Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

Cell Bio Semester 1 > ER > Flashcards

ER Flashcards

1
Q

why are proteins degraded?

A
  • if misfolded

- aged proteins may be damaged

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

consequences of misfolded proteins?

A

progressive neurodegenerative diseases-eg Alzheimers, prion diseases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

how are REGULATORY PROTEINS controlled? give example

A
  • maintained at low levels by having a short half life

- eg if conditions change(trigger) they are rapidly degraded (eg cyclins-rapidly degraded at the end of mitosis)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

how are proteins broken down? Give structural details

What is formed?

A

using PROTEASOME (multi protein complex). Is a protease that uses ATP.

  • hollow tube w/ many subunits
  • proteases face inwards
  • CAP structures on either end act as GATEWAYS
  • cap has ATPase activity which is thought to unfold the target protein
  • short peptides formed
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

how is proteasome entry controlled?

A

UBIQUITIN- short peptide which can be covalently attached to NH2 side chain of LYSINE (lysine specifically because it has NH side chains) residue on the proteins targeted for degradation.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

what decides what UBIQUITIN attaches to?

A

UB binds to UB ACTIVATING ENZYME (E1) which transfers UB to protein called UBIQUITIN LIGASE (E2/E3 complex).
-E2/E3 recognises the protein targeted for degradation and TRANSFERS UB onto it

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

what happens once one UB is added?

A

more are added to create UB chain. Acts as SIGNAL for degradation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

describe UB ligases

A

~300 diff UB ligases for diff purposes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

what does AMPHIPATHIC mean?

A

spontaneously form bilayers

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

structure of phospholipid

A

choline, phosphate and glycerol head (hydrophilic) and fatty acid tails (hydrophobic)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

function of ER

A

SER is the major site of phospholipid synthesis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

how does ER synthesise phospholipids?

A
  • new phospholipids assembled in OUTER LEAFLET of ER membrane by memb. bound enzymes which combine their components
  • SCRAMBLASE is a PHOSPHOLIPID TRANSLOCATOR-causes the two leaflets to EQUILIBRIATE.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

how do new phospholipids get to the Golgi/plasma memb/lysosomes/endosomes?

A

VESICULAR TRANSPORT

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

what do the ribosomes on RER make?

A

-secretory proteins
-transmembrane proteins
-ER AND Golgi proteins
-lysosomal proteins
and more

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

what is the possible pathway of ribosomes to produce

A

polyribosomes go from being on mRNA (IN CYTOSOL) that encodes cytosolic protein (—–> to a COMMON POOL OF RIBSOMAL SUBUNITS (IN CYTOSOL) —-> polyribosomes go to being on mRNA (IN ER MEMB) that encodes protein going to the ER.

ref cell bio, lecture capture, ER, 40:23 mins in

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what does a nascent polypeptide chain mean?

A

a polypeptide chain that has just been made

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

what is the function of the signal peptide on the chain of peptides on the nascent chain?

A

tells the ribosome where to go.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

how does the signal peptide work?

A

as soon as it is synthesised and has left the ribosome,

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

what is a common feature of all signal peptides?

A

they are a chain of HYDROPHOBIC AMINO ACIDS

20
Q

what recognises the signal peptide in co-translational targeting of proteins to the RER?

A

the SIGNAL RECOGNITION PARTICLE- it binds to the SIGNAL PEPTIDE

21
Q

what effect does the SIgnal Recognition Particle binding to the Signal peptide have?

A

it pauses translation - important so protein is not released in wrong place (as this takes place in cytosol)

22
Q

what occurs after the SRP binds to the signal peptide?

A

SRP interacts w/ SRP RECEPTOR in ER memb, (ie docking to receptor in membrane)

23
Q

what are the functions of proteins in the cell plasma membrane?

A
  • receptors (eg that react to hormones outside the cell)

- transporters that allow movement into cell

24
Q

what happens after the SRP complex docks to the receptor?

