DNA AND PROTEIN SYNTHESIS

1. DNA AND PROTEIN SYNTHESIS

2. DNA (DEOXYRIBONUCLEIC ACID) • Nucleic acid that composes chromosomes and carries genetic information.

3. CHROMOSOME ORGANIZATION 1. A chromosome is an enormous strand of super coiled DNA. 2. Sections of DNA on the chromosome that code for proteins are called genes. 3. Noncoding sections of DNA are called “junk DNA” (regulatory or unknown function)

5. BUILDING BLOCKS OF DNA Composed of nucleotides • Nucleotides contain three parts: 1. 5-Carbon Sugar (deoxyribose) 2. Phosphate Group 3. Nitrogen Base (four types, adenine, guanine, thymine and cytosine)

7. Adenine and Guanine are purines (composed of two rings of nitrogen atoms)

8. Thymine and Cytosine are pyrimidines (composed of one ring of nitrogen atoms)

9. STRUCTURE OF DNA • Consists of two strands of nucleotides that form a twisted ladder (double helix) • Sugar and phosphate alternate along the sides of the ladder (linked by strong covalent bonds) • Pairs of nitrogen bases form the rungs of the ladder (linked by weak hydrogen bonds).

10. Specific base pairing arrangement (Chargaff’s Rule) A-T : 2 hydrogen bonds C-G : 3 hydrogen bonds • Nitrogen bases attach to the sugar portion of the side (NOT the phosphate) • Strands run in opposite directions

12. FUNCTION OF DNA • DNA codes for proteins (structural proteins, enzymes, and hormones) • information for building proteins is carried in the sequence of nitrogen bases • proteins determine physical and metabolic traits and regulate growth and development.

14. The Flow of Genetic Information • The Relationship between Genes and Proteins

15. RNA (RIBONUCLEIC ACID) • Nucleic acid involved in the synthesis of proteins Structure - Composed of nucleotides, but differs from DNA in three ways. • Single strand of nucleotides instead of double stranded • Has uracil instead of thymine • Contains the sugar ribose instead of deoxyribose

17. RNA FUNCTION Three forms of RNA involved in protein synthesis 1. mRNA (messenger): copies instructions in DNA and carries these to the ribosome. 2. tRNA (transfer): carries amino acids to the ribosome. 3. rRNA (ribosomal): composes the ribosome.

18. PROTEIN SYNTHESIS Cells build proteins following instructions coded in genes (DNA). • Consists of two parts: 1. Transcription – transcribing genetic information 2. Translation – translating a molecular ‘language’; nucleotides (mRNA) to amino acids (polypeptide chain)

19. TRANSCRIPTION • DNA is copied into a complementary strand of mRNA. WHY? • DNA cannot leave the nucleus. Proteins are made in the cytoplasm. mRNA serves as a “messenger” and carries the protein building instructions to the ribosomes in the cytoplasm.

20. HOW DOES TRANSCRIPTION OCCUR? • RNA polymerase untwists and unzips a section of DNA (usually a single gene) from a chromosome. This is called Initiation. • RNA polymerase pairs free RNA nucleotides to the exposed bases of one of the DNA strands following base pair rules. This is called Elongation. • Uracil replaces thymine • Only 1 strand of DNA serves as a template, the other “hangs out”

21. Newly synthesized mRNA separates from template DNA and DNA zips back up. This is called Termination.

22. RNA Processing • mG (methyl-guanine) cap is added to starting end. • String of adenines added to the other end (a poly-A tail) • These protect the mRNA from being broken down. Cap helps mRNA attach to ribosome. • Splicing occurs to remove non-coding segments called introns. • Remaining, coding segments are exons.

23. RESULT OF TRANSCRIPTION • mRNA strand with instructions for building a protein that leaves the nucleus and goes to the cytoplasm. TRANSCRIPTION EXAMPLE • Transcribe the following DNA Sequence in mRNA DNA - TAC CGG ATC CTA GGA TCA mRNA - AUG GCC UAG GAU CCU AGU

24. Intermediary in Protein Synthesis • Why would the cell want to have an intermediate between DNA and the proteins it encodes? • The DNA can then stay pristine and protected, away from the caustic chemistry of the cytoplasm. • Gene information can be amplified by having many copies of an RNA made from one copy of DNA. • Regulation of gene expression can be effected by having specific controls at each element of the pathway between DNA and proteins. The more elements there are in the pathway, the more opportunities there are to control it in different circumstances.

26. GENETIC CODE The “language” that translates the sequence of nitrogen bases in DNA (mRNA) into the amino acids of a protein. • Codon = three nucleotides on DNA or mRNA • One codon specifies one amino acid • Some codons are redundant (code for the same amino acid) • The genetic code is universal to all organisms

28. DNA: TAC CTT GTG CAT GGG ATC mRNA AUG GAA CAC GUA CCC UAG A.A MET G.A HIS VAL PRO STOP

29. IMPORTANT CODONS • AUG = start translation (Met) • UAA, UAG, UGA= stop translation TRANSLATION - Instructions in mRNA are used to build a protein - Location of Translation - ribosome (in the cytoplasm)

30. PROCESS OF TRANSLATION 1. mRNA binds to the ribosome. 2. Ribosome searches for start codon (AUG) 3. tRNA brings correct amino acid (methionine) to the ribosome. - Each tRNA carries one type of amino acid. - The anti-codon (three nitrogen bases on tRNA) must complement codon for amino acid to be added to protein chain

32. 4. Ribosome reads next codon 5. tRNA’s continue lining up amino acids according to codons 6. Peptide bonds link amino acids together 7. Ribosome reaches STOP codon • Amino acid chain is released

33. RESULT OF TRANSLATION A Protein

34. PROTEIN STRUCTURE • The amino acid sequence causes protein to fold/coil up into unique shapes. The molecule is held in shape by intermolecular bonding. These shapes give a protein its unique function. • Primary, Secondary, Tertiary, and Quaternary structures.

35. - Some proteins must be modified before functional: Endoplasmic Reticulum - Then they may be sent to the membrane or out of the cell: Golgi Apparatus

36. Differences between Prokaryotes and Eukaryotes • In prokaryotes: • One circular gene. • 90% translated, few introns. • Some additional genes may be found on plasmids, smaller DNA circles. • Plasmids can be transferred between bacteria for a type of “sexual reproduction”.

39. Viruses • Tiny particles that have no cells, yet they replicate, and evolve. • Must use host cells gene expression machinery. Viral genetic info can be DNA or RNA. • Retroviruses use Reverse Transcription. (ex. HIV): Genetic code in RNA. In host, viral enzyme called reverse transcriptase makes a DNA copy. DNA copy joins host DNA and more viruses are produced.

40. Errors in Protein Synthesis • Frame shift mutations – initiation starts 1 or 2 bases off b/c insertion or deletion. Changes the reading frame. Results in different amino acid sequence. Ex: Tay-Sachs disease

41. Point mutation a. Change of 1 base pair. Usually results in no change in the organism. Ex: sickle cell anemia and achondroplasia, a form of dwarfism • Somatic cell vs. Sex cell mutations a. Somatic cell mutation affects only one cell. Not inherited. b. Mutation of tumor suppressor genes in somatic cells may lead to cancer. c. Mutations in sex cells are inherited and will be found in all cells of the offspring.

42. Gene amplification - Creates extra copies of genes within a cell. Normal part of development. Specialized cells may need several copies of a gene. • Ex: human pancreatic cells have many copies of gene that codes for insulin. - Ex: Oncogenes (like ras) are often amplified in cancer cells.