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BIOCHEM 405 > Lecture 14 > Flashcards

Lecture 14 Flashcards

1
Q

passive transport

A

type of facilitated diffusion

transport of substrate along its concentration gradient

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2
Q

active transport

A

type of facilitated diffusion

move a substrate against its concentration gradient- requires an input of free energy

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3
Q

na- k pump

A

Na+ and K+ pump acts in all cells to maintain higher concentrations of K+ inside and Na+ outside

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4
Q

How to move Molecules using a Concentration Gradient Diffusion and Facilitated Diffusion

A

Ionophores, Ion Channels, Transporters

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5
Q

How to move material against a Concentration Gradient Active Transport – requires energy

A

Use Proton, Ion, or other concentration gradients

ATP-dependent transport

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6
Q

How to get really big stuff across a membrane

A

Clathrin-mediated Endocytosis – next quarter

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7
Q

How to Transfer Information Across a Membrane (2 Examples)

A

Insulin Receptor, G-Protein Coupled Receptors

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8
Q

hormones and signaling

A

act through second messengers- involve a 3- protien module- receptor, transducer (g-protein), and effector (adenylate cyclase or related enzyme)

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9
Q

To cross a membrane you need an energy source Energy is available from a concentration gradient

A

if ions are involved- there is also a membrane potential (delta V)

before Equil net flux
ΔG < 0

at equil no net flux

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10
Q

Negative ΔG -

A

Movement down concentration gradient

transport can be passive

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11
Q

Positive ΔG –

A

Movement against concentration gradient
requires energy (ATP or Concentration Gradients)
Transport must be an active process

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12
Q

To cross a membrane a molecule must be permeable to the lipid bilayer –

A

Passive Diffusion driven by concentration differences

Diffusion across a membrane Correlates with size and water solubility

H20, CO2, & O2 readily cross the membrane

The concentration of water on both sides of the membrane is very high (55M).

Osmotic Pressure drives the movement of water – minimize the difference in solute concentration across the membrane

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13
Q

permeabilities

H2O
Indole
Glucose
Na+
K+
A 
water-5x10-3
indole- 2x10-4
glucose- 4x10-10
Na+ <1.6x10-13
K+ <9x10-1
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14
Q

Selective Permeability - Facilitated Diffusion

A
  1. Build a peptide cage to replace solvent shell & increase permeability
  2. Direction dependent on concentration difference
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15
Q

Valinomycin (Ionophore)

A

No energetic cost for binding K+
Increases Permeability of K+
30000x preference for K+ over Na+

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16
Q

Facilitated Diffusion: Ion Channels

The Potassium Ion Channel has a selectivity filter

A

K+ Channel is a tetramer

K+ Channel pore is lined with backbone carbonyls

Perfect diameter to
“solvate” K+

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17
Q

Facilitated Diffusion: Ion Channels

The Potassium Ion Channel has a selectivity filter

A

Flow of ions through a channel must be tightly controlled
• ion channels have open and closed conformations
• ligand-gated and voltage-gated ion channels

Exchange solvent shell with coordination by backbone carbonyl groups in the channel

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18
Q

AquaPorins

A

Allows rapid movement of water across the cell membrane

Tetramer with four 2.8Å Pores
Engineered only for water
Excludes ions
Excludes H+ (H3O+)
Equalizes Osmotic Pressure without disrupting ion and H+ gradients
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19
Q

Passive vs. Facilitated Diffusion

A 
Facilitated Diffusion:
• greatly increases Permeability
• is highly Selective
• depends on a limited # of proteins
• rate of diffusion can be Saturated
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20
Q

permeability of water and glucose in synthetic and erythrocyte membrane

A

water- S- 5x10-3 E- 5x10-3

Glucose- S- 4x10-10 E- 2x10-5

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21
Q

Facilitated Diffusion
Family of Glucose Transporters
Glut1 permease

A

Glut1 permease: plasma membrane of erythrocytes
• 12 membrane-spanning helices
• Passive transport - driven by concentration gradient - reversible
• Specific for D-glucose
• Switches between 2 protein conformations (never an open pore)
• Allows for high rates of diffusion across the membrane
• Rate of diffusion shows saturation behavior

22
Q

Facilitated Diffusion via Glucose Transporters

A

Works well for red blood cells - require only small amounts of energy

Large family of transport proteins (14 members grouped into 4 classes)
Class I members: Glut1-4

23
Q

Glut1 –

A

erythrocytes

24
Q

Glut2 –

A

Liver – generally transports glucose OUT for use by other tissue

25
Q

Glut3 –

A

neurons – highest affinity for D-glucose

26
Q

Glut4 –

A

adipose and muscle tissues

Stored in intracellular vesicles. Exposed on cell surface in response to
insulin

27
Q

Primary Active Transport: Requires Energy
Maintain Concentration Gradients
P-type ATPase & ABC-transporters

A

ATP drives conformational changes

1) Open on cytoplasmic side
2) Open on extracellular side

28
Q

ATP-dependent Transport - P-type ATPases

A

P-type ATPases are primarily used to maintain ion gradients (also transport some lipids – eg. flippase)

Phosphorylation & de-Phosphorylation of a critical Asp residue
Phosphorylation drives protein conformational changes and ion transport

29
Q

Ca+2 ATPase (SERCA)

