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Biol 2520 > Lecture 16 > Flashcards

Lecture 16 Flashcards

1
Q

CompartmentaLization

A

Only in eukaryotes

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2
Q

Why is it imp

A

Makes the function much more eefficient

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3
Q

What is not a part of EM and why ?

A

Not physically linked through vesicles or interconnected / fused
Don’t perform synthesis and modification of protein
Peroxisome - origin not known and is not part of the endomembrane systems

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4
Q

What is a lysosome

A

A digestive membrane

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5
Q

What is similar to a lysosome

A

Peroxisome - because it contains a peroxidase enzyme

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6
Q

What is the overall function of EM

A

Synthesis, sorting and secretion pf proteins and small molecules to their appropriate location in the cell

Golgi specifically modifies proteins and lipids

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7
Q

List the structures that are part of EM system

A 
Nuclear envelop
ER
glogi complex
Transport vesicle 
Endosome
Lysosome
Vacuole - not double membrane
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8
Q

Name the membrane enclosed organelles

A 
Cytosol
Nucleus
ER
GOlgi apparatus 
Lysosome
Endosomes
Mitochondria
Chloroplast 
Peroxisomes
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9
Q

What is the function of cytosol

A

Contains many metabolic pathways

Eg- Like protein synthesis , the cytoskeleton

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10
Q

What is the function of nucleus

A

Contains main genome

DNA and RNA synthesis occurs here

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11
Q

Function of endoplasmic reticulum

A

Synthesis of lipids

Synthesis of proteins

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12
Q

Function of Golgi apparatus

A

Further Modification , sorting, packaging of proteins and lipids

SPECIFICALLY

  • sorts proteins for export to other secretory pathway organelles or outside of the cell
  • to Make Glycoproteins- add sugar to proteins
  • make complex carbohydrates to be exported from the cell ( especially in plants )
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13
Q

Function of lysosome

A

Contains digestive enzymes that degrades intracellular

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14
Q

Endosomes

A

Sorting of endocytose material

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15
Q

Mitochondria

A

ATP synthase by oxidative phosphorylation

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16
Q

Function of chloroplasts

A

ATP synthase and carbon fixation by photosynthesis

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17
Q

Peroxisome

A

Oxidative breakdown of toxic molecules

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18
Q

Note , where does ATP synthesis occurs ?

A

Chloroplast
And
Mitochondria

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19
Q

Two types of ER

A

Smooth ER

rough ER

20
Q

Rough ER vs Smooth ER

A

Rough ER

Flattened sacs (cisternae) + internal space (lumen)
Associated with nuclear membrane
Has ribosome on the SURFACE
Ribosome on ER is the site of protein synthesis
Synthesizes only a small amount of lipid

Smooth ER
very curved and tubular membrane spaces
Extends throughout the cytoplasm not just with nucleus
No ribosomes, and main function is the synthesis of lipids ( eg steroids) for making specially membranes
Ca stored in muscle cells - sarcoplasmic reticulum (SER)

Similarities
Found in both plant and animal cells

21
Q

Where does protein synthesis occurs ?

A

Rough ER - on non free ribosome , ( 1/3 of protein synthesis )
These proteins have to go through the endoplasmic membrane
- secreted proteins
- integral membrane proteins
- soluble proteins targeted to ER
-goes to organelles other then chloroplast and mitochondria.

Cytosol- free ribosome. - (2/3 OF protein synthesis )
THESE proteins are used up in the same cell for
- cytoplasmic proteins
- internal plasma membrane peripheral proteins
- nuclear proteins
- soluable mitochondrial and chloroplast proteins

Note - cytosol makes proteins that stay in the cell (cytosol) , however the proteins for:ed by ER can retain in cells or go out

22
Q

Where do all protein translation begin? ⁉️

A

Free ribosomes in cytosol

23
Q

Protein sorting mechanism

A

Some proteins are retained in the cytosol
The others ho through the sorting mechanism in by 3 pathways
1- cytosolic proteins move to the nucleus VIA NUCLEAR PORES
2- cytosolic proteins move to the ER, mitochondria, or chloroplast VIA MEMBRANE TRANSPORT
3- protein from the ER move to other part of endomembrane system ( or between ER spaces) VIA TRANSPORT VESICLES

24
Q

Describe the pathway of the soluble and membrane proteins coming from the ER ?

A

ER contains 2 types of proteins
1- soluble proteins
2- membrane proteins

Soluble proteins sent to
1- some sent to golgi
2- some sent to plasma membrane

Membrane proteins
1- some proteins retained in the ER membrane
2- some sent to OTHER EM ORGANELLES or to the plasma membrane

25
Q

How is a protein sorted/ placed into its appropriate target organelle?

A

There is a signal sequence on the N terminal that helps the protein know which compartment to go
When the ribosome translates the signal sequence ( this can be even bfr the completion of translation of proteins) the ribosome guides the protein to its destination( AGAIN this can occur while the protein is synthesized)
A protein without localization signal is retained in the cytosol

26
Q

Protein synthesis occurs in 2 sites- free ribosomes and non free ribosomes , however, we learnt earlier that protein synthesis behind at the free ribosome. How does the protein synthesis end up occurring at the non - free ribosomes ?

A

Protein synthesis starts at the cytosol, if the mRNA doesn’t have any ER signal then the protein synthesis will remain ongoing in the cytosol
But if the n terminal of the mRNA hAs a localization signal for ER then it is directed towards the ER and the rest of protein synthesis occur there.
Note- polyribosome synthesis can occur at both sites

27
Q

Explain the process from the mRNA translated in the cytosol to the mRNA ending in the ER lumen.

