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Carbohydrates

Carbohydrates. Definition: carbohydrates are aldehyde or ketone compounds with multiple hydroxyl groups. Function: (1) serves as energy stores, fuels,and metabolic intermediates.

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Carbohydrates

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  1. Carbohydrates Definition: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.

  2. Complex carbonhydrate are formed by linkage of monosacchrides Monosaccharides O-glycosidic bonds Oligosaccharides 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

  3. DNA, RNA, and the flow of genetic information

  4. Translation Transcription RNA Protein DNA

  5. A nucleic acid consists of four kinds of bases linked to a sugar-phosphate backbone.

  6. A nucleic acid consists of four kinds of bases linked to a sugar-phosphate backbone. A monomer unit

  7. Backbones of DNA and RNA

  8. Backbones of DNA and RNA

  9. Four kinds of bases G A C U T (RNA only) (DNA only)

  10. 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.

  11. A nucleotide:

  12. A DNA molecule must comprise many nucleotides to carry the genetic information. Electron microscope of part of the E. coli. The E.coli genome is a single DNA molecule consisting of two chains of 4.6 milion nucleotides.

  13. The human genome comprises approximately 3 billion nucleotides, divided among 24 distinct DNA molecules: 22 autosomes, X and Y sex chromosomes.

  14. A muntjak’s chromosomes An indian muntjak: its genome is as large as human genome but is distributed on only 3 chromosomes.

  15. The double-helical structure of DNA facilitates the replication of the genetic material

  16. Watson and Crick,1953

  17. The double-helical structure of DNA facilitates the replication of the genetic material (10 nucleotides)

  18. 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.

  19. The structures of the base pairs proposed by Watson and Crick

  20. 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.

  21. Some DNA molecules are circular and supercoiled Supercoiled form Relaxed form

  22. Stem-loop structures may be formed from single-stranded DNA and RNA molecules

  23. Replication of DNA •DNA : Deoxyribose Nucleic Acid RNA: Ribose Nucleic Acid transcription replication translation • DNA DNA RNA Protein • body－organs－tissues－cells－molecules

  24. mitosis

  25. The double helix facilitates the accurate transmission of hereditary information ● Semiconservative replication

  26. 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

  27. The genes of some viruses are made of RNA 1. Genes in all cellular organisms are made of DNA. 2. For some viruses: RNA-dependent RNA polymerase (1) A single RNA strand RNA replication (2) RNA→DNA→RNA.

  28. Gene Expression: Transcription: DNA →mRNA Translation: mRNA → Protein

  29. RNA polymerases take instructions from DNA template RNA sequence is the precise complement of the DNA template sequence

  30. Transcription begins near promoter sites

  31. 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.

  32. Most eukaryotic genes are mosaics of introns and exons

  33. RNA processing generates mature RNA

  34. RNA processing generates mature RNA • 5’ end: capping • 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.

  35. 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+.

  36. Gene Translation: RNA → Protein

  37. 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.

  38. Gene Translation: RNA → Protein The problem: How does a particular sequence of nucleotidesspecify a particular sequence of amino acids? The answer: by means of transfer RNAmolecules, 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.

  39. Amino acid are encoded by groups of three bases starting from a fixes point

  40. Messenger RNA contains start and stop signals for protein synthesis

  41. ● 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.

  42. Post-translational modification of protein Glycosylation Phosphorylation Methylation ……….

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