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1 - HB > Excitable cells and Cytoskeleton > Flashcards

Excitable cells and Cytoskeleton Flashcards

1
Q

What is the concentration of Na+, K+ and Cl- inside and outside of cells?

A

Na+ - higher outside than inside
inside = 15 mM
outside = 150mM

K+ - higher inside than outside
inside = 140 mM
outside = 5 mM

Cl-
inside = 9 mM
outside = 125 mM

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2
Q

What creates the chemical and electrical gradient in cells?

A

chemical gradient
- created by the Na-K+ pump

electrical gradient
- created by K+ leakage via ion channels
= creates potential difference due to higher negative charge within the cell

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3
Q

How does the Na-K+ pump work?

A

3 Na+ and ATP bind to the pump/transport protein
ATP is hydrolyses into ADP and Pi
- catalyses movement of Na+ outside
2 K+ bind and are moved in using the Pi from ADP

creates a chemical gradient

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4
Q

How does potassium leak from the cell?

A

potassium is higher in the cell than outside

potassium moves down the concentration down out of the cell
- high to low concentration
potassium leaves the cell via the K+ ion channel

leaves large inorganic anions in the cell
creates a separation of charge = means a voltage has been established
- more negative inside the cell than outside

creates a electrical gradient
- there is potential difference

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5
Q

What is membrane potential? What is resting potential?

A

membrane potential

  • voltage established across the membrane
  • can be used to send and receive signals

resting potential

  • membrane potential when the cell is not sending signals
  • normally -70mV in cells
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6
Q

What is an equilibrium potential of an ion, and how does it determine the membrane potential?

A

equilibrium potential
- membrane potential at which the electrical and chemical gradients of a specific ion are balanced

can be used to calculate the resting potential of a cell taking into account the multiple ion permeabilities

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7
Q

What does a change in membrane potential occur? What are the steps in change of membrane potential?

A

membrane potential changes because of gated ion channels
- open and close in response to stimuli

  • depolarisation
  • membrane potential is more positive then resting potential
  • Na+ influx only if the stimuli is strong enough to meet the threshold limit

repolarisation

  • membrane potential returns to resting potential
  • K+ moves out

hyperpolarisation

  • membrane potential is more negative than resting potential
  • excess K+ moves out
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8
Q

What is the purpose of hyperpolarisation? What is hyperpolarisation also known as?

A

hyperpolarisation

  • allows recovery
  • stops new action potentiel from being generated as the previous one is still present

also known as the refractory period

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9
Q

How does an action potential affect cardiac cell? How do they change in membrane potential?

A

stimuli causes depolarisation
depolarisation causes sodium channels to open
- sodium influx, membrane potential rises = more positive
repolarisation begins
- potassium channels open
- calcium channels are activated = causes a plateau as membrane potential is not able to drop as much, no overall change in membrane potential
repolarisation
- calcium channels close
- potassium channels are open = potassium ions move out of the cell
resting state
- most sodium and potassium channels are closed

controls rhythm and synchronicity of the contractions of the heart

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10
Q

What is the difference between neuronal and cardiac depolarisation?

membrane potential?
resting potential?
shape of action potential?
speed/duration of action potential?

A

neuronal

  • resting potential is -70 mV
  • has rapid depolarisation and repolarisation = angled peak
  • action potential last 5 milliseconds
  • threshold for sodium channels to open is -55mV

cardiac
- resting potential is -90 mV = more permeable to K+
- threshold for sodium channels to open is -40 mV
- has rapid depolarisation, plateau then rapid depolarisation
= due to calcium influx causing no overall change in membrane potential
- action potential lasts 300 milliseconds

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11
Q

What is the cytoskeleton? Why is it needed?

A

the cytoskeleton is the skeleton of the cell

is needed to keep the cells shape and modify it in response to environmental cues/changes

is dynamic

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12
Q

What are the different components of the cytoskeleton? What is their function?

A

microtubules
intermediate filaments
actin filaments
= microfilaments

needed for

  • shaping of the cell
  • intracellular movement of organelles
  • cell movement
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13
Q

What is the structure of microfilaments/actin? What are they made up of?

