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Peer teaching > The cell > Flashcards

The cell Flashcards

1
Q

general structure of the cell membrane

A

lipid bilayer containing specialised proteins, in association with surface carbohydrates.

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2
Q

general structure of lipid molecule

A

non polar hydrophobic end (2 fatty acid tails)

polar hydrophilic region (glycerol, phosphate and choline)

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3
Q

what does the polar hydrophobic region contain?

A

glycerol, phosphate, choline

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4
Q

properties of lipid molecules

A

amphipathic

spontaneously form bilayer in water, hydrophobic ends forming an inner layer

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5
Q

functions of cell membrane

A

fluid - lateral diffusion of membrane proteins + mobility
permeable to water, oxygen + small hydrophobic molecules, not to charged ions
breaks/tears sealed
membrane proteins: transport, enzymes, cell attachment and communication

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6
Q

main component of cell membrane

A

lipid forms 50%

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7
Q

major types of membrane lipids

A

phosphoglycerides
cholesterol
glycolipids

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8
Q

phosphoglyceride proportion, location and types

A

50% lipid component
surround membrane proteins anchoring proteins w/ enzymatic/transport functions

phosphatidylcholine
phosphatidylserine
phosphatidylethanolamine

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9
Q

cholesterol

A

limits movement of adjacent phospholipids

less fluid, -> stable

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10
Q

glycolipids location

A

outer face of membrane

associated sugars exposed, for intercellular communication

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11
Q

main types of glycolipid in membranes

A

sphingolipids
galacerebroside - part of myelin
gangliosides - 10% lipid in nerve cells

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12
Q

lipid rafts

A

high conc. of sphingolipids and cholesterol
50nm
carry specific proteins/cell signalling molecules

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13
Q

integral proteins

A

span lipid bilayer

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14
Q

peripheral proteins

A

associated w/ inner or outer

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15
Q

functions of membrane proteins

A

attach cytoskeletal filaments to membrane

attach cells to extracellular matrix

transport molecules in/out

chemical receptors

enzymatic

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16
Q

function of adhesion molecules

A

attach cells to extracellular matrix

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17
Q

function of carrier proteins/membrane pumps/channel proteins

A

transport molecules in/out of cells

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18
Q

movement of membrane proteins

A

some diffuse laterally over surface

some fixed

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19
Q

glycocalyx

A

carbohydrate residues on luminal aspect of inner membrane systems and cell surface

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20
Q

how to demonstrate membrane carbohydrates

A

lectins - proteins extracted from plants

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21
Q

how does transport in/out of cells take place?

A

endocytosis and exocytosis

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22
Q

endocytosis

A

invagination of cell surface.
invaginated membrane forms an endocytotic vesicle/endosome
membrane and material is further processed

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23
Q

endosome

A

small sealed spherical membrane bound body

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24
Q

pinocytosis/potocytosis

A

cells take up fluid and small molecules, forming small 50nm vesicles

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25
Q

endocytosis/phagocytosis

A

cells ingesting large particle to form 250nm+ endosomes

proteins on surface - receptors on cell surface
Fc portion of antibody - receptors
cell signalling activated

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26
Q

exocytosis

A

fusion of vesicle membrane with cell surface

secretion of products
incorporates new membrane

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27
Q

mediation of endocytosis and exocytosis

A

fusogenic proteins

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28
Q

macropinocytosis

A

cell extends processes as sheet to envelop large # ECF

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29
Q

where are the 2 main vesicles involved in transport derived from?

A

surface membrane invaginations

  • coated pits
  • caveoli
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30
Q

what are coated pits?

A

invaginations braced by special membrane proteins with receptors that bind to ligands - bring material in

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31
Q

example of specific coated pit

A

iron is ligand and clathrin is protein

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32
Q

what happens in further assembly of the coat protein?

A

progressive invagination to form coated vesicle

protein dynamin forms collar around neck, assists in budding

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33
Q

what does dynamin do?

