The Cell The Basic Unit of Life.

The Cell The Basic Unit of Life

The Importance of Cells
All organisms are made of cells The cell is the simplest collection of matter that can live Cell structure is correlated to cellular function All cells are related by their descent from earlier cells

Microscopy light microscope (LM)
visible light passes through a specimen and then through glass lenses, which magnify the image Magnify up to 1000x

LE 6-2 10 m Human height 1 m Length of some nerve and muscle cells
Unaided eye Chicken egg 1 cm Frog egg 1 mm Measurements 1 centimeter (cm) = 10–2 meter (m) = 0.4 inch 1 millimeter (mm) = 10–3 m 1 micrometer (µm) = 10–3 mm = 10–6 m 1 nanometer (nm) = 10–3 µm = 10–9 m 100 µm Most plant and animal cells Light microscope 10 µm Nucleus Most bacteria Mitochondrion 1 µm Smallest bacteria Electron microscope 100 nm Viruses Ribosomes 10 nm Proteins Lipids 1 nm Small molecules Atoms 0.1 nm

Brightfield (unstained specimen)
LE 6-3a Brightfield (unstained specimen) 50 µm Brightfield (stained specimen) Phase-contrast

Differential- interference- contrast (Nomarski) Fluorescence 50 µm
LE 6-3b Differential- interference- contrast (Nomarski) Fluorescence 50 µm Confocal 50 µm

electron microscopes (EMs)
are used to study subcellular structures Two types Scanning electron microscopes (SEMs) focus a beam of electrons onto the surface of a specimen providing images that look 3D Transmission electron microscopes (TEMs) focus a beam of electrons through a specimen to study the internal structures of cells

LE 6-4 Scanning electron 1 µm microscopy (SEM) Cilia
Transmission electron microscopy (TEM) Longitudinal section of cilium Cross section of cilium 1 µm

Basic features of all cells:
Plasma membrane Selectively permeable double layer of phospholipids Semifluid substance called the cytosol Includes cytoplasm & organelles Chromosomes (carry genes) Ribosomes (make proteins)

Carbohydrate side chain
LE 6-8 Outside of cell Carbohydrate side chain Hydrophilic region Inside of cell 0.1 µm Hydrophobic region Hydrophilic region Phospholipid Proteins TEM of a plasma membrane Structure of the plasma membrane

DNA is in an unbound region called the nucleoid
Prokaryotic Cells Eukaryotic Cells Have nucleus DNA in nucleus Membrane-bound organelles Usually larger than prokaryotic cells Cell size limited by metabolic activities Include plants, animals, and fungi no nucleus DNA is in an unbound region called the nucleoid No membrane-bound organelles Include bacteria and Achaea

A thin section through the bacterium Bacillus coagulans (TEM)
LE 6-6 Pili Nucleoid Ribosomes Plasma membrane Cell wall Bacterial chromosome Capsule 0.5 µm Flagella A typical rod-shaped bacterium A thin section through the bacterium Bacillus coagulans (TEM)

Surface area increases while Total volume remains constant
5 1 1 Total surface area (height x width x number of sides x number of boxes) 6 150 750 Total volume (height x width x length X number of boxes) 1 125 125 Surface-to-volume ratio (surface area  volume) 6 1.2 6

ENDOPLASMIC RETICULUM (ER
LE 6-9a ENDOPLASMIC RETICULUM (ER Nuclear envelope Flagellum Rough ER Smooth ER Nucleolus NUCLEUS Chromatin Centrosome Plasma membrane CYTOSKELETON Microfilaments Intermediate filaments Microtubules Ribosomes: Microvilli Golgi apparatus Peroxisome Mitochondrion Lysosome In animal cells but not plant cells: Lysosomes Centrioles Flagella (in some plant sperm)

LE 6-9b Nuclear envelope Rough endoplasmic NUCLEUS reticulum Nucleolus
Chromatin Smooth endoplasmic reticulum Centrosome Ribosomes (small brown dots) Central vacuole Golgi apparatus Microfilaments Intermediate filaments CYTOSKELETON Microtubules Mitochondrion Peroxisome Plasma membrane Chloroplast Cell wall Plasmodesmata Wall of adjacent cell In plant cells but not animal cells: Chloroplasts Central vacuole and tonoplast Cell wall Plasmodesmata

