(bio) unit 8 - Tissues and Cell Communities Flashcards
What is Cytoskeleton
a network of fibres forming ‘scaffolding’ within cytoplasm
Why is cytoskeleton important
- determines cell shape, position of organelles
- allows movement of organelles/components within cells (ex. movement of chromosomes during mitosis)
- allows movement of cells (‘motility’)
Do prokaryotes have cytoskeletons?
yes, they play similar roles in eukaryotes too (cell shape, division, polarity etc,)
What are the three types of cytoskeletal filaments
- microtubules
- intermediate filaments
- microfilaments
Intermediate filaments characteristics
(Primary purpose, where can be found, related structures)
- structural / provide mechanical strength (not dynamic)
- forms a network through cytoplasm of most animal cells, extending out to cell periphery
- anchored on plasma membrane at cell-cell junctions -> desmosomes
what do Intermediate filaments consist of/ structure
long, twisted strands of proteins, each with globular N-terminal head, globular C-terminal and alpha helical rod domain
describe the central rod domains and gllbular ends of intermediate filaments
- central rod domains are all similar in size and AA sequence, so form ropes of similar diameter
- globular ends are quite variable, interacting with different components within cell
Do all intermediate filaments consist of the same protein?
no, intermediate filaments in different cells even within the same organism can be composed of different proteins
What are the two major classes and subclasses of intermediate filaments
- Cytoplasmic
- keratins
- vimenten and vimentin-related
- neurofilaments - Nuclear
- nuclear lamins
Where are each class of intermediate filaments found?
- keratins (in epithelia)
- vimentin and vimentin-related (in connective tissue, muscle cells, neuroglial cells)
- neurofilaments (in nerve cells)
- nuclear lamins (in all animal cells)
Characteristic of keratins
- the most diverse class of intermediate filaments
- every type of epithelium in the body has its own mixture of keratin protein
- can be used to classify tumours with respect to original cell type
How is keratin exist on skin
it is near the surface of the skin to protect you from osmotic shock.
Dead flattened cells packed with keratin
How do intermediate filaments support the nuclear envelope and what is it involved in
- nuclear lamins form 2D mesh rather than ropes that lay along the nuclear envelope
- involved in processes such as DNA replication and mitosis , breaks down and reforms as cell mitoses
Characteristics of microtubules
- largest diameter; hollow, relatively stiff
- organizes roles in all eukaryotic cells
- creates a system of tracks for movement of vesicles/organelles
- anchor organelles in place
- form mitotic spindle
- forms stable structures on certain cells - cilia, flagella
Describe microtubule organizing centres and give an example
- structures from which microtubules originate and radiate outward
- in animal cells -> centrosomes
Describe the structure of microtubules
- they are hollow tubes of tubulin
- these tubulin consist of alpha beta heterodimers that polymerize to form protofilaments
- protofilaments buildup to form walls of the hollow tube
- entire tube has polarity due to exposing the alpha portion of the heterodimer on one side and the beta portion on the other side
Are microtubules changing? or stay constant? how
they are changing/dynamic
- they are growing and shrinking as subunits are added or removed
- dimers will add spontaneously to the ‘plus’ end
‘plus’ and ‘minus’ end of protofilament/microtubule
- beta end of a protofilament, referred to as the ‘plus end’ of the microtubule
- this end is where dimers will be added to
- alpha end of a protofilament, referred to as the ‘minus end’ of the microtubule
How can microtubules extend in length?
extended by motor proteins on microtubule tract
What are motor proteins?
biological ‘motors’ that are able to move along a suitable surface powered by the hydrolysis of ATP (convert chemical energy into mechanical work)
What are the two types of microtubule motors and what do they do
- kinesins
- move towards the ‘plus’ end - dyneins
- move toward the ‘minus’ end
- includes motor proteins that drive movement of cili and flagella
How are cilia and flagella formed? Where are the bases of these structures formed?
microtubules extend to reach the capping proteins along the surface of the cell, the microtubules become stable and thus pushes the cell out.
the base of cilia/flagella occurs at the basal body
Describe Eukaryotic Flagella
Eukaryotic flagella:
- made of tubulin
- move by undulating (swimming) motions
- surrounded by plasma membrane
Describe Bacterial Flagella
Bacterial flagella:
- made of flagellin
- move the cell by rotating (‘rotary engine’)
- not surrounded by membrane
Describe microfilaments (actin filaments)
(structure and where it exists)
- smallest diameter , ‘threads’
- polymer of actin subunits called G-actin, create coil of two long strands called F-actin
- ends are + and -, each end of molecules grows (at + end) and shrinks
- exists throughout the entire cytoplasm
- concentrated under plasma membrane
micro filaments (actin filaments) function?
