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Cell Biology > Lecture 3: Intracellular compartments, protein sorting and intracellular membrane trafficking > Flashcards

Lecture 3: Intracellular compartments, protein sorting and intracellular membrane trafficking Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

hat are the 3 major types of protein transport?

A

Gated transport
Transmembrane transport
Vesicular transport

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2
Q

How are proteins sorted and targeted?

A

By signal sequences

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3
Q

Where do you find signal sequences?

A

Proteins contain them at the N-terminus

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4
Q

What are the different signal sequences used to target proteins?

A
  • Nuclear localisation signal = target to nucleus
  • Mitochondrial signal sequence = target to mitochondria (e.g. N-terminal end is cleaved after synthesis)
  • Plasma membrane, ER, Golgi, and secreted proteins made on RER membranes signal sequences = targeted by sequence at N-terminal end
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5
Q

Which organelles are involved in packaging proteins?

A

Golgi apparatus, endosomes, lysosomes, and plasma membrane

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6
Q

How can small molecules diffuse in and out of the nucleus?

A

Through nuclear pores

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7
Q

What transport proteins is found within the nuclear pore and acts as a gate?

A

Nuclear pore complex (NPC)

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8
Q

What is movement of proteins between the nucleus and cytoplasm called?

A

Gated transport

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9
Q

What is imported into the nucleus?

A

Proteins for structure, gene transcription and regulation

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10
Q

What is exported out of the nucleus?

A

mRNA and ribosome components

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11
Q

What happens during regulated nuclear localisation?

A

Nuclear factor of activated T-cell (NF-AT) will interact with protein phosphotase when T-cell is stimulated.
This enzyme removes a phosphate from a protein in high Ca2+ concentrations.
The enzyme blocks the nuclear export signal and exposes the nuclear import signal.
This import signal causes the importation of the protein in protein the nucleus where it can trigger the activation of gene transcription of T-cells.

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12
Q

What happens if there is a mutation in the viral protein-SV40 T-antigen signal?

A

Since the normal signal is composed of 5 positively charged residues, the mutation leading to an uncharged residue.
This causes the protein signal to stay in the cytosol and cannot move to the nucleus during nuclear localisation.

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13
Q

What type of protein transport occurs into the mitochondria and chloroplasts?

A

Transmembrane transport

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14
Q

How are proteins transported into the mitochondria? (Similar process for chloroplasts)

A
  1. Protein is produced by ribosome in the cytosol.
  2. Signal sequence is recognised by the receptor in the TOM complex outer membrane import machinery.
    - This complex is a channel which brings the protein into the space between the membranes.
  3. Protein then joins to the TIM23 complex machinery on the inner membrane which allows the protein to enter the matrix.
  4. Signal is cleaved and protein becomes a mature mitochondrial protein.
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15
Q

What type of protein transport occurs into the Rough ER?

A

Transmembrane transport

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16
Q

How are proteins transported into the RER?

A
  1. Protein made by ribosomes in cytosol.
  2. Signal sequence binds to a receptor of the RER where it is taken up by the ribosomes.
  3. Protein synthesis occurs on the RER.
  4. The protein translocates into the RER membrane during synthesis.
  5. The signal is cleaved.
17
Q

What 2 scenarios can happen with a protein when being transported into the RER?

A
  1. If it’s a soluble protein, the signal is cleaved off and left in the membrane but the protein is present INSIDE the RER.
  2. If the protein is a transmembrane protein, the signal is cleaved off and left in the membrane AS WELL AS the protein = anchored protein.
18
Q

What happens when the proteins enter the RER?

A

They can remain in the RER, travel to other organelles, be exported to the cell surface (e.g. receptor) or secreted (e.g. insulin)

19
Q

Why is vesicular transport important?

A

It is essential for cell survival and reproduction.

20
Q

What 2 processes occur with vesicular transport?

A

Endocytosis and exocytosis

21
Q

What are the 3 different types of protein coat on vesicles?

A

Clathrin, COP I, COP II

22
Q

Where is the Golgi apparatus located?

A

near the nucleus

23
Q

What is the Golgi apparatus?

A

pile of membrane sacs called cisternae

24
Q

How is the golgi polarised?

A

Has a cis and trans side.
The cis side is where vesicles come into the Golgi.
The trans side is where vesicles leave the Golgi.

25
Q

What happens within the Golgi?

A

Proteins are further modified and sorted

26
Q

How are proteins further modified and sorted inside the Golgi apparatus?

A

There are enzymes which trim parts of the core oligosaccharide from the RER.
Other enzymes can add/remove sugars.

27
Q

How is endocytosis caused?

A

By the invagination of structure in the plasma membrane mediated by the formation of clathrin coated vesicles.

28
Q

What does endocytosed material undergo in epithelial cells?

A

Transcytosis = this is when the protein is transferred from the basal membrane to the apical membrane.

29
Q

What is phagocytosis?

A

when a cell is eaten by another one.

30
Q

How do neutrophils phagocytose bacteria?

A
  1. Bacteria sit on the plasma membrane which triggers the formation of pseudopods.
  2. Pseudopods eventually lead to the formation of a vesicle that contains the bacteria = phagosome
31
Q

What characteristics do lysosomes have?

A

They are acidic which allows regulation of the acid hydrolases they contain.

32
Q

How is the pH of the lysosome maintained?

A

By a pump that actively transported protons (H+) into the organelle.

33
Q

What are the 4 distinct degradation pathways of lysosomes?

A

Endocytosis
Macropinocytosis
Autophagy
Phagocytosis

34
Q

What is autophagy?

A

it is the degradation of intracellular structures (e.g. organelles) and parts are recycled.

35
Q

What happens during autophagy?

A
  1. Nucleation and extension occurs = structures are recognised which need to be destroyed.
  2. An autophagosome is formed around the structure.
  3. Lysosome fuses with the autophagosome.
  4. Digestion occurs where the structure is broken down and parts are recycled.
36
Q

What are the 3 different secretory pathways?

A

Regulated secretory pathway
Constitutive secretory pathway
Endosomes

37
Q

What happens in the regulated secretory pathway?

A

These proteins are packaged into vesicles which sit under the plasma membrane and wait for a trigger (e.g. neurotransmitter).

38
Q

What happens in the constitutive secretory pathway?

A

The protein packaged is continuously produced and secreted.

39
Q

What are endosomes?

A

They are a mediated diversion where lysosomes are formed.

Cell Biology (3 decks)

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