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AP® Biology flashcards Biology 101 flashcards
1
Q

What must occur for a cell to operate effectively?

A

The different intracellular process must be separated from one another.

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2
Q

How do prokaryotes and eukaryotes isolate their chemical reactions?

A

Groups the enzymes needed for particular reactions into large, multicomponent complexes.

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3
Q

How do eukaryotes isolate their chemical reactions?

A

Isolate different metabolic processes to different membrane-enclosed compartments.

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4
Q

Protein sorting

A

The transfer process in which proteins are moved from where they are made, to the cytosol, to the compartment where they will be used.

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5
Q

What does protein sorting depend on?

A

Signals in the amino acid sequence of the proteins.

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6
Q

Vesicles

A

Small, membrane-enclosed saces

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7
Q

Vesicular transport

A

The process of vesicles pinching off from one compartment, moving through the cytosol, and fuse with another compartment.

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8
Q

Exocytosis

A

Released proteins from the cell.

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9
Q

Endocytosis

A

Bringing proteins into the cell.

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10
Q

How do the compartments differ in prokaryotes and eukaryotes?

A

Prokaryotes consist of a single compartment whereas eukaryotes are divided into internal membranes.

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11
Q

Nuclear envelope

A

The double membrane that surrounds the nucleus.

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12
Q

How does the nucleus communicate with cytosol?

A

Via nuclear pores in the envelope.

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13
Q

What is the outer membrane of the nucleus continuous with?

A

The membrane of the ER.

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14
Q

What does the ER synthesis?

A

New membranes

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15
Q

Rough ER

A

Ribosomes are attached to the cytosolic surface.

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16
Q

Lumen

A

The interior of the ER.

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17
Q

Smooth ER

A

Lacks ribosomes

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18
Q

What is the purpose of the smooth ER?

A

To make steroid hormones, detoxify molecules in liver cells, and takes up Ca2+ from the cytosol to produce responses to extracellular signals.

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19
Q

What is the purpose of the rough ER?

A

Makes proteins.

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20
Q

Cytosol function

A

Contain metabolic pathways, protein synthesis, and cytoskeleton.

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21
Q

Nucleus function

A

Contains main genome and DNA/RNA synthesis.

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22
Q

ER function

A

Synthesis of lipids and proteins to distribute to other organelles and the plasma membrane.

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23
Q

Golgi apparatus function

A

Modify, sort, and package proteins and lipids from the ER for secretion or delivery to another organelle.

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24
Q

Lysosomes function

A

Contain digestive enzymes for intracellular degradation of worn-out organelles, and other particles taken into the cell by endocytosis.

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25
Q

Endosomes function

A

Sort ingested material and recycle some of them back to the plasma membrane.

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26
Q

Peroxisomes function

A

Have enzymes that use oxidative reactions to break down lipids and destroy toxic molecules.

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27
Q

Mitochondria function

A

ATP synthesis by oxidative phosphorylation

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28
Q

Chloroplast function

A

ATP synthesis and carbon fixation by photosynthesis

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29
Q

How are the membrane-enclosed organelles held in their relative locations?

A

Attachment to the cytoskeleton.

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30
Q

How do organelles and vesicles move around one another?

A

Cytoskeletal filaments provide tracks that are driven by motor proteins through ATP hydrolysis.

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31
Q

How much volume do membrane-enclosed organelles occupy in a eukaryotic cell?

A

About half of the volume with a great majority of it being the ER.

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32
Q

How are organelles separated for studies?

A

Differential centrifugation allowing the organelle and its proteins to be collected/identified. It’s then incubated in a test tube under optimal conditions.

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33
Q

How did the precursors for the first eukaryotic cells appear?

A

Resembled bacteria = a plasma membrane and no internal membranes.

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34
Q

What does the plasma membrane do in bacteria?

A

Besides support, it also provides all membrane-dependent functions like ATP and lipid synthesis.

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35
Q

How is the plasma membrane of bacteria able to sustain all functions?

A

Small size, giving a high surface-to-volume ratio.

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36
Q

How did the increase in the size of eukaryotic cells occur?

A

Development of internal membranes.

