Chapter 6

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

PowerPoint Lectures for Biology, Seventh Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero

Chapter 6Chapter 6

A Tour of the Cell


Microscopy

• Scientists use microscopes to visualize cells too small to see with the naked eye

• In a light microscope (LM), visible light passes through a specimen and then through glass lenses, which magnify the image

• The minimum resolution of an LM is about 200 nanometers (nm), the size of a small bacterium

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Measurements1 centimeter (cm) = 10–2 meter (m) = 0.4 inch1 millimeter (mm) = 10–3 m1 micrometer (µm) = 10–3 mm = 10–6 m1 nanometer (nm) = 10–3 µm = 10–9 m

10 m

1 mHuman height

Length of somenerve andmuscle cells

Chicken egg

0.1 m

1 cm

Frog egg1 mm

100 µm

Most plant andanimal cells

10 µmNucleus

1 µm

Most bacteria

Mitochondrion

Smallest bacteria

Viruses100 nm

10 nmRibosomes

Proteins

Lipids

1 nmSmall molecules

Atoms0.1 nmU

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Lig

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Ele

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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


Comparing Prokaryotic and Eukaryotic Cells

• Basic features of all cells:

– Plasma membrane

– Semifluid substance called the cytosol

– Chromosomes (carry genes)

– Ribosomes (make proteins)


• Prokaryotic cells have no nucleus

• In a prokaryotic cell, DNA is in an unbound region called the nucleoid

• Prokaryotic cells lack membrane-bound organelles

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A typicalrod-shapedbacterium

A thin section through thebacterium Bacilluscoagulans (TEM)

0.5 µm

Pili

Nucleoid

Ribosomes

Plasmamembrane

Cell wall

Capsule

Flagella

Bacterialchromosome


• Eukaryotic cells have DNA in a nucleus that is bounded by a membranous nuclear envelope

• Eukaryotic cells have membrane-bound organelles

• Eukaryotic cells are generally much larger than prokaryotic cells


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

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

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Hydrophilicregion

Hydrophobicregion

Carbohydrate side chain

Structure of the plasma membrane

Hydrophilicregion

Phospholipid Proteins

Outside of cell

Inside of cell 0.1 µm

TEM of a plasma membrane


A Panoramic View of the Eukaryotic Cell

• A eukaryotic cell has internal membranes that partition the cell into organelles

• Plant and animal cells have most of the same organelles

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Flagellum

Centrosome

CYTOSKELETON

Microfilaments

Intermediate filaments

Microtubules

Peroxisome

Microvilli

ENDOPLASMIC RETICULUM (ER

Rough ER Smooth ER

MitochondrionLysosome

Golgi apparatus

Ribosomes:

Plasma membrane

Nuclear envelope

NUCLEUS

In animal cells but not plant cells: LysosomesCentriolesFlagella (in some plant sperm)

Nucleolus

Chromatin

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Roughendoplasmicreticulum

In plant cells but not animal cells: ChloroplastsCentral vacuole and tonoplastCell wallPlasmodesmata

Smoothendoplasmicreticulum

Ribosomes(small brown dots)

Central vacuole

Microfilaments

IntermediatefilamentsMicrotubules

CYTOSKELETON

Chloroplast

Plasmodesmata

Wall of adjacent cell

Cell wall

Nuclearenvelope

Nucleolus

Chromatin

NUCLEUS

Centrosome

Golgiapparatus

Mitochondrion

Peroxisome

Plasmamembrane


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


The Nucleus: Genetic Library of the Cell

• The nucleus contains most of the cell’s genes and

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

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Close-up of nuclearenvelope

Nucleus

Nucleolus

Chromatin

Nuclear envelope:Inner membraneOuter membrane

Nuclear pore

Porecomplex

Ribosome

Pore complexes (TEM) Nuclear lamina (TEM)

1 µm

Rough ER

Nucleus

1 µm

0.25 µm

Surface of nuclear envelope


Ribosomes: Protein Factories in the Cell

• 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 (ER) or the nuclear envelope (bound ribosomes)

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Ribosomes

0.5 µm

ER Cytosol

Endoplasmicreticulum (ER)

