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Uni year 1 > Cell Biology part 1 > Flashcards

Cell Biology part 1 Flashcards

1
Q

What are the mechanisms of protein control?

A
  • expression and degradation
  • effector ligand binding
  • pH
  • interactions
  • localisation
  • protein switches
  • protein modifications
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2
Q

how can expression and degradation be used to control a protein?

A
  • increase/decrease amount of enzyme at rate limiting step
  • amount of protein may be controlled by amount of transcription
  • level of protein can be controlled by controlling degradation
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3
Q

How can effector ligand binding be used to control proteins?

A
  • binding of a molecule (ligand) can induce a conformational change
  • can bind to active site or allosteric site
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4
Q

How can product inhibition be used to control proteins?

A

Can be used as feedback control, when the end product binds to an allosteric site on an earlier enzyme preventing any more product from being made

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5
Q

How can pH influence protein control?

A
  • if protons in excess then proteins may become ionised

- can cause conformational change

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6
Q

How interactions can affect protein control?

A
  • many proteins have domains that control interactions with other molecules
  • certain interactions may inhibit enzyme activity
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7
Q

How can protein switches be used in protein control?

A
  • some protein functions aren’t needed continuously
  • often hydrolysed with nucleotide triphosphate
  • GTPases and ATPases
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8
Q

How can protein modifications be used in protein control?

A
  • modifications can change localisation, activity, interaction, degradation
  • can be irreversible or reversivle
  • eg phosphorylation, acetylation, methylation, hydroxylation, glycosylation
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9
Q

What are the 3 types of protein filament?

A

actin microfilaments

tubulin microtubules intermediate microfilaments

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10
Q

What are the roles of microtubules?

A
  • maintenance of cell shape
  • movement/movement of fluids on surface - flagella/cilia
  • formation of mitotic spindle
  • tracks movements for vesicles, organelles, proteins
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11
Q

What is the structure of microtubules?

A
  • tubulin dimers made up of alpha and beta subunits
  • dimers stack together to form a protofilament
  • 13 stacks in a tubule
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12
Q

what are microtubule organising centres?

A
  • where microtubules grow from
  • they are a complex of gamma-rings
  • MT grows outwards due to polarity
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13
Q

What are the two types of microtubule binding drugs?

A
  • tubulin dimer binding - prevents MT from forming

- tubulin polymer binding - promotes polymerisation of MT

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14
Q

When are microtubule binding drugs used?

A
  • anti-mitotic agents

- anti-cancer agents

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15
Q

What are the functions of microtubule associated proteins (MAPs)?

A
  • stabilise MTs
  • speed up polymerisation of MTs
  • other end projects out to bind to vesicles, actin or other MTs
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16
Q

What are the roles of actin microfilaments?

A
  • maintenance of cell shape
  • cell movement and chemotaxis
  • interaction with environment
  • tracks for movement of vesicles, organelles, proteins
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17
Q

Where are actin microfilaments located?

A
  • microvilli
  • adhesion belt
  • cell cortex (around edges)
  • filopodia
  • lamellipodium
  • stress fibres
  • contractile ring
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18
Q

Structure of actin microfilaments

A

3 types - alpha (muscle), beta (non-muscle) and gamma (non-muscle)
plus end and minus end due to polarity
beads on a string
slight twist

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19
Q

actin binding proteins (ABPs)

A
  • regulate actin filaments

- regulate the polymerisation and bundling

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20
Q

Structure of intermediate filaments

A

alpha helical region coils with another to form a dimer
dimers coil into staggered tetramers
8 tetramers twist into a filament

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21
Q

What is the function of intermediate filaments?

A

structural support - keratin

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22
Q

What are motor proteins?

A

Enzymes that convert chemical energy (ATP) into mechanical energy. The hydrolysis is coupled with a conformational change which moves the motor protein along its track.

23
Q

What are myosins?

A

A superfamily of actin based motor proteins

24
Q

What are the 3 domains of myosins?

A

Head - binds to F-actin and ATP
Neck - acts as a lever
Tail - mediates interactions with cargo

25
Q

What is myosin II for and what is its structure?

