposome with only phosphatidylcholine and sphingomyelin will have a homogenous appearance, a liposome also with cholesterol will appear polka dotted with lipid rafts.

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55
Q

What does cholesterol do?

A
  • inserts between phospholipids with its hydrophilic hydroxyl group facing the membrane surface.
  • The rest is embedded in the lipid bilayer
  • it’s rings are flat and rigid which interfere with movement of phospholipid fatty acids
  • CHOLESTEROL CHANGES THE PHYSICAL STATE OF THE MEMBRANE (it stiffens the membrane)
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56
Q

How does cholesterol interact with other lipids?

A

Cholesterol packs well with sphingolipids and saturated phospholipids. It forms microdomains in the membrane.

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57
Q

True or false lipid rafts are a definite thing in biology?

A

False it is a current controversial concept.

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58
Q

Define fluidity

A

A measure of the ease of flow

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59
Q

Define viscosity

A

A measure of the resistance of flow

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60
Q

Fluidity of lipid bilayer’s is influenced by four factors what are they?

A

Temperature, acyl chain length, acyl chain saturation, and sterol content.

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61
Q

Are bilayers more fluid at higher or lower temperatures?

A

Bilayers or more fluid at higher temperature due to the melting of lipid to lipid interactions

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62
Q

What is the temperature at which phase transition occurs?

A

The temperature at which phase transition occurs is dependent upon the lipids present in the bilayer (transition temperature; TM)
ie. Solid gel phase to liquid disordered phase (fluid phase)

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63
Q

How do the length of fatty acyl sidechains affect the fluidity of the membrane?

A

Longer chains cause the bilayer to be less fluid, shorter chains cause the bilayer to be more fluid. The transition melting point temperature is affected by chain length.

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64
Q

How do the number of unsaturated bonds in fatty acyl chains affect the fluidity of the membrane?

A

Saturated bonds cause the membrane to be less fluid, unsaturated bonds (produce cis-kinks) cause the membrane to be more fluid. Organization of saturated fatty acyl chains is more regular than that of chains with unsaturated bonds. The transition melting point temperature is affected by fatty acyl sidechain saturation. The TM decreases in bilayers with higher amounts of acyl chain unsaturation

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65
Q

How does the presence of cholesterol affect the transition melting point temperature of the membrane?

A

It abolishes sharp transition temperatures and creates a condition of intermediate fluidity (linear line instead of backwards S shaped). the presence of cholesterol decreases permeability and increases durability of the membrane.

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66
Q

How do organisms respond to changes in the external temperature?

A

Membrane remodeling: adaptation to cold temperatures in Bacillus subtilis (gram + bacteria) activation of an acyl-lipid desaturase.
(desaturates the membrane to make it more fluid)

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67
Q

The cellular membranes are composed of lipids and proteins which one of these carries out most of the specific functions for a membrane?

A

Proteins

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68
Q

What is the lipid to protein ratio in the membranes of cells?

A

The lipid to protein ratio varies greatly depending on membrane type and cell type.
ie. Outside the cell vs. inside the cell

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69
Q

What type of membrane proteins are found in membranes?

A

Membrane proteins can vary between different membranes or cell types these differences largely relate to the particular function of the membrane.
ie. glycolipid = lipid with oligosaccharide attached (same with proteins)

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70
Q

Where are carbohydrates/sugars found?

A

Often attached to membrane lipids (glycolipids) and/or proteins (glycoproteins) on the outside of the membrane

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71
Q

What are the three types of membrane proteins and what are their characteristics?

A
  1. integral (intrinsic) membrane proteins: span all or half of the bilayer.
  2. Lipid anchored proteins: attached to head groups of lipids via covalent bonds. The oligosaccharide is attached to the external side of the membrane and lipidation occurs on the intracellular side of the membrane.
  3. Peripheral proteins: attached via noncovalent bonds. It is not interacting with lipid but is interacting with integral membrane proteins. It has the weakest interaction with the membrane.
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72
Q

How can integral membrane proteins be removed from the bilayer?

A

integral membrane proteins passed through the bilayer; they cannot be removed without disruption of the bilayer, usually by using detergents

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73
Q

Where are beta barrel proteins found?

