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Cell Bio > Test 2 Study Guide > Flashcards

Test 2 Study Guide Flashcards

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1
Q

What are the two paths for protiens to be translated?

A
  1. Synthesized by free ribosomes in the cytosol.
  2. Membrane-bound ribosomes
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2
Q

What proteins are synthesized by free ribosomes in the cytosol?

A

Proteins that remain in cytosol or
incorporated into mitochondria,
chloroplast, or nucleus interior or
peroxisomes

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3
Q

What proteins are synthesized by membrane-bound ribosomes?

A

Proteins that are packaged and transported into the ER lumen

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4
Q

What is the endoplasmic reticulum? What are its two subdivisions?

A

Endoplasmic reticulum: membrane
network that surrounds the nucleus.

  • Rough ER: contains ribosomes
  • Smooth ER: synthesize lipids,
    phospholipids, steroid hormones, and cholesterol
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5
Q

What is the sarcoplasmic reticulum?

A

A storage space for calcium.

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6
Q

Describe the Pulse Chase Experiment. What was the point of it?

A

The experiment studied intracellular pathways of secreted proteins.

  • Use a media with radioactive amino acids.
  • Have a 3-minute incubation with radioactive amino acids (pulse)
    (Any proteins synthesized in pulse with be radioactively labeled)
  • Newly synthesized proteins in rough ER
  • Replace media with media containing nonlabelled amino acids (can’t track) and incubated amino acids (chase). Cells will contain a discrete population of radioactively labeled proteins
  • Radioactive proteins from ER to golgi apparatus
  • Moved to secretary vesicles to plasma membrane and cell exterior
  • Chasing pulse labeled with non-labelled amino acids.
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7
Q

Describe the In vitro reconstitution of translocation experiment: B cell

A

Primary response
o Antibodies bind to antigens
o B cells recognize antigen and form clones
o Only expand this kind of B cells

Secondary response
o Humoral response
o Create memory cell in case of reinfection

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8
Q

Describe the In vitro reconstitution of translocation experiment: translation and gel electrophoresis

A

Translation on free ribosome: protein is larger
o Still has signal sequence because no peptidase to cleave it

Translation with ER vesicles present: protein is smaller
o Protein incorporated into vesicles and cleaved to correct size
o Peptidase that can cleave signal sequence

Enzyme peptidase present in ER that cleave signal sequence

Secretory proteins are targeted to ER by amino terminal signal sequence
o When ER derived vesicles are added to system, growing polypeptide chains incorporated into vesicles
- Signal sequences removed by proteolytic cleavage

Signal sequence with hydrophobic amino acids and cleavage site of signal peptidase
o Span 15-25 amino acids with stretch of 7 hydrophobic amino acids

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9
Q

Describe targeting to ER by a signal recognition particle

A
  1. Protein synthesized on free ribosome and SRP (RNP of six polypeptides and RNA)
    recognizes signal sequence and binds
  2. SRP receptor recognizes SRP and binds complex to membrane
    Interaction between SRP and receptor cause GTP hydrolysis to:
    i. Release SRP and bind ribosome to translocon
    ii. Insertion of signal sequence in translocon
    iii. Displacement of translocon plug
  3. Insertion of polypeptide to grow in ER
  4. Signal peptidase cleaves signal sequence in translocon
  5. Signal sequence stays in interior in ER and released in extracellular space
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10
Q

What type of structure are most membrane bound proteins?

A

Alpha Helix

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11
Q

What is the location of the C and N terminus dependent on in a membrane protein?

A

Dependent on growing
polypeptide chains being translocated into ER.

