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BIOL1040 > Module 1: Principles of Cell Function > Flashcards

Module 1: Principles of Cell Function Flashcards

1
Q

what are cellular membranes?

A

> fluid mosaics of lipids and proteins
phospholipids - abundant
phospholipids are amphipathic molecules
‘Fluid mosaic model’ - membrane is fluid with a ‘mosaic’ of proteins embedded in it.

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2
Q

what does amphipathic mean?

A

part hydrophilic and part hydrophobic (membrane bound proteins)

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3
Q

what is cholesterols role in the phospholipid bilayer?

A

> stops membrane from being too thin and fluid at higher temperatures
at low temps, it stops the membrane from being too viscous and thick
has a buffering effect.

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4
Q

what are the components of a cellular membrane?

A 
>Phospholipid bilayer
> Glycoproteins on the surface 
> carbohydrate
> glycolipids
> integral proteins
> peripheral proteins
> microfilaments of cytoskeleton
> cholesterol
> fibres of extracellular matrix
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5
Q

what are the six major functions of membrane proteins?

A

> transport (ion channels and active transport)
enzymatic activity
signal transduction
cell-cell recognition
intercellular joining (into tissues)
attachment to the cytoskeleton and extracellular matrix

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6
Q

how does the membrane structure result in selective permeability?

A

> lipid bilayers are impermeable to most essential molecules and ions (because they are lipids)
some permeability to water molecules and a few other small, uncharged molecules like oxygen and carbon dioxide

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7
Q

what are lipid bilayers not permeable to ?

A

> ions such as K+, Na+, Ca2+, Cl-, HCO3-
small hydrophilic molecules like glucose
macromolecules like proteins and RNA

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8
Q

what is passive transport?

A

is diffusion of a substance across a membrane with no energy investment.

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9
Q

what is osmosis?

A

> diffusion of water through a selectively permeable membrane into another aqueous compartment containing solute at a higher concentration
water wants to be at equilibrium, same number of molecules in each compartment.

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10
Q

what are osmotica

A

> ions - charged
sugars - water soluble
proteins - large
nutrients

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11
Q

what is tonicity?

A

the ability of a solution to cause a cell to gain or lose water - compared to outside the cell etc.

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12
Q

what is an isotonic solution?

A

solute concentration is the same as that inside the cell; no net water movement across the plasma membrane

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13
Q

what is a hypertonic solution?

A

solute concentration is greater than that inside the cell; cell loses water - crenates

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14
Q

what is a hypotonic solution?

A

solute concentration is less than that inside the cell; cell gains water - haemolysis

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15
Q

what is an electrogenic pump?

A

a transport protein that generates voltage across a membrane

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16
Q

what is a sodium-potassium pump?

A

the major electrogenic pump of animal cell

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17
Q

what is the function of transport proteins?

A

to allow the passage of hydrophilic substances across the membrane.
> they are specific for the substance they move
> transport proteins speed the passive movement of molecules across the plasma membrane

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18
Q

what are channel proteins?

A

they have a hydrophilic channel that certain molecules or ions can use as a tunnel
> e.g., aquaporins
> ion channels - open or close in response to a stimulus (gated channels)
> provide corridors that allow a specific molecule or ion to cross the membrane
> form pores through which molecules can pass

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19
Q

what are carrier proteins?

A

they bind molecules and change shape to shuttle them across the membrane

20
Q

what is facilitated diffusion?

A

> passive transport aided by proteins

21
Q

what are the two categories that pore forming proteins fall under?

A

1) channels - facilitated diffusion

2) transporters - facilitated diffusion or active transport

22
Q

what is the difference in molecule flow in passive and active transport?

A

passive - molecules flow down the concentration gradient

active - pumped against concentration gradient

23
Q

what is cotransport?

A

> occurs when active transport of a solute indirectly drives transport of another solute
plants commonly use the gradient of hydrogen ions generated by proton pumps to drive active transport of nutrients into the cell. (Diagram)

24
Q

how does bulk transport across a membrane work?

A

enters via endocytosis

exits via exocytosis

25
Q

what are the different types of endocytosis?

A

> phagocytosis - engulfing of particles (food vaculoes)
pinocytosis - cells drinking - engulfs solution
receptor-mediated - compounds bind to cell surface receptors, vesicle is formed containing both receptor and ligand compound and other fluid.

26
Q

what is a specific purpose for exocytosis?

A

> the mechanism of neurotransmitters release from neurons.

27
Q

what are the different types of cell to cell communication?

