?Compaction of the large DNA molecules and the
control of gene expression in eukaryotes are
achieved by having the DNA complexed with a set
of special proteins to form the protein–DNA
complex called chromatin,The DNA-binding
proteins of chromatin are histones,and
nonhistones.
Chromatin
Histones vs Nonhistone
? Histones are small,very basic proteins rich in lysine
and arginine,The histones are the basic building blocks
of chromatin structure,The nucleoids of prokaryotic
cells also have proteins associated with DNA,but these
proteins are quite different from the histones and do
not seem to form a comparable chromatin structure,
? Nonhistone chromosomal proteins - The histones are
accompanied by a much more diverse group of DNA-
binding proteins called nonhistone chromosomal
proteins.
Bacterial chromosome - Almost all of the DNA of a typical
prokaryote like E,coli is contained in a single,large,
supercoiled circular DNA molecule,with a minor fraction
present in small plasmids,
Eukaryotic chromosomes - The typical eukaryotic cell's
genome is divided into several or many chromosomes,each
of which contains a single,very large,linear DNA molecule,
These DNA molecules are commonly of the order of 107 to
109 bp in length,The number of eukaryotic chromosomes
ranges from 1 (in an Australian ant) to 190 (in a species of
butterfly),
Ploidy - Some eukaryotic cells are highly polyploid,carrying
many copies of each chromosome,
Chromosomes
Eukaryotic chromosome
Considerations in eukaryotic chromosomes
The enormous amount of DNA in eukaryotic cells poses the
following obstacles to cells:
1,Compaction - The length of the total DNA content of a
human cell is nearly 3 meters,yet it must be packed into a
nucleus about 10-5 m in diameter.
2,Selective transcription - In a typical differentiated
eukaryotic cell,only a small fraction of the DNA (5%-10%) is
ever transcribed,Many genes that do undergo transcription
do so only in certain cell lines in particular tissues,and then
often only under special circumstances,To maintain and
regulate such complex programs of selective transcription,the
accessibility of the DNA to RNA Polymerases must be under
strict control.
Biological Molecules(II),Polysaccharides
Polysaccharide Name Monomeric Unit
Glycogen D-Glucose
Cellulose D-Glucose
Chitin N-Acetyl-D-glucosamine
Amylopectin D-Glucose
Amylose D-Glucose
Glucose
? Glucose is a six carbon sugar which can provide a
rapid source of ATP energy via glycolysis,Glucose is
stored in polymer form by plants (starch) and animals
(glycogen),Plants also have cellulose,which is not used
to store glucose,but rather provides structural
integrity to the cells,Glucose has an anomeric carbon,
which can exist in the a and b configurations.Glucose
can exist in both the D and L forms (though the D form
predominates biologically).
Structure of Glucose
Polysaccharides
? Polysaccharides containing a single sugar,such as
glucose,are referred to as glucans,Others,which
contain only mannose,are called mannans,Still others,
containing only xylose,are called xylans.
? Another group of polysaccharides of importance is the
glycosaminoglycans,These are heteropolysaccharides
containing either N-acetylgalactosamine or N-
acetylglucosamine as one of their monomeric units,
Examples include chondroitin sulfates and keratan
sulfates of connective tissue,dermatan sulfates of skin,
and yaluronic acid,All of these are acidic,through the
presence of either sulfate or carboxylate groups.
Example of polymer,Cellulose
Repeating
structures
of some
glycosaminoglycans
Biological Molecules (III),Proteins
Amino Acids
? Amino acids are organic acids containing
an amine group,They are the basic units
of a protein,The most common amino
acids are the L-a-amino acids.
20 kinds of amino acids in our body
Two additional amino acids have
been identified
Selenocysteine,encoded by the RNA nucleotide
triplet UGA found in Archaea,eubacteria and
animals including mammals.
Pyrrolysine,encoded by the RNA nucleotide triplet
UAG,found in Archaea,and eubacteria.
Science (2002) vol,296,1409
Nature may yet surprise us with more directly encoded
amino acids.
Peptide Bonds
Peptide bond,is used to join them together,Peptide
bonds form in the process of translation when the -
amino group of one amino acid residue forms a
covalent bond with the -carboxyl group of another
amino acid residue,
Peptide bond
Polypeptides
Polypeptides are polymers of amino acids,
Polypeptide chains are made by ribosomes
from messenger RNA (mRNA) using
information from the genetic code for
translating the sequence of nucleotides in
mRNA into a specific sequence of amino acids
composing a polypeptide chain.
