Chapter 8 Lecture Outline See PowerPoint Image Slides for all figures and tables pre-inserted into

1. Chapter 8 Lecture Outline See PowerPoint Image Slides for all figures and tables pre-inserted into PowerPoint without notes.

2. DNA and the Importance of Proteins • Proteins play a crucial role in the life of a cell. • Microtubules, intermediate filaments and microfilaments maintain the shape of the cell. • Enzymes catalyze important reactions. • The recipes for proteins are found in the cell’s DNA. • DNA is organized into genes. • Each gene is a recipe for a different protein.

3. Nucleic Acid Structure and Function • DNA accomplishes two things: • Passes genetic information to the next generation • Controls the synthesis of proteins • DNA is able to accomplish these things because of its unique structure.

4. DNA Structure • DNA is a nucleic acid. • Nucleic acids • Large polymers made of nucleotides • A sugar molecule • Deoxyribose for DNA • Ribose for RNA • A phosphate group • A nitrogenous base • Adenine • Guanine • Cytosine • Thymine

5. DNA Structure • DNA is double- stranded. • Held together by hydrogen bonds between the bases • A-T, G-C

6. Base Pairing Aids DNA Replication • DNA replication • Is the process by which DNA is copied • This is done before cell division. • Provides the new cells with a copy of the genetic information • Relies on the base-pairing rules

7. Base Pairing Aids DNA Replication • Is accomplished by DNA polymerase and other enzymes • Helicase binds to DNA and forms a replication bubble by separating the two strands. • DNA polymerase builds new DNA strands that will pair with each old DNA strand. • Where there is an A on the old strand, polymerase will add a T to the new strand. • When DNA polymerase finishes a segment of new DNA, it checks its work and corrects mistakes if they happen.

8. DNA Replication

9. Repairing Genetic Information • If a mistake is made when building the new strand • The old strand still has the correct information. • This information can be used to correct the new strand.

10. The DNA Code • The order of bases in the DNA molecules is the genetic information that codes for proteins. • The sequence of nucleotides forms words that are like a recipe for proteins. • Each word contains three base letters. • ATGC are the four letters that are used to make the words. • Each three-letter word codes for a specific amino acid. • The order of amino acids in the protein is determined by the order of nucleotides in DNA.

11. RNA Structure and Function • RNA vs. DNA • RNA has ribose sugar (DNA has deoxyribose). • RNA contains the bases • Adenine • Guanine • Cytosine • Uracil (DNA has thymine)

12. DNA vs. RNA • RNA’s, like DNA’s, base sequence carries information. • RNA is made in the nucleus and transported to the cytoplasm (DNA stays in the nucleus). • The protein coding information in RNA comes from DNA. • Like DNA replication, RNA synthesis follows the base-pairing rules (A-U; G-C). • RNA is typically single-stranded (DNA is typically double-stranded). • Three types of RNA participate in protein synthesis • mRNA • tRNA • rRNA

13. Protein Synthesis • The sequence of nucleotides in a gene dictates the order of amino acids in a protein. • Before a protein can be made • The information in DNA must be copied into RNA. • This process is called transcription. • The information in the RNA can then be used to make the protein. • This process is called translation.

14. Transcription • During transcription • DNA is used as a template to make RNA • Accomplished by RNA polymerase and follows the base-pairing rules • The process of transcription • Occurs in the nucleus • RNA polymerase separates the two strands of DNA. • Only one of the two strands will be used to create the RNA. • The coding strand • The other DNA strand is called the non-coding strand.

15. Transcription of an RNA Molecule

16. The Process of Transcription • Only a segment of the DNA strand will be used to create each RNA. • These segments are called genes. • Each gene starts with a promoter. • The RNA polymerase binds to the promoter to start building an RNA strand. • Each gene ends with a terminator sequence. • The RNA polymerase will stop transcribing at the terminator sequence.

17. Translation • Three types of RNA participate in translation. • mRNA carries the recipe for making the protein. • tRNA and rRNA are used to read the recipe and build the amino acid chain. • Codons are sets of three nucleotides that code for specific amino acids. • tRNA reads the codons and brings the correct amino acids.

18. The Genetic Code

19. Translation • Ribosomes are organelles that build proteins. • rRNA is found in ribosomes. • mRNA is read on ribosomes. • Ribosomes are found in two places in the cell. • Free-floating in the cytoplasm • Bound to the endoplasmic reticulum

20. Translation Initiation • Translation begins when • The small ribosomal subunit binds to the beginning of the mRNA and searches for the AUG start codon. • At this point, a tRNA brings the first amino acid. • The anticodon in the tRNA matches with a codon on the mRNA. • Each tRNA carries a specific amino acid based on its anticodon. • The start codon, AUG, binds to a tRNA that carries a methionine. • Finally, the large ribosomal subunit joins the complex and the next step, translation elongation, can proceed.