A

> paracrine signalling - neighbouring cells
autocrine signalling - neurotransmitter released from, and acts on, the same cell.
synaptic signalling - pre and post synaptic neurons
hormonal signalling - long distance

28
Q

what are the three stages of cell signalling?

A

1) reception
2) transduction
3) response

29
Q

what are the four receptor types?

A

> G protein coupled receptor
tyrosine kinase receptor
ion channel receptor
steroid receptor

30
Q

what are ion channel receptors?

A 
> plasma membrane receptor
>ligand binds to channel,
> Na+ channels are opened 
> fastest acting receptor
> e.g., Nictoninc receptors
31
Q

what are G protein coupled receptors?

A

> plasma membrane receptor
7 transmembrane spanning domains
largest family of receptors
1000 in human genome
50% of current drugs target GPCRs
activated by various stimuli - light, ions (Ca2+), odourants, gustative molecules, neurotransmitters, hormones, peptides and proteins
interact with heterotrimeric ( 3 different peptides) G proteins to control the activity of enzymes, ion channels, and intracellular signal transduction pathways.

32
Q

what is the process involved in g protein coupled receptors

A

1) GDP is bound to the G - protein - inactive state
2) hormone ligand binds to the receptor, causing a conformational change, resulting in GDP being exchanged with GTP - active state
3) the activated G-protein dissociates from the receptor and diffuses across the membrane to bind to the enzyme Adenylyl cyclase, activating it.
4) adenylyl cyclase catalyses the conversion of ATP to cAMP - second messenger
4) cAMP activating another protein (Protein Kinase A - PKA) leads to a cellular response.

33
Q

what are the different types of enzymes that GPCRs can act on, to produce what second messengers?

A

> enzymes:
Adenylyl cyclases, phospholipases, phosphodiesterases
second messengers:
cAMP, cGMP, IP3, DAG

34
Q

what are tyrosine kinase receptors?

A

> plasma membrane receptor
3rd fastest response
e.g., insulin receptors
used in metabolism, cell growth, cell reproduction

35
Q

what is the process involved in tyrosine kinase receptors?

A

1) before the signalling molecule binds, the receptors exist as individual monomers
2) the binding of signalling molecule causes two monomers to associate closely with each other to form a dimer in a process called dimerisation.
3) dimerisation activates the tyrosine kinase region of each monomer, each tyrosine kinase adds a phosphate from an ATP molecule to a tyrosine on the tail of the other monomer
4) now the receptor is fully activated, it is recognised by specific relay proteins. They too become phosphorylated and go on to activate various cellular responses

36
Q

what are the roles of protein phosphorylation?

A 
> protein is phosphorylated 
> conformational change occurs
> protein-protein interactions
> change in cellular location
> these changes lead to activation or inactivation of the target proteins
37
Q

What are steroid receptors?

A

> intracellular receptor

> slowest response

38
Q

describe the process of steroid receptors

A

1) the ligand passes through the plasma membrane
2) the ligand binds to the receptor in the cytosol, activating it
3) the ‘ligand/hormone receptor complex’ enters the nucleus and binds to specific genes where it eventually influences the transcription of proteins.
* ligand must be small, non-polar, not charged and be hydrophobic.

39
Q

how can communication between adjacent cells occur?

A

through gap junctions with ions such as Na+, K+ and Ca+ (local regulators)

40
Q

how does communication across the extracellular fluid within tissue occur?

A

> growth factors (local regulators) and hormones (long distance regulators)

41
Q

how does communication between tissues occur?

A

secretion of chemical messengers into the circulatory system ( long distance regulators (hormones))

42
Q

how does cotransport work?

A

> a carrier protein, such as sucrose-H+ cotransporter in a plant cell, is able to use the diffusion of H+ down its electrochemical gradient into the cell to drive the uptake of sucrose
the H+ gradient is maintained by an ATP-driven proton pump that concentrates H+ outside the cell, thus storing potential energy that can be used for active transport, in this case sucrose.
Thus, ATP indirectly provides the energy necessary for cotransport.

43
Q

what are cell junctions?

A

> communication by direct cell contact
both animals and plants have cell junctions that allow molecules to pass readily between adjacent cells without crossing plasma membranes

44
Q

what is cell-cell recognition?

A

> communication by direct cell contact
two cells in an animal may communicate by interaction between molecules protruding from their surfaces
important in embryonic development and the immune response

45
Q

What is paracrine signalling?

A

a secreting cell acts on nearby target cells by discharging molecules of a local regulator (growth factor) into the extracellular fluid

BIOL1040 (7 decks)

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