CHE 110 Chapter 22 PowerPoint

Chapter 22: Nucleic Acids, Translation, and Recombinant DNA

22.1 Nucleosides and Nucleotides

• Nucleic Acids: Unbranched polymers made of repeating nucleotide monomers.

  • Two types of nucleic acids: DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).

  • Function:

    • DNA: Stores and transmits genetic information.

    • RNA: Translates genetic information into proteins for cellular functions.

• Components of Nucleotides:

  • Monosaccharide: D-ribose in RNA, D-2-deoxyribose in DNA.

  • N-containing Base: 5 types total (C, U, T for pyrimidines; A, G for purines).

  • Phosphate Group.

• Nucleotide Composition:

  • DNA has several million nucleotides; RNA has a few thousand.

  • DNA found in chromosomes and contains genes (46 chromosomes in humans).

22.1.1 Nucleosides

• Definition: Formed by joining the anomeric carbon of a monosaccharide with a nitrogen atom of a base.

• Naming Conventions:

  • Pyrimidine-based nucleosides: Suffix -idine.

  • Purine-based nucleosides: Suffix -osine.

  • For deoxyribonucleosides, add prefix deoxy-.

22.1.2 Nucleotides

• Formation: Nucleotides result from adding a phosphate group to the 5′-OH of a nucleoside.

• Examples:

  • Cytidine 5′-monophosphate (CMP).

  • Deoxyadenosine 5′-monophosphate (dAMP).

  • ADP: Diphosphate example; ATP: Triphosphate example.

22.2 Nucleic Acids

• Structure: Polymers of nucleotides joined by phosphodiester linkages, forming a backbone of alternating sugar and phosphate groups.

• Primary Structure: Distinguished by the identity and order of bases.

• Ends of a polynucleotide: Free phosphate group at the 5′ end, free hydroxyl group at the 3′ end.

22.3 The DNA Double Helix

• Discovery: Watson and Crick proposed the double helix model in 1953.

• Structure:

  • Composed of two polynucleotide strands running in opposite directions (5′ to 3′ and 3′ to 5′).

  • Sugar-phosphate groups located on the outside; bases oriented towards the inside.

• Base Pairing:

  • Adenine (A) + Thymine (T) with 2 hydrogen bonds.

  • Cytosine (C) + Guanine (G) with 3 hydrogen bonds.

• Functions of DNA:

  • Directs protein synthesis, undergoes replication, and provides a template during transcription.

22.4 Replication

• Process: DNA replication results in two new DNA molecules each containing one parent strand and one newly synthesized strand.

• Replication Fork: Forms as the two DNA strands separate.

• Base Pairing Rules:

  • A pairs with T; G pairs with C.

• Direction of Replication: Occurs in one direction on the template strand (3′ to 5′) producing leading and lagging strands.

22.5 RNA

• Differences from DNA:

  • RNA has ribose as its sugar; uracil (U) replaces thymine (T).

  • Typically single-stranded and smaller than DNA.

• Types of RNA:

  • rRNA: Ribosomal RNA helps in assembling polypeptides during protein synthesis.

  • mRNA: Messenger RNA carries genetic info from DNA to ribosomes.

  • tRNA: Transfer RNA brings specific amino acids to the ribosome.

22.6 Transcription

• Process: Synthesis of mRNA from DNA.

  • DNA unwinds; the template strand is used to synthesize RNA.

  • Formation of mRNA occurs from 5′ to 3′ direction based on the template strand with U replacing T.

22.7 The Genetic Code

• Codons: Triplet sequences of nucleotides coding for specific amino acids.

  • Example: UAC codes for serine, UGC codes for cysteine.

• Translation Process:

  • Each tRNA has an anticodon that is complementary to mRNA codons.

22.8 Translation and Protein Synthesis

• Overview:

  • mRNA dictates amino acid sequence in the protein.

  • tRNA recognizes codons and brings appropriate amino acids to the ribosome.

  • rRNA provides binding sites for protein synthesis.

• Steps in Translation:

  • Initiation: Begins with mRNA binding to ribosome and tRNA bringing methionine (AUG).

  • Elongation: tRNA brings amino acids which are joined by peptide bonds.

  • Termination: Stops when a stop codon is reached (UAA, UAG, UGA).

22.9 Mutations and Genetic Disease

• Mutation: A change in the DNA sequence; can be random or induced by mutagens.

• Types of Mutations:

  • Point Mutation: Substitution of one nucleotide.

  • Deletion: Loss of one or more nucleotides.

  • Insertion: Addition of one or more nucleotides.

• Effects of Mutations:

  • Silent mutations (negligible effects).

  • Changes in amino acids affecting protein function (sickle cell anemia).

• Genetic diseases arise when mutations are detrimental and passed through generations.

22.10 Recombinant DNA

• General Principles: Synthetic DNA containing segments from multiple sources.

• Elements for Formation:

  • DNA molecule for inserting a new segment.

  • Restriction enzymes to cleave DNA.

  • Gene to be inserted from another organism.

• Polymerase Chain Reaction (PCR):

  • Amplifies specific DNA segments using primers and DNA polymerase to synthesize complementary strands.

22.11 Viruses

• Definition: An infectious agent made of DNA or RNA within a protein coat, incapable of independent replication.

• Types: Retroviruses (e.g., HIV), which synthesize DNA from RNA via reverse transcription.

• Impact of Viruses: Cause diseases including the common cold and HIV/AIDS.