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Cells:Chapt. 4

Two Basic Types of Cells

• Prokaryotes:– prounounced: pro-carry-oats

• Eukaryotes– Proun: you-carry-oats

A. Prokaryotes

Small, simple cells (relative to eukaryotes)Size: about 1 µm (1 micron)No internal membrane-bounded organellesNo nucleusSimple cell division

Contain the; 1. true bacteria & 2. archaebacteria

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1. True Bacteria = Eubacteria

• Majority of bacteria

• Examples include: E. coli, Lactobacillus (yoghurt), Lyme disease

Eubacteria

•Peptidoglycan cell walls (carbos & AA)

•Separated into Gram + and - forms

Text pg. 58

Bacteria in the Environment

A) An acid hot spring in Yellowstone is rich in iron and sulfur.B) A black smoker chimney in the deep sea emits iron sulfides

at very high temperatures (270 to 380 degrees C).

example:Iron

utilizing Baceria

A B

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2. Archaebacteria

• Live in extreme environments: high salt, high temps

• Different cell wall• Very different

membrane lipids• Unusual nucleic acid

sequence

Archaea types:

Based on their physiology, Archae can be organized into three types:

• Methanogens (prokaryotes that produce methane); • Extreme halophiles (prokaryotes that live at very

high concentrations of salt (NaCl); • Extreme (hyper) thermophiles (prokaryotes that live

at very high temperatures).

All archaea have features that distinguish them from Bacteria (i.e., no murein in cell wall, ether-linked membrane lipids, etc.). And, these prokaryotes exhibit unique structural or biochemical attributes which adapt them to their particular habitats.

B. Eukaryotes

• Bigger cells: 10-100 µm• True nucleus• Membrane-bounded

structures inside. Called organelles

• Divide by a complex, well-organized mitotic process

Liver Cell 9,400x

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Eukaryotes

• Larger more complex cells that make up most familiar life forms: plants, animals, fungi, algae

• Surrounded by a cell membrane made of lipids

• Text pg 60-61

The Cell Theory

• Cells first observed by R. Hooke 1665• Named for the Monk prayer cells• Cell Theory states that;

1. All life is composed of cells2. Cells are the basic units of life

3. Cells arise from already existing cells

Cells are typically Small

Typical cell size

•Text pg. 56

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Why are Cells Small?

• Cells must exchange gases & other molecules with environment…

• Nutrients in, Wastes out• As size increases, the rate of diffusion

exchange slows down….• This is due to the ratio of surface area to

volume

Surface Area to Volume

• Cell surface area is important in taking in nutrients

• Sfc area increases as the square of cell diameter

• But… entire cell volume needs to be fed• And, cell volume increases as the cube of

cell diameter

Consider 2 Cells...

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Surface Area to Volume

Cell Radius (R)

5 µm 50 µm

Surface Area (4pr2)

314 µm2

31,400 µm2

Volume (4/3pr3)

524 µm3

524,000 µm3

Surface Area to Volume Ratio

0.6

0.06

The Eukaryotic Cell: Components

• Outer cell membrane composed of lipids and proteins

• Cytoplasm: interior region. Composed of water & dissolved chemicals…a gel

• Numerous organelles….

Organelles

• Specialized structures within eukaryotic cells that perform different functions...

• Analogous to small plastic bags within a larger plastic bag.

• Perform functions such as :– protein production (insulin,

lactase…)– Carbohydrates, lipids…

• Text pg 60-61

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Organelles of Note:The Nucleus

• Contains the genetic material (DNA), controls protein synthesis.

