 is the sequence of steps prior to cell division. In eukaryotic cells, the cell cycle is

through the growth and reproduction of cells.
The cell cycle consists of 5 phases:

Interphase contains the phases G1, S, and G2. Over 90% of the cell cycle is spent in interphase! During interphase, the chromatin of the cell is threadlike so when looking at a cell undergoing interphase, a 

is a period of intense growth and activity. 

is used to stand for the synthesis of DNA. In 3️⃣ 

the cell continues to grow in order to finish cell division.

is the part of the cell cycle when the nucleus of the cell is divided. Even though mitosis is one process, it is broken down into 

is the first phase of mitosis. In prophase, the nuclear membrane begins to disintegrate, chromosomes condense, and the spindle begins to form. 

chromosomes begin to line up in the middle of the cell. Also, the 

is when the centromeres finally separate. The spindle pulls apart the now 

begins when the chromosomes move to opposite ends of the cell. The chromosomes begin to uncoil and return to their threadlike shape. 

Mitosis is complete once the cell separates and 2 separate nucleoli form.

is different in plant and animal cells. After mitosis occurs, 

made of stiff sugars is formed and surrounds the cell membrane. In plant cells, the daughter cells do not separate from each other. Instead, a new cell wall is created.

is a groove that is created in the middle of the cell surface. The cytoplasm then begins to separate.

Cell Cycle

A good way to remember the importance of regulation in cell communication and the cell cycle is to think of a checklist. In order for these processes to be done correctly, there must be correct timing and coordination within the cell. 

Unit 4 Overview: Cell Communication and Cell Cycle

The cells in your body communicate in many different ways. Cells must communicate with each other and the environment in order to complete tasks. They communicate through chemical signals. These signals are usually proteins. Multicellular organisms have trillions of cells that communicate in the following ways. 

. Direct contact occurs when the 2 cells are adjacent to another and occur in both plant and animal cells. In plant cells, the

 connect one plant cell to another. In animal cells, 

directly connect the cytoplasm of one animal cell to the cytoplasm of another animal cell. These junctions allow the passage of materials such as ions, signals, and molecules. 

Think of direct contact like a handshake because both people must have direct contact with each other during a handshake!

Another way that cells communicate is through 

Paracrine signaling is communication over short distances. Cell sends out signals to nearby cells which causes a change in the behavior of nearby cells. An example of paracrine signaling is contracting muscles. Chemical signals are sent from the nerve to the muscle. This causes the response of changes in the behavior of muscle so that the muscle contracts.

Think of paracrine signaling as crossing the street. Crossing the street is a short distance and helps me remember that paracrine signaling is between nearby cells. Takes the “right down the street” phrase into a new perspective!

which is the gap between 2 nerve cells. 

Signaling occurs when a neuron releases a neurotransmitter. Then, the neurotransmitter moves across the synapse. After it reaches the end of the gap, the neurotransmitter stimulates the adjacent neuron to fire.

Cell Communication

is the conversion of a signal into a cellular response. Transduction occurs in one step but the majority of the time it takes multiple changes.

The signal transduction pathway is when a small collection of signal molecules produce a large response across the cell. The large response across the cell is called the 

The response of a cascade can be cell growth, gene expression, or secretion of molecules.

A good way to think about the signal transduction pathway is like a waterfall or a line of falling dominoes. 

Regardless of the distance between the cells, cell communication always follows the same 3 steps: reception, transduction, and response. 

 occurs when the signal (can be a chemical, peptide, or protein) is detected when the 

 binds to the receptor protein in a target cell. This causes a change in the shape of the cytoplasm of the inside of the receptor. Then, transduction occurs. In 

, the signal is transmitted through the cell and is amplified. Finally, the third step is the 

. The response is when the signal is carried out. An example of a response is when the cell activates RNA polymerase which leads to the transcription of a gene. 

 are receptors that cover the entire membrane. These receptors are important because most signaling molecules are too big to cross the plasma membrane. 

The plasma membrane contains a phospholipid bilayer. The heads of the phospholipid are “water-loving” which are called 

. The tails of the phospholipid are “water-hating” which are called 

The phospholipid bilayer is very important because it creates a barrier between the inside and outside of the cell.

Ion Channel Receptors involves a channel that opens and closes. The channel is used to allow the passage of ions across the membrane.

Think of ion channel receptors as a toll booth. Just like a channel receptor, a toll both opens and closes after an action is made.

 binds to the outside part of the cell and changes the form of the inside cytoplasm. This causes a G protein to bind and activate the enzyme adenylyl cyclase. Adenylyl cyclase converts ATP (energy) to cyclic-AMP.

 activates other molecules inside the cell which finally leads to the cellular response. 

