What do you remember?

Membrane held in place by mostly hydrophobic interaction “Fluid Mosaic Model” Membrane held in place by mostly hydrophobic interaction Most lipids and some proteins drift randomly

Factors influencing fluidity 1) Phospholipid structure

2)

flowchart

Transport What types of molecules can do this? Passive transport Diffusion Down concentration gradient Simple vs. Facilitated Simple diffusion  molecules diffuse through the lipid portion What types of molecules can do this?

Facilitated Diffusion Requires help (Protein) Why would it need help? Examples: carrier/transport proteins ion channels gated ion channels aquaporins

Osmosis Diffusion of water -through a selectively permeable membrane Uses aquaporins Comparative terms Hypertonic Hypotonic Isotonic ALWAYS refer to SOLUTE concentration

Which direction will water move? What will happen to fluid levels? B B A Selectively permeable membrane Which side has a higher solute concentration? Which side has a higher water concentration? Which side is hypertonic? Which side is hypotonic?

Active Transport Movement of a solute against its concentration gradient -many times use ATP as energy ex: Na+/K+ pump http://highered.mheducation.com/sites/9834092339/student_view0/chapter38/how_the_sodium_potassium_pump_works.html Proton pump is major electrogenic pump in plants, fungi, and bacteria

Cotransport Use the concentration gradient produced by one pump to move a second molecule against its concentration gradient high sucrose low sucrose Ex: Plants use this to load sugar (from photosynthesis) into specialized cells (phloem) so it can be transported throughout the plant http://highered.mheducation.com/sites/9834092339/student_view0/chapter38/cotransport__symport_and_antiport_.html

https://highered. mheducation. com/olcweb/cgi/pluginpop. cgi https://highered.mheducation.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120068/bio02.swf::Endocytosis%20and%20Exocytosis

Apply to a functioning neuron http://highered.mheducation.com/sites/0072495855/student_view0/chapter14/animation__the_nerve_impulse.html

Resting potential  charge difference on either side of membrane

Na+ is main cation Negatively charged proteins are main anions K+ is main cation

Na+ channels behind (toward the cell body) cannot be reactivated for a period of time Ensures that action potentials are one way

Saltatory conduction

https://www.youtube.com/watch?v=y6PUs4Xy_nw

Local signaling Synaptic signaling Electrical signal triggers release of neurotransmitter. Synaptic signaling Neurotransmitter diffuses across synapse. Figure 5.19-2 Local and long-distance cell signaling by secreted molecules in animals (part 2: local signaling, synaptic) Target cell

https://youtu.be/JjHMGSI_h0Q http://www.hhmi.org/biointeractive/prialt-blocks-motor-synapse-fish http://www.hhmi.org/biointeractive/prialt-blocks-pain-signaling-mice

Local signaling Target cells Paracrine signaling -ex: growth factors used to stimulate target cells to grow and divide Secreting cell Figure 5.19-1 Local and long-distance cell signaling by secreted molecules in animals (part 1: local signaling, paracrine) Secretory vesicles Local regulator -ex: growth factor

Long-distance signaling  endocrine signaling …hormones!!! Target cell specifically binds hormone. Endocrine cell Hormone travels in bloodstream. Figure 5.19-3 Local and long-distance cell signaling by secreted molecules in animals (part 3: long distance signaling, endocrine) Blood vessel

Cell signaling occurs in 3 stages EXTRA- CELLULAR FLUID CYTOPLASM Plasma membrane Reception Receptor Figure 5.20-s1 Overview of cell signaling (step 1) Signaling Molecule -ligand

EXTRA- CELLULAR FLUID CYTOPLASM Plasma membrane Reception Transduction Receptor 1 2 3 Relay molecules Figure 5.20-s2 Overview of cell signaling (step 2) Signaling molecule

EXTRA- CELLULAR FLUID CYTOPLASM Plasma membrane Reception Transduction Response Receptor 1 2 3 Activation Relay molecules Figure 5.20-s3 Overview of cell signaling (step 3) Signaling molecule

