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Introduction to Molecular Biology

Introduction to Molecular Biology. MOLECULAR BIOLOGY. 1- Nucleotides 2- DNA 3- RNA. 1- NUCLEOTIDES. 1- Importance of nucleotides 2- Structure of nucleotides 3- Metabolism of nucleotides i. synthesis ii. degradation.

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Introduction to Molecular Biology

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  1. Introduction to Molecular Biology

  2. MOLECULAR BIOLOGY

  3. 1- Nucleotides 2- DNA 3- RNA

  4. 1- NUCLEOTIDES 1- Importance of nucleotides 2- Structureof nucleotides 3- Metabolismof nucleotides i. synthesis ii. degradation

  5. Importanceof nucleotides 1- Building units for nucleic acids (DNA & RNA) 2- Other rules in metabolism & energy storage (e.g. ATP is a nucleotide)

  6. Structureof nucleotides Nucleotides = nitrogenous base + sugar + phosphate (1,2 or 3) Nitrogenous base = PurineORPyrimidine Sugar = Ribose ORDeoxyribose Purine = Adenine OR Guanine Pyrimidine = Thymine, Cytosine ORUracil

  7. PURINE RING C 6 N 7 N 1 C 5 C 8 C 2 C 4 N 3 N 9 Purine ring in adenine & guanine

  8. Pyrimidine RING C 4 N 3 C 5 C 2 C 6 N 1 Pyrimidine ring in thymine, cytosine & uracil

  9. b

  10. Purines : Adenine & Guanine • Pyrimidines: Cytosine, Thymine & Uracil • DNAcontainsAdenine & Guanine (purines) Cytosine & Thymine (pyrimidines) • RNAcontainsAdenine & Guanine (purines) Cytosine & Uracil (pyrimidines)

  11. Metabolismof nucleotides 1- Synthesis (anabolism) i. sources of purine ring atoms ii. sources of pyrimidine ring atoms 2- Degradation (catabolism) i. end products of purine ring ii. end product of pyrimidine ring

  12. Synthesis of purines:Sources of atoms of purine ring

  13. Synthesis of pyrimidines:Sources of atoms of pyrimidine ring

  14. Degradation (catabolism):End products of purine ring degradation • In human cells purine nucleotides is finally degraded to URIC ACID • Uric acidis transported in blood to kidneys • Finally, Uric acidis excreted in urine • If uric acid is increased in blood, the case is called HYPERURICEMIA • Hyperuricemia may lead to GOUT • GOUTis a disease affects joints (arthritis) & kidneys (kidney stones) caused by deposition of uric acid in these tissues

  15. Degradation (catabolism):End products of pyrimidine ring degradation Pyrimidine nucleotides are degraded to highly soluble products : b-alanine & b-aminoisobutyrate

  16. DNA 1- Importance of DNA 2- Location of DNA in human cells 3- Structure of DNA molecule - Structure of a single strand of DNA - Structure of double stranded DNA - Linear & circular DNA

  17. Importanceof DNA 1- Storage of genetic material & information (material ofGENES) 2- Transformation of genetic information to new cells (template for REPLICATION) i.e. synthesis of new DNA for new cells 3- Transformation of information for protein synthesis in cytosol (template forTRANSCRIPTION) i.e. synthesis of mRNA in nucleus

  18. Structureof DNA molecule DNA molecule is formed of double helical strands. (Dounble helix) The two strands are held together by hydrogen bonds Each single strand is formed of polynucleotides Polyncleotides are mononucleotides bound to each other by phosphodiester bonds

  19. Structure of Single strand of DNA Building Units: Polynucleotidesugar: deoxyribose Base: Purine: A or G OR Pyrimidine: T or C Phosphoric acid Mononucleotides areboundtogether byphosphodiester bonds In linear DNA Strand : two ends(5` = phosphate & 3` = OH of deoxyribose) In circular strand: noends

  20. Structure of Single strand of DNA Sequence of DNA

  21. Structure of double stranded DNA Hydrogen bonds link the two single strands together Two strands are anti-parallel (in opposite directions) Hydrogen bonds between bases of opposite strands (A & T , C & G) Denaturation breakdown (loss) of hydrogen bonds between two strands leading to formation of two separate single strands) Causes of denaturation: heating or change of pH of DNA

  22. Linear & Circular DNA 1- Linear DNA in nucleus of eukaryotes(including human cells) i.e. DNA of chromosomes 2-Circular DNA i. in eukaryotes: mitochondria ii. in prokaryoticchromosomes (nucleoid of bacteria) iii. in plasmids of bacteria(extrachromosomal element) iv. in plantchroroplasts

  23. DNA Synthesis (Replication) OLD DNA DUPLEX (PARENTAL) DNA synthesis (replication) is the synthesis of new DNA (daughter) duplexes using a template of old (parental) DNA duplex The two strands of the parental DNA double helix are separated, each can serve as a template for the replication of a new Complementary (daughter) strand. Each of the individual parental strands remains intact in one of the two new Duplexes i.e. one of the parental strands is conserved in each of the two new dublexes DAUGHTER DNA DUPLEXES

  24. RNA 1- Structure (differences from DNA) 3- Types 4- Importance of each type

  25. Structureof RNA • Building units: Polynucleotides (bound together by PDE) • Single strand • Linear (but may fold into complex structure) • with two ends: 5`(phosphate) & 3`(-OH end) • Sugar: Ribose • Purine bases: Adenine & Guanine • Pyrimidine bases: Cytosine & Uracil

  26. Types & Functions of RNA

  27. Ribosomal RNA (rRNA) 80% of total RNA in the cell (most abundant RNA) Location: cytosol Function: machine for protein biosynthesis Types:

  28. Transfer RNA (tRNA) • Smallest of RNAs in cell: 4S • Location: cytosol • At least one specific tRNA for each • of the 20 amino acids found in • proteins • with some unusual bases • with intrachain base-pairing (to • provide the folding structure of • tRNA) • Function: • 1- recognizes genetic code word on • mRNA • 2- then, carries its specific amino • acid for protein biosynthesis

  29. Messenger RNA (mRNA) • synthesized in the nucleus (by transcription): DNA (the gene) is used a template for mRNA synthesis mRNA is synthesized complementary to DNA but in RNA language i.e. U instead of T So, if A in DNA it will be U in RNA , if T in DNA it will be A in mRNA….etc • Carries the genetic information from the nuclear DNA (gene) to the cytosol • In the cytosol, mRNAis used as a template for protein biosynthesis by ribosomes (with help of tRNA)…. This is called Translation or Protein Biosynthesis) Transcription + Translation = GENE EXPRESSION

  30. complementary base-pair between DNA & RNAin transcription

  31. Types of mRNA • PolycistronicmRNA: One single mRNA strand carries information from more than one gene (in prokaryotes) • Monocistronic mRNA: one single mRNA strand carries information from only one gene (in eukaryotes)

  32. Eukaryotic mRNA 5`-end:cap of 7-methylguanosine 3`-end: poly-A tail

  33. The Genetic Code • is a dictionary that identifies the correspondence between a sequence of nucleotide bases & a sequence of amino acids • Each individual word of the code is called a codon a codon is composed three nucleotide bases in mRNA language (A, G, C & U) in 5`-3` direction e.g. 5`-AUG-3` • The four bases are used by three at a time to produce 64 different combinations of bases 61 codons: code for the 20 common amino acids 3 codons UAG, UGA & UAA: do not code for amino acids but are termination (stop) codons

  34. Genetic Code Table

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