EL: INTRODUCTION TO CELL STRUCTURE AND FUNCTION, WITH A FOCUS ON THE PLASMA MEMBRANE MEMBRANES AND CELL ORGANELLES 1

EL: INTRODUCTION TO CELL EL: INTRODUCTION TO CELL STRUCTURE AND FUNCTION, STRUCTURE AND FUNCTION,

WITH A FOCUS ON THE WITH A FOCUS ON THE PLASMA MEMBRANEPLASMA MEMBRANE

MEMBRANES AND CELL MEMBRANES AND CELL ORGANELLESORGANELLES 1 1

CELL STRUCTURE: CELL STRUCTURE: MEETING THE NEEDS OF MEETING THE NEEDS OF

MOLECULESMOLECULES Molecules need to:Molecules need to:

– move in and around cell at a certain rate move in and around cell at a certain rate to reach sites of specific activity (ie where to reach sites of specific activity (ie where they will react with other molecules)they will react with other molecules)

– be in adequate concentrations (ie there be in adequate concentrations (ie there needs to be enough of them) for chemical needs to be enough of them) for chemical reactions to occur at the right rate.reactions to occur at the right rate.

Cell structure therefore needs to facilitate Cell structure therefore needs to facilitate the movement of molecules and maintain the movement of molecules and maintain them in adequate concentrations to maintain them in adequate concentrations to maintain cell function (ie so the cell doesn’t die)cell function (ie so the cell doesn’t die)

The Surface area The Surface area conundrumconundrum

Cells need to maximise their surface Cells need to maximise their surface area to ensure the rapid movement area to ensure the rapid movement of moleculesof molecules

Problem:Problem:– As volume increases, surface area As volume increases, surface area

decreases!decreases!– How do cells deal with this?How do cells deal with this?

Membranes!Membranes!

Types of cellsTypes of cells ProkaryoticProkaryotic

– Very small: less Very small: less than 2than 2m in m in diameterdiameter

– Lack internal Lack internal compartmentscompartments

– Bacteria and Bacteria and archaeansarchaeans

EukaryoticEukaryotic

– Much larger: 10-Much larger: 10-100100m in m in diameterdiameter

– More complex More complex structure – structure – compartments compartments called organellescalled organelles

– Animals, plants, Animals, plants, fungi and protistsfungi and protists

OrganellesOrganelles Large eukaryotic cells Large eukaryotic cells

increase their increase their surface areasurface area by having by having folded folded membranes membranes and internal and internal compartments called compartments called organellesorganelles

Organelles also allow Organelles also allow differentdifferent chemical reactions chemical reactions to occur at the to occur at the same time same time in in differentdifferent places without places without interfering with each otherinterfering with each other

Organelles maintain the Organelles maintain the concentrationconcentration of of moleculesmolecules at levels that at levels that ensure they will ensure they will reactreact with with each other at each other at optimum optimum ratesrates

CELL STRUCTURECELL STRUCTURE

We are now going to learn about the We are now going to learn about the structure of eukaryotic cells and their various structure of eukaryotic cells and their various organelles in the context of cellular organelles in the context of cellular processes.processes.

What is a cell?What is a cell?

CELL BOUNDARY CELL BOUNDARY (PLASMA MEMBRANE)(PLASMA MEMBRANE)

INTRACELLULAR AQUEOUS

ENVIRONMENT – CYTOSOL or CYTOPLASM

EXTRACELLULAR AQUEOUS

ENVIRONMENT

A fluid filled compartment containing atoms and molecules

Cell membrane - structureCell membrane - structureA plasma membrane is an ultra thin and pliable layer with an average thickness of less than 0.01 μm (0.00001 mm).

Cell membrane - structureCell membrane - structure Called fluid mosaic modelCalled fluid mosaic model Lipids are the fluid part of the Lipids are the fluid part of the

membranemembrane Proteins are the mosaic part of the Proteins are the mosaic part of the

membranemembrane

Cell membrane - Cell membrane - functionsfunctions

Define cell boundaryDefine cell boundary

Provide permeability barrier (acts like a Provide permeability barrier (acts like a sieve)sieve)

Provide sites for specific functionsProvide sites for specific functions

Regulate transport of solutesRegulate transport of solutes

Detect electrical and chemical signalsDetect electrical and chemical signals

Assists in cell to cell communicationAssists in cell to cell communication

Summary: crossing the cell Summary: crossing the cell membranemembrane

Type Description Molecules

Diffusion

Osmosis

Facilitated diffusion – carrier proteins

Facilitated diffusion – channel proteins

Active transport

Endo/Exocytosis

1. Diffusion

The movement of molecules from areas of high solute concentration to area of low

solute concentration.

i.e.. Down the concentration gradient.