Since transduction occurs in an animal, bacterial, plant, and yeast cells, it shows that the signal transduction pathway has evolved from a common ancestor.

Isn’t it crazy that all these different organisms could have something in common?!

Introduction to Signal Transduction

As we talked about earlier, cells communicate and respond to changes in the environment. The environment also has the ability to influence cells in order to elicit a response.

Many things in the environment can alter the cell cycle. Some examples of factors are temperature, light, and chemicals. When these factors are present, it can influence how the cell responds to the environment. 

Signal transduction can also result in changes in types of cellular response such as 

Gene expression is when the instructions of our DNA is converted into a product. Signal transduction pathways can affect gene expression by altering the amount of product that is being made. 


The signal transduction pathways can also alter a large number of cell functions such as death, differentiation, shape, and metabolism. Because of this, it is very important that all processes occur correctly in order to avoid harmful disorders and diseases.

Signal Transduction

Changes to any structure in the cell cycle can affect the signal transduction pathway. As we talked about earlier, the signal transduction pathway has the ability to alter cellular processes. Specifically, mutations can lead to detrimental effects on later responses. 

have the ability to greatly impact the cell cycle. For example, mutations in the signal transduction pathway can prevent the cell from regulating its cell cycle. When the cell cycle is unregulated, it can result in unrestricted cell division that could lead to harmful conditions like cancer. 

We will go over more effects that mutations can have on cells in section 4.7 Regulation of Cell Cycle.

have the ability to alter the signal transduction pathway. These chemicals can either activate or hamper the pathway’s response. For example, chemicals such as lead, polychlorinated biphenyls (PCBs), and ethanol have the ability to have neurotoxic effects with specific signal transduction pathways.

Changes in Signal Transduction Pathways

Based upon the environment around the organism, the timing, and coordination, there can be either a positive or negative feedback. Organisms use feedback to maintain 

as well as respond to the environment. 


are the response of reactions and leads to a decrease in those reactions. Negative loops also maintain homeostasis by creating optimal internal environments. Negative loops are also able to return a system back to target homeostasis.

An example of negative feedback loops is 

. When you eat food, blood glucose levels rise. This causes a response by the pancreas to release insulin, which then causes the blood glucose levels to decrease making it a negative feedback loop.

Diabetes would disrupt the negative feedback loop of blood sugar regulation. Diabetes is a condition that can be caused by an imbalance of insulin. There can be either too little insulin or a resistance to insulin. When there is a problem in the negative feedback loop, it can lead to high blood glucose levels that can lead to adverse health effects.

are used to increase the change in the cell by amplifying or speeding up the process. Positive feedback loops can also be called “snowballing” effects. It is also important to remember that without a stop or counterbalance, the positive feedback loop can not be controlled.

An example of a positive feedback loop is 

. During labor, a chemical called oxytocin is released. Labor is a positive feedback loop because oxytocin causes a response for contractions to intensify and occur quicker. After the birth, the loop is interrupted, stretching and contractions end, and the loop is finished.

Feedback

Mistakes in duplication can lead to mutations that can lead to cells being abnormal. Because of this, 

At checkpoints, the progression of the cell cycle is halted until all parts are checked and conditions are correct to continue with duplication. Checkpoints are at the end of G1, at the G2 and M transition, and during metaphase.

. This check occurs at the end of the G1 growth phase. During this checkpoint, it checks whether the cell is big enough and has the proper proteins and nutrients for the synthesis phase. If the cell is not big enough or not ready to go onto the next phase, they enter the G0 phase as you can see on the diagram. In G0, the cell is in a resting phase until it is ready to move on. 

 during the S phase. Here, there is a check to make sure that the DNA has been replicated correctly. If the DNA is replicated correctly, it moves on to the M (Mitosis) phase. 

This occurs in the (M) Mitosis phase and checks whether metaphase is complete. If it is complete, the cell divides and the process repeats. 

However, disruptions in the cell cycle can lead to 

are cells that are unregulated and divide uncontrollably. Cancerous cells have the ability to migrate or 

to other regions of the body that they didn’t originate in.

is programmed cell death. Apoptosis is a normal and controlled process within multicellular organisms. It is very important because it maintains the balance of cells within an organism. 

For example, apoptosis can occur during the development of new cells. If these cells are not divided correctly, they could lead to cancer or a virus. Without apoptosis, these harmful cells could continue dividing and multiplying which could cause an adverse effect on the organism. Apoptosis is very important because if damaged or mutated cells do not get the signal to go through apoptosis, cancer can form.

ap bio

study guide

Unit 4

4.6 Cell Cycle

1️⃣ Interphase

4️⃣ Mitosis

5️⃣ Cytokinesis