- cell shape/support
- cell movement
What is the motor protein of microfilament (actin) ? What is it used for
myosin
- muscle contraction, vesicle and organelle transport, cell motility, cytokinesis
What is the most important cytoskeletal component for motility of eukaryotic cells without flagella is…
(Describe the steps)
- actin filaments pushes cell out to make protrusions at ‘leading edge’
- protrusions stick to surface (integral membrane proteins assist in this)
- rest of the cell drags itself forward
- involves interaction with myosin - motor protein
slide 46
What lies just outside the plasma membrane in animal cells and bacteria cells
animal cells - extracellular matrix (ECM)
bacteria, algae, fungi, plants - cell wall
What are common features of extracellular matrix and cell wall
- strength of support of the cell is provided by cross-linked network of filaments (STEEL RODS)
- semi solid gelatinous matrix to resist compression (CONCRETE)
What makes plant cells different from animal cells
- plant cells have rigid cell walls
- they are sedentary, tissues are fairly rigid, weak/fragile if separated from their cell walls bc they have no intermediate filaments unlike animal cells
primary cell wall of plant cell and what is it made up of
- secreted as cells are growing, relatively thin
- consist of pectins (made in rough ER/golgi, picks up water for gelatinous)
- consists of cellulose (made in plasma membrane)
When are secondary cell wall formed in plant cells
formed once growth of the primary cell wall of the plant cell has stopped
Secondary Cell wall in plant cells
(where are they found and how does it help the cell)
- enclosed by the primary cell wall
-thicker than primary wall allows cell to become rigid - found only in certain cell types as they mature
describe some ways the secondary cell wall in plant cells can be useful for (3)
depends on plant+cell type
- STRUCTURE (high cellulose content)
- WATERPROOF (waxes)
- PROTECTION against pathogens / drought (lignins)
How are plant cells encased in a wall able to grow?
- driving force for growth of a plant cell is a turgor pressure
- orientation of cellulose microfibrils determines the direction of growth of a plant cell
What provides the template for cellulose synthesis and directs cellulose deposition in cell wall
microtubule, see slide 58+59
- microtubules form tracks that guide the movement of cellulose synthesizing complexes
What are cells of animal tissue supported by
cytoskeleton, held together by cell-cell junctions and extracellular matrix (thats secreted by the cell themselves)
What is the biggest feature of connective tissue and what does it help with?
extracellular matrix , provides mechanical support for cells in animal connective tissue
What is the strength of animal connective tissue provided by…. (a protein)
a protein called collagen (cable-like)
types of connective tissue
- tendons, dermis of skin
- bone, cartilage
- adipose (fat)
- aqueous humor of eye
What does the Derivative amino acids of collagen (protein of the extracellular matrix in animal connective tissue) must undergo to make collagen function? (2)
hydroxylation of proline and lysine creates
- hydroxy proline
- hydroxy lysine
(with the help of ascorbic acid as a cofactor)
Characteristics/structure of Proteoglycans, where can it be found
- proteins that are heavily glycosylated , containing core proteins called glycosaminoglycans (GAGs)
- GAGs are made of repeating disacchardie subunits ( chondroitin surface, keratan sulfate, hyaluronate)
- attracts water to provide a porous, hydrated gel
- fill spaces between cells in the extracellular matrix of connective tissue
Functions of Proteoglycans
- resists compression
- forms pores of varying sizes for passage of molecules through ECM
- block, encourage, guide cell migration through ECM by binding to secreted proteins
How does the extracellular matrix connect to the cytoskeleton
via Integrins (integral proteins) , provides the connection to allow actin filament on the inside of the cell communicate to the outside of the plasma membrane
What are the 4 cell-cell junctions in epithelium
- Tight junctions
- Adherens junctions (via actin filaments)
- desmosomes
- gap junctions
Tight junctions in epithelium
FORMING SEALED COMPARTMENTS
- form barrier/seal to prevent diffusion of integral membrane proteins between apical and basolateral parts of the cell
- forcing material to go through rather than between cells
- this creates different membrane domains
- consist of proteins holding adjacent epithelial cells together , ‘tight’ epithelium
Adherens junctions in epithelial cells
SHAPING
- forms ‘belts’ around epithelial cells
- adhesion belt can be tightened in selected regions of cell sheet and create invagination of epithelial sheet
- adhesion belt is associated with actin filaments
Desmosomes in epithelial cells
(What kind of microfilament, it’s function, any mutations)
STRENGTH
- anchor spots for intermediate filaments
- holds epithelial cells together
