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Transcript of cell structure

Ch. 7 Cell StructureBiology

Cytology The Study of Cells

History of Cytology Begins with the invention of the microscope Zacharias Janssen (fix your notes!) credited with the invention of the compound microscope Late 1500 s

Robert Hooke Coined the term cell Did this while observing cork cells Really the cell walls of dead plant cells from bark

Published his observations in the book Micrographia Influenced many others Click here for more on Robert Hooke

Robert Hooke Hooke s microscope was not as good as some (especially those of Leeuwenhoek), but he was still able to make many observations and detailed drawings.

Robert Hooke Hooke s drawings of cork cells He also made many other detailed drawings of organisms he viewed with his microscope. The flea

Anton Van Leeuwenhoek Was not the first microscope maker, but made some of the best early microscopes Very high magnifications for the time up to 300x 1600s

Anton Van Leeuwenhoek Observed first living cells Pond water, various bodily fluids that had bacteria swimming about in them, etc. Remember that the cells Hooke observed were non-living (cork) For more on how his microscope worked, click here.

Anton Van Leeuwenhoek Images he drew of bacteria in plaque removed from his teeth. These are the first known observations of bacteria He called them animalcules

Robert Brown 1st to observe a nucleus in a cell (1833) The instrument is Brown s microscope The image below is what Brown would have seen when he made his discovery. These are cells from an orchid leaf. The nuclei are the small dots in each cell The big things are stomata

Matthias Schleiden Said that all plants are made of cells 1838

Theodore Schwann Said all animals are made of cells 1839

Rudolf Virchow All cells are made from other cells 1855 Before this time it had been thought that cells could arise spontaneously from non-life

The Cell Theory The work of all the scientists listed is compiled into one large idea called The Cell Theory Remember a theory is an explanation for observations that Is supported by a large body of evidence Has been tested MANY times Explains MANY things It may be revised or improved, but stands as our best explanation for observations we have.

The Cell Theory All living things are composed of cells Cells are the basic units of structure and function in living things All cells come from pre-existing cells

Microscopes Compound Dissecting Scanning Electron Transmission Electron

Compound Light Microscope Called compound because TWO lenses are combined to magnify the image not just one. Eyepiece (ocular) Objective lens

Limitations of the Compound Microscope Images must be small and mounted on a slide

Compound Microscope Parts Ocular Also called eyepiece Usually magnifies 10x Needle inside for pointing to objects

Body or Arm

Compound Microscope Parts Revolving nosepiece Holds objective lenses Rotates so that correct objective can be chosen

Objective Lens Usually a low , medium and high power

Compound Microscope Parts Attached to the nosepiece Low Power

Usually 4x Widest field of view Least magnification Used first to observe Coarse focus

High PowerUsually 40x Narrowest field of view Most magnification Use only after low and medium powers Fine focus only

More Microscope Parts Stage Diaphragm Controls the amount of light that strikes the specimen

Focus knobs Coarse Moves the stage in large amounts Used only with low power

Fine Moves the stage in small amounts Used with high power (but can be used with any)

Light source Base

Dissecting Microscope Two oculars Low magnification Large specimens may be observed

About Field of View Wide field of view Large area Specimen appears small Good for specimens that move a lot and quickly

Narrow field of view Small area Specimen appears large Good for specimens that are still and for which you want to see greater detail

Field of View Top image Wide field of view

Bottom image Narrow field of view

Scanning Electron Microscope VERY large magnification 1000s of times

External views 3-D appearance Click here to see how the SEM works and to see images from an SEM

Transmission Electron Microscope VERY large magnifications 1000s of times

Views cross-sections of images Inside a cell

2-D views Click here to see how a TEM works and images from one

Cell Types There are TWO major types of cells Prokaryotic Eukaryotic

Prokaryotic Cells BACTERIA Simple No nucleus No organelles that are surrounded by membranes Most ancient cell type First to evolve

Most primitive

Eukaryotic Cells Everything EXCEPT Bacteria Protists, fungi, plants and animals are made up of this type of cell

Complex Nucleus present Organelles surrounded by membranes The more recent cell type Evolved AFTER prokaryotes

More complex More sophisticated parts and functions

Two Major Types of Eukaryotic Cells Plant Animal

Plant Cells Plant Cells Cell wall made of cellulose Large central vacuole Chloroplasts present

Animal Cells No cell walls No chloroplasts Vacuoles are present, but no large centrally located one.

