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BIO130 Final > Lecture 3 > Flashcards

Lecture 3 Flashcards

1
Q

How much volume does the cytosol take up in the cell?

A

about 50%

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2
Q

How much volume does the mitochondria take up in the cell?

A

about 22%

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3
Q

How much volume does the ER take up in the cell?

A

about 12%

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4
Q

What percentage of the total cell membrane does the ER make up?

A

about 50-60%

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5
Q

What does the rough ER do?

A
  • membrane-bound ribosomes
  • synthesis of soluble proteins and transmembrane proteins for the endomembrane
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6
Q

What does the smooth ER do?

A

phospholipid synthesis, detoxification

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7
Q

What is the definition of an organelle?

A

a discrete structure or subcompartment of a eukaryotic cell that is specialized to carry out a particular function

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8
Q

What are some examples of membrane-enclosed organelles?

A

nucleus
ER
Golgi

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9
Q

What are some examples of organelles that are not membrane-bound?

A

nucleolus
centrosome

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10
Q

How are proteins sorted?

A
  • cytosolic proteins: no sorting signal (default location is cytosol)
  • Proteins with sorting signal: have a signal sequence (specific amino acid sequence)
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11
Q

How are specific proteins sorted to different organelles?

A

sorted by a signal sequence (a stretch of amino acid sequence in a protein) which directs the protein to the correct compartment. Each signal sequence specifies a specific destination in the cell, which is recognized by sorting receptors that take the protein to their destination.

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12
Q

What is post-translational sorting?

A

proteins are nuclear-encoded and fully synthesized in cytosol before sorting

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13
Q

How is transport through nuclear pores done?

A

Folded protein
- signal sequence (nuclear localization signal, NLS) is recognized by sorting receptor and binds
- sorting receptor helps bring the proteins through the nuclear pore into the nucleus

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14
Q

How are proteins sorted to peroxisomes?

A

by recognizing a specific targeting signal (SKL) at their C-terminus. This allows them to be imported directly into the organelle

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15
Q

Do proteins need to unfold for import into peroxisomes?

A

No, unlike mitochondrial and chloroplast import where proteins must be unfolded, proteins targeted for peroxisomes are imported in their folded state.

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16
Q

What is the state of proteins when imported into mitochondria and chloroplast?

A

unfolded

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17
Q

Where are most mitochondrial and chloroplast proteins encoded and where do their synthesis occur?

A

encoded in the nucleus and synthesized in the cytosol and targeted by a signal sequence for import

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18
Q

How do chaperone proteins like Hsp70 assist in protein sorting to mitochondria and chloroplast?

A

delay the folding of certain domains of a protein, keeping it unfolded until it can be imported

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19
Q

What is co-translational sorting?

A

proteins that are synthesized in the nucleus and have an ER signal sequence, which is associated with the ER during protein synthesis in the cytosol

mRNA arrive in the cytoplasm, translation starts on ribosomes in cytosol, proteins with ER signal sequence are inserted into the ER as translation continues

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20
Q

Why do proteins sort to the ER?

A

as an entry point to the endomembrane system (stay in ER or go to golgi, endosomes, etc)

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21
Q

How are proteins sorted into the ER?

A

sorted into the ER co-translationally; they are directed to the ER by specific hydrophobic signal sequences and translocated across or into its membrane.

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22
Q

What types of proteins are transferred from the cytosol to the ER?

A

water-soluble proteins: completely translocated across and released into its lumen
Transmembrane proteins: partly translocated across and embedded in its membrane

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23
Q

What steps occur during co-translational translocation of soluble proteins?

A
  • translation start (N-terminal ER sequence emerges)
  • ER sequence is recognized by signal recognition particles (SRP), protein synthesis stops for a bit
  • SRP-ribosome complex binds to SRP receptor
  • translocon opens
  • proteins synthesis resumes with protein transfer into ER lumen
  • signal peptidase cleaves ER signal sequence (which is hydrophobic, stays in lipid bilayer)
  • protein is released into ER lumen
  • translocon closes
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24
Q

What is the destination of soluble proteins after co-translational translocation?

A

lumen of an endomembrane organelle or secretion at the plasma membrane

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25
Q

What role does the signal recognition particle (SRP) play in co-translational translocation?

A

in targeting ribosomes that are synthesizing proteins with an ER signal sequence to the ER membrane. It binds to both the signal sequence emerging from a translating ribosome and to an SRP receptor on the ER membrane. This interaction pauses translation and facilitates transfer of the ribosome-nascent chain complex to an available protein-conducting channel in the ER.

