DNA, Replication, RNA, Protein Synthesis

1. DNA, Replication, RNA, Protein Synthesis

2. REVIEW OF DNA • DNA stands for Deoxyribonucleic Acid. • DNA contains the genetic codeand the “working instructions” for a cell.

3. Structure of DNA • DNA, which is a nucleic acid, is made up of monomers known as nucleotides. • Parts of a DNA nucleotide - 5carbon sugar called Deoxyribose - Phosphate group - Nitrogen Base – Adenine (A), Thymine (T), Guanine (G), Cytosine (C)

5. Bonding • Hydrogenbonds form between the nitrogenbases of two strands. • These hydrogen bonds occur between 2 specific nitrogen base pairs: A – T and G – C • Memory Helper for base pairing rules: straight letters pair together (A – T) and curved letters pair together (G – C)

7. DNA Replication • DNA replicates during S phaseof interphase. This occurs before cell division (mitosis). • DNA replicates in the nucleus, while in the form of chromatin. • DNA replicates according to Chargaff’s base pairing rules : A – T, G – C

8. DNA Replication – The Process • Replication takes place in a 2 Step Process: 1. An enzyme breaks the hydrogen bondthat is between the nitrogen bases, unzipping DNA. The DNA molecule is unzipped in several places ~ like a “broken zipper”.

9. 2. After DNA is unzipped, a second enzyme, called DNA polymerase helps bind free nucleotides to the exposed nitrogenbases. They bind according to Chargaff’s rules, so A – T, G – C. • This continues along both strands of DNA in both directions.

11. The end result is 2 • identical DNA • molecules. • Each new DNA • molecule consists of • one original strand • and one newly • formed strand. • These 2 DNA • molecules are the • sister chromatids that • undergo mitosis. • Remember this???

12. RNA • RNA stands for Ribonucleic acid • RNA carries out the instructions of DNA by protein synthesis. • DNA is too large (double stranded) to leave the nucleus, so RNA (which carries the code of DNA), leaves the nucleus through the nuclear poresand help make proteins at ribosomes out in the cytoplasm.

13. Structure • RNA, which is a nucleic acid, is made up of monomers known as nucleotides. Parts of a RNA nucleotide • 5carbon sugar called ribose • Phosphate group • NitrogenBase – Adenine (A), Uracil(U), Guanine (G), Cytosine (C). • RNA is a single helix molecule. Nucleotide

14. Compare & Contrast of DNA & RNA

16. Types of RNA • There are 3 forms of RNA involved in carrying out the genetic instructions of DNA: 1. mRNA – messengerRNA; It carries the instructions (message) from DNA in the nucleus to the Ribosomes. 2. tRNA–transfer RNA; It carries (transfers) the amino acidsto the ribosome according to the message of mRNA. 3. rRNA– ribosomal RNA; It is part of the structural component of the ribosomes; it also produces enzymes neededto bond the amino acidstogether to form the proteins.

17. Protein Synthesis Protein synthesis occurs in 2 steps: • The genetic material contained in DNA must be transcribed (rewritten) onto an RNA molecule. • The message contained in RNA must be translated(converted) into a specific molecule.

18. Transcription (DNA transferred to RNA) • Transcription takes place in the nucleusand allows for the genetic code of DNA to be carried out to the ribosome. This happens in G1 of interphase. (Remember G1 where normal cell activities take place?)

19. Steps of Transcription 1. The enzyme, RNA polymerase, unzips part of the DNA molecule.

20. 2. RNA polymerase adds nucleotides(A,U,G,C) according to Chargaff’s rules (A – U, G – C), and RNA is synthesized.

21. Initially mRNA has too many nucleotides, some code for proteins and some do not. • Nucleotides in mRNA are classified as introns or exons. Introns – not requiredfor protein synthesis – they are removedfrom mRNA. Exons – requiredfor protein synthesis – kept and bonded together once the introns are removed. “EX”ONS = “EX” pressed “IN”TRONS = “IN” between the good stuff

24. 3. Then the new mRNA strand breaks apart from DNA, leaves the nucleus through the nuclear pores and goes to the ribosomes, the site of protein synthesis.

25. There are 2 important ways that transcription differs from replication: • Only one side of the DNA molecule is copied in transcription, both sides are copied in replication. • In transcription, RNA is used, so the nitrogen base that pairs with adenine is uracil, in DNA replication, adenine pairs with thymine.

26. http://www.johnkyrk.com/DNAtranscription.html • RNA being made! - transcription

27. Translation (RNA transferred to Proteins) • Translation takes place in the cytoplasm at ribosomes. The message is carried by mRNA, it is interpretedby tRNA, and the final product is a protein.

28. Codon • Codon = a group of 3 nucleotides on mRNA that codes for a specific amino acid. • A codon can be made up of any combination of the 4 nucleotides (A, U, G, C), therefore there are up to 64 possible codons. (b/c 4 x 4 x 4 = 64) Ex: AAA, AAU, AAG, AAC • Many different codons represent the same amino acid b/c there are 64 possible codons, and only 20 amino acids. • Amino acids are the building blocks (or monomers) of proteins. Even though there are only 20 amino acids, there are many, many proteins. It is the number and arrangement of the amino acids that makes every protein unique.

29. Start codon: AUG – starts the making of the amino acid chain. • Stop codon: signal to stop the making of the amino acid chain. • Genetic Code is universal, therefore the codons codesfor the same amino acid in all organisms.

30. The mRNA message is translated by the ribosome using these codons. 1st letter 3rd letter 2nd letter

31. Practice: AUG _________ UCA _________ CGG _________ GAG _________ GAA _________ AAU _________

32. tRNA • The tRNA molecule (which is out in the cytoplasm) has an amino acid on one end and an anticodon on the other end.

33. Anticodon – an anticodon is a group of 3 nucleotides on tRNA that pairs up to the codon on mRNA. • Acts as a binding site- The anticodon bindsto the mRNA codon according to base pairing rules (A-U, G-C) and insures that the proper amino acid is brought to the ribosome. • tRNA - transfersthe amino acidsspecified by the mRNA codon to the inside of the ribosomes for protein synthesis. The amino acid is then transferred to the growing polyopeptidechain. (polypeptide chain = becomes a protein)

35. Building of a protein • The mRNA molecule slides through the ribosome one codon at a time. • The specified amino acids are carried to the ribosome by tRNA. • As another tRNA arrives at the ribosome, the tRNA already there is bumped off, but leaves its amino acidbehind. • This process continues and a chain of aminoacids forms until a stop codon is reached. • Then the ribosome releasesthe amino acidchain, which coilsand folds to form a protein.

37. Steps for translation: • mRNA attaches to the • ribosome • mRNA message in the form • of codons is read by the • ribosome. • Amino acids are made as the • mRNA is being read • tRNA transfers these amino • acids to the inside of the • ribosome • Amino acid chains form in • the ribosome • Stop codon is reached • Protein (amino acid chain) is • released and tRNA and • mRNA is released.

39. http://learn.genetics.utah.edu/units/basics/transcribe/ • Suggested Study Questions • Pp 315 (3-10, 12-16, 18-21, 23)