DNA, RNA, and Protein Synthesis

1. DNA, RNA, andProtein Synthesis Chapter 12

2. Heat-killed, disease-causing bacteria (smooth colonies) Harmless bacteria (rough colonies) Harmless bacteria (rough colonies) Control(no growth) Heat-killed, disease-causing bacteria (smooth colonies) Disease-causing bacteria (smooth colonies) Dies of pneumonia Dies of pneumonia Lives Lives Live, disease-causingbacteria (smooth colonies) Fred Griffith (1928) • discovered transformation - one form of bacteria was transformed into another form …perhaps by a gene.

3. Oswald Avery (1944) • Avery expanded on Griffith’s experiment by destroying various compounds with enzymes and seeing if transformation occurred • found that __________was the molecule responsible for transformation.

4. Hershey and Chase (1952) • Radioactively labeled the PROTEIN of a virus with sulfur and the DNA of a virus with phosphorus • After the virus transmitted genetic material into the bacteria cell, radioactive phosphorus was found in the cell • Means the genetic material is DNA

5. Chargaff

6. Rosalind Franklin • Saw X-shaped pattern with X-ray diffraction

7. Watson and Crick • Published article on DNA structure based on Franklin’s x-rays • Credited with the discovery of the “double helix”

9. Structure of Deoxyribonucleic acid (dna) • Nucleic acids are made of subunits called nucleotides • 3 components of a DNA nucleotide • Deoxyribose sugar (5-carbon, pentagon shaped) • Phosphate group • Nitrogen base – 4 nitrogen bases in 2 categories • Purines: adenine and guanine - double-ringed structure • Pyrimidines: thymine and cytosine - single-ringed structure

10. Purines Pyrimidines Adenine Guanine Cytosine Thymine Deoxyribose Sugar Phosphate group nucleotide Pg 291 What’s missing in this picture?

11. Nucleotide Hydrogen bonds Sugar-phosphate backbone • DNA shape is double stranded, called a “Double Helix” • sugars and phosphates in nucleotides alternate forming the backbone with covalent bonds • bases attach in center by weak hydrogen bonds • Adenine always bonds with Thymine • Guanine always bonds with Cytosine Key Adenine (A) Thymine (T) Cytosine (C) Guanine (G) Pg 294

12. Base pairing rules create two strands that are complementary to one another • Ex: original strand= A G G T C C T A • The amount and order of bases determines genes • DNA has the same molecular structure in all organisms but • single circular strand of DNA in prokaryotes • DNA in the form of X-shaped chromosomes in eukaryotes

13. DNA Replication • Occurs in nucleus • Because strands are complementary, each strand serves as a template for a new strand

14. Steps in Replication • The enzyme helicase causes DNA to unwind then unzip by breaking hydrogen bonds between base pairs • Each strand serves as a template for the attachment of a NEW complementary strand by bringing in new base pairs • The enzyme DNA Polymerase joins the new bases and DNA recoils

15. Replication is “semi-conservative”-each double stranded DNA molecule is composed of one new strand & one old strand Original strand DNA polymerase New strand pg298 Growth DNA polymerase Growth Replication fork Replication fork Nitrogenous bases New strand Original strand

16. RNA – Ribonucleic Acid How is RNA different from DNA? • Single stranded • Ribose sugar • Uracil (U) instead of Thymine Three types of RNA • messenger RNA (mRNA)-carries instructions for assembling proteins from DNA to the ribosome • transfer RNA (tRNA)-brings amino acids to the ribosome • ribosomal RNA (rRNA)-component of ribosome

17. Adenine (DNA and RNA) Cystosine (DNA and RNA) Guanine(DNA and RNA) Thymine (DNA only) Uracil (RNA only) RNApolymerase DNA RNA Transcription • copying info from one form to another (DNA RNA) • occurs in nucleus before protein synthesis • DNA is unzipped by enzymes • mRNA copy of the DNA is made by bases pairing • After completion, mRNA breaks off—DNA strands rejoin after transcription • mRNA leaves nucleus and travels to ribosome for protein synthesis

18. The Genetic Code • Portions of DNA, called genes, code for proteins which control ______. How do genes code for amino acids?

19. Genetic Code (cont) • codon-each set of three consecutive nucleotides that codes for a specific amino acid • There are 64 possible codons (43) for 20 amino acids • 61 code for amino acids, 3 code as “stop” codons • each codon codes for a specific amino acid, but some amino acids are coded for by more than one codon

20. Genetic Code (cont) Examples: Which amino acid is coded for by the following mRNA codons? • AAA • AGA • GAU • UAG Which codon(s) code(s) for the following amino acids? • Valine • Histidine • Serine • Isoleucine

21. Translation (protein synthesis) • occurs at the ribosome • putting the info into a new language (RNA  Protein) • Converts the information in a sequence of nitrogenbases in mRNA into a sequence of aminoacids that make up a protein

22. Steps in Translation • mRNA attaches to a ribosome • The ribosome has 2 bonding sites for tRNA • tRNA brings amino acids to the ribosome • tRNA has three bases called the anticodon (complementary to the codon on mRNA) and a specific amino acid attached to it • AUG is the “start codon” for protein synthesis. Draw the tRNA that will bond to this codon.

23. Nucleus Messenger RNA Messenger RNA is transcribed in the nucleus. Lysine Phenylalanine tRNA Methionine Ribosome Start codon mRNA

24. Steps in Translation • The ribosome attaches the amino acids on tRNA by peptide bonds Lysine tRNA mRNA Translation direction Ribosome

25. Steps in Translation • The ribosome moves down the mRNA strand by codons until it reaches a stop codon Growing polypeptide chain Ribosome tRNA mRNA

26. Gene Mutations • any mistake in DNA is a mutation • source of evolution, genetic disorders, cancer, etc. • can be random, can be caused by environmental factors • x-rays, chemicals, radioactive substances, UV light Two types of gene mutations: • point mutation-change in a single base pair in DNA sequence (also called a substitution) • some do not impact protein function, others are disastrous

27. ex of point mutation THE CAT ATE THE RAT Replace this letter with a C. What happens? THE CAT CTE THE RAT What if the 6th DNA nucleotide was changed instead of the 5th?

28. Gene Mutations (CONT) • frameshift mutation-results from the addition (insertion) or deletion of a single base pair. • Proteins resulting from these mutations are rarely functional and usually disasterous

29. ex of frameshift mutations (insertion and deletion) THE CAT ATE THE RAT DELETE this “A”. What happens? THE CAT TET HER AT The “reading” frame shifts. THE CAT ATE THE RAT INSERT the letter “G”. What happens? THE CAT GAT ETH ERA T The reading frame shifts.