No energy is involved!

Diffusion depends Diffusion depends on…on…

PermeabilityPermeability

Surface AreaSurface Area

Concentration GradientConcentration Gradient

Distance of DiffusionDistance of Diffusion

Which molecule will diffuse?

Fick’s Fick’s Diffusion Diffusion

LawLaw

Surface area of membrane X

Difference in concentration across the membrane

Length of the diffusion path (thickness of the membrane)

Ways to increase Ways to increase diffusiondiffusion

Increasing concentrationIncreasing concentrationIncreasing temperatureIncreasing temperatureIncreasing surface areaIncreasing surface area

Permeable membranePermeable membrane

If the membrane is permeable to both the solute and the solvent, the pattern of

diffusion is unchanged.

Concentration GradientsConcentration Gradients

DiffusionDiffusion

High concentration

Low concentration

No net movement!No net movement!

Once diffusion is complete the Once diffusion is complete the molecules keep moving but molecules keep moving but

the overall distribution the overall distribution remains constant = remains constant =

equilibrium.equilibrium.

Partially Permeable Partially Permeable MembraneMembrane

If the membrane is partially permeable, the solvent can move through but the solute

cannot.


Partially permeable membranePartially permeable membrane

High concentration

Low concentration

2. Osmosis2. Osmosis

A special type of diffusion!A special type of diffusion!

Add SoluteThe solute cannot cross the membrane. To try and balance the concentrations, the water molecules

move to dilute the solution.

Water molecules

Solute

The solute cannot cross the membrane. To try and balance the concentrations, the water molecules move to dilute the most concentrated solution.

High concentration solute

Low concentration solute

Osmotic GradientOsmotic Gradient

Concentrated solute

Dilute solute

The pressure that makes the water move is called the osmotic pressure.

Isotonic = extra and intracellular fluid are same concentration and there will be no net movement of water

Hypertonic = extracellular fluid higher concentration than intracellular fluid and water will diffuse out of cells

Hypotonic = extracellular fluid lower concentration than intracellular fluid and water will diffuse into cell

The net movement of The net movement of water from a region of water from a region of

low solute concentration low solute concentration to a region of high to a region of high

solute concentration is solute concentration is called:called:

A.A. OsmosisOsmosis

B.B. DiffusionDiffusion

C.C. Facilitated diffusionFacilitated diffusion

D.D. Active transportActive transport

ActivityActivity

Complete chapter 1 quick check Complete chapter 1 quick check questions and booklet questions to questions and booklet questions to hand at the end of the weekhand at the end of the week

Put in your PLJ to join wiki space and Put in your PLJ to join wiki space and post on the discussion boardpost on the discussion board

ReflectionReflection

What do you need to go over What do you need to go over thouroughly before your SAC this thouroughly before your SAC this week?week?

Most molecules are too large or too polar Most molecules are too large or too polar to cross membrane by simple diffusionto cross membrane by simple diffusion

Protein assisted movement Protein assisted movement downdown a a concentration gradient – concentration gradient – facilitated facilitated diffusion diffusion can occur in a few different ways can occur in a few different ways

HIGH

LOW

CONCENTRATION GRADIENT

3. Facilitated Diffusion3. Facilitated Diffusion

Facilitated Diffusion

Special channels in the membrane help the diffusion. This channel or carrier mediated movement is selective

and can become saturated. This may inhibit the movement of another molecule. No energy is used.

Facilitated diffusion: carrier Facilitated diffusion: carrier proteinprotein

The molecule binds to its carrier protein, potentially changing its shape, and is carried to the other side

Facilitated diffusion: channel Facilitated diffusion: channel proteinprotein

Channel proteins form pores in the membrane that fill with water and dissolve hydrophillic molecules.

Both simple diffusion Both simple diffusion and facilitated diffusion and facilitated diffusion

involve:involve:A.A. Energy expenditure by the cellEnergy expenditure by the cell

B.B. Movement of a substance down Movement of a substance down its concentration gradientits concentration gradient

C.C. A protein in the plasma A protein in the plasma membrane acting as a carrier membrane acting as a carrier moleculemolecule

D.D. A substance moving from A substance moving from outside to inside a cell across outside to inside a cell across the membrane.the membrane.

