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MBB231 > Midterm 2 (Lectures 8-9) > Flashcards

Midterm 2 (Lectures 8-9) Flashcards

1
Q

properties of microtubules

A

hollow tube with a wall consisting of typically 13 protofilaments. has + and - ends (polarity)

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2
Q

properties of microfilaments

A

two intertwined chains of F-actin. has + and - ends (polarity)

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3
Q

properties of intermediate filaments

A

eight protofilaments joined end to end with staggered overlap. no known polarity

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4
Q

what are the subunits incorporated into the polymer of microtubules

A

GTP-alpha beta-tubulin heterodimer

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5
Q

cell polarity

A

spatial differences in shape, structure, and function within a cell

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6
Q

kinesin

A

anterograde MT motor, moves from negative end to positive end

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7
Q

dynein

A

retrograde MT motor, moves from positive to negative end

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8
Q

what are microtubules

A

straight, hollow cylinders of varied length that consist of (usually 13) longitudinal arrays of polymers called protofilaments

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9
Q

basic subunit of a protofilament

A

a heterodimer of tubulin, one alpha-tubulin and one beta-tubulin (globular proteins) which bind non-covalently to form aB-heterodimer

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10
Q

MAPs

A

microtubule associated proteins. heterogeneous collection of proteins with one domain attached to the side of a microtubule and another domain that projects outwards as a tail

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11
Q

structure of microtubules

A

a dimer of alpha tubulin and beta tubulin noncovalently bound. they are always found together in the cell. a-tubulin has GTP and B-tubulin has GDP. each monomer has a GTP binding site. Taxol is on B-tubulin

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12
Q

GTP in a monomer

A

is physically trapped at the dimer interface. it is never hydrolyzed or exchanged

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13
Q

in the beta-tubulin monomer:

A

the nucleotide can be in either GDP or GTP form and is both hydrolyzable and exchangeable

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14
Q

draw the structure of a MT

A

(-) end has a-tubulin with GTP, (+) end has B-tubulin with GDP

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15
Q

molecular motors

A

move unidirectionally along their cytoskeletal track in a stepwise manner

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16
Q

how do kinesin, dynein, and myosin move

A

kinesin, dynein move along microtubule track, myosin moves along microfilament tracks

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17
Q

kinesins and cytoplasmic dynein moves:

A

similar materials in opposite directions over the same railway network. Organelles may bind kinesin and dynein simultaneously. Dynein and kinase can be found on the same microtubule.

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18
Q

how do vesicles know what membranes to fuse with?

A

SNAPS and SNARE

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19
Q

nucleus

A
  • nuclear envelope
  • mRNA, mRNP and proteins need to exit and enter
  • everything exits and enters via nuclear pores
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20
Q

smooth endoplasmic reticulum is involved in:

A
  • drug detoxification
  • carbohydrate metabolism
  • calcium storage
  • steroid biosynthesis
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21
Q

golgi apparatus function

A

site of post-translational processing of lipids and proteins synthesized in the ER and sorting for transport to other sites in the cell

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22
Q

mitochondria

A
  • not part of endomembrane system but site of ATP formation
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23
Q

peroxisomes

A

breakdown fatty acids two carbons at a time into acetyl CoA, found in all animal cells except RBCs

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24
Q

lysosomes

A

contain ~40 types of hydrolytic enzymes, all of which are acid hydrolyses. also contains transport proteins that carry the products of macromolecule digestion to the cytosol

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25
Q

endomembrane system - biosynthetic pathway

A

proteins are synthesized in the ER, modified at the golgi complex and transported to various destinations

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26
Q

endomembrane system - secretory pathway

A

proteins synthesized in the ER are secreted from the cell

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27
Q

endomembrane system - secretory pathway - constitutive secretion:

A

materials are transported in secretory vesicles discharged in a continual manner

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28
Q

endomembrane system - secretory pathway - regulated response:

A

materials are stored in vesicles and discharged in response to a stimulus

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29
Q

subcellular fractionation

A

homogenization followed by centrifugation

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30
Q

differential centrifugation

A

separation of cell organelles or other particles of different size/density by their different rates of sedimentation in a centrifugal field

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31
Q

density gradient (rate zonal) centrifugation

A

a sample (often isolated first by differential centrifugation) is further separated/fractionated by layering the sample on top of a sucrose gradient

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32
Q

what happens when you centrifuge:
a) at 500 x g for 10 minutes
b) at 10,000 x g for 20 minutes
c) at 100,000 x g for 1 hour

A

a) supernatant - pellet: nuclear fraction
b) pellet: mitochondrial fractions
c) cytosol (soluble proteins) - pellet: microsomal fraction

