Unit 4 Cell Communication & Signaling AP BIO

Set Points

• Values for various physiological conditions that the body tries to maintain

  • Contains normal ranges that can fluctuate

    • e.g. body temperature & glucose levels

Homeostasis

• The state of relatively stable internal conditions

• Balance is maintained through feedback loops and regulatory mechanisms to ensure optimal functioning of biological systems

Feedback Loops

• Can be negative or positive

Stimulus

• A change in the environment that triggers a response in an organism or system.

Receptor/Sensor

• Sensory organs that detect a stimulus & information to the control center (brain)

Effector

• Muscle or gland that will respond to the control center's signal and produce a response that helps maintain homeostasis

Response

• Changes (decreases or increases) the effect of the stimulus and returns the system to homeostasis

Negative Feedback

• The most common feedback mechanism

• Reduces the effect of the stimulus and helps stabilize the system

  • e.g. sweat, blood sugar, breathing rate

Positive Feedback

• A feedback mechanism that amplifies or enhances the changes in a physiological system, moving it further away from homeostasis.

  • e.g. child labor, blood clotting, & fruit ripening

Homeostatic Imbalances

• Conditions that prevent the body from regulating homeostasis

Disease

• When the body is unable to maintain homeostasis

  • Includes - cancer & diabetes

Cell Division

• Allows for reproduction of cells, growth of cells, and tissue repair

Cell Cycle

• The life of a cell from its formation until it divides

• Consists of alternating phases of interphase and mitosis

  • G1 → S → G2 → Mitosis

  • Unfinished

DNA

• Associates with and wraps around the protein histone to form nucleosomes

Chromatin

• Strings of nucleosomes

• When cells aren’t actively dividing, this is in a non-condensed form

• Condenses into chromosomes AFTER DNA replication

Chromosomes

• The result of densely packed chromatins AFTER DNA replication

  • Are tightly packed together to allow for easier division

Centromere

• The region on each sister chromatid where they are most closely attached

Kinetchore

• Proteins attached to the centromere that link each sister chromatic to the mitotic spindle

Genome

• All of a cell’s genetic information (DNA)

Prokaryote Genome

• Singular, circular DNA

Eukaryote Genome

• Linear, double-stranded

Homologous Chromosomes

• Two chromosomes (mama y papa) that are the same length, have the same centromere position, and carry genes controlling the same characteristics

Somatic Cells

• Body cells

• DIPLOID (2n) - two sets of chromosomes, one set from each parent by two

• Divide by mitosis

• Humans 2n = 46

  • 23 from mom

  • 23 from dad

Gametic Cells

• Reproductive cells (eggs/sperm)

• Haploid (n) - one set of chromosomes

• Divide from meiosis

• Humans n = 23

Interphase

• The longest portion of the cell cycle (90%)

  • G1 “first gap” phase

    • The cell grows and carries out normal function

  • S “synthesis” phase

    • DNA replication and chromosome duplication occurs

  • G2 “second gap” phase

    • Final growth and preparation for mitosis

• M Phase

  • Mitosis - nucleus divides

  • Cytokinesis - cytoplasm divides

  • Mitosis results in 2 identical diploid daughter cells

Mitosis

• Prophase

• Prometaphase

• Metaphase

• Telophase & Cytokinesis

Cytokinesis in Animal Cells

• A cleavage furrow appears due to a contractile ring of actin filaments (protein fibers)

Cytokinesis in Plants

• Vesicles produce by the Golgi travel to the middle of the cell and form a cell plate that develops into a new cell wall separating the two daughter cells

  • Vesicles are “bubbles” made up of a phospholipid bilayer that package proteins

Chromatid

• One of two identical halves of a duplicated chromosome, connected by a centromerE

Some/Soma

• Refers to body

Nuclear Envelope

• The double membrane that surrounds the nucleus in eukaryotic cells, regulating the passage of molecules in and out

Cleavage Furrow

• The connecting part of the two cells during cytokinesis in animal cells; it is formed by the inward folding of the cell membrane, leading to cell division

Microtubules

• Extends from the centromeres to grab chromosomes at the kinetochore and contracts to pull chromatids apart from chromosome form

Histones

• A macromolecule composed of proteins

• Packages and condenses DNA into chromatins to allow for efficient cell division and gene regulation

G₁ Checkpoint

• Most important checkpoint

• Chekcs for cell size, growth factors, and DNA damage

• Stop/Go signals

  • “Go” - cell completes the whole cell cycle

  • “Stop” - cell will enter a resting phase or be directed to repair DNA before proceeding

• Can be regulated through Contact (or density) inhibition

G₀ Checkpoint

• Some cells stay in this phase forever (muscle/nerve cells)

• Some cells can be called back into the cell cycle

G₂ Checkpoint

• Check for completion of DNA replication and DNA damage

• “Go” - cell proceeds to mitosis

• “Stop” - cell cycle stops and the cell will attempt to repair damage

  • If damage cannot be repaired the cell will undergo apoptosis

M (Spindle) Checkpoint

• Checks for microtubule attachment to chromosomes at the kinetochores at metaphase

• “Go” - cell proceeds to anaphase and completes mitosis

• “Stop” - cell will pause mitosis to allow for spindles to finish attaching to chromosomes

Internal Cell Cycle Regulators

• Involves an internal control system

  • Cyclins

  • Cyclin-dependent kinases (CDKs)

Cyclins

• An internal cell regulating protein

• Concentration varies

  • Synthesized and degraded at specific stages of the cell cycle

Cyclin-dependent Kinases

• Concentration remains constant through each phase of the cell cycle

  • Active ONLY when its specific cell regulating protein is present

Apoptosis

• Programmed cell death

Cyclin-CDK Complex

• Each formation has a specific regulatory effect

  • When active, they phosphorylate target proteins, which help regulate key events in the cell cycle such as progression through checkpoints and the transition between different phases

External Cell Cycle Regulators

• Growth factors

• Contact (or density) Inhibition

• Anchorage Dependence

Growth Factors

• External cell cycle regulator

  • Hormones released by cells that stimulate cell growth

    • Signal transduction pathway is intiated

      • CDKs are activated leading to progression through the cell cycle

Contact (or density) Inhibition

• External cell cycle regulator

  • Cell surface receptors recognize contact with other cells

    • Initiates signal transduction pathway that stops the cell cycle in G₁ phase

Anchorage Dependence

• External cell cycle regulator

  • Cells rely on attachment to other cells or the extracellular matrix to divide

    • Extracellular matrix is NOT empty space

Cancer

• Cells become cancerous through DNA mutations

  • These cells on average have accumulated 60 or more mutations on genes that regulate cell growth

DNA Mutations

• These are RANDOM changes in the nucleotide sequence of DNA that can lead to alterations in gene function or expression, potentially resulting in diseases such as cancer

Normal Cells

• Follows checkpoints

• Divide on average 20-50 times in culture (in petri dishes)

• Go through apoptosis when there are significant errors

Cancer Cells

• Do not follow checkpoints

• Divide infinitely when in culture

  • Considered to be “immortal”

• Evade apoptosis and continue dividing even with errors

• Uncontrollable growth CAN lead to a tumor

Benign Tumor

• Cells are abnormal, but not considered to be cancerous yet

  • Cells remain only at the tumor site and are unable to spread elsewhere in the body

Malignant Tumor

• Mass of cancerous cells that lose their anchorage dependency and can leave the tumor site

• Undergoes metastasis

Metastasis

• When cells separate from the tumor and spread elsewhere in the body