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12
Q

Integral membrane helices exit translocon laterally

Describe Scenario 1: Transmembrane region (alpha helix)
exits translocon laterally and inserted into ER
membrane

A
  • Polypeptide with signal sequence cleaved by peptidase
  • Sequence with hydrophobic amino acids recognized and slides into translocon (NOT cleaved because does not have cleavage sequence)
  • Becomes embedded into ER: N terminus in ER lumen and C in cytosol
  • Synthesis continues outside in cytosol
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13
Q

Integral membrane helices exit translocon laterally

Describe scenario 2: when proteins lack amino terminal signal sequence

A
  • No signal peptide sequence at N terminus = no signal peptidase cleavage.
  • Internal transmembrane sequence that is recognized (Alpha helix with hydrophobic amino acids recognized by SRP and inserted into translocon)
  • Exits into ER membrane laterally and synthesis continues in ER lumen
  • N terminus in cytosol and C terminus in ER lumen
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14
Q

Integral membrane helices exit translocon laterally

Describe scenario 3: Insertion orients N terminus in ER lumen

A
  • No signal peptide sequence at N terminus = no signal peptidase cleavage.
  • Internal transmembrane sequence that is recognized (Alpha helix with hydrophobic amino acids recognized by SRP and inserted into translocon)
  • Exits into ER membrane laterally and synthesis continues in ER lumen
  • N terminus in ER lumen and C terminus in cytosol.
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15
Q

What factors play a role in the C terminus of a protein being in the ER lumen vs the N terminus?

A

Factors determining orientation not known, but contributing factor is
amino acids immediately flanking transmembrane domain.

Polypeptide chains inserted into translocon with positively charged
residues on cytosolic side.

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16
Q

What is a multi pass transmembrane proteins?

A

A protein that contains more than one transmembrane domain (TMD) that spans a lipid bilayer

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17
Q

How do multi pass transmembrane proteins occur?

A

Aia alternating looping mechanism.

  • Many transmembrane sequences to loop protein in membrane
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18
Q

How do C terminal insertions occur?

A
  • TRC40 binds to C-terminal TM sequence after translation is complete
  • Polypeptide released from ribosome, then TRC40 binds to C-terminal TM sequence
  • TRC40 binds to GET1-GET2 to insert into plasma membrane
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19
Q

What is the difference between a C terminal and an N terminal

A

The N-terminal refers to the end of a protein chain with a free amino group (-NH2), while the C-terminal refers to the end with a free carboxyl group (-COOH).

Essentially, the N-terminal is the “start” of the protein sequence, and the C-terminal is the “end” when reading the chain from left to right.

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20
Q

What are two major modifications that occur in the ER?

A
  1. N-linked glycosylation: adding sugar to asparagine and removing glucose while protein is still in ER.
    a. Prevents protein aggregation in ER
    b. Role in protein folding and sorting
  2. GPI anchor: anchor proteins to membrane
    a. GPI: glycophosphatidylinositol, modified phospholipid with carbohydrate groups

i. Added to carboxy terminus of some proteins through reaction catalyzed by GPI transamidase.

ii. Common to cell surface proteins

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21
Q

What does GPT transamidase do?

A

Cleaves GPI anchored proteins and exchanges C terminal domain for GPI anchor.

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22
Q

True or false: Di-sulfide bonds are formed in the ER?

A

True

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23
Q

How does the environment of ER lumen facilitates disulfide bond formation?

A

Oxidizing environment of lumen facilitates disulfide bond formation; creates a covalent linkage between sulfur containing amino acids

-

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24
Q

What protein facilitates Disulfide bond formation?

A

Facilitated by protein disulfide isomerase (PDI)

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25
Q

What is the purpose of disulfide bonds?

A
  • Many multi subunit proteins stabilized by disulfide bonds
  • Role in structure of secreted and cell surface proteins
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26
Q

What is a flipase?

A

Flipases: enzymes that transfer/flip phospholipids from one half of lipid bilayer to other, typically directed inward.

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27
Q

What is a flopase?

A

enzymes that transfer/flip phospholipids from one half of lipid bilayer to other, typically directed outward.

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28
Q

What is a scramblase?