The Nucleus contains most of the cell’s genes
usually the most conspicuous organelle Enclosed by nuclear envelope

LE 6-10 Nucleus Nucleus 1 µm Nucleolus Chromatin Nuclear envelope:
Inner membrane Outer membrane Nuclear pore Pore complex Rough ER Surface of nuclear envelope Ribosome 1 µm 0.25 µm Close-up of nuclear envelope Pore complexes (TEM) Nuclear lamina (TEM)

Ribosomes made of ribosomal RNA and protein protein synthesis
In the cytosol (free ribosomes) On the outside of the endoplasmic reticulum (ER) or the nuclear envelope (bound ribosomes)

Ribosomes ER Cytosol Endoplasmic reticulum (ER) Free ribosomes
Bound ribosomes Large subunit 0.5 µm Small subunit TEM showing ER and ribosomes Diagram of a ribosome

Endomembrane System Regulate protein traffic
Perform metabolic functions Components of the endomembrane system: Nuclear envelope Endoplasmic reticulum Golgi apparatus Lysosomes Vacuoles Plasma membrane components are either continuous or connected via transfer by vesicles

The Endoplasmic Reticulum (ER)
is continuous with the nuclear envelope two distinct regions of ER: Smooth ER, lacks ribosomes Rough ER with ribosomes studding its surface

Smooth ER Nuclear Rough ER envelope ER lumen Cisternae Ribosomes
Transitional ER Transport vesicle 200 nm Smooth ER Rough ER

Functions of Smooth ER Synthesizes lipids Metabolizes carbohydrates
Stores calcium Detoxifies poison

Functions of Rough ER bound ribosomes Produces proteins and membranes
distributed by transport vesicles is a membrane factory in the cell

The Golgi Apparatus consists of flattened membranous sacs called cisternae Functions of the Golgi apparatus: Modifies products of the ER Manufactures certain macromolecules Sorts and packages materials into transport vesicles

LE 6-13 Golgi apparatus cis face (“receiving” side of Golgi apparatus)
Vesicles move from ER to Golgi Vesicles coalesce to form new cis Golgi cisternae 0.1 µm Vesicles also transport certain proteins back to ER Cisternae Cisternal maturation: Golgi cisternae move in a cis- to-trans direction Vesicles form and leave Golgi, carrying specific proteins to other locations or to the plasma membrane for secretion Vesicles transport specific proteins backward to newer Golgi cisternae trans face (“shipping” side of Golgi apparatus) TEM of Golgi apparatus

Lysosomes membranous sac of hydrolytic enzymes
hydrolyze proteins, fats, polysaccharides, and nucleic acids use enzymes to recycle organelles and macromolecules a process called autophagy

Phagocytosis: lysosome digesting food
LE 6-14a Nucleus 1 µm Lysosome Lysosome contains active hydrolytic enzymes Food vacuole fuses with lysosome Hydrolytic enzymes digest food particles Digestive enzymes Plasma membrane Lysosome Digestion Food vacuole Phagocytosis: lysosome digesting food

two damaged organelles 1 µm
LE 6-14b Lysosome containing two damaged organelles 1 µm Mitochondrion fragment Peroxisome fragment Lysosome fuses with vesicle containing damaged organelle Hydrolytic enzymes digest organelle components Lysosome Digestion Vesicle containing damaged mitochondrion Autophagy: lysosome breaking down damaged organelle

Vacuoles & Vesicles membrane-bound sacs with varied functions
Food vacuoles formed by phagocytosis Contractile vacuoles found in many freshwater protists pump excess water out of cells Central vacuoles found in many mature plant cells hold organic compounds and water

Central vacuole Cytosol Tonoplast Nucleus Central vacuole Cell wall
Chloroplast 5 µm

LE Nucleus Rough ER Smooth ER Nuclear envelope

Nucleus Rough ER Smooth ER Nuclear envelope cis Golgi
Transport vesicle trans Golgi

Nucleus Rough ER Smooth ER Nuclear envelope cis Golgi
Transport vesicle Plasma membrane trans Golgi

Mitochondria & Chloroplasts
sites of cellular respiration not part of the endomembrane system found only in plants and algae the sites of photosynthesis not part of the endomembrane system

