Molecular Biology
Code of Course: 84310024
School of Life Science, CCNU
Prof. Yang Xu
Section A: Cells and Macromolecules
Yang Xu, College of Life Sciences
Section A
Cells and Macromolecules
Section A: Cells and Macromolecules
Yang Xu, College of Life Sciences
A1 Cellular Classification
• Prokaryotes
– Eubacteria
– Archaea
• Eukaryotes
–
–
–
–
Animals
Plants
Fungi
Protists (algae and protozoa)
Section A: Cells and Macromolecules
Yang Xu, College of Life Sciences
Eubacteria
• Structural organization
– Plasma membrane
– Most have a rigid cell wall
– Cytoplasm contains a nucleoid
– Ribosomes
– Pili and flagella
• Other components
cell wall
Plasmids /RNA /proteins and so on
Section A: Cells and Macromolecules
质粒
Yang Xu, College of Life Sciences
Archaea
• Structurally, they are similar to eubacteria;
• In energy production and metabolism they are
most like those of eubacteria;
• In replication, transcription and translation they
are more similar to those of eukaryotes.
Section A: Cells and Macromolecules
Yang Xu, College of Life Sciences
Eukaryotes
• Subcellular compartments
(organelles):
– Nuclei /mitochondria Golgi
complex /endoplasmic
reticula ;
– They bounded by lipid
membranes ;
– They are the sites of distinct
biochemical processes and
define the eukaryotes.
Section A: Cells and Macromolecules
Yang Xu, College of Life Sciences
Eukaryotes
• Cytoskeleton (protein
fibers)
– Microtubules, made of
tubulin
– Microfilaments, made of
actin
Section A: Cells and Macromolecules
Yang Xu, College of Life Sciences
A1 Fig. 2. Schematic diagram
of a typical eukaryotic cell
Section A: Cells and Macromolecules
Yang Xu, College of Life Sciences
A3 Macromolecules
•
•
•
•
•
Proteins (See Section B)
Nucleic acids (See Section C)
Polysaccharides
Lipids
Complex macromolecules
Section A: Cells and Macromolecules
Yang Xu, College of Life Sciences
Polysaccharides (I)
Polysaccharides are polymers of
simple sugars covalently linked
by glycosidic bonds.
Glucose of plants:
Cellulose is a linear polymer with 
(l4) linkages;
Starch contains two components:
- -amylose, a linear polymer with
 (l→4) linkages;
- amylopectin, a branched polymer
with additional  (l→6) linkages.
Section A: Cells and Macromolecules
Yang Xu, College of Life Sciences
A3 Fig.1. The structure of celluose
(b) Starch
 (l→4)linkages
(a) Cellulose
 (l4) linkages
Section A: Cells and Macromolecules
Yang Xu, College of Life Sciences
Polysaccharides (II)
• Glucose polymers of animals:
– Glycogen is a branched polymer
like amylopectin
• Chitin is similar to cellulose,
but the monomer is different
– is found in fungal cell walls, and
– is found in the exoskeleton of
insects
• Muco/poly/saccha/rides form
the gel-like solutions, in which
the fibrous proteins of
connective tissue are embedded.
Section A: Cells and Macromolecules
Yang Xu, College of Life Sciences
Lipids (I)
Lipid molecules are mainly
hydrocarbon
• Glycerides have one, two or
three long-chain fatty acids
esterified to a molecule of
glycerol;
– In animal triglycerides are
solid (fats) at room
temperature;
– In plant triglycerides are
liquids (oils) at room
temperature
Section A: Cells and Macromolecules
Yang Xu, College of Life Sciences
Lipids (II)
• Phospholipids
– are important constituents of all
cell membranes,
– consists of glycerol esterified to
two fatty acids and one
phosphoric acid.
– The phosphate is also usually
esterified to a small molecule：
serine or choline and so on.
• Sphingolipids
• Sphingomyelin
Section A: Cells and Macromolecules
Yang Xu, College of Life Sciences
Complex macromolecules
• Nucleo/proteins
– contain both nucleic acid and protein,
– for example: telomerase and ribonuclease P
• Glyco/proteins and proteo/glycans
– are proteins with covalently attached carbohydrate
– and are generally found on extracellular surfaces
• Lipid-linked proteins: covalently attached
Lipo/proteins: noncovalently attached
• Glycolipids
– covalently linked lipid and carbohydrate
Section A: Cells and Macromolecules
Yang Xu, College of Life Sciences
A3 Fig.3. Glycoprtein structure
Section A: Cells and Macromolecules
Yang Xu, College of Life Sciences
A4 Large Macromolecular
Assemblies
• Protein complexes
• Nucleoprotein
• Membrances
Section A: Cells and Macromolecules
Yang Xu, College of Life Sciences
Protein complexes
• The eukaryotic cytoskeleton consists of
various protein complexes:
– microtubules (made of tubulin)
– Microfilaments (made of actin and
myosin)
– intermediate filaments (containing
various proteins).
• These organize the shape and movement
of cells and subcellular organelles.
• Cilia and flagella are also composed of
– microtubules complexed with dynein
and nexin.
Section A: Cells and Macromolecules
Yang Xu, College of Life Sciences
Nucleoprotein
• Ribosomes
– Bacterial 70S ribosomes have
• a 50S subunit, with 23S and 5S RNA molecules and 31 proteins,
• a 30S subunit, with a 16S RNA molecule and 21 proteins.
– Eukaryotic 80S ribosomes have
• a 60S (28S, 5.8S and 5S RNAs) subunit, and
• a 40S (18S RNA) subunits.
• Chromatin contains DNA and basic histone proteins.
• Viruses are also nucleoprotein complexes.
Section A: Cells and Macromolecules
Yang Xu, College of Life Sciences
Membranes
• Lipid bilayers
– Membrane phospholipids and sphingolipids form bilayers
– the polar groups on the exterior surfaces and
– the hydrocarbon chains in the interior.
• Membrane proteins
– may be peripheral or integral and
– act as receptors, enzymes, transporters or mediators of
cellular interactions.
Section A: Cells and Macromolecules
Yang Xu, College of Life Sciences
A4 Fig. 2. Schematic diagram of a
plasma membrance
Section A: Cells and Macromolecules
Yang Xu, College of Life Sciences
Membrane protein functions
• Receptors for signaling molecules such as
hormones and neurotransmitters;
• Enzymes for degrading extracellular
molecules before uptake (吸收);
• Channels for the selective transport of small,
polar ions and molecules;
• Mediators of cell-cell interactions (mainly
glycoproteins).
Section A: Cells and Macromolecules
Yang Xu, College of Life Sciences
That’s all for Section A
Section A: Cells and Macromolecules
Yang Xu, College of Life Sciences