A

Scramblases equilibrate lipids across the bilayer. They transport lipids at rates that are orders of magnitude greater than the rate of flip and flop catalysed by filppases and floppases.

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29
Q

What is an ERES?

A

ER Exit Site

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30
Q

True or False:
Packaging of ER synthesized proteins into vesicles is highly selective.

A

False

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31
Q

What motifs target proteins to be recycled back to ER?

A

KKXX or KDEL motifs.

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32
Q

How are Proteins and lipids carried from ER to golgi?

A

In transport vesicles that
bud from ER exit sites (ERES)
and then fuse to form the vesicles and tubules of ER-golgi intermediate compartment (ERGIC) and carried to golgi.

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33
Q

What luminal ER proteins are targeted to the golgi?

A

Proteins that are bound to transmembrane proteins that are selectively packaged into vesicles

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34
Q

True or False:
If a protein needs to be exported from ER to golgi, it is recognized by recycling receptor in ERGIC or golgi and selectively returned to ER.

A

True

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35
Q

What is the golgi comprised of?

A

Stacked membrane compartments called cisternae

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36
Q

What is glycosylation?

A

The addition of carbohydrate groups to proteins.

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37
Q

Describe the Modification of
N-linked oligosaccharides

A

3 glucose residues removed in ER and N-linked oligosaccharides of these glycoproteins are further modified as protein travels through golgi.

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38
Q

What modification targets to the lysosome?

A

Mannose-6-phosphate modification specifically targets proteins to lysosome

  • Instead of mannose removed, modified by mannose phosphorylation
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39
Q

What is a GAG? Give two examples.

A

glycosaminoglycan. Important roles in maintaining tissue structure, lubrication, and cell signaling; They are complex sugar molecules with a negative charge that attract water, acting as a “gel-like” substance within the body.

Chondroitin sulfate: cartilage component that breaks down with age

Keratin sulfate: component of extracellular matrix that absorbs stress

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40
Q

What does trafficking depend on?

A

vesicle coat proteins and cargo-receptor interactions

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41
Q

What allows for selective trafficking through the cell?

A

Coat proteins and cargo-specific receptors

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42
Q

Name the three families of coat proteins and what they do

A

COPI - Retrograde (against flow of secretion)
COPII - Anterograde (with flow of secretion)
Clathrin – trans-golgi and beyond

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43
Q

What is the difference between retrograde and anterograde?

A

Retrograde – against normal flow of secretion
Anterograde – with normal flow of secretion

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44
Q

True or False: Receptors in the ER/Golgi bind specific cargo

A

True

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45
Q

What is Arf?

A

Small g-protein involved in coat formation and vesicle budding

Interacts with GEF for GTP hydrolysis (Arf-GTP)

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46
Q

What does Arf-GTP accomplish?

A

Binds adaptor protein that recruits cargo/receptor complex
and initiates coat assembly

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47
Q

What G-Proteins do COPI, COPII, and Clathrin use ro initiate coat assembly?

A

COPI and Clathrin use Arf

COPII use Sar (different Gprotein)

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48
Q

How does the clathrin triskeleton link together?

A

3 subunit trimer that fit together to form coat
* Twist around budding vesicle
* Shape depends on cargo

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49
Q

What is dynamin?

A

Constricts vesicle as it forms and cuts vesicle from lumen

Promotes vesicle fission and budding

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50
Q

True or False:
Clathrin/COPI/COPII coat removed when vesicle reaches target
membrane

A

True

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51
Q

What is a Rab?

A

A small g-protein on surface of vesicle

Binds to tethering factor on target membrane
More than 60 unique Rab proteins identified

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52
Q

What do SNARE complexes do?

A

Mediate the fusion of vesicle and target membrane – requires energy – provided by pairing of SNARE complexes through coiled-coil domains

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53
Q

What does an ERD2 (KDEL) receptor do?

A

Going to move something back to ER. Retrograde.