A

are twisted chains of monomers
- monomers of actin
are the thinnest of the cytoskeleton filaments
are polarised

G-actin = are the actin monomers
F -actin = filamentous form formed by G-actin (monomers) joining up

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14
Q

What are the different forms of actin?

A

there are three isoforms of actin
they are polarised
- have a positive end where addition of monomers is favoured and a negative end where addition is not favoured

alpha actin
- found in muscle cells

beta actin
- found in non-muscle cells

gamma actin
- found in non-muscle cells

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15
Q

How does actin polymerise? What does the length of filament depend on?

A

G actin join up to form F-actin
- G-actin monomers add on at the positive end of the monomers (growth end)

length of the filament depends on concentration of G-actin and presence of actin binding proteins

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16
Q

What are ABPs? What are the different types?

A

ABPs are actin binding proteins

profilin
- facilitates actin polymerisation

thymosin beta 4
- prevents the addition of actin monomers to F-actin

17
Q

What are the 4 different actions of ABPs?

A

Actin Bundling Proteins
- keep F-actin in parallel bundles

Cross-linking proteins
- maintain F-actin in a gel-like meshwork

F-actin severing proteins
- break F-actin into smaller filaments = controls filament length

Motor proteins (Myosin)
- transport of vesicles and/or organelles through actin filaments
18
Q

What are the different functions of actin filaments?

skeletal muscle?
non-muscle cells?
cytokinesis?
cell migration?

A

skeletal muscle

  • arranged in a para-crystalline array integrated with different ABPs
  • interaction with myosin motors allow muscle contraction

non-muscle cells

  • cell cortex : form a thin sheath beneath the plasma membrane
  • associated with myosin form a purse string ring result in cleavage of mitotic cells

cytokinesis
- involvement of an actin-myosin ring = form contractile ring, contraction splits ring into two

cell migration
- the cell pushes out protrusions at its front (lamellipodia and filopodia)
= actin polymerisation

19
Q

What are the intermediate filaments?

A

toughest of the cytoskeletal filaments
- resistance to destruction
rope-like structure with many long strands twisted together and made up of different subunits

20
Q

What are intermediate filaments made up of?

A

rope-like structure with many long strands twisted together and made up of different subunits

Each unit is made of:

  • N-terminal globular head
  • C-terminal globular tail
  • Central elongated rod-like domain

units form stable dimers
ervery 2 dimers form a tetramear
tetramers bind to each other and twist to constitute a rope-like filament

21
Q

What are the different types of intermediate filament?What is the function of intermediate filaments?

A

cytoplasmic and nuclear filaments

cytoplasm
- tensile strength: this enable the cells to withstand mechanical stress (stretch)
structural support by:
- creating a deformable 3D structural framework
- reinforcing cell shape and fix organelle localisation

nucleus
- form mesh rather than “rope-like” structure
- line in the inner face of the nuclear envelope to:
= strengthen it
= provide attachment sites for chromatin

22
Q

What are microtubules?

A

Hollow tubes made up from the protein tubulin
Each filament is polarized (i.e. has direction – head/tail or +/-)
It is a dynamic structure
- can assemble and disassemble in response to cell needs

23
Q

How do microtubules polymerise?

A

assembly starts at the microtubule organism centre
= MTOC
centrosome in the perinuclear region is the MTOC of most cells
MTOC contains gamma tubular ring that initiates microtubule growth
heterodimers of alpha and beta tubulin constitute the microtubule
- it is a polarized growth (i.e. there is an end that grows faster (+end) than the other (- end).

24
Q

What are the different forms of tubulin?

A

alpha tubulin
beta tubulin
gamma tubulin - initiates polymerisation

25
Q

What are the functions of microtubules?

A

intracellular transport
- act like railway tracks on which molecular motors run
different motors for different cargoes
- directionality of filaments is vital (each motor only moves in one direction)

organises position of organelles

  • therefore provides polarisation of cells
  • directionality of filaments is vital

motor proteins = use ATP

  • dynein = only moves towards the negative/minus end
  • kinesin = only moves towards the positive/plus end

1 - HB (23 decks)

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