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37
Q

What organelles make up the endomembrane system?

A

The ER, Golgi apparatus, peroxisomes, endosomes, and lysosomes.

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38
Q

How were nuclear membranes and the ones of the endomembrane system made?

A

Invagination (folding in on itself) of the plasma membrane.

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39
Q

What organisms did mitochondria and chloroplasts develop from?

A

Mitochondria = aerobic prokaryotes engulfed by a larger pre-eukaryotic cell
Chloroplasts = eukaryotic cell with mitochondria engulfed a photosynthetic prokaryote

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40
Q

What organelles aren’t included in vesicular traffic? Why?

A

Mitochondria and chloroplasts due to different origins.

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41
Q

What must a eukaryotic cell do before it divided?

A

Duplicate its membrane-enclosed organelles.

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42
Q

What does organelle growth require?

A

A supply of new lipids and the supply of appropriate proteins.

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43
Q

How are proteins produced in cells that aren’t dividing?

A

Continuously

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44
Q

Which organelles have proteins that are delivered directly from the cytosol?

A

Mitochondria, chloroplasts, peroxisomes, ER, and in the interior of the nucleus.

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45
Q

What organelles have proteins that are delivered indirectly via the ER?

A

Golgi apparatus, lysosomes, endosomes, and the inner nuclear membrane.

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46
Q

Where do the proteins that enter the ER go?

A

Some are retained and most shipped to the Golgi apparatus to be packaged in vesicles to the rest of the cell.

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47
Q

How do proteins understand where to go in the cell?

A

Based on specific address labels in their amino acid sequence.

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48
Q

Where does the synthesis of all proteins occur?

A

On ribosomes in the cytosol.

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49
Q

Sorting signal

A

Directs the protein to the organelle in which it’s required.

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50
Q

What happens to proteins that lack a sorting signal?

A

Remain in the cytosol.

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51
Q

How do proteins move from the cytosol to the nucleus?

A

Nuclear pores in the inner and outer membranes that act as selective gates to actively transport certain macromolecules and diffuse smaller ones.

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52
Q

How do proteins move from the cytosol into the ER, mitochondria, and chloroplasts?

A

Protein translocators.

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53
Q

In order to enter protein translocators, what must happen to the protein?

A

Unfold

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54
Q

Where do bacteria have protein translocators?

A

Proteins moving from the cytosol to the cell exterior.

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55
Q

How do proteins moves from the ER to the rest of the endomembrane system?

A

Transport vesicles.

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56
Q

How do transport vesicles move?

A

Pinch off from the membrane and fuse with the membrane of another.

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57
Q

What happens when a vesicle fuses with the next compartment?

A

It delivers its water-soluble cargo proteins and becomes part of the membrane it attached to.

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58
Q

How long is a sorting signal?

A

15-60 amino acids long

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59
Q

When is a signal sequence removed?

A

When the finished protein has been sorted.

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60
Q

What happens if a signal sequence is deleted from an ER protein?

A

Converts it to a cytosolic protein.

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61
Q

What happens if a ER signal sequence is placed at the beginning of a cytosolic protein?

A

Protein moves to the ER.

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62
Q

What properties affect the function of signal sequences?

A

Physical ones like hydrophobicity and the placement of charged amino acids.

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63
Q

What do ER proteins contain in their amino acid sequence?

A

N-terminal signal sequence.

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64
Q

What proteins does the inner nuclear membrane contain?

A

Those that acts as binding sites and anchor the nuclear lamina.

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65
Q

What is the nuclear lamina?

A

A meshwork of protein filaments that line the inner face of the inner nuclear membrane.

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66
Q

What is the purpose of the nuclear lamina?

A

Provide structural support for the nuclear envelope.

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67
Q

What is the composition of the outer nuclear membrane? Why?

A

Similar to the ER because it is connected to it.

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68
Q

What is a nuclear pore composed of?

A

30 proteins

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69
Q

What do the proteins that line the nuclear pore contain?

A

Extensive, unstructured regions in which the polypeptide chains are disordered.

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70
Q

What is the purpose of the disordered polypeptide chains in a nuclear pore?