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26
Q

How does translation resume during co-translational translocation?

A

Once bound to its receptor on the ER membrane, SRP releases from both its binding sites allowing for GTP hydrolysis and dissociation from its receptor. Translation then resumes with simultaneous threading or “translocating” of nascent polypeptides into or across membranes.

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27
Q

What steps occur during the co-translational translocation of transmembrane proteins?

A
  • translation start (N-terminal ER sequence emerges)
  • ER sequence is recognized by signal recognition particles (SRP), protein synthesis stops for a bit
  • SRP-ribosome complex binds to SRP receptor
  • translocon opens
  • proteins synthesis resumes with protein transfer into ER lumen
  • stop-transfer sequence enters translocon
  • protein transfer stop and transmembrane domain released into lipid bilayer
  • signal peptidase cleaved ER signal sequence and translocon closes
  • protein synthesis is complete
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28
Q

What is an N-terminal ER signal sequence?

A

ER signal sequences located at the N-terminus of a protein. It’s a stretch of hydrophobic amino acids and is removed by signal peptidase and remains embedded in the membrane

29
Q

What is an internal ER signal sequence

A

ER signal sequences located in the middle of a protein. It’s a start-transfer sequence and a stretch of hydrophobic amino acids. It is not removed and remains part of the protein

30
Q

What steps occur during the co-translational translocation of transmembrane proteins that pass through the membrane several times?

A
  • translation start (internal start-transfer sequence emerges)
  • ER sequence is recognized by signal recognition particles (SRP), protein synthesis stops for a bit
  • SRP-ribosome complex binds to SRP receptor
  • translocon opens
  • proteins synthesis resumes with protein transfer into ER lumen
  • stop-transfer sequence enters translocon
  • protein transfer stop
  • start-transfer sequence and stop-transfer sequence are released into lipid bilayer
  • translocon closes
  • protein synthesis is complete
31
Q

What is the destination of co-translational translocation transmembrane proteins?

A

membrane of an endomembrane organelle or in the plasma membrane

32
Q

Which organelles make up the endomembrane system?

A

ER, golgi, endosomes, lysosomes

33
Q

What components do intracellular compartments exchange?

A

lipids and proteins

34
Q

How do lysosomes function within cells?

A

contain hydrolytic enzymes necessary for breaking down macromolecules such as nucleic acids, proteins, carbohydrates, and lipids. They act as waste disposal systems of cells by digesting unwanted materials within cytoplasmic vacuoles or materials taken up from outside of cell via phagocytosis or endocytosis.

35
Q

What is the secretory pathway?

A

Proteins and lipids made in the ER can be delievered to other compartments
- ER to outside (exocytosis)
- ER to lysosomes (by endosomes)

36
Q

What is the endocytic pathway?

A

contents moving into the cell, to endosomes, and into lysosomes

37
Q

What is the retrieval pathway?

A

the retrieval of lipids and elected proteins for reuse
- Endosomes to outside the cell
- endosomes into ER

38
Q

What is exocytosis?

A

when the contents inside a vesicle are delivered to extracellular space. When the vesicle reaches the plasma membrane, the vesicle membrane becomes apart of the plasma membrane

39
Q

What is endocytosis

A

vesicle luminal contents come from extracellular space and the plasma membrane forms the vesicle membrane

40
Q

What are the two main types of endocytosis based on vesicle size?

A

phagocytosis for large particles and pinocytosis for fluids and small molecules.

41
Q

What happens during vesicular transport?

A
  • vesicles start budding
  • attach to a protein that helps dock the vesicle
  • attaches to another protein to help fuse the vesicle into the membrane
42
Q

What are the different types of secretory pathways?

A

constitutive exocytosis pathway

regulated exocytosis pathway

43
Q

What is the constitutive exocytosis pathway?

A

in all eukaryotic cells, there is a continual delivery of proteins and lipids to the plasma membrane (soluble proteins)

44
Q

What is an example of a constitutive exocytosis pathway in the body?

A

secretion of collagen for the extracellular matrix

45
Q

What is the regulated exocytosis pathway?

A

it’s a regulated secretion of proteins stored in specialized secretory vesicles that wait for an extracellular signal to then fuse with the plasma membrane and release it’s contents

46
Q

What is an example of a regulated exocytosis pathway in the body?

A

insulin release with increased blood glucose

47
Q

What is the path of a secreted protein from translation to the plasma membrane?