54
Q

What does a mutation in the ERD2 (KDEL) receptor lead to?

A

Mutation in many of these proteins results in aggregation of cargo in the wrong location.

55
Q

What does a clathrin coat mean for a vesicles final location?

A

It is going to the cell surface for secretion.

56
Q

True or False: The Cell is able to create different size and structure clathrin depending on needs

A

True

57
Q

How is vesicle fusion accomplished?

A

Through snare complexes (AKA Snare pairs)

58
Q

Describe how a cell knows a vesicle is in the right spot.

A

If v-snare and t-snare match, they coil together and pull the vesicle membrane into the target membrane, which leads to a fusion event and the generation of a pore. This incorporates the vesicle into the target membrane.

59
Q

What are v-snares and t-snares?

A

v-snare- Vesicle SNAREs
t-SNARE – Target SNAREs

60
Q

Describe the insulin glucagon relationship

A

Insulin lowers blood sugar by facilitating glucose uptake into cells, while glucagon raises blood sugar by stimulating the liver to release stored glucose; when blood sugar is high, insulin is secreted by pancreatic beta cells, and when it drops too low, pancreatic alpha cells release glucagon to compensate.

61
Q

What is the pancreas?

A

A specialized organ for secretion, regulates osmolarity and blood sugar

62
Q

What is a secretory cell of the pancreas called?

A

A beta cell

63
Q

What is a lysosome?

A

Special digestive organelles that create a low pH via a proton pump

64
Q

What are acidic hydrolases?

A

Digestive organelle that are optimal
active only at pH 5

65
Q

Give two benefits of the acidic environment of the lysosome.

A
  1. Acid hydrolases are optimally active at pH 5, but not at pH 7.
  2. Acidic environment of lysosome also facilitates denaturation of lysosomal contents
66
Q

How is lysosome pH maintained?

A

By proton pumps that
selectively move protons into interior of lysosome

67
Q

What happens if a lysosome ruptures?

A

Hydrolase activity drops, but enough
activity to degrade surroundings

68
Q

What is autophagy?

A

“self eating”
The breakdown of the cell’s own components, including organelles

This is a way to recover energy and materials.

69
Q

What percent of cellular proteins are broken down per hour through autophagy?

A

1%

70
Q

True or False: Autophagy can also be induced as a response to stress/starvation

A

True

71
Q

Describe the roles of Atg9 and Atg2 in autophagy.

A

Atg9 – scramblase necessary for membrane expansion of autophagosome

Atg2 – lipid transfer protein – supplies phospholipids for autophagosome formation

71
Q

How does autophagy work?

A

The Autophagosome fuses with the lysosome which creates a phagolysosome and breaks down materials.

72
Q

If autophagy in neurons is disrupted, what occurs?

A

Harmful aggregate formation.

73
Q

Describe how a autolysosome forms.

A

Vesicles interact with each other to form autophagosome precursor

Membrane expands by adding lipids into ET through Atg2 and/or fusion with ER derived vesicles

Membrane expansion produces phagophore

Released from ER as double membraned autophagosome

Outer membrane fuses with lysosome to create autolysosome

74
Q

What do endosomes represent an intersection between?

A

Secretion and endocytosis

75
Q

What are endosomes involved in?

A

Involved in recycling cell surface receptors and other molecules.

Can also target molecules for degradation in the lysosome

76
Q

What is the Ubiquitin-proteasome pathway?

A

Major pathway for regulated protein
degradation

77
Q

What are two things protein levels in the cell depend on?

A
  1. rate of protein synthesis
  2. rate of protein degradation
78
Q

What does the proteasome recognize? What does it use energy to do?

A

The proteasome recognizes ubiquitinated proteins and uses energy to break peptide bonds.

79
Q

What does the E3 ligase system do? Describe the steps.

