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

Light microscopy- magnification ~ ratio of image size to real size - resolution ~ measure of clarity

Electron microscopy

- TEM~ (transmitting) electron beam to study cell ultrastructure

- SEM~ (scanning) electron beam to study cell surfaces

An electron microscope

Grasshopper Spider

Images:

Isolating Organelles

Cell fractionation– separate organelles from others in the cell– variable density of organelles (heaviest fall

out first)– ultracentrifuge

Cell Theory

All organisms are made up of cells

The cell is the basic living unit of organization for all organisms

All cells come from pre-existing cells

What makes a cell a cell?

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

pro- before karyon- kernel (nucleus)

Nucleoid region: DNA concentration

No membrane-bound organelles

Bacteria cells

Eukaryotic Cells

eu- true karyon- kernel (nucleus)

Larger than prokaryotes

Membrane-bound organelles

Plant and animal cells

Cell Size As cell size increases,

the surface area to volume ratio decreases

Rates of chemical exchange may then be inadequate for cell size

Cell size, therefore, remains small

Cell Size LimitsLower limit smallest bacteria, mycoplasmas

– 0.1 to 1.0 micron (μm = micrometer) most bacteria

– 1-10 microns

Upper limit eukaryotic cells

– 10-100 microns micron = micrometer =

1/1,000,000 meter diameter of human hair = ~20

microns

Nucleus

Genetic material...– chromatin (proteins and DNA)– chromosomes (units of DNA–

humans have 46) Nucleolus: rRNA; ribosome

synthesis Nuclear envelope: double

membrane with pores and nuclear lamina (protein filaments for structure)

Directs protein synthesis (mRNA)

Ribosomes

Protein manufacturing– Free- cytosol; protein function in cell– Bound- endoplasmic reticulum; membranes,

organelles, and export

Endomembrane System

Synthesis of proteins, transport within and outside of cell

Parts involved:– Nuclear envelope– Endoplasmic Reticulum– Golgi apparatus– Lysosomes– Transport vesicles– Plasma membrane

Endoplasmic Reticulum

Continuous with nuclear envelope Smooth ER

– no ribosomes– synthesis of lipids– metabolism of carbohydrates– detoxification of drugs and

poisons Rough ER

– with ribosomes– synthesis of secretory proteins

(glycoproteins), membrane production

Golgi Apparatus ER products are modified, stored, and then shipped Cisternae: flattened membranous sacs

– Opposite sides have different thickness and polarity– cis face (receiving) & trans face (shipping)

Transport vesicles move modified materials to other parts of the cell

Lysosomes

Sac of hydrolytic enzymes in animal cells

Digestion of macromolecules

Phagocytosis- cell eating Autophagy: recycle cell’s

own organic material (damaged organelles, etc.)

Tay-Sachs disease~ lipid-digestion disorder

Vacuoles Membrane-bound sacs

(larger than vesicles) for storage and hydrolysis

May contain proteins, ions, pigments, sap, toxins, etc.

Special types– Food (created in

phagocytosis)– Contractile (pump excess

water in protists)– Central (storage in plants);

surrounded by tonoplast membrane