A
  • translation starts on cytosolic ribosomes (ER signal sequence at N-terminus directs protein to ER)
  • Co-translational translocation of ER (protein inserted through ER membrane by translocon, ER signal sequence cleaved, secreted protein in ER lumen)
  • Secreted protein (moves in transport vesicles through secretory pathway, ER to golgi to plasma membrane, Vesicle membrane fuses with membrane during exocytosis, secreted protein released into extracellular
48
Q

What is the path of a transmembrane protein from translation to the plasma membrane?

A
  • translation starts on cytosolic ribosomes (ER signal sequence at N-terminus or internal directs protein to ER)
  • Co-translational translocation of ER (protein inserted through ER membrane by translocon, different ways that a transmembrane protein can be inserted into ER membrane)
  • Transmembrane protein (moves in transport vesicles through the secretory pathway, ER to Golgi to the plasma membrane, Vesicle membrane fuses with the membrane during exocytosis, transmembrane protein released into extracellular
49
Q

How is the asymmetry of membrane proteins maintained?

A

through vesicular transport

50
Q

What is the primary function of the Golgi apparatus in a eukaryotic cell?

A

receive proteins and lipids from the ER, modify them and then dispatch them to other destinations in the cell

51
Q

How are proteins processed in the Golgi apparatus?

A

Proteins received from the endoplasmic reticulum (ER) undergo further modifications such as glycosylation. Enzymes within different cisternae of the Golgi stack add or remove sugar molecules in a sequential manner as proteins transit from cis to trans compartments.

52
Q

Where does protein glycosylation begin?

A

it starts in the ER, where a single type of oligosaccharide os attached to many proteins

53
Q

How does the structure of the Golgi apparatus facilitate its function?

A

the structure consists of flattened membranous sacs called cisternae arranged in a stack. This organization allows for the efficient processing and sorting of molecules as they move through each compartment toward their final destination

54
Q

What role does vesicle transport play in relation to the Golgi apparatus?

A

transport materials between different compartments within the organelle and also carry modified products away from it towards other destinations like lysosomes or plasma membrane

55
Q

What is protein glycosylation?

A

the process of covalently attaching sugar molecules (oligosaccharides) to proteins.

56
Q

Why is protein glycosylation important?

A

plays crucial roles in protein folding, stability, cellular recognition, and cell-cell interactions

57
Q

What are the different units of the golgi?

A
  • cis Golgi network
  • cis cisterna
  • medial cisterna
  • trans cisterna
  • tran Golgi network
58
Q

Where does the processing of the oligosaccharide complex occur?

A

a multistage processing unit in the Golgi, with different enzymes in each cisterna (performing modifications on proteins)

59
Q

What is the function of endosomes in eukaryotic cells?

A

sorting, recycling, and transport of internalized materials from the plasma membrane to various destinations within the cell. They contain material ingested by endocytosis

60
Q

What happens during late endosome maturation?

A

involves fusion with other late endosomes or preexisting late endosomes, as well as the formation of intraluminal vesicles

60
Q

How is the acidic environment maintained within endosomes?

A

(pH 5-6) within endosomes is maintained by ATP-driven proton pumps that actively transport H+ ions into their lumen from the cytosol

60
Q

Where are early endosomes located?

A

located just beneath the plasma membrane

61
Q

What are lysosomes and what is their primary function in the cell?

A

small sacs of digestive enzymes that degrade worn-out organelles, as well as macromolecules and particles taken into the cell by endocytosis. Their primary function is intracellular degradation

62
Q

Where do lysosomes receive their digestive enzymes from?

A

receive their digestive enzymes from the Golgi apparatus, which modifies them before dispatching them to the lysosome

63
Q

How do lysosomes maintain an environment suitable for their hydrolytic enzymes?

A

The lumen of the lysosome is maintained at an acidic pH by an ATP-driven H+ pump in the membrane that hydrolyzes ATP to pump H+ into the lumen, creating conditions under which the hydrolytic enzymes are active.

64
Q

What is inside the lysosomes?

A

40 types of hydrolytic enzymes
- Acid hydrolases (proteases, nucleases, lipases)

65
Q

What is the function of the lysosomal membrane?

A
  • protects the rest of the cell from digestion
  • its membrane has proteins (noncytosolic side) which are glycosylated for protection from proteases
66
Q

What gives vesicles directionality?

A
  • directed movement of transport vesicles
  • pulled by motor proteins associated with cytoskeleton

BIO130 Final (7 decks)

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