Download I. Cells

Chap. 2 Overview of Biological Systems
I. Cells
Classification
Plants
Eucaryote
Procaryote
真核細胞
原核細胞
Protist
Animal
(原生生物)
Yeast
Mold
Protozoa
酵母菌
黴菌
(單細胞生物)
統稱)
Gram+
Eubacteria
Archaebacteria
真核菌
古細菌
Gram-
halophile
thermoacidophile
Note: The major differences between eucaryotes and procaryotes are the presence or
absence of
Naming Cells:
1.
2.
3.
Microorganisms are named in Latin by a dual name (genus + species)
e.g. Escherichia coli (E., genus; coli, species) (大腸桿菌)
Genus names are often abbreviated.
Substrains are indicated by addition of letters and numbers
e.g. E. coli K12, E. coli JM 109
Shapes of cells
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II. Procaryotes
1.
Archaebacteria: usually live in extreme environments and possess unusual metabolism
e.g.

Methanogen: methane-producing bacteria

Thermoacidophiles: grow at high temperatures and low pH

Halobacteria: only live in very strong salt solutions
2.
Gram positive:
3.
Gram negative:

Size: 0.5-3 m

cell membrane: semi-permeable, selectively retain important cellular compounds
and to exclude undesirable compounds. Inner and outer membranes separated by periplasmic space.

cell wall: confer characteristic shape and permit the cells to live in hypotonic (<the
intracellular salt concentration) environments

ribosome:

chromosome:

plasmid:
that would otherwise cause them to burst.
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

Flagella: facilitate the movement of cells.
Cell walls and peptidoglycan:
Consist of covalently linked polysaccharide and polypeptide chains (peptidoglycan). The
polysaccharide component consists of linear chains of alternating N-acetylglucosamine (NAG)
and N-acetylmuramic acid (NAM). The NAM’s lactic acid residue forms an amide bond with
a tetrapeptide to form the peptidoglycan repeating unit. Neighboring parallel peptidoglycans
are cross-linked through their tetrapeptide side chains.
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Cell Membrane: mainly composed of phospholipids and proteins
glycerol
nonpolar
Phospholipids

The fatty acid chains attached to C1 and C2 are usually saturated 16-18 carbon and 16-20
carbon acyl groups. The most common phospholipid in cell membrane is
phosphatidylcholine (lecithin) whose head group is choline CH2CH2N(CH3)3+.
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
Due to the amphipathic nature, these molecules can form

In addition to the phospholipid, there are many proteins anchored on the membrane,
serving various functions.
III.Eucaryotes:

Includes fungai (真菌) (yeast and mold), algae, protozoa, animal and plant cells

5-10 times larger than procaryotes

with nucleus and cellular organelles

Nucleus:
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
Chromosome: humans have 23 pairs of chromosomes. Each chromosome contains a
single DNA molecule on which a protein called histone is attached.

Mitochondria: power house where respiration and oxidative phosphorylation occur.
C6H12O6+6O2 6CO2+ 6 H2O G= -2823 KJ/mol

Some eucaryotes have cell walls (e.g. plant), some don’t (e.g. animal cells, so animal
cells are fragile, shear sensitive)

Cell membrane compositions are similar to those of procaryotes, and many proteins
are anchored on the cell membrane.

Sensors of external signals: to transmit signals (e.g. G protein; adrenaline (a
hormone) binding to the cell cAMP synthesis many biological responses)

Receptors: bind with foreign molecules (e.g. CD4 protein bind gp120 and enable
HIV entry)
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
Channels: aggregates of two or more polypeptide chains, facilitate diffusion and
active transport of ions or molecules

Endoplasmic reticulum:
Rough ER:
Smooth ER:

Golgi apparatus:

Lysosomes: contain and release digestive enzymes, contribute to the digestion of
nutrients and invading substances.

Peroxisomes: contain peroxidases that generate and destroy hydrogen peroxide.
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IV.
Cell Components
Introduction

Mainly composed of high MW polymeric compounds—proteins, nucleic acids,
polysaccharides, lipids

Also contain metabolites in the form of inorganic salts (NH4+, PO3-, K+, Ca2+, Na+,
SO42-), metabolic intermediates (e.g. pyruvate, acetate) and vitamins.
A. Amino Acids and Proteins


Proteins are most abundant organic molecules in living cells (40-70% dry weight)
Protein function
Examples
structural
Collagen, fibronectin
catalytic
enzymes, e.g amylase, RNA
polymerase
transport
Hemoglobin, ion channels
regulatory
growth factors, insulin
protective
antibodies, thrombin
Proteins are polymers built from amino acids (a.a.) monomers. There are 20 natural
a.a. present in proteins. R represents the side chain, which constitutes the variety of
amino acids.
H
H2N
C
COOH
R
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Note: 1. carboxylic acids can readily lose H+ in aqueous solution to form a negatively charged
ion, which is denoted with suffix “-ate”, e.g. glutamate, aspartate.
2. proline is also non-polar and hydrophobic.
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Polypeptide:
1.
The condensation reaction between two a.a. forms a peptide bond. The continuous
polymerization results in the formation of a polypeptide chain.
2.
The polypeptide chain can fold into a proper 3-D structure to form proteins

Primary structure:

Secondary structure:

Tertiary structure:

Quaternary structure: only for proteins with more than one polypeptide chains, held
together by S-S bonds or by noncovalent bonds as occurred most often between
hydrophobic “patches” on the complementary surfaces of neighboring polypeptides.
e.g. hemoglobin: 4 subunits associate to form a quaternary structure.
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B. Lipids:

Fatty acids are the major components in lipids

Hydrophobic, insoluble in water, but soluble in nonpolar solvents (e.g. benzene,
chloroform and ether)

Forms of Lipids

Lipopolysaccharide (LPS):
1.
2.

Fat: biological fuel-storage molecule

Steroids: hormones that can regulate animal development and metabolism

cholesterol (膽固醇): precursor for many steroids, existing abundantly in
the membranes of animal tissues

Cortisone:
C. Carbohydrates


Monosaccharides: smallest carbohydrates (3-9 carbon atoms)
-ose  sugar
-ase  enzyme

triose (3-carbon): dihydroxyacetone
O
CH2OH-C-CH2OH
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


hexose (6 carbon): glucose

pentose (5-carbon): ribose and deoxyribose
Disaccharides: formed by condensation of monosaccharides:

Sucrose: major sugar found in photosynthetic plants

lactose (乳糖):
Polysaccharides:

Amylose ( 直 鏈 澱 粉 ): molecular massseveral
thousand to 500,000 Da (Da=mass of a hydrogen
atom).
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
Cellulose: The most abundant polysaccharide on earth. Long unbranched chain
with D-glucose. MW50,000 to 1 million.

Chitin (poly(-1,4-N-acetyl-D-glucosamine), 幾 丁 質 ): abundant polysaccharide
present in the shells of crabs or shrimps, or cell walls of plants.

Chitosan (poly(-1,4-D-glucosamine), 幾丁聚醣). Chitin and chitosan have very
good biocompatibility and are now widely used as nutrient supplement, biomaterials
(suture, artificial skin, scaffold, etc.), carrier for enzyme immobilization.
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D. Nucleic Acids: DNA and RNA (discussed in Chap 4)
References:
1.
2.
Shuler ML and Kargi F. (1992) Bioprocess Engineering: Basic Concepts. Prentice Hall
International, London.
Alberts, B., Johnson, A., Lewis, J., Raff, M., Roberts, K., Walter, P. (2002) Molecular
Biology of the Cell, 4th Ed. Garland Science, New York.
V. Appendix
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