Title: Cell types and subcellular structures
URL Source: blob://pdf/6df13722-fc62-44e5-864e-548a523869af
Markdown Content:
Cytoskeleton
Lecture 4
4BBY1030 Cell Biology & Neuroscience
> FoLSM & IoPPN
> Neuroscience Education
Dr Suba
Poopalasundaram
> October 2024 Dr Clemens Kiecker Topic title: Cell types and subcellular structures
Learning outcomes
By the end of this lecture, you should be able to explain:
a) the terms microfilament, intermediate filament and microtubule
b) the structure and polymerisation of actin and the function of myosin
c) the properties of tubulin and microtubules
d) how tubulin polymerises and discuss factors that affect tubulin polymerisation
e) the role of the cytoskeleton in maintaining cell structure and shape, and in cell
motility
f) the role of motor proteins (kinesin and dynein) in organelle transport and the ATP
dependence of their action Dr Clemens Kiecker Topic title: Cell types and subcellular structures
Classes of cytoskeleton
3Dr Clemens Kiecker Topic title: Cell types and subcellular structures
Chapter 1
# Actin and microfilaments
4Dr Clemens Kiecker Topic title: Cell types and subcellular structures
Actin is found in all eukaryotic cells
> 5
A microvilli of intestinal epithelial cells (actin = red, nuclei = blue)
B smooth muscle cells
C maize epidermis
D dividing yeast cells
> Pollard & Earnshaw, Cell Biology, Chapter 33
Dr Clemens Kiecker Topic title: Cell types and subcellular structures
Actin is organised in bundles or meshed networks/branched
arrays
6
Defines the shape of cells and cellular
sub-structures
Exerts force
Cell movement
Cell division
Pollard & Earnshaw, Cell Biology, Chapter 33 Dr Clemens Kiecker Topic title: Cell types and subcellular structures
Actin defines the shape and sub-structure of cells
> 7
wild-type fruit fly eye slingshot mutant
Exerts force (actin-binding proteins)
Cell movement
Cell division Dr Clemens Kiecker Topic title: Cell types and subcellular structures
Actin-based structures in motile cells
> 8
Stress fibres
Contractile actin-myosin bundles in the
cytoplasm
Lamellipodium
Thin, sheet-like extension that contains
dense meshwork of actin filaments
Filopodia
Transient finger-like protrusions that
contains loose bundles of actin
filaments
> The Cytoskeleton and Cell Migration - Actin Cytoskeleton (oeaw.ac.at)
Dr Clemens Kiecker Topic title: Cell types and subcellular structures
Forces and dynamic shape changes: stress fibres
9
Matsubayashi et al. (2017) hemocyte (immune cell of fruitfly) Dr Clemens Kiecker Topic title: Cell types and subcellular structures
The actin molecule
> 10
Most abundant protein in
eukaryotic cells (approx. 15%
+ 10% actin-binding proteins)
375 amino acids
55 kDa monomer (G-actin)
Two similar domains
Binds ATP/ADP
Mutations cause multiple
disorders including muscular
dystrophy and haemolytic
anaemias
> Pollard & Earnshaw, Cell Biology, Chapter 33 Dr Clemens Kiecker Topic title: Cell types and subcellular structures
Dynamic polymerisation of actin filaments
> 11
G-actin reversibly
polymerises into double-
helical fibres = F-actin =
actin filaments =
microfilaments
Diameter 5-8 nm
Plus and minus end
(barbed and pointed end)
Addition of subunits can
happen at both ends, but
it happens faster at the
barbed end; thus,
individual actin molecules
seem to migrate from the
barbed to the pointed end
= actin treadmilling
ATP is hydrolysed to ADP Dr Clemens Kiecker Topic title: Cell types and subcellular structures
Approx. 60 actin-binding proteins regulate microfilament dynamics
12 Dr Clemens Kiecker Topic title: Cell types and subcellular structures
Forces and dynamic shape changes: cell division and muscle fibres
> 13
Cell division: contractile actin-myosin
ring that squeezes cells apart (A).
Actin-myosin (= actomyosin) filaments
in muscle fibres
Yellow fluorescence indicates the z-disc
(anchors actin filamnets; B).
Electron micrograph of sarcomeres (C).
> Pollard & Earnshaw, Cell Biology, Chapter 33 Dr Clemens Kiecker Topic title: Cell types and subcellular structures
Actomyosin in muscle contraction
> 14
A sarcomere is the basic unit of contractile muscle fibres.
