Molecular Genetics DNA Replication Two kinds of nucleic acids in cells: DNA and RNA. DNA function 1: DNA transmits genetic information from parents to offspring. DNA function 2: DNA controls the functions of cells by serving as a blueprint for making proteins. RNA function 1: Assists DNA in the control of cell functions. The flow of genetic information from DNA DNA RNA PROTEIN 1
The study of DNA and RNA functions DNA function 1: ow DNA transmits genetic information from parents to offspring: DNA Replication. DNA function 2: ow DNA controls the functions of cells by serving as a blueprint for making proteins: Transcription and Translation. RNA function 1: ow RNA assists DNA in controlling the functions of cells: Transcription. The flow of genetic information from DNA Replication DNA RNA PROTEIN Transcription Translation DNA function 1: DNA transmits genetic information from parents to offspring: DNA replication. DNA Parent cell divides DNA DNA Daughter cells 2
To understand DNA replication, you must understand the structure of DNA! Nucleic acid structure review Phosphate group Nitrogenous base Sugar Sugar-phosphate backbone DNA nucleotide monomer Phosphate group Nitrogenous base (A, G, C, or T) Thymine (T) Sugar (deoxyribose) DNA nucleotide monomer DNA polynucleotide polymer DNA has four kinds of nitrogenous bases Thymine (T) Pyrimidines Cytosine (C) Adenine (A) Purines Guanine (G) N O O P O O Phosphate group C 2 O N N N N Nitrogenous O base (A) Deoxyribose sugar 3
DNA consists of two sugar phosphate backbones, a double helix. Four different nitrogenous bases are found in DNA = A, T, G, C. A T C A forms hydrogen bonds with T. G forms hydrogen bonds with C. One base pair C G C G T A C G A T T A G C A T A T T A RNA is structurally different from DNA A RNA nucleotide N O O P O O Phosphate group C 2 O O N N O N N Nitrogenous base (A) Ribose sugar RNA structure RNA consists of one, sugar phosphate backbone. Four different nitrogenous bases are found in RNA: A, U, G, C. 4
DNA versus RNA structure DNA versus RNA structure Sugar Nitrogenous bases used # of backbones elix forming DNA RNA deoxyribose ribose A,T,G,C A,U,G,C 2 1 Yes No Base pair DNA is a double helix. 5
ydrogen bond Phosphates on the outside of the double helix. 5 end has a free phosphate group 3 end has a free hydroxyl group 3 end has a free hydroxyl group 5 end has a free phosphate group TE TWO DNA STRANDS ARE ANTIPARELLEL TO EACOTER ow does DNA replication work and allow for the transmission of genetic information? 6
1) DNA replication is the process in which a cell makes an exact copy of its genetic information (DNA) 2) DNA replication is done before a cell divides. DNA replication follows a series of steps: Step 1) The two parental DNA strands separate. Step 2) Each strand is used as a template to produce a complementary strand, using the base pairing rules and enzymes. Step 3) Each new daughter DNA helix has one old strand combined with one new strand. Complementary strands of DNA are essentially the same as sister chromatids! DNA replication depends on specific base pairing DNA DNA DNA Nucleotides Parental molecule of DNA Both parental strands serve as templates Two identical daughter molecules of DNA Steps 1 and 2 Step 3 7
DNA replication must Replication must be fast and accurate. Requires disrupting the double helix structure of DNA. Must copy both, UGE, parental DNA strands at the same time. ow to make DNA replication faster DNA replication proceeds in two directions at many, specific sites along the DNA double helix! Origin of replication Parental strand Daughter strand Two daughter DNA molecules DNA polymerase adds complementary bases to each separated DNA strand at the 3 end 8
5 end has a free phosphate group 3 end has a free hydroxyl group 3 end has a free hydroxyl group 5 end has a free phosphate group TE TWO DNA STRANDS ARE ANTIPARELLEL TO EACOTER 5 3 DNA polymerase protein 3 5 Daughter strand Parental DNA synthesized continuously 3 5 Daughter strand synthesized in pieces 5 3 DNA ligase protein to fill in gaps. Overall direction of DNA replication Molecular Genetics Transcription 9
The study of DNA and RNA functions DNA function 1: ow DNA transmits genetic information from parents to offspring: DNA Replication DNA function 2: ow DNA controls the functions of cells by serving as a blueprint for making proteins: Transcription and Translation. RNA function 1: ow RNA assists DNA in controlling the functions of cells: Transcription. To understand Transcription and Translation, you must understand a bit more about the flow of genetic information. The flow of genetic information from DNA Replication DNA RNA PROTEIN Transcription Translation Each gene gives rise to one protein. One gene one polypeptide hypothesis 10
The flow of genetic information from DNA DNA Transcription NUCLEUS RNA Protein Translation CYTOPLASM Transcription occurs in the nucleus (eukaryotic cells). Translation occurs at ribosomes. The complete set of genes from an organism is called a genome. For example, our DNA genome contains ~20,000 genes. Genetic information written in codons is translated into amino acid sequences DNA strand Transcription RNA Translation Codon Polypeptide Amino acid 11
Dictionary of the genetic code (codons( codons) Second base First base Third base Characteristics of the genetic code 3 nucleotides, which make up a codon, specify 1 amino acid. AUG codes for the amino acid methionine and signals the start of translation. 3 stop codons signal the end of translation. Sometimes there is more than 1 codon for a given amino acid. Transcription is the process of making each DNA gene into. Three types of RNA in cells: 1) (messenger RNA). 2) trna (transfer RNA). 3) rrna (ribosomal RNA). 12
