Unit 4: Cell communication and cell cycle

on the fundamental level what are the two ways that cells communicate with eachother

• Direct

  • cell to cell communication

  • some sort of cell junction between adjacent cells

• Signaling

  • Via signals

  • ligands

  • hormones are long distance

what is qurom sensing

Quorum sensing is a process where bacteria release and detect chemical signals to sense population density. When enough signals accumulate, it triggers a coordinated response like biofilm formation or gene expression, showing how even simple cells communicate.

paracrine vs endoctine vs autocrine

Paracrine Signaling

One cell sends a message to nearby different cells. It's like whispering to the people sitting around you.

Example: Nerve cells release chemicals that tell nearby muscle cells to contract, making you move.

Autocrine Signaling

A cell sends a message to itself. It's like writing yourself a reminder note!

Example: Cancer cells often release growth signals that they themselves respond to, causing them to divide uncontrollably.

Endocrine Signaling

Specialized cells release hormones into the bloodstream that affect cells throughout the body. It's like broadcasting a message over the radio for everyone to hear.

Example: When you eat something sugary, your pancreas releases insulin that travels through your blood, telling cells all over your body to absorb the extra sugar.

Two types of cell signals (long and short distance)

• hormones

  • Long distance

• Local regulator

  • Short distance

intracellular receptors vs plasma membrane receptors/cell surface receptors

• Intracellular receptors

  • found inside the plasma membrane in the cytoplasm or nucleus

  • the signal molecule must cross the plasma membrane and therfore be hydrophobic

• plasma membrane receptors or cell surface receptors

  • bind to water soluable ligands

What are ligands

• ligands are signaling molecules that bind to a receptor to get an effect out of a cell

• many ligands are hormones

• Receptors have to have complementary shape

Cell signaling involving 3 steps

• reception of a ligand

• Signal transduction

• cellular response

what happens during the reception phase of cell signaling

• the signal molecule binds with a specific receptor molecule thats embedded in the PM

What happens during the transduction and response phases of cell signaling

• receptor interacts with membrane proteins to produce a second messenger

• the secondmessanger with other with other relay molecules bring the message to the cytoplasm which can activate enzymes

How is the mechanism of steroid (nonpolar) hormones different than those of water soluable hormones

• these hormones diffuse through the phospholipid bilayer

• Bind with cytoplasmic receptors which can diffuse into the nucleus and activate genes

water soluable hormones

• bind with receptors and create second messangers

explain g protein receptor

• • Set up in membrane

    • There is a G protein-coupled receptor that is awaiting epinephrine

    • There is a G protein next to the receptor

      • membrane-embedding protein

    • membrane-embedded enzyme called adenylyl cyclase

  • reception

    • Epinephrine binds to the G protein-coupled receptor

    • When the epinephrine binds to the receptor, it changes a different site, which makes the G protein active and interacts with the receptor

    • This causes the GDP to bind with GTP to make it more energy-dense

    • It drifts into the protein and then binds with the adenylate cycle, which then converts ATP to cyclic AMP, which is the second messenger

  • Cellular response

    • The cyclic AMP causes a chain of relay molecules

    • These are kinases that go through a phosphorylation cascade

      • one kinase activating the next, activating the next

      • adds phosphate to each one to go to next step

  • result is signal amplification

    • adenylyl cyclase activates multiple cyclic AMP which activates multiple protein kinases, and it’s just this whole long thing

• The receptor ejects and unbinds fast

homeostasis

the tendency of a living system to maintain its internal conditions at a relatively constant level

feedback

when the output can also be an input

negative feedback

• allow organisms to maintain homeostasis as they respond to internal and external changes

• The output feeds back to the system in a way that reduces the system's production.

• negative feedback encourages homeostasis

positive feedback

Can accelerate internal changes and drive a process forward

out put of a system feeds back, increasing the activity and production of the system, which drives to a conclusion, after which it shuts down

what is a set point

• a set point is a value around which a homeostatic process fluctuates

antagonistic negative feedback

• one negative feedback system that responds when conditions are above the set point

• trying to get back to set point

Mitosis purpose

• duplicates the chromosomes of a eukaryotic cell, transmitting that cells entire genome to its daughter cells

• how multicellular organisms corw

• How unicellular organisms divide

Interphase of mitosis

• G1

  • growth phase

• S

  • DNA replication

• G2

  • growth of structrues needed for cellular division

prophase

• chromosomes condense, the nuclear membrane disintegrates, and a spindle apparatus begins to grow from each centrosome

metaphase

• the spindle fibers pull each chromosme to the metaphase plate

anaphase

• sister chromatids are pulled apart and are dragged to opposite ends of the cell

telophase

• a new nuclear membrane starts to grow and then they decondense and the nucelolus starts to from

G0 phase

• not all cells go through the entire cell cycle

• spealcized cells leave the cell cycle and enterG0 where they wont divide

G1 checkpoint

happens at the of G1 phase

checks for cell size, nutrients dna damage and growth signals

G2 checkpoint

• end of G2 phase

• checks fro

  • Dna replication, damage and cell size

M checkpoint

• happens during metaphase of mitosis

• happens to check for proper chromosome alignment

• Spindle attachment

cyclins

• molecules whose concentrations rises and fall throughout the cell cycle

ligand gated ion channels

• a channel that requires a specific signal molecule to open or close

• regulates flow of specific ions

• when the ligand opens the channel and ions flow in it can change cell activity

phosphorlation cascade

• addition of a phosphate group to a molecule

protein kinases

• enzymes that phosphorylate and activate many proteins at the next level

• allows for cellular response

density dependent inhibition

• the phenomenon in which crowded cells stop dividing

Anchorage dependency

• in which normal cells must be attached to a substratum, such as the extracellular matrix of a tisssue, to divide