4. Active transport4. Active transport

When the cell spends energy When the cell spends energy to move molecules to move molecules againstagainst the concentration gradient.the concentration gradient.


Active transportActive transport

High concentration

Low concentration

Against the concentration gradient!

Transport/Carrier Transport/Carrier proteinsproteins

Form a channel for molecules to pass Form a channel for molecules to pass through.through.

They are selective, may become saturated and inhibit the movement of other

molecules.

Space filling model of rabbit calcium ATPase. Calcium ATPase is a membrane transport protein which

transfers calcium after a muscle has contracted.

Sodium-Sodium-Potassium Potassium

PumpsPumpsThe The sodium-sodium-

potassium potassium pumppump is a protein is a protein in the membrane in the membrane that exchanges that exchanges

sodium ions (Nasodium ions (Na++) ) for potassium ions for potassium ions

(K(K++) across the ) across the membrane.membrane.

Extracellular fluid

Plasma membrane

Cell cytoplasm

Carrier protein

ATPATP

NaNa++

Na+ moves to its binding site

NaNa++

NaNa++

NaNa++

KK++

KK++

KK++

Proton pumpsProton pumps use the energy use the energy

from ATP to from ATP to move move hydrogen hydrogen ionsions (H (H++) from ) from

inside the cell to inside the cell to the outside. the outside.

ProtonProtonPumpsPumps

Extracellular fluid

Plasma membrane

Cell cytoplasm

Carrier protein

ATPATP HH++

HH++

HH++

HH++HH++

HH++

HH++

Coupled transportCoupled transport is also called is also called co-co-

transporttransport..Plant cells use the Plant cells use the hydrogen gradient hydrogen gradient created by proton created by proton pumps to actively pumps to actively transport nutrients transport nutrients

into the cell.into the cell.

Coupled Coupled TransportTransport

Sucrose

Extracellular fluid

Plasma membrane

Cell cytoplasm

Diffusion of hydrogen ions down their

concentration gradient

HH++

HH++

HH++

HH++

HH++

Carrier protein

Summary-Membrane PumpsSummary-Membrane PumpsMembrane pumps are proteins,which require energy Membrane pumps are proteins,which require energy (often as ATP) to transport molecules across the cell (often as ATP) to transport molecules across the cell membrane.membrane.

..

HH++

HH++

HH++

HH++

HH++

HH++

KK++

NaNa++

NaNa++NaNa++

NaNa++

KK++

KK++

Extracellular fluid

Plasma membrane

Cell cytoplasm

ATPATP ATPATP

HH++

HH++

The activity of pumps may be The activity of pumps may be coupled, e.g. the accumulation of Hcoupled, e.g. the accumulation of H++ from the proton pump is used to drive from the proton pump is used to drive the transport of sucrose against its the transport of sucrose against its concentration gradient.concentration gradient.

The role of proteins and The role of proteins and protein complexes in the protein complexes in the plasma membrane of a plasma membrane of a

cell includes their role as:cell includes their role as:A.A. A receptor proteinA receptor protein

B.B. A channel or poreA channel or pore

C.C. An antigenAn antigen

D.D. All of the aboveAll of the above

5. Cytosis5. Cytosis

When the cell spends energy When the cell spends energy to move LARGE molecules.to move LARGE molecules.

Moving large moleculesMoving large molecules Sometimes, large molecules need to be moved around in the cell, stored within, or Sometimes, large molecules need to be moved around in the cell, stored within, or

moved outside the cellmoved outside the cell

To do this, cells make very small containers or sacs called To do this, cells make very small containers or sacs called vesicles vesicles from the plasma from the plasma membranemembrane

Transporting out of the cell: Transporting out of the cell: exocytosisexocytosis

Transporting into of the cell: Transporting into of the cell: endocytosisendocytosis

Active Transport: Active Transport: CytosisCytosis

Membrane-bound Membrane-bound vesicles or vesicles or

vacuoles are vacuoles are formed by formed by infolding infolding

(invagination) or (invagination) or outfolding outfolding

(evaginated) to (evaginated) to transport transport

substances across substances across the membrane.the membrane.