Reception Gate closed Ions Signaling molecule (ligand) Plasma membrane Ligand-gated ion channel receptor Figure 5.22-s1 Ion channel receptor (step 1)

Gate open Gate closed Ions Signaling molecule (ligand) Cellular response Plasma membrane Ligand-gated ion channel receptor Figure 5.22-s2 Ion channel receptor (step 2)

Gate open Gate closed Ions Signaling molecule (ligand) Cellular response Plasma membrane Ligand-gated ion channel receptor Gate closed Figure 5.22-s3 Ion channel receptor (step 3)

G protein-coupled receptor Inactive enzyme Signaling molecule Activated GPCR Figure 5.21-s1 GTP Plasma membrane Activated G protein CYTOPLASM G protein-coupled receptor -large class of receptors that have a variety of responses -similar in structure … evolved early in life’s history Figure 5.21-s1 A G protein-coupled receptor (GPCR) in action (step 1)

Activated G protein and activated protein is the transduction Inactive enzyme Signaling molecule Activated GPCR Figure 5.21-s2 GTP Plasma membrane Activated G protein CYTOPLASM Activated enzyme Figure 5.21-s2 A G protein-coupled receptor (GPCR) in action (step 2) GTP Activated G protein and activated protein is the transduction Cellular response

Why can aldosterone do this? Hormone (aldosterone) EXTRA- CELLULAR FLUID Receptor inside cell Why can aldosterone do this? Figure 5.23 Plasma membrane Receptor protein Hormone- receptor complex Target cells are kidney Cause Na+ to be reabsorbed into the blood Result on blood volume and pressure? Figure 5.23 Steroid hormone interacting with an intracellular receptor DNA mRNA New protein NUCLEUS CYTOPLASM

Many signal cascades utilize protein kinases Kinases phosphorylate other molecules (often proteins) Responses can be amplified https://media.pearsoncmg.com/bc/bc_campbell_biology_7/media/interactivemedia/activities/load.html?11&C

Phosphorylation cascade Signaling molecule Activated relay molecule Receptor Inactive protein kinase 1 Active protein kinase 1 Inactive protein kinase 2 Phosphorylation cascade ATP ADP P Active protein kinase 2 Figure 5.24 A phosphorylation cascade PP P i Inactive protein ATP ADP P Active protein Cellular response PP P i

Ex: breaking down glycogen First messenger (signaling molecule such as epinephrine) Adenylyl cyclase G protein GTP G protein-coupled receptor ATP Second messenger cAMP https://media.pearsoncmg.com/bc/bc_campbell_biology_7/media/interactivemedia/activities/load.html?11&D Figure 5.25 cAMP as a second messenger in a G protein signaling pathway Protein kinase A Cellular responses Ex: breaking down glycogen

Response could be activated enzyme or turning on a gene Growth factor Reception Figure 5.26 Receptor Phosphorylation cascade Transduction CYTOPLASM Inactive transcription factor Active transcription factor Figure 5.26 Nuclear response to a signal: the activation of a specific gene by a growth factor Response P DNA Gene NUCLEUS mRNA

Other roles of membrane proteins Signaling molecule Figure 5.7 Receptor Enzymes ATP Signal transduction (a) Transport (b) Enzymatic activity (c) Signal transduction Figure 5.7 Some functions of membrane proteins Glyco- protein (d) Cell-cell recognition (e) Intercellular joining (f) Attachment to the cytoskeleton and extra- cellular matrix (ECM)

Intercellular joining Examples in animal cells -tight junctions -gap junctions -desmosomes

Prevent leakage of fluid from between cells Tight Junctions Prevent leakage of fluid from between cells

Function like rivets, anchoring cells together Function like rivets, anchoring cells together. Membrane proteins are attached to intermediate filaments (part of cytoskeleton). Found in cells that undergo mechanical stress (epithelial in intestines, skin)

Gap Junctions Allow for passage of molecules from cytoplasm of one cell to the next. Allows for direct communication. Found in cardiac muscle and some neurons. Speeds impulse transmission

Cardiac muscle cells

Animal junctions review

Plant cell junctions