DNA --> RNA --> Protein• Surrounded by a double

membrane with pores

• Contains the chromosomes= fibers of coiled DNA & protein

• Text pg. 62

Chromosomes

All Chromosomes from a single cell

One chromosomePulled apart

A single chromosomeShowing the amount of DNA within

Mitochondria• Generate cellular energy in the

form of ATP molecules• ATP is generated by the

systematic breakdown of glucose = cell respiration

• Also, surrounded by 2 membrane layers

• Contain their own DNA!• A typical liver cell may have

1,700 mitoch.• All your mitoch. come from

your mother..• Text pg. 68

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Chloroplasts

• Found in plants, algae and some bacteria. Responsible for capturing sunlight and converting it to food = photosynthesis.

• Surrounded by 2 membranes

• And…contain DNA

• Text pg. 69

Ribosomes

• Size ~20nm• Made of two subunits

(large and small)• Composed of RNA

and over 30 proteins• Come in two

sizes…80S and 70S• S units =

Sedimentation speed

Ribosomes• DNA --> RNA --> Protein• The RNA to Protein step

(termed translation) is done on cytoplasmicprotein/RNA particles termed ribosomes.

• Contain the protein synthesis machinery

• Ribosomes bind to RNA and produce protein.

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Endoplasmic Reticulum = ER

• Cytoplasm is packed w. membrane system which move molecules about the cell and to outside

• An internal cellular subway system

• Outer sfc of ER may be smooth (SER)

• Or Rough (RER) • ER functions in lipid and

protein synthesis and transport

Golgi Complex• Stacks of

membranes…• Involved in modifying

proteins and lipids into final form…– Adds the sugars to

make glyco-proteins and glyco-lipids

• Also, makes vesicles to release stuff from cell

• Text pg. 66-67

ER to Golgi network

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Lysosomes• important in breaking

down bacteria and old cell components

• contains many digestive enzymes

• The ‘garbage disposal’ or ‘recycling unit’ of a cell

• Malfunctioning lysosomesresult in some diseases (Tay-Sachs disease)

• Or may self-destruct cell such as in asbestosis

• Text pg 67

Cytoskeleton

• Composed of 3 filamentous proteins:

MicrotubulesMicrofilaments

Intermediate filaments

• All produce a complex network of structural fibers within cell

• Text pgs. 72-76

The specimen is human lung cell double-stained to expose microtubules and actin microfilaments using a mixture of FITC and rhodamine-phalloidin . Photo taken with an Olympus microscope.

Microtubules

• Universal in eukaryotes• Involved in cell shape,

mitosis, flagellarmovement, organelle movement

• Long, rigid, hollow tubes ~25nm wide

• Composed of α and ß tubulin (small globular proteins)

• Text pg. 72

http://www.cytochemistry.net/Cell-biology/

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Microfilaments

• Thin filaments (7nm diam.) made of the globular protein actin.

• Actin filaments form a helical structure

• Involved in cell movement (contraction, crawling, cell extensions)

• Text pg. 72

Intermediate filaments

• Fibers ~10nm diam.• Very stable,

heterogeneous group• Examples:Lamins : hold nucleus shapeKeratin: in epithelial cells Vimentin: gives structure to

connective tissueNeurofilaments: in nerve

cells Text pg. 72

Image of Lamins which reside in the nucleus just under the nuclear envelope

Cell Motility:Flagella & Cilia

• Both cilia & flagella are constructed the same

• In cross section: 9+2 arrangement of microtubules (MT)

• MTs slide against each other to produce movement

• Text p 74

Human Sperm: TOTO -3 iodide for DNA (blue) and Nile red for membrane lipid (red)

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How Flagella Move a Cell

Possible Origins of Eukaryotic Cells

Infolding of outer membranes Uptake of prokaryotes

• Text pg 70

Endosymbiosis

• Theory that eukaryotic cells arose from an early prokaryote (1) engulfing a second, smaller prokaryote (2)

• The internalized #2 was not digested but became a symbiote.

• Today’s mitochondria & chloroplasts may have arisen this way

• Text pg. 70

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Evidence for Endosymbiosis

• Double membrane around both organelles• Both organelles have their own DNA• Both organelles have smaller (70S)

ribosomes…• Both organelles divide by simple fission