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BIOPHYSICS > LECTURE 6 (Membrane transport II) > Flashcards

LECTURE 6 (Membrane transport II) Flashcards

1
Q

What are the three classes of Primary active pumps?

A
  • P-class pumps (E1-E2 type pumps)
  • ABC (ATP binding cassette) transporters
  • FoF1 type pumps (ATP synthase complex)
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2
Q

What is the difference between a Uniporter, Symporter and Antiporter?

A

Uniporter = carries one molecule or ion

Symporter = carries two different molecules or ions in the same direction

Antiporter = carries two different molecules or ions in different directions

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3
Q

What equation shows the work performed by the cell when transporting against the gradient?

A

A = m R T ln C1/C2

A = work
m = substance mole quantity
C1 + C2 = substance concentrations in different compartments
R = gas constant
T = absolute temperature

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4
Q

What happens if substance is transported through electrically polarised membrane?

A

The work is performed against diffusion forces as well as electric forces of the membrane

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5
Q

What is Faraday’s number equal to?

A

1g-eqv ion charge

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6
Q

ATP-dependent ion pumps are grouped into classes based on what?

A
  • Transport mechanism
  • Genetic & Structural homology
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7
Q

What are the properties of Active transport?

A
  • Carries out by pumps
  • Pumps have high specificity and produce substance transport at high speed
  • Main function of pumps = maintenance of gradients which are necessary for the life of the cell
  • Pumps use energy from ATP-HYDROLYSIS or ENERGY OF LIGHT
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8
Q

What is ATP?

A
  • The cell’s energy shuttle
  • Composed of ribose (sugar), adenine (nitrogenous base) and three phosphate groups
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9
Q

What are the properties of ATP hydrolysis?

A
  • Hydrolysis breaks bonds between terminal phosphate groups
  • Exergonic reaction
  • Release of energy comes from the chemical change to a state of lower free energy, not from the phosphate bonds themselves
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10
Q

What is the difference between Exergonic and Endergonic reactions?

A

Exergonic reactions (catabolism) -> drive the formation of ATP (endergonic)

Endergonic reactions (cellular work) -> drive the hydrolysis of ATP (exergonic)

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11
Q

Describe the Na+/K+ pump

A
  • Expressed on plasma membranes of highest eukaryotes
  • High content in nerve cells
  • Integral glycoprotein
  • Contains 4 subunits (two alpha + two beta)
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12
Q

Describe the alpha and beta subunits of the Na+/K+ pump

A

SMALL BETA SUBUNITS
- outer surface of membrane
- join to membrane through oligosaccharides
- contains only 1 transmembrane domain

LARGE ALPHA SUBUNITS
- enzymatic activity
- 8-10 transmembrane domains
- P-PO4 and N (nucleotide connective) intracellular subunits

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13
Q

Describe how the Na/K+ pump works

A

1) Na+ in cytoplasmic side bind to the pump which causes it to be phosphorylated + conformational change -> binding site of ions moves to outer side of membrane -> STRONG ELECTROSTATIC REPULSION BETWEEN NA+ IONS -> ions released in extracellular space
2) conformational change -> bound Na+ faces outside + binding sites are altered -> ions released into intracellular space
3) 3 Na+ ions out, 2 K+ ions in

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14
Q

What is Ouabain?

A

Ouabain (G-STROPHANTHIN) is a plant-derived toxic substance traditionally used as an arrow poison in Eastern Africa.

Small doses = treats Hypotension, Angina Pectoris, Cardiac Arrhythmias

Large doses = can cause death
- Rapid twitching of the neck and chest muscles
- Respiratory distress
- Increased and irregular heartbeat
- Rise in blood pressure
- Convulsions
- Wheezing
- Clicking and Gasping rattling

MECHANISM:
blocks Na+/K+ ATPase -> Intracellular Na+ remains high -> Na+/Ca+ antiport cannot remove Ca+ ions from the cardiac muscles -> Intensification of myocardium contraction activity -> heart rate falls and increase in power -> accumulation of intracellular Na+ ions in cardiomyocytes sarcoplasm -> decrease in myocardium excitation -> rhythm functional changes

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15
Q

Describe the Ca2+ ATPase pump

A
  • Maintains maintenance of Ca2+ low content
  • Transport calcium from cytoplasm in the intracellular space
  • Located in Sarcoplasmic reticulum
  • Small cytoplasmic Ca2+ concentration compared with extracellular Ca2+
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16
Q

What is control of Ca2+ important for?

A
  • Transmitter release
  • Ion channel activation
  • Regulation of cytoplasmic enzymes
17
Q

What is the formation of the Ca2+ ATPase pump?

A
  • 2 subunits (large alpha + small beta)
  • Alpha subunit has Ca2+ ion binding + AMINOACYL RESIDUE in phosphorylating process
  • For every 1 ATP molecule, 2 Ca2+ ions
18
Q

What do mutations of Ca2+ ATPase result in?

A

Disorders of relaxation of skeletal muscle and tone increase

19
Q

Describe the Gastric mucosal H+/K+ ATPase

A
  • Integral membrane protein located on membranes connected with tubovascular and secretory channels of parietal cells
  • H+ ions in the secretory channels of parietal cells
  • 2 alpha + 2 beta subunits
    [ beta = regulatory role, alpha = H+ ions connective site and aspartate aminoacyl residue sites (phosphorylation) ]
20
Q

Which drugs are Proton pump inhibitors?