A

The E3 ligase system marks protein for degradation by adding ubiquitin to them

  1. Ubiquitin added to ubiquitin-activating enzyme, E1 (requires ATP hydrolysis)
  2. Ubiquitin transferred to ubiquitin conjugating enzyme, E2
  3. E2 then interacts with ubiquitin ligase (E3), which selectively targets proteins. Ubiquitin is then transferred to target protein
  4. Polyubiquitination of protein targets it for proteasomal degradation
80
Q

What is a proteasome made of? What does it do?

A

A complex of proteases – cleaves peptide bonds between amino acids

This requires energy (ATP hydrolysis)

81
Q

What are the three parts of cell signaling?

A
  1. Signal perception
  2. Intracellular signal transduction
  3. Cellular response
82
Q

List and describe the four types of signaling we covered

A
  1. Paracrine signaling: signaling to neighboring target cells
  2. Autocrine signaling: self-signaling
    Ex: tumors secrete growth factors to provide own signals to grow
  3. Direct cell-cell signaling: Sharing cytosol to make pore (gap junction)
    Ex: heart with gap junction to coordinate contractions
  4. Endocrine signaling: signaling by secreted molecules
    o Long distance signals
    o Released in circulatory system to travel to target cells
83
Q

What are the Hallmarks of signal transduction?

A
  • Conversion of signal
  • Modulation of signal can cause amplification or sustained response
  • Crosstalk: transducing signal can be modulated by other pathways
  • Multiple responses per signal based on receptors, etc.
84
Q

How can signals regulate themselves?

A

Feedback loops.

Positive Feedback: (ex: childbirth)
Negative Feedback: (ex: odor reception)

85
Q

What is crosstalk?

A

Interaction of one signaling pathway with another
- Context dependent
- Activity of one pathway can modulate activity of another
- Cellular response depends on combination of multiple signals

86
Q

What do several steroid hormone receptors do upon ligand binding?

A

translocate to nucleus

87
Q

How do steroid hormones enter the cell?

A

Steroid hormones (estrogen, testosterone, and glucocorticoids) o Diffuse across plasma membrane, as they are nonpolar and hydrophobic.

88
Q

How do glucocorticoids impact transcription?

A
  • Diffuse across plasma membrane
  • Glucocorticoid bind to hormone receptor and displace Hsp90
  • Inactive receptor in cytosol becomes active by forming dimer
  • Receptor dimer translocates into nucleus and interacts with HAT
  • Increase transcription of target genes
89
Q

What are two common methods for transducing signals?

A
  1. Confirmational changes by small molecule binding
    ex- cAMP induces conformational change in regulatory subunits – dissociates from catalytic subunits
  2. Protein Phosphorylation and Dephosphorylation
    Phosphate groups can be added to serine, threonine, and tyrosine amino acids
    -Charge
    -Conformation
    -Activity
90
Q

What do steroid hormones primarily induce in the cell?

A

Primarily induce transcriptional changes.

91
Q

How do androgens like testosterone impact transcription?

A

Signal through a similar mechanism to glucocorticoids

  • Diffuse across plasma membrane
  • Bind to hormone receptor and displace Hsp90
  • Inactive receptor in cytosol becomes active by forming dimer
  • Activated receptor dimers bind to Androgen Response Elements (ARE) in DNA to regulate transcription of target genes
92
Q

How does thyroid hormone go through its binding process?

A

The receptor for thyroid hormone binds to DNA regardless of whether its ligand is present, stays poised on promoters waiting to bind their ligand.

Thyroid hormone binding changes the receptor from a repressor (associated with HDAC) to an activator (associated with HAT)

Thyroid hormones play a major role in the regulation of metabolism and growth

93
Q

What does retinoic acid do?

A

Role in tissue development and regeneration

Provides positional information during limb regeneration in
amphibians

94
Q

Other small molecules may act as signaling triggers. Give some examples of these molecules and what they do.

