AP BIOLOGY | UNIT IV - Cell Communication + Cell Cycle

key concepts and vocabulary to know for this unit

Types of Cell Signaling

Local Signaling:

1. Juxtracrine: when two cells are connected by channels, and signaling occurs

2. Paracrine: when the cells are close by one another, signaling occurs

3. Autocrine: cell creates its own ligand to use for signaling

The Process of Cell Signaling

1. Reception: a ligand [signaling molecule] will bind to a receptor embedded in the plasma membrane of a cell, beginning the cell signaling process

2. Transduction: a transduction pathway [cascade] will amplify the signal in the cytoplasm of the cell

   • secondary messengers: small, nonpolar, water-soluble molecules or ions that will relay signals to the cell’s target location

     • ex. cAMP or Ca⁺

3. Response: cell growth, transcription, gene expression, apoptosis, protein synthesis, secretions, etc.

The Cell Cycle - Interphase

A cell spends most of its life in interphase. There are three phases and two important checkpoints that occur during this time.

1. G1 Phase: the cell starts its preparations to divide, duplicating organelles, creating enough materials to grow, growing to accommodate the new materials, etc.

   • G1 Checkpoint: The cell will not continue to the S Phase until it has enough materials

2. S Phase: DNA replicates, and other DNA components will start to form

3. G2 Phase: The cell will continue to grow and expand, ensuring the cell will be ready for mitosis

   • G2 Checkpoint: the cell will make sure that it has enough materials, as well as check if any DNA is damaged, before moving on

The Cell Cycle - Mitosis [Miotic Phase]

Mitosis is the process by which a diploid parent cell divides and creates two diploid daughter cells identical to the parent …

• Prophase: chromatin will thicken to create the distinct shape of sister chromatids, spindle fibers will start to form at the poles, and the nuclear envelope will start to dissolve

• Metaphase: the sister chromatids will align at the metaphase plate, and spindle fibers will attach onto the centromere of the chromosome

  • M Checkpoint: third checkpoint, which occurs during mitosis… will ensure that the spindle fibers are correctly attached to the chromosome before moving onto anaphase

• Anaphase: the spindle fibers will start to pull the sister chromatids apart and towards the opposite poles of the cell

• Telophase: nuclear envelopes will develop around the newly separated sister chromatids

• Cytokinesis: visible cleavage is an indictaion of cytokinesis is occurring… when the cytoplasm of the cells splits and two new diploid daughter cells are created

Cancer, Tumors, and The Cell Cycle

Proto-Oncogenes: stimulating proteins that allow the cell cycle to advance and division to occur

Tumor Suppressor Genes: inhibiting proteins that will stop the cell cycle from occurring

***Mutations in any of these proteins will result in uncontrolled cell growth [cancer]

Checkpoints: failure in any checkpoint can result in problems with the cell cycle