chap 3- intercellular communications (b1- foundation) Flashcards

Question

indirect communication: **cytokines** + examples

Answer 1

peptides (small proteins) that **any cell can release**, especially immune cells - can act in *autocrine, paracrine, or endocrine* ways depending on the situation - help regulate immune responses, inflammation, and cell growth **examples**: - **Interleukins** – regulate immune cell behavior - **Lymphokines** – from lymphocytes - **Adipokines** – released from fat (adipose) tissue Purpose: Versatile signals used heavily in the immune system and inflammation

Answer 2

tiny tunnels/pores that **directly connect the insides of two neighboring cells** - pores made of proteins called **connexins** - *ions and small molecules* (like calcium, glucose, or second messengers) move directly from one cell to another

Answer 3

**long, thin tubes made from the cell’s cytoskeleton** that connect cells over **longer distances** - larger than gap junctions, allow cells to pass **larger cargo**, like proteins, organelles (like mitochondria), even viruses - are **temporary structures** — cells build them when needed *extra info*: - found in immune cells, cancer cells, neurons, etc. - can be used for both normal communication and sometimes spreading infections (like viruses or misfolded proteins in neurodegenerative diseases)

Answer 4

cells communicate by **physically recognizing each other’s surface proteins** — like shaking hands to recognize someone - one cell has specific protein (ligand) on its surface - other cell has a receptor that fits that ligand - when bind, triggers a response inside the cells **example**: Immune T cells recognizing infected or cancer cells: The infected cell shows a “bad” marker on its surface. The T cell’s receptor recognizes it and kills that specific cell. This ensures that only undesirable cells are destroyed, not healthy ones.

Answer 5

signaling molecule (eg. hormone) binds to receptor **outside cell** → conformational change in receptor that activates it → starts message relay inside cell → **second messengers activated** (intracellular signaling molecules) that spread the signal inside cell (*like cAMP, Ca2+*) → **signal amplificiation** (signaling cascade that is a chain of events that amplifies the signal) → eventually, signal reaches **target proteins** that are activated and lead to **cell's response**

Answer 6

**plasma membrane receptors**: located on outside surface of cell membrane, detect **water soluble (lipid-insoluble) messengers** - messengers cannot cross membrane so need receptors on surface - receptors that function as: - *ligand gated ion channels - enzymes* - bound to and activate *cytoplasmic enzymes* - receptors that *activate G proteins* **intracellular receptors**: located inside cell (either cytoplasm or nucleus), detect **lipid-soluble messengers** like steroid hormones - *cytoplasmic receptors* - *nuclear receptors*

Answer 7

1. **Ligand-gated ion channels**: - when signal binds, channel opens or closes - *ex. nicotinic ACh receptors* 2. receptors that function as **enzymes** (usually tyrosine kinase receptors) - receptor is enzyme or becomes 1 when activated - when signal binds, receptors activates enzyme activity inside cell - *ex. insulin receptor that activates kinase to increase glucose uptake* - *growth factors such as nerve growth factor & epidermal growth factor* (help regulate cell growth & division) 3. **Enzyme-linked receptors/Catalytic receptors**: receptors that are bound to & activate cytoplasmic enzymes - receptor itself isn't enzyme but connected to enzyme inside cell - signals bonds = receptors activates that enzyme - *ex. JAK/STAT pathway* 4. **G-protein coupled receptors**: type of membrane receptor that initiates a # of metabolic steps to modulate cell activity - *ex. adrenergic receptors*

Answer 8

1. **nuclear receptors**: already in nucleus - bind messenger directly & act as transcription factors - turn genes on or off - *ex. thyroid hormone binds nuclear receptor* 2. **cytoplasmic receptors**: found in cytoplasm, signal molecule binds and complex moves into nucleus = changes gene expression - *ex. cortisol binds cytoplasmic receptors*

Answer 9

**down regulation**: cell reduces its sensitivity to signal (protection from overstimulation if too much signal), two ways: 1. **internalization (receptor-mediated endocytosis)**: receptors on membrane pulled into cell by endocytosis so fewer receptors left on cell surface 2. **desensitization (chemical modification)**: receptors stays on membrane, but is chemically changed (eg. phosphorylation) - makes it inactive or less responsive - like turning off switch without removing it **upregulation**: cell becomes more sensitive to a signal - b/c less of a signal available so cell increases # of receptors on surface

Answer 10

binding of ligand to target cell → activates enzyme **janus kinase (JAK)** attached to cytosolic side of receptor → JAK phosphorylates **STAT** (signal transducers & activators of transcription) within cytosol → **phosphorylated STAT** moves to nucleus → turns on **gene transcription** → synthesis of new proteins that **carry out cellular response**

Answer 11

**protein phosphatases** remove phosphate groups from designated proteins - quickly shut off signal transduction pathway if its signal molecule is no longer bound at the cell surface

Answer 12

**cancer of the bone marrow** where blood cells are made - problem in white blood cells formation & control (grow too much & don't mature properly) caused by: 1. **unregulated tyrosine kinase activity**: mutation causes enzyme *tyrosine kinase* to always be "on" (phosphorylated) when it shouldn't be = keeps **phosphorylating signaling proteins** 2. **increased expression of growth regulatory genes**: constant signaling = genes that control growth are overactive = leads to **too many white blood cells being made** even when body doesn't need them