Mitochondria in nearly all eukaryotic cells smooth outer membrane
inner membrane folded into cristae creates two compartments: intermembrane space mitochondrial matrix Folding creates more surface area for enzymes that synthesize ATP

Mitochondrion Intermembrane space Outer membrane Free ribosomes in the
LE 6-17 Mitochondrion Intermembrane space Outer membrane Free ribosomes in the mitochondrial matrix Inner membrane Cristae Matrix Mitochondrial DNA 100 nm

Chloroplasts Type of plastid contain the green pigment chlorophyll
contains enzymes and other molecules that function in photosynthesis found in leaves and other green organs of plants and in algae Chloroplast structure includes: Thylakoids membranous sacs Stroma the internal fluid

LE 6-18 Chloroplast Ribosomes Stroma Chloroplast DNA Inner and outer
membranes Granum 1 µm Thylakoid

Plastids Responsible for photosynthesis
Storage of products (ie. Starch) Synthesis of molecules (ie. Fatty acids)

Peroxisomes specialized metabolic compartments single membrane
produce hydrogen peroxide and convert it to water are oxidative organelles Aid in breakdown of lipids

LE 6-19 Chloroplast Peroxisome Mitochondrion 1 µm

Cytoskeleton network of fibers extending throughout the cytoplasm
organizes the cell’s structures and activities anchors many organelles composed of: Microtubules Microfilaments Intermediate filaments

LE 6-20 Microtubule Microfilaments 0.25 µm

Roles of the Cytoskeleton
support the cell maintain cell shape interacts with motor proteins to produce motility Inside the cell, vesicles can travel along “monorails” provided by the cytoskeleton may help regulate biochemical activities

Centrosomes and Centrioles
microtubules grow out from a centrosome near the nucleus “microtubule-organizing center” In animal cells, the centrosome has a pair of centrioles

LE 6-22 Centrosome Microtubule Centrioles Longitudinal section
of one centriole Microtubules Cross section of the other centriole

Cilia and Flagella Beating controlled by microtubules
sheathed by the plasma membrane Dynein Motor protein drives the bending movements of a cilium or flagellum

LE 6-23a Direction of swimming Motion of flagella 5 µm

Direction of active stroke Direction of recovery stroke
LE 6-23b Direction of organism’s movement Direction of active stroke Direction of recovery stroke Motion of cilia 15 µm

Microfilaments (Actin Filaments)
twisted double chain of actin subunits Also have myosin if the microfilaments are used for movement bear tension, resisting pulling forces within the cell form a 3D network just inside the plasma membrane to help support the cell’s shape Bundles of microfilaments make up the core of microvilli

Microfilaments (actin filaments)
LE 6-26 Microvillus Plasma membrane Microfilaments (actin filaments) Intermediate filaments 0.25 µm

Cortex (outer cytoplasm): gel with actin network
LE 6-27b Cortex (outer cytoplasm): gel with actin network Inner cytoplasm: sol with actin subunits Extending pseudopodium Amoeboid movement

Cytoplasmic streaming
circular flow of cytoplasm within cells speeds distribution of materials within the cell In plant cells, actin-myosin interactions and sol-gel transformations drive cytoplasmic streaming

Cytoplasmic streaming in plant cells
LE 6-27c Nonmoving cytoplasm (gel) Chloroplast Streaming cytoplasm (sol) Vacuole Parallel actin filaments Cell wall Cytoplasmic streaming in plant cells

Intermediate Filaments
range in diameter from 8–12 nanometers larger than microfilaments smaller than microtubules support cell shape fix organelles in place

Extracellular Structures
These extracellular structures include: Cell walls of plants The extracellular matrix (ECM) of animal cells Intercellular junctions

Cell Walls of Plants distinguishes plant cells from animal cells
protects the plant cell maintains cell shape prevents excessive uptake of water made of cellulose fibers embedded in other polysaccharides and protein

Cell Walls of Plants Plant cell walls may have multiple layers:
Primary cell wall relatively thin and flexible Middle lamella thin layer between primary walls of adjacent cells Secondary cell wall (in some cells) added between the plasma membrane and the primary cell wall Plasmodesmata are channels between adjacent plant cells

LE 6-28 Central vacuole Plasma of cell membrane Secondary cell wall
Primary cell wall Central vacuole of cell Middle lamella 1 µm Central vacuole Cytosol Plasma membrane Plant cell walls Plasmodesmata