A

protein forms collar around neck of vesicle, assists in budding

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34
Q

what happens when the vesicle is internalised?

A

coat protein shed and returned to surface - recycled.

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35
Q

what is recepor mediated endocytosis a feature of?

A

internalisation of iron, LDL and growth factors

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36
Q

what are caveoli and how do they differ from coated pits?

A

invaginations of cell surface braced by protein caveolin

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37
Q

3 cellular roles of caveoli

A

contain receptor proteins, concentration substances into the cell via potocytosis

transcytosis - endothelial cells

intracellular signalling

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38
Q

where can transcytosis occur?

A

cells like endothelial cells

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39
Q

what are the 2 types of secretory mechanisms?

A

constitutive secretory pathway

regulated secretory pathway

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40
Q

what is a constitutive secretory pathway?

A

secretion occurring by a constant fusion of vesicles with surface membranes

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41
Q

what is a regulated secretory pathway?

A

fusion of secretory vesicles with surface having to be signal-triggered

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42
Q

Rab family of GTPases

A

controls specificity of trafficking and docking and recruits tethering and fusion factors

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43
Q

SNARE proteins

A

from SNAp REceptor - tether and dock the vesicle to the membrane
differences/specificity

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44
Q

NSF protein

A

N-ethylmaleimde- sensitive fusion protein interact with SNAPs proteins (soluble NSF attachment proteins) to mediate membrane fusion

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45
Q

clathrin structure

A

protein bracing coated pit membranes

forms hexagonal lattice structure which develops as a coat around vesicle surface

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46
Q

what is the cytosol?

A

concentrated, dense fluid

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47
Q

what components does the cytosol contain?

A

machinery in protein synthesis, protein degradation and carbohydrate metabolism - enzymes

filamentous proteins - cytoskeleton

metabolism products

ribosomes

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48
Q

examples of products of metabolism

A

glycogen and free lipids - storage component

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49
Q

what do ribosomes do?

A

synchronise alignment of mRNA and tRNA in the production of peptide chains during protein synthesis.

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50
Q

ribosome appearance on H&E

A

basophilic

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51
Q

what are ribosomes composed of?

A

small subunit binding RNA

large subunit catalyses the formation of peptide bonds

specific ribosomal RNA and proteins

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52
Q

where is ribosomal RNA manufactured?

A

nucleolus

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53
Q

what is the nucleus?

A

largest single membrane-bound cell compartment

contains cellular DNA

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54
Q

H&E appearances of nuclei

A

spherical/ovoid

5-10um diameter

basophilic

nucleolus

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55
Q

what are nuclei bound by?

A

2 concentric membranes - inner and outer

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56
Q

function of inner nuclear membrane

A

contains specific membrane proteins - act as attachment points for filamentous proteins (lamins) - forms scaffolding to maintain spherical shape

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57
Q

what are lamins?

A

filamentous proteins that attach to the inner nuclear membrane and form scaffolding to maintain the spherical shape

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58
Q

function of outer nuclear membrane

A

binds perinuclear space, which is continuous with the lumen of the ER - may be associated with ribosomes

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59
Q

function of nuclear pores

A

continuity between cytosol and nuclear lumen containing chromatin

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60
Q

appearance of nuclear pores in TEMs

A

gaps

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61
Q

structure of nuclear pores

A

top to bottom:

cytoplasmic filaments

cytoplasmic ring

luminal ring

nuclear ring

basket filament

terminal ring

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62
Q

nuclear basket

A

rings and filaments in the nuclear space

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63
Q

what is DNA wound around?

A

histones - proteins

forms nucleosomes

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64
Q

what are nucleosomes?

A

histones with DNA wound around them

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65
Q

nucleosome packing

A

nucleosome string is wound into filaments

30nm diameter

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66
Q

what does the nucleosome string make up?

A

chromatin - then coiled, and coiled into a supercoiled metaphase chromosome

67
Q

what are the types of chromatin?

