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Cell Biology (BY1CB1) > Week 10(Cellular Compartments II Endo- and Exocytosis) > Flashcards

Week 10(Cellular Compartments II Endo- and Exocytosis) Flashcards

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1
Q

Secretion Overview

A

Synthesis/ER →Golgi →PM (plasma membrane)/extracellular space.

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2
Q

Secretory Pathway: step 1

A

Co-translational trans-membrane transport

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3
Q

Most Proteins Are Covalently Modified in the ER

A

➢Important changes to a protein structure
➢Glycosylation
•sugars added to proteins (glycoproteins)
•major function of ER
•most soluble & membrane-bound proteins are glycoproteins
•cytosolic proteins are simply or not glycosylated
•often essential for function

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4
Q

Glycosylation in ER

A

A complex of 14 sugars is added en bloc
➢Sugars transferred from a lipid (dolichol)
➢To asparagine residue by protein transferase
➢Not all Asn are glycosylated
•consensus Asn-X (any AA except proline)Ser/Thr
•N-linked glycosylation (Asn = N)

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5
Q

ER Chaperones (proteins) ensure quality

A

Chaperones bind unfolded proteins- prevents aggregation and ensures that the protein is folded properly before release (speeds up folding process)

➢Binding keeps them in the ER

➢Important for correct folding and assembly of multimeric proteins

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6
Q

Antibodies

A

•4 polypeptide chains (2 heavy and 2 light)

➢BiP (chaperone) retains Ab in the ER until it is complete

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7
Q

What happens to Improperly folded proteins?

A

They are exported out of ER and degraded in the cytosol

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8
Q

What happens to misfolded proteins in the ER?

A

If they start to accumulate in ER, they activate Unfolded Protein Response (UPR)
-Signal to nucleus to reduce translation of proteins
Or
-Signal to increase amount of chaperones

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9
Q

Secretory Pathway: step 2

A

Vesicular transport to the Golgi for further modification and onwards

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10
Q

Glycosylation in Golgi

A

➢O-linked glycosylation (not as frequent as N-linked)

➢Poorly understood

➢sugars bind to -OH groups of amino acid side chains (ser/thr)

➢less frequent than N-linked

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11
Q

Secretion pathway- step 3: EXOCYTOSIS

A

Secretion to the Plasma membrane/extracellular space

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12
Q

Where are Proteins sorted?

A
  • in the trans Golgi network
  • and transported in vesicles to their final destinations (fuse with plasma membrane- Transmembrane protein will be inserted in plasma membrane or if the cargo is Soluble it will be released into the extracellular space)after activation
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13
Q

Protein Coats Drive vesicle budding

A

Vesicles have a distinctive protein coat (cytosolic)

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14
Q

Vesicle Coat Protein function:

A
  • Shapes membrane (cage-like)
  • Helps capture cargo molecules for onward transport
  • Helps induce membrane bending (coated bud)
  • Helps coordinate membrane scission/vesicle release
  • Must disassemble to allow vesicle fusion of with target membrane
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15
Q

What are major components of protein coats?

A
  • Clathrin and COP (Coat Proteins) I and II

- Other components mark where the different vesicles function

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16
Q

Different coats in vesicular trafficking

A

➢Adaptor proteins (based on the compartment the vesicles originated) necessary for clathrin coat formation and cargo sequestering

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17
Q

Vesicle tethering depends on Rab GTPases

A

➢Rab GTPases ensure the specificity of vesicular transport
➢Functions via Rab effectors to ensure tethering and docking of vesicles to the membrane (=first connection between donor and target compartments)
•Can link 2 membranes that are >200nm apart

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18
Q

Vesicle docking and fusion depends on SNAREs: v-SNARE

A

on vesicle

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19
Q

Vesicle docking and fusion depends on SNAREs: t-SNARE

A

on target

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20
Q

Describe the action of SNARES

A
  • Wind together

* Squeeze the vesicle and cell membranes together for fusion

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21
Q

Vesicles move along cytoskeletal fibres:

A

➢FROM donor compartment (origin)

➢TO target compartment (destination)

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22
Q

Why doesn’t the cell just keep getting bigger?

A

➢Exocytosis adds membrane to the plasma membrane

23
Q

ENDOCYTOSIS

A

Cells are constantly bringing material in

Relies on vesicles

24
Q

What are the two types of endocytosis?

A

PINOCYTOSIS and PHAGOCYTOSIS

25
Q

PHAGOCYTOSIS

A

(Eating)
Vesicles >250nm
Specialised cells eat large particles

26
Q

PINOCYTOSIS

A

(Drinking)

Vesicles <150nm

27
Q

What does PINOCYTOSIS involve?

