Cell Communication and Cell Cycle

Cell Communication

cell’s response to its environment , certain stimuli etc.

Taxis

movement of an organism in response to a stimuli that is being made ( either toward or away).

• Chemotaxis: movement in response to chemicals. ( bacteria could control flagella rotations to redirect their rotation to avoid harmful repellents ( poisons) or find favorable chemicals / locations of high concentration of attractants ( food)

Types of Cell Communication

• Direct Contact ( Juxtacrine )

  • two cells coming together with direct contact and exchanging signals / information to the other cell with gap junctions ( small gaps that allow cell molecules / particles to pass thru )

    • Cell Signalling: protein attached to one cell, binds to a receptor on another cell → communication

• Local Signalling: ( “ passing notes” )

  • ParaCrine Signalling: cell #1 sends local signals which diffuse onto Cell #2 and recieves signal → communication.

  • Synaptic Signalling: ( nuerons) an axon/ nerve part sends electric / chemical signals, and a dendrite fuse together ( with a synapse), and get the message.

• Long Distance Signalling: ( a P.A)

  • ( Endrocine system): sending hromones / signalling molecules into the blood stream → gets sent out to every part of the body.

Signal Transduction

-an external signal is transmitted to inside of a cell.

• 3 Main steps:

  • signaling molecule binds to a specific receptor

    • activation fo a signal tranduction pathway ( phosphoraltes by adding phosphates [cascade]

      • production of a cellular response.

• signalling molecules ( called ligands ) bind to receptors and trigger a response by changing the shape of receptor proteins.

Liands / Receptors

• molecule that interacts with receptor in order to transmit a signal into the cell to facilitate communication.

• Receptors:

  • binding to a ligand to facilitate signals

  • hydrophobic ( nonpolar) signalling molecules: can diffuse across cell membrane → receptors will be inside and often travel directly to the nucleus to regulate gene expression.

  • membrane receptors: signalling molecules that cannot directly enter cell→ use plasma membrane receptors ( on cell surface).

Types of Membrane Receptors

1) Ligand-gated ion channels:

• receptor is embedded into a plasma membrane, the channel opens and lets ions pass thru once ligand binds to receptor.

2) G-Protein Coupled Receptors:

• receptor is coupled with a G- Protein

  • signalling molecule ( ligand ) binds to receptor → activates G - protein → activates secondary messagers within the cell ( cAMP) → cascade of phosphorylation.

• Receptor Tyrosine Kinases

  • two receptors, when molecules bind to each→ receptors come tgth and phosphorylates a bunch of tyrosine.

Signal transduction cascades

• helpful to amplify a signal.

• many transduction pathways include protein kinases → which add phosphate group to next protein in sequence → phosphorylation cascade.

• helpful in quickly turning a response on / off → lead to important changes in gene expression. ( gene expression , apoptosis )

Feedback Groups

• processes that regulate biological activities by using feedback mechanisms to maintain homeostasis. ( body tries to maintain a “ steady” state for survival)

• Negative Feedback ( Feedback Inhibition): works by turning itself off using the end product of the pathway

  • end product inhibits the process from beginning → shuts down the pahtway. ( common to conserve energy)

  • organism is getting negative ( away from homeostasis → tries to undo the changes)

    • organism is getting negative → undo the negativity by going back.

• Positive Feedback Group:

  • amplify the original stimulus and further stimulates it.

    • oxcytocin ( contractions)

    • ethelyne ( fruit ripens → sends signal to other plants that it is time to ripen → other surrounding fruit start to ripen as well).

    • organism is positive → happy → make more happy.

Cell Cycle

1) interphase ( takes up majority ) “growing phase”

mitosis

Interphase

• reffered to as the “growing phase”

• cell carries out regular activities

  • all proteins and enzymes it needs to grow are produced in this phase.

• Divided into 3 phases: G1 (gap 1), S (synthesis), and G2 (gap 2) where the DNA is replicated and prepares for mitosis.

  • G1: cell grows the enzymes and proteins it needs , carries out normal metabollic functions

  • S phase: Synthesis = Replicate = Create: Repliation occurs, each chromosome of DNA is duplicated.

  • G2 ( Gap / Growth 2 Phase): cell preps for mitosis, by making organelles or proteins that are going to be required for cell division.

Mitosis

• cell divison part

• involved for growth , repair, asexual reproduction

• PMAT

  • Prophase: nucleus membrane gets deleted, chromosomes are condensed ( chromatins form coils and thicken → chromosomes) prepping for metaphase.

    • start to move away from each other, and centrioles spin spindle fibers→ attach to kinetochore ( centromere of on chromatid).

  • Metaphase: spindle fibers are attached, and the chromosomes begin to line up or “meet” a the bindle

  • Anaphase: the spindle fibers pull away the sister chromatids of each chromosome to opposite ends of the cell ( like how sisters anna and elsa got seperated)

  • Telophase: a nuclear membrane starts to form around each set of chromosomes, nuclei starts to appear.

    • cell begins to divide along the cleavage furrow ( the middle ) during cytokinesis. → splits into 2 daughter cells.

      • plants have cell plates instead.