Cell Communication

Cell communication is vital survival of both unicellular and multicellular organisms

• Cells talk and listen to each other

• Signals are most often chemicals

Two types of cell commutation

• Paracrine (local) communication

• endocrine (long disance)

  • Local signaling , cells talk by direct contract

• Gap junctions is in animal cells

• Plasmadesmata between pant cells

• Proteins aid in cel to cell recognition

• Cells close to to each other release chemicals and travel short distances and interact with cells nearby

  • Paracrine signaling i when ells secrete chemicals and other cells use sensory to understand and talk

• Special type called synaptic cignaling using nerves

  • Nerves run from brain to tissues releasing chemicals calls neurotransmitter

    • This tells the cell what to do

• Long distance signaling uses hormones called endocrine system

  • Cells release hormones that circulate all around the body through the blood stream until they find cells that will respond

    • Insulin/pancreas

• These signals interact with a receptor , molecule that is normally a protein and on the surface on the cell that the signaling molecules bind too

  • Ability of the cell to respond depends now ether of not they have the receptors

    • Only cells with receptors specific to that signal can respond

3 main stages of cell signaling

1. Reception

2. Transduction

3. Response

• In reception the target cell detects a signaling molecule that binds to a receptor protein on the cell surface

• In transduction the binding of the signaling molecule alters the receptor and initiates a signal transduction pathway

• In response, the transducers signal triggers a specific responde in the target cell

Receptor binding

• The binding between a signal molecule (ligand) and receptor is highly specific

  • Will only bind one chemical signal

• When a ligand binds, there is a shape change in the receptor

  • Sets off transduction pathway

• Most receptors are in the plasma membrane , most span the entire membrane range

  • Cell surface pereptors make up 30% of all human proteins

  • 3 main types of membrane receptors

    • G protein coupled receptors

    • Receptor tyrosine kinases

  • Ion channel receptors

G protein receptors

• Cell surface transmembrane receptors that work by activating a G protein

• Target family of cell surface receptors

• Genes are about 800 are known %4 of human genome

• Have 7 trans membrane spans

  • One protein that crosses the membrane seven times

• Are small trimmer is proteins on eat cytoplasmic side of the membrane

• The 3 subunits are called alpha beta gamma

  • Alpha subunit binded to gpd (guanosine diphosphate)

  • When it binds, it actives something called a agonist

    • Changes the shape of the gdp, changes it into a GTP

    • Causes trimeric molecule to split into two parts

      • Alpha subunit with gtp, activates a enzyme to initiate the transduction stage - dropping a phosphate

      • Also contains an enzyme that converts the GTP back to GDP and recombines it with the bA subunits

• Gs and Gi

  • Gs stimulates

  • Gi prohibits

Receptor tyrosine kinases RTK

• Kinase is an enzyme that transfers a phosphate group

• Transfers a phosphate onto the amino acid tyrosine

  • Monomer that has ligan binding site that has a long receptor tail

• When signaling molecules come in, they bind two the monomers and get they get together (2) to form a dimer

  • Goes through ATP , puts phopshates on the tyrosines to get a fully activated phophorylated dimer

  • They are bind and start signal transductions

• Different from GPCR because they can activate ten or more different transduction pathways rather than one at a time

  • Involved in growth Of cells

  • Uncontrolled activity of RTK is the causes of many cancers

Ligan gate ion channels

• Channels are ion channels that have a receptor side for a ligand

• When there is no ligand, the channel is closed

• When it binds it causes a shape change at allows the channel to open and an ion to take place

  • When the channel opens, the ion travels down and causes a cellular response , gate closes when the ligand comes off

Intracellular receptors

• Not all are on the plasma membrane

• Respond to hydrophobic messengers

Transduction

• Has multiple steps

  • One main step is how to amplify the signal

• Normally involve protein activation

• Brought about by phosophorylation

  • Sticking phosphate groups on proteins

• Protein kinases transfer phosphates from ATP to protein normally serine to threonine amino acids not tyrosine like the receptor tyrosine kinases

• Many relay molecules in signal transduction path always are protein kinases creating a phosphorylation cascade

• Protein phosphates rapidly remove the phosphates from proteins a process called de phosphorylation

  • Acts as molecular switch when a signaling molecule binds to a receptor and activates the system ,

    • There is an inactive kinase that gets activated, and activates another, which actives another and so on

    • Until one actives a protein that starts a cellular response

    • While this is happening , they are getting turned off

Second messenger

• Many signaling pathways involve second messengers

• Second messengers are small no protein molecules that are spread throughout the cell by diffusion

• Activated by the ligand binding and stead through the cell by diffusion

• Typically used in GCPR

• THREE MOST COMMON

  • Cyclic nucleotides

  • Phosphatidlyidi

  • Calcium

• Cyclic AMP

  • Most Widely used messengers

    • Diffuses into the cell activating protein kinases staring a transduction casca ending with the activation of glycogen phophorylase

    • Terminated by the enzyme phosphodiesterase That break it down to AMP

• Activates protein kinases which starts the cascade

  • Iigan goes into receptor, which actives g protection, which activates the cascade