The Extracellular Matrix (ECM) of Animal Cells
made up of glycoproteins and other macromolecules Functions of the ECM: Support Adhesion Movement Regulation

Intercellular Junctions
facilitate contact between cells Adhesion Interaction Communication

Plants: Plasmodesmata
channels that perforate plant cell walls water and small solutes (and sometimes proteins and RNA) can pass from cell to cell

LE 6-30 Cell walls Interior of cell Interior of cell 0.5 µm
Plasmodesmata Plasma membranes

Animals: Tight Junctions, Desmosomes, and Gap Junctions
membranes of neighboring cells are pressed together prevents leakage of extracellular fluid Desmosomes (anchoring junctions) fasten cells together into strong sheets Gap junctions (communicating junctions) provide cytoplasmic channels between adjacent cells

LE 6-31 Tight junctions prevent Tight junction fluid from moving
across a layer of cells Tight junction 0.5 µm Tight junction Intermediate filaments Desmosome 1 µm Gap junctions Space between cells Plasma membranes of adjacent cells Gap junction Extracellular matrix 0.1 µm

Fluid Mosaic Model Phospholipids hydrophobic fatty acid tails
hydrophilic phosphate heads

LE 7-2 WATER Hydrophilic head Hydrophobic tail WATER

Fluidity of Membranes Phospholipids move within the bilayer
Most of the lipids, and some proteins, drift laterally Cool temperatures membranes switch from a fluid state to a solid state Membranes must be fluid to work properly Consistency of oil

Cholesterol Steroid present in cell membrane Maintains fluidity
At warm temperatures (such as 37°C) restrains movement At cool temperatures prevents tight packing

Cholesterol within the animal cell membrane
LE 7-5c Cholesterol Cholesterol within the animal cell membrane

Membrane Proteins Peripheral proteins Integral proteins not embedded
penetrate the hydrophobic core often span the membrane transmembrane proteins

LE 7-7 Fibers of extracellular matrix (ECM) Glycoprotein Carbohydrate
Glycolipid EXTRACELLULAR SIDE OF MEMBRANE Cholesterol Microfilaments of cytoskeleton Peripheral proteins Integral protein CYTOPLASMIC SIDE OF MEMBRANE

Six major functions of membrane proteins:
Transport Enzymatic activity Signal transduction Cell-cell recognition Intercellular joining Attachment to the cytoskeleton and extracellular matrix (ECM)

Transport Enzymatic activity Signal transduction Signal Enzymes
LE 7-9a Signal Enzymes Receptor ATP Transport Enzymatic activity Signal transduction

Cell-cell recognition Intercellular joining Attachment to the
LE 7-9b Glyco- protein Cell-cell recognition Intercellular joining Attachment to the cytoskeleton and extracellular matrix (ECM)

Carbohydrates Cell to cell recognition Bonded to lipids = glycolipids
Bonded to proteins = glycoproteins (more common)

Selective Permeability
Permeability factors Molecular size Solubility in lipids ex. Oxygen, carbon dioxide, steroid hormones Charge of ions Presence of carrier molecules

Carrier Molecules transport proteins channel proteins carrier proteins
bind to molecules change shape to shuttle them across the membrane

Animation: Membrane Selectivity
Diffusion Net direction of movement from areas of high to low concentration Continues until equilibrium has been met Movement continues at equal rates in both directions Animation: Membrane Selectivity Animation: Diffusion

Diffusion of one solute
LE 7-11a Molecules of dye Membrane (cross section) WATER Net diffusion Net diffusion Equilibrium Diffusion of one solute

Osmosis diffusion of water
direction of osmosis is determined by a difference in total solute concentration Movement from region of lower solute concentration to the region of higher solute concentration

Tonicity Isotonic solution: Hypertonic solution Hypotonic solution
the ability of a solution to cause a cell to gain or lose water Isotonic solution: solute concentration is the same as that inside the cell no net water movement across the plasma membrane Hypertonic solution solute concentration is greater than that inside the cell cell loses water Hypotonic solution solute concentration is less than that inside the cell cell gains water

Cells without Cell Walls
Special adaptations for osmoregulation Control of water balance Ex. Contractile vacuole in Paramecium