This cell is carrying out a form of endocytosis called pinocytosis in which the plasma membrane forms invaginations to enclose liquids and bring them into the cell.

Plasma membrane folding inwards

Membrane-bound vesicle

EndocytosisEndocytosisDuring endocytosis During endocytosis

the plasma the plasma membrane membrane

invaginatesinvaginates (folds (folds in) around the in) around the

molecules to be molecules to be transported into transported into

the cell. the cell.

Pinocytosis


Phagocytosis

CD

C

Solid particle

EndocytosisEndocytosisPlasma

membrane

Cell cytoplasm

Materials that are to be collected and brought into the cell are engulfed by an invagination of the plasma membrane.

1

Vesicle buds off from the plasma membrane.

2

The vesicle carries molecules into the cell. The contents may then be digested by enzymes delivered to the vacuole by lysosomes.

3

Types of endocytosis:Types of endocytosis:

phagocytosisphagocytosis: the engulfment of solid : the engulfment of solid particles. particles.

pinocytosispinocytosis: the engulfment of liquid : the engulfment of liquid particles.particles.

receptor mediatedreceptor mediated: engulfment of : engulfment of specific particles according to membrane specific particles according to membrane receptors.receptors.

PhagocytosisPhagocytosis (cell eating)(cell eating)

The particles are The particles are contained within a contained within a

membrane enclosed membrane enclosed sac (a sac (a vacuolevacuole).).

Digestion of the particles Digestion of the particles occur when the vacuole occur when the vacuole fuses with a lysosome fuses with a lysosome containing digestive containing digestive

enzymes.enzymes.

Amoeba pseudopod

Food particle

Engulfed bacterium

PinocytosisPinocytosis

Invaginations of the Invaginations of the plasma membrane plasma membrane enclose the liquid enclose the liquid

droplets within small droplets within small vesicles.vesicles.

The fluid within the The fluid within the vesicle is transferred vesicle is transferred

to the cytosol.to the cytosol.

Plasma membrane engulfing liquid substance.


Pinocytosis by a capillary endothelial cell. TEM (X12,880)

Receptor-Mediated Receptor-Mediated EndocytosisEndocytosis

The cell membrane has The cell membrane has regions of specific regions of specific

receptor proteins receptor proteins exposed to the exposed to the extracellular extracellular environment.environment.

The receptor proteins occur The receptor proteins occur in clusters (called in clusters (called

coated pitscoated pits) and have ) and have binding sites that will binding sites that will

only bind specific only bind specific molecules. molecules.

Cytoplasm

Receptor protein

Plasma membrane

Extracellular fluid

Receptor-Mediated EndocytosisReceptor-Mediated Endocytosis

Clathrin protein

Target molecule

Coated vesicle

The cytoplasmic side of the coated pit is lined with a special protein called clathrin protein, which provides membrane stability (right).

When the target molecule (ligand) binds to the receptor protein (left), a coated vesicle forms around it, allowing the molecule to be imported into the cell.

A cell that is A cell that is phagocytosing a phagocytosing a

bacteria cell could be bacteria cell could be expected to:expected to:

A.A. Have a cell wallHave a cell wall

B.B. Be expending energyBe expending energy

C.C. Be producing oxygenBe producing oxygen

D.D. Contain a chloroplastContain a chloroplast

ExocytosisExocytosisExocytosisExocytosis releases releases

molecules from the molecules from the insideinside of the cell to of the cell to outsideoutside of of

the cell. the cell.

Exocytosis occurs by fusion Exocytosis occurs by fusion of a vesicle membrane of a vesicle membrane

with the plasma with the plasma membrane. The vesicle membrane. The vesicle

contents are then contents are then released to the outside of released to the outside of

the cell.the cell. Cross section through the plasma membrane of cardiac muscle showing the presence of transport vesicles. TEM X 162,000

Transport vesicle

ExocytosisExocytosis

Vesicle carrying molecules for export moves to the perimeter of the cell.

1

Vesicle fuses with the plasma membrane.

2

The contents of the vesicle are expelled into the intercellular space (which may be into the bloodstream).

3

Plasma membranes that Plasma membranes that are able to bend and fold are able to bend and fold

are necessary for the are necessary for the movement of which movement of which

substances into or out of a substances into or out of a cell?cell?