A

Fill the center of the channel preventing large molecules from passing.

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71
Q

How do large molecules like RNA and ribosomal units pass move from the nucleus to cytosol?

A

Have a nuclear localization signal to gain access to the pores.

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72
Q

What is the composition of nuclear localization signals?

A

One or two short sequences of positively charged lysines or arginines.

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73
Q

How are proteins with the nuclear localization signal recognized (those that want entry to the nucleus)?

A

Nuclear import receptors on cytosolic proteins.

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74
Q

How do nuclear import receptors interact with the incoming protein?

A

Direct it to a nuclear pore by interacting with the tentacle-like fibrils that extend from the rim of the pore into the cytosol.

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75
Q

How do the nuclear import receptors penetrate the nuclear pore?

A

Grab onto short, repeated amino acid sequences within the nuclear pore, opening a passageway through them. They bump along from one repeat sequence to the next until they enter the nucleus and release their contents.

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76
Q

What happens to the sequences when the nuclear pore is empty?

A

Bind to one another forming a loosely packed gel.

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77
Q

What happens to an empty nuclear import receptor in the nucleus?

A

Returns to the cytosol via the nuclear pore for reuse.

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78
Q

What energy does the import of nuclear proteins use?

A

Hydrolysis of GTP mediated by Ran.

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79
Q

How do proteins appear when transported through a nuclear pore?

A

Into their fully folded conformation.

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80
Q

How does GTP help in nuclear import?

A
  1. Ran-GTP binds to the import receptor in the nucleus to allow it to release the protein
  2. Ran released GTP once the import receptor is released into the cytosol = Ran-GDP
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81
Q

What additional membrane do chloroplasts contain?

A

Thylakoid membrane

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82
Q

Where do the signal sequences exist for proteins made by the nucleus for mitochondria and chloroplasts?

A

N-terminus

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83
Q

How do proteins cross mitochondria and chloroplasts?

A

Through protein translocators that are exist at certain sites in the inner and outer membranes.

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84
Q

When is the signal sequence of mitochondrial and chloroplast proteins removed?

A

When they enter their organelles.

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85
Q

What is the purpose of chaperon proteins for mitochondria and chloroplasts?

A

Pull the proteins across the two membranes and fold it once inside.

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86
Q

Why do mitochondrial and chloroplast proteins contain several sorting signals?

A

Due to transport to a particular site within that organelle, the inner, outer, or thylakoid membrane.

87
Q

When are the later sorting signals exposed on proteins for mitochondria and chloroplasts?

A

Once the first signal sequence is removed.

88
Q

How are membrane phospholipids brought to mitochondria and chloroplasts?

A

Via the ER.

89
Q

How are phospholipids transported to the mitochondria and chloroplasts?

A

Via lipid carrying proteins that transport it to specific junctions where these membranes are held in close proximity to the ER.

90
Q

What do peroxisomes produced?

A

Hydrogen peroxide

91
Q

What do peroxisomes synthesize?

A

Phospholipids used in myelin sheaths.

92
Q

Where to must of peroxisomes proteins come from? How?

A

The cytosol via selective transport.

93
Q

What is the import signal for peroxisomal proteins?

A

Short sequence of only three amino acids.

94
Q

How are proteins delivered to peroxisomes?

A

Sequences recognized by receptors proteins in the cytosol that move the protein all the way to a peroxisome, where it enters a protein translocator.

95
Q

How must proteins enter a peroxisome?

A

In their fully folded configuration.

96
Q

How do peroxisomes receive proteins from the ER?

A

Via vesicles that bud off, fusing with peroxisomes or import ones in the cytosol that can grow into mature peroxisomes.

97
Q

What is Zellweger syndrome caused by?

A

Mutations that block peroxisomal protein import.

98
Q

What does Zellweger syndrome lead to?

A

Severe abnormalities in the brain, liver, and kidneys, leading to early death (six months of life).

99
Q

Can proteins re-enter the cytosol once entering the ER?

A

No

100
Q

What proteins are transferred from the cytosol to ER?

A
  1. Water-soluble proteins
  2. Transmembrane proteins
101
Q

How are water-soluble proteins transferred from the cytosol to the ER?