Polypeptide
control of gene expression in eukaryotes are
achieved by having the DNA complexed with a set
of special proteins to form the protein–DNA
complex called chromatin,The DNA-binding
proteins of chromatin are histones,and
nonhistones.
Chromatin
Histones vs Nonhistone
? Histones are small,very basic proteins rich in lysine
and arginine,The histones are the basic building blocks
of chromatin structure,The nucleoids of prokaryotic
cells also have proteins associated with DNA,but these
proteins are quite different from the histones and do
not seem to form a comparable chromatin structure,
? Nonhistone chromosomal proteins - The histones are
accompanied by a much more diverse group of DNA-
binding proteins called nonhistone chromosomal
proteins.
Bacterial chromosome - Almost all of the DNA of a typical
prokaryote like E,coli is contained in a single,large,
supercoiled circular DNA molecule,with a minor fraction
present in small plasmids,
Eukaryotic chromosomes - The typical eukaryotic cell's
genome is divided into several or many chromosomes,each
of which contains a single,very large,linear DNA molecule,
These DNA molecules are commonly of the order of 107 to
109 bp in length,The number of eukaryotic chromosomes
ranges from 1 (in an Australian ant) to 190 (in a species of
butterfly),
Ploidy - Some eukaryotic cells are highly polyploid,carrying
many copies of each chromosome,
Chromosomes
Eukaryotic chromosome
Considerations in eukaryotic chromosomes
The enormous amount of DNA in eukaryotic cells poses the
following obstacles to cells:
1,Compaction - The length of the total DNA content of a
human cell is nearly 3 meters,yet it must be packed into a
nucleus about 10-5 m in diameter.
2,Selective transcription - In a typical differentiated
eukaryotic cell,only a small fraction of the DNA (5%-10%) is
ever transcribed,Many genes that do undergo transcription
do so only in certain cell lines in particular tissues,and then
often only under special circumstances,To maintain and
regulate such complex programs of selective transcription,the
accessibility of the DNA to RNA Polymerases must be under
strict control.
Biological Molecules(II),Polysaccharides
Polysaccharide Name Monomeric Unit
Glycogen D-Glucose
Cellulose D-Glucose
Chitin N-Acetyl-D-glucosamine
Amylopectin D-Glucose
Amylose D-Glucose
Glucose
? Glucose is a six carbon sugar which can provide a
rapid source of ATP energy via glycolysis,Glucose is
stored in polymer form by plants (starch) and animals
(glycogen),Plants also have cellulose,which is not used
to store glucose,but rather provides structural
integrity to the cells,Glucose has an anomeric carbon,
which can exist in the a and b configurations.Glucose
can exist in both the D and L forms (though the D form
predominates biologically).
Structure of Glucose
Polysaccharides
? Polysaccharides containing a single sugar,such as
glucose,are referred to as glucans,Others,which
contain only mannose,are called mannans,Still others,
containing only xylose,are called xylans.
? Another group of polysaccharides of importance is the
glycosaminoglycans,These are heteropolysaccharides
containing either N-acetylgalactosamine or N-
acetylglucosamine as one of their monomeric units,
Examples include chondroitin sulfates and keratan
sulfates of connective tissue,dermatan sulfates of skin,
and yaluronic acid,All of these are acidic,through the
presence of either sulfate or carboxylate groups.
Example of polymer,Cellulose
Repeating
structures
of some
glycosaminoglycans
Biological Molecules (III),Proteins
Amino Acids
? Amino acids are organic acids containing
an amine group,They are the basic units
of a protein,The most common amino
acids are the L-a-amino acids.
20 kinds of amino acids in our body
Two additional amino acids have
been identified
Selenocysteine,encoded by the RNA nucleotide
triplet UGA found in Archaea,eubacteria and
animals including mammals.
Pyrrolysine,encoded by the RNA nucleotide triplet
UAG,found in Archaea,and eubacteria.
Science (2002) vol,296,1409
Nature may yet surprise us with more directly encoded
amino acids.
Peptide Bonds
Peptide bond,is used to join them together,Peptide
bonds form in the process of translation when the -
amino group of one amino acid residue forms a
covalent bond with the -carboxyl group of another
amino acid residue,
Peptide bond
Polypeptides
Polypeptides are polymers of amino acids,
Polypeptide chains are made by ribosomes
from messenger RNA (mRNA) using
information from the genetic code for
translating the sequence of nucleotides in
mRNA into a specific sequence of amino acids
composing a polypeptide chain.
Polypeptide
