MT1 Flashcards
what is the cytoskeleton’s function?
distribution/transport of organelles
mechanical strength
movement
contractile
what is the structure of microtubules?
alpha (a) and beta (b) tubulin form heterodimers, polymerise into protofilaments
13 protofilaments form microtubule
what is dynamic instability of microtubules and how does it occur?
Rapid conversion between growth and shrinkage
tubulins bind GTP, b-tubulin hydrolyses it to GDP (a-tubulin is trapped). GTP-bound ends polymerise, GDP-bound depolymerise. GDP catches up to GTP
what are microtubule binding proteins?
MAPs
modulate microtubule dynamics
MAP and Tau mutations lead to neurodegeneration
what is an MTOC?
microtubule organising centre
negative end of microtubules anchored inside, plus end grows freely out towards cytoplasm
usually a centrosome
what are motor proteins along microtubules?
kinesin -> stepwise motion. towards plus end (anterograde)
dynein -> rotational movement. towards minus end (retrograde)
what is the axoneme?
structural core of motile cilia
9 outer double microtubules, 2 central singlet microtubules
outer MTs slid by dynein relative to central MTs
when dynein moves, axonemes bend
what are some functions of microtubules?
bend axonemes
organelle transport
form mitotic spindle and pull apart chromatids in mitosis
what is the structure of actin filaments?
actin monomers assemble into filamentous actin
right handed helix, 8nm diameter
asymmetric
flexible
why are actin filaments polar?
plus end -> faster growth, barbed. has ATP binding cleft
minus end -> slower growth, pointed
what is treadmilling in actin?
ATP-actin at plus end polymerises, ADP-actin at minus end depolymerises. Equal rates, no change in shape
how does actin allow for cell migration?
protrusions form due to treadmilling, allows for crawling mechanism
what is the structure of intermediate filaments?
8 tetramer monomers wound together, multiple tetramers form filament
antiparallel
non-polar
what are examples of intermediate filaments?
keratins in epithelial cells, hair, nails
neurofilaments (light, medium, heavy) in neurons stabilise axons
nuclear laminate anchor nuclear pores and chromosomes
what are the different types of cell junctions?
tight, adherens, desmosomes, hemidesmosomes, cell-matrix
what are tight junctions?
molecular seal for intercellular space
prevent paracellular movement of ions
what are adherens junctions?
made of actin
cell:cell adhesion
what are desmosomes and hemidesmosomes?
intermediate filaments
desmosomes -> cell:cell adhesion
hemidesmosomes -> anchor cell to basement membrane, connect IMs to extracellular matrix
what is a cell matrix junction?
integrins connect extracellular matrix to actin
what are gap junctions and how are they formed?
membrane channels between adjacent cells allowing for transport of ions
connexin monomers - 6 form a connexon
do blood vessels supply cartilage?
no
cells obtain oxygen/nutrients by diffusion
what are the types of ossification?
intramembranous -> direct replacement of mesenchyme
endochondral -> cartilage model from mesenchyme forms
how does endochondral ossification occur?
cartilage model forms, growths and then calcifies. this prevents nutrients from reaching chondrocytes, so they die, leaving fragmented matrix that acts as ‘model’. osteoprogenitor cells and blood vessels invade from periosteum, proliferate into osteoblasts, which lay down bone
what is the diaphysis and epiphysis?
diaphysis -> where primary ossification centre forms. houses yellow marrow
epiphysis -> secondary ossification centre. at ends of bones. houses red marrow
what is the epiphyseal growth plate?
where growth occurs
resting, proliferation, hypertrophic zones
fuse at the end of growth
what are the two types of bone?
compact and trabecular
what is the structure and function of compact bone type?
strength for weight bearing, resistance to bending, minimal deformation
stiff, inflexible, low strain tolerance
greatest in middle of shaft
what is the structure and function of trabecular bone type?
porous, elastic structure
shock absorbers
realign trabecular pattern if stress line changes, undergoes deformation
what is bone remodelling?
osteogenesis and osteoclasis taking place at different sites in response to mechanical loading
can occur at same site to replace previous bone, maintaining bone integrity
what is the difference between hypertrophy and hyperplasia?
hypertrophy -> cell size increases
hyperplasia -> cell number increases
what is gastrulation?
formation of primary germ layers: hypoblast cells replaced with endoderm, then space filled by mesoderm. epiblast becomes ectoderm
what are the checkpoints of cell division?