A

Completely translocated across the ER membrane and released into the ER lumen.

102
Q

How are transmembrane proteins transferred from the cytosol to the ER?

A

Partly translocated to the ER lumen and some become embedded in it.

103
Q

What happens to the water-soluble proteins transport once in the ER?

A

Either secreted from the cells surface or for the lumen of another organelle.

104
Q

What happens to the transmembrane proteins transport once in the ER?

A

Stay in the ER membrane, membrane of other organelles, or the plasma membrane.

105
Q

What signal sequence do all proteins that are directed to the ER contain?

A

Eight or more hydrophobic amino acids.

106
Q

What happens to proteins that enter the ER?

A

Threaded through the membrane before the polypeptide chain is completely synthesized.

107
Q

What do the proteins need that enter the ER?

A

A ribosome synthesizing protein attached to the ER membrane.

108
Q

What side are membrane-bound proteins attached to in the ER?

A

Cytosolic side

109
Q

What do free ribosomes make?

A

All of the other proteins encoded by the nuclear DNA.

110
Q

What do membrane-bound ribosomes make?

A

Make proteins that are being translocated into the ER.

111
Q

How do membrane-bound and free ribosomes differ?

A

ONLY in the proteins that they make.

112
Q

What happens when a ribosome is making a protein with an ER signal sequence?

A

Directs the ribosome to the ER membrane.

113
Q

What allows the proteins with ER signal sequence to move through the ER membrane?

A

The elongation of each polypeptide pushes the growing chain through the ER membrane.

114
Q

What happens to a polyribosome that’s on a protein with an ER signal sequence?

A

Becomes attached to the ER membrane.

115
Q

What proteins guide the ER signal sequences to the ER membrane?

A
  1. Signal-recognition proteins (SRP)
  2. SRP receptor
116
Q

What does a SRP do?

A

Binds to the ribosome and the ER signal sequence when it emerges from the ribosome.

117
Q

What does a SRP receptor?

A

Recognizes the SRP.

118
Q

How long does the binding of the SRP to a ribosome with an ER signal sequence slow down protein synthesis?

A

Until the SRP engages with an SRP receptor on the ER.

119
Q

What happens with the SRP receptor binds to the SRP?

A

The SRP is released and the receptor passed the ribosome to a protein translocator in the ER membrane where protein synthesis will continue.

120
Q

Once the protein is fully synthesized in the ER, what happens?

A

Threaded through a channel in the protein translocator.

121
Q

How does the protein in the ER open the channel in the protein translocator?

A

The signal sequence remains bound to the channel until the entire protein is threaded through.

122
Q

How is the signal sequence removed from an ER protein translocator?

A

By a transmembrane signal peptidase.

123
Q

What happens to the removed signal sequence in the ER?

A

Released from the translocation channel into the lipid bilayer where it’s degraded.

124
Q

When is the protein released into the ER lumen?

A

Once the C-terminus passes through the translocation channel.

125
Q

How is the transfer process of a transmembrane protein stopped?

A

Stop-transfer sequence in the polypeptide chain that released the chain sideways into the lipid bilayer.

126
Q

Stop-transfer sequence

A

Sequence of hydrophobic amino acids in a transmembrane protein.

127
Q

What happens to the signal sequence and stop-transfer sequence in a transmembrane protein?

A

Signal sequence = cleaved
Stop-transfer sequence = remains in the bilayer forming an a-helical membrane segment that anchors the protein

128
Q

What is the orientation of transmembrane proteins?

A

N-terminus = lumenal side
C-terminus = cytosolic side

129
Q

Can a transmembrane protein move?

A

No, once inserted in the membrane, it stays put.

130
Q

Start-transfer sequence

A

An internal amino acid sequence in transmembrane proteins that initiate the protein transfer (NEVER removed).

131
Q

What proteins do start-transfer sequences occur in?

A

In transmembrane proteins that span the lipid bilayer multiple times.

132
Q

What happens to start-transfer sequences once a stop-transfer sequence is reached?

A

Exist in the lipid bilayer as a-helical membrane-spanning segments.

