Unit 4: Cell Communication and Cell Cycle

AP Biology | 2024-2025

What do unicellular organisms do?

detect and respond to environmental signals

What is taxis?

the movement of an organism in response to a stimulus that can be positive or negative

When is taxis positive?

when the movement is toward the stimulus

When is taxis negative?

when the movement is away from the stimulus

True or false: taxes are innate behavioral responses

true

What is chemotaxis?

movement in response to chemicals

Why must cells of multi-celled organisms communicate with one another?

to coordinate the activities of the organism as a whole

How do cells communicate?

through cell-to-cell contact or through cell signaling

What is short-range cell signaling?

when signaling only affects nearby cells

What is long-range cell signaling?

when cells throughout the organism are affected

What can signaling be done by?

cell junctions or ligands

What are ligands?

signaling molecules that bind to receptors ad trigger a response by changing the shape of the receptor protein

What is signal transduction?

the process by which an external signal is transmitted to the inside of a cell

What are the 3 steps of signal transduction?

1. a signaling molecule binding to a specific receptor

2. activation of a signal transduction pathway

3. production of a cellular response

When is a plasma membrane receptor required for signaling?

when signaling molecules cannot enter the cell

What do plasma membrane receptors make up?

an important class of integral membrane proteins that transmit signals from the extracellular space into the cytoplasm

What are the 3 classes of membrane receptors?

1. ligand-gated ion channels

2. catalytic (enzyme-linked) receptors

3. G-protein linked receptor

Where are ligand-gated ion channels located?

in the plasma membrane

What do ligand-gated ion channels do?

open or close an ion channel upon binding a particular ligand

What do ligand-gated ion channels open in response to?

acetylcholine

What do catalytic receptors have?

an enzymatic active site on the cytoplasmic side of the membrane

What is enzymatic activity initiated by?

ligand binding at the extracellular surface

What does the G-protein linked receptor do instead of acting as an enzyme?

it binds to a different version of a G-protein on the intracellular side when a ligand is bound extracellularly, which causes activation of secondary messengers within the cell

What are signal transduction cascades helpful for?

amplifying a signal

What is homeostasis?

the set of conditions under which living things can successfully survive

What are insulin and glucagon?

two hormones released from the pancreas that regulate blood glucose levels

What are many responses controlled by?

feedback pathways

What do positive feedback pathways do?

amplify a reaction, driving a process to completion

What are examples of positive feedback pathways?

blood clotting, fruit ripening, childbirth, ovulation

What do negative feedback pathways do?

reduce or dampen the processes that lead to an output

What are examples of negative feedback pathways?

thermoregulation, blood sugar, hormone production

What is the cell cycle?

the cell’s life cycle – the period from the beginning of one division to the beginning of the next

What are the 2 periods that the cell cycle is divided into?

interphase and mitosis

What is interphase?

the time span from one cell division to another

What are the 3 stages of interphase?

G1, S, and G2

What is the most important stage of interphase?

the S stage

What occurs in the S stage of interphase?

the cell replicates its genetic material

What occurs during interphase?

every single chromosome in the nucleus is duplicated

What sister chromatids?

the identical strands of DNA produced in interphase

What are the sister chromatids held together by?

a structure called the centromere

Why aren’t the sister chromatids called chromosomes?

because they remain attached

What must the sister chromatids do in order to be called chromosomes?

each needs to have its own centromere

When do the chromatids become full-fledged chromosomes?

once the chromatids separate

What happens during the G1 and G2 stages of interphase?

the cell performs metabolic reactions and produces organelles, proteins, and enzymes

What does the “G” in G1 and G2 stand for?

gap

What are the three stages of interphase highly regulated by?

checkpoints and special proteins called cyclins and cyclin-dependent kinases (CDKs)

What are cell cycle checkpoints?

control mechanisms that make sure cell division is happening properly in eukaryotic cells

When do checkpoint pathways in eukaryotic cells mainly function?

at phase boundaries such as the G1 – S transition and G2 – M transition

What happens when damaged DNA is found?

checkpoints are activated and cell cycle progression stops, and the cell uses the extra time to repair damage in DNA

What happens if the DNA damage is so extensive that it cannot be repaired?

the cell can undergo apoptosis

What is apoptosis?

programmed cell death

How do cell cycle checkpoints control cell cycle progression?

by regulating 2 families of proteins: cyclins and cyclin-dependent kinases (CDKs)

How is cell cycle progression induced?

an inactive CDK binds a regulatory cyclin, and once together, the complex is activated, which can affect many proteins in the cell and causes the cell cycle to continue

How is cell cycle progression inhibited?

CDKs and cyclins are kept separate

When does cancer occur?

when normal cells start behaving and growing very abnormally and spread to other parts of the body

What are oncogenes?

mutated genes that convert normal cells into cancerous cells

What are proto-oncogenes?

genes that help cells grow and divide normally

What do tumor suppressor genes produce?

proteins that prevent the conversion of normal cells into cancer cells

What can tumor suppressor genes do?

• detect damage to the cell and work with CDK/cyclin complexes to stop cell growth until the damage can be repaired

• trigger apoptosis if the damage is too severe to be repaired

What is mitosis?

cellular division

What are the 4 stages of mitosis?

1. prophase

2. metaphase

3. anaphase

4. telophase

What happens in prophase?

the nuclear envelope disappears and chromosomes condense

What happens in metaphase?

chromosomes align at the metaphase plate and mitotic spindles attach to kinetochores

What happens during anaphase?

chromosomes are pulled away from the center

What happens during telophase?

mitosis is terminated and two new nuclei form

What happens during the process of cytokinesis?

mitosis ends as the cytoplasm and plasma membranes pinch to form two distinct, identical daughter cells

What happens once the daughter cells are produced?

they re-enter the initial phase (interphase) and the whole process starts over, with the cell going back to its original state

What 2 things does mitosis achieve?

• the production of daughter cells that are identical copies of the parent cell, maintaining the proper number of chromosomes from generation to generation

• fulfilling the organism’s need for growth, tissue reparation, or asexual reproduction