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Cells

What is a cell?A cell is a membrane bound unit containing hereditary material and other compounds that make metabolism, growth and reproduction possible.

Plasma membrane

Hereditarymaterial

Cytoplasm

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Cells Overview of cell structure

Cells are surrounded by a plasma membrane.

DNA the hereditary material is packaged in one or more chromosomes located in a nuclear region or nucleus.

The cytoplasm contains molecules and organelles needed for cellular activities.

Ribosomes are the factories in which proteins are manufactured.

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Cells How were cells discovered?

1665 Robert HookeExamined cork in simple microscope.

Saw empty compartments and

called them ‘cellulae’ (small rooms).

1650 - 1700 Anton Van LeeuwenhoekMade his own microscope that could

magnify 200 X.

Observed living things.

Called them ‘Animacules’ (little animals).

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Cells Formation of the cell theory

1838 Matthias SchleidenConcludes that all plants are made of

cells or their derivatives.

He called this theory phytogenesis

1839 Theodore SchwannAll animal tissue is made of cells and

within an organism these cells are identical.

The theory they presented from these observations is often called the Schleiden and Schwann Cell Theory

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Cells 1855 Rudolph Virchow

Studied pathenogens and concluded

‘omnis cellula e cellua’ which means that all cells arise from pre-existing cells.

Principles of the Cell Theory All organisms are composed of one

or more cells. Cells are the basic unit of life. Cells arise only by division of a

previously existing cell.

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Cells Cell size

Does small cell sizes have advantages? The surface area increases as the square

(10 )of the diameter of a sphere, but the volume increases as the cube (10 ).

small cube - surface area

small cube - volume

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10 m10 m) = 600 m6 x (10 m x

10 m x 10 m x 10 m = 1000 m 3

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Cells big cell - surface area

big cell - volume

30 m x 30 m x 30 m = 27000 m 3

6 x (30 m x 30 m) = 5400 m 2

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Cells Comparing different sizes

Surface area 1 small = 600 m

27 small = 16.200 m

1 big = 5400 m

Volume is the same for 1 big and 27 small

The ratio of surface to volume

27 small 16200/27000 = 0,6 1 big 5400/27000 = 0,2 surface area of small is 3X greater

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Cell size

Why aren´t cells larger? limitations of molecular diffusion

faster passage through small cells more efficient communication

limitations of surface/volume ratio with in size greater in volume interaction occurs only at surface insufficient exchange of materials at

plasma membrane

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Structure of prokaryotes

Strong cell wall made of carbohydrate matrix and peptide units. Slime capsule (some times with pili),

not always present.

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Structure of prokaryotes

Simple interior organization lack internal compartmentalization reactions not separated, one

metabolic unit lack membrane-bound organelles infolding of plasma membrane

Rotating flagella cell movement - screw like motion

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Structure of prokaryotes

Ribosomes in the cytoplasm protein synthesis

Circular nuclear matter (DNA) located in the nucleoid region

Plasmids small independent circular DNA

Mesosome infolding of plasma membrane often

associated with photosynthesis

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Structure of eukaryotes

More complex than prokaryotes They are compartmentalized

possess internal membrane bound organelles ribosomes rough endoplasmic reticulum (rER) lysosomes Golgi apparatus (complex) mitochondria nucleus chloroplasts

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Structure of eukaryotes

Nucleus the largest organelle the nuclear envelope

double layer of membranes, outer continuous with ER nuclear pores restrict passage of molecules to proteins

and RNA

chromosomes - chromatid contain hereditary material divided into linear chromosomes,

associated with histone protein

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Structure of eukaryotes the nucleolus

an assembly plant for ribosomal subunits

ribosomal proteins are made in the cytoplasm

ribosomal RNA made in the nucleus

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Organelles Endoplasmic reticulum

Thin membrane not visible in the light microscope.

Divides interior into compartments. Cytoskeleton, holds the cell shape.

Rough ER covered with ribosomes manufactures proteins for export

Smooth ER lacks ribosomes carbohydrate and lipid synthesis

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Organelles

Ribosomes Made of two parts. Made in the nucleus. Assist in the manufacture of

proteins.

Golgi apparatus

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Organelles

Mitochondrion

Lysosome

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Organelles

Chloroplast

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Cells

State two similarities between prokaryotic and eukaryotic cells.

State two differences between the eukaryotic nucleus and the prokaryotic nuclear material.

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Endosymbiosis Symbiosis is two organisms living in

close association.

Mitochondria and chloroplasts are thought to be ancient bacteria that became incorporated into eukaryotic cells. Evidence supporting Theory:

both are surrounded by double membranes mitochondria and bacteria hvae similar

size mitochondrial ribosomes resemble

bacterial ribosomes both have circular DNA like bacteria mitochondria divide by simple fission

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The Plant Cell Wall