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33
Q

what is the purpose of a microscope

A

detect, magnify, resolve

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34
Q

magnification

A

enlarges but does not distinguish between two points

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35
Q

resolution

A

the minimum distance that can distinguish between 2 points

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36
Q

decreasing wavelength -

A

increases resolution

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37
Q

light microscopy

A
  • live cells and tissues lack compounds that absorb light and are therefore nearly invisible in a light microscope
  • unstained
    4 types:
  • bright field
  • phase contrast (improves contrast)
  • Nomarski optics (uses special prism to split illuminating light beam into 2 separate rays)
  • dark field (excludes unscattered beam from the image)
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38
Q

microscopy: fixation

A

preserves cells; prevents decay/degradation, uses heat, formalin, glutaraldehyde

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39
Q

microscopy: staining

A
  • doesn’t increase resolution, just enhances visualization
  • adds colour for contrast
  • basic dyes bind to (-) charges on proteins and nucleic acids, acidic dyes bind to + charges on proteins and phospholipids
40
Q

microscopy: fluorescent dyes

A
  • used to increase resolution and localize and quantify specific molecules in fixed and living cells
  • light is absorbed at one wavelength and emitted at a longer wavelength
  • used for staining cells
41
Q

using flurochromes (fluorescent dyes)

A
  • labels specific proteins by attaching the dyes to an antibody molecule
  • antibody is attached to a protein, the fluorescent marker attaches to the antibody
42
Q

direct immunofluorescence

A
  1. specific antibodies against antigen
  2. antibodies labeled with fluorescent dye
  3. allow antibodies to bind to antigen
43
Q

indirect immunofluorescence

A
  1. specific antibodies against antigen (primary antibody)
  2. allow antibodies to bind to antigen
  3. add labeled antibodies that bind to primary antibodies (secondary antibody)
44
Q

trans golgi network

A

functions in sorting proteins either to the membrane or various intracellular destinations

45
Q

medial cisternaie

A

where processing takes place

46
Q

cis golgi network

A

functions to sort proteins in the ER or the next golgi station

47
Q

glycosylation

A

oligosaccharide processing in the golgi complex

48
Q

O-linked glycoproteins

A

not as abundant as N-linked. abundant in extracellular matrix

49
Q

glycosylation of ceramide:

A

occurs in the golgi apparatus

50
Q

ceramide:

A

sphingosine backbone and a fatty acid tail

51
Q

vesicular transport model

A

vesicle budding from cis to trans golgi via antegrade transport along with retrograde transport

52
Q

cisternal maturation

A

cis golgi network matures into medial golgi and then trans golgi network but also retrograde transport

53
Q

materials are carried between compartments using

A

coated vesicles

54
Q

protein coats have two distinct functions

A
  1. cause the membrane to curve and form a vesicle
  2. select the components to be carried by a vesicle
55
Q

KDEL sequence

A

is both necessary and sufficient to result in a protein containing this sequence to be located in the ER
- KDEL sequence binds to a KEDL receptor - a transmembrane protein

56
Q

if you added the KDEL sequence to a protein that is normally secreted - what will happen to it?

A

won’t be secreted, will come back to the ER

57
Q

T-SNARE and V-SNARE

A

T - for target membrane
V - for vesicle membrane

58
Q

clatherin coats

A
  • involved in trans-golgi network to late endosomes/lysosomes
  • plasma membrane to early endosomes
59
Q

clatherin:

A

major protein component of clathrin coated vesicles

60
Q

Triskelion

A

a clathrin molecule
- each clathrin molecule consists of three large and three small polypeptide chain

61
Q

sorting and transport of lysosomal enzymes

A
  • utilizes clathrin-coated vesicles
  • lysosomal proteins are tagged in the cis golgi with phosphorylated mannose residues
  • tagged lysosomal enzymes are recognized and captured by mannose 6-phosphate receptors (MPRs), which are bound by coat proteins
62
Q

early endosomes:

A

are generated by clathrin coated receptor mediated endocytosis

63
Q

autophagosome

A

a double-membrane sequestering vesicle that forms when a double membrane structure envelops an organelle

64
Q

autophagosome fuses with a lysosome and the enclosed contents are degraded in a:

A

autolysosome

65
Q

lipofuscin granule:

A

when the contents of a residual body are retained inside the cell

66
Q

exocytosis

A

discharge of a secretory vesicle or granule after fusion with plasma membrane. process triggered by an increase in Ca2+

67
Q

steps of exocytosis:

A
  1. approach of secretory vesicle to plasma membrane
  2. fusion of membranes
  3. rupture of plasma membrane
  4. discharge of vesicle contents to the outside of the cell
68
Q

endocytosis:

A

a process by which the cell internalizes cell-surface receptors and bound extracellular ligands