Cell Size Cells are small. Why? Cells must have a large surface area to volume ratio large surface area and small volume allows for adequate amounts of materials to move in and out of the cell to nourish a relatively small volume If cell volume were larger, the cell surface size would not increase enough with volume to service the whole cell.

Folds in Cells Whenever you see a folded surface in a cell, you can pretty much bet that it is there to increase surface area of the structure in question

Organelles Cell parts or compartments little organs Separate chemical processes Allow chemical processes that are incompatible with each other to occur within a single cell.

Generalized Eukaryotic Cell

Cell Size Most cells are relatively small because as size increases, volume increases much more rapidly. This makes for a longer diffusion time

Visualizing Cells

Prokaryotic Cells Simplest organisms Cytoplasm is surrounded by plasma membrane and encased in a rigid cell wall composed of peptidoglycan. no distinct interior compartments gram-positive thick single layer wall that retains a violet dye from Gram stain procedure gram-negative multilayered wall does not retain dye Susceptibility of bacteria to antibiotics depends on cell wall structure.

Prokaryotic Cells Some use flagellum for locomotion threadlike structures protruding from cell surfaceBacterial cell wall Rotary motor



Eukaryotic Cells Characterized by compartmentalization by an endomembrane system, and the presence of membrane-bound organelles. Central vacuole plants, storage Vesicles (smaller) Chromosomes - DNA and protein Cytoskeleton (internal protein scaffolding) Cell walls plants and fungi

Nucleus Repository for genetic material Directs activities of the cell Usually single, some cells several, RBC none Nucleolus ribosome sub-units are made here;

Surface of nucleus bound by two phospholipid bilayer membranes nuclear membrane Nuclear pores protein gatekeepers Usually proteins going in and RNA going out


Chromosomes DNA of eukaryotes is divided into linear chromosomes. exist as strands of chromatin, except during cell division associated with packaging histones, packaging proteins nucleosomes

Endomembrane System of Compartmentalizes cell, channeling passagemolecules through cell s interior. Endoplasmic reticulum Rough ER - studded with ribosomes Smooth ER - few ribosomes

Endoplasmic reticulumLargest internal membrane Composed of Lipid bilayer Serves as system of channels from the nucleus Functions in storage and secretion Rough ER is rough because of associated ribosomes (sites of protein synthesis Smooth ER - lack associated ribosomes contained embedded enzymes, catalyze synthesis of carbohydrate and lipid molecules.

Endomembrane System Golgi apparatus collection of Golgi bodies collect, package, and distribute molecules synthesized at one location in the cell and utilized at another location Front - cis , Back trans Cisternae stacked membrane folds

Cisternae cis face Proteins

trans face Transport vesicle Golgi apparatus


Vesicle Migrating budding transport from rough vesicle endoplasmic reticulum Ribosome

Fusion of vesicle with Golgi apparatus

Endomembrane Vesicles


Lysosomes - membrane-bound vesicles containing digestive enzymes from Golgi Microbodies - enzyme-bearing, membrane-enclosed vesicles. Peroxisomes - contain enzymes that catalyze the removal of electrons and associated hydrogen atoms Peroxisome named for hydrogen peroxide produced as a by-product Enzyme breaks H2O2 down to water and oxygen

Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

CytoplasmPhagocytosis Food vesicle

Endoplasmic reticulum Golgi apparatus


Plasma membrane

Digestion of phagocytized food particles or cells

Transport vesicle Old or damaged organelle Breakdown of old organelle

Extracellular fluid

Ribosomes Ribosomes are RNA-protein complexes composed of two subunits that join and attach to messenger RNA. site of protein synthesis assembled in nucleoli

Organelles With DNA Mitochondria bounded by exterior and interior membranes interior partitioned by cristae

Chloroplasts have enclosed internal compartments o