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Cell Biology Term 1 > Cell Organelles > Flashcards

Cell Organelles Flashcards

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1
Q

Where is the site of ribosome production?

A

The Nucleolus

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2
Q

Which is transcriptionally active, Euchromatin or Hetrochromatin?

A

Euchromatin

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3
Q

What is the difference between transport of proteins inside the nucleus vs import into the ER or Mitochondria?

A

The Nuclear Pore Complex (NPC) is large enough to transport completely folded proteins. Only unfolded proteins are small enough to cross the membrane into the ER or mitochondria

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4
Q

What does a protein require to be imported into the nucleus?

A

Nuclear Localization Sequence (NLS)

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5
Q

What does a protein require to be exported out of the nucleus?

A

Nuclear Export Sequence (NES)

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6
Q

What are the receptors/carriers that recognize targeting signals on nuclear cargo called?

A

Karyopherins

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7
Q

What happens to importin after it carries its cargo through the nuclear pore?

A

It travels back into the cytoplasm and keeps transporting

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8
Q

Where is Ran-GTP abundant?

A

Inside the nucleus

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9
Q

Where is Ran-GDP abundant?

A

In the cytosol

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10
Q

When does Ran-GTP become Ran-GDP?

A

When it binds to Importin (Beta) inside the nucleus and transports it outside of the nucleus

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11
Q

What determines if a ribosome is free or attached to the Rough-ER?

A

The translated mRNA (Protein) which that ribosome is attached to at that point in time

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12
Q

What directs the ribosomal complex to the ER membrane?

A

The signal sequence in the nascent protein

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13
Q

Is the signal sequence made of hydrophilic or hydrophobic amino acids?

A

Hydrophobic

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14
Q

How many amino acids are required for a polypeptide to span a lipid bilayer as a helix?

A

20

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15
Q

How does the signal sequence bind to the membrane of the ER?

A

A free signal recognition particle binds to the signal sequence in the cytosol, then both bind to the signal recognition particle (SRP) receptor.

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16
Q

How is a transmembrane protein inserted into the membrane?

A

The Signal sequence in the nascent polypeptide strand is located in the middle of the polypeptide rather than at the end. The signal sequence becomes the hydrophobic portion of the peptide that spans the lipid membrane

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17
Q

What enzyme catalyzes the oxidation of free sulfhydryl (SH) groups to for disulfides (S-S) in the lumen of the ER?

A

Protein Disulfide Isomerase (PDI)

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18
Q

Why don’t disulfide bonds form in protein domains exposed to the cytoplasm?

A

The reducing nature of the cytoplasm (Glutathione)

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19
Q

What is the purpose of a GPI anchor?

A

Acts as a sorting signal to direct membrane proteins to special regions of the plasma membrane

20
Q

What (normally) has to happen for a protein to leave the ER?

A

correct folding-release from chaperones

21
Q

What type of enzymes are located in the smooth ER?

A

membrane-bound enzymes used to degrade hormones and neutralize noxious substances (Liver)

22
Q

What does N-linked glycosylation do for proteins and where does it occur?

A

It aids in correct protein folding. Occurs in the ER lumen.

23
Q

The most common mutation leading to cystic fibrosis results from the deletion of Phe508 in ________.

A

CFTR

24
Q

What happens when the CFTR protein misfolds (Cystic fibrosis?

A

it becomes trapped in the ER

25
Q

What disorder can cause emphysema and pediatric liver cirrhosis?

A

Alpha 1-antitrypsin deficiency

26
Q

What happens to proteins that misfold in the ER?

A
  1. Interaction with chaperones
  2. Escorted out of the ER
  3. Tagged with ubiquitin4. Degraded by proteosome
27
Q

What signals that it is time for a misfolded protein to be degraded?

A

Prolonged duration of non-native protein structure. Sugars, mannose

28
Q

What does the KDEL receptor do?

A

Activates a retention/retrieval signal for soluble ER resident proteins

29
Q

How does tetanus work?

A

it is a protease that cleaves receptors used for teh movement of synaptic vesicles in inhibitory neurons. Blocks secretion of inhibitory NT’s that normally control muscle movement, causing lockjaw

30
Q

How does Botulinum toxin work?

A

Cleaves receptors that normally lead to release of ACh. Leads to paralysis at the neuromuscular junction

31
Q

What is a molecular signal that target newly synthesized proteins to lysosomes?

A

Mannose 6-phosphate (M6P)

32
Q

What causes I-cell disease?

A

Deficiency of ability to phosphorylate mannose

33
Q

What are the symptoms of I-cell disease?

A

skeletal abnormalities, restricted joint movement, coarse facial features, and severe psychomotor impairment-death usually occurs by 8 yrs old

34
Q

What happens when a cell lacks hydrolytic enzymes?

A

the lysosomes accumulate material that is normally destroyed

35
Q

What causes Tay-sach’s disease?

A

an absence of hexosaminidase A, which normally breaks down glycolipids in the lysosomes

36
Q

What are the symptoms of Tay-sachs disease?

A

-Normal at birth-Manifest relentless motor and mental deterioration and increasing dementia beginning ~6mo of age-death usually 2-3 yrs old

37
Q

Where are mitochondrial replication enzymes and RNA polymerases made?

A

Cytosol of the cell

38
Q

What 2’ protein structure do proteins on the mitochondrial surface recognize?

A

alpha helix

39
Q

What dictates protein topology in the mitochondria?

A

the number and placement of sorting signals

40
Q

What are the functions of peroxisomes?

A
  • oxidation of fatty acids and other lipids
  • oxidation of purines, amino acids, and other metabolites
  • Biosynthesis of cholesterol, bile acids, ether based lipids
  • contain large amounts of catalase which can convert excess hydrogen peroxide into water
  • production of myelin
41
Q

What are the two import signals for peroxisomal protein import?

A

PTS1 and PTS2

42
Q

PTS1

A

found in most matrix proteins of the lysosome-three final C-terminal amino acids are usually Ser-Lys-Leu-Sorting signal is not cleaved after translocation

43
Q

PTS2

A
  • Found in a sumset of lysosomal matrix proteins
  • Usually within the first 20-30 amino acids
  • sorting signal can be cleaved
44
Q

What evidence is there for the ER as the origin of the peroxisomal membrane?

A

EM immunolabeling shows clustered peroxisomal membrane proteins in the rough ER membrane

45
Q

Zellweger’s syndrome

A
  • a general defect in importing proteins into peroxisomes
  • probably because PEX5 doesn’t work properly
  • individuals die soon after birth
46
Q

How is protein transport into the peroxisome different from other organelles?

A

1) peroxisomes can import folded proteins instead of only unfolded
2) no chaperones exist within the peroxisomal matrix
3) The translocation channel has yet to be detected

Cell Biology Term 1 (7 decks)

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