I. Cell Theory II. Studying cells III. Prokaryotic vs ... 120 Lectures/NVC... · 1 Chapter 6 - The...

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Chapter 6 - The Cell Outline

I. Cell TheoryII. Studying cellsIII. Prokaryotic vs EukaryoticIV. Eukaryotic

A. Animal cellsB. Plant cells

Cells

Cells are the basic unit of life

Cells maintain homeostasis

They are enclosed in a phospholipid membrane - the Plasma Membrane

Cells vary in size but there is a limit on how big a cell can be and survive

There are different types of cells –specialized cells

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Cell Theory

Cells were discovered in 1665 by Robert Hooke.

Early studies of cells were conducted by- Mathias Schleiden (1838)- Theodor Schwann (1839)

Schleiden and Schwann proposed the Cell Theory.

Cell Theory

1. All organisms are composed of cells.2. Cells are the smallest living things.3. Cells arise only from pre-existing cells.

All cells today represent a continuous line of descent from the first living cells.

5 6

Cell Size

Cell size is limited.-As cell size increases, it takes longer for material to diffuse from the cell membrane to the interior of the cell.

Small cells have a greater surface area relative to volume

Surface area-to-volume ratio: as a cell increases in size, the volume increases 10x faster than the surface area

2

Surface area increases whiletotal volume remains constant

Total surface area[sum of the surface areas(height width) of all boxsides number of boxes]

Total volume[height width length number of boxes]

Surface-to-volume(S-to-V) ratio[surface area volume]

1

5

6 150 750

1

1251251

1.26 6

Figure 6.7 Some organisms are just one cell - yeast

Multi-celled organisms have specialized cells

Blood Cells Nerve Cells

Some cells are very small

Figure 6.2 10 m

1 m

0.1 m

1 cm

1 mm

100 m

10 m

1 m

100 nm

10 nm

1 nm

0.1 nm Atoms

Small molecules

Lipids

Proteins

Ribosomes

VirusesSmallest bacteria

MitochondrionMost bacteriaNucleus

Most plant andanimal cells

Human egg

Frog egg

Chicken egg

Length of somenerve andmuscle cells

Human height

Una

ided

eye

Ligh

t mic

rosc

opy

Ele

ctro

n m

icro

scop

y

Super-resolution

microscopy

10 m

1 m

0.1 m

1 cm

1 mm

100 m Human egg

Frog egg

Chicken egg

Length of somenerve andmuscle cells

Human height

Una

ided

eye

Figure 6.2a

3

Figure 6.2b

1 mm

100 m

10 m

1 m

100 nm

10 nm

1 nm

0.1 nm Atoms

Small molecules

LipidsProteins

Ribosomes

VirusesSmallest bacteria

MitochondrionMost bacteriaNucleus

Most plant andanimal cells

Human egg

Ligh

t mic

rosc

opy

Ele

ctro

n m

icro

scop

y

Super-resolution

microscopy

1 cm

Frog egg

Copyright © 2009 Pearson Education, Inc.

As the size of a cell increase, the surface:volume ratio

1 2 3

33% 33%33%1. Increase2. Decrease3. Stays the same

Studying Cells

Microscopes1. Light microscopes Also called compound microscopes

because it uses multiple lens

2. Electron microscope Transmission electron microscopeScanning electron microscope

Microscopes

Two features determine how clearly an object is viewed:

1. Magnification = ocular lens x magnifying lens

2. Resolution – quality of lens and type of light

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Microscopes

Light microscopes can resolve structures that are 200nm apart.

Electron microscopes can resolve structures that are 0.2nm apart.

Electron Microscope

Transmission Electron Microscopes –specimens are first embedded in plastic then sliced thin

Scanning Electron Microscope – specimen is coated with film, scans surface only

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Figure 6.3a

(unstained specimen)50

m

Brightfield

Figure 6.3b

Brightfield(stained specimen)

Figure 6.3c

Phase-contrast

Figure 6.3d

Differential-interference-contrast (Nomarski)

Figure 6.3e

Fluorescence

10 m

Figure 6.3i

Cilia

2 mScanning electronmicroscopy (SEM)

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Figure 6.3j

Longitudinal sectionof cilium

Cross sectionof cilium

2 m

Transmission electronmicroscopy (TEM)

Cell fractionation

Used to study organelles Homogenize the sample Lyse the cells (break open) and the resulting

cell extract spun in a centrifuge

Centrifugal force separates extractPellet – bottom of tube, contains large

components of cell, organelles like nucleusSupernatant – liquid on top of pellet, contains

lighter components

Figure 6.4a

TECHNIQUE

Homogenization

Tissuecells

Homogenate

Centrifugation

Differentialcentrifugation

Centrifuged at1,000 g

(1,000 times theforce of gravity)

for 10 min Supernatantpoured intonext tube

20 min

60 minPellet rich innuclei andcellular debris

3 hr

Pellet rich inmitochondria(and chloro-plasts if cellsare from a plant)