A

Found in prokaryotes such as bacteria and also found in the outer membrane of mitochondria and chloroplasts.

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74
Q

What are the features of a lipid anchored protein?

A

A hydrophobic group allows the protein to insert into the internal/cytoplasmic leaflet. They do not pass all the way through the bilayer

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75
Q

What are some post translational modifications of lipid anchored proteins?

A

Lipidation, methylation, acetylation, and phosphorylation; usually reversible and transient. (Modification happens in the cytosolic leaflet).

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76
Q

What are the three different types of lipid anchors in lipid anchored proteins and how are they produced?

A
  • Myristoyl anchor: produced via myristoylation (C14:0 14carbons no double bonds).
  • Palmitoyl anchor: produced via palmitoylation (C16 acyl chain)
  • Farnesyl anchor: produced via farnesylation (15C isoprenoid chain)
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77
Q

How do Glycolphosphatidylinositol, (GPI)-anchored proteins, attach to the membrane?

A

They specifically insert into the external leaflet of the bilayer through a glycosidic linkage. The protein portion is covalently attached by glycosylation to the head group of a phosphatidylinositol

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78
Q

How are proteins distributed across cellular membranes?

A

Asymmetrically; most sugar groups of glycoproteins and glycolipids (and carbohydrates) are on the outerside of the plasma membrane.

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79
Q

True or false peripheral membrane proteins insert into the bilayer.

A

False they do not insert into the bilayer, they are found on either side of the membrane.

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80
Q

What type of compounds to peripheral proteins interact with?

A

They interact with phospholipids or with integral membrane proteins and sometimes they interact with both at the same time.

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81
Q

How do you remove peripheral membrane proteins from the membrane?

A

Removed with high salt/high pH, etc. this is done without disrupting the lipid bilayer.

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82
Q

Are integral membrane proteins single spanning or multiple spanning?

A

They are both.

83
Q

How are lipid anchored proteins removed from the membrane?

A

Mild detergent (salt wash)

84
Q

What are the main features that distinguishes an integral protein from a peripheral membrane protein?

A
  • Integral membrane proteins interact very strongly with the membrane and pass through both leaflets of the lipid bilayer, isolation from the membrane requires detergent solubilization, and they are more resistant to proteases.
  • peripheral proteins sit at phospholipid surfaces and are attached via charged interactions with the membrane (ionic), they can be isolated from the membrane with high salt washes, and can be cleaved by proteases.
85
Q

During membrane preparation from erythrocytes, after the solution has been centrifuged what is found in the supernatant and what is found in the pellet?

A

The pellet contains insoluble material (membranes) and the supernatant contains soluble material

86
Q

What are the properties of SDS detergent and why do we use it?

A

SDS has a hydrophobic chain and a negatively charged head group thus it is amphipathic. SDS binds to positively charged and hydrophobic residues of the protein to give the protein a uniformly negative charge which unfolds many regions of the protein, denaturing the protein.

87
Q

Where are heavy and light proteins found in an SDS-page?

A

Heavy proteins are found at the top and lighter proteins are found at the bottom of the gel as proteins travel further when their molecular weight is smaller.

88
Q

What is a property of strong detergent?

A

It can remove ALL proteins from the membrane.

89
Q

How does the treatment of cell membranes with salts, enzymes, and detergents selectively isolate the type of membrane protein using SDS page?

A
  • salts help break ionic bonds between proteins
  • detergent solubilize/disrupt lipids
  • enzyme such as proteases can recognize and cut peptide bonds in proteins.
90
Q

Would membrane proteins tightly associated to lipids run in SDS page according to their molecular weight?

A

No, because there is altered SDS binding to proteins and proteins bound to lipids are less soluble altering their electrophoretic mobility

91
Q

Since phospholipid membranes are fluid according to the Fluid Mosaic model then we should see evidence of membrane protein mobility. What are the four types of mobility in the membrane?

A
  • Lateral diffusion: where proteins in the lipid bilayer diffuse laterally.
  • flexion: movement of the tails
  • rotation: rotation of the membrane proteins
  • flip-flop: where are proteins pass from the intracellular side to the extracellular side of the bilayer (or vice versa); this rarely occurs
92
Q

What was the Fryre and Edidin Cell Fusion experiment?

