Unit 4: Cell Communication and Cell Cycle

Slogan: Homeostasis

Unit notes

Homeostasis & Feedback loops

Homeostasis: The internal environment of the body is in a dynamic state of equilibrium

Feedback: Can be described as a “loop.“ There are two ways in which a system can respond to a signal ↴

Negative Feedback: The goal of negative feedback is to keep internal conditions stable / return to stability and therefore homeostasis

Working in the opposite direction (You’re sweaty HOT, you sweat to COOL down)

• Example: Thermoregulation: environment gets colder → you shiver → the movement of your muscles produce heat → you warm up → you’ve returned to homeostasis

Positive Feedback: The main goal is to increase the effect/product in a living system

Working in the same direction (Fruit ripening produce ethylene gas, which then ripens the fruit more and produces more gas)

• Example: Contractions during labor. The onset of contractions stimulates the release of oxytocin, which stimulates more contractions

Receptor- The signal

    ↳ A coordinator at Publix who sees a spill on aisle 5 and reports it to the manager

Control Center- The manager

    ↳ The manager sends an employee to clean the spill

Effector- The thing that makes a change

    ↳ The employee cleans the spill

    ↳ NEVER A HORMONE

*However the three separate ideas may not be physically separate in what things actually do them*

    ↳ The manager for instance may see the spill and clean it up themself, thus performing all three jobs

Cell Communications

yip yip!!

Signaling pathway symbols

“-” is inhibition

“+” is activator

Practice ↴

1. What is P53’s function in the pathway?

2. What is MDM2 function in the pathway?

3. How does DNA damage affect the outcome of the pathway?

Ligand- A signal MOLECULE

    ↳ The chemical structure of molecule determines how ligand enters the cell

    ↳ Ex: RANKL

Receptor- A MOLECULE that a ligand activates

    ↳ Ex: RANK

Cytoplasmic receptors- accepts hydrophobic molecules which pass through the membrane easily

Membrane receptors- accepts hydrophilic molecules and ions that need assistance to enter the membrane

Types of Cellular communication:

Juxtracrine- Involves contact between cells in which a ligand on one cell surface binds to a receptor on the other

    ↳ Juxta- Latin for near/beside

Paracrine- Occurs only when molecules travel short distances

    ↳ Tends to have a faster response but a short-lived effect

    ↳ Parasailing- a short distance

Endocrine- Used for long distance communications

    ↳ In humans, found in endocrine glands

    ↳ Tends to have a slower response and a longer-lasting effect

Autocrine- Factor that is secreted acts on the same cell and then elicits a response

    ↳ “Self signaling“

    ↳ independent queen

Signaling pathway

1. Signal goes to signal receptor

2. the G Protein is phosphorylated to become active

3. G Protein moves to enzyme to activate it

Tyrosine Kinase Receptor

1. Two sticks: signal molecules on both sides of the sticks

2. called dimerizing when they bind

3. The sticks together combined phosphorates to become activated

4. They activate new target proteins

The phosphate acts as a switch

cAMP Pathway ↴

cAMP is a second messenger

Neurons and muscle cells

These cells are excitable

• a specialized cell capable of generating and propagating electrical signals, known as action potentials, in response to stimuli

Most cell maintain a constant voltage; Resting potential

Bone Remodeling

Osteoblasts- Builds the bone

    ↳ Bone remodeling

    ↳ Produces RANKL and OPG

Osteocytes- Occur when osteoblasts get stuck in the bone while remodeling

Osteoclasts- chaos/crash/clast- breaks the bone

    ↳ Bone resorption

RANK- Receptor found on osteoclasts

RANKL- Ligand which can bind to RANK or OPG

    ↳ Found on Osteoblasts

OPG- Binds to RANKL which indirectly inhibits osteoclasts

Resting potential- Nothing is actively happening

Threshold- the membrane potential that must be crossed to cause a reaction

    ↳ All or nothing

Depolarization- The inside of the membrane becomes less negative

    ↳ Neurons are polarized

    ↳ Sodium gates are opened, Potassium gates are closed

Repolarization- The membrane returns the resting membrane potential

    ↳ The sodium inactivation gate closes

    ↳ Potassium gates open

Hyperpolarization- The inside of the membrane becomes more negative than the resting potential