Pellet rich in“microsomes”

Pellet rich inribosomes

20,000 g

80,000 g

150,000 g

TECHNIQUE (cont.)Figure 6.4b

Cell Fractionation

1000 g x 10 min = nuclei in pellet 20,000 g x 30 min = mitochondria, chloroplast 80,000 g x 60 min = microsomal fraction contains:

ER, Golgi, plasma membrane 150,000 g x 3 hr = ribosomes

To separate the ER, Golgi and plasma membrane you can use a density gradientcentrifuge

If you centrifuge cells at 80,000 g which fraction will contain the endoplasmic reticulum?

1. Pellet2. Supernate

Pellet

Supernate

50%50%

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Inner Life of a Cell - Harvard

Inner life of a cell - short version, music only

32

Cell Structures

All cells have certain structures in common.

1. genetic material – in a nucleoid or nucleus

2. cytoplasm – a semifluid matrix (fluid portion is the cytosol)

3. plasma membrane – a phospholipid bilayer

4. Ribosomes (make proteins)

The plasma membrane is a selective barrier that allows sufficient passage of oxygen, nutrients, and waste to service the volume of every cell

The general structure of a biological membrane is a double layer of phospholipids

© 2011 Pearson Education, Inc.

Plasma Membrane Figure 6.6

Outside of cell

Inside of cell0.1 m

(a) TEM of a plasmamembrane

Hydrophilicregion

Hydrophobicregion

Hydrophilicregion

Carbohydrate side chains

ProteinsPhospholipid

(b) Structure of the plasma membrane


The main component of the plasma membrane is:

1 2 3 4

25% 25%25%25%1. Trigylcerides2. Cholesterol3. Protein4. Phospholipids

Prokaryotic vs Eukaryotic

Prokaryotic – Pro (before) karyotic (nucleus)

Eukaryotic – Eu (true) karyotic (nucleus)

The presence or absence of a nucleus is the most obvious difference between these types of cells.

7

Eukaryotic cells have internal membranes that compartmentalize their functions

The basic structural and functional unit of every organism is one of two types of cells: prokaryotic or eukaryotic

Only organisms of the domains Bacteria and Archaea consist of prokaryotic cells

Protists, fungi, animals, and plants all consist of eukaryotic cells


Fimbriae

Bacterialchromosome

A typicalrod-shapedbacterium

(a)

Nucleoid

Ribosomes

Plasmamembrane

Cell wall

Capsule

Flagella A thin sectionthrough thebacterium Bacilluscoagulans (TEM)

(b)0.5 m

Figure 6.5

Figure 6.5a

A thin section through thebacterium Bacillus coagulans(TEM)

(b)

0.5 m

Prokaryotic Cells – Characteristics and Features

1. Include bacteria and archaea

2. Has no nucleus, have nucleoid region

3. Also lack membrane bound compartments (organelles)

4. Many use folds in the plasma membrane to accomplish the tasks of organelles

5. Many prokaryotic cells have cell walls

6. Some have a capsule

Prokaryotic Cells – Characteristics and Features

6. Have a plasma membrane

7. Have cytoplasm

8. Many have flagella for locomotion

9. Contain ribosomes for protein production

10. Have storage granules – contain glycogen, lipids, and phosphate compounds

11. Some can perform photosynthesis

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Prokaryotic Cells

8

Prokaryotic cells have a nucleus

1. True2. False

True

False

50%50%


Do prokaryotic cells contain ribosomes?

1 2 3

33% 33%33%1. Yes2. No3. Some do

Eukaryotic cells

Highly organized, have organelles including a nucleus. Eukaryotic cells are generally much larger than prokaryotic cells

Animal cells Plant cells Protists Fungi

Major Features of Animal Cells

Structures:

1. Plasma membrane – controls entry in/out of cell2. Cytoplasm – semi-fluid matrix outside the

nucleus, liquid portion is the cytosol3. Ribosomes - assembling polypeptide chains4. Chromosomes - DNA5. Cytoskeleton - gives shape, structure, transport6. Flagella - movement

Major Features of Animal Cells (page 79)

Membrane bound Organelles 1. Nucleus – contains the DNA 2. Mitochondria – energy production 3. Endoplasmic reticulum – modifies new polypeptide

chains (rough) and synthesizes lipids (smooth) 4. Golgi body – modifies, sorts, ships new proteins

and lipids5. Vesicles – storage, transport, digestion6. Lysosomes – digestion7. Peroxisomes – lipid metabolism, detoxification