A

As soon as an ER signal is translated the SRP attaches to the mRNA and ribosome
The SRP guides the ribosome to the the ER
Once it reaches ER , the SRP binds to the SRP receptor on the ER membrane
This binding causes the release of SRP
The ribosome is then translocated from SRP receptor to a protein translocator
Protein synthesis resume at original speed and the protein translocator , and positions the protein across the lipid bilayer
The protein translocator binds to the signal sequence and passes the rest of the growing polypeptide into the lumen
At a point SIGNAL PEPTIDASE cuts the polypeptide from the signal sequence, and the signal sequence is ejected in the bilayer and is degraded.
Once the protein synthesis is completed , the TRANSLOCATED POLYPEPTIDE is released as a soluble protein into the ER lumen, and the protein translocator closes

28
Q

What is the most extensive organelle

A

ER

29
Q

Describe vesicles structure

A

Small blebs of lipid bilayer membrane surrounding an aqueous interior.

30
Q

What can vesicles carry

A
  • soluble proteins and small molecules in the interior
  • integral membrane in the membrane of the vesicle
    —— membrane in a membrane is how membrane of other organelles grow
31
Q

There are two types of proteins are embedded into the membrane list them.
Also describe the function of start and stop signals

A

1- A single pass transmembrane protein embedded in the lipid bilayer
2- A double pass protein that has an internal ER signal sequence
Start and stop determines the arrangement of a transmembrane protein in the lipid bilayer

32
Q

How is a protein embedded in the membrane- SINGLE PASS

A

There are 2 signalling sequence in the in the protein
-The Start sequence at N terminal ER signal
-And a hydrophobic stop transfer sequence
The N sequence is attached to the protein translocator and initiates the TRANSFER .
The protein translocator positions the polypeptide across the bilipid layer until the hydrophobic signal is reached
The N terminal signal is cleaved by signal peptidase and the growing polypeptide is discharged into the LIPID BILAYER
The N terminal signal stays in the lipid bilayer and is degraded
The polypeptide continues to grow on the cytosolic side and continues to discharge into the lipid bilayer
Note| the single pass transmembrane protein is retained in the lipid bilayer and doesn’t fall into the lumen , because it is supposed to be embedded in the lipid bilayer

33
Q

How is protein embedded in the membrane -DOUBLE PASS

A

The double pass transmembrane protein has an internal ER signal while the single pass had an N terminal ER sequence
The same process of bringing the Ribosome to ER occurs involving a SRP , however this time it attaches to the internal hydrophobic ER signal sequence ( as there is no N terminal ER signal sequence )
The internal ER sequence acts as 1- start transfer signal and 2- anchors the final protein in the membrane
The protein translocator attaches to the hydrophobic ER signal sequence and positions the rest of the polypeptide across the lipid bilayer until hydrophobic sequence is reached
When a stop sequence is recognized, both sequences , the growing COOH and the N terminal sequence are released into the Lipid bilayer .
No sequence is cleaved off and the entire polypeptide remains anchored to the LIPID BILAYER

Note - both the internal and stop transferase signal are hydrophobic

34
Q

Describe the Polarity and structure of integral membrane proteins.

A

Cytosol side of membrane proteins - + charged
ER LUMEN OF PROTEIN- - charged
This polarity is present when being synthesized
The integral membrane is made of alpha helices
The amino acid in the centre of protein is are hydrophobic
And the charged amino acid can interact with the hydrophilic

35
Q

Types of protein modification that occurs in the ER

A

They three types of protein modification are
1- disulphides bond formation
2- glycosylation
3- protein folding

36
Q

What do the modification do?

A

1- disulphide bridges - stabilizes the structure of secretory proteins
2- glycosylation- short branched ovligosacharides are added from a lipid to protein by an enzyme called GLYCOSYL TRANSFERASE
This helps
- protection from degradation
- cell cell recognition
- facilitate protein folding
3- protein folding - chaperones bind and alter the folding of newly forming proteins
Folding is required before proteins carry out their function

37
Q

Where do glycosylation occurs ?

A

Golgi and ER

38
Q

What happens to modified proteins⁉️

A

Leave the ER - can be retained within the cell or can be secreted outside
OR
Retain within the ER if misfolded or if used as membrane proteins

39
Q

How is the exit at ER controlled to ensure protein quality ?

A

By ensuring
- if a protein has ER retention signal ( recognized by ER membrane receptors and retained)
- IF a secretory protein is folded properly
- If they are misfolded CHAPERONES bind to it and retain them in ER until they are folded properly
If they still dont fold properly they are destroyed

40
Q

What is important in the folding of proteins and why ?

A

Correct tertiary state - native state - for functioning properly

41
Q

Proteins can be misfolded due to

A

Heat

Chemicals such as urea

42
Q

What is UPR and when is it activated?

A

When misfolded protein are retained in theER
They accumulate in ER
The accumulation activiate an unfolding protein - UPR
UPR causes the activation of genes that increase protein folding capacity

43
Q

What are the 3 main factors involved in UPR

A

1- IREI
2- PERK
3- ATF6
These 3 factors are required for activation of UPR

44
Q

Translocation also cones to a haul to avoid accumulation of misfolded proteins .. T F

A

T

45
Q

Where does most modification occur

A

In the ER

Biol 2520 (16 decks)

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