A
  • Nitric oxide: blood vessel tone regulation
  • Acetylcholine: neurotransmitters
  • GABA: neurotransmitter
  • Auxin: plant growth hormone
  • Hydrogen peroxide: forms gradient after injury to show injury location
95
Q

Many signaling molecules in animals are proteins. Describe them

A
  • Cannot cross membrane; must bind to cell-surface receptors
  • Peptide hormones and neuropeptides with post translational modifications
  • Increase stability and alter charge and structure of peptide
  • Disulfide bond linkage
  • Glycosylation
  • N-terminal acetylation and C-terminal amidation
96
Q

What are disulfide bonds?

A

Strong covalent connections found on extracellular proteins

97
Q

Describe how disulfide bonds form

A
  • Oxidizing environment of ER lumen facilitates disulfide bond formation
  • Covalent linkage between sulfur containing amino acids (cysteine)
  • Disulfide bond formation facilitated by protein disulfide isomerase (PDI)
  • Cleavage of signal sequence and removal of connecting peptide
  • Many multi subunit proteins stabilized by disulfide bonds
98
Q

True or false:
Insulin is structured around a disulfide bond?

A

True

99
Q

What can conformational change trigger?

A

Dimerization, which is needed for downstream signaling

100
Q

What does PDGF accelerate?

A

Wound closure in culture and is necessary for regeneration in vivo

  • PDGFR inhibitor = prevent regeneration
  • Need many signals and receptors for regeneration
101
Q

What is a GPCR?

A

A G Protein coupled receptor. A large protein family of receptors that detect molecules outside the cell and activate internal signal transduction pathways and cellular responses.

102
Q

What is cAMP?

A

Cyclic adenosine monophosphate.
A second messenger that works through GPCR signaling

  • Responsible for intracellular
    responses following ligand binding
103
Q

Describe how GPCR signaling and heterotrimeric G (GTPase) Proteins work together.

A
  1. Ligand binds and receptor changes
    conformation
  2. Receptor acts as GEF to exchange GDP for GTP and activate signal
    a. Alpha dissociates to activate adenylyl cyclase and produce cAMP
    b. Beta/gamma goes to other targets
  3. GRK phosphorylates intracellular sites
  4. Downstream effects: gene expression, cAMP production, cell excitability
    - To turn off receptor, remove from membrane
  5. Alpha G protein subunit activity terminated by hydrolysis of GTP
    o Stimulated by RGS protein
    o GDP bound alpha subunit
    reassociates with beta/gamma
    complex
104
Q

Describe the cAMP/PKA Pathway

A

Two primary pathways of GPCR signaling rely on modulating intracellular cAMP or Ca levels

  • Epinephrine binding its receptor activates coupled heterotrimeric G-proteins
    o Activated subunit increase adenylyl cyclase activity
    o Generates cAMP from ATP
  • Pathway 1: cAMP binds to regulatory subunits of PKA to activate it
    o PKA activates downstream kinases lading to breakdown of glycogen stores
  • Pathway 2: cAMP drives transcriptional changes in cell through CREB phosphorylation
    o CRE: cAMP response element
    o CREB: cAMP response element binding protein
    o PKA catalytic subunit goes into nucleus to target CREB
  • DNA region regulatory element affects transcription
105
Q

What is GPCR desensitization is mediated by? Describe the desensitization process.

A

Mediated by GRKs and Arrestin

  • Desensitization: decreased response to ligand usually through receptor removal from the membrane
  • Following receptor activation, G-protein coupled receptor kinases (GRK) phosphorylates intracellular amino acids on receptor
  • Phosphorylation recruits arrestin proteins, which bind to receptor
    o Targets it for internalization in clathrin coated vesicles
  • Internalized receptors targeted to endosome
    o Degraded in lysosome or recycled back to cell surface through recycling endosome
106
Q

What is a primary signal in an ameoba?

A

cAMP

107
Q

What do Receptor tyrosine kinases (RTKs) do after ligand-based dimerization?