Figure 6.8a

ENDOPLASMIC RETICULUM (ER)

RoughER

SmoothER

NuclearenvelopeNucleolusChromatin

Plasmamembrane

Ribosomes

Golgi apparatus

LysosomeMitochondrion

Peroxisome

Microvilli

MicrotubulesIntermediate filaments

Microfilaments

Centrosome

CYTOSKELETON:

Flagellum NUCLEUS

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NUCLEUS

Nuclearenvelope

NucleolusChromatin

Golgiapparatus

Mitochondrion

PeroxisomePlasma membrane

Cell wall

Wall of adjacent cell

Plasmodesmata

Chloroplast

Microtubules

Intermediatefilaments

Microfilaments

CYTOSKELETON

Central vacuole

Ribosomes

Smoothendoplasmicreticulum

Roughendoplasmic

reticulum

Figure 6.8c


BioFlix: Tour of an Animal Cell


BioFlix: Tour of a Plant Cell

Cell Membranes

1. Plasma membrane: Divides outside from inside of cell

2. Organelles: specialized membrane bound compartments

Organelles

Compartments allow the cells to keep reactive compounds from causing injury

Some membranes form vesicles that are used for transporting things

Some membranes are attached to other membranes

Organelle/feature Function

Nucleus Contains DNADNA is copied to make RNA

Ribosomes “reads” mRNA to assemble amino acids into a polypeptide chain

Rough Endo Ret Polypeptide chain that are to be exported or membrane bound are processed here

Golgi complex Further processes and sorts proteins to be exported or membrane bound

Vesicles Transports proteins

Protein Production/Synthesis

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The eukaryotic cell’s genetic instructions are housed in the nucleus and carried out by the ribosomes

The nucleus contains most of the DNA in a eukaryotic cell

Ribosomes use the information from the DNA to make proteins


Nucleus

Nucleus protects DNA

Separates DNA from rest of cell

Place where DNA replicates itself

Place where DNA is copied to make RNA

The Nucleus: Information Central

The nucleus contains most of the cell’s genes and is usually the most conspicuous organelle

The nuclear envelope encloses the nucleus, separating it from the cytoplasm

The nuclear membrane is a double membrane; each membrane consists of a lipid bilayer


Nucleus

Rough ER

Nucleolus

Chromatin

Nuclear envelope:Inner membraneOuter membraneNuclear pore

Chromatin

Ribosome

Porecomplex

Close-upof nuclearenvelope

Figure 6.9a

Figure 6.9b

Nuclear envelope:

Inner membraneOuter membraneNuclear pore

Surface of nuclearenvelope

1 mFigure 6.9c

Pore complexes (TEM)

0.25

m

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Pores regulate the entry and exit of molecules from the nucleus

The shape of the nucleus is maintained by the nuclear lamina, which is composed of protein


In the nucleus, DNA is organized into discrete units called chromosomes

Each chromosome is composed of a single DNA molecule associated with proteins

The DNA and proteins = histones are together called chromatin

Chromatin condenses to form discrete chromosomes as a cell prepares to divide

The nucleolus is located within the nucleus and is the site of ribosomal RNA (rRNA) synthesis


Parts of the Nucleus

2. Nucleolus – dense area in the nucleus is where rRNA are produced and ribosomesare assembled

3. Nucleoplasm – area within nucleus

Ribosomes: Protein Factories

Ribosomes are particles made of ribosomal RNA and protein

Ribosomes carry out protein synthesis in two locations In the cytosol (free ribosomes) On the outside of the endoplasmic reticulum or the

nuclear envelope (bound ribosomes)


Ribosomes

Has two components: a small subunit and a large subunit

Each subunit is made up of strands of rRNA and many proteins

The ribosome is like the workbench for assembling polypeptide chains. It is here that amino acids are bound together with a peptide bond.

