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

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

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

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 cells

2. Cells are the basic units of life

3. Cells arise from already existing cells

Cells are typically Small

Typical cell size

•Text pg. 56

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...

Surface Area to Volume

Cell Radius (R)

5 µm 50 µm

Surface Area

(4πr2) 314 µm2

31,400 µm2

Volume (4/ 3πr3)

524 µm3

524,000 µm3

Surf ace 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

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 chromosome Pulled 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

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 cytoplasmic protein/RNA particles termed ribosomes.

• Contain the protein synthesis machinery

• Ribosomes bind to RNA and produce protein.

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

Lysosomes • important in breaking down

bacteria and old cell components

• contains many digestive enzymes

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

• Malfunctioning lysosomes result 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, flagellar movement, organelle movement

• Long, rigid, hollow tubes ~25nm wide

• Composed of and ß tubulin (small globular proteins)

• Text pg. 72

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

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)

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

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