Module 10: Cell and Tissue Form Flashcards
In a multicellular organism cell come together to form…
tissues
a collection of cells work together to perform a …
specific function
Two or more tissues combine and function together to make up an…
organ
The shape of cells and organs reflects what?
their function
Function is determined and maintained by…
structural protein networks in the cytoplasm
- also called the cytoskeleton
What are the two main layers of skin?
Epidermis: the outer layer that serves as a water resistant and protective barrier
Dermis: the layer beneath the epidermis supports the epidermis and supplies it with nutrients
The structural integrity of a tissue or organ depends on the ability of the cells:
- to adhere to one another via cellular junctions
- to adhere to a meshwork of proteins and polysaccharides outside the cell called the extracellular matrix (ECM)
Connective Tissue
- provides structure and support
- the dermis supports the epidermis
- the dermis is mostly made up of connective tissue, a lot of ECM
- the main cell type found in the dermis is fibroblast, produces the extracellular matrix
- also contains nerves and blood vessels
Epithelial tissue
covers the outside of the body and lines many internal structures of the body
The Epidermis
- primarily composed of epithelial cells called keratinocytes, specialized to protect underlying tissues and organs
- contains melanocytes that produce the pigments of skin
- the basal lamina, supports the epithelial cells
– a specialized ECM below the bottom layer of the epidermis - supports the epithelial cells
- the bottom layer of keratinocytes are attached to the basal lamina, cell junctions
Protein fibers of the cytoskeleton provide what?
internal support for cells, like bones provide internal support for the whole body
What is the cytoskeleton formed from?
long chains of protein subunits joined together
- they provide structural support and enable the movement of substances within cells
All eukaryotic cells have at least two cytoskeletal elements, what are they?
Microtubules and Microfilaments
What cytoskeletal element do animals also have?
intermediate filaments
Microtubules Makeup
- tubelike structures made of polymers of protein dimers
- each dimer are made of 2 tubulin proteins
– alpha tubulin
– beta tubulin - one alpha tubulin and one beta tubulin combine to form tubulin dimer
– these dimers assemble to form microtubules
Microtubule Function
- microtubules found in animal cells radiate outward to the cell periphery
– they form at the centrosome - this arrangement helps maintain the cells shape and allows it to withstand compression
– many organelles are secured to microtubules, guides the arrangement of organelles in the cell
Microfilaments Makeup and Location
- polymers of actin monomers that are arranged into a helix
- thinnest of the cytoskeletal fibers
- relatively short and extensively branched just beneath the cell membrane of a cell
- reinforce the cell membrane and organize the proteins associated with it
- present in various locations in the cytoplasm
Epithelial cells of the small intestine contain ____ on their surface. Within the ______ are bundles of _________
microvilli
microvilli
microfilaments
What do microfilaments form in epithelial cells?
they form a band of longer filaments that extends around the circumference of epithelial cells
- the band provides structural support to the individual epithelial cells as well as the entire layer of epithelial cells
- the band is attached to a cell junction that connect neighbouring cells
Microfilaments also take part in what three things?
- transport of materials inside cells
- shortening of muscle cells during contraction
- separation of daughter cells at the end of animal cell division
Microtubules and Microfilaments are always _____
how?
changing
- become longer by adding subunits
or shrink by losing subunits
- these polymers grow faster at one end then the other
– faster growing end is the plus end
– slower growing end it the minus end
Which end is the microtubule positioned at the organizing center of the chromosome?
the minus end
Microtubules undergo random cycles of…..
- rapid shrinkage, depolymerization
- slower growth, polymerization
What is the cycle of polymerization and depolymerization in microtubules know as?
Dynamic Instability
a dramatic shrinkage in a microtubule results in what?
microtubule catastrophe
Dynamic instability in microtubules allows for what?
allows cells to rapidly re-organize the cytoskeleton when needed
- microtubules explore the space of the cell by growing into new areas and then shrinking back
- for example, spindle microtubules use this process to quickly find and attach to chromosomes during cell division
Microtubules and microfilaments ca be joined by small accessory proteins called…
motor proteins
Microtubules function as tracks for transport within the cell. What two motor proteins associate with the tracks? How are they powered?
- Kinesin moves the cargo toward the microtubules plus end
-
Dynein moves the cargo towards the microtubules minus end
- the energy for this movement is driven by conformational changes in the motor proteins and is powered by ATP
Microtubules are found in structures that propel the movement of…
cells, flagella
- substances surrounding cells, cilia
- in cilia and flagella microtubules associate with the motor proteins dynein that causes movement
Intermediate filaments
- found in animal cells
- diameter is intermediate to microfilaments and microtubules
- provide mechanical strength to the cell
- form strong cable like polymers of proteins
Types of Intermediate Filaments
- more then 100 different types of intermediate filaments
- made up of different proteins depending on the cell type
for example - epithelial cells, keratin
- fibroblasts, vimentins
- neurons, neurofilaments
- nucleus, Lamins
What do multicellular organisms use cell junctions for?
to physically connect one cell to another cell or to the ECM
Cells exhibit polarity because of…
- differences between one side and the other
- spatial differences in shape structure and function within a cell
For epithelial cells if its facing out side body or lumen it is….
apical (top side)
For epithelial cells if its attached to the basal lamina it is….
basal (bottom, base)
Cadherins
- integral transmembrane glycoproteins for cell-to-cell attatchment
How do Cadherins work?