A

euchromatin

heterochromatin

68
Q

what is euchromatin?

A

light staining electron lucent areas

actively transcribed DNA

69
Q

what is heterochromatin?

A

dense staining area

adjacent to nuclear membrane

highly condensed, transcriptionally inactive

70
Q

distribution of chromatin

A

not uniform

reflects varying degrees of unfolding according to whether genes are being transcribed

71
Q

nucleolus appearance

A

spherical area within nucleus

1-3um diameter

acidophilic and basophilic

72
Q

nucleolus and metabolic activity

A

increase in size and number with metabolic activity

vice versa for metabolically inactive cells

73
Q

function of nucleolus

A

produces ribosomal RNAs - packaged with proteins to form ribosomal subunits and exported to the cytosol via
pores

74
Q

which 3 regions of the nucleolus can be distinguished by electron microscopy?

A

pars amorpha

pars fibrosa

pars granulosa

75
Q

what is the pars amorpha?

A

pale areas

nuclear organising regions with specific RNA binding proteins, correspond to large loops of transcribing DNA containing ribosomal RNA genes

76
Q

what is the pars fibrosa?

A

dense staining regions

correspond to transcripts of ribosomal RNA genes beginning to form ribosomes

77
Q

what is the pars granulosa?

A

correspond to RNA containing maturing ribosomal subunit particles

78
Q

what is the nuclear lamina?

A

network of protein filaments 20nm thick lining internal nuclear membrane.

scaffoldng which maintains shape of nucleus

79
Q

what proteins does the nuclear lamina consist of?

A

nuclear lamins A, B and C

organised into filaments and form a regular square lattice beneath membrane

80
Q

what does the nuclear lamina network interact with?

A

nuclear membrane proteins - acts as cytoskeleton

possibly interacts with chromatin in spatial organisation of nucleus

81
Q

mitochondria appearance and function

A

membrane bound cylindrical organelles
0.5-2um legth

ATP production
energy through oxidative phosphorylation

82
Q

mitochondria evolution

A

believed to have evolved as symbiotic prokaryotic organisms similar to bacteria

own DNA and systems of protein synthesis without cell nucleus

83
Q

mitochondrial membranes and functions of their associated enzymes

A

outer membrane - lipid synthesis, fatty acid metabolism

inner membrane - respiratory chain, ATP production

matrix - TCA/Krebs

intermembranous space - nucleotide phosphorylation (ADP -> ATP)

84
Q

things contained by the outer membrane and their functions

A

specialised transport proteins (porin) allowing free permeability in for molecules up to 10 kDa weight

transmembrane pores that assemble and open to release mitochondrial proteins into cytosol. triggered by cell stimuli, leads to activation of cell death mechanisms

85
Q

example of a specialised transport protein in mitochondrion

A

porin - outer membrane

86
Q

what are 2 properties of the inner mitochondrial membrane and their functions?

A

highly impermeable to small ions (due to high cardiolipin), allows development of electrochemical gradients in producing high energy cell metabolites

folded into pleats/cristae - increased SA

87
Q

what is located on the inner mitochondrial membrane?

A

respiratory chain enzymes

ATP synthetase

88
Q

what does the intermembranous space contain?

A

metabolic substrates diffusing through outer membrane

ATP

ions pumped out of matrix during oxidative phosphorylation

89
Q

what does the matrix contain?

A

enzymes to oxidise FAs, pyruvate and those needed in Krebs

mitochondrial DNA

enzymes for mitochondrial DNA transcription

90
Q

appearance of mitochondria in cells with high oxidative metabolism

A

large and serpiginous

91
Q

appearance of mitochondria in steroid-hormone secreting cells

A

cristae are tubular structures, not flat plates

92
Q

what are the ER and Golgi?

