AP Biology - Unit 4: Cellular Communication & Cell Cycle

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NOTICE: (If this appears during a learn session or test, disregard.)

Before using this set, it is critical you understand the liver-epinephrine signaling pathway. I personally used sciencemusicvideos’ Unit 4 video for this. This pathway is a great example to mention on your FRQs, too.

Mitosis

Process in which somatic cells divide (reproduce if unicellular). Starts as diploid (2n) and ends as diploid.

Meiosis

The process by which gametes (sex cells) are produced. Starts as diploid (2n) and ends as haploid (n).

Why is meiosis considered a “Reduction Division?”

The final product of meiosis has less chromosomes than the starting product.

What process (or stage of cell cycle) takes place when not actively dividing?

Interphase

Cell growth, DNA Replication, cell functions

Interphase

Why do we say there are 46 chromosomes present despite the chromosome having “duplicated?”

Chromosomes are counted by the amount of centromeres present. The “92” chromosomes you may be thinking of are actually CHROMATIDS.

Mnemonic device to remember the cell cycle

PMAT

How many divisions in mitosis?

One

How many divisions in meiosis?

Two

At what point do cells reach “haploid” in meiosis?

After meiosis I

Prophase

Chromosomes condense, nuclear envelope dissolves, centrioles begin forming spindle fibers, chromosomes line up with homologous pairs

Prophase I

Where crossing over occurs

What are chromosomes that have undergone crossing over?

Recombinant chromosomes

Metaphase

Chromosomes line up in the middle of the cell, nucleus is disassembled, microtubules (spindle fibers) attach to kinetichore proteins

Anaphase

Chromsomes are pulled by spindle fibers to the cellular poles (A = Away)

Telophase

Chromosomes are at cellular poles, nuclear envelopes begin reforming

Cytokinesis

Cleavage furrow (ANIMAL CELLS) forms and cytoplasm is split, forming two identical daughter cells

Cell plate

Plant cell equivalent of the cleavage furrow

What is the purpose of mitosis?

Growth and repair of an organism

What is the purpose of meiosis?

Produce genetically varying gamete cells for reproduction

What is a ligand?

Molecule that binds to a receptor to form a complex, triggering a biological response (like signaling in cells). Can include hormones, neurotransmitters, and other signaling molecules

What is a G-Protein?

A G-protein is a Guanine-Nucleotide binding protein that acts as a “molecular switch” within the cell.

What indicates the “activation” of a G-Protein?

GDP (dormant) is swapped with GTP (High energy, much like ADP and ATP)

What is a GCPR?

G-protein Coupled Receptor. This receptor operates when a ligand binds to the receptor protein (usually in cell membrane) and triggers a change in shape. This change in shape activates the G-protein.

What is the “relay molecule” in the case of the epinephrine pathway?

G-Protein

What is the “effector enzyme” in the epinephrine pathway?

Adenylyl Cyclase

What is the “second messenger” in the epinephrine pathway?

cAMP

What is a phosphorylation cascade?

Series of proteins (usually kinases) that “activate” each other by adding a phosphate group

How does a GCPR “amplify” the effects of a singular ligand?

The receptor activates multiple G-proteins, creating multiple phosphorylation cascades

In the case of the liver epinephrine pathway, what is the cellular response?

Activation of enzyme liver glycogen phosphorylase - breaks glycogen stored in the liver down to glucose which is used for energy.

How is glycogen phosphorylase activated?

By phosphorylation from a protein kinase

What is quorum sensing?

Method of cell communication in bacteria where bacterial cells produce chemical signaling molecules (autoinducers) to sense population density and coordinate group behaviors.

Where are ligand receptors in quorum sensing? How is this different from membrane-bound reception?

In the cytoplasm (for gram-negative; dont worry about this tho.) This is different from membrane-bound reception (like in liver-epinephrine) as that takes place in the cell membrane and not the cytoplasm.

What happens in quorum sensing in the example of plaque formation on the teeth?

What is a “quorum?”

When many bacterial cells are close in proximity to eachother

What is triggered in the bacterial quorum sensing in the mouth?

A buildup of plaque on the teeth when bacterial ligands are activated, producing a poly-saccharide

Why should you brush your teeth?

To prevent a “quorum” from forming and a resultant mass of plaque on your teeth. You should have already been doing this before…

What is the cell cycle?

A repeating sequence of phases (G1, S, G2, M) that describe the life cycle of a cell.

What happens in the G1 phase of the cell cycle?

A newly divided cell undergoes growth in size and produces essential proteins/RNA.

What happens during the S phase of the cell cycle?

A cell replicates an entire genome and duplicates chromatids (still 2n)

What happens during the G2 phase of the cell cycle?

The cell continues growing, synthesizes proteins/organelles, and maintains critical growth regulation/quality control

What happens during the M Phase of the cell cycle?

Mitosis: The cell divides

What is the phase when a cell exits the cell cycle? Why does this happen?

The cell enters G0. This is a nondividing phase that the cell will enter if it detects genomic instability/damage. This also occurs in nondividing cells like neurons or muscle cells.

What is apoptosis?

Programmed cell death. The cytoplasm will split into small, spherical “blebs” when the cytoskeleton detatches from the membrane

What is a cell checkpoint?

Control mechanism in the cell cycle that ensures proper progression through the cycle, monitoring for errors/damage before allowing the cell to proceed to the next stage

What is a cyclin?

A family of proteins that “Rise and fall” throughout the cell cycle.

CDK

A cyclin dependent kinase (CDK) is an enzyme that drives the cell cycle forward. They are activated when they are binded to a cyclin protein, acting as an “on and off” switch.

Kinase

An “on/off” switch in cells that adds phosphate groups to proteins in order to activate them

Receptor desensitizatoin

When a cell becomes less responsive to a signal after prolonged exposure to a ligand

How are receptors desensitized?

When they are phosphorylated by downstream kinases and binding of arrestins

Why does phosphorylation desensitize a receptor?

It binds to the intracellular tail of the receptor, triggering a change in shape (much like when a ligand binds.) It also allows arrestins to bind

Arrestin

Proteins that bind to phosphorylated GCPRs, physically blocking them from attaching to a G-protein

Proto-oncogene

A normal gene that can become an oncogene due to mutations or increased expression, playing a role in cell growth and division.

Oncogene

A mutated or overexpressed gene that contributes to cancer progression by promoting uncontrolled cell growth and division.

Growth factors

Signals that stimulate cell proliferation and differentiation.