A

Cross phosphorylate.

Ligand binds to domain, causing tyrosine kinase to cross phosphorylate each other

108
Q

List three types of growth factor

A
  1. EGF: epidermal growth factor
  2. PDGF: platelet derived growth factor
  3. VEGF: vascular endothelial growth factor
109
Q

True or false:

Ligands and receptors can NOT have homo or hetero dimerization

A

False

  • Many ways to put receptors together
  • Signaling based on receptor/ligand structure
110
Q

What does Cross phosphorylation of RTKs do?

A

Increase kinase activity.

  • Creates scaffolding sites for proteins to dock on receptor
  • Downstream signaling proteins with SH2 domains bind to phosphorylated tyrosine residues
  • SH2: Src homology 2 domains
    o About 100 amino acids, facilitates
    binding to phosphotyrosine
111
Q

How are non-receptor tyrosine kinases activated?

A

Cytokine receptors with no tyrosine kinase activity.

o Cytokine: signaling molecules commonly secreted by immune cells, critical role in immune response
- Need associated helper kinase to phosphorylate

112
Q

Describe the Jak/Stat pathway: an example of a non receptor tyrosine kinase

A
  1. Cytokine binding induces dimerization of receptor monomers
  2. JAK (Janus Kinase): phosphorylate tyrosine residues on receptor C
    terminus
  3. STAT proteins recruited via SH2 domains to phosphotyrosine residues on receptor
  4. JAK phosphorylates STAT following recruitment
  5. Phosphorylated STAT proteins active and dimerize
    a. Act as transcription factors following translocation to nucleus
113
Q

Describe how Src-family non-receptor tyrosine kinases modulate cell adhesion

A
  1. Integrins bind to extracellular matrix proteins
  2. Clustering of integrins facilitates autophosphorylation of FAK
    a. FAK: focal adhesion kinase
  3. Phosphorylated FAK allow Src proteins with SH2 domains to bind
  4. Src further phosphorylates other FAK tyrosine residues
    a. Serve as binding sites for other proteins in cell
    - Can modulate adhesion/cell motility
114
Q

What are Src-family non-receptor tyrosine kinases

A

Src: nonreceptor tyrosine kinase family initially identified in Rous
sarcoma virus (protooncogene)
o First example of cancer caused by virus
- Developed tumor at injection site
- Transmissible cancer mediated by tyrosine kinase

115
Q

Describe how Mitogen activating protein kinase (MAP) pathway is utilized in cell growth and differentiation

A

MAP/ERK kinase (extracellular signal
regulated kinase)
o Often activated downstream of
growth factors binding to RTKs

  1. Receptor activation recruits GEF with SH2 domains
    a. Facilitates exchange of GDP for
    GTP on Ras
    i. Ras: small G protein that is
    active in GTP bound state
  2. Ras-GTP activates Raf kinase, which
    phosphorylates MEK
  3. MEK phosphorylates ERK kinases, which phosphorylates nuclear and cytoplasmic target proteins
    a. Regulates cell proliferation,
    growth, and apoptosis
    b. 1 growth factor can activate many Raf, MEK, etc.
116
Q

What is the key signal that starts the MAP Kinase pathway and is a potent oncogene?

A

Ras.

Ras converted to active GTP-bound state, which is stimulated by GEFs
o Ras activity terminated by GTP hydrolysis

  • 25% of human cancers due to Ras gain of function mutations
  • Active for too long=too much growth (tumors)
117
Q

How is Ras anchored in the membrane?

A

Ras anchored in plasma membrane by both prenylation and Palmitoylation

118
Q

What acts as a scafforld to bring the (MAP) kinase pathway together?

A

KSR- Kinase suppressor of Raf – scaffolding protein that aids in MAP/ERK cascade

119
Q

What is the final destination of phosphorylated ERK?

A

nuclear activation of growth response genes.