LE 7-14 50 µm Filling vacuole 50 µm Contracting vacuole

Cells with Cell Walls Cell walls help maintain water balance
hypotonic solution swells until the wall opposes uptake the cell is now turgid (firm) Isotonic is no net movement of water into the cell the cell becomes flaccid (limp), and the plant may wilt hypertonic environment plant cells lose water the membrane pulls away from the wall a usually lethal effect called plasmolysis

LE 7-13 Hypotonic solution Isotonic solution Hypertonic solution
Animal cell H2O H2O H2O H2O Lysed Normal Shriveled Plant cell H2O H2O H2O H2O Turgid (normal) Flaccid Plasmolyzed

Facilitated diffusion
passive solute moves down its concentration gradient Transport proteins Channel proteins Carrier proteins

LE 7-15a EXTRACELLULAR FLUID Channel protein Solute CYTOPLASM

LE 7-15b Carrier protein Solute

Animation: Active Transport
moves substances against their concentration gradient requires energy, usually in the form of ATP Integral proteins Ex. sodium-potassium pump Animation: Active Transport

Facilitated diffusion
LE 7-17 Passive transport Active transport ATP Diffusion Facilitated diffusion

Electrochemical gradient
Membrane potential voltage difference across a membrane Electrochemical gradient drives the diffusion of ions across a membrane Includes : A chemical force the ion’s concentration gradient An electrical force the effect of the membrane potential on the ion’s movement

electrogenic pump transport protein
generates the voltage across a membrane main electrogenic pump of plants, fungi, and bacteria is a proton pump

– EXTRACELLULAR + FLUID ATP – + H+ H+ Proton pump H+ – + H+ H+ – +
LE 7-18 – EXTRACELLULAR FLUID + ATP – + H+ H+ Proton pump H+ – + H+ H+ – + CYTOPLASM H+ – +

Cotransport active transport of a solute indirectly drives transport of another solute Ex. Plants - gradient of hydrogen ions generated by proton pumps drives active transport of nutrients into the cell

Sucrose-H+ cotransporter
LE 7-19 – + ATP H+ H+ – + Proton pump H+ H+ – + H+ – + H+ Diffusion of H+ Sucrose-H+ cotransporter H+ – + – + Sucrose

Exocytosis Type of active transport
transport vesicles migrate to the membrane, fuse with it, and release their contents

Three types of endocytosis:
cell takes in macromolecules by forming vesicles from the plasma membrane reversal of exocytosis involves different proteins Three types of endocytosis: Phagocytosis “cellular eating” Cell engulfs particle in a vacuole Pinocytosis “cellular drinking” Cell creates vesicle around fluid Receptor-mediated endocytosis Binding of ligands to receptors triggers vesicle formation

