Adhesion, Compartmentalization, Communication/signaling

How do tissues form in multicellular organisms? What happens without it?

Forms through: the adhesion of like cells

What happens without: tissues don’t form or can’t work as well

What are the 3 most common types of cell adhesion? explain briefly what each do

1) gap junctions = GAPS, CHANNELS BTWN NEIGHBOURING ANIMAL CELLS SO small ions + molecules can pass directly btwn them

2) tight junctions = TIGHT, SEAL NEIGHBOURING CELLS TGTHER SO SUBSTANCES CANT LEAK

3) desmosomes = DURABLE, anchor neighboring cells together, helps tissues resist PULLING + STRETCHING forces

What do certain types of adhesion do? What’s their sole purpose?

Function: allow or restrict the flow of ions and molecules between cells

• purely for adhering cells together or cells to the extracellular matrix

What do desmosomes do? What is a result of this?

Function:

tightly attach cells together

Result:

• increase rigidity of the tissue b/c they hold the cells securely together

What is the main component of a desmosome? Why is it important? (2)

Main component: plaque

Importance:

1) they produce cadherin → the thing that forms the connection between desmosomes

2) they attach to the intermediate fibers of the cytoskeleton → holds them in place

What are the 3 varieties of desmosomes?

1) spot desmosome

2) belt desmosome

3) hemidesmosome

Describe spot desmosome (1), what does it look like?

• SINGLE points of adhesion

eg: spot welding or placing a rivet

appearance: like buttons

Describe hemidesmosome (1), what is it similar to?

Function: connect a cell to the extracellular matrix

Similar: spot desmosomes

Describe belt desmosome(1), how long can it span?

• plaques are elongated, forming a belt

span: the perimeter of a cell

What is the importance of desmosome in the body? (3)

1) provides strong adhesion between skin cells → helps maintain integrity and resilience of the skin against mechanical stress

2) In the heart: ensures that cardiac cells stay together during INTENSE CONTRACTIONS

3) In the urinary bladder: helps the bladder organ structure to withstand the stretching and contracting that occurs as the bladder FILLS & EMPTIES

What do gap junctions do? Where do they connect? What does this do?

Function:

They allow cells to exchange particles

Connection:

• Directly connect the cytoplasm of two cells

Purpose:

• allows various molecules, ions, and electrical impulses to directly pass through a regulated gate between cells

What is the important protein in gap junctions? How many are needed to form a gap junction and how do they form a gap junction?

Protein:

Connexon

• 6 connexin proteins assemble together in a cell membrane to form a ring-shaped cylinder called a connexon (or hemichannel)

How it forms a gap junction:

• When two connexons from neighboring cells dock end-to-end, they create a complete gap junction channel

appearance + where are connexons found (in general in the body)?

Appearance: can be open or closed

Found:

General:

• between most cells within the body b/c they are found between all cells that are directly touching other cells

Where are gap junctions found in the body? (2 specific places) And what is the importance of them there?

Heart:

• ions (Ca2+ & K+) move through gap junctions to allow rapid and coordinated transmission of electrical impulses across the heart muscle

• importance: Ensures synchronized contractions

Digestive tract:

• enables the cells to communicate and contract in a coordinated manner (peristalsis)

How are tight junctions similar to desmosomes?

Similarity:

• they are both protein connections between cells

What are the two purposes of tight junctions and how do they do them? (only for 1)

1) LIMIT the passage of molecules and ions between cells (extracellular fluid)

• does this by making a barrier between cells, PREVENTS MOVEMENT of materials AROUND CELLS

2) MEMBRANE PROTEINS from moving away from the place THEY HAVE THE MOST FUNCTION!!!!!!!

How are tight junctions different form cell membranes?

Difference:

• cell membranes → create barrier for things moving IN or OUT of the cell

• tight junctions → create a barrier BETWEEN cells

What are the important proteins in tight junctions?

• Claudins/occludins/ZOs/JAMS

What do tight junctions do in the skin and digestive tract? What is the importance of them there and the benefit of it?

• prevent materials passing into your body through spaces between cells (PARA TRANSPORT)

Importance:

• ensures that molecules and ions must move INTO cells (through active & passive transport)

• NOT JUST BY MOVING AROUND YOUR CELLS

benefit:

• gives your cells/tissues/body precise control on what materials pass into it

What is the difference between Eukaryotic and Prokaryotic cells?

Prokaryotic cell:

• less complex

• smaller

Eukaryotic:

• larger

• more complex (membrane bound organelles)

What is needed for cells to function efficiently? (3, 3rd one has 2 subpoints)

Metabolic processes (chemical reactions) need to take place:

1) QUICKLY

2) OFTEN

3) Internal environment must remain conductive to continuing this process

(inside of the cell must have the right conditions for the process to keep happening)

FFC

1. FAST (quickly)

Metabolic reactions must happen quickly enough for the cell to function properly.

2. FREQUENTLY (often)

Reactions must occur repeatedly to meet the cell's ongoing needs.

