Ch 4

Tour of the Cell

Microscopic Worlds

• Microscopes led to the discovery of the cell– Light microscopes

– Cell membrane - yes– Large macromolecules - no– Microtubules - no– Mitochondria - maybe just

barely– Many bacteria - yes

Microscopic Worlds

• Electron scanning microscope• Scanning electron microscope• Transmission electron microscope

Cell Size

• House DNA, protein molecules and internal structures

• Obtain nutrients and diffuse nutrients and O2

• Smaller cells have a greater surface area to volume ratio than do larger cells– Surface area is significant for diffusion and

osmosis

Surface area : Volume

• Volume= 30 um *30 um* 30 um=27000um • SA (large)= 6*(30um*30um)=5,400 um• SA (small)=(6*(10um*10um))*27=16,200 um

30 m 10 m

30 m 10 m

Surface areaof one large cube 5,400 m2

Total surface areaof 27 small cubes 16,200 m2

Domains of Life

• The 3 domains of life – Bacteria (prokaryotic cells)– Archaea (prokaryotic cells)– Eukarya (all other life forms)

Cells• Prokaryotic

– Bacteria & Archaea• Eukaryotic

– Protists, fungi, plants, animals

Prokaryotic cells are simpler & usually smaller than Eukaryotic cells

Prokaryotic cell

Nucleoidregion

Nucleus

Eukar yotic cell Organelles

Co

loriz

ed

TE

M 1

5,0

00

In Common

• Bounded by plasma membrane• Ribosomes• Cytoplasm• DNA as genetic material

Prokaryote• Do not have membrane

bound nucleus• Have a cell wall outside

their plasma membrane• Circular DNA strands• No membrane bound

organelles

Prokar yoticflagella

Ribosomes

Capsule

Cell wall

Plasmamembrane

Nucleoid region (DNA)

Pili

Eukaryote

• Membrane bound nucleus

• Linear DNA• Membrane

bound organelles

NucleusSmooth endoplasmicreticulumRough

endoplasmicreticulum

Ribosomes

Golgiapparatus

Plasma membrane

Mitochondrion

Flagellum

Not in mostplant cells Lysosome

Centriole

Microtubule

CytoskeletonIntermediatefilament

Microfilament

Peroxisome

Size of cell Smaller Larger

Nucleus No nuclear membrane True nucleus, consisting of nuclear membrane & nucleoli

Membrane-enclosed organelles

Absent Present

Cell wall Usually present; chemically complex

When present, chemically simple

Plasma membrane Present Present

Cytoplasm Present Present

Ribosomes Present Present

Chromosome (DNA) arrangement

Single circular chromosome; lacks histones

Multiple linear chromosomes with histones

Sexual reproduction No meiosis; transfer of DNA fragments through cell-to-cell contact

Involves meiosis

Eukaryotic Cells• A typical animal cell:

• Contains a variety of membranous organelles (underlined)

NucleusSmooth endoplasmicreticulum

Roughendoplasmicreticulum

Ribosomes

Golgiapparatus

Plasma membrane

Mitochondrion

Flagellum

Not in mostplant cells Lysosome

Centriole

Microtubule

CytoskeletonIntermediatefilament

Microfilament

Peroxisome

Figure 4.4A

Categories of Organelles• Manufacturing

– Nucleus, ribosomes, endoplasmic reticulum, Golgi apparatus

• Hydrolysis– Lysosomes (animals), vacuoles (plants),

peroxisomes• Energy processing

– Mitochondria (animal), chloroplasts (plants)• Structural support, movement, communication

– Cytoskeleton, plasma membrane, cell wall (plants)

Plasma Membrane• Forms boundary

around cell• Controls and

regulates material transport

• Phospholipid bilayer

Nucleus• Contains most of the

cells DNA• Nucleus enclosed by

nuclear envelope• rRNA synthesized in the

nucleolus

NucleusChromatin

Nucleolus

Pore

Ribosomes

Roughendoplasmicreticulum

Two membranesof nuclearenvelope

Ribosomes

• Synthesize proteins• Free and bound ribosomes• Composed of 2 subunits

Endoplasmic Reticulum• Smooth lacks attached

ribosomes– Synthesis of lipids, oils,

phospholipids, and steroids

– Processes toxins and drugs in liver cells

– Stores and releases calcium ions in muscle cells

Smooth ER

Rough ER

Nuclearenvelope

Rough ERRibosomes

Smooth ER

TE

M 4

5,00

0

Figure 4.7

ER

• Makes more membrane & proteins• Rough ER has attached ribosome

– Produce proteins that are secreted, inserted into membranes, or transport ed in vesicles to other organelles