entry into s-phase -> commits cells to cycle
dna -> quality check, triggers entry into mitosis
spindle -> if chromatids are ready for separation, triggers entry into anaphase
what are cyclins and CDKs?
cyclins bind to and activate cyclin dependent kinases, regulate the cell cycle
S-cyclin must be abundant for cell cycle to continue
what are the functions of connective tissue?
mechanical, metabolic, defence, repair, growth
what are the types of connective tissue?
loose, dense regular, dense irregular, elastic, adipose
what is the structure of loose connective tissue?
fibroblasts, macrophages
moderate collagen, elastic and reticular fibres
delicate, flexible, vascularised, not stress resistant
what is the function of loose connective tissue?
supports structures under pressure and low friction
fills space between muscle cells, supports
what is the structure of dense connective tissue?
fewer cells, predominance of collagen fibres, less flexible, stress resistant
irregular -> collagen in bundles, no orientation, 3D network
regular -> collagen in linear orientation of fibroblasts along stress lines
what is the function of dense connective tissue?
resistance, protection
irregular -> stress resistant in all directions (eg dermis of skin)
regular -> stress resistant in one direction (eg tendon attaching striated muscle to bone)
what connective tissue is under the skin?
dense irregular in superficial dermis - anchors epithelium
loose deeper to allow skin to move over muscle
adipose in areas of fat in the loose layer
what is the structure and function of white adipose?
single large droplet of triglyceride fat, little cytoplasm
energy storage, insulation, padding
what is the structure and function of brown adipose?
multiple small fat droplets, more cytoplasm, many mitochondria
sympathetic innervation, heat generation
what is the structure of elastic tissue?
bundles of thick, parallel elastic fibres
fibres of elastin associated with glycoprotein
what is the basement membrane and what is its function?
specialised sheet of extracellular matrix proteins and GAGs associated with epithelial layers, muscle cells, blood vessels
cell adhesion, cell organisation, diffusion barrier
what cells are in loose connective tissue?
fibroblasts, macrophages, mast cells, leukocytes
what are fibroblasts?
secrete most extracellular matrix molecules
lays down fibres in particular orientation
what are macrophages?
tissue phagocytes
initiate and down regulate inflammatory response
recruit polymorphonuclear leukocytes to kill pathogens
what are mast cells?
secretory granules filled with bioactive molecules
activated by activation of IgE receptors
can phagocytose bacteria
what are the different types of white blood cells and what are their functions?
basophil -> release of pharmacological compounds
eosinophil -> allergic and vasoactive reactions, control mast cells, inflammation
neutrophil -> phagocytosis
how do neutrophils migrate to an area of inflammation?
intercellular cell adhesion molecule binds to integrin on neutrophil membrane
what is the extracellular matrix and what makes it up?
scaffold, active regulation of cells, determines tissue physical properties
made up of fibrous proteins and glycosaminoglycan (highly hydrated, gel-like ‘ground substance’)
what fibres make up the connective tissue?
collagen fibres, reticular fibres, elastic fibres
what is the structure of collagen?
string of repeated glycine-containing motifs. 3 chains assemble end-to-end and staggered to form collagen fibrils, then fibres in triple helix
glycine used as it is the only amino acid small enough to fit inside the triple helix crowded interior
what diseases are related to collagen?
Ehlers-Danos
osteogenesis imperfecta
scurvy
what is the structure and function of reticular fibres?
reticulin - fibres of type 3 collagen
short, thin fibres
form mesh work holding tissue elements together
in haemopoietic tissue
what is the structure of elastic fibres?
elastin core (coiled polypeptide chains of tropoelastin) cross linked covalently to form 3D mesh work, with fibrillin on surface (micro fibrils of glycoprotein).
elastin fibres can branch, stretch and recoil
in lung, skin and blood vessel walls
what disease is linked to elastic fibres?
Marfan’s Syndrome
what is a glycosaminoglycan?
long, unbranched polysaccharide chains
highly anionic
attract sodium and water, form porous hydrated gels
what is a proteoglycan?
GAGs covalently attached to proteins
form gels of varying pore size: molecular sieves
resist mechanical compression forces
what makes up the ‘ground substance’?
GAGs
proteoglycans
polysaccharides
what are caspases used for?
apoptosis
what is a paracrine ligand?
secretes a signal to change nearby cell behaviour
diffusable
what is a juxtacrine ligand?
ligand on one cell binds to a receptor on an adjacent cell. present in gap junctions
what is mosaic development?
fate of a cell is determined before or during fertilisation
what are the types of muscle?
smooth and striated
