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ABI 102 WINTER QTR > Midterm 3 > Flashcards

Midterm 3 Flashcards

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
Q

T/F: The membrane has a dynamic environment

A

T

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26
Q

Membranes are ________

A

stable, not static

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27
Q

Lipids and proteins move very fast, how do scientists see this movement?

A

FRAP - fluorescence we recovery after photobleaching

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28
Q

It was mentioned that lipids and proteins move very fast, why is the movement restricted?

A
  • movement can only occur within a leaflet
  • movement to another leaflet is very slow if uncatalyzed
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29
Q

Movement to another leaflet is possible when?

A

there are enzymes available
flippase, floppase, scramblase

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30
Q

restricted enzymes partly explain what?

A

lipids and proteins are asymmetric

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31
Q

How are rafts formed?

A

sphingolipids and cholesterol

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32
Q

What are the reasons for rafts?

A
  • sphingolipids have long saturated chains
  • cholesterol has long rings
    = together they are stable than glycerophospholipids
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33
Q

What other certain proteins are found in rafts?

A
  • GPI linked proteins = long lipid anchors
  • proteins with hydrophobic regions that are long
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34
Q

What do rafts form?

A

caveolae

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35
Q

What do caveolae make in the process?

A
  • inward curves of membranes
  • caveolae = little caves
    - can be seen with an electron microscope
  • formed by the protein caveolin
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36
Q

What are protein caveolin?

A
  • they are found on inner leave of rafts
  • form dimer to pus membrane inwards
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37
Q

T/F: Membranes fuse with each other constantly

A

T

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38
Q

T/F: can membranes fuse spontaneous or protein mediated?

A

T

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39
Q

What are the rules of neurotransmitter release?

A
  • 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
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40
Q

Why is solute transport important to cells?

A
  • cells must take up nutrients and release waste products
  • few molecules can cross the membrane unassisted
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41
Q

What is simple diffusion?

A
  • molecules that can cross the membrane unassisted
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42
Q

Example of simple diffusion?

A
  • water
  • nonpolar molecules
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43
Q

What is not possible in simple diffusion?

A
  • 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
Q

What is a transporter?

A
  • 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
Q

What are the two types of transport?

A
  • passive
  • active
46
Q

What is passive transport?

A
  • 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
Q

What is active transport?

A
  • against the conc. gradient or electrical gradient
  • needs input of energy.
48
Q

Two types of active transport?

A

Primary and Secondary

49
Q

what is primary active transport?

A

needs atp

— atp is the source of energy

50
Q

what is secondary active transport?

A
  • second solute is the source of energy
    = second solute have to move with gradient
51
Q

What are the methods of transport?

A
  • uniport
  • cotransport
52
Q

what is a uniport?

A

one solute is transported

53
Q

what are the two types of cotransport?

A

symport - two solute same direction
antiport - two solutes opposite direction

54
Q

What are the types of transport?

A
  • carrier
  • channel
  • ion channel
55
Q

What is carrier transport?

A
  • solute binds to carrier
  • specific for certain solutes
56
Q

what is channel transport?

A
  • solutes flow through without binding
  • very fast
57
Q

what are ion channels?

A
  • gated to control flow
  • may be gated on one or both sides
58
Q

What mediates passive transport of glucose?

A

GLUT1

59
Q

How does GLUT 1 mediate passive transport of glucose?

A
  • 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
Q

What does the transport of glucose follow?

A

Michaelis-Menten Kinetics

61
Q

What is the Km to transport glucose?

A

Km = 3mM
- close to the concentration of glucose in the blood (5mM)

62
Q

How is the transport of other carbohydrates possible?

A

-higher Km
- shows binding of carrier to glucose is specific

63
Q

What is a member of a large family of glucose transporters?

A

GLUT1 to GLUT2
– differ in tissues, Km and roles

64
Q

What mediates active transport of ions?

A

NA+K ATPase

65
Q

How does Na+K+ATPase mediate active transport ofions?

A
  • 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
Q

What kind of transport does lactose permease have?

A

Secondary active transport

67
Q

What is lactose responsible for?

A
  • uptake of lactose in ecoli
68
Q

What type of transport does lactose use?

A

secondary active transport
- H+ gradient drives the transport

69
Q

How is H+ built up?