A

protein being synthesised is inserted into the pore. srp is done, translation can continue, protein is pushed through the PROTEIN TRANSLOCATOR

25
what is the function of the Sec61 translocon?
protein complex that mediates the translocation of proteins into the ER lumen and the insertion of transmembrane domains into the ER membrane
26
why is the process of getting proteins to the RER called co-translational?
because the protein is being synthesised/translated AT THE SAME TIME AS it is being pushed through the into the ER lumen
27
how do soluble proteins move from the pore to be free in the ER lumen? why is made more difficult?
the SIGNAL PEPTIDE is HYDROPHOBIC and therefore does not want to leave the environment of the membrane. the protein is moved from the membrane by SIGNAL PEPTIDASE- cuts between signal peptide and rest of protein. O SIGNAL PEPTIDE remains in memb (& will be degraded)and the mature soluble protein is in the ER LUMEN
28
how are signal peptides useful in transmembrane proteins?
the signal peptide is HYDROPHOBIC O this anchors the protein in the membrane.
29
how are transmembrane proteins formed? how is it made into a structure comprised of 2 or more transmembrane proteins?
- SRP binds to SIGNAL PEPTIDE (also called START-TRANSFER SEQ in the case of transmem proteins) - brings complex to TRANSLOCON - SIGNAL PEPTIDE/START-TRANSFER SEQUENCE docks - protein formed is pushed through the pore into ER LUMEN forming SINGLE SPANNING TRANS MEMB PROTEIN - STOP TRANSFER SEQ binds, ribosome stops to transfer the protein into the ER lumen and rest of the chain is released on the cytosol side of the membrane - process terminated, looping transmembrane protein formed
30
where do the signal peptides and stop transfer sequences bind on the translocon?
signal peptides and stop transfer sequences are hydrophobic and O they bind to the hydrophobic regions of the translocon
31
what anchors the protein in the membrane?
the hydrophobic regions are attracted to each other
32
what is the difference between a signal peptide and a stop transfer sequence?
signal peptide is cleaved off, stop transfer isn't as it needs to keep the protein attached to the membrane
33
is the translocon hydrophilic or hydrophobic?
pore is hydrophilic but there are regions on the inner memb that are hydrophobic(where signal peptides & stop transfer seq will bind)
34
how do proteins leave the translocon to be in the membrane?
the translocon has a cleft which allows transmembrane protein to leave and go into the membrane, allowing the next chain to come into the translocon
35
what is N-glycosylation? why is it called 'N-linked'?
adding carbohydrate side chains to a protein. N linked because it is added to the nitrogen of the amine group of the protein
36
what is added to a protein to glycosylate it? where is it added?
a 14 sugar modification added to [ Asparagine-X-Serine/Threonine]
37
where does N-linked glycosylation occur?
while the protein is coming into the ER lumen
38
how is the 14 sugar modification added to a protein in N-linked glycosylation?
a LIPID molecule called PHOSPHODOLICHOL in ER membrane has the precursor OLIGOSACCHARIDE assembled onto it. OLIGOSACCHARIDE is transferred to the elongating peptide chain by OLIGOSACCHARYL TRANSFERASE enzyme (from ER lumen)
39
what is the function of carbohydrate side chains on membrane proteins?
- signal molecule for cell to cell communication - act as a recognition site for receptors - monitor if a protein is folding into the correct shape
40
where does protein folding occur?
ER lumen
41
what is the function of calnexin?
is a chaperone protein: assist the covalent folding or unfolding and the assembly or disassembly of other macromolecular structures.
42
how does calnexin work?
during the initial phases of folding, 2 of the 3 terminal glucose molecules are removed. - calnexin recognises and binds to the final glucose - gives protein more time to fold and preventing export to Golgi - the final glucose is removed - if not fully folded, GLUCOSYL TRANSFERASE adds another glucose and Calnexin binds again
43
what happens to misfolded proteins?
chaperoned back to the dislocation complex and sent to cytoplasm for degradation (retro-translocation)
44
what happens to correctly folded proteins from the ER?
go to be exported to Golgi ( or remain in ER)
45
what are the major functions of SER?
- phospholipid synthesis - site of steroid hormone (hydrophobic hormones) synthesis - calcium ion store
46
how does the SER detoxify drugs in the hepatocytes of the liver?
- proteins like cytochrome P450 in the ER membrane bind to lipophilic drugs and OXIDISE them - this makes the drug more HYDROPHILIC O more water soluble - O can be modified for EXCRETION through bile or urine

Cell Bio Semester 1 (5 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions