© 2010 Pearson Education, Inc. Cells Cells are the smallest unit of living substance Cell theory...

© 2010 Pearson Education, Inc.

CellsCells are the smallest unit of living substance

Cell theory is one of the premier foundations of biology. The theory states that all living things are made of cells.

Think about this. Is it true?


THE MICROSCOPIC WORLD OF CELLS• Organisms are either

– Single-celled, such as most prokaryotes and protists or

– Multicelled, such as plants, animals, and most fungi

Light Micrograph (LM)(for viewing living cells)

Light micrograph of a protist, Paramecium

LM

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Scanning Electron Micrograph (SEM)(for viewing surface features)

Scanning electron micrograph of Paramecium

TYPES OF MICROGRAPHS

Transmission Electron Micrograph (TEM)(for viewing internal structures)

Transmission electron micrograph of Paramecium

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Figure 4.1


• Cells were first described in 1665 by Robert Hooke.

• The accumulation of scientific evidence led to the cell theory.

– All living things are composed of cells.

– All cells come from other cells.

10 m

1 m

10 cm

1 cm

1 mm

100 mm

10 mm

Human height

Chicken egg

Frog eggs

Length of somenerve andmuscle cells

Un

aid

ed e

ye

Lig

ht

mic

rosc

op

e

Plant andanimal cells

Most bacteriaNucleus

Mitochondrion1 mm

100 nm

10 nm

1 nm

0.1 nm

Smallest bacteria

Viruses

Ribosomes

Proteins

Lipids

Small molecules

Atoms

Ele

ctro

n m

icro

sco

pe

Figure 4.3


The Two Major Categories of Cells• The countless cells on earth fall into two categories:

– Prokaryotic cells — Bacteria and Archaea

– Eukaryotic cells — plants, fungi, and animals

• All cells have several basic features.

– They are all bound by a thin plasma membrane.

– All cells have DNA and ribosomes, tiny structures that build proteins.


• Prokaryotes

– Are smaller than eukaryotic cells

– Lack internal structures surrounded by membranes

– Lack a nucleus

– Have a rigid cell wall


• Eukaryotes

– Only eukaryotic cells have organelles, membrane-bound structures that perform specific functions.

– The most important organelle is the nucleus, which houses most of a eukaryotic cell’s DNA.

Plasma membrane(encloses cytoplasm)

Cell wall (provides rigidity)

Capsule (sticky coating)

Prokaryoticflagellum(for propulsion)

Ribosomes(synthesizeproteins)

Nucleoid(contains DNA)

Pili (attachment structures)Figure 4.4a

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Figure 4.4b


An Overview of Eukaryotic Cells• Eukaryotic cells are fundamentally similar.

• The region between the nucleus and plasma membrane is the cytoplasm.

• The cytoplasm consists of various organelles suspended in fluid.

KNOW THIS!


• Unlike animal cells, plant cells have

– Protective cell walls

– Chloroplasts, which convert light energy to the chemical energy of food

– Watch This: http://youtu.be/1Z9pqST72is

http://youtu.be/1Z9pqST72is

Cytoskeleton

Ribosomes CentrioleLysosome

Flagellum

Nucleus

Plasmamembrane

Mitochondrion

Roughendoplasmic

reticulum (ER)

Golgiapparatus

Smoothendoplasmicreticulum (ER)

Idealized animal cell

Not in mostplant cells

Figure 4.5a

Centrosome

Idealized plant cell

Cytoskeleton

Mitochondrion

Nucleus

Rough endoplasmicreticulum (ER)

Ribosomes

Smoothendoplasmic

reticulum (ER)

Golgi apparatus

Plasmamembrane

Channels betweencells

CentralvacuoleCell wallChloroplast

Not inanimal cells

Figure 4.5b


Plant cells have cell walls and a plasma membrane

Animal cells have only a plasma membrane


MEMBRANE STRUCTURE• The plasma membrane separates the living cell from its nonliving

surroundings.

The Plasma Membrane: A Fluid Mosaic of Lipids and Proteins• The membranes of cells are composed mostly of

– Lipids

– Proteins



• The lipids belong to a special category called phospholipids.

• Phospholipids form a two-layered membrane, the phospholipid bilayer.

• Watch this: http://youtu.be/S7CJ7xZOjm0

http://youtu.be/S7CJ7xZOjm0

(a) Phospholipid bilayer of membrane

Outside of cell

Hydrophilichead

Hydrophobictail

Phospholipid

Cytoplasm (inside of cell)

Figure 4.6a

(b) Fluid mosaic model of membrane

Outside of cell

Hydrophilicregion of

protein

Hydrophilichead

Hydrophobictail

Hydrophobicregions of

protein

Phospholipidbilayer

Proteins


Figure 4.6b


• Most membranes have specific proteins embedded in the phospholipid bilayer.

• These proteins help regulate traffic across the membrane and perform other functions.


• The plasma membrane is a fluid mosaic:

– Fluid because molecules can move freely past one another

– A mosaic because of the diversity of proteins in the membrane


Cell Surfaces• Plant cells have rigid cell walls surrounding the membrane.

• Plant cell walls

– Are made of cellulose

– Protect the cells

– Maintain cell shape

– Keep the cells from absorbing too much water


• Animal cells

– Lack cell walls

– Have an extracellular matrix, which

– Helps hold cells together in tissues

– Protects and supports them

• The surfaces of most animal cells contain cell junctions, structures that connect to other cells.

THE NUCLEUS AND RIBOSOMES:GENETIC CONTROL OF THE CELL• The nucleus is the chief executive of the cell. REALLY?

• Think about it. If you cut out the nucleus of the cell does it die?

• NO! In reality, the nucleus is ONLY a repository of the blueprints for the proteins of the body.

– Genes in the nucleus store information necessary to produce proteins.

– Proteins do most of the work of the cell.



Structure and Function of the Nucleus• The nucleus is bordered by a double membrane called the

nuclear envelope.

• Pores in the envelope allow materials to move between the nucleus and cytoplasm.

• The nucleus contains a nucleolus where ribosomes are made.

Ribosomes Chromatin Nucleolus PoreNuclearenvelope

Surface of nuclear envelope Nuclear pores

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Figure 4.8


• Stored in the nucleus are long DNA molecules and associated proteins that form fibers called chromatin.

• Each long chromatin fiber constitutes one chromosome.

• The number of chromosomes in a cell depends on the species.

DNA molecule

Chromosome

Proteins

Chromatinfiber

Figure 4.9


Ribosomes• Ribosomes are responsible for protein synthesis.

• Ribosome components are made in the nucleolus but assembled in the cytoplasm.

Ribosome

Protein

mRNA

Figure 4.10


• Ribosomes may assemble proteins:

– Suspended in the fluid of the cytoplasm or

– Attached to the outside of an organelle called the endoplasmic reticulum

Ribosomes incytoplasm

Ribosomes attachedto endoplasmicreticulum

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Figure 4.11


How DNA Directs Protein Production• DNA directs protein production by transferring its coded

information into messenger RNA (mRNA).

• Messenger RNA exits the nucleus through pores in the nuclear envelope.

• A ribosome moves along the mRNA translating the genetic message into a protein with a specific amino acid sequence.

Synthesis ofmRNA in thenucleus

Nucleus

DNA

mRNA

Cytoplasm

Figure 4.12-1


Nucleus

DNA

mRNA

Cytoplasm

mRNAMovement ofmRNA intocytoplasmvianuclear pore

Figure 4.12-2


Nucleus

DNA

mRNA

Cytoplasm

mRNAMovement ofmRNA intocytoplasmvianuclear pore

Ribosome

Protein

Synthesis ofprotein in thecytoplasm

Figure 4.12-3

THE ENDOMEMBRANE SYSTEM: MANUFACTURING AND DISTRIBUTING CELLULAR PRODUCTS

• Many membranous organelles forming the endomembrane system in a cell are interconnected either

– Directly or

– Through the transfer of membrane segments between them



The Endoplasmic Reticulum• The endoplasmic reticulum (ER) is one of the main

manufacturing facilities in a cell.

• The ER

– Produces an enormous variety of molecules

– Is composed of smooth and rough ER

Nuclearenvelope

Smooth ERRough ER

Ribosomes

Ribosomes

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Figure 4.13


Rough ER

• The “rough” in the rough ER is due to ribosomes that stud the outside of the ER membrane.

• These ribosomes produce membrane proteins and secretory proteins.

• After the rough ER synthesizes a molecule, it packages the molecule into transport vesicles.

Proteins areoften modified inthe ER.

Secretoryproteins depart intransport vesicles.

Vesicles bud offfrom the ER.

A ribosomelinks amino acidsinto apolypeptide.

RibosomeTransportvesicle

Polypeptide

ProteinRough ER

Figure 4.14


Smooth ER

• The smooth ER

– Lacks surface ribosomes

– Produces lipids, including steroids

– Helps liver cells detoxify circulating drugs


The Golgi Apparatus• The Golgi apparatus

– Works in partnership with the ER

– Receives, refines, stores, and distributes chemical products of the cell

“Receiving” side of Golgi apparatus

New vesicle forming

Transport vesiclefrom rough ER

“Receiving” sideof Golgiapparatus

Newvesicleforming

Transportvesiclefrom theGolgi

Plasmamembrane

“Shipping” sideof Golgi

apparatus

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Figure 4.15


Lysosomes• A lysosome is a sac of digestive enzymes found in animal cells.

• Enzymes in a lysosome can break down large molecules such as

– Proteins

– Polysaccharides

– Fats

– Nucleic acids


• Lysosomes have several types of digestive functions.

– Many cells engulf nutrients in tiny cytoplasmic sacs called food vacuoles.

– These food vacuoles fuse with lysosomes, exposing food to enzymes to digest the food.

– Small molecules from digestion leave the lysosome and nourish the cell.

Plasma membrane Digestive enzymes

Lysosome

Digestion

Food vacuole

Lysosome

Digestion

(a) Lysosome digesting food (b) Lysosome breaking down the molecules of damaged organelles

Vesicle containingdamaged organelle

Vesicle containing twodamaged organelles

Organelle fragment

Organelle fragment

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Figure 4.16


• Lysosomes can also

– Destroy harmful bacteria

– Break down damaged organelles


Vacuoles• Vacuoles are membranous sacs that bud from the

– ER

– Golgi

– Plasma membrane


• Contractile vacuoles of protists pump out excess water in the cell.

• Central vacuoles of plants

– Store nutrients

– Absorb water

– May contain pigments or poisons

Vacuole filling with water

Vacuole contracting

(a) Contractile vacuole in Paramecium

(b) Central vacuole in a plant cell

Central vacuoleC

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EM

LM

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Figure 4.17


• To review, the endomembrane system interconnects the

– Nuclear envelope

– ER

– Golgi

– Lysosomes

– Vacuoles

– Plasma membrane

– Watch this: http://youtu.be/bNxPXyFJ2Yo

http://youtu.be/bNxPXyFJ2Yo


Centrosomes vs centriolesA centrosome is an organelle that is found close to the nucleus within the cytoplasm of cells. Centrosomes are key to the division of cells and produce the spindle fibers that are required during metaphase of mitosis. Each centrosome consists of two centrioles that are orientated at right-angles to each other. Each centriole is a cylindrical array of 9 microtubules.

Golgi apparatus

Transport vesicle

Plasma membrane

Secretory protein

New vesicle forming

Transport vesicle fromthe Golgi

Vacuoles store somecell products.

Lysosomes carrying digestiveenzymes can fuse with other vesicles.

Transport vesicles carry enzymesand other proteins from the roughER to the Golgi for processing.

Some productsare secretedfrom the cell.

Golgi apparatus

Rough ER

Vacuole

Lysosome

Transportvesicle

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Figure 4.18

CHLOROPLASTS AND MITOCHONDRIA: ENERGY CONVERSION• Cells require a constant energy supply to perform the work of

life.



