Week 1 - Cells and Tissue Flashcards
3 types of integral plasma membrane proteins
pumps, carriers and channels
site of protein synthesis
rough ER
smooth ER function
lipid synthesis and calcium storage
function of Golgi apparatus
where proteins are sent for further modifications after coming from ER
post translational modification process
proteins are carried in vesicles which fuse to become the cis cisterns and then move though the stacks - as they do they undergo enzymatic modification which labels them for specific cell destination
endosome function
vesicles from plasma membrane which fuse with lysosomes to deliver their contents
describe peroxisomes
small vesicle containing oxidases and catalase
is involved in a number of oxidative reactions such as biosynthesis of bile acids, fatty acid metabolism and detoxification
describe a lysosome
a vesicle with an impermeable membrane that contains hydrolytic enzymes - used to degrade unwanted molecules
cause of tay-sachs disease
build up of lipid storage and neuronal bodies resulting in neurological regression, seizures and blindness
functions of the cytoskeleton
organise cell structure and maintain shape of cell
helps cells resist mechanical stress by providing mechanical linkages that let the cell/tissue bear stress
transports intracellular cargo
facilitates movement of organelles and other procedures such as cell division, growth, motility
three types of cytoskeleton filaments and their components
microtubules - tubular (dynein, kinesin)
intermediate filaments - keratin, lamina, vimentin, desmin
microfilaments - actin (myosin)
microbes and microfilaments have molecular motor proteins
uses of microfilaments (Actin)
cell projections - microvilli stereocilia
cytoplasm - cell contraction, shape change
membrane extensions - cell motility
contractile ring - cytokinesis
describe how an intermediate filaments structure relates to its function
filaments are composed of smaller subunits that are twisted into strong, rope-like structures - have high tensile strength
found in cells that require a lot of strength such as epithelial cells
what are keratins
a family of intermediate filaments that are present in keratinocytes of the epidermis
what are lamins
intermediate filaments that regulate chromatin organisation and other processes
nuclear lamins support nuclear shape and stability
what are microtubules
highly dynamic cylindrical tubes that continuously grow and shrink, pushing and pulling associated structures
responsible for movement of vesicles and organelles around the cell
important role in cell division (as a component of the mitotic spindle that attaches to chromosomes and segregates chromosome pairs into daughter cells)
what is the centrosome
a major microtubule organising centre located near nucleus and it imitates microtubule growth towards the periphery
what is an axoneme
axonemes are types of microtubules
a component of the cilia and flagella - helps to bend the structure
cause of kartagener’s syndrome
defects in the cilia and flagella are associated with this disease as a result of mutations in the dynein motor protein
patients will suffer from recurrent respiratory infections and males suffer from infertility
what are cell junctions
transmembrane protein complexes that interact with similar proteins on adjacent cells
links the cells and their cytoskeletons
functions of tight junctions
junction creates a seal preventing diffusion of molecules between adjacent cells - creating a barrier for epithelial cells
also creates a barrier within epithelial cell membranes which prevents mixing of membrane proteins - creates two distinct membranes: apical and basolateral membranes
function of gap junctions
provide a route for intercellular movement of small molecules
describe gap junctions
intracellular channels that connect the cytoplasm of adjacent cells
made up for connexions which are a large family of proteins
function of an adherens junction
joins cells together
function of a desmosome in skin
provides integrity of epidermis - between keratinocytes
function of hemidesmosomes in skin
holds epidermis to dermis (at demo-epidermal junction)
function of focal adhesions
connects cells to the underlying extra cellular matrix
function of an adherens junction in skin
joins epithelial cells together
which cells do not have mitochondria
RBCs
how does the structure of a muscle cell allow it to have extensive calcium storage
they contain a specialised ER called a sarcoplasmic reticulum
how does a plasma cells structure relate to its function
function is to produce immunoglobulin and so they have an extensive rough ER
consequence of defective mitochondria
mitochondrial cytopathies - defects in oxidative phosphorylation
consequence of defective lysosomes
tay-sachs disease - lysosomal storage disorder - destroy neurons
consequence of defective microtubules
kartagener syndrome - mutation in dynein motor protein - immotile cilia
consequence of defective gap junctions
recessive mutation in Cx26 leads to sensorineural hearing loss
consequence of defective IFs/hemidesmosomes
lack of integrity at demo-epidermal junction - epidermolysis bullosa simplex
two strategies for segregating two separate intracellular processes
multicomponent complexes eg. ribosome or proteasome
compartmentalisation in membrane bound organelles separates reactions
how do hydrophilic proteins get across the hydrophobic membrane
nuclear pores - for going to nucleus
via membrane translocator - for proteins living form cytosol; to ER, mitochondria or peroxisomes
transport vesicles - gone to ER then going somewhere else
how do proteins know where to go
through a signal sequence which is a short amino acid sequence attached at N terminal - usually removed once protein reaches its destination
protein sorting process