Free ribosomes

Bound ribosomes

Largesubunit

Smallsubunit

Diagram ofa ribosome

TEM showing ERand ribosomes


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 ER membrane is continuous with the nuclear envelope

• There are two distinct regions of ER:

– Smooth ER, which lacks ribosomes

– Rough ER, with ribosomes studding its surface

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Ribosomes

Smooth ER

Rough ER

ER lumen

Cisternae

Transport vesicle

Smooth ER Rough ER

Transitional ER

200 nm

Nuclearenvelope


Functions of Smooth ER

• The smooth ER

– Synthesizes lipids

– Metabolizes carbohydrates

– Stores calcium

– Detoxifies poison


Functions of Rough ER

• The rough ER

– Has bound ribosomes

– Produces proteins and membranes, which are distributed by transport vesicles

– Is a membrane factory for 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

The Golgi Apparatus: Shipping and Receiving Center

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trans face(“shipping” side ofGolgi apparatus) TEM of Golgi apparatus

0.1 µm

Golgi apparatus

cis face(“receiving” side ofGolgi apparatus)

Vesicles coalesce toform new cis Golgi cisternae Vesicles also

transport certainproteins back to ER

Vesicles movefrom ER to Golgi

Vesicles transport specificproteins backward to newerGolgi cisternae

Cisternalmaturation:Golgi cisternaemove in a cis-to-transdirection

Vesicles form andleave Golgi, carryingspecific proteins toother locations or tothe plasma mem-brane for secretion

Cisternae


Lysosomes: Digestive Compartments

• A lysosome is a membranous sac of hydrolytic enzymes

• Lysosomal enzymes can hydrolyze proteins, fats, polysaccharides, and nucleic acids

• Lysosomes also use enzymes to recycle organelles and macromolecules, a process called autophagy

Animation: Lysosome Formation

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Phagocytosis: lysosome digesting food

1 µm

Plasmamembrane

Food vacuole

Lysosome

Nucleus

Digestiveenzymes

Digestion

Lysosome

Lysosome containsactive hydrolyticenzymes

Food vacuolefuses withlysosome

Hydrolyticenzymes digestfood particles

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Autophagy: lysosome breaking down damaged organelle

1 µm

Vesicle containingdamaged mitochondrion

Mitochondrionfragment

Lysosome containingtwo damaged organelles

Digestion

Lysosome

Lysosome fuses withvesicle containingdamaged organelle

Peroxisomefragment

Hydrolytic enzymesdigest organellecomponents


Vacuoles: Diverse Maintenance Compartments

• Vesicles and vacuoles (larger versions of vacuoles) are membrane-bound sacs with varied functions

• A plant cell or fungal cell may have one or several vacuoles


• 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

Video: Paramecium Vacuole

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5 µm

Central vacuole

Cytosol

Tonoplast

Central vacuole

Nucleus

Cell wall

Chloroplast


Mitochondria and chloroplasts change energy from one form to another

• Mitochondria are the sites of cellular respiration

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


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


The cytoskeleton is a network of fibers that organizes structures and activities in the cell

• The cytoskeleton is a network of fibers extending throughout the cytoplasm

• It organizes the cell’s structures and activities, anchoring many organelles

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Microtubule

Microfilaments0.25 µm


Roles of the Cytoskeleton: Support, Motility, and Regulation

• The cytoskeleton helps to support the cell and maintain its shape


Centrosomes and Centrioles

• In many cells, microtubules grow out from a centrosome near the nucleus

• The centrosome is a “microtubule-organizing center”


Cilia and Flagella

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5 µm

Direction of swimming

Motion of flagella

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15 µm

Direction of organism’s movement

Motion of cilia

Direction ofactive stroke

Direction ofrecovery stroke


Cell Walls of Plants

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

• 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


The Cell: A Living Unit Greater Than the Sum of Its Parts

• Cells rely on the integration of structures and organelles in order to function

• For example, a macrophage’s ability to destroy bacteria involves the whole cell, coordinating components such as the cytoskeleton, lysosomes, and plasma membrane

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5 µ

m

Chapter 6

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