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Cell Biology > Unit 2 > Flashcards

Unit 2 Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

How many proteins are found in eukaryotic cells

A

~10,000

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2
Q

Where does protein synthesis begin

A

Free ribosomes in ER

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3
Q

What directs the ribosome to sit down on the ER

A

Signal sequence at the N terminal end of the protein. As soon as the signal sequence of AAs exits the ribosome translations stops and ribosome sits dow on ER.

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4
Q

General pathway of a secretory protein

A

cytosol (free ribosome)

Bound to ER

Moved through translocon into ER

Modified in ER

Moved by budding into Golgi

Modified in Golgi

Packed in vesicle and moved out

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5
Q

What does this picture show

A

ER is mostly rough

SER is in the middle

Lumen of ER is continuous

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6
Q
A
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7
Q

Homegenization of cells causes

A

ER to break up into microsomes. Rough and smooth separate

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8
Q

What fraction of density gradient centrifugation contains secretory proteins

A

Rough microsomes

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9
Q

Why are secretory proteins in the ER smaller (lower mol. wgt) than those not yet in ER or unable to enter ER?

A

Signal sequence is only cleaved off in ER

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10
Q
A

If you add microsomes AFTER protein is completed then they can’t enter.

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11
Q

How can you tell that a protein has been extruded into a microsome?

A

Resistant to proteases unless treated with a detergent.

Become glycoslyated by enzymes only found within microsomes.

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12
Q

How does the signal sequence direct a protein to the ER?

A

A signal sequence binds a signal recognition particle.

SRP stops translation.

Moves to ribosome where SRP binds to the SRP receptor.

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13
Q

SRP is a

A

Riboprotein complex

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14
Q

Translocons

A

Open up once SRP binds receptor.

Do not require ATP (ATP used in translation operates the translocon)

Open only to protein and not other small molecules.

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15
Q

How does Post-Translation Translocation differ from production of a typical secretory protein

A

Riosome does not attach to ER.

Protein is completed in cytosol.

Signal sequence moves protein to translocon.

Binds / uses ATP to prevent slipping backwards in translocon.

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16
Q

What is the first part of this picture showing

A

Proteins can have different orientations in the membrane (N or C terminus in the cytosol or lumen)

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17
Q

How is orientation of multi-pass proteins determined

A

Even numer of passes = N and C term on same side.

Odd number of passes = N and C term on different sides.

**Proteins will not function without proper orientation in membrane.

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18
Q

Type 1 Membrane proteins

A

C term in cytosol

Majority of protein in lumen

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19
Q

Type II protein

A

N term in cytosol

Majority of protein in lumen

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20
Q

Type III Protein

A

C term and majority of protein in cytosol

**Tail anchored = C term embedded in membrane

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21
Q

Type IV Protein

A

Multipass proteins

Type IV - A: N and C on same side

Type IV-B: N and C on different sides

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22
Q

True or False: proteins embeded in the RER remain in the membrane as they move to their final destination.

A
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23
Q

Which end is considered to be the “tail” of the protein?

A

C terminus

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24
Q

Topology of a protein

A
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25
Q

Membrane spanning segments are usually made of

A

20 - 25 hydrophobic amino acids

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26
Q

Type II Proteins

A

Do NOT have a cleavable ER signal sequence

Oriented wth hydrophilic N-terminal region on cytosolic face

Oriented with hydrophilic C-terminal region on exoplasmic face

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27
Q

Type III

A

Same orientation as Type I due to hydrophobic membrane-spanning segment at N - terminus.

DO NOT contain a cleavable signal sequence

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28
Q

Tail Anchored Proteins

A

hydrophobic segment at C-term that spans membrane

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29
Q

What are the three main types of topogenic sequences used to direct proteins to the ER membrane?

A

N-terminal signal sequences

Stop transfer signal sequences (internal)

Signal-anchor sequences (internal)

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30
Q

What do stop-transfer anchor sequences do?

A

Stop passage of polypeptide chain through the translocon

Anchor the polypeptide to the membrane

Both type II And type III have these

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31
Q

What is the key difference between type II and III proteins?

A

orientation of hydrophobic transmemrane segment as it binds to the hydrophobic signal-sequence inding site at the edige of the Sec61alpha

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32
Q

What determines the orientation of a signal anchor sequence in the membrane

A

high density of positively charged amino acids adjacent to one end of the hydrophobic segment

Type II have + residues on N term side

Type III have + residues on C term side

**Mutations can cause these to flip

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33
Q

Why don’t tail anchored proteins get treated the same?

A

hydrophobic region at C terminus is only “visible” once the protein is done being translated and has left the ribosome.