133
Q

Outward vesicular transport

A

ER to plasma membrane

134
Q

Inward vesicular transport

A

Plasma membrane to lysosomes

135
Q

Outward secretory pathway components

A

Synthesis of proteins on the ER membrane and their entry into the ER; leading to Golgi apparatus to the cell surface.

136
Q

Inward endocytic pathway components

A

Moving materials from the plasma membrane to the endosomes and lysosomes to ingest and degrade extracellular molecules.

137
Q

How must a transport vesicle function optimally?

A

Takes only the proteins appropriate to its destination and fuse ONLY with the appropriate target membrane.

138
Q

What does the recognition of transport vesicles depend on?

A

Proteins displayed on its surface.

139
Q

Coated vesicles

A

Vesicles that bud from membranes gaining a distinctive protein coat on their cytosolic surface.

140
Q

When does the vesicle shed the protein coat?

A

Once it buds from its parent organelle.

141
Q

What is the purpose of the coat in vesicles?

A

Shapes the membrane into a bud and captures molecules for onward transport.

142
Q

Where do clathrin-coated vesicles bud?

A

The Golgi apparatus on the outward secretory pathway and the plasma membrane on the inward endocytic pathway.

143
Q

How do clathrin-coated vesicles bud off their parent membrane?

A
  1. Clathrin molecules assemble on the cytosolic surface of the membrane shaping a vesicle
  2. GTP-binding protein called dynamin assembles as a ring around the neck of the pit
  3. Dynamin constricts the ring so the vesicle can pinch off
144
Q

What do adaptins do?

A

Secure the clathrin coat to the vesicle membrane and help select cargo molecules for transport.

145
Q

How do adaptins trap cargo molecules?

A

Trap the cargo receptors on the membranes of the organelles that bind to the specific transport signals of the onward molecules.

146
Q

Do adaptins differ?

A

Yes, ones in the Golgi apparatus and the plasma membrane differ.

147
Q

What do COP-coated vesicles do?

A

Transport molecules between the ER and the Golgi apparatus, and from one part of the G. apparatus to another.

148
Q

How are vesicles transported?

A

By motor proteins that move along cytoskeletal fibers.

149
Q

When can the vesicle release its contents and fuse with the target membrane?

A

Once it recognizes and docks with its specific organelle.

150
Q

How is the vesicle recognized by its target membrane?

A

Vesicle = molecular markers on surface to identify the vesicle according its origin and cargo
Target organelle = complementary receptors

151
Q

What do Rab proteins (GTPases) do?

A

Exist on the surface of vesicles, so that they can recognized by corresponding tethering proteins on the cytosolic surface of the target membrane.

152
Q

SNAREs

A

Transmembrane proteins

153
Q

What does SNAREs so?

A

Once tethered, SNAREs on the vesicle (v-SNAREs) interact with the complementary SNAREs on the target membrane (t-SNAREs) to firmly dock the vesicle in place + catalyze membrane fusion for releasing contents.

154
Q

What does the fusion of the vesicle with its target membrane require?

A

SNARE proteins create a fusion complex, wrapping around one another to pull the two lipid bilayer close, displacing the water from their surfaces.

155
Q

How close do SNAREs need to be for docking?

A

Close enough that the protruding SNAREs from the two lipid bilayers came interact.

156
Q

What must occur when a molecule is undergoing the exocytic pathway?

A

As it passes from one compartment to another, it’s monitored so that it’s folded properly and assembled with its appropriate partners.

157
Q

What happens in the exocytic pathway if there is incorrect assembly?

A

The protein is degraded inside the cell.

158
Q

How are proteins chemically modified when they enter the ER?

A

Disulfide bonds are formed by the oxidation of pairs of cysteine side chains.

159
Q

What do disulfide bonds do?

A

Stabilize the structure of proteins that encounter degradative enzymes and changes in pH outside of the cell.

160
Q

Why don’t disulfide bonds form in the cytosol?

A

Because the environment is reducing (less oxygen).

161
Q

How are proteins in the ER converted into glycoproteins?

A

Covalent attachment of short branched oligosaccharide side chains composed of multiple sugars (glycosylation).