Phosphorylated ERK can translocate to nucleus and phosphorylate transcription factors that regulate immediate-early genes – modulate response of downstream secondary response genes which in turn regulate cell growth, proliferation, and other responses

SRF – serum response factor
SRE – serum response element

120
Q

Describe the PI3 PIP3 pathway.

A

Activates several downstream Cell survival pathways

  • PI3 kinase binds to RTKs via SH2 domains
  • PI3 kinase: phosphorylates PIP2 to PIP3
  • Akt is recruited to the plasma membrane by binding to PIP3 via PH domain.
  • mTOR and PDK1: phosphorylate Akt, activating kinase activity
    o Akt activity regulates cell growth,
    autophagy
121
Q

Describe the Akt pathway

A

Akt antagonizes cell death by promoting pathways.

Without growth factors = FOXO
translocate to nucleus and acts as
transcription factors

o Activates genes involved in cell
death (apoptosis)
o FOXO binds to transcription
factors involved in apoptosis
- With growth factors: Akt phosphorylates FOXO, allowing it to bind chaperones and prevent it from translocating to nucleus

122
Q

Describe Cross talk between PI3-K and MAPK pathways

A
  • mTORC1: downstream that regulates protein synthesis and autophagy depending on cell energy
  • AKT inhibits TSC = mTORC1 active
123
Q

What is Transforming growth factor -Beta (TGF-Beta) receptor? What does it do?

A

Serine/threonine kinase
that phosphorylates Smad transcription factor pairs.

  • Phosphorylation occurs at serine/threonine residues and not tyrosine resides
  • TFG-beta binding induces receptor
    phosphorylation
  • Phosphorylated receptor phosphorylates Smad
    o Smad forms complexes that act as
    transcription fact
124
Q

What is NF-KappaB is involved in?

A

cell inflammation and immune
cell function

125
Q

Describe NF-KappaB pathway cascade

A

-Inhibited by Ikappa-B
- TNF: tumor necrosis factor

  1. TNF receptor activation leads to activation of IKappa-B kinase
  2. IKappa-B kinase phosphorylates IKappa-B, targeting it for degradation
  3. No IKappa-B inhibition = NF-KappaB proteins act as transcription factors
    a. Modulates transcription of target genes
  • Negative feedback loop during NF-KappaB signaling
126
Q

What does the WNT pathway revolve around?

A

The degradation of the structural and transcription factor protein, Beta-catenin

127
Q

Describe the WNT pathway with and without WNT.

A

Absence of Wnt
o Beta-catenin phosphorylated by destruction complex
o Targets it for ubiquitination and degradation (E3 ubiquitin ligase pathway)

Presence of Wnt
o Dishevelled recruited to frizzled and LRP receptors
- Recruiting and disruption destruction complex
- Prevents breakdown of Beta-catenin
o Beta-catenin translocates into nucleus
o Acts as co-activator to convert Tcf from repressor to activator

128
Q

True or false:
Wnt pathway controls head vs. tail identification in planarian regeneration

A

True.

Disrupt beta-catenin = two heads regenerate
o Over activation of beta-catenin = two tails regenerate

129
Q

Describe the NOTCH pathway

A

An important example of direct cell-cell signaling.

Highly conserved developmental pathway that control cell fate

  • Notch receptor binds to cell surface proteins (Delta)
    o Leads to cleavage of notch by gamma secretase
  • Notch intracellular domain translocates to nucleus and interacts with transcriptional factor CSL
    o Converts CSL from repressor to activator
  • Mutant = abnormal wing in drosophila
130
Q

What do Gap junctions allow?

A

Direct cytoplasmic coupling between cells.

  • Selective permeable (less than 1kDa)
131
Q

Describe the makeup of a gap junction.

A
  • 6 connexins form connexon hemichannel (12 subunit compound0
    o Joined with other connexons of adjacent cell to form gap junction
  • Regulated by cell and open/close in response to signal

Cell Bio (3 decks)

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