A
  • human and mouse cells were fused together to give a single cell with two nuclei and one continuous membrane.
  • human and mouse cells, along with two different fluorescently labeled anti-bodies were used (antihuman membrane protein anti-bodies, and anti-mouse membrane protein anti-bodies).
  • Results: after 40 minutes each species membrane proteins appeared uniformly distributed; therefore membrane proteins are mobile. (this is true for all membrane proteins but some move very slowly).
93
Q

What is florescence recovery after photobleaching (FRAP)?

A
  • A particular membrane protein is fluorescently labeled
  • A small region of the membrane is irradiated to bleach the labelled protein
  • this membrane region is visually monitored overtime to determine the extent of fluorescence recovery (can determine how fast some proteins move by how fast they occupy the bleach area)
94
Q

Why do we use photobleaching?

A

Photo bleaching can be used to determine how fast fluorescently labeled regions of the membrane can recover.

95
Q

define florescence

A

-Fluorescence: The light absorbed by a florphore that is reemitted at a lower wavelength

96
Q

Define photobleaching

A

-Photo bleaching: the fluorescent molecule that is illuminated with intense light of the appropriate wavelength that can no longer re-emit light

97
Q

What are some problems with using FRAP?

A
  • FRAP shows the raider florescence recovery and provides a direct measurement of the rate of protein diffusion, however, 30-70% of membrane proteins studied were not able to move back into the circle.
  • membrane proteins moved much more slowly in plasma membrane than in pure lipid bilayers
98
Q

If the FRAP Experment were performed at 10°C how would the results have differed?

A

Fluorescent recovery within the circle would be slower than at 30°C

99
Q

True or false membrane proteins move much more slowly in plasma membranes than in pure lipid bilayers?

A

True

100
Q

Why does the plasma membrane have slower membrane protein diffusion rates than proteins with pure artificial phospholipid membranes?

A
  • artificial membranes have a looser packing which increases mobility
  • plasma membrane’s have protein and lipid domains that can obstruct diffusion
  • artificial membranes lack proteins that hinder mobility
101
Q

How do small molecules move through cell membranes?

A

They move across membranes through intrinsic membrane proteins (transporters)

102
Q

What is the selectivity for hydrophobic molecules passing across the cell membrane (O2, CO2, N2, steroid hormones, etc)?

A

There is no selectivity, hydrophobic molecules pass through the membrane easily

103
Q

What is the selectivity for the movement of small uncharged polar molecules across the membrane (H2O, urea, glycerol)?

A

There is some selectivity

104
Q

What is the selectivity for movement of large uncharged polar molecules across the membrane (glucose and sucrose)?

A

Extremely slow and selective

105
Q

What is the selectivity for the movement of ions across the cell membrane ( H+, Na+, HCO3-, K+, Ca2+, Cl-, Mg2+, etc)?

A

Completely impermeable

106
Q

Define diffusion

A

The spontaneous movement of material from a region of high concentration to a region of low concentration

107
Q

What does the free energy change during diffusion of non-electrolytes depend on?

A

The chemical concentration gradient

108
Q

What does the free energy change during diffusion of electrolytes (ions) depend on?

A

The electrochemical gradients (concentration and voltage)

109
Q

What is passive transport?

A

The movement of molecules across a membrane down the concentration gradient (from high to low concentration) that does not require metabolic energy

110
Q

What is active transport?

A

The movement of molecules across a membrane against a concentration gradient requires a source of metabolic energy

111
Q

What are the two types of active transport and how is the transport accomplished?

A
  • Primary and secondary active transport.
  • Primary active transport is accomplished DIRECTLY via ATP hydrolysis
  • secondary active transport/cotransport uses ATP hydrolysis INDIRECTLY
112
Q

What are the three types of passive transport?

A
  • Diffusion (hydrophobic molecules)
  • Protein pore (ion channels)
  • Transporter mediated
113
Q

What are the two types of secondary transport and how is secondary transport accomplished?

A
  • Symport (same direction) and anti-port (opposite directions).
  • takes advantage of primary transporter to create a gradient (Active transport of a molecule down its concentration gradient allows for the transport of another molecule across its electrochemical gradient)
114
Q

What is another name for passive transporter mediated diffusion?