69
Q

two types of endocytosis

A
  1. bulk phase - non specific uptake of extracellular fluids
  2. receptor-mediated or clathrin-mediated - brings about the uptake of specific ligands following their binding to receptors on the external surface of the plasma membrane
70
Q

steps of endocytosis

A
  1. membrane invaginates, forming a pocket containing macromolecules or other materials from the exterior of the cell
  2. pocket begins to pinch off, enclosing the extracellular material
  3. membrane closes around the invaginated material, forming a vesicle
  4. vesicle separates from the plasma membrane, carrying material from the exterior within a membrane derived from the plasma membrane
71
Q

receptor mediated endocytosis

A

RME provides a selective and efficient uptake of macromolecules. receptors are concentrated in coated pits at 10-20 times their level in the remainder of the plasma membrane. substances that enter the cell through clathrin-mediated RME become bound to coated pits on the plasma membrane

72
Q

low density lipoproteins

A
  • complex of cholesterol and proteins
  • LDL receptors are transported to the plasma membrane and bound to a coated pit
  • LDLs are taken up by RME and taken to the lysosomes, releasing the cholesterol for use by the cells
73
Q

transcytosis

A

a combination of endocytosis and exocytosis

74
Q

pulse-chase

A

follows the movements of newly synthesized molecules by observing a wave of radioactive material moving through the cytoplasmic organelles from one location to the next until the process is complete

75
Q

what is the difference between RER and SER

A

RER has ribosomes bound to its cytosolic surface, whereas the SER lacks associated ribosomes

76
Q

about ____ of proteins are synthesized in the RER

A

one third

77
Q

what proteins are synthesized in the RER

A
  • secreted proteins
  • integral membrane proteins
  • soluble proteins that reside in the ER, golgi, lysosomes, endosomes, vesicles and plant vacuoles
78
Q

polypeptides synthesized on ‘free’ ribosomes in the cytosol include

A
  • proteins destined to stay in the cytosol
  • peripheral proteins of the cytosolic surface of membranes
  • proteins that are transported to the nucleus and those incorporated into peroxisomes, chloroplasts, and mitochondria
79
Q

co-translational translocation

A

transport of most secretory proteins into the ER lumen begins while the protein is still being synthesized on the ribosome. ER is all co-translational

80
Q

post-translational translocation

A

if translocation takes place after the protein is synthesized

81
Q

SRP:

A
  • signal recognition particle
    binds simultaneously and transiently to:
  • signal sequence in a nascent protein
  • large ribosomal unit
    SRP then binds (docks) to SRP receptor
82
Q

single-spanning membrane proteins can have an orientation with:

A

their N-terminus facing either the cytosol or the lumen of the ER

83
Q

chaperones and other ER proteins:

A

facilitate folding and assembly of proteins

84
Q

only proteins that are properly folded can:

A

leave the ER.

85
Q

what happens to proteins that are misfolded

A
  • they are initially retained in the ER
  • an accumulation of misfolded proteins functions as a signal for the cell to make more ER = unfolded protein response
  • this response can only go on for so long. will eventually lead to apoptosis
86
Q

dislocation or retrotranslocation

A

the movement of misfolded proteins from the ER to the cytosol

87
Q

ERAD

A
  • ER associated degradation proteins
  • export improperly folded proteins from the ER to the cytosol for degradation by proteosome
88
Q

phagocytosis

A

carried out by cells specialized for the uptake of relatively large particles. folds fuse to produce a vacuole (phagosome) that pinches off inwardly from the plasma membrane and fuses with a lysosome (phagolysosome)

89
Q

posttranslational uptake of proteins by peroxisomes, mitochondria

A
  • cannot fold
  • unlike RER, which generally imports its proteins cotranslationally
  • the proteins of these other organelles are imported posttranslationally, following their complete synthesis on free ribosomes in the cytosol
90
Q

signal sequences

A
  • direct proteins to the correct organelle
  • is often removed following protein sorting
  • are absolutely necessary for sorting
91
Q

nucleoporins

A
  • collective name for the group of proteins that make up the nuclear pore complex (NPC) (~30 different proteins)
  • ions, small metabolites, and globular proteins can diffuse through the NPC
  • larger proteins and protein complexes are selectively transported with the assistance of soluble transporter
92
Q

GTPase

A
  • very small proteins that bind guanine nucleotides
  • hydrolyzes GTP that is bound to them
  • have to hydrolyze GTP if you don’t want it on
93
Q

GTPase switch proteins exist in two forms

A
  1. GTP bound - GTP is then hydrolyzed to GDP
  2. GDP bound - GTP is displaced by GDP
94
Q

ran-GAP

A

GTPase Activating Protein
- found in the cytosol

95
Q

ran-GEF

A

Guanine-nucleotide Exchange Factor
- found in the nucleus complexed to chromatin

96
Q

importin

A

nuclear transport protein/receptor in cytosol that binds to cargo protein with an NLS and translocates to nucleus

97
Q

exportin

A

nuclear transport protein/receptor in nucleus that binds to Ran-GTP which promotes binding to cargo protein

MBB231 (10 decks)

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