A.A. Glucose moleculesGlucose molecules

B.B. Sodium ionsSodium ions

C.C. Fatty acid moleculesFatty acid molecules

D.D. Protein moleculesProtein molecules

The plasma membrane is partially permeable, allowing some molecules to

pass through, and preventing the passage of others.

Plasma membrane

Cell cytoplasm

There are two types of There are two types of transport in a cell.transport in a cell.1. Passive1. Passive (not requiring (not requiring

energy)energy)diffusion and facilitated diffusiondiffusion and facilitated diffusion

osmosisosmosis

2. Active2. Active or energy requiring or energy requiringActive transportActive transport

Cytosis (exocytosis, endocytosis Cytosis (exocytosis, endocytosis etc)etc)

Summary

The three types of movement The three types of movement across a membrane are correctly across a membrane are correctly

described asdescribed asXX YY ZZ

AA active active transporttransport

diffusiondiffusion facilitated facilitated diffusiondiffusion

BB active active transporttransport

facilitated facilitated diffusiondiffusion

diffusiondiffusion

CC facilitated facilitated diffusiondiffusion

active active transporttransport

diffusiondiffusion

DD diffusiondiffusion active active transporttransport

facilitated facilitated diffusiondiffusion

E

SUMMARYSUMMARY

Summary: crossing the cell Summary: crossing the cell membranemembrane

TypeType DescriptionDescription MoleculesMoleculesSimple diffusionSimple diffusion Unassisted (passive) movement of solutes down a Unassisted (passive) movement of solutes down a

concentration gradient (ie from area of concentration gradient (ie from area of high solute high solute concentrationconcentration to area of to area of low solute concentration)low solute concentration)

Small polar or non Small polar or non polar molecules, eg polar molecules, eg oxygen, carbon oxygen, carbon dioxide dioxide

OsmosisOsmosis Simple diffusion of Simple diffusion of waterwater from an area of from an area of low solute low solute concentrationconcentration to an area of to an area of high solute high solute concentrationconcentration

WaterWater

Facilitated Facilitated diffusion – diffusion – carrier proteinscarrier proteins

Protein assisted movement Protein assisted movement downdown a concentration a concentration gradient -molecule binds to its gradient -molecule binds to its carrier carrier protein, protein, potentially changing its shape, and is carried to the potentially changing its shape, and is carried to the other side other side

Charged or polar Charged or polar moleculesmolecules

Facilitated Facilitated diffusion – diffusion – channel proteinschannel proteins

Protein assisted movement Protein assisted movement downdown a concentration a concentration gradient -gradient -Channel proteins Channel proteins form pores in the form pores in the membrane that fill with water and dissolve hydrophillic membrane that fill with water and dissolve hydrophillic molecules molecules

Molecules that Molecules that dissolve in water eg dissolve in water eg ions (imp to note: ions (imp to note: channel proteins are channel proteins are selective to particular selective to particular proteins)proteins)

Active transportActive transport Protein assisted movement Protein assisted movement up (ie from low up (ie from low concentration to high concentration) concentration to high concentration) a a concentration gradient, requiring energy inputconcentration gradient, requiring energy input

Nutrients, glucose, Nutrients, glucose, waste productswaste products

Endo/ExocytosisEndo/Exocytosis Movement of large molecules into (Movement of large molecules into (endocytosiendocytosis) or s) or out of (out of (exocytosisexocytosis) the cell) the cell

Large molecules of Large molecules of groups of groups of macromolecules (eg macromolecules (eg hormones, mucus)hormones, mucus)

ACTIVITYACTIVITY

Design and make a 3D model of a Design and make a 3D model of a plasma membrane, which includes at plasma membrane, which includes at least two of the ways to cross the least two of the ways to cross the membranemembrane

This will be assessed as part of SAC 1 This will be assessed as part of SAC 1 and will be due on the first day back and will be due on the first day back next termnext term


Develop a rhyme to remember the Develop a rhyme to remember the different ways molecules cross the different ways molecules cross the plasma membrane.plasma membrane.

Homework: Work on your model and Homework: Work on your model and chapter 2 questionschapter 2 questions

EL: To complete the EL: To complete the experimental component to experimental component to

SAC 1SAC 1



How well did your group work How well did your group work together today?together today?

EL: To complete the write up of EL: To complete the write up of SAC 1SAC 1



How well did you work today?How well did you work today?

