1. DNA Structure

2. DNA Structure Objectives
Identify the full name of DNA.  
List the basic building blocks of DNA.  
List the three components of a nucleotide.  
List the four nitrogen bases found in DNA.  
Distinguish between a purine and a pyrimidine.  
Explain the base-pairing rule.  
Identify and explain the structure of DNA.  
Identify the chemical bonds that connect nitrogen bases.  

3. DNA: Deoxyribonucleic Acid
Named for deoxyribose – the sugar in DNA
Found in the nucleus of a cell
Functions as the “blueprint of life,” containing the codes for the body’s proteins

4. The Shape of DNA
Double helix – twisted ladder made of nucleotide building blocks. The two sides of the helix are held together by Hydrogen bonds (weak).
Made of Nucleotides

5. To Review* A Nucleotide is made of:
Deoxyribose sugar
Phosphate group
Nitrogenous base
*Because it’s important!

6. Notice that in the nucleotide shown, the nitrogenous base is attached to the sugar. The sugar is then attached to the phosphate.
To form a DNA strand, the phosphate of one nucleotide bonds to the sugar of another nucleotide. This forms the backbone of the DNA helix.
The nitrogenous base bonds to the nitrogenous base of another nucleotide, forming the rungs of the DNA ladder.

7. Nitrogenous Bases Nitrogenous bases come in two forms:
Purines: two-ring structure. 
Adenine and Guanine are purines.
Pyrimidines: one-ring structure. 
Thymine and Cytosine are pyrimidines.

8. .(One purine with one pyrimidine)
DNA Base Pairing Rules
Adenine (A) always bonds with Thymine (T)
Cytosine (C) always bonds with Guanine (G)
A-T, G-C
.(One purine with one pyrimidine)

9. The Genetic Code The genetic code is in the order of bases
(ATGC) in a strand of DNA

10. DNA- drawn out, showing the whole molecule, with hydrogen bonds.

11. Nucleotides Bonded Together
What binds in the middle?
2. What makes up the outside of the ladder?
3. What atoms cause the bonds in the middle?

12. Were You Correct? Bases bind in the middle
Phosphate and Sugar make up the outside of the ladder
Hydrogen creates hydrogen bonds between the bases in the middle.

13. DNA Structure Review What do the letters DNA stand for?
What is the shape of the DNA molecule?
DNA is composed of chains of ____.
Identify one of the two chemicals (groups) that forms the backbone of the molecule.
What chemicals form the rungs across the middle of the molecule?
DNA is ____ - stranded.
According to base-pairing, adenine joins with ____.
Identify the sugar molecule found in DNA.
Where is DNA located in the cell?
Identify the bonds that join the nitrogen bases.

14. Who discovered the shape of DNA?
James Watson and Francis Crick are credited with the discovery of the double helical shape of DNA, creating their model in They were awarded the Nobel Prize for their work in 1962.
FYI: If you win the Nobel Prize, you get this nifty medal, a personal diploma, and a cash award.

15. How did they arrive at their conclusions?
They built many models, always perplexed at how it fit together, until one day, when they wandered into the office of a fellow scientist, Dr. Rosalind Franklin.

16. Along with Dr. Maurice Wilkins, she had taken x-ray crystallography photos of DNA. They saw her photos and realized the great secret- that DNA was coiled like a spring. They then made their model in 1954 and won the Nobel Prize in 1962.
Franklin’s famous photo of DNA

17. DNA Replication Objectives
Describe the events during DNA replication.
Know why is DNA replication referred to as semi-conservative.
Be familiar with the different enzymes involved in DNA replication and their roles.
Know what an origin of replication is and what role it plays in DNA replication.
Understand the role do RNA primers play in DNA replication.
Understand the pattern of complementary base-pairing.

18. Definition
DNA replication – The process of copying a cell's DNA, so that the cell has two, rather than one, copies of its DNA.
**Semi-conservative replication – After replication, each new DNA consists of old and new strands.

19. 3 Important Enzymes
DNA helicase - "‘unzips" the DNA molecule, opening the double helix as they move. Many replication forks occur.
DNA polymerase - adds new nucleotides to a growing strand of DNA.
DNA ligase – puts together the new pieces of DNA that are made at each fork.