3. CONTINUOUSLY (keep going)

The internal environment must remain conducive to metabolic processes, meaning it must have suitable conditions for reactions to continue.

• Right conditions: appropriate temperature, pH, and concentrations of substances.

• Ongoing supply: the cell needs materials and energy to keep reactions going.

How can the internal environment remain conductive to continuing the process of metabolic reactions? (2)

1) NO SHORTAGE OF REQUIRED REACTANTS

2) waste needs to be REMOVED → might interfere with the CONTINUATION of this process

What does cellular efficiency require? (2)

1) reactants & nutrients going where they are needed

2) waste being removed quickly from the cell

Why are eukaryotic cells not efficient? (3)

1) SA: Volume ratio is smaller

2) there is LONGER DISTANCE for nutrients and reactants for metabolic processes to go

→ LONGER TIME FOR MATERIALS TO GET WHERE THEY NEED TO DO

→ LONG TIMES = LESS METABOLIC ACTIVITY = CELL DEATH

3) Having every particle simply being in the same cytoplasm → components for each important reaction may interfere with other important reactions (LESS EFFICIENT)

How have eukaryotic cells evolved to become more efficient? How is this helpful?

Gained: INTERNAL MEMBRANES

How it helps: membrane-bound organelles have specialized compartments

• important functions that cells need to perform have been compartmentalized

• each membrane bound organelle is controlled (protein) microenvironment (barrier) that efficiently conducts the functions of those organelles

How do compartments help large cells perform metabolic tasks? (3)

1) Microenvironments: maintain specific environments

eg: keep a compartment acidic, basic, form a chemical gradient

2) Efficiency: keep important proteins and other components inside so they are always available

3) Surface area: Increase surface area available to perform a metabolic task, more membrane available = more of these tasks can be performed → higher efficiency

What does more membrane mean? (3)

• More membrane surface area = more room for proteins.

• More proteins = more reactions can happen simultaneously.

• More reactions at once = greater efficiency.

Why are smaller cells/prokaryotes efficient? (3)

1) shorter distances to move → nutrients and reactants readily available where they are needed

2) Fewer molecules around → less interference by other processes

3) Do NOT need COMPARTMENTS, b/c small cells already run efficiently due to their size → less complex/no internal membranes

Multicellular organs need to _____ in order to form ____, _____, ______ (3)

Communicate effectively in order to form working tissues, organs, and organ systems

What is the class of membrane protein that is involved with communication?

receptors

What are the molecules that bind/interact with receptor proteins? What are some examples? (3)

Ligand

1) Hormones: Chemical messengers that travel through the blood to target cells. Example: insulin signals cells to take up glucose.

2) Neurotransmitters: Chemical messengers released by neurons to communicate with other cells.

3) Cytokines (cell defence): Signaling proteins that help cells communicate, especially during immune responses.

What happens when a ligand interacts with its receptor? What does this cause afterwards?

It changes the shape/conformation of the receptor protein

Causes:

• signal TRANSDUCTION mechanism/pathway

What does the signal transduction mechanism/pathway effect?

• effects the behavior of a chain of several other proteins that ultimately change the BEHAVIOR OF THE CELL

What is gene regulation?

• Caused by many signals received by a cell → turns a gene on or off

what molecule do many signals involve? what is it? what does it do?

Molecule involved: cAMP/cyclic AMP (cyclic adenosine monophosphate)

→ secondary messenger

• transfers the signal from the membrane protein receptor (CANT MOVE) to somewhere else in the cell where it binds to a protein and activates it

What is a protein kinase?

• molecule that modifies proteins by ADDING A PHOSPHATE GROUP to them

What does adding a phosphate group to a protein do?

• changes the structure of the protein → therefore also changes the function

• when a phosphate is added to a protein by kinase, it is turned “ON”

What can also happen to the affected proteins?

• the phosphate groups can be REMOVED later → REVERTS them back to their PREVIOUS structure

• goes back to “OFF”

Signal transduction pathways can be both ___ and ___

SIMPLE and COMPLEX

what is special ab steroid hormones

• some types of signaling molecules pass through the cell membrane and can DIRECTLY activate the gene or proteins w/o the involvement of SECONDARY MESSENGERS

What do receptors do? what does the transduction pathway do? What happens without this capability?

Receptor:

acquire information from the environment/other cells

Pathway:

creates the appropriate response to those environmental conditions/other cells

without:

CELLS WOULD NOT BE CONSIDERED ALIVE

What is adding a phosphate group called?

Phosphorylation

Why is long times to transport stuff bad?

long times = less metabolic activity = cell death

• Long transport time: Nutrients and reactants take too long to reach where they are needed, and waste takes too long to leave.

• Less metabolic activity: Reactions slow down because the cell lacks needed materials or waste accumulates.

• Cell death: If the disruption is severe or lasts too long, the cell may no longer be able to survive.

why are cells compartmentalized?

to avoid the loss of efficiency in eukaryotic cells from them being large and complex