Unit 6: Cell Communication

Question 1

Identify the abbreviation

ECM

Answer 1

extracellular matrix

Question 2

Define / describe the

extracellular matrix

Answer 2

Network of proteins and other molecules that surround, support, and help anchor cells

Question 3

Why do cells communicate?

Answer 3

• Help maintain homeostasis
• Determine when to grow & develop

Question 4

Identify the types of

Cell Junctions

Answer 4

In animals: gap junctions
In plants: plasmodesmata

Question 5

How do cells communicate via cell junctions?

Answer 5

Chemical messages within the cells can be transferred directly from one cell to another
Note that no extracellular (outside of the cell) ligand is required

Question 6

Describe

Cell communication via direct contact

Answer 6

Protein, glycoprotein, or glycolipid that is embedded on membrane of one cell acts as a ligand for a receptor on another cell
The two cells must come into direct contact

AKA juxtacrine signaling

Question 7

Cell communication via
direct contact
Examples / commonly found in…

Answer 7

Immune system (ex: when white blood cell contacts pathogen)
Embryonic development

Question 8

Cell communication via
cell junctions
Examples / commonly found in…

Answer 8

Smooth and cardiac muscle - allows for very rapid transmission of signal between cells within a muscle fiber

Question 9

Define

Paracrine signaling

Answer 9

Sending molecule secretes ligand into area
Target cells are nearby
Note: This type of signaling often depends on concentration of ligand; more ligand may mean a stronger response or the target cell may require a certain threshold of ligand before it can respond

Question 10

Paracrine signaling
Examples / commonly found in…

Answer 10

Immune system - ex: immune cells may secrete histamine or other cytokines, which cause nearby cells to respond
Synaptic transmission is technically a form of paracrine signaling

Question 11

Define

Synaptic transmission

Answer 11

A specialized form of paracrine signaling that occurs in the nervous system, between the terminal end of one neuron and a dendrite of another neuron
The two neurons are close to each other, with a gap between them (the synapse) into which the ligand is secreted

Question 12

Define

Endocrine signaling

Answer 12

Long distance cell signaling where a ligand is secreted from a gland into the blood stream
Can allow for very small amounts of ligand to cause response throughout the entire body

Question 13

Ligands in the immune system are called

Answer 13

cytokines

Question 14

Ligands in the endocrine system are called

Answer 14

hormones

Question 15

Ligands in the nervous system are called

Answer 15

neurotransmitters

Question 16

List the

Three stages of
signal transduction

Answer 16

1. Reception
2. Transduction
3. Response

Question 17

What characteristic of ligands determines if it will bind to extracellular or intracellular receptors?

Answer 17

Small, nonpolar substances diffuse through the membrane and bind to intracellular receptors
Large and/or polar substances cannot diffuse into the cell and must bind to cell surface receptor

Question 18

List three common examples of
cell surface receptors

Answer 18

• GPCRs
• RTKs
• Ligand-gated ion channels

Question 19

Define

GPCR

Answer 19

G Protein Coupled Receptor
* Cell surface receptor that is associated with a G-protein within the cell
* Binding of ligand often causes a change to the G-protein and whether it is attached to GDP (in inactive state) or GTP (in active state)

Question 20

Define

RTK

Answer 20

Receptor Tyrosine Kinase
* Cell surface receptor that has an intracellular kinase domain
* Binding of a ligand often causes one RTK to find another active RTK (called dimerization)
* Dimerized RTKs phosphorylate each other to become active, then can phosphorylate other relay proteins within the cell

Question 21

Define

Ligand Gated Ion Channels

Answer 21

• Ion channels that have a receptor for specific ligand
• Binding of the ligand often opens (or sometimes closes) the channel
• Remember: Like all channels, these are still specific to the substance that can move through and the substances will still diffuse down their concentration or electrochemical gradients

Question 22

Define

Intracellular Receptors

Answer 22

• Have ligand that is small and nonpolar, such as steroid-based hormones (made from cholesterol)
• Binding of ligand often causes movement of ligand/receptor into the nucleus, where it acts as a transcription factor

Question 23

What are common components of signal transduction pathways in the cell?

Answer 23

• Cytoplasmic region of receptor has enzymatic activity to start process
• Phosphorylation cascades
• Amplification
• Second messengers

Question 24

Describe

Cell-surface receptors

Answer 24

Transmembrane proteins that have two important regions:
* Outside of the cell (extracellular domain) has a receptor, which is capable of binding to a specific ligand
* Inside the cell (cytoplasmic domain) has an enzyme or protein-binding area that is only active when the extracellular domain is bound to its ligand

Question 25

# Describe Phosphorylation Cascades

Answer 25

Addition of phosphate group (AKA **phosphorylation**) causes activation of protein * **Kinases**: Add phosphate groups to specific proteins (often other kinases) * **Phosphatases**: Remove phosphate groups

Question 26

# Define/describe Kinases

Answer 26

Enzymes that add phosphate groups to other proteins Usually uses ATP

Question 27

# Define/describe Phosphatases

Answer 27

Enzymes that remove phosphate groups from other proteins

Question 28

# Define/describe Second messengers

Answer 28

Small, polar, non-protein substances Able to be made and diffuse quickly in the cytoplasm Lead to changes in activity of other proteins

Question 29

# List Common second messengers

Answer 29

To know for AP Biology: * Ca²⁺ * cAMP Also worth knowing... * IP3 (inositol triphosphate) * DAG (diacylglycerol)

Question 30

# Describe cAMP

Answer 30

**C**yclic **A**denosine **M**ono**p**hosphate Made from ATP

Question 31

What enzyme makes cAMP

Answer 31

Adenylyl cyclase (sometimes called adenylate cyclase)

Question 32

# What is Amplification

Answer 32

Each part of a signal transduction pathway can cause a greater and greater effect, allowing one or only a few molecules to lead to faster/ bigger responses Often due to each protein in a pathway being able to activate many of the next protein in the pathway

Question 33

What are common responses in cell signaling pathways?

Answer 33

* Regulation of gene expression * Regulation of enzyme activities or other protein activities * Cell growth / division * Movement of material within the cell (including moving vesicles for endo- or exocytosis) * Movement of the cell itself * Apoptosis

Question 34

# Define Apoptosis

Answer 34

Programmed cell death Often for cells that are not needed by the organism (such as cells between fingers or immune cells that are self-reactive) or for damaged cells

Question 35

Why can different cells respond to the same ligand in different ways?

Answer 35

All cell types express different sets of genes (**differential gene expression**) This leads to different cells having different combinations of receptors and signal transduction pathway molecules ## Footnote Ex: Insulin can cause fusion of vesicle containing GLUT4 proteins to a cell membrane in a cell that has active genes for insulin receptors, GLUT4 proteins, and all necessary proteins in the pathway. Cells that don't express those genes won't make the proteins to allow for this response.

Question 36

What do these symbols: → ⊣ mean in signaling pathways?

Answer 36

→ causes, activates, increases, phosphylates, etc ⊣ blocks, stops, deactivates, decreases, etc