Phagocytosis Foreign object CYTOPLASM EXTRACELLULAR FLUID Figure 3-11
Cell membrane of phagocytic cell A phagocytic cell comes in contact with the foreign object and sends pseudopodia (cytoplasmic extensions) around it. Foreign object CYTOPLASM Pseudopodium (cytoplasmic extension) EXTRACELLULAR FLUID Figure 3-11 2 of 8 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Phagocytosis Foreign object CYTOPLASM EXTRACELLULAR FLUID Figure 3-11
Cell membrane of phagocytic cell A phagocytic cell comes in contact with the foreign object and sends pseudopodia (cytoplasmic extensions) around it. The pseudopodia approach one another and fuse to trap the material within the vesicle. Foreign object CYTOPLASM Pseudopodium (cytoplasmic extension) EXTRACELLULAR FLUID Figure 3-11 3 of 8 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Vesicle Foreign object
Phagocytosis Cell membrane of phagocytic cell A phagocytic cell comes in contact with the foreign object and sends pseudopodia (cytoplasmic extensions) around it. The pseudopodia approach one another and fuse to trap the material within the vesicle. The vesicle moves into the cytoplasm. Vesicle Foreign object CYTOPLASM Pseudopodium (cytoplasmic extension) EXTRACELLULAR FLUID Figure 3-11 4 of 8 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Phagocytosis Cell membrane of phagocytic cell Lysosomes A phagocytic cell comes in contact with the foreign object and sends pseudopodia (cytoplasmic extensions) around it. The pseudopodia approach one another and fuse to trap the material within the vesicle. The vesicle moves into the cytoplasm. Vesicle Lysosomes fuse with the vesicle. Foreign object CYTOPLASM Pseudopodium (cytoplasmic extension) EXTRACELLULAR FLUID Figure 3-11 5 of 8 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Phagocytosis Cell membrane of phagocytic cell Lysosomes A phagocytic cell comes in contact with the foreign object and sends pseudopodia (cytoplasmic extensions) around it. The pseudopodia approach one another and fuse to trap the material within the vesicle. The vesicle moves into the cytoplasm. Vesicle Lysosomes fuse with the vesicle. Foreign object This fusion activates digestive enzymes. CYTOPLASM Pseudopodium (cytoplasmic extension) EXTRACELLULAR FLUID Figure 3-11 6 of 8 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Phagocytosis Cell membrane of phagocytic cell Lysosomes A phagocytic cell comes in contact with the foreign object and sends pseudopodia (cytoplasmic extensions) around it. The pseudopodia approach one another and fuse to trap the material within the vesicle. The vesicle moves into the cytoplasm. Vesicle Lysosomes fuse with the vesicle. Foreign object This fusion activates digestive enzymes. CYTOPLASM Pseudopodium (cytoplasmic extension) The enzymes break down the structure of the phagocytized material. EXTRACELLULAR FLUID Figure 3-11 7 of 8 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Vesicle Foreign object Undissolved residue
Phagocytosis Cell membrane of phagocytic cell Lysosomes A phagocytic cell comes in contact with the foreign object and sends pseudopodia (cytoplasmic extensions) around it. The pseudopodia approach one another and fuse to trap the material within the vesicle. The vesicle moves into the cytoplasm. Vesicle Lysosomes fuse with the vesicle. Foreign object This fusion activates digestive enzymes. CYTOPLASM Pseudopodium (cytoplasmic extension) Undissolved residue The enzymes break down the structure of the phagocytized material. EXTRACELLULAR FLUID Residue is then ejected from the cell by exocytosis. Figure 3-11 8 of 8 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

RECEPTOR-MEDIATED ENDOCYTOSIS
LE 7-20c RECEPTOR-MEDIATED ENDOCYTOSIS Coat protein Receptor Coated vesicle Coated pit Ligand A coated pit and a coated vesicle formed during receptor- mediated endocytosis (TEMs). Coat protein Plasma membrane 0.25 µm

Ligands Ligand receptors CYTOPLASM
EXTRACELLULAR FLUID Ligands Receptor-Mediated Endocytosis Ligands binding to receptors Target molecules (ligands) bind to receptors in cell membrane. Ligand receptors CYTOPLASM Figure 3-10 2 of 8 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

EXTRACELLULAR FLUID Ligands Receptor-Mediated Endocytosis Ligands binding to receptors Target molecules (ligands) bind to receptors in cell membrane. Endocytosis Ligand receptors Areas coated with ligands form deep pockets in membrane surface. CYTOPLASM Figure 3-10 3 of 8 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

EXTRACELLULAR FLUID Ligands Receptor-Mediated Endocytosis Ligands binding to receptors Target molecules (ligands) bind to receptors in cell membrane. Endocytosis Ligand receptors Areas coated with ligands form deep pockets in membrane surface. Pockets pinch off, forming vesicles. Coated vesicle CYTOPLASM Figure 3-10 4 of 8 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Ligands Ligand receptors CYTOPLASM Fused vesicle and lysosome
EXTRACELLULAR FLUID Ligands Receptor-Mediated Endocytosis Ligands binding to receptors Target molecules (ligands) bind to receptors in cell membrane. Endocytosis Ligand receptors Areas coated with ligands form deep pockets in membrane surface. Pockets pinch off, forming vesicles. Coated vesicle CYTOPLASM Vesicles fuse with lysosomes. Fusion Lysosome Fused vesicle and lysosome Figure 3-10 5 of 8 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Ligands Ligand receptors CYTOPLASM Fused vesicle and lysosome
EXTRACELLULAR FLUID Ligands Receptor-Mediated Endocytosis Ligands binding to receptors Target molecules (ligands) bind to receptors in cell membrane. Endocytosis Ligand receptors Areas coated with ligands form deep pockets in membrane surface. Pockets pinch off, forming vesicles. Coated vesicle CYTOPLASM Vesicles fuse with lysosomes. Ligands are removed and absorbed into the cytoplasm. Fusion Lysosome Fused vesicle and lysosome Figure 3-10 6 of 8 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

