The cell Flashcards
1
Q
general structure of the cell membrane
A
lipid bilayer containing specialised proteins, in association with surface carbohydrates.
2
Q
general structure of lipid molecule
A
non polar hydrophobic end (2 fatty acid tails)
polar hydrophilic region (glycerol, phosphate and choline)
3
Q
what does the polar hydrophobic region contain?
A
glycerol, phosphate, choline
4
Q
properties of lipid molecules
A
amphipathic
spontaneously form bilayer in water, hydrophobic ends forming an inner layer
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
6
Q
main component of cell membrane
A
lipid forms 50%
7
Q
major types of membrane lipids
A
phosphoglycerides
cholesterol
glycolipids
8
Q
phosphoglyceride proportion, location and types
A
50% lipid component
surround membrane proteins anchoring proteins w/ enzymatic/transport functions
phosphatidylcholine
phosphatidylserine
phosphatidylethanolamine
9
Q
cholesterol
A
limits movement of adjacent phospholipids
less fluid, -> stable
10
Q
glycolipids location
A
outer face of membrane
associated sugars exposed, for intercellular communication
11
Q
main types of glycolipid in membranes
A
sphingolipids
galacerebroside - part of myelin
gangliosides - 10% lipid in nerve cells
12
Q
lipid rafts
A
high conc. of sphingolipids and cholesterol
50nm
carry specific proteins/cell signalling molecules
13
Q
integral proteins
A
span lipid bilayer
14
Q
peripheral proteins
A
associated w/ inner or outer
15
Q
functions of membrane proteins
A
attach cytoskeletal filaments to membrane
attach cells to extracellular matrix
transport molecules in/out
chemical receptors
enzymatic
16
Q
function of adhesion molecules
A
attach cells to extracellular matrix
17
Q
function of carrier proteins/membrane pumps/channel proteins
A
transport molecules in/out of cells
18
Q
movement of membrane proteins
A
some diffuse laterally over surface
some fixed
19
Q
glycocalyx
A
carbohydrate residues on luminal aspect of inner membrane systems and cell surface
20
Q
how to demonstrate membrane carbohydrates
A
lectins - proteins extracted from plants
21
Q
how does transport in/out of cells take place?
A
endocytosis and exocytosis
22
Q
endocytosis
A
invagination of cell surface.
invaginated membrane forms an endocytotic vesicle/endosome
membrane and material is further processed
23
Q
endosome
A
small sealed spherical membrane bound body
24
Q
pinocytosis/potocytosis
A
cells take up fluid and small molecules, forming small 50nm vesicles
25
endocytosis/phagocytosis
cells ingesting large particle to form 250nm+ endosomes
proteins on surface - receptors on cell surface
Fc portion of antibody - receptors
cell signalling activated
26
exocytosis
fusion of vesicle membrane with cell surface
secretion of products
incorporates new membrane
27
mediation of endocytosis and exocytosis
fusogenic proteins
28
macropinocytosis
cell extends processes as sheet to envelop large # ECF
29
where are the 2 main vesicles involved in transport derived from?
surface membrane invaginations
- coated pits
- caveoli
30
what are coated pits?
invaginations braced by special membrane proteins with receptors that bind to ligands - bring material in
31
example of specific coated pit
iron is ligand and clathrin is protein
32
what happens in further assembly of the coat protein?
progressive invagination to form coated vesicle
protein dynamin forms collar around neck, assists in budding
33
what does dynamin do?
protein forms collar around neck of vesicle, assists in budding
34
what happens when the vesicle is internalised?
coat protein shed and returned to surface - recycled.
