A Tour of the CellLecture 2, Part 1

Fall 2008

Cell Theory

Cells are the basic unit of structure and function

• The lowest level of structure that can perform all activities required for life– Reproduction– Metabolic activity

• Cell Theory:– All organisms are made of cells– All cells arise from other cells

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How do we study cells?

Fig. 6.2

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How do we study cells?

Fig. 6.4

Fig. 6.5

Cell Fractionation

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Size & Function

• Limits to size• Surface area to

volume ratio

Fig. 6.8

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Prokaryotes & Eukaryotes5

Prokaryotes Eukaryotes

Prokaryotes vs. Eukaryotes

What differences do you see?

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Eukaryote

Prokaryote

Fig. 6.6

Characteristics of all cells

• Plasma membrane• Cytosol• Chromosomes• Ribosomes

Fig. 6.7

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Plasma MembranePresent in all cell typesFunction:• Separates the internal from the external

environment• Regulate chemical exchanges within the

environment– Chemical reactions more efficient

• Dynamic selective barrier

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Major differencesProkaryotes• No nucleus

– Nucleoid region

• Simple• No membrane bound

organelles

• Smaller (1-5 nm)• Evolutionarily older

Eukaryotes• Nucleus

– (DNA in a membrane-bound region)

• Complex• Membrane bound

organelles– Organelle – a structure with a

specified function w/i a cell

• Larger (10-100 nm)• Evolutionarily younger

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Views of Prokaryote Cells10

See Fig. 27.2

The Origin of Eukaryotic Cells

Evolution of the endomembrane system

• All the membrane bound organelles within a cell, except for mitochondria and chloroplasts

• Inward folding of plasma membrane formed nuclear envelope, organelles

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Eukaryotes: Animal & Plant CellsAnimal cell structures:• Plasma membrane• Nucleus• Cytosol • Ribosomes• Endoplasmic reticulum• Golgi apparatus• Mitochondria• Cytoskeleton• Vacuoles• Peroxisome

Not typically found in plants:• Centrosome• Lysosomes• Flagella

See Fig. 6.9 –Animal cell

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Views of Animal Cells13

Cheek cells (400X)

Cardiac muscle cells

Intestinal (smooth) muscle cells

Brain cells (astrocytes)

Eukaryotes: Animal & Plant CellsPlant cell structures:• Plasma membrane• Nucleus• Cytosol • Ribosomes• Endoplasmic reticulum• Golgi apparatus• Mitochondria• Cytoskeleton• Peroxisome

Not found in animals:• Cell Wall w/plasmodesmata• Plastids (Chloroplasts,

Amyloplasts, Chromoplasts)• Central vacuole

Fig. 4.6 –Animal cell

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See Fig. 6.9 – Plant cell

Views of Plant Cells15

Leaf cells

Leaf cells w/chloroplasts

Plant cell

Root cell w/amyloplasts

Leaf epidermal (surface) cells

Cytosol

Cytoplasm• Area between the

nucleus and the plasma membrane

Cytosol• Fluid of the

cytoplasm

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NucleusFunctions• Store genes on chromosomes• Regulate gene expression• Transport regulatory factors and gene

products• Produce messages (mRNA) that code

for proteins• Produce the components of ribosomes• Replication of genetic material

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NucleusNuclear envelope• Double

membrane

Pore complexes• Gatekeepers

Nuclear lamina• Protein filaments• Maintains shape

of nucleus

Fig. 6.10

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Nucleus

Chromosomes• Discrete units of DNA• Chromatin - Association of

DNA molecules and proteins

• One chromatin = one chromosome

Nucleolus• Ball-like mass of fibers &

granules• Produces ribosomal RNA

(rRNA)• Assembles components of

ribosomes

Fig. 6.10

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RibosomesComplex of proteins & rRNAFunction: Protein synthesis• Ribosome parts are made in nucleus by

nucleolus• Parts travel out of nucleus, into cytoplasmTwo types: • Bound ribosome

– Bound to endoplasmic reticulum (ER)– Make proteins for membranes or exportation from cell