A

2 distinct regions of an intercommunicating membrane bound compartment involved in the biosynthesis and transport of cellular proteins and lipids

93
Q

additional functions of the ER

A

detoxification or activation of foreign compounds including drugs, by ER proteins - cytochrome P450 proteins

storage of intracellular calcium

94
Q

arrangement of ER and Golgi

A

deeply folded flattened membrane sheets or as elongated tubular profiles

95
Q

quantity of ER and golgi

A

depends on metabolic requirements

little ER in most metabolically inactive cells
vast amounts in cells synthesising and secreting protein containing molecules

most cells have small amount of smooth ER, except those secreting or processing lipids

96
Q

protein synthesis 1

A

begins in cytosol, mRNA attaches to free ribosomes and translation produces new peptide

first portion of RNA produces a signal sequence

proteins destined to remain in the cytosol have different signal sequence from those destined for entry into membane/ secretion

97
Q

protein synthesis 2

A

ribosomes producing peptides with signal sequence for membrane or secretion become attached to the surface of ER - rest of peptide is translated

attachment of ribosomes to ER is rough ER

original signal sequence is cleaved and peptide forms in lumen

newly made proteins enter SER for transport to Golgi

98
Q

SER function

A

processes synthesised proteins

synthesises lipids (e.g. membrane phospholipids) 
lipid synthetic enzymes are on the outer face with access to lipid precursors

once incorporated into bilayer, they’re flipped to inside by flipases (transport proteins)

99
Q

3 roles of the Golgi

A

modification of macromolecules by addition of sugar to form oligosaccharides

proteolysis of peptides into active forms

sorting of macromolecules into specific membrane bound vesicles

100
Q

function of cis face golgi

A

receives transport vesicles from SER and phosphorylates proteins

101
Q

function of medial Golgi

A

adds sugar residues to lipids and peptides to form complex oligiosaccharides

102
Q

function of trans Golgi

A

protein proteolysis

lipid and protein sorting

addition of sugar residues

103
Q

where can vesicles from the trans Golgi go to?

A

incorporation of new cell membrane

special cell vesicles (lysosomes)

secretion by exocytosis

104
Q

what are vesicles?

A

small spherical membrane-bound organelles

105
Q

how are vesicles formed?

A

by budding off of existing areas of membrane

106
Q

what are the functions of vesicles?

A

transport or store material within their lumen

allow the exchange of cell membrane between different cell compartments

107
Q

what are the main types of vesicle?

A 
cell surface derived endocytotic
Golgi derived transport and secretory 
ER derived transport
lysosomes
peroxisomes
108
Q

how can the cellular distribution of vesicles be determined?

A

immunohistochemical staining for vesicle-associated proteins or contents

109
Q

what is a lysosome?

A

membrane-bound organelle with a high content of hydrolytic enzymes operating in an acid pH

110
Q

what do lysosomes do?

A

intracellular digestion system

processes material ingested by the cell or effete cellular components

111
Q

acid vesicle system

A

common membrane H+ -ATPase (vacuolar ATPase) which can decrease their luminal pH to 5. low pH activates powerful acid hydrolase enzymes, which are derived from vesicles that bud from Golgi

112
Q

initial Golgi hydrolase vesicles

A

membrane proteins required for lysosome function are not present in the initial Golgi hydrolase vesicles.

113
Q

how do initial Golgi hydrolase vesicles appear?

A

membrane-bound vesicles with dense core

200-400nm diameter

114
Q

how is an endolysosome formed?

A

acid environment with hydrolases

fusion of hydrolase vesicles with endosomes containing correct membrane proteins to form endolysosomes

115
Q

formation of phagolysosomes

A

endolysosomes fusing with endosomes derived from phagocytosis - particulate matter brought into cell is digested

116
Q

demonstrating presence of lysosomes

A

histochemical staining for acid hydrolases - e.g acid phosphatases

cathespin-beta and beta-glucuronidase

117
Q

what is autophagy? how are effete organelles eliminated by the cell?

