BIO230/255 Section 2: Lectures 1-6

Cell Polarization

Cells which are different at each end which can have different functions at different cell regions, define the inside versus the outside of regions, and can transmit signals from one end to the other

Membrane Trafficking

It can send different proteins to different domains but also determines where proteins end up

Endocytosis

A process in which a vesicle is formed on the inside of the plasma membrane and allows water, solutes, and larger molecules that cannot pass through the cell membrane to enter the cell

Exocytosis

A process in which a vesicle fuses with the plasma membrane and releases contents such as waste products and unwanted material out of the cell

Pinocytosis

It involves the non-specific uptake of liquids or fine suspensions into the cell to form small pinocytic vesicles and is primarily used to absorb extracellular fluid

Phagocytosis

Where the cell engulfs solid material to form large vesicles or vacuoles

Secretion

The process where a cell or gland produces and releases a useful substance for a specific function

Constitutive Secretion

The continuous and unregulated transport of proteins, lipids, and other molecules from the Golgi apparatus to the cell surface and extracellular space via secretory vesicle; it is the "default" pathway

Regulated Secretion

Vesicles are fully-formed but do not fuse with the plasma membrane until a signal is received and can also release material in response to a signal; it can also can have transmembrane proteins, though less common, as well as deliver extra membrane material

Signal-Mediated Diversion

A biological process where a specific signal, like a protein tag, redirects a molecule's path within a cell

Endosome

A membrane-bound vesicle within eukaryotic cells that plays a crucial role in the endocytic pathway, sorting and transporting materials, including proteins and lipids, from the cell surface to other compartments

Lysosome

Membrane-enclosed organelle that breaks down worn-out proteins and organelles and other waste materials, as well as molecules taken up by endocytosis; contains digestive enzymes that are typically most active at the acid pH found inside these organelles

Endocytosed Proteins

Proteins which can either be recycled to the same domain of the plasma membrane, transcytosis to the other domain of the plasma membrane, or degraded in the lysosome

Vesicle Fusion

In which a vesicle merges with a target membrane

ESCRT Proteins

They can form vesicles away from the cytoplasm (into lumen or extracellular space), and the vesicle formation machinery is in the cytoplasm

PI3P Protein

Multi-ubiquitinated protein which passes molecules to ESCRITA then passes to ESCRT II then passes to ESCRT III then fuses to form vesicles

Phosphoinositides (PIPs)

They have a head group made of an inositol sugar and a glycerophospholipid made of a phosphate group attached to the head group, followed by a glycerol, and lipid tails

GEF

Exchanges GDP for GRP

Rab-5 GTP

Recruits PI3-kinase by binding to the GDI to stop GTP from leaving; positive feedback loop

SNAREs

A family of proteins that help with membrane fusion and vesicle docking, often working together with Rab

Interphase

This takes place when the cell is preparing for cell division which is comprised of the G1, G2, and S phases

Synthesis

The stage in interphase where the cell synthesizes (replicates) an entire copy of its DNA

Mitosis

Where the cell is dividing, made up of prophase, metaphase, anaphase, telophase, cytokinesis

Prophase

The first stage in mitosis where the chromatin condenses to form a chromosome with two sister chromatids

Metaphase

The stage in mitosis where the chromosomes move to the middle and the mitotic spindles from the centrioles attach to the centromere

Anaphase

The stage in mitosis where the sister chromatids split into individual chromosomes, and each chromosome is pulled to an opposite pole by the centriole

Telophase

The final phase of mitosis where the cell begins to divides into two

Cytokinesis

The splitting of the cell where microtubules keep cell components separate and actin forms the contractile ring

Microtubules

Long, stiff, cylindrical structure composed of the protein tubulin which are used by eukaryotic cells to organize their cytoplasm and guide the intracellular transport of macromolecules and organelles

Tubulin

Protein from which microtubules are mad

Tubulin Dimers

A subunit of a microtubule made up of a positive and negative end

T-Formed Heterodimers

Has ⍺ and β-tubulin stuck to GTP; more likely to have addition or growth

D-Formed Heterodimers

Has the ⍺-tubulin as GTP while the β-tubulin has been cut to GDP; more likely to have subtraction or shrinkage