EL: TO LEARN/REVISE THE EL: TO LEARN/REVISE THE STRUCTURE AND FUNCTION STRUCTURE AND FUNCTION

OF OTHER CELL ORGANELLESOF OTHER CELL ORGANELLES

MEMBRANES AND CELL MEMBRANES AND CELL ORGANELLESORGANELLES

OrganellesOrganellesWithin the EUKARYOTIC cell, various Within the EUKARYOTIC cell, various organelles work together to:organelles work together to:move substances from one part of the cell move substances from one part of the cell to anotherto anotherprepare other substances for export from prepare other substances for export from the cell the cell

Inside the cellInside the cell Each living cell is a small compartment with Each living cell is a small compartment with

an outer boundary, the an outer boundary, the plasma membraneplasma membrane. .

Within this one compartment that makes up a Within this one compartment that makes up a living eukaryotic cell is a fluid, called living eukaryotic cell is a fluid, called cytosolcytosol, , that consists mainly of water containing that consists mainly of water containing many dissolved substances (see table 2.1, many dissolved substances (see table 2.1, page 38) and membrane-bound organelles.page 38) and membrane-bound organelles.

NB Cytoplasm = cytosol+organellesNB Cytoplasm = cytosol+organelles

ActivityActivity

In groups of 2-3, randomly select an In groups of 2-3, randomly select an organelle. Spend 10 mins coming up organelle. Spend 10 mins coming up with a way of explaining it to the with a way of explaining it to the class, which MUST be interactive (eg. class, which MUST be interactive (eg. Quiz, role play etc)Quiz, role play etc)

You have 2-5 mins to deliver your You have 2-5 mins to deliver your lessonlesson

At the end, all students should be able At the end, all students should be able to fill in following tableto fill in following table

Cell structure summaryCell structure summary

Organelle Structure (can be a picture)

Function

1.Nucleus

2.Mitochondria

3. Ribosomes

4. Endoplasmic reticulum and Golgi complex

5. Lysosomes

6. Chloroplasts

7. Cytoskeleton and extracellular matrix

NucleusNucleus

Information and control centre Information and control centre of the cellof the cell

Controls production of all Controls production of all proteins via DNA in proteins via DNA in chromosomeschromosomes

NucleusNucleus Nucleus contained within double membraned Nucleus contained within double membraned nuclear envelopenuclear envelope, which:, which:

– is continuous with the endoplasmic reticulum (helps distribute is continuous with the endoplasmic reticulum (helps distribute materials through cell)materials through cell)

– Contains numerous openings, called Contains numerous openings, called nuclear poresnuclear pores, channels for , channels for moving water solublemoving water soluble

NuceoliNuceoli in the nucleus synthesise ribosomal RNA (rRNA) and ribosomes in the nucleus synthesise ribosomal RNA (rRNA) and ribosomes

Protein pathwaysProtein pathways Eukaryotic cells have mechanisms to Eukaryotic cells have mechanisms to

assemble, package and transport assemble, package and transport proteins within a cellproteins within a cell

Protein pathways: Protein pathways: productionproduction

RIBOSOMESRIBOSOMES Proteins are synthesised on Proteins are synthesised on extremely small extremely small organelles called organelles called ribosomesribosomes

There are enormous numbers of ribosomes in a cell to make all the proteins neededThere are enormous numbers of ribosomes in a cell to make all the proteins needed

Lack a membrane and are composed of 2 sub-units – RNA and proteinLack a membrane and are composed of 2 sub-units – RNA and protein

rRNA synthesised in the nucleolus passes through nuclear pores into the cytosol and to the rRNA synthesised in the nucleolus passes through nuclear pores into the cytosol and to the ribosomes for protein synethesis ribosomes for protein synethesis

Protein pathways: Protein pathways: productionproduction

Protein pathways: Protein pathways: transporttransport

ENDOPLASMIC RETICULUM (ER)ENDOPLASMIC RETICULUM (ER) In eukaryotic cells, ribosomes are attached to membranes of the In eukaryotic cells, ribosomes are attached to membranes of the endoplasmic reticulumendoplasmic reticulum

(ER: described as rough ER(ER: described as rough ER).).

The ER is a series of folded membranes and tubules found in the cytosol.The ER is a series of folded membranes and tubules found in the cytosol.