162
Q

What is glycosylation carried out by?

A

Glycosylating enzymes in the ER.

163
Q

What is the purpose of oligosaccharide on proteins?

A

Protect a protein from degradation, hold it in the ER until properly folded, or guide it to the correct organelle (act as a transport signal for packing the protein).

164
Q

Glycocalyx

A

When oligosaccharides are displayed on the cell surface, forming an outer carbohydrate layer.

165
Q

How are oligosaccharides added to proteins in the ER?

A

14 sugars are attached all at once to a protein.

166
Q

Dolichol

A

The specialized lipid that the oligosaccharide is attached to in the ER before attaching to a protein.

167
Q

How does the oligosaccharide move from the dolichol to a protein?

A

Transferred to the amino group of an asparagine side chain on the protein (happens immediately when a target asparagine enters the ER lumen).

168
Q

N-linked

A

Oligosaccharide side chains linked to a asparagine NH2 group.

169
Q

ER retention signal

A

A C-terminal sequence of four amino acids that retain a protein in the ER.

170
Q

What is the ER retention signal recoginzed by?

A

A membrane-bound receptor protein on the ER and G. apparatus (leave G to go back to the ER).

171
Q

How is exit from the ER highly selective?

A

Proteins that don’t fold correctly or multimeric proteins that do not assemble correctly are retained in the ER by chaperone proteins until proper folding and assembly.

172
Q

What happens if an ER protein doesn’t properly fold or assemble?

A

The protein is exported to the cytosol for degradation.

173
Q

How do antibodies demonstrate the selectivity of the ER?

A

Leave to other organelles = all four polypeptide chains assembled
Leave to be degraded = the chains fail to assemble

174
Q

What is cystic fibrosis caused by?

A

A plasma-membrane transport protein is slightly misfolded is retained in the ER until degradation (the protein is still active, but the ER doesn’t recognize this).

175
Q

Unfolded protein response (UPR)

A

A complex program triggered by the large buildup of misfolded proteins in the ER, leading to the production chaperone proteins the increase protein folding and one sensor inhibits protein synthesis (reduces flow of protein through the ER). It allows adjusts the size of ER.

176
Q

How can UPR cause a cell to self-destruct? Use the example of adult-onset diabetes.

A

Tissues become resistant to effects of insulin, leading to the pancreas producing more. The ER reaches maximum capacity, in which the UPR triggers cell death.

177
Q

What is composition of the G. apparatus?

A

Flattened, membrane-enclosed sacs of 3-20 cisternae.

178
Q

What are the faces of the Golgi stack?

A

Cis face (entry) = adjacent to the ER
Trans face (exit) = faces the plasma membrane

179
Q

What is the outermost cisterna connected to?

A

Connected to a network of interconnected tubes and vesicles.

180
Q

How do the cisternae interact with one another?

A

Proteins travel via transport vesicles that bud from one cisternae and fuse with the other.

181
Q

How are cis cisternae important for protein sorting?

A

Proteins that enter the cis Golgi network can either move through each stack or be returned to the ER if they contain an ER retention signal.

182
Q

How are trans cisternae important for protein sorting?

A

Proteins exiting from the trans Golgi network are sorted according to whether they are destined for lysosomes or the cell surface.

183
Q

What modifications do oligosaccharide chains go through in the G. apparatus?

A

Sugars are added or removed by a series of enzymes that act in a certain sequence as the protein passes through the Golgi stack.

184
Q

Constitutive exocytosis pathway

A

Supplies the plasma membrane with newly made lipids and proteins to expand for cell division; and soluble proteins to be released outside via secretion.

185
Q

What does entry into the constitutive pathway not require?

A

A particular signal sequence.

186
Q

Regulated exocytosis pathway

A

Operates in specialized secretory cells that produce large quantities of a product that are stored in secretory vesicles for release.

187
Q

Where do secretory vesicle exist?

A

Bud off the trans Golgi network

188
Q

What must happen for the secretory vesicle to fuse with the plasma membrane?

A

An extracellular signal.

189
Q

What do secretory proteins contain to cause aggregation in ionic conditions (acidic pH and high Ca2+)?