A

Facilitated diffusion: large or hydrophilic substances require a facilitative transporter to cross membranes.
-proceeds via substrate binding to the transporter

115
Q

What are glucose transporters regulated by?

A

Insulin

116
Q

Both facilitated and simple diffusion are passive. What are the main differences between facilitated diffusion and simple diffusion?

A

-facilitated diffusion is SPECIFIC, SATURABLE, and REGULATED

117
Q

What is the main feature of primary active transport pumps?

A

Deal directly with ATP hydrolysis

118
Q

What are the three types of primary active transport pumps?

A
  • P-type pumps: transient phosphorylation; becomes phosphorylated during the process of opening and closing (transports hydrogen, potassium, sodium, and calcium ions out of the cell)
  • F-type (and V-type) proton pump: pumps protons into the cell and synthesizes ATP; uses the transport of another ion to do this
    ex. ATP synthase protein in the mitochondria
  • ABC transporter: hydrolyze ATP to pump things out of the cell.
    ie. Small molecules
119
Q

What are the main features of a P type pump?

A

P-type pumps are transiently phosphorylated during the transport of ions across the membrane • Examples:

1) Na+/ K+ ATPases can pump Na+ from the cytoplasm in exchange for K+ (higher eukaryotes)
2) Ca2+ ATPase will pump Ca2+ out of the cell but will also pump Ca2+ into internal membrane bound stores (all eukaryotes)
3) H+/ K+ ATPase = acidification of stomach
4) H+ pumps in the plasma membrane of bacteria, plants and fungi (important to maintaining the pH of the cell)

120
Q

Where is calcium mostly stored in the cell?

A

In the ER in the mitochondria

121
Q

True or false cells have a charge?

A

False, cells need to maintain an equal amount of anions and cations to remain neutral

122
Q

What are V-type pumps?

A

Multi-subunit pumps found in membranes of vesicles and vacuoles (lysosomes in mammalian cells); these are membrane enclosed organelles.

  • Phosphate from ATP is not transferred to the pump during ATP hydrolysis
  • Generally pump H+ which is essential for numerous cellular processes
123
Q

Why do vesicles and vacuoles pump protons?

A

Pump protons in order to control the pH (lower it) inside the cell.

  • needed for the proper activity of some enzymes
    ex. Inside cell pH=7.2, inside vacuole=5
124
Q

What are F-type pumps?

A

-Usually run backwards: Under certain experimental conditions all pumps can be made to “run backwards” resulting in the production of ATP from an ion gradient.
-ATP synthases that produce ATP in bacteria, mitochondria and chloroplasts are pumps
“running backwards”
-Convert free energy from the ion gradient to make ATP

125
Q

What are ABC transporters and how do they function?

A
  • a super family that moves lipophilic molecules and can function as flippases.
  • forms a tetramer with transmembrane and cytosolic subunits
  • In bacterial plasma membranes: amino acid, sugar, and peptide transporters.
  • in mammalian plasma membranes: phospholipid, small lipophilic drugs, cholesterol, and other small molecule transporters.
126
Q

How does secondary active transport make use of ATP and free energy?

A

• ATP is used to form a gradient of another
secondary molecule that is used to drive the
transport of other molecules
• Free energy released during the transport of
the secondary molecule drives the movement
of the desired solute
– co-transport = symport or antiport

127
Q

What types of pumps are in the lumen that allow for the uptake of glucose?

A
  • Na+/glucose co-transporter: secondary active symporter where glucose is moved against its concentration gradient and sodium moves down it’s electrochemical gradient.
  • glucose transporter (GLUT2): facilitated diffusion of glucose from the lumen into the blood (passive facilitated diffusion; passive transporter mediated)
  • Na+/K+ - ATPase (P-type pump): primary active transport of three sodium ions out of the cell with two potassium ions coming into the cell down it’s electrochemical gradient which hydrolyzes ATP.
128
Q

Is the movement of a positively charged molecule towards the positively charged side of the membrane the same, greater, or less than if the membrane had a neutral charge? Want about if the molecule was negatively charged?

