AP Biology/Cell Communication and Cell Cycle

Introduces how cells grow and reproduce, as well as how cells communicate.

Objectives and Skills

Topics may include:

• The mechanisms of cell communication
• Signal transduction
• Cellular responses and feedback mechanisms
• The events in a cell cycle

Cellular Communication

How do cells directly communicate with each other?

Direct Contact

Molecules from the 1st cell, after being triggered to produce molecules, are sent to the proteins of the 2nd cell, to which it triggers a response. In plants, this is done through the plasmodesmata, while in animals, this is done through the gap junction.

Through surface proteins, they can bind to each other, altering the protein's shape--this can trigger a response in both cells.

Water filled channels allow intracellular mediators to diffuse between the cells. Big molecules, like proteins, require special assistance to get through.

Rember

• Intra = Inside
• Inter = Outside

Paracrine Signaling

Short distance communication: a protein sends ligands through either diffusion or vesicles... and the ligands go to the cell with the right receptors.

Endocrine Signaling

Long-distance communication: a hormone being sent into the bloodstream and reaches the receptor.

Autocrine Signaling (Self)

A cell secretes a ligand which attaches to a receptor on the same cell, triggering a response.

Unicellular Cells Communication

• Quorum Sensing (bacteria) - Bacteria monitor how much of themselves are in a given area. When the signaling reaches a threshold (enough bacteria in that place of the species), then the bacteria in that place will do their cellular response (attack the host/send fluorescent light). It is a form of paracrine signaling.

Signal Transduction

See pic for diagram.

Types

• Ligand-gated ion channels
• G-protein coupled receptors
• Tyrosine kinase receptors

Ligand Receptors

• Polar cannot diffuse in; nonpolar can though

1. Change in the receptor's shape causes an intracellular response.
2. Steroid hormones = Lipids (nonpolar) - water-hating.
3. Ligand-gated ion channels = Ions (polar) are prevaled from touching the hydrophobic tails.
4. A G-protein attached to GTP = Active.
5. A G-protein attached to GDP = Inactive.
6. Gases that act as ligands can diffuse across the plasma membrane (due to its small size).
7. Cell-receptors (protein receptors) bind to POLAR ligands.

Signal Relay Pathways

1. Bind to intracellular protein: The signaling process is complete.
2. Bind to intercellular protein: The signaling process continues.
3. Upstream: Earlier in the relay channel
4. Downstream: Later in relay chain
5. Second messenger: Small, non-protein molecules (intracellular) that pass a signal from the "first messenger" (intercellular).
6. cAMP: Second-messenger molecule made from ATP (activates protein kinase A). Amplifies intracellular signals. [ATP --> cAMP with the addition of adenylyl cyclase].
7. Same singling molecule may produce different results because the receptors are different kinds and therefore trigger dif. pathways.

Homeostasis

"Stability"

Negative-feedback - Counteracts changes of various properties from their target values.

Positive-feedback - An increase in product results in increasing the rate of the synthesis of that product. Amplifies initial stimuli and moves the system away from its starting point.

• Example: Childbirth - stretching of uterine walls cause contractions that further stretch the wall and continues until birth. Lactation - the child feeding stimulates milk production which causes more feeding until the baby stops feeding.

1. Too much glucose!
2. Receptors in the body senses a change in glucose levels.
3. Beta cells of the pancreas release insulin, a hormone that stores glucose (protein). Insulin causes the liver to take up glucose and stores it as glycogen. Body cells also take up glucose.
4. Blood glucose declines. The pancreas stops releasing insulin.

1. Too little glucose!
2. Alpha cells of the pancreas are alerted to release glucagon, a ligand, into the blood.
3. Glucagon travels to liver receptors - causes the liver to break down glycogen --> glucose. Glucose is released to the blood.
4. Blood glucose increases. The liver stops breaking down glycogen as glucagon (the release) has been stopped.

Cell Cycle

Tell the difference between a cell in mitosis vs interphase (see nucleus vs. condensing/no nucleus).

• Mitosis
• Meiosis

Bacteria: Binary Fusion instead of Mitosis

• 1 chromosome (nucleoid)
• Some changes occurred (evolutionary) between cell division and binary fission.

Protein Signals

• Cyclins
• Cdks

Chi-Square

• Used for count categorical data (used in genetics).
• Null hypothesis: No difference between expected numbers and observed numbers - no change [is the difference statistically significant or not?].
• Degrees of Freedom: [# of groups - 1].
• Significant: p=.05 (95% confident)
• "Fail to Reject" = "Accept" --> Calculated value > Critical value = "reject the null hypothesis".

References

← Cellular Energetics

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