• Free ribosomes– make proteins that stay

in cytosol

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Fig. 6.11

DNA Control of the Cell

DNA – Protein production

1. mRNA synthesis

2. mRNA travels to ribosomes

3. Ribosomes use mRNA to synthesize proteins

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Endomembrane System

Functions: • Manufacturing and distributing cellular products• Detoxification of poisons

Contains:• Nuclear envelope• The endoplasmic reticulum (ER)• The Golgi apparatus• Lysosomes & Vacuoles• Plasma membrane not Endo, but related

Membranes unique in structure & function

Membranes dynamic

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Endoplasmic Reticulum

Function: manufacturing of many cellular products• Large – more than ½ of all membrane in cell• Continuous with nuclear envelope• Cisternae

– Membranous tubules & sacs– Cisternal space

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Fig. 6.12

Endoplasmic Reticulum

Smooth ER• No ribosomes

Functions:• Lipid production

– E.g., steroids, phospholipds

• Metabolism of carbohydrates

• Detoxification of drugs• Calcium ion storage

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Fig. 6.12

Endoplasmic Reticulum

Rough ER• Ribosomes bound to ERFunction:• Produces secretory

proteins– Glycoproteins– Transport vesicles

• Produces membrane proteins

• Makes phospholipids for membrane

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Fig. 6.12

The Golgi ApparatusFunction:• Receives products from ER• Modifies products• Stores products• Delivers products

– Other parts of cell– Other cells (secretion/exportation)

• Manufactures some macromolecules

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Fig. 6.13

The Golgi Apparatus

Cis face – receivingTrans face – shipping• Products identified and “tagged”

e.g., phosphate groups added to products

e.g., recognition proteins on transport vesicles

Cisternal maturation model• Dynamic process• Cisturnae move from cis to trans• Products modified as cisturnae

move

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Fig. 6.13

LysosomesLysosome• Membrane bound sac of hydrolytic

enzymes• Keeps enzymes from rest of cell• Higher pH in lysosome optimal for

lysosomal enzymesProduction:• ER makes hydrolytic enzymes &

lysosomal membranes• Transported to GA for processing• Some bud directly from GA

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Fig. 6.14

LysosomesFunction:• Nutrient digestion

– Part of phagocytosis• Destroy harmful bacteria• Recycle damaged organelles

– Autophagy• Embryonic development

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Fig. 6.14

Vacuoles: Animal Cells

Membrane bound sacs that form (“bud”) from the ER, Golgi apparatus or plasma membrane.

Function:• Contain material• Food vacuole• Water pumps• Contractile vacuoles

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Central Vacuole: Plant CellsCentral Vacuole• Large – can occupy 90% volume

of cell• Coalescence of many smaller

vacuoles from ER, GA• Single membrane• Water, salts, other molecules

inside• Few enzymesFunction• Storage• Growth of cell• Protection• Helps concentrate enzymes in

rest of cell

Fig 6.15

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Endomembrane System32

Fig. 6.16

MitochondriaFunction: • Cellular respiration

– Converts carbon compounds into ATP– ATP (adenosine triphosphate) –energy for cellular work

• Found in most eukaryotic cells• Not part of endomembrane systems

• Contains its own DNA

• Has a double membrane– Membrane proteins

made by free ribosomes

• Cristae – infoldings of inner membrane

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Fig. 6.17

ChloroplastsFunction: Photosynthesis• Creates carbon compounds using energy from the sun• Contain chlorophyll a & other pigments• Not part of endomembrane systems• Contains its own DNA• Has a double membrane• Thylakoids – flattened interconnected stacks• Granum – stacks of thylakoids• Stroma – fluid outside thylakoids

• Intermembrane space

• Stroma

• Thylakoid space

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Fig. 6.18

Other PlastidsPlastid• Organelle with 2 membranes• Has its own DNA & RNA• Found in plants, some protists

Three main types• Chloroplasts• Chromoplasts

– Function: Stores lipid soluble pigments – Usually colored

• Amyloplasts– Function: Stores starch

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Peroxisomes• Specialized membrane compartment• Single membraneFunction:• Contains enzymes that transfer hydrogen to

oxygen, producing hydrogen peroxide• Breaks down fatty acids• Detoxify

Composed of:• Proteins from cytosol• Lipids from ER• Lipids synthesized in

Peroxisome

Fig. 6.19

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