Figure 6.10

0.25 m

Free ribosomes in cytosol

Endoplasmic reticulum (ER)

Ribosomes bound to ERLargesubunit

Smallsubunit

Diagram of a ribosomeTEM showing ER andribosomes

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The endomembrane system regulates protein traffic and performs metabolic functions in the cell

Components of the endomembrane system Nuclear envelope Endoplasmic reticulum Golgi apparatus Lysosomes Vacuoles Plasma membrane

These components are either continuous or connected via transfer by vesicles


The Endoplasmic Reticulum: Biosynthetic Factory

The endoplasmic reticulum (ER) accounts for more than half of the total membrane in many eukaryotic cells

The ER membrane is continuous with the nuclear envelope

There are two distinct regions of ER Smooth ER, which lacks ribosomes Rough ER, surface is studded with ribosomes


Endoplasmic reticulum

Network of folded internal membranes located in the cytoplasm

Attached to nucleus

Lumen = space inside endoplasmic reticulum

Figure 6.11 Smooth ER

Rough ER

ER lumen

CisternaeRibosomes

Smooth ERTransport vesicle

Transitional ER

Rough ER 200 nm

Nuclearenvelope

Functions of Smooth ER

The smooth ER Synthesizes lipids Metabolizes carbohydrates Detoxifies drugs and poisons Stores calcium ions


Functions of Rough ER

The rough ER

Has bound ribosomes

Creates transport vesicles


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Rough Endoplasmic Reticulum (RER)

Ribosomes that are producing polypeptide chains for export or to be embedded in membranes dock with the surface of the RER

The growing polypeptide chain enters the lumen of the RER

Functions of Rough Endoplasmic Reticulum (RER)

In the RER the polypetide chain is folded

Enzymes called molecular chaperones aid in the folding of the polypeptide chains into proteins

Some of the polypeptide chains may get modified here “tagged” with carbohydrate chain = glycoproteins

The polypeptide chains/proteins are put into transport vesicles

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 Produces lysosomes

The Golgi Apparatus: Shipping and Receiving Center


Figure 6.12

cis face(“receiving” side ofGolgi apparatus)

trans face(“shipping” side ofGolgi apparatus)

0.1 m

TEM of Golgi apparatus

Cisternae

V Cell Movie

Golgi – Protein Trafficking


All polypeptide chains go to the RER

1 2

50%50%1. True2. False

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Protein Production - Overview1. DNA in the nucleus are the instructions for making

protein

2. A copy of the DNA is made = mRNA

3. mRNA leaves the nucleus

4. mRNA docks with a ribosome to assemble a chain of amino acids.

5. tRNA brings amino acids to ribosomes

6. At the ribosome the amino acids are linked together with a peptide bond to form a polypeptide chain

Protein Production Cont

7. Ribosome with the growing polypeptide chain docks with the rough endoplasmic reticulum if the protein is to be exported or embedded in a membrane

8. The polypeptide chain enters the lumen of the RER where they are folded and may get a carbohydrate “tag” attached to it

9. The RER buds off a transport vesicles that can carry the newly formed proteins to the golgi

Protein Production Cont

10. The golgi processes, sorts, packages proteins and lipids from the RER and SER

11. Proteins that are exported are shipped in transport vesicles to the plasma membrane

12. Proteins may be put into lysosomes

13. Proteins that are membrane bound are embedded in the transport vesicles membrane

Cytosolic proteins

Proteins that are not shipped out of cell are made on free floating ribosomes

Chaperone proteins fold the proteins in the cytosol

Lysosomes

Produced by the Golgi

Lysosomes are small membrane bound sacs that contain digestive enzymes. The pH is relatively acidic (pH 5) in the lysosomes.

Because the lysosomes are acidic and contain digestive enzymes, their contents must be kept separate from the rest of the cell

Lysosomes

1. Contain strong acids and enzymes

2. Engulf molecules and digest them or

3. Fuse with other organelles and vesicles to destroy them

4. Can fuse with plasma membrane to expel waste

5. Destroy bacteria

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Some types of cell can engulf another cell by phagocytosis; this forms a food vacuole

A lysosome fuses with the food vacuole and digests the molecules

Lysosomes also use enzymes to recycle the cell’s own organelles and macromolecules, a process called autophagy


Fig. 4.14


Animation: Lysosome FormationRight-click slide / select “Play”

Figure 6.13

Nucleus

Lysosome

1 m

Digestiveenzymes

Digestion

Food vacuole

LysosomePlasma membrane

(a) Phagocytosis

Vesicle containingtwo damagedorganelles

1 m

Mitochondrionfragment

Peroxisomefragment

(b) Autophagy

Peroxisome

VesicleMitochondrion

Lysosome

Digestion

Scavenger cells

Throughout the body there are scavenger cells that engulf bacteria, foreign material or old cellular material

Tay-Sachs Disease

Tay-Sachs is a hereditary disease –

people with this disease don’t have an enzyme normally found in lysosomes that breaks down lipids in nerve cells.

