Midterm 3 Flashcards

(107 cards)

1
Q

Why are membranes important to organisms?

A
  • Surround cells, organelles, and other structures
  • Gatekeeper for entry and exit of molecules
  • Transmits signals from outside to inside of cells
  • Location of key reactions in cells
    - mitochondrial membrane site of ATP
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2
Q

What is the composition of membranes?

A

mixed with lipids and proteins

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3
Q

What are the Lipids involved in the membrane?

A
  • Major Phospholipids = Glycerophospholipids and Sphingolipids
    Glycerophospholipids includes:
    Phosphatidylcholine and Phosphatidylethanolamine
  • Sterol = major sterol is cholesterol
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4
Q

What are the proteins involved in the membrane?

A
  • mostly containing proteins
  • often contain carbohydrates that are glycosylated
  • makes up 75% = more than the lipid bilayer — packed proteins
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5
Q

Membrane lipids form a bilayer

A

polar head group = faces out
fatty acids = faces in
two layers = fatty acids are not exposed to water

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6
Q

Why does the bilayer fold into a sphere?

A
  • fatty acids are not exposed to water
  • it creates inner aqueous cavity (cytosol) which holds the cell contents
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7
Q

Lipids can also form micelles, what are micelles?

A
  • single layer that does not contain an aqueous cavity
  • formed by fatty acids (not phospholipids)
    - wedge shape of fatty acids encourages the formation
  • micelles are formed during the digestion of fats
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8
Q

Membranes are asymmetric, what does this mean?

A
  • leaves of the bilayer are asymmetric = one leaf may have the components while the other leaf does not.
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9
Q

Examples of membranes being asymmetric.

A

ER and Golgi
- starts symmetric in the ER and becomes asymmetric in the Golgi

Plasma Membranes are also asymmetric

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10
Q

What is added to the Golgi that makes it asymmetric?

A

Sphingolipids

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11
Q

What are the 3 types of protein?

A

Integral
Peripheral
Amphitrophic

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12
Q

What are integral proteins?

A
  • embedded in the bilayer

two types:
- monotopic ( one leaflet)
- polytopic (both leaflets (top and bottom))

  • can only be removed chemically in the lab with detergents
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13
Q

What is the structure of an integral protein?

A
  • hydrophobic = non polar = embedded in the membrane
  • hydrophilic = polar = not embedded in the membrane
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14
Q

What does it mean when the hydropathy index is higher/positive

A

Amino acid is more hydrophobic

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15
Q

What is the hydropathy index?

A
  • it measures how hydrophobic an amino acid is
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16
Q

_______ define the different regions

A

Amino Acids

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17
Q

Hydrophobic regions have

A

amino acids that have high hydropathy index

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18
Q

Regions with high hydropathy index will likely to be

A

integral proteins

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19
Q

__________ are common in regions embedded in membrane

A

certain protein structures

– ∂ helix
– ß barrel ( r groups are facing outwards)

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20
Q

What are the amino acids that are common at the outer edge of the membrane

A

Tyr and Trp

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21
Q

Tyr and Trp have

A

r groups that have intermediate hydropathy index = nonpolar or neither polar (good for this environment)
- Large R groups = better for stability and serves as an anchor

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22
Q

What are peripheral proteins?

A
  • can be chemically removed in the lab via high ph and carbonate (used too purify the protein)
  • peripheral proteins are attached to integral proteins via hydrogen bonds and electrostatic interactions
  • attached to integral but not embedded in the membrane
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23
Q

What is amphitropic proteins?

A
  • Proteins that are 50/50 when attaching to membranes (sometimes attached sometimes not)
  • the attachment is regulated biologically by the cells
  • can attach end detaches which is controlled by cells (enzymes)
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24
Q

Example of amphitropic proteins?