Proteins produced by the ribosomes enter the tubules and are transported around the cellProteins produced by the ribosomes enter the tubules and are transported around the cell

Proteins may also be modified in ERProteins may also be modified in ER

Protein pathways: Protein pathways: packagingpackaging

GOLGI BODYGOLGI BODY Receives proteins from ER, where they may undergo Receives proteins from ER, where they may undergo

further modification and/or storagefurther modification and/or storage

Proteins are placed in a vesicle and transported to other Proteins are placed in a vesicle and transported to other parts of the cell or the plasma membrane for parts of the cell or the plasma membrane for exocytosisexocytosis

Protein pathways: Protein pathways: packagingpackaging

Protein secretory Protein secretory pathwaypathway

GTAC: crossing the plasma membrane presentation: crossing the plasma membrane presentation

See text figure 2.19See text figure 2.19

http://www.johnkyrk.com/er.html

Cellular recyclers: Cellular recyclers: LysosomesLysosomes

Lysosomes Lysosomes are vesicles containing powerful are vesicles containing powerful digestive enzymesdigestive enzymes

Can break down macromolecules and even Can break down macromolecules and even organelles into simpler molecules. organelles into simpler molecules.

Any material that is not reused inside the cell is Any material that is not reused inside the cell is released from the lysosome by released from the lysosome by exocytosisexocytosis into into the extracellular fluidthe extracellular fluid

In white blood cells, they also digest pathogens In white blood cells, they also digest pathogens (discussed later in Unit 3)(discussed later in Unit 3)

Cellular recyclers: Cellular recyclers: lysosomeslysosomes

http://highered.mcgraw-hill.com/olc/dl/120067/bio01.swf

Cell movements and connections: Cell movements and connections: cytoskeletoncytoskeleton

The The cytoskeleton cytoskeleton consists of a consists of a network of protein fibresnetwork of protein fibres

Fibre Function

Microtubules Movement of chromosomes, organelles, cilia and flagella

Intermediate filaments

Provide tensile strength for the attachment of cells to each other and their external environment

Microfilaments Composed of contractile filaments of actin that, together with myosin, control muscle contraction, maintain cell shape and carry out cellular movements

Cell movements and connections: cytoskeleton

Cell movements and connections: Cell movements and connections: extracellular matrixextracellular matrix

Most cells have an Most cells have an extracellular matrix extracellular matrix (ECM) (ECM) that are an integral part of the that are an integral part of the structure and function of the cell:structure and function of the cell:– eg cell wall in plantseg cell wall in plants– Bone and cartilage in animals are Bone and cartilage in animals are

connective tissues largely made up of connective tissues largely made up of ECMECM

ECM has important role in determining ECM has important role in determining shape and mechanical properties of tissues shape and mechanical properties of tissues and organsand organs

Organelles for energy: Organelles for energy: mitochondriamitochondria

Organelles for energy: Organelles for energy: mitochondriamitochondria

Small, cigar-shaped organelles found in cytosol Small, cigar-shaped organelles found in cytosol

Consists of smooth outer membrane and highly folded Consists of smooth outer membrane and highly folded inner membrane (the folds are called inner membrane (the folds are called cristae)cristae)

Fluid filled Fluid filled intermembrane spaceintermembrane space

Protein-rich fluid called Protein-rich fluid called matrixmatrix in internal space in internal space

Have own genetic material: Have own genetic material: mtDNA and RNA and mtDNA and RNA and ribosomes. ribosomes. This allows them to undergo division.This allows them to undergo division.

Organelles for energy: Organelles for energy: chloroplastschloroplasts

Chloroplasts Chloroplasts are found in green are found in green plant cells and some protists and are plant cells and some protists and are the site of the site of photosynthesisphotosynthesis

Have an inner and outer membrane Have an inner and outer membrane

Enclosed by the inner membrane is Enclosed by the inner membrane is the the stroma stroma – a gel-like enzyme-rich – a gel-like enzyme-rich matrixmatrix



Suspended in the stroma is a third Suspended in the stroma is a third membrane structure called the membrane structure called the thylakoid membranesthylakoid membranes: flat sac-like : flat sac-like structures called structures called grana grana when when grouped together into stacksgrouped together into stacks

Like mitochondria, have own genetic Like mitochondria, have own genetic material: material: DNA and RNA and DNA and RNA and ribosomesribosomes

ActivityActivity

Look at some prepared slides under the Look at some prepared slides under the microscopemicroscope