A

another transporter = proton pump

70
Q

What would happen to the H+ gradient is there is no proton pump?

A

gradient will be depleted

71
Q

What are aquaporins?

A

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
Q

What are Ionophores?

A

they interfere with transport

73
Q

How does ionophores interphere with transport?

A
  • they shuttle positively charged ions across the membranes
    -no transporters involved
  • it collapse the ion gradients that are made by Na+ K+ ATPase
74
Q

What is the mechanism of ionophores?

A
  • bind positively charged ions
  • surround charged with lipophilic ring
  • pass through the membrane
  • releasing ions to the other side
75
Q

How does ionophores apply in animals?

A

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
Q

Why is biosignaling important?

A
  • 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
Q

What is signaling in a nutshell?

A
  • ligand binds to receptor membrane
    -receptor sends signal inside the cell
    -signal acts on target
    • phosphorylated protein alters
      activity of enzyme
78
Q

What are the four types of signaling?

A
  • G-protein coupled receptor
  • Receptor enzyme
  • Gated ion channels
  • Nuclear receptor
79
Q

G-protein coupled receptor

A

— 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
Q

Receptor Enzyme

A
  • Phosphorylate intracellular proteins
    1. ligand binds to receptor
    2. receptor phosphorylates itself
    3. receptor phosphorylates intracellular proteins
    4. proteins acts on target
81
Q

Gates ion channels

A
  • 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
Q

Nuclear receptor

A
  1. ligand crosses cell membrane
  2. ligand binds receptors in nucleus
  3. receptor regulates expression of gene
83
Q

What are the shared feautures of biosignaling?

A

-specificity
- amplification
- modularity
- integration
- desensitization
- localized response

84
Q

What is specificity?

A
  • ligands are specified to fit a certain receptor
  • no other ligands can fit
85
Q

What is amplification?

A
  • increase by enzymes
  • enzyme cascade
86
Q

What is modularity?

A
  • multiple and interchangeable parts
  • phosphorylation = reversible points of interaction
87
Q

What is integration?

A
  • 2 signalling pathways may produce the same secondary messenger
88
Q

What is desensitization?

A

-self limiting

89
Q

what is localized response?

A
  • second messengers are quickly degraded
  • response = localized and brief
90
Q

ß - adregernic pathway + G protein coupled receptor

A

Purpose: mediates response to epinepherine
Receptor: ß - adergernic pathway
Target: enzymes regulated by epinepherine

91
Q

What are the steps of the ß- adrenergic pathway + G protein-coupled receptor

A
  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
Q

What are the shared features of ß- adrenergic pathway?

A
  • 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
Q

What is the antagonist in the ßadrenergic pathway receptor?

A

Ractopamine

94
Q

What is Ractopamine?

A
  • 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
Q

What is Ractopamine?

A
  • 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
Q

What is an agonist?

A
  • ligand activating
97
Q

Two-component enzyme in Ecoli = receptor enzyme

A
  • Purpose = steers bacteria to swim towards sugars and other nutrients
  • Receptor - histidine kinase
  • Target - flagellum
98
Q

What are the steps of a two-component enzyme in Ecoli = receptor enzyme

A
  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
Q

What is Ractopamine?

A
  • 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
Q

What is Ractopamine?

A
  • 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
Q

Receptor Tyrosine Kinase in mammals = receptor enzymes

A

Purpose: promote cell division in response to insulin
Receptor: Insulin Receptor
Target: expression of genes for cell division

102
Q

What are the steps of receptor tyrosine kinase in mammals = receptor enzyme

A
  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
Q

Ion channels in neutral transmission = ion channels

A

purpose: transmits nerve impulse down nerve cell
receptor: Na+ and Ca+ channels
Target: downstream channels + vesciels containing neurotransmitter

104
Q

What are the steps in ions channels in neural transmission = ion channels

A
  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
Q

Estrogen receptor = nuclear receptor

A

Purpose: mediates the response to estrogen
Receptor: Estrogen receptor
Target: gene expression in nucleus

106
Q

What are the steps of estrogen receptor = nuclear receptor

A
  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
Q

What is tamoxifen?

A
  • 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

ABI 102 WINTER QTR (4 decks)

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