A

A positively charged molecule moving towards the positively charged side of the membrane will have less movement than if the membrane did not have a charge because the two charges repel each other.
A negatively charged molecules moving towards the positively charged side of the membrane would have a greater movement but if the membrane did not have a charge because the two charges attract each other.

129
Q

What does the asymmetric distribution of ions across the plasma membrane produce?

A

1) chemical (concentration) gradient
eg. Na+ gradient used for symport/ antiport
transporters
2) electrical (voltage) gradient
eg. Na+/K+ ATPase is an electrogenic pump
-each cycle 3 Na+ ions are pumped out but only 2 K+ ions are pumped into cell
-generates a concentration gradient and a difference in charge across the membrane.
-results in the accumulation of a negative charge on the inside of the plasma membrane

130
Q

What is the membrane potential/voltage gradient?

A

The difference in electric charge across the

plasma membrane

131
Q

What happens when the concentration gradient and membrane potential balance each other?

A

The electrochemical gradient for the ion is ZERO and there is no NET flow of the ion through the channel

• The membrane potential at which this equilibrium is reached is called the equilibrium potential for the ion

132
Q

How do we calculate the equilibrium potential for each ion?

A

The equilibrium potential for each ion can be calculated using the Nernst equation (this is given on the exam)

133
Q

What ion contributes the most to the membrane potential of a cell? How do you tell?

A

Potassium is the main thing that contributes to the membrane potential. We see this because the membrane potential is -70 mV and potassium is equilibrium potential is -90 mV (sodium’s equilibrium potential is +55 mV)

134
Q

What is the main feature of non-excitable cells?

A

Membrane potential is fairly constant (around -70 mV)
– unable to change rapidly in response to a
stimulus

135
Q

What is the main feature of an excitable cell?

A

membrane potential is called resting potential and can change rapidly in response to a stimulus
(nerve cells and muscle cells)

136
Q

What causes the electrical change and excitable cell?

A

Rapid electrical change is due to ion flow downthe concentration gradient through ion channels.
-These ion channels are usually selective for one type of ion (Eg. K+, Ca2+, Na+ etc.)

137
Q

What are the four classes of ion channels?

A
  1. voltage gated channels: membrane potential decreases, ion channels open, ions move down there concentration gradient
  2. extracellular ligand gated channels
  3. Intracellular ligand gated channels: could also be phosphorylated by a protein kinase
  4. mechanically gated channels: stretching or shrinking of the membrane opens channel
138
Q

How do voltage gated ion channels open?

A

• ion channels open in response to
depolarization of the membrane (membrane electron potential decreases)
-Voltage- gated Na+, K+, Ca2+, Cl- channels

139
Q

Define depolarization

A

depolarization: decrease in the polarity between the two sides of the membrane

140
Q

How do ligand gated channels open?

A

Refers to ion channels that open upon binding a chemical messenger
• eg. binding of the neurotransmitter acetylcholine (ACh) to its receptor (nAChR) opens the Na+ channel allowing influx of Na+

141
Q

How do stretch/pressure (mechano-) gated channels open?

A

Channel opens in response to stretching or deformation of the cells surface.
-Cation channels open in response to the movement of stereocilia in the ear in response to sound

142
Q

What are nerve impulses/action potentials?

A

Rapid, transient, self-propagating electrical excitation in the plasma membrane of neurons or muscle cells (need a strong signal because axons are long and weak signals maybe lost)

143
Q

What is responsible for the generation of action potentials in electrically excitable cells?

A

Voltage-gated cation channels (Na+/K+ pump)

144
Q

What is meant by term refractory period?

A

A time during the action potential where another action potential cannot be propagated. (this is due to inactivated sodium channels)

145
Q

What is the difference between an inactivated channel and a closed channel?

A

A closed channel is closed but can be opened (responsive), an inactivated channel is closed and is unresponsive until the membrane returns to resting membrane potential

146
Q

Why is a nerve impulse only propagated in one direction?

A

After nerve a impulse is propagated the sodium channels that were once open close and become inactivated. Because these channels are unable to be opened again this prevents the action potential from going backwards.

147
Q

What is the pump the repolarizes the cell membrane?