21. Initiation

22. Translation Elongation • The next tRNA binds with the next codon on the mRNA. • The ribosome adds this amino acid to the growing polypeptide. • The ribosome then moves down to the next codon. • The process repeats itself. For each step, a new amino acid is added to the growing protein.

23. Elongation

24. Translation Termination • Elongation continues until the ribosome encounters a stop codon. • UAA, UAG, UGA are stop codons. • A release factor binds to the stop codon. • This causes the ribosome to release the polypeptide. • The ribosomal subunits separate and release the mRNA. • The mRNA can be translated again by another ribosome.

25. Termination

26. Summary of Protein Synthesis

27. The Genetic Code is Nearly Universal • The process of making proteins from the information in DNA is used by nearly all cells. • Nearly all organisms studied to date use the same genetic code. • Because of this, we are able to use bacteria as factories to make massive amounts of proteins. • Insulin, growth factor, etc.

28. Control of Protein Synthesis • Gene expression is how the cell makes a protein from the information in a gene. • Cell types are different from one another because they express different sets of genes. • Therefore, have different sets of proteins • Cells control gene expression in response to different environmental conditions. • Cells can alter gene expression • Controls the quantity of a protein • Controls the amino acid sequence of a protein

29. Control of Protein Quantity • Cells can regulate how much of a given protein is made by • Controlling how much mRNA is available for translation • Cells do this in a number of ways: • Regulating how tightly the chromatin is coiled in a certain region • The more tightly the chromatin is coiled, the less likely a gene in that region will be transcribed.

30. Eukaryotic Genome Packaging

31. Control of Protein Quantity • By increasing or decreasing the rate of transcription of the gene by enhancer and silencer regions on the DNA • Activation of enhancer regions increases transcription. • Activation of silencer regions decreases transcription. • Through the binding of transcription factors, • These proteins bind to the promoter and facilitate RNA polymerase binding and transcription. • By limiting the amount of time the mRNA exists in the cytoplasm, • Some mRNA molecules are more stable and will exist longer in the cytoplasm, yielding more protein.

32. Different Proteins from One Gene • Eukaryotic cells can use one gene to make more than one protein. • In eukaryotic genes, non-coding sequences called introns, are scattered throughout the sequence. • After transcription, the introns must be cut out and the coding regions, called exons, must be put back together. • This is called splicing.

33. Transcription of mRNA in Eukaryotic Cells

34. Alternative Splicing • Different combinations of exons from a single gene can be joined to build a number of different mRNAs for a number of different proteins.

35. Mutations and Protein Synthesis • A mutation is any change in the DNA sequence of an organism. • Can be caused by mistakes in DNA replication • Can be caused by external factors • Carcinogens, radiation, drugs, viral infections • Only mutations in coding regions of gene will change the proteins themselves.

36. Point Mutations ̶ a Change in a Single Nucleotide of the DNA Sequence Three types: • A nonsense mutation changes a codon to a stop codon. • This causes the ribosome to stop translation prematurely. • CAA (Gln) to UAA (stop) • A missensemutation causes a change in the type of amino acid added to a polypeptide. • This may change the way in which a protein functions. • UUU (Phe) to GUU (Val) • A silent mutation does not cause a change in the amino acid sequence. • UUU to UUC; both code for Phe

37. Point Mutations

38. Sickle Cell Anemia • Results from a missense mutation in the gene for hemoglobin • GAA to GUA • Glutamic acid to valine change • Causes the hemoglobin protein to change shape • The molecules stick together in low oxygen conditions. • Get stuck in blood vessels, causing the vessels to break apart easily, leading to anemia • Also causes blood vessels to clog, preventing oxygen delivery to tissues, which results in tissue damage • Causes weakness, brain damage, painful joints, etc.

39. Normal and Sickled Red Blood Cells

40. Insertions and Deletions • An insertion mutation occurs when one or more nucleotides is added to the normal DNA sequence. • A deletion mutation occurs when one or more nucleotides is removed from the normal DNA sequence. • Insertions and deletions cause a frameshift. • Ribosomes will read the wrong set of three nucleotides. • Changes the amino acid sequence dramatically • Changes the function of the protein dramatically

41. Frameshift

42. Mutations Caused by Viruses • Viruses can insert their genetic material into the DNA of the host cell. • The presence of the viral material may interfere with the host cell’s ability to use the genetic material in that area because of this insertion. • Insertion of human papillomavirus (HPV) causes an increased risk of cancer.

43. Chromosomal Aberrations • Involves a major change in DNA at the level of the chromosome • Inversions occur when a chromosome breaks, and the broken piece becomes reattached in the wrong orientation. • A translocation occurs when the broken segment becomes integrated into a different chromosome. • A duplication occurs when a segment of a chromosome is replicated and attached to the original segment in sequence. • A deletion occurs when a broken piece is lost or destroyed. • All of these effect many genes, thus many proteins. • In humans, these mutations may cause problems with fetal development.