carbohydrates definition: carbohydrates are aldehyde or ketone compounds with multiple hydroxyl...
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CarbohydratesDefinition: carbohydrates are aldehyde or ketone compounds with multiple hydroxyl groups.
Function: (1) serves as energy stores, fuels,and metabolic intermediates.
(2) ribose and deoxyribose sugars form part of the structure framework of RNA and DNA.
(3) polysaccharides are structural elements in the cell walls of bacteria and plants. Cellulose, the main constituent of plant cell walls, is one of the most abundant organic compounds in the biosphere.
(4) carbohydrates are linked to many proteins and lipids, where they play key roles in mediateng interactions among cells and interactions between cells and other elements in the cellular environment.
Complex carbonhydrate are formed by linkage of monosacchrides
Oligosaccharides
O-glycosidic bonds
Monosaccharides
O-Glycosidic bond: between the anomeric carbon atom of glucose and the hydroxyl oxygen atom of methonol.
N-Glycosidic bond: anomeric carbon atom – nitrogen atom of an amine
DNA, RNA, and the flow of genetic information
DNA RNA ProteinTranscription
Translation
A nucleic acid consists of four kinds of bases linked to a sugar-phosphate backbone.
A nucleic acid consists of four kinds of bases linked to a sugar-phosphate backbone.
A monomer unit
Backbones of DNA and RNA
Backbones of DNA and RNA
(RNA only) (DNA only)
Four kinds of bases
A
UC
G
T
Structure of DNA chain: the chain has a 5′ end, which is usually attached to a phosphate, and a 3′ end, which is uaually a free hydroxyl group.
A nucleotide:
A DNA molecule must comprise many nucleotides to carry the genetic information.
The E.coli genome is a single DNA molecule consisting of two chains of 4.6 milion nucleotides.
Electron microscope of part of the E. coli.
The human genome comprises approximately 3 billion nucleotides, divided among 24 distinct DNA molecules: 22 autosomes, X and Y sex chromosomes.
An indian muntjak: its genome is as large as human genome but is distributed on only 3 chromosomes.
A muntjak’s chromosomes
The double-helical structure of DNA facilitates the replication of the genetic material
Watson and Crick, 1953
The double-helical structure of DNA facilitates the replication of the genetic material
(10 nucleotides)
The features of Watson-Crick model of DNA deduced from the diffraction patterns are:
1. Two helical polynucleotide chains are coiled around a common axis. The chains run in opposite directions.
2. The sugar-phosphate backbones are on the outside and, therefore, the purine and pyrimidine base lie on the inside of the helix.
3. The bases are nearly perpendicular to the helix axis, and adjacent bases are seperated by 3.4A. The helical structure repeats every 34A, so there are 10 bases per ture of helix.
4. The diameter of the helix is 20 A.
The structures of the base pairs proposed by Watson and Crick
The double helix can be reversibly melted
Single –stranded DNA absorbs light more effectively than does double-helical DNA-----Hypochromism.
The absorbance of a DNA solution at 260nm increased when the double helix is melted into single strands.
Some DNA molecules are circular and supercoiled
Relaxed form
Supercoiled form
Stem-loop structures may be formed from single-stranded
DNA and RNA molecules
•DNA : Deoxyribose Nucleic Acid
RNA: Ribose Nucleic Acid
• body － organs － tissues － cells －molecules
• DNA RNA ProteinDNAreplication transcription translation
Replication of DNA
mitosis
The double helix facilitates the accurate transmission of hereditary information
● Semiconservative replication
DNA polymerase catalyzes phosphodiester-bond formation
○ DNA polymerases catalyze the step-by-step addition of deoxyribonucleotide units to a DNA chain
○ Importantly, the new DNA chain is assembled directly on a preexisting DNA template
The genes of some viruses are made of RNA
1. Genes in all cellular organisms are made of DNA.
2. For some viruses:
(1) A single RNA strand
RNA-dependent RNA polymerase RNA replication
(2) RNA→DNA→RNA.
Gene Expression:
Transcription: DNA →mRNA
Translation: mRNA → Protein
RNA polymerases take instructions from DNA template
RNA sequence is the precise complement of the DNA template sequence
Transcription begins near promoter sites
Transcription ends at terminator sites
●RNA polymerase proceeds along the DNA template, transcribing one of its strands untill it reaches a terminator sequence.
● The terminator sequence in E. coli encode a base-pair hairpin in newly synthesized RNA molecule.
● Less is known about the termination of transcription in eukaryotes.
Most eukaryotic genes are mosaics of introns and exons
RNA processing generates mature RNA
5’ end: capping
1.Protect mRNA from the attack of RNase.
2. Associating with the cap-binding complex of protein which facilitates the binding of mRNA to ribosomes.
3’ end: addition of poly-A
Why ?
1. Prevent mRNA from the attack by RNAse, stablizing the mRNA.
2. Maintain the activity of mRNA as a template of translation.
RNA processing generates mature RNA
All cellular RNA is synthesized by RNA polymerase
RNA polymerase requires the following components:
1. A template
2. Activated precursors. All four ribonucleoside triphosphates ATP, GTP,UTP and CTP are required.
3. A divalent metal ion. Mg2+ or Mn2+.
Gene Translation: RNA → Protein
Several kinds of RNA play key roles in gene translation
1. Messemger RNA (mRNA) is the template for protein synthesis or translation
2. Transfer RNA (tRNA) carries Amino acids in an activated form th the ribosome for peptide-bond formation, in a sequence dictated by the mRNA template.
3. Ribosomal RNA (rRNA), the major component of ribosomes, plays both a catalytic and a structureal role in protein synthesis.
The problem: How does a particular sequence of nucleotides specify a particular sequence of amino acids?
The answer: by means of transfer RNA molecules, each specific for one amino acid and for a particular triplet of nucleotides in mRNA called a codon. The family of tRNA molecules enables the codons in a mRNA molecule to be translated into the sequence of amino acids in the protein.
Gene Translation: RNA → Protein
Amino acid are encoded by groups of three bases
starting from a fixes point
Messenger RNA contains start and stop signals for protein synthesis
● In eukaryotes, the processes of transcription and translation are separated both spatially and in time. Transcription of DNA into mRNA occurs in the nucleus. Translation of mRNA into polypeptides occurs on ribosomes.
Post-translational modification of protein
Glycosylation
Phosphorylation
Methylation……….
Bonifacino JS and Glick BS, 2004
DNA damage and DNA repair
From molecular level:
• DNA damage = DNA mutation
• This mutation could happen in just one dNMP residue, this is called point mutation.
spontaneous mutation
• DNA mutation is the molecular base for evolution and differentiation.
• Evolution is built on continued DNA mutation.
death
Programmed Cell Death （ apoptosis）
Un-repairable damage
tadpole frog
Genetics pioneer Dr. J. Craig Venter
Genetics pioneer Dr. J. Craig Venter
Scientists create artificial life
Genetics pioneer Dr. J. Craig Venter
Scientists create artificial life
This undated handout image provided by the J. Craig Venter Institute shows negatively stained transmission electron micrographs of aggregated M. mycoides. Scientists announced a bold step Thursday in the enduring quest to create artificial life. They've produced a living cell powered by manmade DNA. (AP Photo/J. Craig Venter Institute)
“Church warns cell scientists not to play God ！”
“Towards artificial life: Cell powered by man-made DNA”
“a scientific milestone”
“Artificial life: time to debate implications”