A

Sodium potassium ATPase

148
Q

What happens during the depolarization of the cell membrane?

A

• the membrane potential voltages change from negative to positive. This decreases polarity over both sides of the membrane = depolarization

149
Q

True or false potassium channels in the membrane are always closed?

A

False potassium channels are always open, they are leaky

150
Q

How do ions generate an action potential?

A

Action potential occurs due to sequential changes in Na+ and K+ permeability
-channel open/ closures cause charge differences to build up on the membrane

NOTE: THERE IS NO LARGE CHANGE IN ION CONCENTRATION DURING AN ACTION POTENTIAL. IT IS THE LARGE NET ION DISPLACEMENT THAT IS CRITICAL.

151
Q

How are action potentials initiated and propagated?

A

Action potential is usually initiated at the
chemical synapse via ligand-gated ion
channels (chemical binding site) and propagated along the axon by
opening of voltage-gated channels

152
Q

What does myelin do on the neurons?

A

myelinated neurons increase the speed at which electrical impulse is propogated in vertebrates
-dielectric property of myelin (80% lipid & 20 % protein) insulates the axon

153
Q

What is myelin made out of?

A

Very rich in sphingomyelin

154
Q

True or false, myelin is not continuous

A

True, nodes of Ranvier separate myelin on the axon

155
Q

What are the nodes of Ranvier?

A

Places on the axon where you find voltage gated channels

  • nodes are located between adjacent Schwann cells
  • channels open in response to voltage change
156
Q

What is the name of the cell that makes myelin?

A

Schwann cells

157
Q

What 2 types of lipids are found predominantly on the outside of the membrane?

A

Sphingomyelin (SM) and phosphatidylcholine (PC)

158
Q

What three lipids are found predominantly on the inside of the membrane?

A

Phosphatidylethanolamine (PE), phosphatidylinositol (PI), and phosphatidylserine (PS).

159
Q

What lipid is found equally on both sides of the bilayer?

A

Cholesterol (Cl)

160
Q

What is meant by the term electrogenic pump? Give an example.

A

A pump that generates a concentration gradient and a difference in charge across the membrane.
ex. Na+/K+ ATPase

161
Q

What system is unique to eukaryotic cells?

A

The Endomembrane system

162
Q

What organelles does the Endomembrane system contain?

A
  • Endoplasmic Reticulum (ER) contiguous to the nuclear envelope
  • Golgi complex
  • endosomes
  • lysosomes (vacuoles)
  • secretory vesicles
163
Q

What 2 things do a neuron and baker’s yeast have in common?

A

They have an Endomembrane system and they are both polarized cells

164
Q

Where is sphingomyelin made?

A

Sphingomyelin is synthesized in the Golgi from precursors from the ER

165
Q

Where are proteins and lipids made?

A

Proteins are synthesized in the rough ER and lipids are synthesized in the smooth ER

166
Q

What are the physical features of the ER?

A
  • Composed of a network of flattened sacs (cistenae)
  • Continuous with the outer membrane of the nuclear envelope
  • Can have ribosomes on its cytosolic surface.
  • Makes contact with ALL organelles
167
Q

True or false, the composition of the luminal space inside ER membranes is the same as the surrounding cytosolic space.

A

False, it is different

168
Q

True or false, all cells have the same composition of the two types of ER.

A

False, Different types of cells have different ratios of the two types of ER, depending on activities of the cell.
ie. Muscle cells have mostly smooth ER and pancreatic cells have mostly rough ER

169
Q

What are polysomes and where are they found?

A

Many ribosomes translating the same mRNA at the same time in different phases and they form a spiral shape. They are found in the rough ER

170
Q

Where are membrane lipids (glycerolipids, sterols, and ceramide) synthesized?

A

In the rough ER

171
Q

Where are ALL extracellular proteins made?

A

In the rough ER

172
Q

The rough ER serves as a pathway for the synthesis and integration of all integral membrane proteins except for:

A

Integral membrane proteins found in the mitochondria and chloroplast

173
Q

What two types of proteins are made in the rough ER and stay there? What are their functions?