- the extracellular domain of a cadherin molecule binds to the extracellular domain of a cadherin of the same type on an adjacent cell
- the cytoplasmic part of the cadherin is linked to the internal cytoskeleton (attached to the microfilament sometimes)
How do cadherins help with structure?
- provides structural continuity from the cytoskeleton of one cell to the cytoskeleton of another
- increase the strength of tissues and organs
Integrins
- internal transmembrane glycoproteins for cells to attach to ECM
- cytoplasmic domain interacts with the ECM, important for the structural integrity of tissues under physical stress
Cell junctions do what?
- connect cells to other cells or to the basal lamina and are reinforced by the cytoskeleton
What are the five types of cell junctions?
- Adherens junctions
- Desmosomes
- Hemidosmosomes
- Tight junctions
- Gap junctions
Cadherins are found in which two cell junctions?
adherens junctions and desmosomes
Adherens Junctions
- a belt-like junctional complex of cadherins that goes around the circumference of the cell
Intracellularly
- the belt of cadherins attaches to a band of actin microfilaments in the cytoplasm
extracellularly
- the cadherins in adjacent cells attach to each other
- creates stability
Desmosomes
- button-like points of adhesion that hold the cell membrane of adjacent cells together
- cadherins strengthen the connection between cells
- the cadherins in the desmosomes of one cell binds to the cadherins in the desmosomes of adjacent cells
- the cytoplasmic domains of cadherins are linked to intermediate filaments of the cytoskeleton
Hemidesmosomes
- epithelial cells are firmly anchored to the basal lamina
- attached via a structure similar to desmosomes called hemidesmosomes
- integrins are the most prominent cell adhesion molecules in hemidesmosomes
- the extracellular domains of integrins bind to the ECM proteins in the basal lamina
- the cytoplasmic domains of integrins are linked to intermediate filaments of the cytoskeleton
Tight Junctions
- since adherens junctions & desmosomes do not prevent the passage of materials between the cells, they need another mechanism to prevent the movement of materials
- tight junctions are able to seal the extracellular space
- the only way a substance can travel from one side of a sheet of epithelial cells to the other is by moving through the cells by means of a cellular transport mechanism
Gap Junctions
- Cell-to-cell communication
- extremely small channels (connexons) span a small gap (2-4 nm) between cells
- connexons allow for cytoplasmic continuity between adjacent cells, but only low molecular weight material can pass between cells (really fast)
– like ions - integrate activities of individual cells of a tissue
Plasmodesmata
- specific to plants
- allow plant cells to transfer RNA molecules and proteins
- much larger than gap junctions
- the cell membranes between the two cells are continuous, allow plants to send signals to one another despite being enclosed within rigid cell walls
What is the the ECM?
- the layer of material secreted beyond the region of the cell membrane in the extracellular area
- formed from insoluble meshwork of proteins and polysaccharides
What are the two general functions of the ECM?
- act as a supportive protective material
- allow for expression of different cell functions
Plant ECM Composition
- the ECM is the layer of material secreted beyond the region of the cell membrane in the extracellular area
What is the cell wall?
a type of extracellular matrix
What are the three layers of the plant ECM/cell wall?
- middle lamella
- made of carbohydrates
- main mechanism by which plant cells adhere to one another - primary cell wall
- thin and flexible
- made of cellulose fibers, pectin, and several other proteins - secondary cell wall
- rigid
- made of cellulose and lignin, hardens the cell wall and makes it water-resistant
Animal ECM Composition
- the connective tissue of animals is extensive in ECM
- a mixture of proteins and polysaccharides secreted by cells
- it is composed of large fibrous proteins, including collagen, elastin and laminin
- these proteins are found in the gel-like polysaccharide matrix
Collagen
- most abundant protein in the animal ECM
- most abundant animal protein, 1/4th of the protein in the body
- more than 20 different forms of collagen exist
- type 1 collagen is the most abundant
- found in the dermis of human skin it provides support
- composed of intertwined fibers that make it stronger than if it were a single fiber of the same diameter
- it consists of three polypeptides wound around one another
- forms a triple helix
- a bundle of these molecules forms a fibril, with fibrils then being assembled into fibers
Basal Lamina
- the basal lamina is a specialized layer of the extracellular matrix that is present beneath all the epithelial tissues
- it provides a structural foundation for epithelial tissues
- consists of several proteins, including a type of collagen
- provides flexible support
- acts as a scaffold for other proteins to assemble on
