Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

Biochem 385 Unit 3 > Lecture 36: Protein Targeting > Flashcards

Lecture 36: Protein Targeting Flashcards

1
Q

protein targeting (just in eukaryotic cells)

A

gest proteins where they need to go

glycosylation

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

protein synth signal sequences

A

signal sequences at N terminus

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

signal sequences at N terminus

A

of nascent polypeps

direct protein transport

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

How do signal sequences at N terminus direct protein transport?

A

by interacting with receptors and processing enzymes

signal sequences are 10-30 aas long
highly conserved

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

Signal Recognition Particle (SRP)

A

directs ribosome w/ nascent polypets destinred for:
secretion
insertiion into plasma membrane
or inclusion into lysosomes

to ER to complete protein synth

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

what do the 3 vesicle transport systems do?

A

sort ER localized proteins (many are glycosylated) to various destinations by packing into vesciles

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

what are the 3 vesicle transport systems

A

COPI, COPII, clathrin

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

ubiquitinated proteins…

A

are recycled by proteasomes in order to regulate protein turn over

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

Function of N-terminal sequence in protein transport

A

direct protien to right subcellular compartment

how? bind receptor protein

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

most signal sequences…

A

15-35 amino acids
10-15 aas are hydrophobic
have either lisine or argenine at beginning (POSTIVELY CHARGED)

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

what can hydrophobic aas do?

A

transverse the ER membrane

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

where is the N terminus

A

FIRST

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Why lisine or argenine?

A

they are positively charged!

so pos charged residue followed by hydrophobic stuff

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

What marks the C terminal end of sequence

A

protease cleaveage site

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

why are signal sequences cleaved and what by

A

cleaved by specific proteases

in order to generate a new N-terminus in mature polypeptide

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

signal sequence

A

positive charge (lys or arg) followed by hydrophobic amino acids

targets protein with this sequence to the ER

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

if no signal sequence

A

protein is retained in cytoplasm

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

So proteins destined for ____1_____ are insterted into ___2__ by ___3___

A

1: secretion, integration into plasma membrane, inclusion into lysosomes
2: lumen of ER
3: SRP (signal recognition complex)

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

signal sequence directs protein transport

A

signal peptide of end terminus synthed first (N terminus)

hydrophobic sequence recognized, tells ribsome to bind to ER membrane

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

where is rest of growing protein inserted?

A

through membrane protein

so that growing polypep chain can keep growing in ER

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

if you take a cytosolic protein and manipulate it to encode an end terminal signal peptide on the protein…

A

protein will go into the ER!!!

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

if you take a protein that usually has ER signal sequence (should be in ER) and remove the signal sequence…

A

it stays in the cytosol

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Based on these experimental data, are signal sequences necessary BUT NOT sufficient (to direct localization) or necessary AND sufficient?

A

necessary AND sufficient
if it has tag it goes into ER, if it doesn’t it doesn’t, stays in cytoplasm

this tag is enough, doesn’t need other properties

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

SPR cycle does what

A

inserts proteins into ER lumen

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
if a signal sequence is present on growing polypep chain at n terminus...
SRP recognizes it and it interacts with the SRP receptor on ER membrane as polypep grows, it goes through pore and ends up in ER this is driven by GTP
26
how long is protein synth halted
till ribosome, mRNA, and SRP-polypep complex is bound to peptide translocation complex
27
What biochemical property of signal sequences facilitattes binding to the translocon protein?
hydrophobic property!!!!
28
SRP cycle slide 6
slide 6
29
what is synthed frist
signal sequence | recognized by SRP
30
interaction with translocation complex in ER membrane
docking of ribosome happens newly synthed chain ends up in lumen
31
do mature proteins retain the signal peptide
No, they are processed
32
how are proteins processed?
``` by protease (cleaves proteins) mature end terminus and mature protein left in ER ```
33
glycosylation
adding of sugar units to proteins | happens in ER
34
what do we do with glycolyated proteins
transport them into plasma membrane | they are used in membrane for cell recognition function
35
why glycosylate proteins?
for cell cell recognition happens AS synthesized NOT in RNA code!
36
things that happen in ER
glycosylation | formation of disulfide bonds between SH and cystine residues
37
how to glycosylated
link sugar unit to aspariagine residue of protein sugar first binds in cytosol process completed in ER
38
core glycan
the first sugars that are added
39
How are proteins degredaded
proteosomes | lysosomes (not talked about much, low pH, have proteases in them, degrade more than just proteins)
40
proteosomes
just degrade proteins recognize proteins for degredation because tagged with ubiquitin allow cell to regulate proten levels
41
cellular protein life times
finite degraded at end tagged
42
ubiqutin
small (76 amino acids) covalently linked to lysine residues in proteins marked for destruction very well conserved across species
43
important features of ubiquitin
lysine residues | cc-terminus
44
importance of lysine residues
sites where ubiqutin can be conjucated to other ubiquitin molecs so chains of ubiquitin molecs can form
45
What enzymes ubiquinate
E1 E2 E3 target proteins for ubiquitination for degredation
46
E1
attached ubiquitin to itself | forms covalent bond
47
E2
ubiquitin transferred here | another covalent bond formed so that Ub is bound to E2 enzymes
48
E3
E3 binds to E2 and substrate | Substrate is protein tagged for degradation here
49
making a chain of ubiquitin
after E3 step... | ubiquitin transferred from E2 to substrate FOUR times (at least) to make chain of ubiqutin molecs attached to substrate
50
what is the substrate
the protein tagged for degredation! | need at least 4 Ubs attached for the protein to be marked for degredation
51
what happens after substrate is marked by at least 4 Ubs
signal for degredation sent proteosme protyolizes proteins, degrades it (using ATP) Ubs recycled so it can happen again
52
Proteosome structure
20S core | two 19 S caps (one per end)
53
what to the caps on the proteosome do?
can cause conformation change and open to let the protein to be degraded in they have binding sites for ubiquitinated proteins encode ATP hydrolyzing enzymes
54
proteasome core
protease sites are here | proteolyze protein down to peptides (which are released when cap opens up again)
55
The inner chamber contains the protease enzymes, what doe the outer chamber to do "prepare" proteins for degredation?
1) cap recognizes targeted ubiquitinated proteins | 2) unfolds the protein so sites are accessible for proteases in the core
56
how many kinds of proteases?
Just one! uses ATP for unfolding general because all it has to recognize is the ubiqutinated part
57
Ubiquitinatation requires 3 classes of enzymes
1) E1 enzymes ACTIVATE ubiquitin (C-terminus) transfer to 2) E2 enzymes CONJUGATE ubiquitin to target proteins at lysine residues interact with 3) E3 enzymes RECOGNIZE TARGET PROTEINS and facilitate ubiquitination by forming complexes with E2 enzymes
58
remember... why do we need lysine and C terminus
to form the ubiquitin chain
59
so how do we ID how long the half life of a protein is?
based on what the amino acid after Met is (b/c Met is often taken off)
60
really brief overview of ubiquitination
Ub is added to E1, transferred to E2, interaction between E2 and E3 happens, Ub transferred to target protein
61
N-end rule
identifies proteins with N-terminal amino acid after Met is removed tells us how long the protein will be around in cells
62
Explain why humans have 2 E1 genes, 40 E2 genes, but 400 E3 genes.
E1 works independently of the target protein, just works with Ub E2 enzymes have to interact with LOTS of E3 genes E3: lots of genes so that you can degrade a lot.

Biochem 385 Unit 3 (11 decks)

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