A
  • GPI anchor proteins
    • linked to membrane lipid through an oligosaccharide
    • releases when an enzyme (phospholipase C cleaves oligosaccharides
      from lipids)
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25
T/F: The membrane has a dynamic environment
T
26
Membranes are ________
stable, not static
27
Lipids and proteins move very fast, how do scientists see this movement?
FRAP - fluorescence we recovery after photobleaching
28
It was mentioned that lipids and proteins move very fast, why is the movement restricted?
- movement can only occur within a leaflet - movement to another leaflet is very slow if uncatalyzed
29
Movement to another leaflet is possible when?
there are enzymes available flippase, floppase, scramblase
30
restricted enzymes partly explain what?
lipids and proteins are asymmetric
31
How are rafts formed?
sphingolipids and cholesterol
32
What are the reasons for rafts?
- sphingolipids have long saturated chains - cholesterol has long rings = together they are stable than glycerophospholipids
33
What other certain proteins are found in rafts?
- GPI linked proteins = long lipid anchors - proteins with hydrophobic regions that are long
34
What do rafts form?
caveolae
35
What do caveolae make in the process?
- inward curves of membranes - caveolae = little caves - can be seen with an electron microscope - formed by the protein caveolin
36
What are protein caveolin?
- they are found on inner leave of rafts - form dimer to pus membrane inwards
37
T/F: Membranes fuse with each other constantly
T
38
T/F: can membranes fuse spontaneous or protein mediated?
T
39
What are the rules of neurotransmitter release?
- neurotransmitter is release via exocytosis - vesicles are full and approach plasma membrane - fuse with membrane releasing neurotransmitter outside of cell (into synapse) - fusion is mediated by SNARE proteins - V-SNARE on vesicles binds to T-SNARE on plasma membrane
40
Why is solute transport important to cells?
- cells must take up nutrients and release waste products - few molecules can cross the membrane unassisted
41
What is simple diffusion?
- molecules that can cross the membrane unassisted
42
Example of simple diffusion?
- water - nonpolar molecules
43
What is not possible in simple diffusion?
- polar molecules (energetic barrier) - molecules that have coat of water (hydration shell) - shell must shed before crossing the membrane - shedding shell is energetically unfavorable
44
What is a transporter?
- offers an alternate path - energetic barriers is lower - molecules that have the hydration shell must ched - transporters form a hydrophilic pathway - forms hydrogen bonds with molecules + replaces hydrogen bonds with water
45
What are the two types of transport?
- passive - active
46
What is passive transport?
- goes along with the conc. gradient - facilitated diffusion (another term) -- this passive transport goes along with the conc gradient NOT against - molecules cannot be concentrated in the cell -- electrically charged molecules must go along with their electrical gradient
47
What is active transport?
- against the conc. gradient or electrical gradient - needs input of energy.
48
Two types of active transport?
Primary and Secondary
49
what is primary active transport?
needs atp --- atp is the source of energy
50
what is secondary active transport?
- second solute is the source of energy = second solute have to move with gradient
51
What are the methods of transport?
- uniport - cotransport
52
what is a uniport?
one solute is transported
53
what are the two types of cotransport?
symport - two solute same direction antiport - two solutes opposite direction
54
What are the types of transport?
- carrier - channel - ion channel
55
What is carrier transport?
- solute binds to carrier - specific for certain solutes
56
what is channel transport?
- solutes flow through without binding - very fast
57
what are ion channels?
- gated to control flow - may be gated on one or both sides
58
What mediates passive transport of glucose?
GLUT1
59
How does GLUT 1 mediate passive transport of glucose?
- transporter in erythrocytes - speeds entry of glucose 50,000 fold over simple diffusion - carrier that binds to glucose 1. glucose enters from outside 2. glucose binds 3. conformation changes 4. glucose released inside - transport is passive - of higher glucose conc. inside --> direction reversed
60
What does the transport of glucose follow?
Michaelis-Menten Kinetics
61
What is the Km to transport glucose?
Km = 3mM - close to the concentration of glucose in the blood (5mM)
62
How is the transport of other carbohydrates possible?
-higher Km - shows binding of carrier to glucose is specific
63
What is a member of a large family of glucose transporters?
GLUT1 to GLUT2 -- differ in tissues, Km and roles
64
What mediates active transport of ions?
NA+K ATPase
65
How does Na+K+ATPase mediate active transport ofions?
- important to maintining correct balance of ions-across membranes -antiport of Na+ and K+ - Na out & K in - driven by ATP energy - in humans, accounts for 25% of energy consumption at rest - member of P-type ATPase transporter - differ by types of ions transported
66
What kind of transport does lactose permease have?
Secondary active transport
67
What is lactose responsible for?
- uptake of lactose in ecoli
68
What type of transport does lactose use?
secondary active transport - H+ gradient drives the transport
69
How is H+ built up?
another transporter = proton pump
70
What would happen to the H+ gradient is there is no proton pump?
gradient will be depleted
71
What are aquaporins?
moves water through channels -important for cells and tissues that produce liquid -ex. glands - this shows that passive diffusion has its limits even with water - channels are narrow - water molecules flow in single file - ions cannot pass - very very fast ++ faster that catalase
72
What are Ionophores?
they interfere with transport
73
How does ionophores interphere with transport?
- they shuttle positively charged ions across the membranes -no transporters involved - it collapse the ion gradients that are made by Na+ K+ ATPase
74
What is the mechanism of ionophores?
- bind positively charged ions - surround charged with lipophilic ring - pass through the membrane - releasing ions to the other side
75
How does ionophores apply in animals?
used for weight gain in cattles acts as an antibiotic towards bad rumen bacteria - ones that lead to production to methane, lactate and degrade amino acids
76
Why is biosignaling important?
- cells receive constant input from its surroundings (nutrients, hormones, light and chemicals) - need to respond to these signals - signal transduction = transmission of signal from out to inside the cell
77
What is signaling in a nutshell?
- ligand binds to receptor membrane -receptor sends signal inside the cell -signal acts on target - phosphorylated protein alters activity of enzyme
78
What are the four types of signaling?
- G-protein coupled receptor - Receptor enzyme - Gated ion channels - Nuclear receptor
79
G-protein coupled receptor
--- generates intracellular secondary messenger 1. ligand binds receptor 2. receptor activates g-protein 3. g-protein activates enzymes 4. enzymes generate secondary messenger 5. secondary messenger to target
80
Receptor Enzyme
- Phosphorylate intracellular proteins 1. ligand binds to receptor 2. receptor phosphorylates itself 3. receptor phosphorylates intracellular proteins 4. proteins acts on target
81
Gates ion channels
- increase ion conc. in cells 1. ligand binds to receptor 2. gate on receptors open 3. ions flood in 4. ions activate intracellular proteins or other channels
82
Nuclear receptor
1. ligand crosses cell membrane 2. ligand binds receptors in nucleus 3. receptor regulates expression of gene
83
What are the shared feautures of biosignaling?
-specificity - amplification - modularity - integration - desensitization - localized response
84
What is specificity?
- ligands are specified to fit a certain receptor - no other ligands can fit
85
What is amplification?
- increase by enzymes - enzyme cascade
86
What is modularity?
- multiple and interchangeable parts - phosphorylation = reversible points of interaction
87
What is integration?
- 2 signalling pathways may produce the same secondary messenger
88
What is desensitization?
-self limiting
89
what is localized response?
- second messengers are quickly degraded - response = localized and brief
90
ß - adregernic pathway + G protein coupled receptor
Purpose: mediates response to epinepherine Receptor: ß - adergernic pathway Target: enzymes regulated by epinepherine
91
What are the steps of the ß- adrenergic pathway + G protein-coupled receptor
1. epinephrine binds to receptor 2. GTP binding protein releases GDP and bonds GTP 3. Gs∂ dissociates from GTP binding protein 4. Gs∂ activates adenylyl cyclase 5. Adenylyl cyclase activates cAMP 6. cAMP forms pKA 7. pKA phosphorylates target protein
92
What are the shared features of ß- adrenergic pathway?
- amplification ---- one epinephrine release 100,000 glucose from glycogen - desensitization --- Gs∂ diassociates --> GsBY is left behind = triggers sequence of events + ß-adernergic receptor is removed from plasma membrane - localized response --- Gs∂ eventually hydrolyzes GTP to GDP ==== GTP will no long be able to stimulate adenylyl cyclase
93
What is the antagonist in the ß adrenergic pathway receptor?
Ractopamine
94
What is Ractopamine?
- antagonist of the ß-adrenergic receptor - used commercially in pigs and cattle operations (Paylean) - stimulates protein synthesis in muscle and lipolysis in adispose tissue - leaner and larger muscles
95
What is Ractopamine?
- agonist of the ß-adrenergic receptor - used commercially in pigs and cattle operations (Paylean) - stimulates protein synthesis in muscle and lipolysis in adipose tissue - leaner and larger muscles
96
What is an agonist?
- ligand activating
97
Two-component enzyme in Ecoli = receptor enzyme
- Purpose = steers bacteria to swim towards sugars and other nutrients - Receptor - histidine kinase - Target - flagellum
98
What are the steps of a two-component enzyme in Ecoli = receptor enzyme
1. nutrients bind to the receptor 2. receptor kinase autophosphorylates 3. receptor kinase 4. phosphorylate the response regulator Asp 5. response regulator triggers the flagellum to propel forward
99
What is Ractopamine?
- antagonist of the ß-adrenergic receptor - used commercially in pigs and cattle operations (Paylean) - stimulates protein synthesis in muscle and lipolysis in adipose tissue - leaner and larger muscles
100
What is Ractopamine?
- antagonist of the ß-adrenergic receptor - used commercially in pigs and cattle operations (Paylean) - stimulates protein synthesis in muscle and lipolysis in adipose tissue - leaner and larger muscles
101
Receptor Tyrosine Kinase in mammals = receptor enzymes
Purpose: promote cell division in response to insulin Receptor: Insulin Receptor Target: expression of genes for cell division
102
What are the steps of receptor tyrosine kinase in mammals = receptor enzyme
1. insulin binds to the receptor 2. Insulin receptor autophosphorylates 3. Insulin receptor phosphorylates IRS-1 4. Another protein ERK is phosphorylated 5. ERK activates nuclear transcription factors 6. Genes for cell division expressed
103
Ion channels in neutral transmission = ion channels
purpose: transmits nerve impulse down nerve cell receptor: Na+ and Ca+ channels Target: downstream channels + vesciels containing neurotransmitter
104
What are the steps in ions channels in neural transmission = ion channels
1. stimulus causes a few voltage-gated 2. Na+ channels to open Na+ rushes in, causing depolarization (positive membrane potential) 3. More Na+ channels opens = domino effect 4. Ca2+ channels open 5. High [Ca 2+] triggers exocytosis of vesicles containing acetylcholine 6. Acetylcholine triggers the same events in the next neuron
105
Estrogen receptor = nuclear receptor
Purpose: mediates the response to estrogen Receptor: Estrogen receptor Target: gene expression in nucleus
106
What are the steps of estrogen receptor = nuclear receptor
1. Estrogen binds nuclear receptor 2. Estrogen-receptor complex binds other complexes 3. Complexes bind to hormone response elements in DNA 4. Coactivator or corepressor proteins are recruited 5. Transcription of adjacent genes is altered
107
What is tamoxifen?
- used in the treatment of breast cancer - types caused by estrigen - antagonist for receptor - ligand that binds receptor, has little effect on gene expression - blocks the effect of estrogen -slows or stops growth of cancer cells - a form of hormonal therapy - used in combination with chemotherapy or surgery to remove most cells