GTP Cap

Occurs when ⍺ and β heterodimers are bound to GTP and absence of this causes shrinkage

Gamma Tubulin

Helps to nucleate microtubules, interacts with ⍺-tubulin, nucleates or stabilizes, and protects microtubules from depolymerization at the minus end

Centrosome

Has a pair of centrioles, pericentriolar material around the centrioles and nucleating sites (𝛾-tubulin ring complexes) on the pericentriolar material

Centriole

Cylindrical array of microtubules usually found in pairs at the center of a centrosome in animal cells; also found at the base of cilia and flagella, where they are called basal bodies

Dynamic Instability

Plus ends of microtubules grow and shrink which is needed for remodelling

Motor Proteins

Protein such as myosin or kinesin that uses energy derived from the hydrolysis of a tightly bound ATP molecule to propel itself along a protein filament or other polymeric molecule

Kinesins

A large family of motor proteins that uses the energy of ATP hydrolysis to move toward the plus end of a microtubule

Dyneins

Motor protein that uses the energy of ATP hydrolysis to move toward the minus end of a microtubule; one form of the protein is responsible for the bending of cilia

Actin Filaments

Thin, flexible protein filament made from a chain of globular actin molecules; a major constituent of all eukaryotic cells, this cytoskeletal element is essential for cell movement and for the contraction of muscle cells

Actin Monomers

Are asymmetric and polar, and they can bind and hydrolyze ATP

Treadmilling

Process by which a protein filament simultaneously adds subunits at one end while losing them at the other; in the process, an individual subunit will move along the length of the filament, which itself may remain stationary (like a passenger riding an escalator); occurs in both microtubules and actin filaments

ARP2/3 Complex

Nucleates the minus end of actin filaments and protects them from depolymerization

NPF

Recruits ARP2/3 to start nucleation and to make a new actin filament to keep moving the whole network forward and hence, the entire network undergoes treadmilling

Lamellipodium

Protrusion on the leading edge of a crawling cell, formed by a dense meshwork of actin filaments; the growing actin network pushes cell forward

Lagging Edge

Actin and myosin contract to drag the network forward on this side

Myosin

Type of motor protein that uses ATP to drive movements along actin filaments; one subtype interacts with actin to form the thick contractile bundles of skeletal muscle

Extracellular Matrix

Specialized material outside the cell

Integrin

One of a family of transmembrane proteins present on cell surfaces that enable cells to make and break attachments to the extracellular matrix, helping them to crawl through a tissue

Cdc42 GAP

Over-activation of this causes actin rearrangement

Rac GAP

Over-activation of this causes an increased of leading-edge two dimensional structures

Rho GAP

Over-activation of this contributes to an increased number of actin-myosin re-arrangements

Lateral

Facing the neighbouring cells

Basal

Facing the basal-luminal cells

Basal Lamina

A specialized type of ECM which underlies all epithelia; is thin (40-120 nm thick), secreted by the epithelial cells, and influences cell polarity (apical–basal), and separates epithelium from underlying tissue and prevents fibroblasts in underlying connective tissue from interacting with epithelial cells

Epithelial Tissue

Protective tissue covering all external and internal surfaces; cells are directly connected to each other with minimal extracellular matrix, adhesion to the basal lamina extracellular matrix

Connective Tissue

Supports, connects, and separates other tissues and organs in the body; cells are dispersed through the extracellular matrix, cell interaction with the extracellular matrix and cell movement

Epithelial Cells

They are polarized and line surfaces, cavities, and organs; these cell surfaces define the inside vs the outside of the organism or tissue

Tight Junctions

Seals the gap between epithelial cells, are sealing strands, stops direct diffusion into connective tissue, and keep the correct transporters in their correct domains of the cell, meaning that apical proteins are kept on the apical surface and the basolateral proteins on the basolateral surface

Adherens Junctions

Connects with filament bundle in one cell with that in the next cell, forming an adhesion belt

