1. Biology 250Chapter 10 From DNA to RNA to Protein

2. The Structure of DNA DNA is made up of nucleotides which consist of a sugar, phosphate and a nitrogen base.

3. DNA structure cont. There are four different nitrogen bases – Adenine (A) – Thymine (T) – Cytosine (C) – Guanine (G)

4. DNA structure cont. DNA stands for deoxyribonucleic acid. The sugar in DNA is called deoxyribose. In 1953, James Watson and Francis Crick proposed a model for the structure of DNA. DNA is made of two chains of nucleotides which wrap around each other to form a double helix. The two men relied heavily upon research done by Rosalind Franklin and Maurice Wilkins.

5. DNA structure cont. Two chains of nucleotides. Connected by hydrogen bonds.

6. DNA structure cont. Complementary base-pairing rules: – Adenine bonds with Thymine (A to T) – Cytosine bonds with Guanine (C to G)

7. Drawing DNA For our purposes, we will use the ladder structure of DNA The sugar and phosphates of the nucleotides will make up the sides of the ladder. The nitrogen bases connected by hydrogen bonds will make up the rungs of the ladder.

8. Drawing DNA cont. A A Phosphate Sugar

9. Drawing DNA cont. A A G G T T T T A A C C

10. Let’s Practice! Draw the ladder structure of DNA if the following are the bases on the LEFT SIDE: ATCGCT

11. DNA Replication The process of copying DNA in the cell. 1.An enzyme called helicase breaks the hydrogen bonds holding the two chains together. (The point at which the two strands separate is called a Replication Fork) 2.An enzyme called DNA Polymerase attaches to the two strands and begins adding in complementary nucleotides. 3.Eventually, two complete and identical DNA strands are formed.

12. DNA Replication cont.

13. Let’s Practice Replication! Following Mrs. Shinault’s example do the following: Draw the ladder structure of DNA with the following bases down the LEFT side: ACGA Then, show the steps of replication of this DNA strand. Remember, you need 3 pictures!

14. DNA Replication cont. Mutation – A change in the DNA nucleotide sequence. Replication is fairly accurate, only about 1 in 10,000 base-pairs is paired incorrectly. Proofreading reduces this number to 1 in 1 billion base pairs. No mutations, yay!

15. Structure of RNA RNA stands for ribonucleic acid. The sugar in RNA is ribose. RNA is single stranded. RNA does not contain thymine, instead of thymine a new base, uracil is used which bonds with adenine.

16. Structure of RNA cont. There are 3 types of RNA – rRNA – Ribosomal RNA – Has a globular shape and makes up ribosomes. – tRNA – Transfer RNA – In the shape of a hairpin loop and carries amino acids to their proper place in a protein. – mRNA – Messenger RNA – a single, uncoiled strand of nucleotides. Holds the instructions for making proteins.

17. Let’s practice drawing mRNA! Draw a strand of mRNA if the nitrogen bases it contains are: AUCCG

18. Transcription The process of making RNA from a DNA strand. 1.An enzyme called RNA Polymerase attaches to the DNA strand near a promoter which marks the beginning of a gene to be copied. 2.When the RNA polymerase attaches to the DNA, the DNA in that area unwinds and separates. 3.RNA Polymerase then adds complementary RNA nucleotides to ONE SIDE of the DNA strand. 4.RNA polymerase continues until it reaches a termination signal which marks the end of a gene to be copied. 5.The RNA polymerase then detaches, the RNA strand is complete and the DNA goes back together.

19. Transcription cont.

20. Let’s Practice Drawing Transcription! Draw a DNA strand with the following bases on the LEFT side: TACCG Then, using Mrs. Fruit’s example, draw the steps of transcription. Be sure to include all 3 drawings!

21. From DNA to RNA to Protein The DNA in the nucleus of your cells contains the directions for making proteins. DNA is first transcribed into RNA. The RNA then leaves the nucleus and travels to a ribosome (remember? They make proteins.) Using all 3 types of RNA, the ribosome creates a chain of amino acids (they make up proteins) from the information on the mRNA strand.

22. Translation Making a polypeptide chain (amino acid chain) from the information on an mRNA strand. Genetic Code – The correlation between an mRNA nucleotide sequence and an amino acid sequence. All organisms have the same genetic code, we just have our nitrogen bases in different orders!

23. Translation cont. Codons and Anti-Codons – A codon is a series of 3 mRNA nucleotides which codes for a specific amino acid. – An anticodon is a series of 3 tRNA nucleotides which is complementary to and binds with an mRNA codon – It is the codon-anticodon combination which ensures the proper amino acid is taken to the correct place in the amino acid chain. Amino Acid Anticodon

24. Translation cont. Assembling a Protein! – mRNA leaves the nucleus and migrates to a ribosome. – The ribosome begins by attaching to the start codon (AUG – also codes for the amino acid methionine) – The ribosome moves along the mRNA strand one codon at a time attaching tRNA molecules whose anticodons are complementary to the codons. – After the codon and anticodon bond, the amino acid the tRNA is carrying detaches and joins the growing amino acid chain. – This continues until the ribosome hits a stop codon (UAA, UGA, or UAG)

25. Translation cont.

26. Codon Chart