AP Biology - Unit 4 Test

Local (“short”) Signaling

a secreting cell that will release chemical messages that will travel short distance through extracellular fluid

Examples: Paracrine and Synaptic Signaling

Paracrine Signaling

secretory cells release local regulators (i.e. growth factor via exocytosis to an adjacent cell

Synaptic Signaling

occurs in the animal nervous system; neurons secrete neurotransmitters that will then diffuse across the synaptic cleft (I.e. space between the nerve and target cells)

Long-distance Signaling

animals and plants use hormones for long distance signaling

• plants: release hormones that travel through their vascular tissue (xylem and phloem)

• animals: use endocrine signaling in which specialized cells release hormones into the circulatory system where they reach target cells (ex: Insulin)

Receptor

macromolecule that binds to a ligand (signal molecule) - highly specific*

Plasma Membrane Receptors

most common type of receptor; binds to ligands that are polar, water-soluble, and large

Intracellular Receptors

found in the cytoplasm or nucleus of the target cell; binds to ligands that can pass through the plasma membrane (I.e. hydrophobic molecules - steroids and thyroid hormones)

Second Mesengers

Small, non-protein molecules and ions that help relay the message and amplify the response during transduction.

Cyclic AMP (cAMP) is a common second messenger.

Cell Signaling

1. Reception

2. Transduction

3. Response

Reception

the detection and receiving of a ligand by a receptor in the target cell

when the ligand binds to the receptor activates, allowing the receptor to interact with other cellular molecules (can be plasma membrane or intracellular)

Transduction

the conversion of an extracellular signal to an intracellular signal that will bring about a cellular response

• Phosphorylation by the enzyme protein kinase (relays the signal)

• Dephosphorylation by the enzyme protein phosphate (shuts off pathways)

Response

the final molecule in the signaling pathway converts the signal to a response that will alter a cellular process

• examples:

  • Protein that can alter membrane permeability

  • Enzyme that will change a metabolic pathway

  • Protein that turns genes on or off

Direct Contact

• Plants: plasmodesmata

• Animals: gap junctinos

Long Distance Signaling

• Plants: vascular tissue (xylem and phloem)

• Animals: endocrine signaling via circulatory system

Homeostasis

the state of relatively stable internal conditions

Negative Feedback

reduces the effect of the stimulus

examples: sweat, blood sugar, breathing rate

Positive Feedback

increases the effect of a stimulus

examples: child labor, blood clotting, fruit ripening

Chromatin

formed from strings of nucleosomes; when the cell is not actively dividing, chromatin is a non-condensed form

Chromosomes

formed after DNA replication; condensed form of chromatins; densely packed

Sister Chromatids

After DNA replication, each chromosomes has a duplicated copy that it will join with

Centromere

the region on each sister chromatid where they are most closely attached

Kinetochore

proteins attached to the centromere that link each sister chromatid to the mitotic spindle

Somatic Cells

• Body cells

• Diploid (2n)

• Divide by mitosis

• Humans: 2n=46

Gamete Cells

• Reproductive cells (eggs/sperm)

• Haploid (n)

• Divide by meiosis

• Humans: n=23

Diploid (2n)

two sets of chromosomes, one set from each parent

Haploid (n)

one set of chromosomes

Order of the Cell Cycle

1. Interphase

2. Mitosis

3. Cytokineses

Interphase (90%)

• G1 “first gap” phase

  • The cell grows and carries out normal functions

• S “synthesis” phase

  • DNA replication and chromosome duplication occurs

• G2 “second gap” phase

  • Final growth and preparation for mitosis

Mitosis

nucleus divides

Cytokinesis

cytoplasm divides

Homologous Chromosomes

two chromosomes (one from mom, one from dad) that are the same length, have the same centromere position, and carry genes controlling the same characteristics

Stages of Mitosis

1. Prophase

2. Prometaphase

3. Metaphase

4. Anaphase

5. Telophase/Cytokinesis

Prophase

• Chromatin condenses

• Nucleoli disappear

• Duplicated chromosomes appear as sister chromatids

• Mitotic spindle begins to form

Prometaphase

• nuclear envelope fragment

• microtubules enter nuclear area and some attach to kinetochores

Metaphase

• centrosomes are at opposite poles

• chromosomes line up at the metaphase plate

• microtubules are attached to kinetochore

Anaphase

• Sister chromatids separate and move to opposite ends of the cell due to the microtubules shortening

• cell elongates

Telophase/Cytokinesis

• two daughter nuclei form

• nuclei reappear

• chromosomes become less condensed

• Cytokineses occurs

  • Animals: a cleavage furrow appears due to a contractile ring of actin filaments

  • Plants: vesicles produced by the Golgi travel to the middle cell and from a cell plate

How is body temperature maintained through negative feedback?

Negative feedback reduce the effect of a stimuli. When the body is exposed to external stressors like heat and cold, that stimulus will send signals to the temperature Receptors in the skin. In turn sweat glands will begin to produce sweat (for heat only) to cool down the body, or the muscles will contract and begin shivering to produce heat (for cold).

Internal Cell Cycle Regulators

1. Cyclins - proteins that are synthesized and degraded at specific stages of the cell cycle

2. Cyclin-dependent Kinases - concentration remains constant through each phase of the cell cycle; phosphorylate target proteins, which help regulate key events in the cell cycle

External Cell Cycle Regulators

1. Growth factors - hormones released by cells that stimulate growth

2. Contact Inhibition - cell surface receptors that stops the cell cycle in G1 phase

3. Anchorage dependence - cells rely on attachment to other cells or the extracellular matrix to divide