Unit 7: Nucleic Acids and Protein Synthesis

1. Unit 7: Nucleic Acids and Protein Synthesis Mrs. P

2. DNA: The blue print of Life • All living organisms have deoxyribonucleic acid in the nucleus of their cells that controls all of the reactions and events that are needed for life to exist.

3. DNA • The DNA of a cell is contained in structures called chromosomes (look like an X). • Chromosomes are made of chromatin. • Chromatin is a mixture of DNA wrapped around small proteins called histones.

4. Watch this clip about the structure of chromosomes

5. THE MOLECULAR STRUCTURE OF DNA • The structure of DNA was discovered by two scientists, James Watson and Francis Crick, in 1956. • They were also assisted by work of Rosalind Franklin.

6. DNA Structure • The DNA molecule is made of two strands that wrap around each other to form a long, twisted ladder called a double helix. • Each strand is made up of repeating monomers called nucleotides.

7. Each nucleotide has three components of its own: • nitrogen base (adenine, thymine, guanine, cytosine, uracil) • 5 carbon sugar (deoxyribose or ribose) • Phosphate group

8. A nucleotide can have one of four bases: • Adenine – a purine (double rings) • Guanine – a purine (double rings) • Cytosine – a pyrimidine (single ring) • Thymine – a pyrimidine (single ring)

9. Connecting the two strands • The sides of the “DNA ladder” are made of sugar and phosphate groups, • while the “rungs” are made of two nitrogenous bases.

10. Connecting the Strands The nitrogenous bases pair up in a particular way: • Adenine pairs with Thymine • Cytosine pairs with Guanine This is known as Chargaff’s rule

11. This matching of bases is called base pairing. • The two strands are said to be complementary. • This means if you know the order of bases in one strand, you’ll know the order of bases in the other strand.

12. Watch this video about base pairing

13. The two strands run in opposite directions of each other. • Each strand has a 5’ end and a 3’ end. The 5’ end always has a phosphate group and the 3’ always has an OH (hydroxyl) group. • The 5’ end of one strand always matches up with the 3’ end of the second strand.

14. The two strands are linked together by hydrogen bonds Hydrogen Bonds

16. DNA REPLICATION • Before the cell can divide (mitosis/meiosis/binary fission) the DNA must be replicated or copied. • This copying is known as DNA replication. • DNA replication occurs in the S-Phase of the cell cycle.

17. Steps to replication: • Because DNA is twisted, the first step in replication is to unwind the double helix by breaking the fragile hydrogen bonds with the enzyme helicase.

18. Replication • The DNA strands form a replication fork. Because of the complementary nature of the base pairs, the two old strands can now act as a template for new strands.

19. Replication • An enzyme called DNA polymerase adds new nucleotides to make the new strands.

20. Replication • When DNA is replicated, we don’t end up with two entirely new molecules. Each new molecule has half of the original molecule. • Because DNA replicates in this way, by conserving part of the old molecule in the two new ones, it is said to be semi-conservative. • DNA Replication

21. DNA to PROTEINS • DNA’s main role is directing the making of proteins. • These proteins, in turn, regulate everything that occurs in the cell.

22. DNA to Proteins • BUT DNA does not directly make the proteins. Instead, DNA passes its information to ribonucleic acid (RNA), which makes the proteins. • The central doctrine of molecular biology (the most important thing): DNA g RNA g proteins

23. This path occurs through 2 different processes: • Transcription, • and Translation

24. DNAg transription gRNAgtranslation gprotein (nucleus) (cytoplasm)

25. RNA Although RNA is also made up of nucleotides, it is different from DNA in three ways. • There is only one strand of nucleotides, instead of two. • The sugar is ribose instead of deoxyribose. • Adenine pairs with Uracil, rather than Thymine.

26. RNA There are also three different types of RNA. You need to know all of them!! • Messenger RNA (mRNA) – copies the information stored in the strand of DNA.

27. RNA • Ribosomal RNA (rRNA) – makes up part of the ribosomes (where proteins are made). • Transfer RNA (tRNA) – takes amino acids to the ribosomes to build the new proteins.

28. TRANSCRIPTION • Transcription occurs when RNA molecules are produced by copying part of the nucleotide sequence of DNA into a complementary RNA strand.

29. Steps of transcription: • Helicase unwinds the two DNA strands. • Because RNA is single stranded, instead of two, only one side of the DNA is used as a template.

30. RNA polymerase adds RNA nucleotides that match the DNA strand. • Instead of pairing thymine with adenine, RNA uses uracil.

31. Transcription • Once the mRNA is finished adding nucleotides, it separates from the DNA molecule and now has an RNA copy of the DNA sequence. • mRNA leaves the nucleus and goes out to the cytoplasm to find a ribosome. • transcription • Transcription Animation 2

32. Transcription Practice DNA: ATG CCT GAG TTC ACC mRNA:

33. Transcription Practice DNA: ATG CCT GAG TTC ACC mRNA: UAC

34. Transcription Practice DNA: ATG CCT GAG TTC ACC mRNA: UAC GGA

35. Transcription Practice DNA: ATG CCT GAG TTC ACC mRNA: UAC GGA CUC

36. Transcription Practice DNA: ATG CCT GAG TTC ACC mRNA: UAC GGA CUC AAG

37. Transcription Practice DNA: ATG CCT GAG TTC ACC mRNA: UAC GGA CUC AAG UGG

38. THE GENETIC CODE • Proteins are made by joining amino acids together into long chains of polypeptides. • The properties of proteins are determined by the order in which different amino acids are joined together to produce polypeptides.

39. But how does the cell know what amino acids to join together? • The mRNA molecule carries a message from the DNA in the form of a codon, a group of three bases, or “letters” that matches with one of the amino acids.

40. There are 64 different codons that can code for 20 different amino acids. • There are also start and stop codons, that let the cell know when to begin and end making proteins.

41. TRANSLATION • During translation, the cell uses information from messenger RNA (mRNA) to produce proteins.

42. Steps of translation: • mRNA molecule attaches to a ribosome. Each codon of the mRNA moves through the ribosome (beginning with the START codon)

43. Translation • As each codon is read by the ribosome, tRNA brings the proper amino acid to the ribosome. • Each tRNA molecule carries one specific amino acid because it has an anticodon (the opposite bases of the codon).

44. Translation • In the ribosome, the amino acid is attached to the growing polypeptide by forming a peptide bond with the previous amino acid. • The ribosome also breaks the amino acid’s bond with its tRNA.

45. Translation • The polypeptide chain continues to grow until the ribosome reaches a stop codon on the mRNA. • Translation Animation

46. Translation Practice mRNA: AUG UCG GGG ACC GCG AMINO: Met.

47. Translation Practice mRNA: AUG UCG GGG ACC GCG AMINO: Met. Ser.

48. Translation Practice mRNA: AUG UCG GGG ACC GCG AMINO: Met. Ser. Gly.

49. Translation Practice mRNA: AUG UCG GGG ACC GCG AMINO: Met. Ser. Gly. Thr.

50. Translation Practice mRNA: AUG UCG GGG ACC GCG AMINO: Met. Ser. Gly. Thr. Ala.