Do not use SRP / SRP receptor

Use Get3 pathway and GTP hydrolysis

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34
Q

What serve as signal anchors in multipass proteis

A

First N-term alpha helix

odd numbered sequences

**Even numbered act as stop-transfer anchor sequences

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35
Q

What is the difference between a signal anchor and a stop transfer sequence?

A

Signal anchor: oriented with N - term toward cytoplasm

Stop - transfer: N - term toward exoplasmic face

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36
Q

What are the 4 prinicple modifications of proteins BEFORE they reach their destination

A
  1. Covalent addition and processing of carbs
  2. Formation of disulfide bonds
  3. Proper folding
  4. Specific proteolytic cleavages
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37
Q

WHat is the structure of all N-linked oligosaccharides

A

three glucose

nine mannose

two N-acetylglucosamine

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38
Q

How are N-linked oligosaccharides modified

A

addition or removal of monosaccharides in ER or Golgi

A core of 5 - 14 residues is conserved

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39
Q

Where are the enzymes that add monosaccharides to N-linked oligosaccharides found

A

on the cytosolic or luminal faces of the ER membrane

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40
Q

What are the steps to create a final N-linked Oligosaccharide

A

glycosidases remove 3 glucoses and one mannose

Three glucoses are a signal that the side chain is ready to be added to a protein

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41
Q

What is the purpose of adding N-linked oligosaccharides?

A

Promote proper folding of proteins

increase stability

Cell to cell adhesion (if on cell surface)

Induce immune response

42
Q

Where do disulfide bonds form?

A

in the lumen of the rough ER

in solube secretory proteins

on exoplasmic domains of membrane proteins

43
Q

What order to disulfide bonds form in?

A

first: stabilize small domains

Second: stabilize distant sections

44
Q

What is the enzyme that creates and changes disulfide bonds

A

protein disulfide isomerase

45
Q

What is contained in lysosome

A

low pH

acid hydrolases

Only active at low pH so this protects cell

46
Q

What plant organelle can function like a lysosome

A

vacuoe

47
Q

What directs proteins to lysosome

A

A signal sequence:

a phosphorylated mannose residue

“signal patch” found in AA chain

48
Q

Why are lysosomal disorders called storage diseases

A

missing hydrolytic enzyme so something doesn’t get broken down and it will be stored in lysosome.

49
Q

What side of golgi has vesicle budding

A

trans

50
Q

Vesicles budding from trans gogli can contain what

A

proteins to be added to cell membrane

proteins for other organelles in the cell

proteins / materials for secretion (hormones, enzymes, neurotransmitters etc)

51
Q

Transport into the cell via a vesicle includes what

A

endocytosis

(pino / phago)

recepter mediated endocytosis

52
Q
A
53
Q

Phagocytosis

A

Not random.

Specific

54
Q

Pinocytosis

A

Random and nonspecific

55
Q
A
56
Q

Receptor mediated endocytosis

A

receptors randomly caught up in pits

receptors bind molecules and then they are also in pit.

molecules released during pH change in late endosome

57
Q

Fate of receptors in receptor mediated endocytosis

A

recycled

degraded

transcytosis: moved to a different domain of membrane

58
Q

What two pathways use clathrin coated vesicles

A

trans golgi to lysosome

receptor mediated endocytosis

59
Q

What are the three types of proteins that coat vesicles

A

clathrin

cop1

cop2

COP = coatomer

60
Q

What is the process that forms / buds / pinches vesicle

A
  1. surface proteins spontaneously assemble on membrane
  2. adaptin binds the proteins to the membrane by binding its receptor
  3. protein pulls on membrane and creates the budding of vesicle
  4. Dynamin acts like a spring and squeezes off the esicle
61
Q

GTPase examples

A

Sar 1

ARF

62
Q

GTPase activation

A

Inactive with GDP

Active with GTP

63
Q

V class snares

A

are attached to donor organelle vesicle

64
Q

T class snare

A

are attached to fusing organelle

65
Q

How do Rabs and snares help with vesicle fusion?

A

Rab GTPases help vesicle find the correct membrane and forma weak interaction.

V snares then bind with T snares and pull the vesicle into the membrane

66
Q

What are the key areas in which cytoskeleton plays a role?

A

Shape changes

Coordinated movement (directional)

Division

Organize intracellular space

67
Q

What are the three types of cytoskeleton?

A

Micofilaments (actin)

Intermediate filaments

Microtubules

68
Q

Where will actin be in each of the following cell types:

polarized cells

motile cells

Dividing cells

A

Polarized: in the core structure

Motile: leading edge

Dividing: Contractile ring

69
Q

Shape of each of the following:

Actin (microfilaments)

Intermediate filaments

Microtubules

A

Actin: helical

Intermediate: rope like

Microtubule: hollow, cylindrical

70
Q

Which type of cytoplasm is rigid

A

Microtubules (still dynamic)

71
Q

G-actin is added to which end of the growing actin polymer?