A sarcomere is composed of actin and myosin. Dr Clemens Kiecker Topic title: Cell types and subcellular structures
Actomyosin in muscle contraction
15
Z disk M line Z disk
Light band Light band Dark band Dr Clemens Kiecker Topic title: Cell types and subcellular structures
Myosin II is a motor protein that interacts with F-actin
16
Actin Dr Clemens Kiecker Topic title: Cell types and subcellular structures
Emmeline Jean Hanson a pioneer of muscle studies at Kings
17 Dr Clemens Kiecker Topic title: Cell types and subcellular structures
Chapter 2
# Intermediate filaments
18 Dr Clemens Kiecker Topic title: Cell types and subcellular structures
Classes of intermediate filaments
> 19
Intermediate filaments provide stability and cohesion against stretch. Dr Clemens Kiecker Topic title: Cell types and subcellular structures
Keratin monomers are fibrous proteins
20 Dr Clemens Kiecker Topic title: Cell types and subcellular structures
Intermediate filaments provide support against mechanical stress
21 Dr Clemens Kiecker Topic title: Cell types and subcellular structures
Mutations in keratin can cause epidermolysis bullosa (EB)
22 Dr Clemens Kiecker Topic title: Cell types and subcellular structures
Nuclear lamins
23
Control Lamin A/B knockout Dr Clemens Kiecker Topic title: Cell types and subcellular structures
Chapter 3
# Microtubules
24 Dr Clemens Kiecker Topic title: Cell types and subcellular structures
Microtubules are the main component of the mitotic spindle
25
HeLa cell in mitosis - YouTube
Pollard & Earnshaw, Cell Biology, Chapter 33 Dr Clemens Kiecker Topic title: Cell types and subcellular structures
Microtubules originate in MTOCs such as the centrosome
> 26
MTOC = microtubule
organising centre
The centrosome is a
MTOC it becomes
duplicated during
mitosis.
A significant % of
cancers have abnormal
centrosomes. Dr Clemens Kiecker Topic title: Cell types and subcellular structures
Microtubules are the substrate of organelle transport and the major component of
cellular cilia
> 27
> Pollard & Earnshaw, Cell Biology, Chapter 33
Ciliated epithelial cells (lung) Dr Clemens Kiecker Topic title: Cell types and subcellular structures
Microtubule stability is regulated by a large number of microtubule-associated proteins
28
Pollard & Earnshaw, Cell Biology, Chapter 33 Dr Clemens Kiecker Topic title: Cell types and subcellular structures
Drugs can affect microtubule stability
> 29
Drug Origin Effect Application
Colchicine Plants (certain crocuses and
lilies)
Inhibits microtubule
formation by binding to
tubulin
Treatment of gout, Behcets
disease
Generating seedless fruit
Nocodazole Synthetic Inhibits microtubule
formation
Cancer chemotherapy
Taxol (commercial name:
Paclitaxel, PTX)
Yew tree ( Taxus brevifolia ) Stabilises microtubules Cancer chemotherapy
Vinblastine (commercial
name: Velban, VBL)
Plants (Madagascan
periwinkle)
Inhibits microtubule
formation
Cancer chemotherapy Dr Clemens Kiecker Topic title: Cell types and subcellular structures
Classes of cytoskeleton
30 Dr Clemens Kiecker Topic title: Cell types and subcellular structures
Classes of cytoskeleton
31
Actin microfilaments Intermediate filaments Microtubules Dr Clemens Kiecker Topic title: Cell types and subcellular structures
Chapter 4
# Motor proteins
32 Dr Clemens Kiecker Topic title: Cell types and subcellular structures
Motor proteins that act on microtubules
> 33
Kinesin : from minus to plus end Utilise ATP to generate kinetic energy
Dynein : from plus to minus end Cargo: proteins, RNAs, vesicles, organelles etc. Dr Clemens Kiecker Topic title: Cell types and subcellular structures
Microtubule-based axonal transport in neurons
34 Dr Clemens Kiecker Topic title: Cell types and subcellular structures
A form of dynein enables cilia to beat
> 35
> Pollard & Earnshaw, Cell Biology, Chapter 33
Beating cilia on epithelia (e.g. removal of mucus)
Cilia as signalling antennae
Cilia in sperm motility
All these roles can be affected by ciliary mutations including
those in ciliary dyneins Bardet-Biedl Syndrome Dr Clemens Kiecker Topic title: Cell types and subcellular structures
Motor proteins that interact with actin: myosin
> 36
But no motor proteins that work on intermediate filaments (at least to my knowledge)! Why?? Thank you for your attention
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