    ↳ Overshoots the polarization

Saltatory conduction- Signals jump to occur faster through nodes of Ranvier

    ↳ Prevents short circuiting in nerves

Synaptic delay- Rate limiting step or neural transmission

    ↳ Time for neural transmitter to bind to neural receptor

    ↳ Stops neural transmission from going out of control

        ↳ Prevents short circuiting

Plant communication

Auxin- Stimulates growth in shoots

    ↳ Inhibits growth in roots

Cytokinin- Cell division in shoots and roots

    ↳ Promotes lateral growth

    ↳ Delays decay

Gibberellins- Promote cell elongation in shoots

Ethylene- Promotes ripening and maturation

Abscisic Acid- Produces mature leaves and fruits

    ↳ Protects plants from the environment

Pathogens

• Cause diseases

Immune responses in plants

Continuous defense:

• Made as a part of the cell structure

• Energy efficient

• EX: Cell walls, bark

Inducible defenses:

• Initiated by detection of pathogens

• Need a bunch of energy

• EX: Poison Ivy’s toxins

Transpiration

Cell Cycle & Regulation

Genomes- is all of a ce

lls genetic information

Chromosomes have a short arm (q) and a long arm (p)

Two chromatids are attached together with a centromere to create a chromosome

Interphase contains G1, S, G2

G1- Cells continue normal function

    ↳ Great day!

S- Chromosomes Duplicate

G2- Prepare for cell division

     ↳ Makes organelles that mitosis will need

Miotic (M) Phase: Contains mitosis and cytokinesis

Mitosis- PMAT

     ↳ Prophase- Chromosomes become visible

         ↳ Chromatin condenses

     ↳ Metaphase- chromosomes line in the middle & the spindle fibers attach

     ↳ Anaphase- The spindle fibers are shortened: chromosomes are pulled apart

     ↳ Telophase- Chromosomes gather at opposite ends

Cytokinesis- Cytoplasm pinches in half

    ↳ Cytoplasm Cut

    ↳ animals cells = cleavage furrow

    ↳ plant cells = cell plate forms

Cell cycle regulation

G1 checkpoint- The most important

G2 checkpoint- make sure everything is in order, no mutations

M spindle (metaphase) checkpoint- make sure spindle fibers attached properly

Internal regulatory molecules

• Kinases- adding a phosphate and active when connected to cyclin

• Cyclin- attached to kinases to activate

• MPF- the maturation promoting factor

  • allows cells to pass G2 and go to M phase

  • it’s the cyclin-CDK complex

• Growth factor

• Density dependent

• anchorage dependence- must stay where it is, on the outside of the cell

Cancer cells

Kahoot/Additional notes to be moved later

Plants community by sending small molecules, ions through PLASMODESMATA

Examples of a typical first messenger: Hormones and neurotransmitters

When a ligand binds to its receptor protein, the protein typically does what?

    ↳ Changes shape

Transduction my involve al of the following except: binding of ligand to receptor protein

Cyclin + CDK = MPF, MPF formation depends on the increasing concertation of CYCLIN

An example of external signal can trigger the cell cycle/mitosis is/are GROWTH FACTORS

At the end of meiosis 1, there are: 2 haploid cells, ready to go through Meiosis 2

During anaphase 1 of meiosis 1, what separates?

    ↳ homologous pairs

During anaphase 2 of meiosis 2, what separates?

    ↳ sister chromatids

Genetic diversity increases fitness!

What is used for long distance signaling?

    ↳ hormones

Receptor tyrosine kinases: trigger multiple responses connecting phosphates to tyrosine

Which cell messenger system acts as a gate?

    ↳ Ligand-gated ion channel

Where are intracellular receptor proteins found?

    ↳ In the cytosol and nucleus

cAMP activates and deactivates other proteins through phosphorylation

phosphorylase removes the phosphate from an activated protein kinase

Essential Questions

1. How do organisms use positive feedback to return to homeostasis? Have a solid example to reference

2. How do organisms use negative feedback to maintain homeostasis? Have a solid example to reference

3. How do cells communicate using signals, receptors, and transduction pathways?

4. What is some example pathways that can be used by animals and plants to initiate cell responses?

5. How could mutations in a ligand or a receptor protein alter cell signaling?

6. What are some cell functions and processes that are controlled by cell signlaing?

7. How is the cell controlled? How does the cell move through the cell cycle to accomplish cell division?