signal recognition particle attaches to the translated ribosomes and guides it towards a SRP receptor in ER membrane - once attached, protein can enter through transcolon - signal peptidase cleaves off the signal sequence - transport vesicles bud from ER and take protein to Golgi where they undergo enzymatic modification which labels them for a specific location
why are ribosomes the main antibiotic targets of a bacterial cell
bacteria have different sized ribosomes to humans
two pathways for the transport vesicles after they’ve budded from Golgi apparatus
protein will either end up in the plasma membrane or will be packaged into a lysosome
process of proteins going to lysosome
address label for lysosomal is mannose-6- phospate (M6P). Proteins labelled with M6P bind to a specific receptor in the golgi membrane before budding off as an endosome. The endosome matures to become a lysosome. An example of a protein targeted in this way is the enzyme hrydolase
process of proteins going to plasma membrane
the C terminus of the protein has a ‘stop translocation’ code which tells it to remain anchored to the ER membrane. Vesicles from the ER then fuse with the plasma membrane
when do proteins stay in the cytosol
if there is no signal peptide it will stay in cytosol
process of proteins going to nucleus
nuclear localisation signal in their protein sequence
importin receptor and nuclear pore are the equivalent go SRP receptor and ER pore
enzyme that is responsible for protein degradation
proteases
how to proteases degrade proteins
they hydrolyse the peptide bonds between amino acids
two methods of protein degradation
lysosomal degradation and proteosomal
when is lysosomal degradation used
to degrade proteins with a long half life (autophagy)
can be extracellular proteins brought in via receptor-mediated endocytosis or membrane proteins brought in by endocytosis
also for pathogenic proteins brought into cell via phagocytosis
when is proteosomal degradation used
for proteins with a short half life and need to be removed quickly from the cytosol
process of proteosomal degradation
Each end of the protein contains a protein stopper which bind to proteins destined for degradation and then, using ATP hydrolysis, they feed the proteins into the inner chamber of the cylinder
how do proteosomes know which protein to degrade
due to the covalent attachment of a protein called ubiquitin
ubiquitylated proteins are recognised and sucked into the proteasome by the protein stopper where they are unfolded and translocated
functions of skin
protection from mechanical impacts, internal or external pressure, stretching in response to movement, variations in temp, microorganisms, radiation
physiological function - regulates body temp, fluid balance, synthesis of vitamin D
sensation - network of nerve cells that detect and relay changes in environment
major layers of skin
epidermis, dermis and subcutis/hypodermis
layers of the epidermis
outer layer is stratum corneum, then stratum granulosum, stratum spinosum, stratum basale and basement membrane
extra layer called stratum lucidum found only in thick skin
describe the stratum basale layer
mitotically active and contains stem cells that are responsible for populating all layers of epidermis
attached to the basement membrane by hemidesmosomes
lies adjacent to the dermoepidermal junction which separates the dermis and epidermis
merkel cells found in this layer which are involved in sensation
structure of the stratum spinosum layer
made up of several layers of keratinocytes held together by desmosomes
describe the granulosum layer
cells contain keratohyalin granules which contain molecules that are important for aggregating keratin filaments
describe the stratum corneum
outer layer
varies in thickness
flattened dead cells have lost their nuclei here and are filled with bundled keratin
lipids between cells provide a water barrier
process of skin regeneration (not in wound healing)
as keratinocytes in the stratum basale divide and mature, they progress towards the skin surface – in the next layer where they form the stratum spinosum, desmosomes begin to appear on the cells – these cells begin to flatten and they lose their nuclei and cytoplasm acquires a granular appearance – when the cells reach the outermost layer they are no longer viable
components of the dermis
fibroblasts, collagen type one, elastin, ground substance, blood vessels, nerves
two layers of the dermis
papillary layer and lower reticular layer
difference between two dermis layers
superficial papillary layer of the dermis is loose and contains very fine interlacing collagen fibres - this is where most blood vessels are found
In the lower reticular layer, the collagen bundles are much stronger, and elastin fibres are much larger
blood vessels more concentrated in papillary layer
what separates the dermis and epidermis
demo-epidermal junction
functions of demo-epidermal junction
provides a regulated barrier both for movement of molecules from the epidermis to the dermis and in the opposite direction
provides a site of attachment for the epidermis through hemidesmosomes
it aligns cells of the epidermis
serves a base for re-epithelialisation in wound healing
what is the subcutis composed of
adipose tissue
functions of subcutis
provides an energy source
insulation
acts as a shock absorber
which skin layer(s) are nerves located in
most free nerve endings end in the dermis but others extend into epidermis where they attach with Merkel cells
the glands found in skin and their function
eccrine glands - excrete sweat
apocrine glands - restricted to the axillae and genital area - produce a scent
sebaceous glands - produce sebum which lubricates skin and hair shaft to protect against friction and make it more impervious to moisture
function of langerhans cells
antigen presenting - plays a role in immunosurveillance
its cytoplasmic processes support its role to detect foreign antigens in epidermis
type of dendritic cell
what are Merkel cells
found in basal layer