Inositols an DAG

• Inositol and DAG are 2nd messengers that area ctivates in the same way as CAMP

• A signal molecule binds to the recperotis activates a G protein

• DAG activates protein kinase C and starts a cascade

Calcium ions

• 2nd messenger because concentration in the cytoskeleton is normally much lower than the concentration outside the cell

• Kept low by the cell actively pumping it out of the cell

• Only need a small change in the calcium concentration to produce an effect

• Designated channel for calcium in the Endoplasmic reticulum where the calcium flows threw tht signals a receptor to come and bind

Regulation of the response

1. Signal amplification - bigger the signal the bigger the response

2. Specificity of the response so all things have their own way to work

3. Efficiency

4. Termination of the signal - have to terminate it so they do not keep going

Signal amplification

• Enzyme cascades amplify the cells response to the signal

• At each step the number activates products is much greater than the predefined step

Specificity

• Specific receptors for specific cells

Efficiency

• Scaffolding proteins are large relay proteins to which other relay proteins are attached

• Can increase the signal transduction efficiency by grouping together different proteins involved in the same pathway

• In some cases, scaffolding proteins may also help activate some of the relay problems

Termination if the signal

• Inactivation mechanism are essential

• If the ligand concentration fails, fewer receptions will be bound

• Unbound receptor revert to an inactive state

MISSING SOME SLIDES

How is glucose metabolized through cellular respiration

‘ Most important reactions that transfer electrons called redox reactions

• Oxidation is a loss of electrons

• In reduction, substance gains electrons

• Electron donor is a reducing agent

• Electron receptor is called oxidizing agent

  • Some reactions do not completely transfer, but change the electron sharing in covalent bonds

• When electrons are pulled closer from to the atom, they lose energy because they don’t need as much

• Cellular respiration occurs in a series off steps not all at once

  • Dehydrogenase enzymes break off 2 electrons and 2 protons )2 hydrogens= a a time

    • One proton and one two electrons are usually first transferred to a NAD

    • NADH plus functions as an oxidizing agent during cellular respeiration, each one represent the storming of energy

  • There is no energy lost when there is the same amount of ellectronegataivity {like carbon and hydrogeń}

  • If nadh passsed the hydrogen straightt to the oxygen there would be a large uncontrolled release of energy

    • The electron transport chain is what allows little bits of energy to be let out at a time

Cell respiration is harvesting the energy stores in glucose

• Glycolosis - breaks down glucose into molecules of pyruvate

• Citric acid cycle - completes the breakdown of glucose into co2

• Oxidative phosphorylation- accounts for 90% if ATP synthesis

Glycolosis

• Produces a small amount of ATP

• For each molecuole fo glucose degrade to co2 and water by respiration, the cell makes up to 32 molecules to ATP

• Glycolysis breaks down two molecules of private

  • Occurs sin the cytoplasm an has two major phases [everything else in the mitochondria]

    • Energy investment phase

    • Energy payoff phase

    • Energy goes in ATP - get 4 ADP out,

  • Occurs wether or not on O2 is present

• phospofructokinase - splits 6 carbon molecule into 2 carbon molecule

• Before the citric acid cycle can begin, pyruvate must be converted to acetylene CoA which links molecules_

• Citric acid cycle

  • 8 steps

    • Stats with acetyl CoA by combing in with oxaoacetate, forming citrate - 7 steps after decompose the citrate back to oxaliacatate

    • Citrate gets converted to isocitrate

    • Converted to alpha. Ketoglutarate

    • Converts to succinyl CoA

    • Convertís to succionaste

    • Converted to fumerate

    • Converted to malaate

    • Converted back to oxoacetate

• Things need to know

  • Glucose

  • Pyruvatre

  • Acetyl CoA

  • Citric acid

  • Oxaloaxcetis acid

  • Glyceralidehyde 2 phosphate G3P

  • Where they aren and their carbons

  • Enzymes

  • Phoshp

Oxidative phosphorylation

• Electron transport chain in the mitochondria that powers it

  • Steps are transport and chemiosmosis

• Pathway of the electron transport chain

  • Found in inner membrane of the mitochondria

  • 4 connected complexes in the inner membrane (Cristae)

    • Most of these are proteins and all differ in electronegativity, with each one being slight more negative than the other, but all less electronegative than oxegyn

    • Carriers alternate between reducing and oxidization states at they donate electrons

    • Energy is released everytime the electrons are moved down the chain

    • The chain doesn’t generate any ATP directly

      • Releasing energy a little bit at a time so it’s manageable

• Next step is chemiosmosis

  • Energy released get used o pump protons out of the mitochondria and then come back in

    • Only path for hydrogen to get back across the membrane through the protein complex calles ATP synthase

    • Uses energy in the protein gradient to phosphorolate ATP

    • Energy stored here could the redox reaction of the electron transport chain to ATP synthetic

      • This is referred to as a proton motive force,

energy flows through glucose to nadh o the electron transport chain to proton motive force to atp

About 34% of the energy in a glucose molecule is transferred to ATP during cellular respiration