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Lec 12 level 3-nu (gene expression and synthesis of protein)


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Lec 12 level 3-nu (gene expression and synthesis of protein)

  1. 1. Nursing - 12 Gene expression and synthesis of protein1
  2. 2. Nucleotides• Nucleotides are precursors of the nucleic acids, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).• The nucleic acids are concerned with the storage and transfer of genetic information. 2
  3. 3. Composition of nucleotidesA nucleotide is made up of three components:1. Nitrogenous base, (a purine or a pyrimidine).2. Pentose sugar, either ribose or deoxyribose.3. Phosphate groups esterified to the3 sugar
  4. 4. • Nucleoside: Formed when a base combines with a pentose sugar.• Nucleotide: Formed when nucleoside is esterified to phosphate group. It also called nucleoside monophosphate.• The nucleic acids (DNA and RNA) are polymers of nucleoside monophosphates. 4
  5. 5. Bases present in the nucleic acids1- Purine bases:• The purine bases present in RNA and DNA are the same; adenine and guanine.• Uric acid is formed as the end product of the catabolism of other purine bases.• 2- Pyrimidine bases• The pyrimidine bases present in nucleic acids are cytosine, thymine and uracil.• Cytosine is present in both DNA and RNA.• Thymine is present in DNA and uracil in RNA. 5
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  7. 7. 2- Pyrimidine bases• The pyrimidine bases present in nucleic acids are cytosine, thymine and uracil.• Cytosine is present in both DNA and RNA.• Thymine is present in DNA and uracil in RNA.7
  8. 8. Nucleoside structure• Base + Sugar → Nucleoside• Ribonucleosides: Adenine + Ribose → Adenosine Guanine + Ribose → Guanosine Uracil + Ribose → Uradine Cytosine + Ribose → Cytidine Hypoxanthine + Ribose → Inosine Xanthine + Ribose → Xanthosine 8
  9. 9. • Deoxy ribonucleosides:Adenine + Deoxyribose → Deoxyadenosine (d-adenosine)Guanine + Deoxyribose → d-GuanosineCytosine + Deoxyribose → d-CytidineThymine + Deoxyribose → d-thymidine9
  10. 10. Nucleotide structure• Base + Sugar + Phosphate• Types of nucleotide:1- Nucleoside monophosphatee.g. Adenosine + Pi → Adenosine monophosphate (Adenylic acid ) (AMP).2- Nucleoside diphosphatee.g. Adenosine + 2Pi → Adenosine diphosphate (ADP).3- Nucleoside triphosphatee.g. Adenosine + 3Pi → Adenosine triphosphate (ATP). 10
  11. 11. Nucleotide structure11
  12. 12. Structure of DNA• Deoxyribonucleic acid (DNA) is composed of four deoxyribonucleotides:Deoxyadenylate (A) - Deoxyguanylate (G)Deoxycytidylate (C) - Deoxythymidylate (T)• These units are combined through 3’ to 5’ phosphodiester bonds to polymerize into a long chain.• The nucleotide is formed by a combination of base + sugar + phosphoric acid.• The 3’-hydroxyl of one sugar is combined to the 5’- hydroxyl of another sugar through a phosphate group. 12
  13. 13. Polynucleotide13
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  15. 15. • In the DNA, the base sequence is of paramount importance.• The genetic information is coded in the specific sequence of bases; if the base is altered, the information is also altered.• The deoxyribose and phosphodiester linkages are the same in all the repeating nucleotides.• Therefore, the message will be conveyed, even if the base sequences alone are mentioned as e.g.5’P-Thymine-Cytosine-Adenine-3’OHor 5’-T-C-A-3’. 15
  16. 16. Watson-Grick model af DNA structure1. Right handed double helix:• DNA consists of two polydeoxy ribonucleotide chains twisted around one another in a right handed double helix similar to a spiral staircase.• The sugar and phosphate groups comprise the handrail and the bases jutting inside represent the steps of the staircase. The bases are located perpendicular to the helix axis, whereas sugars are nearly at right angles to the axis. 16
  17. 17. 2- The base pairing rule:• Always the two strands are complementary to each other.• So, the adenine of one strand will pair with thymine of the opposite strand, while guanine will pair with cytosine.• The base pairing (A with T; G with C) is called Chargaff’s rule, which states that the number of purines is equal to the number of pyrimidines.3- Hydrogen bonding:• The DNA strands are held together mainly by hydrogen bonds between the purine and pyrimidine bases.• There are two hydrogen bonds between A and T while there are three hydrogen bonds between C and G. 17