35
what is recepor mediated endocytosis a feature of?
internalisation of iron, LDL and growth factors
36
what are caveoli and how do they differ from coated pits?
invaginations of cell surface braced by protein caveolin
37
3 cellular roles of caveoli
contain receptor proteins, concentration substances into the cell via potocytosis
transcytosis - endothelial cells
intracellular signalling
38
where can transcytosis occur?
cells like endothelial cells
39
what are the 2 types of secretory mechanisms?
constitutive secretory pathway
regulated secretory pathway
40
what is a constitutive secretory pathway?
secretion occurring by a constant fusion of vesicles with surface membranes
41
what is a regulated secretory pathway?
fusion of secretory vesicles with surface having to be signal-triggered
42
Rab family of GTPases
controls specificity of trafficking and docking and recruits tethering and fusion factors
43
SNARE proteins
from SNAp REceptor - tether and dock the vesicle to the membrane
differences/specificity
44
NSF protein
N-ethylmaleimde- sensitive fusion protein interact with SNAPs proteins (soluble NSF attachment proteins) to mediate membrane fusion
45
clathrin structure
protein bracing coated pit membranes
| forms hexagonal lattice structure which develops as a coat around vesicle surface
46
what is the cytosol?
concentrated, dense fluid
47
what components does the cytosol contain?
machinery in protein synthesis, protein degradation and carbohydrate metabolism - enzymes
filamentous proteins - cytoskeleton
metabolism products
ribosomes
48
examples of products of metabolism
glycogen and free lipids - storage component
49
what do ribosomes do?
synchronise alignment of mRNA and tRNA in the production of peptide chains during protein synthesis.
50
ribosome appearance on H&E
basophilic
51
what are ribosomes composed of?
small subunit binding RNA
large subunit catalyses the formation of peptide bonds
specific ribosomal RNA and proteins
52
where is ribosomal RNA manufactured?
nucleolus
53
what is the nucleus?
largest single membrane-bound cell compartment
| contains cellular DNA
54
H&E appearances of nuclei
spherical/ovoid
5-10um diameter
basophilic
nucleolus
55
what are nuclei bound by?
2 concentric membranes - inner and outer
56
function of inner nuclear membrane
contains specific membrane proteins - act as attachment points for filamentous proteins (lamins) - forms scaffolding to maintain spherical shape
57
what are lamins?
filamentous proteins that attach to the inner nuclear membrane and form scaffolding to maintain the spherical shape
58
function of outer nuclear membrane
binds perinuclear space, which is continuous with the lumen of the ER - may be associated with ribosomes
59
function of nuclear pores
continuity between cytosol and nuclear lumen containing chromatin
60
appearance of nuclear pores in TEMs
gaps
61
structure of nuclear pores
top to bottom:
cytoplasmic filaments
cytoplasmic ring
luminal ring
nuclear ring
basket filament
terminal ring
62
nuclear basket
rings and filaments in the nuclear space
63
what is DNA wound around?
histones - proteins
forms nucleosomes
64
what are nucleosomes?
histones with DNA wound around them
65
nucleosome packing
nucleosome string is wound into filaments
| 30nm diameter
66
what does the nucleosome string make up?
chromatin - then coiled, and coiled into a supercoiled metaphase chromosome
67
what are the types of chromatin?
euchromatin
heterochromatin
68
what is euchromatin?
light staining electron lucent areas
actively transcribed DNA
69
what is heterochromatin?
dense staining area
adjacent to nuclear membrane
highly condensed, transcriptionally inactive
70
distribution of chromatin
not uniform
reflects varying degrees of unfolding according to whether genes are being transcribed
71
nucleolus appearance
spherical area within nucleus
1-3um diameter
acidophilic and basophilic
72
nucleolus and metabolic activity
increase in size and number with metabolic activity
| vice versa for metabolically inactive cells
73
function of nucleolus
produces ribosomal RNAs - packaged with proteins to form ribosomal subunits and exported to the cytosol via
pores
74
which 3 regions of the nucleolus can be distinguished by electron microscopy?
pars amorpha
pars fibrosa
pars granulosa
75
what is the pars amorpha?
pale areas
nuclear organising regions with specific RNA binding proteins, correspond to large loops of transcribing DNA containing ribosomal RNA genes
76
what is the pars fibrosa?
dense staining regions
correspond to transcripts of ribosomal RNA genes beginning to form ribosomes
77
what is the pars granulosa?