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Vacuoles: Diverse Maintenance Compartments

Plant cell, protists, and fungal cells may have one or several vacuoles, derived from endoplasmic reticulum and Golgi apparatus


Food vacuoles are 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


Vacuoles: Diverse Maintenance Compartments


Video: Paramecium Vacuole

Figure 6.14

Central vacuole

Cytosol

Nucleus

Cell wall

Chloroplast

Centralvacuole

5 m

Central Vacuole in Plants

Plant central vacuoles Large area of cell space – up to 90% Fluid filled with water, amino acids, sugars,

H+ ions, and wastes. Stores nutrients Digests wastes – similar to lysosomes in

animal cells

The Endomembrane System: A Review

The endomembrane system is a complex and dynamic player in the cell’s compartmental organization


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Figure 6.15-1

Smooth ER

Nucleus

Rough ER

Plasmamembrane

Figure 6.15-2

Smooth ER

Nucleus

Rough ER

Plasmamembrane

cis Golgi

trans Golgi

Figure 6.15-3

Smooth ER

Nucleus

Rough ER

Plasmamembrane

cis Golgi

trans Golgi

Mitochondria and chloroplasts change energy from one form to another

• Mitochondria are the sites of cellular respiration, a metabolic process that uses oxygen to generate ATP

Chloroplasts, found in plants and algae, are the sites of photosynthesis


Mitochondria and chloroplasts have similarities with bacteria Enveloped by a double membrane Contain free ribosomes and circular DNA

molecules Grow and reproduce somewhat independently in

cells


The Evolutionary Origins of Mitochondria and Chloroplasts

The Endosymbiont theory An early ancestor of eukaryotic cells engulfed a

nonphotosynthetic prokaryotic cell, which formed an endosymbiont relationship with its host The host cell and endosymbiont merged into a

single organism, a eukaryotic cell with a mitochondrion At least one of these cells may have taken up a

photosynthetic prokaryote, becoming the ancestor of cells that contain chloroplasts


The Evolutionary Origins of Mitochondria and Chloroplasts

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NucleusEndoplasmicreticulum

Nuclear envelope

Ancestor ofeukaryotic cells(host cell)

Engulfing of oxygen-using nonphotosyntheticprokaryote, whichbecomes a mitochondrion

Mitochondrion

Nonphotosyntheticeukaryote

Mitochondrion

At leastone cell

Photosynthetic eukaryote

Engulfing ofphotosyntheticprokaryote

Chloroplast

Figure 6.16 Mitochondria

Most all Eukaryotic cells (plants, animals, fungi and protists) contain mitochondria

Produces energy for the cell (ATP)

Cells that require lots of energy have lots of mitochondria (liver cells can have over 1000 mitochondria

Requires oxygen = site of aerobic respiration

Important in apoptosis (programmed cell death)

Mitochondria - Structure

Bound by a double membrane Forms two compartments Outer membrane faces cytoplasm Inner membrane folded forming cristae which

increases surface area The cristae contain many enzymes and other proteins

important for cellular respiration Intermembrane space is between outer and inner

membrane Mitochondria contain its own DNA

Mitochondria

The double membrane structure is important in its function (cellular respiration) and to keep dangerous oxygen species and free radicals from damaging the cells.

Apoptosis

Apoptosis is planned cell death

In contrast, necrosis is uncontrolled cell death

When a cell is no longer needed or is not functioning properly, the cell will undergo apoptosis.

Apoptosis

Mitochondria can initiate apoptosis in several ways – one way is through a cascade of enzymatic reactions.

When the mitochondria gets the signal to begin apoptosis it releases cytochrome c, which activates a group of enzymes called caspases

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Figure 6.17

Intermembrane space

Outermembrane

DNA

Innermembrane

Cristae

Matrix

Freeribosomesin themitochondrialmatrix

(a) Diagram and TEM of mitochondrion (b) Network of mitochondria in a protistcell (LM)

0.1 m

MitochondrialDNA

Nuclear DNA

Mitochondria

10 m

Apoptosis Video

Apoptosis

Chloroplasts: Capture of Light Energy

Chloroplasts contain the green pigment chlorophyll, as well as enzymes and other molecules that function in photosynthesis

Chloroplasts are found in leaves and other green organs of plants and in algae


Chloroplast structure includes Thylakoids, membranous sacs, stacked to form a

granum

Stroma, the internal fluid

The chloroplast is one of a group of plant organelles, called plastids


Chloroplasts: Capture of Light Energy

20

115

Chloroplasts Figure 6.18

RibosomesStroma

Inner and outermembranes

Granum

1 mIntermembrane spaceThylakoid(a) Diagram and TEM of chloroplast (b) Chloroplasts in an algal cell

Chloroplasts(red)

50 m

DNA

Peroxisomes

Peroxisomes are membrane bound vesicles that contain oxidative enzymes

These enzymes function by oxidizing their substrates (many of their substrates are fatty acids)

Peroxisomes

Oxidation is when a substance loses an electron

RH2 + O2 → RH + H2O2

This produces H2O2 which is dangerous therefore another enzyme, catalase, removes the H2O2

2 H2O2 → O2 + 2H2O

Functions of Peroxisomes

Involved in lipid metabolism and detoxification

Contain enzymes that produce and degrade hydrogen peroxide

Fig. 4.15

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What organelle produces energy (ATP)?

