Presentation is loading. Please wait.

Presentation is loading. Please wait.

Signal Transduction Pathways “ From signal to gene expression ”

Similar presentations


Presentation on theme: "Signal Transduction Pathways “ From signal to gene expression ”"— Presentation transcript:

1 Signal Transduction Pathways “ From signal to gene expression ”

2 Signal Transduction Pathways The biochemical events that conduct the signal of a hormone or growth factor from the cell exterior, through the cell membrane and into the cytoplasm which involve a number of molecules including receptors, proteins, and messengers a series of steps by which a signal on a cell’s surface is converted into a specific cellular response

3 1.The stream of signals to which plant cells react is continuous and complex 2.Signal transduction uses a network of interactions within cells, and throughout the plants Overview on Plant Signal Transduction

4 Analogy view of cell signaling transduction pathway Input (command) Keyboard Signal perception Endogenous: phytohormone Exogenous: environmental cue CPU (Central Processing Unit) Chip Signal Transduction Network Compiling, Integration, processing Output (performance) Printer Signal Response Morphogenesis change, Growth development differentiation

5 EXTRACELLULAR FLUID Reception Plasma membrane TransductionCYTOPLASM Receptor Signal molecule

6 EXTRACELLULAR FLUID Reception Plasma membrane Transduction CYTOPLASM Receptor Signal molecule Relay molecules in a signal transduction pathway

7 EXTRACELLULAR FLUID Reception Plasma membrane Transduction CYTOPLASM Receptor Signal molecule Relay molecules in a signal transduction pathway Response Activation of cellular response

8 1.The stream of signals to which plant cells react is continuous and complex 2.Signal transduction uses a network of interactions within cells, and throughout the plants Overview on Plant Signal Transduction

9

10 STIMULUS R R Ca 2+ G-prot Kin Phos TF Plasma membrane Nuclear membrane DNA Signal transduction (Simplified model)

11 Stimulus Hormones, physical environment, pathogens Receptor On the plasmamembrane, or internal Secondary messengers Ca 2+, G-proteins, Inositol Phosphate Effector molecules Protein kinases or phosphatases Transcription factors Response Stomatal closure Change in growth direction Signal Transduction Components

12 How many signal factors which Plant will respond to? --biotic and abiotic factors-- STIMULUS

13 Stimulus

14 Reception The binding between a signal molecule (ligand) and receptor is highly specific –A conformational change in a receptor is often the initial transduction of the signal –Most signal receptors are plasma membrane proteins A signal molecule binds to a receptor protein, causing it to change shape

15 Intracellular Receptors Some intracellular receptor proteins are found in the cytosol or nucleus of target cells Small or hydrophobic chemical messengers can readily cross the membrane and activate receptors An activated hormone-receptor complex can act as a transcription factor, turning on specific genes

16 Receptors in the Plasma Membrane Most water-soluble signal molecules bind to specific sites on receptor proteins in the plasma membrane There are three main types of membrane receptors: 1. G-protein-linked receptors 2. Receptor tyrosine kinases 3. Ion channel receptors

17 It is a plasma membrane receptor that works with the help of a G protein The G-protein acts as an on/off switch If GDP is bound to the G protein, the G protein is inactive G-protein-linked Receptor

18 Segment that interacts with G proteins Signal-binding site G-protein-linked receptor

19 Regulates cell growth and cell reproduction Tyrosine kinase catalyzes transfer of phosphate group from ATP to tyrosines Can trigger ten or more signal transduction pathways at once Abnormal tyrosine kinases that work even without a signal molecule may contribute to some cancers Receptor Tyrosine Kinases

20 Signal molecule  Helix in the membrane Signal-binding site Tyr Tyrosines Receptor tyrosine kinase proteins (inactive monomers) CYTOPLASM Tyr Activated tyrosine- kinase regions (unphosphorylated dimer) Signal molecule Dimer Fully activated receptor tyrosine-kinase (phosphorylated dimer) Tyr P P P P P P ATP 6 ADP Tyr P P P P P P Inactive relay proteins Cellular response 2 Cellular response 1 Activated relay proteins 6

