DNA Replication and Protein Synthesis - Week 4 PDF

DNA replication and protein synthesis PHRM 105 General Biology Prepared by Dr Abdulrahman Aljabri Outline 1. Introduction Be the end of this session, students should be able to: 2. Genetic materials...

DNA replication and protein synthesis PHRM 105 General Biology Prepared by Dr Abdulrahman Aljabri Outline 1. Introduction Be the end of this session, students should be able to: 2. Genetic materials Nucleic acid (DNA and Define the DNA and RNA RNA) List the difference between DNA and RNA 3. DNA replication Demonstrate the DNA replication Describe the DNA replication steps 4. Repair mechanism Describe the protein synthesis List the basic difference between nucleic 5. Protein Synthesis acid and protein (Transcription & translation ) 1. Introduction  Molecular structure of the genetic material:  Until 1940: Protein is the genetic material.  Discovery of DNA as Genetic Material (1952): Scientists Hershey and Chase proved that DNA, not proteins, carries genetic information, showing that DNA is the key to inheritance.  Watson and Crick’s DNA Model (1953): Watson and Crick discovered the double-helix shape of DNA, explaining how genetic information is passed from one generation to the next. ‫لإلطالع‬ 2. Genetic materials (Nucleic acid( Nucleotide Nucleic acids are found in two basic structural forms: Base 1- Deoxyribonucleic acid (DNA). 2- Ribonucleic acid (RNA). Phosphate Nucleotides are building Sugar blocks of nucleic acids. A Nucleotide consists of: 1. Nitrogenous base, X=H: DNA (deoxyribose) 2. Pentose sugar, X=OH: RNA (ribose) 3. Phosphate group. 2. Genetic materials (Nucleic acid( Nitrogen bases of DNA and RNA: Purines Five kinds of nitrogenous bases: Purine bases Pyrimidine bases (DNA & RNA) Pyrimidines thymine (DNA & (DNA) RNA) 2. Genetic materials (Nucleic acid( DNA Structure: DNA Composed of (2) polynucleotide chains twisted into a helical shape C G A T Sugar-phosphate – Sugar-phosphate backbone is (outside) T A backbone C G Phosphate A T group – Nitrogen bases are perpendicular to the G G C A A Nitrogenous backbone (inside) base Nitrogenous base A T Covalent (can be A, G, C, or T ) G C bond Sugar joining – Pairs of bases give the helix a uniform T A C C T A nucleotides shape C T G A DNA Thymine (T) A DNA T nucleotide T – A (Adenine) pairs with T (Thymine), G double helix Phosphate group (Guanine) pairs with C (Cytosine) G G Sugar (deoxyribose ) DNA nucleotide G G Two representations of a DNA polynucleotide  2. Genetic materials (Nucleic acid( Three presentations of DNA and complement pairing Adenine pairs with Thymine Two hydrogen bonds Hydrogen bond A T Base pair Cytosine pairs with Guanine Three hydrogen bonds C G Ribbon model Partial chemical structure Computer model 2. Genetic materials (Nucleic acid( Comparison between DNA and RNA Feature DNA RNA Number of 2 1 strands in molecule Type of Deoxyribose ribose sugar in nucleotide Nitrogenous A,C,G,T A,C,G,U bases contained Basic Nucleotide Nucleotide subunits Nucleotide Sugar, base, Sugar, base, components phosphate phosphate This Presentation is NOT an Alternative to the Textbook! 2nd semester 2020/2021 3. DNA replication What is DNA Replication? DNA Replication is the process of making a copy of the genetic information contained in DNA and is catalyzed by a type of enzyme called DNA polymerase. Why is this process necessary? -Cell division -the transfer of genetic information from one generation to the next. -Renew cell How does DNA Replication occur? DNA Replication occurs through the semi-conservative mechanism, where each strand of the DNA double helix acts as a template for the synthesis of a new complementary strand.  3. DNA replication DNA replication proceeds in two directions at many sites simultaneously DNA replication begins at the origins of One replication. Parental DNA Origin of Parental strand DNA unwinds (open) at the origin to molecule replication Daughter strand produce a “bubble,” Replication proceeds in both directions from the origin, “Bubble” Replication ends when products from the bubbles merge with each other. Eukaryotic DNA has many origins to start replication simultaneously, shortening the total time. Two daughter DNA molecules This Presentation is NOT an Alternative to the Textbook! 2nd semester 2020/2021  3. DNA replication (Semiconservative model) The two DNA strands separate A T G C Each strand (from parent Parental strand used as a pattern A A T T Parental DNA molecule) is used as a pattern to T A molecule produce a complementary strand, Daughter strand used as using specific base pairing. complementary strand Daughter strand Parental Each new DNA helix has one old strand strand with one new strand DNA replication follows a semiconservative model. Daughter DNA molecules This Presentation is NOT an Alternative to the Textbook! 