CELLS!

Cytology= the study of cells Viewed a slice of cork and thought the tiny boxes looked like the rooms that monks lived in… so he named them “cells”. Microscopes opened up the world of cells The 1st cytologist– Robert Hooke (1665)

Microscopes n Light microscopy - magnification ~ ratio of image size to real size - resolution ~ measure of clarity n Electron microscopy - TEM~ (transmitting) electron beam to study cell ultrastructure - SEM~ (scanning) electron beam to study cell surfaces

An electron microscope  GrasshopperSpider Images:

Isolating Organelles n Cell fractionation – separate organelles from others in the cell – variable density of organelles (heaviest fall out first) – ultracentrifuge

Cell Theory n All organisms are made up of cells n The cell is the basic living unit of organization for all organisms n All cells come from pre-existing cells

What makes a cell a cell? n All cells: – surrounded by a plasma membrane – have cytosol (semi-fluid substance within the membrane) – cytoplasm = cytosol + organelles – contain chromosomes (have genes in the form of DNA) – have ribosomes (tiny “organelles” that make proteins using instructions contained in genes)

Prokaryotic Cells n pro- before karyon- kernel (nucleus) n Nucleoid region: DNA concentration n No membrane-bound organelles n Bacteria cells

Eukaryotic Cells n eu- true karyon- kernel (nucleus) n Larger than prokaryotes n Membrane-bound organelles n Plant and animal cells

Cell Size n As cell size increases, the surface area to volume ratio decreases n Rates of chemical exchange may then be inadequate for cell size n Cell size, therefore, remains small

Cell Size Limits Lower limit n smallest bacteria, mycoplasmas – 0.1 to 1.0 micron (μm = micrometer) n most bacteria – 1-10 microns Upper limit n eukaryotic cells – microns n micron = micrometer = 1/1,000,000 meter n diameter of human hair = ~20 microns

Nucleus n Genetic material... – chromatin (proteins and DNA) – chromosomes (units of DNA– humans have 46) n Nucleolus: rRNA; ribosome synthesis n Nuclear envelope: double membrane with pores and nuclear lamina (protein filaments for structure) n Directs protein synthesis (mRNA)

Ribosomes n Protein manufacturing – Free- cytosol; protein function in cell – Bound- endoplasmic reticulum; membranes, organelles, and export

Endomembrane System n Synthesis of proteins, transport within and outside of cell n Parts involved: – Nuclear envelope – Endoplasmic Reticulum – Golgi apparatus – Lysosomes – Transport vesicles – Plasma membrane

Endoplasmic Reticulum n Continuous with nuclear envelope n Smooth ER – no ribosomes – synthesis of lipids – metabolism of carbohydrates – detoxification of drugs and poisons n Rough ER – with ribosomes – synthesis of secretory proteins (glycoproteins), membrane production

Golgi Apparatus n ER products are modified, stored, and then shipped n Cisternae: flattened membranous sacs – Opposite sides have different thickness and polarity – cis face (receiving) & trans face (shipping) n Transport vesicles move modified materials to other parts of the cell

Lysosomes n Sac of hydrolytic enzymes in animal cells n Digestion of macromolecules n Phagocytosis- cell eating n Autophagy: recycle cell’s own organic material (damaged organelles, etc.) n Tay-Sachs disease~ lipid-digestion disorder

Vacuoles n Membrane-bound sacs (larger than vesicles) for storage and hydrolysis n May contain proteins, ions, pigments, sap, toxins, etc. n Special types – Food (created in phagocytosis) – Contractile (pump excess water in protists) – Central (storage in plants); surrounded by tonoplast membrane