1 2 3 4 5

20% 20% 20%20%20%1. Ribosomes2. Golgi complex3. Mitochondria4. SER5. Lysosomes

Where are polypeptide chains assembled?

1 2 3 4

25% 25%25%25%1. Ribosomes2. Golgi complex3. SER4. RER

Where are lipids synthesized?

1 2 3 4 5

20% 20% 20%20%20%1. Ribosomes2. Golgi complex3. Peroxisomes4. SER5. Lysosomes

These are membrane bound sacs with digestive enzymes

1 2 3 4 5

20% 20% 20%20%20%1. Ribosomes2. Golgi complex3. Mitochondria4. SER5. Lysosomes

Inner Life of a Cell - Harvard

Inner Life of a Cell Narrated, long version

Cytoskeleton

Interconnected system of fibers and lattices

Gives cells their organization, shape, ability to move, transport things in cell, important in cell division

Some permanent others only present when needed Microtubules Microfilaments Intermediate filaments

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Components of the Cytoskeleton

Three main types of fibers make up the cytoskeleton Microtubules are the thickest of the three

components of the cytoskeleton Microfilaments, also called actin filaments, are the

thinnest components Intermediate filaments are fibers with diameters in

a middle range


Fig. 4.20

Tubulin dimer

25 nm

Column of tubulin dimers

10 m

Table 6.1a Microtubules

Thickest type of cytoskeleton

Important in The structure of cell Cell division – separates the chromosomes Transport of organelles in the cell Movement of cells (cilia and flagella)

Microtubules

Composed of two proteins that form a dimer: α-tubulin and β-tubulin.

These assemble by adding dimers and disassemble by removing them

Structural microtubule-associated proteins (MAPs) regulate microtubule assembly

-Tubulin

-Tubulin

Dimer

Plus end

Minus endDimer on

Dimers off

(a)

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Tubulin dimer

25 nm

Column of tubulin dimers

10 m

Microtubule Anchoring

Microtubules may be anchored in the microtubule-organizing centers (MTOCs)

In animal cells the main MTOC is the centrosome – this is important in cell division

The centrosome is composed of two centrioles

The centrioles have nine sets of three microtubules

Centrosome

Longitudinalsection ofone centriole

Centrioles

Microtubule

0.25 m

Microtubules Cross sectionof the other centriole

Figure 6.22 Fig. 4.21

Microtubules – cell division

During cell division much of the cytoskeleton breaks down and microtubule form that will help in cell division = spindles

Spindles move the chromosomes so when the cell divides the chromosomes are evenly divided

24

Microtubule – transport of organelles

Microtubule can be used to transport vesicles and other structures.

The microtubule is stationary, transport proteins (kinesin and dynein) move the item.

Kinesin moves items in one direction (+) and Dynein moves items in the opposite direction (-)

Fig. 4.22

Cilia and flagella

Microtubules important in movement of the cell

Project from cell surface

Flagella are long microtubules

Cilia are short microtubules

Flagella are found on sperm and many one celled organisms

Cilia found on many one celled organisms and on cells that line passageways in multi-celled organisms

142

Cilia and Flagella

Flagella and Cilia

Both flagella and cilia have nine pairs of microtubules in an outer ring and a pair in the center (9 + 2).

Anchored by a basal body

A motor protein called dynein, which drives the bending movements of a cilium or flagellum


Animation: Cilia and FlagellaRight-click slide / select “Play”

25

Microtubules

Plasmamembrane

Basal body

Longitudinal sectionof motile cilium

(a)0.5 m 0.1 m

0.1 m

(b) Cross section ofmotile cilium

Outer microtubuledoubletDynein proteins

CentralmicrotubuleRadialspoke

Cross-linkingproteins betweenouter doublets

Plasma membrane

Triplet

(c) Cross section ofbasal body

Figure 6.24

How dynein “walking” moves flagella and cilia

Dynein arms alternately grab, move, and release the outer microtubules Protein cross-links limit sliding Forces exerted by dynein arms cause doublets to

curve, bending the cilium or flagellum


Flagella and Cilia

Figure 6.25 Microtubuledoublets

Dynein protein

ATP

(a) Effect of unrestrained dynein movement

Cross-linking proteinsbetween outer doublets ATP

Anchoragein cell

(b) Effect of cross-linking proteins

(c) Wavelike motion

1

2

3

Fig. 4.24b

26

Direction of swimming

(b) Motion of cilia

Direction of organism’s movement

Power stroke Recovery stroke

(a) Motion of flagella 5 m

15 m

Figure 6.23 Cilia

Microfilaments

Microfilaments are made two chains of actinprotein molecules

Important in:1. providing support for cell structures2. movement of cells (ameoba-like movement)3. dividing cells in two

