ULTRASTRUCTURE OF CELLS

1.2

Essential Idea: Eukaryotes have a much more complex structure than prokaryotes1.2 Ultrastructure of CellsUnderstandings: Prokaryotes have simple cell structure without compartmentalization Eukaryotes have a compartmentalized cell structure Electron microscopes have a much higher resolution that light

microscopesApplications: Structure and function of organelles within exocrine gland cells of the

pancreas and within palisade mesophyll cells of the leaf Prokaryotes divide by binary fissionSkills: Draw the ultrastructure of prokaryotic cells based on electron

micrographs

Draw the ultrastructure of eukaryotic cells based on electron micrographs

Interpret electron micrographs to identify organelles Deduce the function of specialized cells

I. PROKARYOTES

A. Small (1-10um) with no compartmentalization B. Features

1. Cell Wall – protects & maintains shape a. Composed of peptidoglycanb. Some have additional layer of polysaccharides

called a capsule – helps them stick to things (teeth, food, etc)

2. Cell Membrane – controls what enters and leaves the cell

3. Pili – hair-like growths on outside of cell walla. Used to join together and transfer DNA between

bacteria (sexual reproduction)4. Flagella – movement5. Ribosomes – 70s, protein synthesis

6. Nucleoid region – single, long circle of DNA (chromosome) a. NOT associated with proteins

7. Plasmids – extra tiny circles of DNAa. Replicate independentlyb. Not required for normal conditions but helpful adapt under

stress (antibiotics, temperature/pH changes)

D. Binary Fission1. DNA is replicated2. Daughter

chromosomes attach to different spots on the plasma membrane

3. Cell elongates and pinches in two

II. EUKARYOTESA. Larger – 5-100umB. Contain a nucleus and membrane bound organellesC. Compartmentalized – separates chemical reactions and

increases efficiency

1. Cytoplasm – region between membrane and nucleusa. Cytosol – jelly-like filler

2. Endoplasmic Reticulum – network of tubules and channels composed of lipid bilayer that extends throughout cytoplasm (attaches to nuclear membrane and cell membrane)

a. Transport of materials through cellb. Smooth ER – no ribosomes associated

-production of lipids and carbs-production of sex hormones (testosterone and

estrogen)-detoxification of drugs/toxins in the liver-storage of Ca++ in muscle cells-transport of lipid-based compounds-helps liver release glucose when needed

c. Rough ER – studded with ribosomes

-site of protein synthesis

-protein development and transport

-usually closer to nucleus than

Smooth ER

3. Ribosomes – site of protein synthesisa. Can be free floating or associated with Rough ERb. No exterior membranec. Composed of ribosomal RNA and proteinsd. Consist of 2 subunitse. 80s size in eukaryotes

4. Lysosomes – digestive centers-Arise from Golgi apparatus-No internal structures – just a sac of enzymes-Enzymes all hydrolytic-Fuse with old organelles to breakdown and recycle-Acidic pH

5. Golgi apparatus-Flattened stacks of membrane called cisternae-Collects, modifies, packages, distributes cell products-cis side – near RER, receives proteins-trans side – releases proteins in vesicles -most prevalent in glandular cells that produce and secrete

6. Mitochondria-About the size of a bacteria cell-Contain their own DNA in circular chromosome-Double membrane – inner membrane folded to increase SA-Concerts food to ATP-Produces and contains its own 70s ribosomes-Can reproduce independently

7. Nucleus-Surrounded by membrane – nuclear

envelope-DNA can carry out function without

being effected by other cellular processes-Envelop contains pores to allow

communication with rest of cell-DNA in form of chromatin/

chromosomes and is associated with histone proteins

-Nucleolus – dense region of DNA where rRNA (component of ribosomes) is

produced

9. Chloroplasts-In algae and plant cells-Double membrane, size of bacteria cell, own circular DNA, 70s ribosomes, can reproduce independently-Thylakoids – membrane sacs that can absorb light-Stroma – like cytosol, full of enzymes for photosynthesis

10. Centrosome – region near nucleus where microtubules are produced

-Microtubules provide structure and allow movement-Centrioles – used for cell division in animal cells

11.Vacuoles – storage vesicles-Can store water, food, waste, toxins-Bud off of Golgi-Very large in plants, small, temporary or not present in animals-Increase a cell’s SA:V ratio

12. Cell Membrane-Phospholipid bilayer-In animal cells, secretes substances to create an extra cellular matrix (ECM)

-Composed mostly of glycoproteins and collagen-Anchored to membrane-Involved in cell-to-cell communication and signaling -Important for cell differentiation

13. Cell Wall-Gives shape and support -Limits water uptake

Organism Type of Cell Wall

Bacteria Peptidoglycan

Yeast Glucan

Other Fungi Chitin

Algae & Plants Cellulose

Animals No cell wall

III. PROKARYOTES VS. EUKARYOTESProkaryotes Eukaryotes

Circular DNA Linear DNADNA not associated with proteins

DNA associated with histone proteins

No membrane-bound organelles

Membrane-bound organelles

70s ribosomes 80s ribosomes

Both are surrounded by a cell membrane, contain DNA, and carry out the functions of life

IV. PLANT CELLS VS. ANIMAL CELLSPlants Animals

Cell wall & cell membrane

Cell membrane only

Chloroplasts & mitochondria

Mitochondria only

Carbohydrates stored as starch

Carbohydrates stored as glycogen

No centrioles Contain centrioles during cell replication

Fixed shape More flexible, rounded