A

+ end.

In vitro - end will grow, but in vivo it doesn’t grow quickly.

72
Q

What are the three steps in actin polymerization

A
  1. Nucleation **Rate limiting step
  2. Elongation at + end
  3. Steady state where rate of addition = rate of loss
73
Q

What is Cc?

A

G - actin critical concentration.

IF [Gactin] > Cc G actin will polymerize into F actin until Cc is reached.

IF [G-actin] < Cc, F actin will depolymerize into G-actin until Cc is reached.

74
Q

G actin monomers are able to bind _____________so are classified as ________________.

A

ATP

ATP binding proteins

75
Q

What is the role that ATP plays in actin polymerization?

A
76
Q

What causes “treadmilling” in actin polymerization?

A

G actin added at + end as G actin is lost at - end.

77
Q

What protein plays a role in acin polymerization

A

Actin binding protein

78
Q

Three toxins: cytochalasin, lactrunculin, and phalloidin interfer with actin what is the mechanism of each?

A

cytochalasin: causes depolymerization
latrunculin: causes depolymerization
phalloidin: causes stabiliation

79
Q

How does cofilin aid in depolymerization of actin filaments?

A

binds to the filament where ADP is high and destabilizes. Causes chunks to break off and treadmilling to increase in rate.

80
Q

What are the four steps involved in actin mediated motility?

A
  1. Extension: leading edge moves out and forms lamellipodium
  2. New adhesions form
  3. Translocation - cell moves over
  4. Breaking of old adhesion
81
Q

What does profilin do?

How is ARP (actin related protein) involved

A

mediating growth related to branched filaminets of actin.

ARP2/3 promotes branching. Branching generates the force needed to move the cell.

82
Q

What does ARP have to bind in order to cause branching

A

NPF

83
Q

Proteins polymerize into __________as the basis of cytoskeleton

A

dynamic filaments

84
Q

Three levels of cytoskeleton

A
85
Q

What is the most rigid type of cytoskeleton

A

microtubules

86
Q

Two different forms of actin and growth patterns

A

Globular G-actin

Filamentous F-actin

growth occurs faster at + end than at - end.

87
Q

What are the three steps of actin polymerization

A
  1. Nucleation *rate limiting
  2. Elongation
  3. Steady state
88
Q

What is the role that ATP plays in actin polymerization

A

without ATP can’t’ depolymerize

89
Q

How does the critical concentration compare at + and - end?

A

Cc is higher at - end so - end requires higher amount of G actin in order to polymerize.

90
Q

What do actin binding proteins do?

A

Interact with the microfilaminets

Length: cofflin

Branching: Arp2/3

Cross-linking: Filamin

Motor Proteins: Myosin

Stability: CapZ and Tropomodulin

Organization: Nebulin

91
Q

Steps in cell locomotion

A
  1. Extenstion to form lamellipodium
  2. New adhesions form
  3. Translocation
  4. Break old adhesions
92
Q

Which part of a motor protein has the ATP binding (ATPase) activity?

A

Head domain

93
Q

WHat ion is required for myosin movement along actin filaments?

A

Ca+2

94
Q

Which step of ATP hydrolysis is the “power stroke” of vesicle transport?

A

Release of Pi

95
Q

How do myosin II proteins combine to form thick filaments?

A

Aggregation of tail ends.

96
Q

Muscle cell description

A

Muscle cells = muscle fibers

long multi-nucleated cells…1 cell = 1 fiber

Bundles of fibers contain actin and myosin II

Single sarcomere runs Z disc to Z disc

97
Q

What causes muscle contractions?

A

Globular heads come off actin.

Move toward + end

Z discs contract

Happens in 100,000s of sarcomeres at once

98
Q

What can cause multinucleated cells?

A

Dysfunction of myosin II

99
Q

Role of intermediate filaments

A

Structural integrity to cells

Network in cells and @ tight junctions

Surround nucleus to form nuclear lamina (protect nucleus from sheer forces in cell).

Support organelles

100
Q

Basic structure of microtubules?

A

hollow, rigid, polymers of tubulin

101
Q

Functions of microtubules

A

Organization of organelles and transport vesicles

Beating of cilia and flagella

Structure of nerve cells, blood cells, and cilia / flagella

Chromosome alignment and separation

102
Q

Compare / contrast kinesins and dyneins

A

Kinesins move to + end

Dyneins move to - end

Both move along microtubules

Cell Biology (3 decks)

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