A

Chaperones and Quality control of proteins;

  • Chaperones and other complexes assist proper protein insertion into the membrane or assures soluble protein conformation and location (lumen of RER or in cytoplasm)
  • Quality control proteins ensure that misfolded proteins are targeted and degraded properly
174
Q

What types of proteins are made in the cytosol by ribosomes?

A
  1. cytosolic proteins
  2. peripheral membrane proteins,
  3. nuclear proteins,
  4. proteins incorporated into chloroplasts, mitochondria, and peroxisomes
175
Q

What is the most conserved pathway in eukaryotic cells?

A

The secretory pathway

176
Q

What is the name of the protein that recognizes the protein signal sequence?

A

Signal reception protein (a ribonucleoprotein complex)

177
Q

What is a G protein?

A

Proteins that can hydrolyze GTP

178
Q

What is topology?

A

The way a membrane protein is arranged in the membrane

179
Q

What determines topology?

A

Charge drives topology; ie. Where the positive charge is localized (dependent on amino acid residues Lys and Arg)

180
Q

What specific amino acid sequence does N-linked glycosylation target?

A

Asn-(any a.a.)-Ser/Thr

181
Q

What are the three terminal glucose residues?

A

Glucose, mannose, and N-acetylglucosamine

182
Q

What is the name of the enzyme that transfers the oligosaccharide group from the lipid bilateral to the protein in N-linked glycosylation? How does it do this?

A

Oligosaccharyl transferase; it cleaves the oligosaccharide away from the phosphate group in the bilayer and binds it to the Asn group in the a.a. targeting sequence.

183
Q

Where are ALL misfolded proteins destroyed and what are they destroyed by?

A

Destroyed in the cytoplasm by proteasomes.

184
Q

What is Calnexin?

A

Chaperone that recognizes misfolded

GLYCOproteins; uses glucose as a signal

185
Q

What are BiP + membrane sensor proteins

A

chaperones that recognize misfolded proteins

186
Q

How are misfolded proteins targeted for refolding?

A

Misfolded proteins are tagged by a terminal
glucose and recognized by chaperones for
refolding.

187
Q

How are proteins targeted for degradation?

A

When proteins are polyubiquitinated this is a target for degradation by the proteasome

188
Q

What is the function of clathrin?

A

Clathrin mediates Golgi to and endosome transport, and plasma membrane to endosome transport.

189
Q

What types of chains does the Clathrin triskelion have?

A

3 heavy chains and 3 light chains; at its ends it has globular proteins

190
Q

What is the structure of the vesicles that are typically found between the Golgi and the plasma membrane (ie. Clathrin)?

A

Polyhedral

191
Q

Where are ALL coating proteins found? What types of proteins are they when they are bound to vesicles?

A

Found in the cytosol; they are peripheral membrane proteins when bound

192
Q

How do vesicles travel?

A

Travel down microtubules via motor proteins

193
Q

True or false, motor proteins only walk in 1 direction

A

True

194
Q

Why does the vesicle coat have to be removed?

A

Prevents vesicles from fusing

195
Q

When vesicles fuse what is the structure called?

A

A vesicular tubule cluster

196
Q

True or false, the movement of vesicular tubular clusters diffuse down their concentration gradient until they reach the plasma membrane.

A

False, VTC’s are moved by motor proteins down microtubules in an ATP-dependent process

197
Q

Other than movement, what is one of the functions of retrograde transport?

A

Removes certain compounds, purifying and concentrating the secretory cargo further.

198
Q

What do SNARE’s do?

A

Provide specificity to fusion

199
Q

How is specificity of the fusion reaction of vesicles accomplished?

A

V-SNAREs and T-SNAREs; and Rab-GTP and Rab-effector

200
Q

How are v-SNAREs recruited?

A

Incorporated into transport vesicles during budding

201
Q

What is the sequence of the vesicle arriving at the membrane?

A

Tethering, docking, fusion

202
Q

What signals tethering and docking of a vesicle?

A

Ca2+

203
Q

For a monomeric GTPase (G protein) to hydrolyze GTP what must it come into contact with?

A

A GTPase activating protein

204
Q

How does an inactive monomeric GTPase (G protein) get GTP?

A

Trades it’s GDP for a GTP when it makes contact with the Guanine Nucleotide Exchange Factor.

CMMB (5 decks)

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