Sketch what you see and label visible Sketch what you see and label visible organellesorganelles– Make sure you use pencilMake sure you use pencil– Rule lines to label (don’t cross lines Rule lines to label (don’t cross lines

over)over)– Make sure you write the magnification Make sure you write the magnification

down (e.g. x10)down (e.g. x10)

If timer permits/HomeworkIf timer permits/Homework Complete cell webquest on Wiki and email to meComplete cell webquest on Wiki and email to me

Complete cell quiz at Complete cell quiz at www.gtac.edu.au – on – on student support pagestudent support page

Quick check qu 7-18Quick check qu 7-18

Biochallenge qu 1&3Biochallenge qu 1&3

Chapter review qu 2, 3 & 11 (& 12 if you feel like it)Chapter review qu 2, 3 & 11 (& 12 if you feel like it)


What is one thing you really What is one thing you really understood about YOUR organelle understood about YOUR organelle and one thing from another groups and one thing from another groups organelle?organelle?

EL: To learn about how cells EL: To learn about how cells connect with and connect with and

communicate with each other communicate with each other and revise for your testand revise for your test

MEMBRANES AND CELL MEMBRANES AND CELL ORGANELLESORGANELLES

Cell connection and Cell connection and communicationcommunication

Although some cells, (e.g. blood Although some cells, (e.g. blood cells), are free to move as cells), are free to move as individuals, most cells remain as individuals, most cells remain as members of a group and need to members of a group and need to communicate with each othercommunicate with each other

Animal CellsAnimal Cells

There are three different types of There are three different types of junctions in animal cells: junctions in animal cells: occluding, occluding, communicating (gap) communicating (gap) andand anchoring (desmosomes) anchoring (desmosomes) junctions junctions (see figure 2.25).(see figure 2.25).

Occluding junctions involve cell membranes coming together in contact with each other. There is no movement of material between cells.

Communicating junctions consist of protein-lined pores in the membranes of adjacent cells. The proteins are aligned rather like a series of rods in a circle with a gap down the centre and permit the passage of salt ions, sugars, amino acids and other small molecules as well as electrical signals from one cell to another.

Anchoring junctions are the most common form of junction between epithelial cells. Dense plaques of protein exist at the junction between two cells. Fine fibrils extend from each side of these plaques and into the cytosol of the two cells involved. This structure has great tensile strength and acts throughout a group of cells because of the connections fromone cell to another.

Plant cellsPlant cells Plants have rigid cell walls. Hence, plant cells have no Plants have rigid cell walls. Hence, plant cells have no

need for a structure such as the anchoring junctions need for a structure such as the anchoring junctions of animal cells.of animal cells.

Secondary walls are laid down in each cell on the Secondary walls are laid down in each cell on the cytosol side of the primary wall so that the structure cytosol side of the primary wall so that the structure across two cells is relatively wide, at least 0.1 μm across two cells is relatively wide, at least 0.1 μm thick.thick.

The junctions that exist in plant cells to allow The junctions that exist in plant cells to allow communication between adjacent cells in spite of the communication between adjacent cells in spite of the thick wall are thick wall are plasmodesmata (singular: plasmodesmata (singular: plasmodesma) plasmodesma)

Plant cellsPlant cells Because of the way in which plant cell Because of the way in which plant cell

walls are built up, the gap or pore walls are built up, the gap or pore between two cells is lined with plasma between two cells is lined with plasma membrane so that the plasma membrane so that the plasma membrane of the two cells is membrane of the two cells is continuous. continuous.

A structure that bridges the ‘gap’ is also A structure that bridges the ‘gap’ is also continuous with the smooth continuous with the smooth endoplasmic reticulum of each cell.endoplasmic reticulum of each cell.

ActivityActivity

Quick check qu 18-19Quick check qu 18-19

Biochallenge qu 2Biochallenge qu 2

In the last 15 minutes, we’ll play Cell In the last 15 minutes, we’ll play Cell Jeopardy revision game for your test Jeopardy revision game for your test next lessonnext lesson


What letter grade/% would you like What letter grade/% would you like to get on your test and how will YOU to get on your test and how will YOU make it happen?make it happen?

Documents

EL: INTRODUCTION TO CELL STRUCTURE AND FUNCTION, WITH A FOCUS ON THE PLASMA MEMBRANE MEMBRANES AND CELL ORGANELLES 1