Transcription occurs in steps: 1) The DNA double helix is separated. 2) RNA polymerase (an enzyme) binds to the promoter sequence of the DNA, which is the start site of transcription. This step is called initiation. 3) RNA polymerase makes an copy of the gene. This is called elongation. 4) RNA polymerase stops transcription at the terminator sequence of the DNA; this is called termination. 5) The DNA comes back together into a double helix. RNA polymerase DNA of gene Promoter DNA 1 Initiation Terminator DNA 2 Elongation Area shown in Figure 10.9A 3 Termination Growing RNA Completed RNA (5 3 ) RNA polymerase RNA polymerase RNA nucleotides Direction of transcription Template DNA Newly made 13
Molecular Genetics Translation Eukaryotic is modified before leaving the nucleus! DNA Transcription NUCLEUS RNA Protein Translation CYTOPLASM Eukaryotic is modified before leaving the nucleus contains codons for making a protein. Eukaryotic has codon-interrupting sequences called introns, separated by codon-containing regions called exons. Intron: DNA region (sequence) within a gene that is not translated into protein Exons: DNA region (sequence) that is are expressed or translated into protein. 14
Eukaryotic is modified before leaving the nucleus, the steps: 1) A 5 cap and 3 tail are added to the. The 5 cap is is a singe guanine (G). The 3 tail is a stretch of A s (Adenine). 2) Introns are removed from the. 3) Exons are bonded together. 4) Mature can now exit the nucleus for translation. DNA Cap RNA transcript with cap and tail Exon Intron Exon Intron Exon Transcription Addition of cap and tail Introns removed Tail Exons spliced together Coding sequence Nucleus Cytoplasm Why have exons and introns in eukaryotes? Exons DNA 1 2 3 4 5 RNA transcript 1 2 3 4 5 RNA splicing or 1 2 3 5 1 2 4 5 15
Transcription plays a key role in cell specialization Muscle cell Pancreas cells Blood cells Different functions and features, but all contain the same ~20,000 genes. Cell specialization is influenced by turning on or off specific genes. Translation involves the following molecules and cell structures: Ribosomes trna Enzymes Proteins A source of energy, ATP trna molecules convert RNA language (codons)) to protein language! trna matches an amino acid to its RNA codon. An amino acid attachment site allows each trna to carry a specific amino acid (1 of the 20). An anticodon allows the trna to bind to a specific codon, complementary in sequence. 16
Amino acid attachment site trna molecule (1 trna for each amino acid) Anticodon Translation occurs at the ribosomes Ribosomes are composed of two subunits. Ribosomes have binding sites for and trna. Large subunit trna-binding sites binding site Small subunit Growing polypeptide Next amino acid to be added to polypeptide trna Codons 17
Translation occurs in three major steps: 1) Initiation. 2) Elongation. 3) Termination. Translation occurs in three major steps: 1) Initiation: A binds to the small subunit of the ribosome. The first trna binds to the start codon of the. The large subunit of the ribosome then joins the small subunit. The first trna occupies the P-site, which will hold the growing polypeptide. The A-site is available to receive a trna. Start of to be made into protein- start codon. Stop codon. 18
trna Met P site Met Large ribosomal subunit A site Start codon Small ribosomal subunit Initiation of translation, step 1 of translation. Translation occurs in three major steps: 2) Elongation and 3) Termination: The next trna binds to the A-site. The polypeptide at the P-site forms a new peptide bond with the amino acid at the A-site. The P-site trna now leaves the ribosome. The trna plus polypeptide in the A-site now moves to the empty P-site. The next codon in the is now the A-site. Termination stops this process at a stop codon. Polypeptide Amino acid P site Codons A site Anticodon 1 Codon recognition 2) Elongation and 3) Termination 19
Polypeptide Amino acid P site Codons A site Anticodon 1 Codon recognition 2 Peptide bond formation 2) Elongation and 3) Termination Polypeptide Amino acid P site Codons A site Anticodon 1 Codon recognition New peptide bond 2 Peptide bond formation 3 Translocation 2) Elongation and 3) Termination Polypeptide Amino acid P site Codons A site Anticodon 1 Codon recognition movement Stop codon New peptide bond 2 Peptide bond formation 3 Translocation 2) Elongation and 3) Termination 20
The study of DNA and RNA functions DNA function 1: ow DNA transmits genetic information from parents to offspring: DNA Replication DNA function 2: ow DNA controls the functions of cells by serving as a blueprint for making proteins: Transcription and Translation. RNA function 1: ow RNA assists DNA in controlling the functions of cells: Transcription. The flow of genetic information from DNA Replication DNA Transcription RNA Translation PROTEIN DNA Transcription RNA polymerase is transcribed from a DNA template. Amino acid Translation Enzyme Each amino acid attaches to its proper trna with the help of a specific enzyme and ATP. trna ATP Anticodon trna Start Codon Large ribosomal subunit Small ribosomal subunit 1 Initiation of polypeptide synthesis. The, the first trna, and the ribosomal sub-units come together. 21
Growing polypeptide New peptide bond forming Codons 2 Elongation A succession of trnas add their amino acids to the polypeptide chain as the is moved through the ribosome, one codon at a time. Polypeptide (protein) Stop codon 3 Termination The ribosome recognizes a stop codon. The polypeptide is terminated and released. 22