Unit 4 Cell Communication and Cell Cycle

Direct contact

communication through cell junctions, signaling substances and other material dissolved in the cytoplasm can pass freely between adjacent cells

Gap junctions

cell junction in animal cells

Plasmodesmata

cell junction in plant cells

Local regulators

a secreting cell will release chemical messages (local regulators/ligands) that travel a short distance through the extracellular fluid

Paracrine signaling

secretory cells release local regulators (ie growth factors) via exocytosis to an adjacent cell

Synaptic signaling

occurs in animal nervous systems

Endocrine signaling

specialized cells in animals release hormones into the circulatory system where they reach target cells

Long distance signalling

involves communication between cells that are far apart, typically utilizing hormones in the bloodstream

Reception

the detection and receiving of a ligand by a

receptor in the target cell

Transduction

the conversion of an extracellular signal to an intracellular signal that will bring about a cellular response

Response

the final molecule in the signaling pathway converts the signal to a response that will alter a cellular process

Receptor

macromolecule that binds to a signal molecule (ligand)

Signal transduction pathway

a sequence of changes in a series of molecules

Protein kinase

modifies other proteins by adding phosphate groups

Protein phosphatase

enzymes that remove phosphate groups from proteins, reversing the action of protein kinases

Second messengers

small, non-protein molecules and ions help relay the message and amplify the response (e.g Cyclic AMP)

G protein coupled receptors (GPCRs)

transmembrane proteins that transmit signals through the cell membrane and activate G proteins in response to external stimuli

Ligand gated ion channels

membrane proteins that open or close in response to the binding of a specific ligand, allowing ions to flow across the membrane

Set points

values for various physiological conditions that the body tries to maintain

Homeostasis

the state of relatively stable internal conditions

Stimulus

a variable that will cause a response

Receptor/sensor

sensory organs that detect a stimulus. This information is sent to the control center (brain)

Effector

muscle or gland that will respond

Response

changes (decreases or increases) the effect of the stimulus

Negative feedback mechanism

a process that counteracts a change in a physiological variable by initiating responses that restore the variable to its set point (e.g sweating, shivering()

Positive feedback mechanism

a process that enhances or amplifies changes in a physiological variable, leading to a greater response until a specific event occurs (e.g. childbirth)

Disease

when the body is unable to maintain homeostasis

Cell cycle

the life of a cell from its formation until it divides

Histones

proteins that package and structure DNA into chromatin, playing a key role in gene regulation and cell division

Centromere

the region on each sister chromatid where they are most closely attached

Kinetochore

proteins attached to the centromere that link each sister chromatid to the mitotic spindle

Genome

all of a cell’s genetic information (DNA)

Homologous chromosomes

two chromosomes that are the same length, have the same centromere position, and carry genes controlling the same characteristics

Interphase

the longest portion of the cell cycle (90%)

G1 “first gap” phase

the cell grows and carries out normal functions

S “synthesis” phase

DNA replication and chromosome duplication occurs

G2 “second gap” phase

final growth and preparation for mitosis

M phase

mitosis

Mitosis

the process of cell division that results in two genetically identical daughter cells

Cytokinesis

the division of the cytoplasm that occurs after mitosis, leading to the formation of two distinct daughter cells

Prophase

• Chromatin condenses

• Nucleoli disappear

• Duplicated chromosomes appear as sister chromatids

• Mitotic spindle begins to form

• Centrosomes move away from each other

Prometaphase

• Nuclear envelope fragments

• Microtubules enter nuclear area and some attach to kinetochores

Metaphase

• Centrosomes are at opposite poles

• Chromosomes line up at the metaphase plate

• Microtubules are attached to each kinetochore

Anaphase

• Sister chromatids separate and move to opposite ends of the cell due to the microtubules shortening

• Cell elongates

Telophase and Cytokinesis

• Two daughter nuclei form

• Nucleoli reappear

• Chromosomes become less condensed

Checkpoints

regulatory mechanisms in the cell cycle that ensure the proper progression and division of the cell

G₁ Checkpoint

• Most important checkpoint

• Checks for cell size, growth factors, and DNA damage

G₀

nondividing stage, some cells stay in G0 forever (muscle/nerve cells), some cells can be called back into the cell cycle

G₂ Checkpoint

checks for completion of DNA replication and DNA damage

M (Spindle) Checkpoint

checks for microtubule attachment to chromosomes at the kinetochores at metaphase

Cyclins

proteins that regulate the cell cycle by activating cyclin-dependent kinases (CDKs) through binding, ensuring proper progression through different phases

Cyclin Dependent Kinases (CDKs)

when activated by cyclins, drive the cell cycle forward and regulate progression through various phases

Growth factors

hormones released by cells that stimulate cell growth, signal transduction pathway is initiated, CDKs are activated leading to progression through the cell cycle

Contact (or density) inhibition

cell surface receptors recognize contact with other cells, initiates signal transduction pathway that stops the cell cycle in G1 phase

Anchorage dependence

cells rely on attachment to other cells or the extracellular matrix to divide

Tumor

an abnormal mass of tissue resulting from excessive cell division

Cancer cells

cells that grow uncontrollably and can invade nearby tissues, often disregarding normal cell communication and signaling mechanisms.