Chloroplasts• Most of the living world runs on the energy provided by

photosynthesis.

• Photosynthesis is the conversion of light energy from the sun to the chemical energy of sugar.

• Chloroplasts are the organelles that perform photosynthesis.


• Chloroplasts have three major compartments:

– The space between the two membranes

– The stroma, a thick fluid within the chloroplast

– The space within grana, the structures that trap light energy and convert it to chemical energy

Inner and outermembranes

Space betweenmembranes

Stroma (fluid in chloroplast) Granum

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Figure 4.19


Mitochondria• Mitochondria are the sites of cellular respiration, which produce

ATP from the energy of food molecules.

• Mitochondria are found in almost all eukaryotic cells.


• An envelope of two membranes encloses the mitochondrion. These consist of

– An outer smooth membrane

– An inner membrane that has numerous infoldings called cristae

Outermembrane

Innermembrane

Cristae

Matrix

Space betweenmembranes

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Figure 4.20


• Mitochondria and chloroplasts contain their own DNA, which encodes some of their proteins.

• This DNA is evidence that mitochondria and chloroplasts evolved from free-living prokaryotes in the distant past.

THE CYTOSKELETON: CELL SHAPE AND MOVEMENT

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



Maintaining Cell Shape• The cytoskeleton

– Provides mechanical support to the cell

– Maintains its shape


• The cytoskeleton contains several types of fibers made from different proteins:

– Microtubules

– Are straight and hollow

– Guide the movement of organelles and chromosomes

– Intermediate filaments and microfilaments are thinner and solid.

(a) Microtubulesin the cytoskeleton

(b) Microtubulesand movement

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Figure 4.21


• The cytoskeleton is dynamic.

• Changes in the cytoskeleton contribute to the amoeboid motion of an Amoeba.


Cilia and Flagella• Cilia and flagella aid in movement.

– Flagella propel the cell in a whiplike motion.

– Cilia move in a coordinated back-and-forth motion.

– Cilia and flagella have the same basic architecture.

(a) Flagellum of a human sperm cell

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(b) Cilia on a protist

(c) Cilia lining therespiratory tract

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Figure 4.22


• Cilia may extend from nonmoving cells.

• On cells lining the human trachea, cilia help sweep mucus out of the lungs.


The Remaining Slides

Are for your review only


Know the organelles and their functions

What is the name of the area between the nuclear envelope and the plasma membrane?

Functions and anatomy of the plasma membrane

Why do phospholipids form a good barrier?

The nuclear is a double membrane

DNA is wound up with histones, a protein

Protein synthesis takes place on ribosomes, either free or on the RER

Information travels from nucleus to ribosomes via mRNA

Hormones are made on ribosomes on RER

Functions of SER?

Transport vesicles move ER products to Golgi apparatus

The golgi app. Modifies proteins for transport

Figure 4.UN1

Figure 4.UN2

Figure 4.UN3

Figure 4.UN4

Figure 4.UN5

Figure 4.UN6

Figure 4.UN7

Figure 4.UN8

Figure 4.UN9

Figure 4.UN10

Figure 4.UN11

Prokaryotic Cells Eukaryotic Cells

• Smaller

• Simpler

• Most do not have organelles

• Found in bacteria and archaea

• Larger

• More complex

• Have organelles

• Found in protists, plants,

fungi, animals

CATEGORIES OF CELLS

Figure 4.UN12

Outside of cell


Protein

Phospholipid

Hydrophilic

Hydrophilic

Hydrophobic

Figure 4.UN13

Light energy

Chloroplast

Mitochondrion

Chemicalenergy(food)

ATPPHOTOSYNTHESISCELLULAR

RESPIRATION

Figure 4.UN14

© 2010 Pearson Education, Inc. Cells Cells are the smallest unit of living substance Cell theory...

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Transcript of © 2010 Pearson Education, Inc. Cells Cells are the smallest unit of living substance Cell theory...