2.2, 2.3 Ultrastructure of cells

Light Microscopes• Has resolution that is

sufficient to view images up to 0.2 micrometers, due to the limitations of the wavelength of light.

• Scientists ran in to problems when they wanted to see smaller things, such as in Figure 1.

New technology was needed, and thus came the Electron Microscope

Figure 1. Image from www.cytochemistry.net

Electron Microscopes• Uses beams of

electrons, rather than light, so a much clearer resolution can be achieved.

• Useful to view images down to 1 nm (0.001 micrometers)

• Useful to see images such as those of viruses and small organelles.

2.2 – Ultrastructure of cellsProkaryotes

What are they?• Prokaryotes are cells that

have no membrane-bound organelles

• Smaller than animal or plant cells

• Very Old! ~3.5 billion years old

Basic Prokaryote Structure – E.coli• One BIG

compartment

Diagrams vs Reality

Vs.

Functions of the named structures in prokaryotes

• Cell wall – provides structure, protection for the cell

• Cell membrane – provides shape, allows materials in and out of the cell (selectively permeable)

• Pili – allow attachment to other bacteria in order to share DNA

• Ribosomes – synthesize proteins for the cell• Nucleoid – region containing DNA, instructions for

cell processes• Cytoplasm – space in which metabolic reactions

can take place• Flagella – utilize whip-like motion to move the cell

Reproduction• Prokaryotes use a

method of asexual reproduction termed Binary Fission.• Binary fission allows

prokaryotes to divide in to two identical bacterium

2.3 Ultrastructure of cellsEukaryotes

Comparison of structures in Prokaryotic vs. Eukaryotic

Size DNA Nucleus Organelle

Ribosomes

Mitochondria

Prokaryote

1-3 micrometer

Closed loop

DNA in cytoplasm

“cell parts”

70S (small)

No

Eukaryotes

10-100 micrometer

Double helix

Has nuclear membrane

Membrane bound

80S (big) yes

Eukaryotic cells - Liver Cell Diagram• Draw overall

structure and label the following based on the diagram:• Golgi Apparatus• Lysosome• Mitochondrion• Free Ribosomes• Chloroplast• Vacuoles• Microtubules• Centrioles• Cilia/flagella (not

pictured)• Rough ER• Nucleus

Comparing images to diagrams

vs.

Compartmentalization• Eukaryotic cells are compartmentalized• Advantages of being so include:• Enzymes and substrates for a particular process can be

much more concentrated than if they were spread out• Potentially harmful substances can be quarantined• pH and other homeostatic levels can be managed much

more effectively• Organelles with their contents can be moved around

within the cell

Organelles and their functions• Nucleus – contains chromosomes, which are

organized raw DNA• Most of the time, they are visible as chromatin, an

unorganized form of DNA

Rough Endoplasmic Reticulum• Consists of flattened

sacs – cisternae• Ribosomes attach to

them, and fulfill protein synthesis

Golgi Apparatus• Consists of flattened membrane sacs called

cisternae, similar to the rough ER• These cisternae are shorter, have no ribosomes

attached, and have many vesicles nearby• Golgi Apparatus processes proteins brought to it

from the rER

Lysosomes• Little spherical

organelles, formed out of golgi vesicles

• Have a high concentration of protein, mostly digestive enzymes that they use to break down food particles

• Also responsible for breaking down “old” organelles and intruders, such as bacteria

Mitochondrion• Double membrane! – inner membrane is

invaginated (folded inwards) to form structures called cristae

• Produce ATP (energy for the cell) by aerobic respiration

Free Ribosomes• No membrane! – same size as ribosomes attached

to the rER, only 20 nm in length• Synthesize proteins for the cell and its

surroundings• Produced in the nucleolus

Chloroplast• Only found in photosynthetic cells• Double membrane! – performs photosynthesis• Photosynthesis produces a wide variety of compounds,

including glucose

Vacuoles• Vacuoles vary widely in size

– • Very small in animals (generally)• Very large in plants (generally)

• Used for a variety of purposes, including digestion, water balance, transport

• What do you think the function of this palisade mesophyll cell is?

Microtubules/Centrioles• Small, cylindrical fibers called microtubules that

provide structure to the cell• Centrioles are present in animal cells, and provide

an anchoring point for microtubules during mitosis

Cilia/Flagella• Whip-like structures that allow the cell to move• Comprised of a ring of double microtubules and

two central ones• While cilia and flagella can both be used for

locomotion, cilia can also be used to create a current next to the cell

Structure/Function• What do you think these

structures indicate about the cell’s function in Figure 1? SOC

What about the cell in Figure 2?SOC

Figure 1.

Figure 2.

Plant Cells• Eukaryotic, and

therefore have all the characteristics of a eukaryotic cell

• In addition to the organelles present in animal cells, plant cells also have chloroplast, a cell wall, and an enlarged vacuole.

plant

SOC