Desmosome

Connects intermediate filaments in one cell to those in the next cell at specific spots, does not go through the cell

Gap Junction

Allows the passage of small water-soluble molecules from cell to cell

Hemidesmosome

Anchors intermediate filaments in cells to extracellular matrix

Actin-Linked Cell-Matrix Junctions

Anchors actin filaments in cells to extracellular matrix

Junctional Complex

Can link to the cytoskeleton and include cell-to-cell and cell-to-matrix junctions

Cell-Cell Junctions

Protein complexes linking cells to other cells, and are usually mediated by cadherins

Cell-Extracellular Matrix Junctions

Protein complexes linking cells to ECM, and are usually mediated by integrins

Cadherins

They are transmembrane proteins expressed by both cells being anchored which mediate cell-cell connections at adherens junctions; their extracellular domains directly interact with each other, and they interact homophilic interactions of their extracellular domains and interactions require Ca2+ ions

Homophilic Interactions

The binding of a cell adhesion molecule (CAM) on one cell to an identical CAM on an adjacent cell

Heterophilic Interactions

Where different cell adhesion molecules (CAMs) bind to each other

Adhesion Belt

A continuous band of actin filaments and cadherins that forms between adjacent cells, contractions pulls cells to form a tube

Claudin

A family of tetraspan transmembrane proteins that are key components of tight junctions, forming a barrier and regulating the permeability of the space between cells (paracellular space) in epithelial and endothelial tissues

Occludin

A transmembrane protein that regulates the permeability of epithelial and endothelial barriers

Apical

Describes the top or the tip of a cell, structure, or organ; in an epithelial cell, for example, this surface is opposite the base, or basal surface

Integrin

One of a family of transmembrane proteins present on cell surfaces that enable cells to make and break attachments to the ECM; heterodimers mediate cell-to-cell-matrix junctions by anchoring actin filaments to the extracellular matrix by binding directly to ECM

Crumbs Complex

Transmembrane protein which helps to keep epithelial cell apical during cellular shape changes

PAR Complex

Works with Crumb complex to maintain epithelial cell polarity

Scribble Complex

Is activated in basolateral domains and tight junctions from apical to the adherens junctions

Landmark

Can be a structure, a protein, a signal, or a process which generates subsequent patterns

Protrusion

A projection of a cell's membrane, supported by the internal cytoskeleton, that extends outward from the cell

Multicellular Development

How organisms grow and change

Cell Proliferation

Increase in cell numbers via cell division

Cell Differentiation

Changes in cell fate via cell signalling & differential genome expression

Cell Morphogenesis

Changes in cell shape, interactions and/or location

Embryogenesis

It is used as a model for multicellular development and begins with an egg plus sperm, ending shortly before birth

Gastrulation

The change from ball of cells to embryo with a gut & 3 germ layers: the ectoderm cells which forms epidermis and nervous system; the mesoderm cells which forms muscles, connective tissue, bones; blood, kidney; and the endoderm which forms the lungs, pancreas, liver, etc.

Ingression

Cells internalize by moving inward

Delamination

Cells internalize by splitting or separating into layers

Mesenchyme

A loose, undifferentiated cell tissue

Invagination

Cells internalize by forming a cavity or a pouch

Involution

Cells internalize by curling inward

Neural Tube

The embryonic precursor to the central nervous system, which is made up of the brain and spinal cord

Ectoderm

The outermost layer of cells or tissue of an embryo in early development, or the parts derived from this, which include the epidermis and nerve tissue

Mesoderm

The middle layer of the three germ layers that develops during gastrulation in the very early development of the embryo of most animals

Endoderm

The innermost layer of cells or tissue of an embryo in early development, or the parts derived from this, which include the lining of the gut and associated structures

Elongation

Can occur via convergent extension, meaning that cells converge or crawl together to extend, or form a line, and can also occur via mass cell migration

Collective Cell Migration

Cells can move as individuals or as a group to form different shapes

Turgor Pressure

Also known as hydrostatic pressure, it is the force within the cell that pushes the plasma membrane against the cell wall