A

all cells must turn over proteins and organelles

effete organelles are wrapped up in membrane derived from the ER

bodies fuse with an endolysosome to form an autophagolysosome - old or damaged organelles are recycled

118
Q

how are proteins in the cell membrane eliminated?

A

formation of multivesicular bodies

cell membrane containing unwanted proteins is internalised into a body containing multiple bubble-like vesicles (multivesicular body).

bodies fuse with vesicles containing lysosomal hydrolases, leading to protein degradation.

119
Q

residual bodies

A

following digestion of material by acid hydrolases, indigestible amorphous and membranous debris may be seen in large membrane-bound vesicles (residual bodies)

120
Q

what are peroxisomes?

A

small membrane-bound organelles containing enzymes involved in the oxidation of substances, e.g. beta-oxidation of VLFAs (c18+)

121
Q

appearance of peroxisomes

A

small spherical bodies
0.5 to 1 um
electron dense core

122
Q

enzymes in peroxisomes

A

some enzymes in peroxisomes oxidise their substrate and reduce O2 to H2O2.
catalase decomposes H202 to O2 and H20

123
Q

how are filaments formed?

A

cytoskeletal proteins form filaments which brace the internal structure of the cell

124
Q

three classes of cytoskeletal proteins

A

microfilaments

intermediate filaments

microtubules

125
Q

what are microfilaments?

A

5nm diameter

composed of actin protein

126
Q

what are intermediate filaments?

A

10nm in diameter

composed of 6 main proteins, varying in different cell types

127
Q

what are microtubules?

A

25nm in diameter

composed of 2 tubulin proteins

128
Q

scaffolding of the cell

A

filamentous proteins become attached to cell membranes and to eachother by anchoring and joining proteins to form a dynamic 3d internal scaffolding

129
Q

assembly and disassembly of the cell scaffolding

A

continual state of assembly and disassembly - periods of stability serve functional roles

130
Q

roles served by periods of stability of cell scaffolding

A

maintaining cell architecture

facilitating cell motility

anchoring cells together

facilitating transport of material around the cytosol

dividing cytosol into functionally separate areas

131
Q

what is actin?

A

5% of total protein in most cell types

globular protein (G-actin) polymerises to form filaments (F-actin) with all actin subunits facing in one direction

132
Q

what are polar filaments?

A

actin subunits all face in one direction

133
Q

isoforms of actin

A

several molecular variants of actin with specific distributions in different cell types, e.g. ones restricted to smooth or skeletal muscle

134
Q

what does actin do?

A

form a layer beneath the cell membrane in association with other proteins. arranged into a stiff cross linked meshwork by linking proteins (filamin is most abundant)

135
Q

what is the most abundant linking protein in the meshwork?

A

filamin

also contains spectrin acid

136
Q

what does the meshwork do?

A

resists sudden deformational forces but allows changes in cell shape by reforming - facilitated by actin severing proteins

137
Q

what are examples of membrane anchoring proteins?

A

spectrin and ankyrin in RBCs

best characterised

138
Q

adherent junctions/focal contacts

A

actin is linked to transmembrane proteins in specialised areas of the plasma

139
Q

stabilisation of microvilli

A

actin filaments can form rigid bundles to stabilise protrusions of microvilli
in the bundles, actin is associated with small linking proteins - fimbrin and fascin most abundant

140
Q

generation of motile forces

A

actin filaments interact with a protein called myosin.

myosin is an actin-activated ATPase composed of 2 heavy chains and 4 light chains arranged in a long tail and a globular head

myosin heads can bind to actin and hydrolyse ATP to ADP

141
Q

forces driving local outgrowths of cell cytoplasm

A

polymerisation of actin filaments

142
Q

microtubules structure

A

2 protein subunits - alpha and beta tubulin

polymerise in a head to tail pattern to form protofilaments

arranged in groups of 13 to form hollow tubes 25nm in diameter

143
Q

where are microtubules present?

A

in all cells except erythrocytes

144
Q

what are centrioles and cilia made up of?