21 Acts as a gate when the receptor changes shape Signal molecule binds as a ligand to the receptor, the gate allows specific ions, such as Na + or Ca 2+, through a channel in the receptor Ion Channel Receptor

22 Receptor

23

24

25

26

27

28

29 Transduction Transduction usually involves multiple steps Multistep pathways can amplify a signal: A few molecules can produce a large cellular response Multistep pathways provide more opportunities for coordination and regulation Cascades of molecular interactions relay signals from receptors to target molecules in the cell

30 Signal Transduction Pathways The molecules that relay a signal from receptor to response are mostly proteins Like falling dominoes, the receptor activates another protein, which activates another, and so on, until the protein producing the response is activated At each step, the signal is transduced into a different form, usually a conformational change

31 Protein Phosphorylation and Dephosphorylation In many pathways, the signal is transmitted by a cascade of protein phosphorylations Phosphatase enzymes remove the phosphates This phosphorylation and dephosphorylation system acts as a molecular switch, turning activities on and off

32 Signal molecule Activated relay molecule Receptor Inactive protein kinase 1 Active protein kinase 1 Inactive protein kinase 2 Active protein kinase 2 Inactive protein kinase 3 Active protein kinase 3 ADP Inactive protein Active protein Cellular response Phosphorylation cascade ATP PP P i ADP ATP PP P i ADP ATP PP P i P P P

33 Small Molecules and Ions as Second Messengers Second messengers are small, nonprotein, water- soluble molecules or ions The extracellular signal molecule that binds to the membrane is a pathway’s “first messenger” Second messengers can readily spread throughout cells by diffusion Second messengers participate in pathways initiated by G-protein-linked receptors and receptor tyrosine kinases

34 Cyclic AMP Cyclic AMP (cAMP) is one of the most widely used second messengers Adenylyl cyclase, an enzyme in the plasma membrane, converts ATP to cAMP in response to an extracellular signal Many signal molecules trigger formation of cAMP Other components of cAMP pathways are G proteins, G-protein- linked receptors, and protein kinases cAMP usually activates protein kinase A, which phosphorylates various other proteins Further regulation of cell metabolism is provided by G-protein systems that inhibit adenylyl cyclase

35 ATPCyclic AMPAMP Adenylyl cyclase Pyrophosphate PP i Phosphodiesterase H2OH2O

36 cAMP ATP Second messenger First messenger (signal molecule such as epinephrine) G-protein-linked receptor G protein Adenylyl cyclase Protein kinase A Cellular responses GTP

37 Calcium ions and Inositol Triphosphate (IP 3 ) Calcium ions (Ca 2+ ) act as a second messenger in many pathways Calcium is an important second messenger because cells can regulate its concentration A signal relayed by a signal transduction pathway may trigger an increase in calcium in the cytosol Pathways leading to the release of calcium involve inositol triphosphate (IP 3 ) and diacylglycerol (DAG) as second messengers

38 CYTOSOL Ca 2+ Endoplasmic reticulum (ER) IP 3 -gated calcium channel IP 3 (second messenger) DAG PIP 2 G-protein-linked receptor Phospholipase C G protein Signal molecule (first messenger) EXTRACELLULAR FLUID GTP

39 CYTOSOL Ca 2+ Endoplasmic reticulum (ER) IP 3 -gated calcium channel IP 3 (second messenger) DAG PIP 2 G-protein-linked receptor Phospholipase C G protein Signal molecule (first messenger) EXTRACELLULAR FLUID GTP Ca 2+ (second messenger)

40 CYTOSOL Ca 2+ Endoplasmic reticulum (ER) IP 3 -gated calcium channel IP 3 (second messenger) DAG PIP 2 G-protein-linked receptor Phospholipase C G protein Signal molecule (first messenger) EXTRACELLULAR FLUID GTP Ca 2+ (second messenger) Various proteins activated Cellular re- sponses

41

42

43

44

45

46

47

48


Download ppt "Signal Transduction Pathways “ From signal to gene expression ”"

Similar presentations


Ads by Google