Relationships between neighboring cells and the extracellular matrix Flashcards
where does the formation of tissues start?
emrbyo
what are the two ways that specialized cells for tissue in an embryo?
- specialized cell junction
- migration of cells over great distances to meet up with other cells at a new location and form a tissue
what organism is unicellular but aggregate in groups to resemble multicellular organisms and use contact guidance to do this?
myxobacteria
explain how myxobacteria uses contact guidance?
- bacteria leaves behind a trail of extracellular matrix that other myxobacteria can follow
- movement of a single bacterium is made possible by its interaction with fellow bacteria so the whole colony keeps moving together
what organism migrates over long distances, is an amoeba, and makes aggregation centers that gives rise to spores and more amoebae occuring via chemotaxis?
dictyostelium discoideum
define chemotaxis
the directed motion of an organism towards a chemical signal
what is the chemical signal of D. discoideum produced during the hydrolysis of ATP?
cyclic AMP
Inflammation in one part of the body can induce the release of several signals including _______ and _________ that attract other immune cells to come to the site to clear the infection
cytokines
chemokines
Other examples of cell adhesion include the development of the human embryo. In this case, embryonic cells associate with each other using an _____________ that is calcium-dependent.
aggregation factor
what are cell junctions?
way in which cells are held together in multicellular organisms
what are ways we can see cell junctions?
thin-section microscopy
freeze-fracture microscopy
what are the three functional categories of cell junctions?
- adhering junctions
- impermeable junctions
- communicating junctions
what is the main type of adhering junction?
desmosome
what is the main type of impermeable junction?
tight junction
what are the two main types of communicating junctions?
gap junctions and chemical synapses
where are desmosomes most commonly found?
cardiac muscle
skin epithelium
neck of uterus
what are the three kinds of desmosomes?
- belt
- spot
- hemidesmosomes
which desmosomes make a continuous band around each of the interacting cells in an epithelial sheet and are found near the apical end of the cell?
belt desmosomes
which desmosomes are like screws that hold cells together at small points of contact and act as anchoring sites for keratin filaments which help form a structural framework for the cytoplasm?
spot desmosomes
which desmosome do not join adjacent cells together?
hemidesmosome
hemidesmosomes join the basal surface of the cell with ____________
basal lamina
which two desmosomes work together to spread any shearing force through the epithelium?
spot and hemidesmosomes
describe bullous pemphigoid
- disease characterized by blister formation causing the epithelium to detach from the basal lamina
- pruritic skin disease common in people over 60
what is bullous pemphigoid caused by?
autoimmune attack on different protein components of the hemidesmosome
what can the presence of bullous pemphigoid blisters be a side effect from?
furosemide or vildagliptin
what is the main function of the epithelial cell sheets that line all body cavities?
highly selective barrier to prevent the mixing of fluids from both sides
how are epithelial cell sheets mediated?
tight junctions
where are tight junctions commonly found?
transitional epithelium/urothelium
why are tight junctions important for the urinary tract?
to prevent urine from being reabsorbed into the body, it retains the seal even when the epithelium is stretched when the bladder is full
what is the most common type of cell junction and found in many different tissues?
gap junction
what is the purpose of gap junctions?
communicating junction that allow small, water soluble molecules to pass directly between the cytoplasm of one cell to the other
- couples the cell electrically and metabolically
what are examples in the body of gap junctions?
- cardiac muscle: gap junctions connect the heart muscle cells with neighboring cells to synchronize their contractions so that the entire chamber of the heart can contract and relax together.
- nerve cells: allow the spread of an action potential quickly from one cell to the next
what are the protein assemblies that make up gap junctions?
connexons
how many connexon proteins are connexons made up of?
6
One Connexon is a ________, and each cell provides one half to make an interacting, complete gap junction. It comes together like a snap button.
hemichannel
list what the extracellular matrix (ECM) is an important component of?
cartilage
tendons
basal laminae
bones
teeth
what are some functions of ecm?
form or support for cells and can regulate cellular behavior
what molecules of the ecm are synthesized and secreted by local cells?
fibroblasts
what are the two main classes of molecules that make up the ecm?
collagens and glycosaminoglycans
what are glycosaminoglycans (GAGs) linked to what protein?
proteoglycans (PGs)
what does the collagen fibers of the ECM do?
provide strength and organization for the matrix and “aqueous” nature of the matrix allows for diffusion of nutrients, metabolites, and hormones between blood and tissue cells
list other components of the ECM besides collagen
elastin
fibronectin
laminin
what are collagens
most abundant fibrous proteins found in all multicellular animals
what is collagen composed of?
triple helix of three alpha-chains that make a rigid rope like structure that can be cross-linked with the matrix
what is the very specific amino acid sequence that makes up collagen?
every third amino acid is a glycine with many proline and hydroxyproline residues that promote “kinking” and help collagen coil tightly
what is the main amino acid residue that maintains the stability of collagen?
hydroxyproline
how is the hydroxyproline formed?
hydroxylation of proline residues on the collagen molecule through the action of prolyl hydroxylase that requires vitamin C as a cofactor
which collagen fiber type is the largest collagen fiber and present in 90% of the connective tissue including bone
type I
which collagen type is fine and present in cartilage?
type II
which collagen fiber type is fibrillar and present in many tissue?
type III
what is another name for osteogenesis imperfecta type I?
brittle bone disease
osteogenesis imperfecta type I is caused by a mutation in either of which two type I collagen genes?
COL1A1 and COL1A2
the formation of the two genes COL1A1 and COL1A2 leads to the formation of what?
two pro-alpha1 chains and one pro-alpha2 chain that come together to form the triple helix of collagen type I
what are signs of osteogenesis imperfecta tarda?
- long bone fractures during childhood after minor trauma (commonly mistaken for abuse)
- hearing loss
- blue sclera
what is the purpose of elastin?
a “spring” that allows for the recoil of tissues back to their original state
how is the cross-linkage in elastin possible?
through oxidation of lysine residues
how is the oxidation of lysine residues accomplished?
by lysyl oxidase that requires copper as a cofactor
When the lysine is oxidized, it forms bonds with other lysine or _______ residues to make ________, which is only found in elastin.
allysine
desmosine
how many collagen types are there?
5
Desmosine is made up of one _____ and 3 _______ residues and has an ___________, which is what gives elastin its characteristic yellow color.
lysine
allysine
aromatic chain
describe marfan syndrome
autosomal dominant disorder caused by a mutation in the fibrillin-1 (FBN1) gene on chromosome 16
what is fibrillin?
glycoprotein essential for formation of elastic fibers
where are elastic fibers commonly found?
- walls of large arteries (aorta)
- suspensory ligaments of the lens in the eye
what are distinct characteristics of marfan syndrome?
- long limbs
- arachnodactyly
- pectus excavatum
- lens discoloration
- aortic aneurysm
- abnormal formation of rib cage