Microfilaments (Actin Filaments)

Microfilaments are solid rods about 7 nm in diameter, built as a twisted double chain of actinsubunits

The structural role of microfilaments is to bear tension, resisting pulling forces within the cell

They form a 3-D network called the cortex just inside the plasma membrane to help support the cell’s shape

Bundles of microfilaments make up the core of microvilli of intestinal cells


Microfilaments are in green Microfilaments

Actin molecules will assemble to form microfilaments

Microfilaments are important in formation of microvilli

27

Figure 6.26Microvillus

Plasma membrane

Microfilaments (actinfilaments)

Intermediate filaments

0.25 m

Microfilaments that function in cellular motility contain the protein myosin in addition to actin

In muscle cells, thousands of actin filaments are arranged parallel to one another

Thicker filaments composed of myosin interdigitatewith the thinner actin fibers


Microfilaments Role in Movement - Muscle

Figure 6.27a Muscle Cells

Muscle cell

ActinfilamentMyosin

Myosinfilament

(a) Myosin motors in muscle cell contraction

0.5 m

head

Localized contraction brought about by actin and myosin also drives amoeboid movement

Pseudopodia (cellular extensions) extend and contract through the reversible assembly and contraction of actin subunits into microfilaments


Microfilaments Role in Movement - Pseudopodia

Figure 6.27b

100 m

Cortex (outer cytoplasm):gel with actin network

Inner cytoplasm: solwith actin subunits

(b) Amoeboid movement

Extendingpseudopodium

28

Cytoplasmic streaming is a circular flow of cytoplasm within cells

This streaming speeds distribution of materials within the cell

In plant cells, actin-myosin interactions drive cytoplasmic streaming


Microfilaments Role in Movement – Cytoplasmic streaming Figure 6.27c

30 m(c) Cytoplasmic streaming in plant cells

Chloroplast


Video: Cytoplasmic Streaming


Do not self assemble/disassemble –permanent

Important in cell shape

Tough but flexible fibers

Found in high amounts in cells that are subjected to mechanical stress (in skin)


Amyotrophic lateral sclerosis (ALS) is caused by abnormal intermediate filaments in nerve cells

Fig. 4.20.c

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Cilia and flagella are composed of this type of cytoskeleton

1. Microtubules2. Microfilaments3. Intermediate

filaments

Micr

otubule

s M

icrofi

lamen

ts In

termed

iate f

ilamen

ts

33% 33%33%

Microfilaments are composed of:

1 2 3 4

25% 25%25%25%1. Kinesin2. Actin3. Tubulin4. Dynein


This type of cytoskeleton is more permanent

1 2 3

33% 33%33%1. Microtubules2. Microfilaments3. Intermediate

Fibers

Extracellular components and connections between cells help coordinate cellular activities

Most cells synthesize and secrete materials that are external to the plasma membrane

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


Cell Walls of Plants

The cell wall is an extracellular structure that distinguishes plant cells from animal cells

Prokaryotes, fungi, and some protists also have cell walls

The cell wall protects the plant cell, maintains its shape, and prevents excessive uptake of water

Plant cell walls are made of cellulose fibers embedded in other polysaccharides and protein


Cell Wall

Composed of :

1. Cellulose2. Lignins3. Sticky polysaccharides4. Glycoproteins

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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


Cell Wall - LayersSecondarycell wallPrimarycell wallMiddlelamella

Central vacuoleCytosolPlasma membrane

Plant cell walls

Plasmodesmata

1 m

Figure 6.28

Figure 6.28a

Secondarycell wallPrimarycell wall

Middlelamella

1 m

Plasma membrane

The Extracellular Matrix (ECM) of Animal Cells

Animal cells lack cell walls but are covered by an elaborate extracellular matrix (ECM)

The ECM is made up of glycoproteins such as collagen, proteoglycans, and fibronectin

