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30 cell biology > L16 - protein sorting and trafficking > Flashcards

L16 - protein sorting and trafficking Flashcards

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1
Q

List the different pathways for newly synthesised proteins

A
  1. cytoplasmic pathway

2. endoplasmic reticulum pathway

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2
Q

list the possible destinations of newly synthesised proteins and the pathway that takes them there.

A 
mitochondria (cytoplasmic)
nucleus (cytoplasmic)
peroxisome (cytoplasmic or ER)
cytoplasm (cytoplasmic)
secretory vesicles (ER)
lysosomes (ER)
ER (ER)
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3
Q

what are the possible destinations of newly synthesised proteins via the cytoplasmic pathway

A

mitochondria
cytoplasm
peroxisomes
nucleus

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4
Q

what are the possible destinations of newly synthesised proteins via the ER pathway

A

peroxisomes
lysosomes
ER
secretory vesicles

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5
Q

what determines a proteins end destination within a cell?

A

internal ‘post codes’ - sequences in polypeptide which direct to certain organelles

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6
Q

briefly explain cytoplasmic pathway

A

cytoplasmic ribosome synthesises protein
folded protein released into cytoplasm and travels to nucleus/peroxisome/cytoplasm
or
unfolded protein released into cytoplasm which travels to mitochondria to be folded

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7
Q

what are Glycosyltransferases and where are they located

A

enzymes that add sugars to proteins
golgi
(blood group antigens)

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8
Q

what is the lysosomal post code and where is it added to the protein

A

mannose 6 phosphate

Golgi

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9
Q

what is I‐cell disease

A
  • mutations in M6P or M6P receptor in golgi
  • leads to no mannose 6 phos being added to proteins
    proteins fail to make it to lysosomes and are secreted
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10
Q

define cis and trans golgi

A

cis - region of golgi that faces RER

trans - region of golgi that faces membrane

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11
Q

generally describe the ER pathway

A

proteins synthesised in ER
travel in vesicles to golgi
through golgi into vesicles
secreted/ lysosomes/ peroxisomes / membrane

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12
Q

what do proteins in the ER all have in common?

A

signal sequence at the N terminal

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13
Q

describe the signal sequence

A

n terminal

stretches of hydrophobic residues

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14
Q

what protein recognises signal sequences and will result in the protein being transported into ER

A

signal recognition protein SRP

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15
Q

describe the process of uptake of a protein into the ER

A
  1. signal sequence of PP (still bound to ribosome) is bound to by SRP
  2. ER membrane contains SRP receptor that binds to SRP
  3. SRP displaced and recycled
  4. ribosome- mRNA complex is transferred to transmembrane channel
  5. ribosome continues to synthesise protein, injecting the pp chain into the ER lumen
    6.
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16
Q

what are the two outcomes for a protein entering the ER

A
  1. embedded in membrane due to more HPhobic stretches in the PP chain (transmembrane protein eg ion channel)
  2. ends up in ER lumen, transported into vesicles for transport / secretion
17
Q

what does signal peptidase enzyme do?

A

cleaves the signal sequence (because it gets stuck in the channel as its Hphobic) so the pp can be injected into the lumen

18
Q

what protein modification happens in ER

A
  1. folding (aided by chaperone proteins)

2. forming disulfide bonds

19
Q

what protein modification occurs in golgi

A
  1. adding of ‘post codes’

2. glycosylation (forming glycoprotiens)

20
Q

why is it important to have a specific lysosomal postcode?

A

lysosomes are acidic and contain degradative enzymes so we dont want the wrong proteins to be able to make it there easily

21
Q

is the environment of the
cytoplasm
ER lumen
oxidising or reducing

A

cytoplasm - reducing

ER lumen - oxidising

22
Q

describe the cytoplasmic pathway of proteins to mitochondria

A
  1. PP chan fully translated in cytosol and left partially unfolded by chaperones
  2. signal seq. recognised by receptor on M membrane
  3. TOM (outer membrane channel) and TIM23 (inner membrane channel) can associate which catalyses the entrance of the entire PP chain into M matrix
  4. signal seq cleaved
23
Q

describe the signal seq for proteins destined for mitochondria

A

10-70 AA long

alternating Hphobic and positive residues which create amphipathic helix (one side hphobic one side +ve)

24
Q

is import of proteins into
mitochondria
ER
co-translational or post-translational

A

M - post

ER - co

25
Q

what keeps polypeptides destined for mitochondria partially unfolded?

A

chaperones

26
Q

what happens if only TOM is present?

A

the protein may end up between the inner and outer membrane

27
Q

what can cause a protein to become imbedded in a mitochondrial membrane

A

hphobic stretches of sequence

28
Q

what do pores of the nucleus have that aid in protein transport?

A

spokes

fibrils

29
Q

which way do the
spokes
fibrils
of nuclear pores point

A

spokes - point into nucleoplasm

fibrils - point out into cytoplasm

30
Q

what is needed for a protein to be imported into the nucleus?

A

nuclear localisation signal (NLS)

31
Q

describe NLS

A

short
positively charged
residues such as Lys, Arg

32
Q

describe the process of importing a protein into nucleus

A
  1. protein carrying NLS is recognised by importin protein which binds to it
  2. complex binds to fibrils catalysing entrance
  3. complex is recognised by Ran (small GTPase) which displaces the protein from importin
  4. there is now a Ran-importin complex which is recognised by spokes
  5. spokes mediate the exit of the ran-importin complex
  6. Ran hydrolyses GTP to GDP releasing importin
33
Q

describe the process of exporting a protein from nucleus

A
  1. protein has nuclear exit signal (NES)
  2. exportin recognises NES signal and binds to the protein
  3. Ran then binds to this complex
  4. exportin - protein - ran complex binds to spokes which mediate exit into cytoplasm
  5. ran hydrolyses GTP to GDP releasing protein and exportin
  6. exportin recognised by fibrils that reimport it into nucleus

30 cell biology (21 decks)

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