2nd semester 2020/2021 3. DNA replication DNA replication steps: 1. Untangles and relieves DNA stress by DNA Topisomerase. 2. Unzips DNA strands by Helicase. 3. Add RNA primer by primase, as starting point for DNA polymerase to begin synthesis of the new strand. 4. Adds complementary nucleotides by DNA polymerase. 5. Check and correct mistakes by DNA polymerase. 6. Seals gaps in DNA strands by DNA ligase. the leading continuousling strand is synthesized and the lagging strand is synthesized in fragments called Okazaki fragments. ‫لإليضاح‬ 3. DNA replication DNA Replication Significance End product: Two double-stranded DNA molecules, each with one new and one old strand. DNA replication occurs before cell division, ensuring identical genetic information in all cells. Essential for inheritance: Offspring receive identical DNA copies.  3. DNA replication When things go wrong… during DNA replication! Mutations: changes in the DNA sequence, that may be passed along to future generations. Point mutations: a single base substitution GCTACCGGTC GCTACCGCTC Deletion: a small DNA segment is lost Insertion: a segment of DNA is added Frame-shift mutation: modification of the reading frame after a deletion or insertion, resulting in all codons downstreams being different. 4. Repair mechanism Repair Mechanisms Mismatch Repair Base Excision and Proofreading by DNA Nucleotide Excision Polymerase DNA polymerase Repair Corrects replication errors by Corrects mismatched base pairs left Repairs single-base errors and checking and fixing incorrect after DNA replication proofreading. larger DNA structural distortions nucleotides immediately. efficiently. 5. Protein Synthesis A gene: a specific sequence of a DNA that directs the synthesis of a specific protein. How ?? This is through CENTRAL DOGMA and protein synthesis 1 2 Transcription Translation DNA RNA Proteins 5. Protein Synthesis 1. Transcription: DNA  RNA Where: Transcription occurs in the nucleus. Step 1: DNA unwinds in one part. Step 2: mRNA is made by matching bases with the DNA strand. Step 3: mRNA takes the instructions from the DNA to the ribosome to make a protein. 5. Protein Synthesis 2. Translation RNA  Protein Translation: Making a protein using the code in mRNA. In other word, switching from the nucleotide “language” to amino acid “language” Where: Occurs at the ribosome in the cell's cytoplasm. Ribosomal RNA (rRNA): Helps mRNA attach to the ribosome for protein synthesis. Transfer RNA (tRNA): Delivers the right amino acids to the ribosome to build the protein. 5. Protein Synthesis Transfer RNA (tRNA) Transport molecule that carries specific amino acid to a ribosome. Each tRNA recognizes the correct codon on the mRNA molecule. A codon: consisting of (3) nucleotides Each amino acid is specified by a codon  5. Protein Synthesis Translation steps Step 1: mRNA leaves the nucleus and goes to the ribosome. Step 2: mRNA attaches to the small ribosome subunit. Large subunit Step 3: tRNA brings an amino acid to the ribosome; its ribosome Small subunit anticodon matches with the mRNA codon. protein ribosome Step 4: Amino acids link together to form a growing mRNA protein chain. Step 5: tRNA without an amino acid leaves the ribosome. Step 6: More tRNAs bring amino acids until the protein is complete. 5. Protein Synthesis Summary transcription translation Definition Purpose Products Location protein Name 3 different RNA molecules involved in protein synthesis? 1. mRNA (messenger RNA) ---- transcription 2. rRNA (ribosomal RNA) ----- translation 3. tRNA (transfer RNA) --------- translation  Comparison of Nucleic Acids (DNA and RNA) and Proteins Category Nucleic Acids (DNA ) Nucleic Acids (RNA) Proteins Basic Unit Nucleotides Nucleotides Amino Acids Primary Function Genetic information Genetic information Catalysis of biochemical storage and storage and reactions, structural transmission transmission roles, signaling, and more Structure Double-stranded helix Single-stranded Primary, secondary, tertiary, and quaternary structures; complex folding Components Deoxyribose sugar, Ribose sugar, 20 standard amino Nitrogenous bases (A, T, Nitrogenous bases (A, acids G, C), phosphate U, G, C), phosphate Location Mainly in nucleus Nucleus and cytoplasm Found throughout the (eukaryotes) cell (cytoplasm, organelles, etc.)