correspond to RNA containing maturing ribosomal subunit particles
78
what is the nuclear lamina?
network of protein filaments 20nm thick lining internal nuclear membrane.
scaffoldng which maintains shape of nucleus
79
what proteins does the nuclear lamina consist of?
nuclear lamins A, B and C
organised into filaments and form a regular square lattice beneath membrane
80
what does the nuclear lamina network interact with?
nuclear membrane proteins - acts as cytoskeleton
possibly interacts with chromatin in spatial organisation of nucleus
81
mitochondria appearance and function
membrane bound cylindrical organelles
0.5-2um legth
ATP production
energy through oxidative phosphorylation
82
mitochondria evolution
believed to have evolved as symbiotic prokaryotic organisms similar to bacteria
own DNA and systems of protein synthesis without cell nucleus
83
mitochondrial membranes and functions of their associated enzymes
outer membrane - lipid synthesis, fatty acid metabolism
inner membrane - respiratory chain, ATP production
matrix - TCA/Krebs
intermembranous space - nucleotide phosphorylation (ADP -> ATP)
84
things contained by the outer membrane and their functions
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
example of a specialised transport protein in mitochondrion
porin - outer membrane
86
what are 2 properties of the inner mitochondrial membrane and their functions?
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
what is located on the inner mitochondrial membrane?
respiratory chain enzymes
| ATP synthetase
88
what does the intermembranous space contain?
metabolic substrates diffusing through outer membrane
ATP
ions pumped out of matrix during oxidative phosphorylation
89
what does the matrix contain?
enzymes to oxidise FAs, pyruvate and those needed in Krebs
mitochondrial DNA
enzymes for mitochondrial DNA transcription
90
appearance of mitochondria in cells with high oxidative metabolism
large and serpiginous
91
appearance of mitochondria in steroid-hormone secreting cells
cristae are tubular structures, not flat plates
92
what are the ER and Golgi?
2 distinct regions of an intercommunicating membrane bound compartment involved in the biosynthesis and transport of cellular proteins and lipids
93
additional functions of the ER
detoxification or activation of foreign compounds including drugs, by ER proteins - cytochrome P450 proteins
storage of intracellular calcium
94
arrangement of ER and Golgi
deeply folded flattened membrane sheets or as elongated tubular profiles
95
quantity of ER and golgi
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
protein synthesis 1
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
protein synthesis 2
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
SER function
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
3 roles of the Golgi
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
function of cis face golgi
receives transport vesicles from SER and phosphorylates proteins
101
function of medial Golgi
adds sugar residues to lipids and peptides to form complex oligiosaccharides
102
function of trans Golgi
protein proteolysis
lipid and protein sorting
addition of sugar residues
103
where can vesicles from the trans Golgi go to?
incorporation of new cell membrane
special cell vesicles (lysosomes)
secretion by exocytosis
104
what are vesicles?
small spherical membrane-bound organelles
105
how are vesicles formed?
by budding off of existing areas of membrane
106
what are the functions of vesicles?
transport or store material within their lumen
allow the exchange of cell membrane between different cell compartments
107
what are the main types of vesicle?
```
cell surface derived endocytotic
Golgi derived transport and secretory
ER derived transport
lysosomes
peroxisomes
```
108
how can the cellular distribution of vesicles be determined?
immunohistochemical staining for vesicle-associated proteins or contents
109
what is a lysosome?
membrane-bound organelle with a high content of hydrolytic enzymes operating in an acid pH
110
what do lysosomes do?
intracellular digestion system
processes material ingested by the cell or effete cellular components
111
acid vesicle system
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
initial Golgi hydrolase vesicles
membrane proteins required for lysosome function are not present in the initial Golgi hydrolase vesicles.
