Cell Cell interactions

cAMP

Cyclic adenosine monophosphate

Extracellular membrane (ECM)

helps define cell shape, attaches in to other cells, acts as a first defense

Bacteria cell walls

consists primarily of polysaccharide peptidoglycan polymers connected by peptide bonds

Archaea celll walls

absence of peptidoglycan, cell walls form dense coat of proteins (S-layer)

Extracellular membrane in animals

Cable-like protein is mostly collagen• Binds together to form flexible extracellular layer• Ground substance is made of proteoglycans • Proteins attached to many polysaccharides• Attracts water and forms a gel (fiber composite)

Collagen protein (ECM)

consists of three polypeptide chains that wind around one another to form the fibrous component of the animal ECM.

Ground substance of the animal ECM

made of complexes of gelatinous proteoglycans form

Bone and cartilage have

large ECM

Laminins

Cross-linking glycoproteins that bind to integrins on surface• Attach the ECM to the membrane• Integrins anchor the cytoskeleton to the ECM and help transmit signals

Integrins

connects the extracellular matrix to the cytoskeleton

Expansins

proteins that disrupt cross-linking between microfibrils and allows cell to grow (plant cellsO

Secondary cell wall

is between the membrane and primary cell wall

Secondary cell wall structures

waxes (leaf cells), lignin (wood cells)

Middle lamella

in plants is what glues the cells together, comprised of gelatinous pectins

Animal cells are held together by…

Tight junctions and desmosomes

Tight junctions

seal cells together with a water tight seal and can close and open, usually found in the epithelia

Desmosomes

proteins that connect the cytoskeletons of adjacent cells, they resist pulling and shearing forces, commonly found in epithelial and muscle tissue.

Gap junctions

act as channels between cells, aid in communication and transfer, allow the flow of small molecules between cells

Plasmodesmata

plasma membrane separates plant tissues into Symplast and Apoplast, plamsa membranes, cytoplasm, amd smooth ER of two cells connect

Symplast

shared cytoplasm

Apoplast

extracellular space

Ways distant cells comunicate…

using neurotransmitters and hormones

Neurotransmitters

may open or close channels in distant cells, allowing the brain to control the body

Hormones

are information-carrying molecules secreted by plant and animal cells into bodily fluids to act on distant target cells , circulates in cells

Small molecules

peptides, steroids, or even gases

Lipid-soluble

permeable to plasma membrane, receptors in the target cells’ cytoplasm

Hormones bind to

signal receptor molecules

Signal receptors

• number of receptors in a cell may change

• ability of receptor to bind a hormone may change

• Sensitivity of a cell to a particular hormone may change over time

• they can be blocked

Lipid-insoluable

cannot cross membrane, receptors on the cell’s plasma membrane

Intracellular signals may be…

amplified and diversified

Two types of signal transduction systems

G-protein-coupled receptors and Enzyme-linked receptors

G-protein receptors

Closely associated with transmembrane signal receptors• Activated by a signal receptor when a G protein binds to guanosine triphosphate (GTP), its shape is altered and it is activated• Trigger production of a 2nd messenger

Enzyme linked receptors

Bind a hormone signal• Directly catalyze a reaction inside the cell• Receptor tyrosine kinases (RTKs)are the best-known group of enzyme-linked receptors• They trigger a phosphorylation cascade of protein kinases

Secondary messengers

Effective because they are small molecules• Diffuse rapidly throughout cell• Can be produced quickly in large quantities• Amplify hormone signals, some second messengers activate protein kinases

Secondary messenger examples

• Calcium ion

• Cyclic adenosine, monophosphate (cAMP)

• Cyclic guanosine monophosphate (cGMP)

• Diacylglycerol (DAG)

• Inositol Triphosphate (IP3)

Calcium ion (secondary)

Binds to a protein called calmodulin; Ca2+/calmodulin complex then activates proteins

Cyclic guanosine monophosphate (cGMP)

Opens ion channels; activates certain protein kinases

Diacylglycerol (DAG)

Activates certain protein kinases

Inositol Triphosphate (IP3)

Opens calcium channels, allowing stored calcium ions to enter cytosol

Receptor tyrosine kinases

are the best-known group of enzyme-linked receptors

Kinase

an enzyme that attaches a phosphate group to a protein. Turns protein on

Phosphatase

An enzyme that removes a phosphate group from a protein. Turns protein off

Crosstalk’s diverse signals

• can inhibit steps in second pathway (reduce cell response to second pathway)

• can stimulate steps in second pathway (leads to two different responses to signal

Quorum sensing

signaling pathways that respond to population density

Bacteria release species-

specific signaling molecules when their numbers reach a specific threshold

Examples of responses to quorum sensing

Some bacteria use it to help glue community of microbes to a biofilm (such as plaque on teeth)• Allows unicellular organisms to coordinate activities