- “half” desmosomes (hemidesmosomes) anchors to epithelial layer to basement membrane (basal lamina)
Mutations in proteins in hemidesmosomes in epithelial cells
- will affect the way the epithelial anchors to the basement membrane
- lifting of epithelial layer off basement membrane
Gap junctions in epithelial cells
(subunits, function)
COMMUNICATION
- connects animal cells
- connexon subunits
- allows passage of very small molecules (relatively non-selective)
- connecting cells via gap junctions allows cells to coordinate activities and work as a team
What channel exists between plant cells , describe them
Plasmodesmata , they are like gap junctions in animal cells
- connect the cytoplasm of adjacent cells
Difference between plasmodesmata in plant cells from gap junctions in animal cells
- plasmodesmata are lined with plasma membrane
- plasmodesmata can dilate significantly to permit passage
- large macromolecules can move from nucleoplasm of one cell to the cytoplasm of distant cells
How do cells become more specialized
they remember previous signals they have received
Describe stem cells
- undifferentiated cells found throughout the body that divide to provide supply types of terminally differentiated cells
- replenish dying cells and repair damaged tissue
Two properties of stem cells
- self renewal: ability to go through numerous cell division while maintaining the undifferentiated state
- multipotency: ability to generate progency of several distinct cell types
Explain the renewal of intestinal lining
Epithelial migration from ‘birth’ at bottom (where cell division can be controlled) of crypt to loss at top of villus
Where do stem cells renew themselves in animal tissue
in basal lamina
Where do all blood cell types in circulation descend from
descends from hematopoietic stem cells
- its job is to replace itself and diffferentiate into major pathways
- these steps are mitotic
Embryonic stem cells are pluripotent, what does this mean
- original egg cell divides repeatedly, all containing the same genome, but are specialized in various ways
- they express different patterns of genes/proteins
ex. early embryo can divide to become fat cell, neuron, macrophage, smooth muscle cell, gilal cells
Are tumors cancer? What are tumors? What types of tumors are there?
not necessarily because cancer has tumors thatare invasive and not all are invasive, tumors are cluster of cells undergoing uncontrolled division
- Benign tumors
- Malignant tumors
Benign tumors
Tumors are noninvasive and noncancerous
Malignant tumors
invasive tumors that spread throughout the body via the blood or lymph to initiate secondary tumors
describe metastasis and what tumor does this occur
The detachment from original tumor and invasion of other tissues when there is a loss of cell adhesion . occurs in malignant tumors
Somatic mutation
any alteration of somatic cell that can give rise to cancers , affect during the development of cell
Causes/mutations of cancer? (4)
- DNA replication and repair
- cell cycle checkpoints
- pathways that drive mitosis/cell cycle
- mistakes in mitosis (aneuploidy)
General Features of Cancer Cells?
- not independent on signals for growth, survival and division (ex. Ras mutation)
- less likely to kill themselves (apoptosis)
- can divide indefinitely (immortal)
- genetically unstable
- invasive (loss of cell adhesion molecules that
How does Colorectal cancer begin
- begins with the inactivation of both copies of the tumor suppressor gene APC (Adenomatous Polyposis Coli)
What kind of cancer type is carcinoma
epithelial cancer
What kind of cancer type is sarcoma
- mesenchymal
connective tissue type cancer (bone, cartilage, muscle, fat, vascular)
What kind of cancer type is hematopoietic
leukemia, lymphoma
(related to red blood cells)
Where do cancers mostly originate
epithelial origin
Describe Dominant mutation
(gain of function)
- mutation in one copy of PROTO-ONCOGENE creates oncogene
- leads to hyperactive oncogene
Describe Recessive mutation
(loss of function)
- mutation inactivates one copy of tumor suppressor gene
- second mutation inactivates second gene copy
- results in complete loss of tunor suppressor gene activity
Assuming no ethical limitations. organoids resembling mammalian tissues/organs can be derived by culturing ____________ under the appropriate conditions.
- cells from very early embryos
- adult stem cells obtained from organs such as liver and pancreas.
- reprogrammed (de-differentiated) adult cells such as skin fibroblasts.
The transport of vesicles of secretory product to the plasma membrane requires …
microtubules, kinesin, ATP
Which type of cytoskeletal component would help reinforce the effectiveness of desmosomes in epithelial cells?
keratins
What is the most abundant protein within animal cells?
actin
What is a major difference in the extracellular matrix (ECM) of animal cells and plant cell walls?
The plant cell wall is primarily carbohydrate, whereas animal ECM is mostly protein based, with some carbohydrate.