A

tubulin in the form of doublet or triplet tubules

145
Q

polymerisation and stabilisation of microtubules

A

constantly polymerising and depolymerising in the cell and grow out from the microtubule organising centre

stabilised by associating with other proteins (MAPs e.g. Tau protein) which convert the network into a relatively permanent framework

stabilised by proteins that cap the growing end an dprevent depolymerisation

146
Q

where do microtubules originate?

A

microtubule organising centre

147
Q

centrosome

A

organelle containing a pair of centrioles

microtubule organising centre

can act as a centre for about 250 microtubules

148
Q

centrosome function

A

acts as a nucleation centre for the polymerisation of microtubules

149
Q

roles of centriole

A

organises the cytoplasmic microtubular network in normal and dividing cells

organises the development of specialised microtubules in motile cilia

acts as centre for cellular reorganisation in the aggresomal response

150
Q

microtubules and attachment proteins

A

form a network allowing transport around the cell via attachment proteins

dynein moves down the microtubule toward the cell centre
kinesin moves up the microtubule towards the cell periphery

associated with membranes of vesicles and organelles and facilitates their movement

151
Q

intermediate filaments

A

group of filamentous cytoskeletal proteins - 6 main types with specific distribution in different cell types

form ill-defined bundles or masses in cell cytosol

152
Q

localisation of different intermediate filaments

A 
cytokeratins - epithelial cells
desmin - smooth and striated muscle
glial fibrillary acidic protein (GFAP) - astrocytic glial cells 
neurofilament protein - neurons
nuclear lamin - nucleus of all cells
vimentin - many mesenchymal cells
153
Q

attachment and function of intermediate filaments

A

anchored to transmembrane proteins at special sites on the cell membrane (desmosomes and hemidesmosomes) and spread tensile forces evenly throughout a tissue so single cells aren’t disrupted

154
Q

intermediate filaments in epithelial skin cells

A

ketatin intermediate filaments become compacted with other link proteins to form a tough outer layer - impermeable barrier and main constituent of hair and nail

155
Q

intermediate filaments in neurons

A

neurofilaments have long side arms - maintain cylindrical architecture of nerve cell processes when subjected to lateral tensile forces in bending.

anchor membrane ion channel proteins via link protein ankyrin to facilitate nerve conduction.

156
Q

what happens when cells are damaged? what is this response called?

A

intermediate filament network collapses around the centriole to form a perinuclear spherical mass associated with abnormal or damaged cellular proteins of ubiquitin-proteasome system

aggresomal response

157
Q

what system is used in protein degradation?

A

ubiquitin-proteasome system

158
Q

what happens after cell recovery?

A

intermediate filament network reexpands

may act to cocoon damaged components for elimination by proteolysis or autophagy

159
Q

aggresomal response in liver cells

A

persistent alcohol excess

collapsed bundles of cytokeratin intermediate filaments (Mallory’s hyaline) accumulate. also happens in neurons in brains with Parkinson’s - Lewy bodies

160
Q

histochemical detection of filaments

A

cytokeratin - epithelial origin
desmin - muscle derivation
GFAP - specialised cns tumors

161
Q

what is lipofuscin? where is it common/most evident in?

A

lipofuscin is a pigment composed mainly of phospholipid

membrane-bound orange-brown granular material within the cytoplasm

derived from residual bodies containing a mix of phospholipids from cell degradation

prominent in old cells, e.g. nerve, cardiac and liver cells

162
Q

lipid storage

A

stored as non-membrane-bound vacuoles

appear as large clear spaces in the cytoplasm because paraffin wax processing dissolves out the fat - can be stained if frozen and cut in a freezing microtome

adipocytes and hepatocytes

163
Q

glycogen

A

polymer and storage product of glucose - forms as granules in cell cytoplasm. converted into glucose for energy.

visible by electron microscopy
PAS method

in some cells, large amounts of glycogen causes pale staining/apparent vacuolation of cell cytoplasm

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