A

➢Cell drinking
➢Uptake of fluid & macromolecules
➢May be indiscriminate
-Captures local fluids as membrane invaginates

28
Q

properties of PINOCYTOSIS

A

➢May show specificity
➢RECEPTOR-MEDIATED ENDOCYTOSIS (bind specific cargo molecules)
➢Receptors concentrate desired molecule for uptake with the help of the clatherin coat

29
Q

Destination of endocytosed cargo

A

➢PM→Early Endosome→Late Endosome→Lysosome.
Recycling Endosome→recycled back to PM without being degraded

➢Early Endosomes (EE) sort cargo for onwards destination; ligand dissociates from the receptor - has a low pH, receptor can then be recycled back to plasma membrane
➢Late Endosomes (LE) / multivesicular bodies (MVB) prepare cargo for degradation/secretion, it will either mature or fuse with a lysosome
➢Lysosomes degrade cargo

30
Q

Explain PHAGOCYTOSIS in detail

A

➢Specialized Phagocytic Cells Ingest Large Particles
➢Phagocytes
•Macrophages
•Neutrophils
➢Large particles (e.g. bacteria) bind receptors
➢Pseudopodia extend around particle (supported by actin cytoskeleton) and fuse together to engulf the particle
➢Tips fuse to create PHAGOSOME
➢Lysosomes fuse and bacterium is degraded
➢Also involved in removal of dead cells

31
Q

Lysosomes degrade cargo from:

A

Endosomes
•Phagosomes
•Autophagosomes

32
Q

Give a Summary of Exocytosis

A 
ER→Golgi →PM
➢Signal sequence dictates path
➢Chaperones check quality
➢Sugar modifications made on journey through ER and Golgi
➢Vesicular transport transfers proteins
➢Vesicles are protein coated
➢Membrane fusion deposits protein cargo
33
Q

Give a Summary of Endocytosis

A 
ENDOCYTOSIS (reverse mechanism)
•PM→EE→LE→Lysosome
•PM→EE→RE→PM
•Uptake of membrane &amp; other cargo
•Pinocytosis
•Receptor mediated endocytosis
•Phagocytosis (specialised)
•Lysosomes degrade ingested material
34
Q

What are the main options for proteins after they reach the trans Golgi network?

A

Lysosome
Plasma membrane
Secretory vesicle

35
Q

COP 1 coats travel to:

A

Travel to ER

36
Q

COP 2 coats come from:

A

On ER membrane

37
Q

What type of glycosylation occurs in ER?

A

N

38
Q

What is autophagy?

A

A double membrane enclosed a damaged organelle and brought to the lysosome

Cell removes damaged organelles

39
Q

What is the origin and destination of vesicles with Clathrin + adaptin 1 coats?

A

Origin: Trans Golgi network

Destination : lysosome

40
Q

What is the origin and destination of vesicles with Clathrin + adaptin 2 coats?

A

Origin: Plasma membrane
Destination: endosome

41
Q

What is the origin and destination of vesicles with COP 1 coats?

A

origin: Forming at the Golgi
Destination: travelling to ER

42
Q

Where is the cis Golgi network?

A

Faces the side closest to the nucleus

43
Q

Where is the Golgi stack?

A

in the middle of the cis and trans Golgi network

44
Q

Where is the trans Golgi network?

A

facing away from the nucleus (towards plasma membrane)

45
Q

What are pseudopods?

A

sheetlike projections of the plasma membrane that surround the invading microorganisms.
supported by actin

46
Q

What class of enzyme do caspases belong?

A

protease

47
Q

What is BAX protein?

A

Apoptosis regulator BAX, also known as bcl-2-like protein

48
Q

If the genes encoding Bax and Bak are both inactivated

A

cells are remarkably resistant to most apoptosis-inducing stimuli, indicating

49
Q

What are BAX and BAK activated by?

A

Bax and Bak are themselves activated by other apoptosis-promoting members of the Bcl-2 family such as Bid.

50
Q

What is the function of the Bcl-2 family?

A

TheBcl-2 familyof intracellular proteins helps regulate the activation of procaspases

51
Q

What is the apoptosome?

A

The apoptosome is a large quaternary protein structure formed in the process of apoptosis. Its formation is triggered by the release of cytochrome c from the mitochondria in response to an internal (intrinsic) or external (extrinsic) cell death stimulus

52
Q

Which members of the Bcl-2 family inhibit apoptosis?

A

Some members of this family, likeBcl-2itself orBcl-XL, inhibitapoptosis

53
Q

is crm-A anti apoptotic?

A

yes

54
Q

Is the BAD protein anti apopototic?

A

No
It is pro apoptotic
-BAD is a member of the BH3-only family, a subfamily of the Bcl-2 family
-It inhibits antiapoptotic BCL-2 and BCL-xL

Cell Biology (BY1CB1) (16 decks)

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