A

muscle contraction
6 polypeptides - 2 heavy, 4 light chains
coiled coil rod

26
Q

Which direction do myosins move

A

All but myosin VI move to the plus end of the filament

27
Q

Actin-myosin crossbridge cycle

A
  1. myosin bound to actin, ATP binding site empty
  2. ATP binds causing conformational change so head unbinds
  3. hydrolysis of ATP to ADP + P, head displaces further along filament
  4. release of P triggers power stroke, head regains original conformation
  5. myosin bound to actin but at new position
28
Q

What are non-processive motors and give an example

A
  • heads move independently of each other
  • uncoordinated attachment and detachment of myosin along filament
  • heads can move along filament at different times to each other
  • myosin II
29
Q

What are processive motors and give an example

A
  • heads move in a coordinated manner
  • ensures cargo stays attached so
  • myosin V
30
Q

What are myosins important for in non-muscle cells

A
  • cytokinesis
  • transport
  • cell locomotion
  • cytoplasmic streaming
31
Q

What are kinesins

A

A type of microtubule motor protein which move along microtubule filaments. The head domain binds to microtubules and hydrolyses ATP to generate force.

32
Q

Which direction do kinesins move in

A

towards the positive end of the microtubule

33
Q

Are kinesins processive or non-processive?

A

processive - locking down of leading head on MT throws trailing head forward

34
Q

How are kinesins regulated?

A
  • folding of tail
  • folded form can;t attach to the MT
  • when the cargo binds it extends the tail so it can now bind to the MT
35
Q

What are the 2 classes of dyneins?

A

Cytosolic - movement of vesicles and chromosomes

Axonemal - beating of cilia and flagella

36
Q

How do dyneins work?

A

They are processive motors
When ATP is bound the dynein is not attached to the MT. ATP hydrolysis causes attachment. Release of ADP and P causes conformational change causing power stroke.

37
Q

What are nucleoporins (NUPs)

A

proteins that compose the nuclear pore complex

38
Q

What are the different types of NUPs?

A
  • Core scaffold anchor into membrane
  • FG Nups line channel
  • linker Nups anchor FG nups into position
  • cytoplasmic filaments anchor NPC to cytoskeleton
  • basket nups link NPC with nucleus
39
Q

What is the export and import of proteins into the nucleus regulated by?

A
  • protein cargo
  • nuclear transport receptors
  • small GTPase Ran
40
Q

The process of import and export of proteins into nucleus

A
  1. cargo recognised and bound by nuclear transport receptor
  2. NTR-cargo docks onto NPC via FG nups
  3. NTR-cargo disassociates
41
Q

What are importins and what is the structure

A

importins are nuclear import receptors. They are a heterodimer of importin-a and importin-beta

42
Q

What does importin-a do?

A

recognises nuclear localisation sequence on cargo protein

43
Q

What does importin-beta do?

A

interacts with pre-complex via FG repeats within nups

44
Q

What is required for export of proteins from nucleus?

A
  • export sequences are leucine rich

- RanGTP interacts with cargo, hydrolysed to RanGDP

45
Q

How does phosphorylation regulate import into the nucleus?

A

It increases import by:
increasing binding affinity of cargo to importin-a
enhanced recognition of cargo by importin-a
induced conformational change exposing NLS
It decreases import as the phosphorylation sites overlap NLS

46
Q

Steps of nuclear export

A
  1. transcription and capping
  2. splicing
  3. 3’ end processing
  4. localisation to NPC periphery
  5. docking
  6. translocation
  7. cytoplasmic release
47
Q

What is the main mRNA export factor?

A

NXF1

48
Q

Crossing the ER membrane

A
  • signal recognition particle recognises signal peptide
  • ribosome-SRP complex localised into translocator
  • SRP dissociates from ribosome
  • signal peptide cleaved by signal peptidase and protein released into ER lumen
49
Q

What are the main events in the ER?

A
  • signal peptide is cleaved
  • protein is glycosylated
  • protein folds into 3D conformation
  • disulfide bonds form
  • multimerisation
50
Q

What happens when proteins exit the ER

A
  • proteins must be properly folded or it will be degraded

- vesicles containing proteins bud from the ER and transit to the cis face of the golgi

51
Q

What is the constitutive secretory pathway?

A
  • operates continuously to release protein all the time

- supplies plasma membrane with newly synthesised membrane spanning proteins

52
Q

What is the regulated secretory pathway?

A
  • releases proteins in response to a signal
  • sorted into secretory granules and stored until required
  • release triggered by extracellular signal
53
Q

How are lipids carried to the cell surface?

A

Via the secretory pathway after being synthesised in ER

Uni year 1 (19 decks)

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