A

Special surface properties

190
Q

Do constitutive proteins aggregate?

A

No as they are automatically carried to the plasma membrane.

191
Q

What is the purpose of selective aggregation?

A

Secretory proteins are packaged into secretory vesicle at high concentrations much higher than unaggregated ones in the Golgi lumen

192
Q

Why doesn’t the fusion of secretory vesicles increase the surface area of the plasma membrane?

A

Membrane components removed from endocytosis are added quickly by exocytosis.

193
Q

How is an endocytic vesicle formed?

A

The ingested material is enclosed by a portion of the plasma membrane that buds inwards and pinches off.

194
Q

Where is an endocytic vesicle delievered first?

A

To endosomes.

195
Q

What do endosomes do with the endocytic vesicles’s contents?

A

Recycle to plasma membrane or send to lysosomes for digestion.

196
Q

What happens to the materials that the lysosomes digest?

A

Transferred to the cytosol to be used by the cell.

197
Q

Pinocytosis

A

Ingestion of fluid and molecules via SMALL pinocytic vesicles.

198
Q

Phagocytosis

A

Ingestion of large particles, like microorganisms and cell debris, via LARGE vesicles called phagosomes.

199
Q

How does a protozoa use phagocytosis?

A

Take up large food particles into phagosomes and fuse with lysosomes to digest them (FEEDING).

200
Q

How do macrophages digest invaders?

A
  1. Bind to the phagocytic cell surface and activate surface receptors known as antibodies
  2. Induces pseudopods to engulf the bacterium and fuse at their tips to form a phagosome
  3. Phagosome fuses with a lysosomes where the microbe is destroyed
201
Q

How can pathogenic bacterium avoid being eaten?

A

Some inhibit membrane fusion that unites the phagosomes with lysosomes.

202
Q

What does the rate at which the plasma membrane is internalized in pinocytic vesicles depend on?

A

Depend on cell type:
- macrophage = removes 3% of its plasma membrane per minute
- fibroblasts = very slow

203
Q

What is the purpose of clathrin-coated pits in pinocytic vesicles?

A

Shed coat after budding off plasma membrane to fuse with endosome.

204
Q

Why are pinocytic vesicles not selective?

A

Trap any molecules that happen to be present in the extracellular fluid.

205
Q

How can pinocytosis be selective?

A

Taking up specific macromolecules that bind to complementary receptors on the cell surface and enter the cell as receptor-macromolecular complexes in clathrin-coated vesicles known as receptor-mediated endocytosis.

206
Q

How does cholesterol demonstrate receptor-mediated endocytosis?

A

Bind to receptors on cell surfaces causing the receptor-LDL complexes to be ingested and delivered to endosomes.

207
Q

What happens when LDL-cholesterol reaches the endosome?

A

LDL dissociates from its receptor and brought to lysosomes where its broken down, releasing the cholesterol into the cytosol for membrane synthesis.

208
Q

What happens to those who have a defective LDL receptor protein?

A

Cells can’t take up LDL leading to cholesterol that accumulates in the blood, leading to heart attacks.

209
Q

How does vitamin B12 and iron use receptor-mediated endocytosis?

A

Enter immature red blood cells as a complex with receptor proteins that allow for the synthesis of hemoglobin.

210
Q

What happens to cell-surface receptors ingested by receptor-mediated endocytosis?

A

Either returned to the plasma membrane for reuse or degraded by lysosomes.

211
Q

How can a protein with a signal sequence be made?

A
  1. Cell-free translation of a purified mRNA
  2. Radioactive amino acids labelled
  3. Labelled protein incubated with organelle and monitored
212
Q

How is a radioactive protein monitored?

A

Protease added to protect it from digestion or add detergent to disrupt the organelle its in, degrading the protein.

213
Q

How is secretion studied in yeast cells?

A

Raise temperature (proteins inactivated at higher temps) to see the secretion proteins accumulate inappropriately in the ER, G. apparatus, or transport vesicles.

214
Q

What is a protein tagged with?

A

Green fluorescent protein (GFP)

Intro Molecular Biology (5 decks)

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