ECM proteins bind to receptor proteins in the plasma membrane called integrins


Figure 6.30a

EXTRACELLULAR FLUIDCollagen

Fibronectin

Plasmamembrane

Micro-filaments

CYTOPLASM

Integrins

Proteoglycancomplex

Functions of the ECM Support Adhesion Movement Regulation


Functions of the Extracellular Matrix (ECM) of Animal Cells

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Cell Junctions

Neighboring cells in tissues, organs, or organ systems often adhere, interact, and communicate through direct physical contact

Intercellular junctions facilitate this contact

There are several types of intercellular junctions Plasmodesmata Tight junctions Desmosomes Gap junctions


Plasmodesmata in Plant Cells

Plasmodesmata are channels that perforate plant cell walls

Through plasmodesmata, water and small solutes (and sometimes proteins and RNA) can pass from cell to cell


Figure 6.31

Interiorof cell

Interiorof cell

0.5 m Plasmodesmata Plasma membranes

Cell walls

Cell Junctions in Animal Cells

At tight junctions, membranes of neighboring cells are pressed together, preventing leakage of extracellular fluid

Desmosomes (anchoring junctions) fasten cells together into strong sheets

Gap junctions (communicating junctions) provide cytoplasmic channels between adjacent cells


Figure 6.32

Tight junctions preventfluid from movingacross a layer of cells

Tight junction

Tight junction

TEM0.5 m

TEM1 m

TE

M

0.1 m

ExtracellularmatrixPlasma membranes

of adjacent cells

Spacebetween cells

Ions or smallmolecules

Desmosome

Intermediatefilaments

Gapjunction


Animation: Tight JunctionsRight-click slide / select “Play”

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Tight junctions

Tight junctions: prevent substances from leaking across tissues

Found in high concentration between cells: Lining the intestine Lining capillaries in the brain


Animation: Desmosomes Right-click slide / select “Play”

Desmosomes Anchoring junctions

Desmosomes - Anchoring junctions: hold adjacent cells together (like glue) and allow tissues to be flexible

Found in high concentration in skin epithelial cells Integrin and Cadherin proteins Attach to cytoskeleton


Animation: Gap JunctionsRight-click slide / select “Play”

Communicating Junctions

Gap junctions – open channels between cells allowing rapid communication due to quick transfer of ions and small molecules between neighboring cells

These junctions can be opened or closed High concentration of gap junctions are

found in heart tissue

Animal and Plant cells

Both animal and plant cells have: Plasma membrane Nucleus Smooth and rough endoplasmic reticulum Ribosomes Golgi complex Vesicles Peroxisomes Mitochodria Cytoskeleton Lysosomes

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Plant Cells

Main Plant cell components not present in animal cells Cell wall Vacuoles (usually central) Plastids including Chloroplast Glyoxysomes

Not present in plant cells: centrioles

Found only in Animal Cells

Animal cells have centrioles, plants have a different type of MTOCs

Glyoxysomes

Plants also have a type of organelle called glyoxysomes

Glyoxysomes contain enzymes that convert stored fatty acids to sugar that is used for energy, this is especially important in germinating seedlings.

Animal cells do not have these type of peroxisomes (we can’t convert fatty acids to sugar)

Plastids

Chromoplasts – contain pigments, give plant color, attract pollinators

Amyloplasts – store starch

Chlorplasts – contain a green pigment, chlorophyll and carotenoids – yellow and orange pigments. Site of photosynthesis.

Plant cells do not contain:

1 2 3 4

25% 25%25%25%1. Mitochondria2. Centrioles3. Nucleus4. Ribosomes

Important Concepts

Know the vocabulary in the lecture

Be able to describe cell theory and the properties of cells and structures common to all cells.

Know how cells are studied, the types of microscopy, the centrifugation techniques. How would you separate the organelles of the cell?

What are the main difference between prokaryotic cells and eukaryotic cells, and examples of each type?

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Important Concepts

What are the features and characteristics of prokaryotic cells?

What is apoptosis and what organelle is an important player in the process? What molecules are released and activated during apoptosis?

What are the major features of eukaryotic cells, their location, features, structure, and their function – both plants and animals?

Important Concepts

Describe the steps needed to make a protein and ship it out of the cells, or embed the protein in a membrane, or have the protein stay in the cytosol.

What is the cause of Tay Sachs disease?

What are the differences between plant and animal cells?

Be able to describe the endosymbiont theory

Important Concepts

What are the types of cytoskeleton – what are their functions, structure, what proteins are they composed of, and how they are assembled?

How are microtubules assembled, anchored, how do they transport items and what proteins are used by microtubles to transport items.

What is the cause of ALS?

What are cell walls composed of, what are the layers?

Know the types of cell junctions, their functions and locations where there are found in high concentration

Know the role and components of extracellular matrix

Important Concepts

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