EXTRACELLULAR FLUID Ligands Ligands binding to receptors Endocytosis
Receptor-Mediated Endocytosis Ligands binding to receptors Target molecules (ligands) bind to receptors in cell membrane. Endocytosis Ligand receptors Areas coated with ligands form deep pockets in membrane surface. Pockets pinch off, forming vesicles. Coated vesicle CYTOPLASM Vesicles fuse with lysosomes. Ligands are removed and absorbed into the cytoplasm. Fusion Detachment The membrane containing the receptor molecules separates from the lysosome. Lysosome Ligands removed Fused vesicle and lysosome Figure 3-10 7 of 8 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

EXTRACELLULAR FLUID Ligands Ligands binding to receptors Exocytosis
Receptor-Mediated Endocytosis Ligands binding to receptors Target molecules (ligands) bind to receptors in cell membrane. Exocytosis Endocytosis Ligand receptors Areas coated with ligands form deep pockets in membrane surface. Pockets pinch off, forming vesicles. Coated vesicle CYTOPLASM Vesicles fuse with lysosomes. Ligands are removed and absorbed into the cytoplasm. Fusion Detachment The membrane containing the receptor molecules separates from the lysosome. Lysosome Ligands removed Fused vesicle and lysosome The vesicle returns to the surface. Figure 3-10 8 of 8 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Cell to Cell Communication
signal-transduction pathway A signal on a cell’s surface is converted into a specific cellular response chemical messengers cell junctions directly connect the cytoplasm of adjacent cells local signaling communicate by direct contact Some animal cells

LE 11-3 Plasma membranes Gap junctions between animal cells Plasmodesmata between plant cells Cell junctions Cell-cell recognition

long-distance signaling
local regulators messenger molecules that travel only short distances Some animal cells long-distance signaling Hormones plants and animals

LE 11-4 Local signaling Long-distance signaling Target cell
Electrical signal along nerve cell triggers release of neurotransmitter Endocrine cell Blood vessel Neurotransmitter diffuses across synapse Secreting cell Secretory vesicle Hormone travels in bloodstream to target cells Local regulator diffuses through extracellular fluid Target cell is stimulated Target cell Paracrine signaling Synaptic signaling Hormonal signaling

Cell Signaling Cells receiving signals went through three processes:
Reception Transduction Response

LE 11-5_1 EXTRACELLULAR FLUID CYTOPLASM Plasma membrane Reception
Transduction Receptor Signal molecule

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

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

Reception binding between a signal molecule (ligand) and receptor
highly specific conformational change in a receptor Often the initial transduction of the signal Most signal receptors are plasma membrane proteins

LE 11-7c Signal molecule (ligand) Gate closed Ions Plasma membrane
Ligand-gated ion channel receptor Gate open Cellular response Gate closed

Transduction Multistep pathways can amplify a signal
opportunities for coordination and regulation

Multistep pathways have two important benefits:
Amplifying the signal (and thus the response) Contributing to the specificity of the response

LE 11-8 Signal molecule Receptor Activated relay molecule Inactive
protein kinase 1 Active protein kinase 1 Inactive protein kinase 2 ATP ADP Active protein kinase 2 P Phosphorylation cascade PP P i Inactive protein kinase 3 ATP ADP Active protein kinase 3 P PP P i Inactive protein ATP ADP P Active protein Cellular response PP P i

Cyclic AMP (cAMP) one of the most widely used second messengers
Adenylyl cyclase enzyme in the plasma membrane converts ATP to cAMP in response to an extracellular signal

Terminating the Signal
signal molecules leave the receptor receptor reverts to its inactive state

The Cell The Basic Unit of Life.

Similar presentations

Presentation on theme: "The Cell The Basic Unit of Life."— Presentation transcript:

Similar presentations

About project

Feedback

Log in

Auth with social network:

The Cell The Basic Unit of Life.

Similar presentations

Presentation on theme: "The Cell The Basic Unit of Life."— Presentation transcript:

Similar presentations

About project

Feedback