  18. 18. 4- Antiparallel:• The two strands in a DNA molecule run antiparallel, which means that one strand runs in the 5’ to 3’ direction, while the other is in the 3’ to 5’ direction.• This is similar to a road divided into two, each half carrying traffic in the opposite direction. 18
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  21. 21. Replication of DNA• During cell division, each daughter cell gets an exact copy of the genetic information of the mother cell.• This process of copying the DNA is known as DNA replication.• In the daughter cell, one strand I derived from the mother cell; while the other strand is newly synthesized.• This is called semi-conservative type of DNA replication. 21
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  23. 23. Steps of Replication1. Each strand serves as a template or mold, over which a new complementary strand is synthesized.2. The base pairing rule is always maintained. The new strand is joined to the old strand by hydrogen bonds between base pairs (A with T and G with C).3. Polymerization of the new strand of DNA is taking place from 5’ to 3’ direction. This means that the template is read in the 3’ to 5’ direction. So, tha 3’ end of the last nucleotide is free. 23
  24. 24. Ribonucleic acid (RNA) • RNA is also a polymer of purine and pyrimidine nucleotides linked by phosphodiester bonds24
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  26. 26. Differences between RNA and DNARNA DNAMainly seen in cytoplasm Mostly inside nucleusUsually 100-5000 bases Millions of base pairsGenerally single stranded Double strandedSugar is ribose Sugar is deoxyribosePurins: Adenine, Guanine Purins: Adenine, GuaninePyrimidines: Cytosine, Uracil Pyrimidines: Cytosine, ThymineGuanine content is not equal Guanine content is equal toto cytosine and adenine is cytosine and adenine is equalnot equal to uracil to thymineEasily destroyed by alkali 26 Alkali resistant
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  28. 28. Types of RNA• Messenger RNA (mRNA).• Transfer RNA (tRNA) or (sRNA).• Ribosomal RNA (rRNA).28
  29. 29. Messenger RNA or mRNA• It acts as a messenger of the information in the gene in DNA to the protein synthesizing machinery in cytoplasm. It carries the message to be translated to a protein.• The template strand of DNA is transcribed into a single stranded mRNA. The is accomplished by the DNA dependent RNA polymerase. 29
  30. 30. Transfer RNA (tRNA) or (sRNA)• They transfer amino acids from cytoplasm to the ribosomal protein synthesizing machinery; hence the name transfer RNA.• Since they are easily soluble, they are also referred to as soluble RNA or sRNA.• They are RNA molecules present in the cytoplasm.• Each molecule is only 73-93 nucleotides in length; much shorter than mRNA molecules. 30
  31. 31. Transfer RNA31
  32. 32. Ribosomal RNA (rRNA)• Ribosomes provide necessary infrastructure for the mRNA, tRNA and amino acids to interact with each other for the translation process.• Thus, ribosomal assembly is the protein synthesizing machinery.• They contain different rRNAs and specific proteins. 32
  33. 33. Overview on protein synthesisThe information available in the DNA is passed to messengerRNA, which is then used for synthesis of a particular protein. 33
  34. 34. Steps of protein synthesis1. Replication:• DNA replication is like printing a copy of all the pages of a book.• The replication process occurs only at the time of cell division.2. Transcription:• It is taking place all the time. Only certain areas of the DNA are copied (selected region on the sense strand). 34
  35. 35. • The genetic information of DNA is transcribed (copied) to the messenger RNA (mRNA).• During transcription, the message from the DNA is copied in the language of nucleotides.3. Translation:• The mRNA then reaches the cytoplasm where it is translated into functional proteins.• During translation, the nucleotide sequence is translated to the language of amino acid sequence. 35
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