A

pumps Ca+2 into sarcoplasmic reticulum

[Ca+2 cytoplasm] = 0.1mM [Ca+2 SR] = 1.5mM

30
Q

Cytosol

A

[K+] = 140mM [Na+] = 12mM

31
Q

Extracellular

A 
[K+] = 4mM
[Na+] = 145mM
32
Q

Mechanism of P-type ATPases
2 main states:
changes in conformation driven by ATP

A
  • Digitalis and Ouabain bind to the E2 conformation of the Na+/K + pump
  • Proton Pump Inhibitors (like Nexium and Prilosec) are used to treat acid reflux by inhibiting the gastric proton pump.
33
Q

ATP-dependent Transport – ABC Transporters

A

Large Family of Transporters
Transport amino acids, peptides, metal ions, lipids, bile salts, toxins and drugs against concentration gradients

  • Certain ABC Transporters are responsible for multi drug resistance
  • Defects in an ABC Cl- ion Transporter is associated with Cystic Fibrosis (build-up of mucus in the lungs).
34
Q

Secondary Active Transport:

Intestinal Glucose/Na+ Symporter

A

Secondary Active Transport
One solute moving down its concentration gradient can transport another moving against a gradient

(transporters in your intestine allows you to scavenge all the available glucose after a meal)

35
Q

Symport

A

– move molecules in
the same direction

Terms apply to both active
and passive transporters

36
Q

Antiport –

A

move molecules in
opposite directions

Terms apply to both active
and passive transporters

37
Q

Moving Information across a membrane
Features of Signal Transducing Systems

• Modularity

A

• Adapt similar structures to respond to different signals

38
Q

Moving Information across a membrane
Features of Signal Transducing Systems

• Specificity

A

• Specific receptor is responsive to a specific ligand

39
Q

Moving Information across a membrane
Features of Signal Transducing Systems

• Amplification

A

• One ligand binding event outside a cell can activate 1000s of enzymes inside a cell – large, rapid response

40
Q

Moving Information across a membrane
Features of Signal Transducing Systems

• Termination

A

• Mechanisms of turning off a signal

41
Q

Receptor Tyrosine Kinases (RTKs) –

A

Insulin Receptor

Large family of plasma membrane receptors

Extracellular ligand binding domain linked to an intracellular catalytic domain

Insulin Receptor is a
dimer. Other RTKs are monomers in the membrane.
Ligand binding induces dimerization and activation

42
Q

insulin

A
  • Insulin is a peptide hormone – dispersed via circulatory system
  • Binds to extracellular receptor domain
  • Binding activates Tyrosine Kinase catalytic domain inside the cell
43
Q

Receptor Tyrosine Kinases – Insulin Receptor

A

Ligand binding induces a conformational change
that brings kinase domains together

  • Kinase self-activation (Auto-Phosphorylation)
  • The start of a signaling cascade.
44
Q

Receptor Tyrosine Kinases – Insulin Receptor

A

One branch of Insulin Signaling triggers glucose uptake in muscle cells

Phospholipid modifications recruit new kinases to the membrane

45
Q

Transfer of Information linked to Cellular uptake of Glucose

A

(one of many cellular responses to insulin)

  • PDK1 (PIP3-dependent protein kinase) activation -> activation of additional kinases (signaling cascade)
  • promotes movement of Glut4 transporters, stored in the membranes of intracellular vesicles, to move to the plasma membrane
  • increased uptake and storage of Glucose
46
Q

What is are the structural changes behind activation of the Insulin Receptor
Tyrosine Kinase?

A

Movement and phosphorylation of the Activation Loop open up the kinase active
site.

47
Q

Information Transfer: G-Protein Coupled Receptors

A

Epinephrine binding outside stimulates cAMP production and Ca2+ influx

  • 7-Trans-membrane receptor (blue)
  • Ligand binding stimulates:
  1. Association of the G protein complex with the receptor
  2. Exchange of GTP for GDP on the α-subunit (orange)

• GTP binding leads to dissociation of the complex and activation of other enzymes or channels
(generate 2nd Messengers)

• One ligand bound receptor can activate multiple Gα subunits

• Slow hydrolysis of GTP
inactivates α-subunit and causes re-assembly of heterotrimeric G-Protein complex
(Built-in timing mechanism)

48
Q

Information Transfer: G-Protein Coupled Receptors

Signal Amplification - Generation of Second Messengers

A
  • GCPRs are responsible for most of the cellular responses to:
  • Hormones, Neurotransmitters, Senses (Light, Olifaction, Taste)
  • Different Heterotrimeric G-Proteins in Different Tissues determine response
  • Types of second messengers
  • cAMP, Ca2+
  • PIP2 converted by Phospholipase C into:
  • Diacylglycerol (DAG) and Inositol-1,4,5-trisphosphate (IP3)
  • 1/3 to 1/2 of all drugs on the market target GCPRs
  • Hypertension, cardiac arrhythmia, glaucoma, anxiety, migraine headaches
49
Q

Summary

Diffusion is Driven by Concentration Differences

A

• Understand the differences between Simple and Facilitated Diffusion
• Examples of facilitated Diffusion: Ionophores, Ion Channels, Glut1
Permease

50
Q

Summary

Active Transport

A
  • Transport against a concentration gradient requires energy
  • Understand the difference between Primary Active Transport (P-type ATPases) and Secondary Active Transport (Intestinal Glucose/Na+ Symporter)
51
Q

Summary

Movement of Information

A

• Receptor Tyrosine Kinases – Protein activation by Phosphorylation and phosporylation cascades

  • G-Protein-Coupled Receptors (GPCRs)
  • Generation of Second Messengers
  • Internal GTPase Clock to turn off signaling

BIOCHEM 405 (25 decks)

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