A
  • Omeprazole
  • Lansoprazole
  • Pantoprazole
  • Rabeprazole
21
Q

What is the function of P-type ATPases?

A

Ensure heavy metal transport in the cell membrane

22
Q

What is Menkes disease?

A

A disease caused by a defective ATP 7A gene that regulates the metabolism of copper in the body which primarily affects male infants

CAUSES:
Copper accumulates at ABNORMALLY LOW levels in the LIVER and BRAIN but HIGHER than normal in the KIDNEY and INTESTINAL LINING -> Affected infants born prematurely but seem normal at birth -> Symptoms appear after 6-8 weeks

SYMPTOMS:
- Floppy muscle tone
- Seizures
- Failure to thrive
- Subnormal body temperature
- Kinky, colourless/steel-coloured hair that breaks easily
- Extensive neurodegeneration of brain
- Osteoporosis
- Arterial dissection

23
Q

What is Wilson disease?

A

An autosomal recessive disorder that is caused by a mutation in gene ATP7B which prevents the body from expelling excess copper

CAUSES:
Copper builds up in the liver, brain, kidneys and eyes and over time the copper causes irreversible organ damage

TREATMENT:
- Penicillamine (removes excess copper with a zinc supplement)

24
Q

Describe ABC (ATP binding cassette) transporters

A

Transmembrane proteins that utilise the energy of ATP hydrolysis to carry out certain biological processes

PROPERTIES:
- 6/12 transmembrane helices with 2 ATP binding sites
- Translocate substances across membranes, translation of RNA & DNA repair
- Resistant to several drugs

25
Q

What happens in the Electron transport chain?

A

Electrons are passed from one protein in the transport chain to another in a series of REDOX REACTIONS -> Energy released is captured as a proton gradient used to make ATP (CHEMIOSMOSIS) -> Electron transport chain make up OXIDATIVE PHOSPHORYLATION

26
Q

What are the steps of Oxidative phosphorylation?

A

1) Delivery of electrons by NADH and FADH
2) Electron transfer and proton pumping
3) Splitting of oxygen to form water
4) Gradient-driven synthesis of ATP

27
Q

What is the difference between NADH and FADH?

A

NADH
- very good at donating electrons in redox reactions
- transfers electrons directly to complex I
- energy released + used to pump protons from matrix to inter membrane space

FADH
- not good at donating electrons
- transfers electrons to complex II
- does not pump protons across membrane

28
Q

What happens after NADH and FADH donate electrons?

A

Both complex I and II pass electrons to UNIQUINONE (Q) which is reduced to QH and travels through membrane -> delivers electrons to complex III -> more H+ pumped across membrane -> electrons delivered to CYTOCHROME C -> electrons moved to complex IV where electrons are passed to O2 to form H2O

29
Q

What is the function of the F-type pump?

A
  • Ensures the transport of protons from the mitochondrial matrix into the inter membrane space with ATP hydrolysis
  • Eliminates H+ gradient from inter membrane space into matrix + catalyses synthesis of ATP
30
Q

What are the inhibitors of F-type receptors?

A

Function: block H+ transport coupled to ATP synthesis or hydrolysis

INHIBITORS
- Oligomycin
- DCCD (dicyclohexylcarbodiimide) = reacts with carboxyl groups in hydrophobic environments forming a covalent adduct

31
Q

What happens in Brown fat?

A

Brown fat = participates in body thermal regulation

Brown fat mitochondria contain the UNIPORTER OF MITOCHONDRIAL MEMBRANES (UCP) -> UCP uncouples H+ flow from ATP synthesis by dissipating the proton gradient -> Instead of flowing through ATP synthase, protons escape through UCP uniporter and produce heat (do not produce ATP)

32
Q

What happens in Secondary Active Transport?

A

The movement of a driving ion down an electrochemical gradient is used to drive the uphill transport of another ion/molecule against a concentration/electrochemical gradient

33
Q

What are the two types of Active transport?

A

Cotransport = direction of transport is the same for both the driving ion and driven ion/molecule

Exchange = driving ion and driven ion/molecule move in opposite directions

34
Q

Define Concentrative capacity

A

A measure of how well the driven ion/molecule is concentrated against a concentration gradient

[defines the effectiveness of the transport process]

35
Q

What is the difference between Electrogenic/Electroneutral cotransporters/exchangers?

A

Electrogenic = A transporter that leads to the net translocation of charge across the membrane

Electroneutral = When no net charge is transported across the membrane per transport cycle

36
Q

What is the function of Kidneys?

A
  • Regulate concentration of electrolytes and water in the organism
  • Acid-base balance
  • Excretion of toxic metabolites
  • Filtration/reabsorption mechanisms
37
Q

Describe the reabsorption of glucose in the kidneys

A

1) In APICAL MEMBRANE of epitheliocytes of RENAL TUBULES glucose is transported through SYMPORT with Na+ (SGLT1/2)
2) In opposite site of cell towards interstitial fluid there is facilitated passive transporter GLUT-2 -> causes glucose passive diffusion towards PERITUBULAR BLOOD CAPILLARY -> Returns glucose back to circulatory system

38
Q
A

BIOPHYSICS (15 decks)

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