involved in sensation
function of a melanocyte
synthesises melanin in melanosomes which are then transferred into neighbouring keratinocytes - melanosomes within a keratinocyte then form cap over the nucleus – protecting DNA from UV
where does vitamin d synthesis take place
initiated in the plasma membrane of basal and suprabasal keratinocytes
function and location of profilaggrin
found in keratohyalin granules
converted to filaggrin which aggregates keratin filaments into tight bundles
function and location of involucrin
formation of a cell envelope around cells in the stratum corneum
located in keratohyalin granules
function and location of loricrin
found in keratohyalin granules
cross links to involucrin
where are polysaccharides, glycoproteins and lipids found in the epidermis
lamellar granules
function of fibroblasts in the dermis
principle cell of connective tissue and are responsible for producing collagen, elastin and most components on connective tissue
important role in sending and receiving signals from other molecules
also have a role in wound healing
damage caused by abrasions, erosions or ulcerations of skin
only damage is to the epidermis
what does a partial thickness wound damage
structures in the epidermis and parts of the dermis
what does a full thickness wound damage
removes epidermis, dermis and deeper structures
3 phases of repairing damaged skin
inflammation
proliferation
remodelling
what happens in the inflammation phase of wound healing
partial or full thickness would will result in a blood clot
inflammatory cells recruited to the area
proliferation phase of would healing
re-epithelialisation occurs
In deeper wounds, epithelium covers the clot, fibroblasts are recruited to replace lost molecules - they produce collagen type 3 to form granulation tissue and endothelial cells proliferate to repair and form new blood vessels
remodelling phase of wound healing
granulation tissue gets replaced by collagen type one (its stronger and organised into big bundles)
some fibroblasts differentiate into myo-fibroblasts which generate contractile force to close the wound
remaining granulation tissue matures into connective scar tissue with very few cells present
function of epidermal growth factor (EGF)
signals to cells about re-epithelialisation
local factors affecting wound healing
infection, foreign body, oxygenation, vascular supply
systemic factors of wound healing
age, disease, alcohol, smoking, immunocompromised conditions, obesity, medications
tissue definition
groups of similar cells working together to carry out a common function
types of tissue and their functions
Connective tissue – protects and supports eg. Fat
Epithelial tissue – covers body surfaces eg. Skin
Muscle tissue – cells contract to generate force
Nervous tissue – generate electrical signals in response to environment
organ definition
made up of several tissue types compromised in a morphologically recognisable structure
metastasis
the spread of disease-producing agency (eg. Cancer cells) from the initial or primary site of disease to another part of the body
steps of tissue processing
fixation - freezing or chemical fixation using aldehyde based chemical - preserves the tissue
embedding - provides support for the tissue when sectioning, can use paraffin wax or a water based alternative
sectioning - cutting into very thin slices using a microtome
staining - to colour cells and ECM so they’re visible with microscope
what colour would a basic dye stain cells
purple/blue - stains acidic structures
what colour would a acidic dye stain cells
red/pink
two types of epithelia
covering epithelia which lines body surfaces
glandular epithelia which is secretory epithelium arranged into glands
simple epithelia
single layer, good for absorption/secretion
stratified epithelia
2 or more layers of cells, good for protection
pseudostratified epithelia
one layer with mixture of cell shapes
four shapes of epithelial cells
squamous - flat shaped
cuboidal - cube shaped
columnar - tall cylindrical shaped
transitional - readily change shape, accommodates stretching
function and location of simple squamous epithelium
mainly diffusion, filtration, some secretion, absorption
little barrier/protection against friction
found in the lining of blood vessels, the heart, alveoli, lining of serous membranes of the body cavities, lining of some kidney tubules
function and location of simple cuboidal epithelium
diffusion, secretion and absorption
found in kidney tubules, glands and their ducts, lining of terminal bronchioles of lungs, surfaces of ovaries
function and location of simple columnar epithelium
movement of substances, absorption and secretion, offers more protection than flatter cells
found in glands and some ducts, bronchioles of lungs, auditory tubes, uterus, uterine tubes, stomach, intestines, gallbladder, bile ducts, ventricles of brain
function and location of stratified squamous epithelium
protection against abrasion, barrier against infection, reduction of water loss from body
when keratinised its found in skin
nonkeratinised is found in mouth, throat, anus, vagina, larynx, inferior urethra, cornea , esophagus
describe pseudostratified epithelium
structure - technically single layer, some cells reach the free surface others dont
nuclei at different levels so appears stratified
function - synthesise and secrete mucus and moves mucus that contains foreign particles over the surface
location - lining of nasal cavity, nasal sinuses, auditory tubes, pharynx, trachea, bronchi of lungs
describe transitional epithelium
structure - cuboidal/columnar when not stretched and squamous/flattened when stretched - number of layers from 5/6 to 2/3 when stretched function - accommodate fluctuations in the volume of fluid in organs or tubes and protects against caustic effects of urine location - lining of urinary bladder, ureters,superior urethra, pelvis of kidney