Fig. 4-9b

Transport vesiclebuds off

Secretoryproteininside trans-port vesicle

Glycoprotein

Polypeptide

Ribosome

Sugarchain

Rough ER

1

2

3

4

Golgi Apparatus

• Finishes, sorts, and ships cell products– Stacks of membranous sacs receive and modify ER

products then ship them to other organelles or the cell surface

Figure 4.9

Golgi apparatus

TE

M 1

30

,00

0

Transportvesicle fromthe Golgi“Shipping” side

of Golgi apparatus

Golgiapparatus

“Receiving” side ofGolgi apparatus

Transportvesiclefrom ER

New vesicleforming

Lysosomes

• Digestive functions in many single celled organisms

• In white blood cells, they destroy ingested bacteria

• Also recycle damaged organelles

Lysosomes

Figure 4.10AFigure 4.10A

Golgiapparatus

Plasmamembrane

“Food”

Foodvacuole

Lysosomes

2Lysosomeengulfingdamagedorganelle

5

Digestion4

3

Engulfmentof particle

Transport vesicle(containing inactivehydrolytic enzymes)

1

Rough ER

Vacuoles • Function in the general maintenance of the cell

– Plant cells contain a large central vacuole, which has lysosomal and storage functions

Chloroplast

Centralvacuole

Nucleus

Col

oriz

ed T

EM

8,7

00

Figure 4.12A

Endomembrane System• Interconnected structurally and functionally

Nucleus

Smooth ER Nuclear envelope Golgi apparatus

Lysosome

Vacuole

Plasmamembrane

Rough ERTransport vesiclefrom ER to Golgi

Transport vesicle fromGolgi to plasma membrane

Mitochondria• Cellular respiration

– Converts chemical energy to ATP

– Phospholipid bilayer membrane

– Has own DNA and ribosomes

Mitochondrion

Outermembrane

Intermembranespace

Matrix

Innermembrane

Cristae

TE

M 4

4,8

80

Chloroplasts• Convert solar energy to chemical energy (photosynthesis)• Stroma

– Contains DNA, ribosomes and enzymes• Thylakoids

– Interconnected sacs that form stacks called granum

Endosymbosis

• Hypothesis of endosymbosis– Mitochondria and chloroplasts were once small

prokaryotes living independently– At some point, began living within larger cells

The Cytoskeleton and Related Structures

The cell’s internal skeleton helps organize its structure and activities– A network of protein fibers make up the cytoskeleton

Actin subunit

Microfilament

7 nm

Fibrous subunits

10 nm

Intermediate filament Microtubule

25 nm

Tubulin subunit

– Microfilaments (actin filiments) • Enable cells to change shape and move

– Intermediate filaments • Reinforce the cell and anchor cer tain organelles

– Microtubules give the cell rigidity• And provide anchors for organelles and act as tracks for

organelle movement

Actin subunit

Microfilament

7 nm

Fibrous subunits

10 nm

Intermediate filament Microtubule

25 nm

Tubulin subunit

MovementCilia and flagella move when microtubules bend

– Eukaryotic cilia and flagella are locomotor appendages that protrude from cer tain cells

LM

60

0

Co

loriz

ed

SE

M 4

,10

0

Figure 4.17A Figure 4.17B

Cell Junctions•Tight junctions can bind cells together into leakproof sheets•Anchoring junctions link animal cells into strong tissues•Gap junctions allow substances to flow from cell to cell

Anchoring junction

Tight junctions

Gap junctions

Extracellular matrix

Space between cells

Plasma membranes of adjacent cellsFigure 4.18B

Plants and Cell Walls•Supported by rigid cell walls made largely of cellulose•Connect by plasmodesmata

•Connecting channels

Plasma membrane

Cytoplasm

Plasmodesmata

Vacuole

Layers of one plant cell wall

Walls of two adjacent plant cells

Figure 4.18A

Fig. 4-23