113
how do initial Golgi hydrolase vesicles appear?
membrane-bound vesicles with dense core
| 200-400nm diameter
114
how is an endolysosome formed?
acid environment with hydrolases
fusion of hydrolase vesicles with endosomes containing correct membrane proteins to form endolysosomes
115
formation of phagolysosomes
endolysosomes fusing with endosomes derived from phagocytosis - particulate matter brought into cell is digested
116
demonstrating presence of lysosomes
histochemical staining for acid hydrolases - e.g acid phosphatases
cathespin-beta and beta-glucuronidase
117
what is autophagy? how are effete organelles eliminated by the cell?
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
how are proteins in the cell membrane eliminated?
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
residual bodies
following digestion of material by acid hydrolases, indigestible amorphous and membranous debris may be seen in large membrane-bound vesicles (residual bodies)
120
what are peroxisomes?
small membrane-bound organelles containing enzymes involved in the oxidation of substances, e.g. beta-oxidation of VLFAs (c18+)
121
appearance of peroxisomes
small spherical bodies
0.5 to 1 um
electron dense core
122
enzymes in peroxisomes
some enzymes in peroxisomes oxidise their substrate and reduce O2 to H2O2.
catalase decomposes H202 to O2 and H20
123
how are filaments formed?
cytoskeletal proteins form filaments which brace the internal structure of the cell
124
three classes of cytoskeletal proteins
microfilaments
intermediate filaments
microtubules
125
what are microfilaments?
5nm diameter
composed of actin protein
126
what are intermediate filaments?
10nm in diameter
composed of 6 main proteins, varying in different cell types
127
what are microtubules?
25nm in diameter
composed of 2 tubulin proteins
128
scaffolding of the cell
filamentous proteins become attached to cell membranes and to eachother by anchoring and joining proteins to form a dynamic 3d internal scaffolding
129
assembly and disassembly of the cell scaffolding
continual state of assembly and disassembly - periods of stability serve functional roles
130
roles served by periods of stability of cell scaffolding
maintaining cell architecture
facilitating cell motility
anchoring cells together
facilitating transport of material around the cytosol
dividing cytosol into functionally separate areas
131
what is actin?
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
what are polar filaments?
actin subunits all face in one direction
133
isoforms of actin
several molecular variants of actin with specific distributions in different cell types, e.g. ones restricted to smooth or skeletal muscle
134
what does actin do?
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
what is the most abundant linking protein in the meshwork?
filamin
also contains spectrin acid
136
what does the meshwork do?
resists sudden deformational forces but allows changes in cell shape by reforming - facilitated by actin severing proteins
137
what are examples of membrane anchoring proteins?
spectrin and ankyrin in RBCs
best characterised
138
adherent junctions/focal contacts
actin is linked to transmembrane proteins in specialised areas of the plasma
139
stabilisation of microvilli
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
generation of motile forces
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
forces driving local outgrowths of cell cytoplasm
polymerisation of actin filaments
142
microtubules structure
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
where are microtubules present?
in all cells except erythrocytes
144
what are centrioles and cilia made up of?
tubulin in the form of doublet or triplet tubules
145
polymerisation and stabilisation of microtubules
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
where do microtubules originate?
microtubule organising centre
147
centrosome
organelle containing a pair of centrioles
microtubule organising centre
can act as a centre for about 250 microtubules
148
centrosome function
acts as a nucleation centre for the polymerisation of microtubules
149
roles of centriole
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
microtubules and attachment proteins
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
intermediate filaments
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
localisation of different intermediate filaments
```
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
attachment and function of intermediate filaments
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
intermediate filaments in epithelial skin cells
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
intermediate filaments in neurons
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
what happens when cells are damaged? what is this response called?
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
what system is used in protein degradation?
ubiquitin-proteasome system
158
what happens after cell recovery?
intermediate filament network reexpands
may act to cocoon damaged components for elimination by proteolysis or autophagy
159
aggresomal response in liver cells
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
histochemical detection of filaments
cytokeratin - epithelial origin
desmin - muscle derivation
GFAP - specialised cns tumors
161
what is lipofuscin? where is it common/most evident in?
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
lipid storage
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
glycogen
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
