Tour of the Cell 1 (Ch. 6)

Dead White Men Who Discovered (and were made of) Cells: Anton Van Leeuwenhoek Robert Hooke

Where the Magic Happened

The size range of cells Nucleus Most bacteria Measurements 1 centimeter (cm) = 10  2 meter (m) = 0.4 inch 1 millimeter (mm) = 10 –3 m 1 micrometer (µm) = 10 –3 mm = 10  6 m 1 nanometer (nm) = 10 –3 µm = 10  9 m 10 m 1 m 0.1 m 1 cm 1 mm 100 µm 10 µm 1 µm 100 nm 10 nm 1 nm 0.1 nm Human height Length of some nerve and muscle cells Chicken egg Frog egg Most plant and animal cells Mitochondrion Smallest bacteria Viruses Ribosomes Proteins Lipids Small molecules Atoms Unaided eye Light microscope Electron microscope nucleus Most bacteria

Comparing the size of a virus, a bacterium, and an animal cell While we’re on the topic of size...

Why Cells Are So Small: The SA:V Ratio Surface area increases while total volume remains constant Total surface area (height  width  number of sides  number of boxes) Total volume (height  width  length  number of boxes) Surface-to-volume ratio (surface area  volume) Diffusion: The movement of molecules from an area of high concentration to low concentration.

Cell Fractionation APPLICATION Cell fractionation is used to isolate (fractionate) cell components, based on size and density. TECHNIQUE First, cells are homogenized in a blender to break them up. The resulting mixture (cell homogenate) is then centrifuged at various speeds and durations to fractionate the cell components, forming a series of pellets. Tissue cells Homogenization Homogenate 1000 g (1000 times the force of gravity) 10 min Differential centrifugation Supernatant poured into next tube 20,000 g 20 min Pellet rich in nuclei and cellular debris Pellet rich in mitochondria (and chloro- plasts if cells are from a plant) Pellet rich in “microsomes” (pieces of plasma mem- branes and cells’ internal membranes) Pellet rich in ribosomes 150,000 g 3 hr 80,000 g 60 min RESULTS In the original experiments, the researchers used microscopy to identify the organelles in each pellet, establishing a baseline for further experiments. In the next series of experiments, researchers used biochemical methods to determine the metabolic functions associated with each type of organelle. Researchers currently use cell fractionation to isolate particular organelles in order to study further details of their function.

Prokaryote bacteria cells Types of cells Eukaryote animal cells - no organelles - organelles Eukaryote plant cells

Why organelles? Specialized structures – specialized functions Containers – Compartments = different local environments pH, concentration differences – distinct & incompatible functions lysosome & its digestive enzymes Membranes as sites for chemical reactions – Unique lipids & proteins – embedded enzymes & reaction centers chloroplasts & mitochondria

Cells gotta work to live! – make proteins proteins control every cell function – make energy for daily life for growth – make more cells growth repair renewal

Proteins do all the work! cells DNA proteins organism Repeat after me… Proteins do all the work!

Cell functions Building proteins – copy DNA – DNA -> RNA – build proteins – process proteins Folding, modifying – Remove amino acids – Add molecules (e.g. glycoproteins) – address & transport proteins

Protein Synthesis Organelles involved – nucleus – ribosomes – endoplasmic reticulum (ER) – Golgi apparatus – vesicles nucleusribosomeER Golgi apparatus vesicles The Protein Assembly Line The Endomembrane System

nuclear pores nuclear pore nuclear envelope nucleolus Function – protects DNA Structure – nuclear envelope double membrane membrane fused in spots to create pores Nucleus What kind of molecules need to pass through?

production of mRNA from DNA in nucleus mRNA travels from nucleus to ribosome in cytoplasm through nuclear pore 1 2

Nucleolus Function – ribosome production build ribosome subunits from rRNA & proteins Ribosome assembly is completed in cytoplasm small subunit large subunit ribosome rRNA & proteins nucleolus

small subunit large subunit Ribosomes Function – protein production Structure – rRNA & protein – 2 subunits combine 0.08  m Ribosomes Rough ER Smooth ER

membrane proteins Types of Ribosomes Free ribosomes – suspended in cytosol – synthesize proteins that stay in cytosol Bound ribosomes – attached to endoplasmic reticulum – synthesize proteins for export or membranes

Endoplasmic Reticulum Function – processes proteins – manufactures membrane – synthesis & hydrolysis of many compounds Structure – membrane connected to nuclear envelope & extends throughout cell

Types of ER rough smooth

Smooth ER function Membrane production Metabolic processes – Lipid Synthesis – Glycogen hydrolysis (in liver) – Drug detoxification (in liver)

Membrane Factory Build new membrane – synthesize phospholipids – ER membrane expands buds off & transfers to other parts of cell.

Rough ER function Produces proteins for export out of cell – protein secreting cells – packaged into transport vesicles for export Which cells have lot of rough ER?

Synthesizing proteins ribosome

Golgi Apparatus Which cells have lots of Golgi? Function – finishes, sorts, tags & ships products like “UPS shipping department” – ships products in vesicles membrane sacs “UPS trucks”

Golgi Apparatus

Vesicle transport vesicle budding from rough ER fusion of vesicle with Golgi apparatus migrating transport vesicle protein ribosome

proteins transport vesicle Golgi apparatus vesicle smooth ER rough ER nuclear pore nucleus ribosome cell membrane protein secreted cytoplasm The Endomembrane System Putting it together…

Any Questions!!

Review Questions

1.. In which cell would you expect to find the most smooth endoplasmic reticulum? A.Muscle cell in the thigh muscle of a long-distance runner B.Pancreatic cell that manufactures digestive enzymes C.Macrophage (white blood cell) that engulfs bacteria D.Epithelial cells lining the digestive tract E.Ovarian cell that produces estrogen (a steroid hormone)

2. In which cell would you expect to find the most bound ribosomes? A.Muscle cell in the thigh muscle of a long-distance runner B.Pancreatic cell that manufactures digestive enzymes C.Macrophage (white blood cell) that engulfs bacteria D.Epithelial cells lining the digestive tract E.Ovarian cell that produces estrogen (a steroid hormone)

3. Of the following, which is probably the most common route for membrane flow in the endomembrane system? A.Golgi → lysosome → ER → plasma membrane B.tonoplast → plasma membrane → nuclear envelope → smooth ER C.nuclear envelope → lysosome → Golgi → plasma membrane D.rough ER → vesicles → Golgi → plasma membrane E.ER → chloroplasts → mitochondrion → cell membrane