20. Complementary Base-Pairing1
Starting at the 3’ End, which nucleotides would be added on and in what order? 2 3 4 5 6 7 8

21. The correct sequence was:
Were You Correct?
The correct sequence was: 5 8 4 1

22. Spell Check by DNA Polymerase

23. Overview

24. Accuracy and Repair
There is 1 error per 10,000 nucleotides, on average.
These errors are called mutations- changes in the nucleotide sequence.
DNA proofreads and repairs errors to keep them at 1 error per billion nucleotides (we have over 3 billion in total).

25. Replication Review What enzyme unzips DNA?
Does DNA have 1 or many replication forks?
What enzyme adds more nucleotides to the parent DNA strand?
What enzyme puts the new pieces of DNA together?
What enzyme proofreads DNA?
Why is DNA considered semi-conservative?
What is an error in DNA called?

26. RNA and Protein Synthesis
Section 12-3
RNA and Protein Synthesis

27. What is RNA and Why do we need it?
Ribonucleic Acid
It is used to build proteins!

28. The “Central Dogma” of Molecular Genetics
Transcription
Translation
DNA
RNA
Protein
Trait
RNA processing

29. Structure of RNA Sugar- Ribose Phosphate Group
Nitrogen-containing bases
Adenine
Uracil (substituted for Thymine)
Guanine
Cytosine
Note- RNA is single-stranded, unlike DNA.

30. Comparisons to DNA
RNA is very similar to DNA with the following exceptions:
it is single stranded
it has uracil instead of thymine
it has the sugar ribose, instead of deoxyribose

31. RNA Structure Review What do the letters RNA stand for?
What is RNA used for?
What are the bases in RNA?
What is the shape of RNA?
What is the sugar in RNA?

32. 3 Types of RNA
Messenger RNA (mRNA)- carries the instructions from DNA to the ribosomes.
Transfer RNA (tRNA)- carries message from mRNA to find the specific amino acids.
Ribosomal RNA (rRNA)- makes up ribosomes, it puts the proteins together.

33. Protein Synthesis- Stages
The first stage is :
Transcription- The copying of information from DNA to RNA
This takes place in the nucleus.
RNA is made at this time, using the base-pair rule.

34. Steps in Transcription
The base-pair rule is followed during transcription, except instead of pairing thymine with adenine when creating an RNA strand, uracil is used:
DNA Strand: T G C A T C A G A
RNA Strand: A C G U A G U C U

35. How it works DNA “unzips”, exposing codons (3 bases in a row).
RNA Polymerase adds RNA nucleotides (U to A, A to T, C to G, G to C) to form mRNA codons.
mRNA strand pulls away, leaves nucleus.
mRNA goes to ribosome (made of rRNA)

36. Transcription
The enzyme RNA polymerase opens the DNA strands and synthesizes an RNA complementary to only one of the DNA strands.

37. Translation
The code has been written in mRNA and has traveled to the ribosome.
Now it’s time to make the protein- called Translation!

38. What are proteins again?
Proteins are polymers, each is made with a specific sequence of amino acids
The genetic code is used to translate mRNA into proteins by building specific sequences of amino acids.

39. The Genetic Language Uses 4 Letters Written Into 3-Letter Words
The Genetic Language Uses 4 Letters Written Into 3-Letter Words. These words are called codons.

40. How to use the Codon Chart
Test for Understanding: A DNA sequence has the following bases:
T A C - A G A - T T A - G G G - A T T What amino acids does it code for? (You'll need to use the codon chart)

41. What Translation Accomplishes:
In translation, information present in the mRNA is read by the ribosome to synthesize a polypeptide.

42. How is this done? 1. mRNA travels to the ribosome (rRNA)
2. The code is transferred to tRNA.
3. The tRNA takes the code, makes its own anti-codon, and finds the amino acids in the cytoplasm, returns to the ribosome.
4. Amino acids are assembled in order by the rRNA.
5. Voila! A protein is made!!!

43. Summary DNA Transcription RNA Translation Protein DNA RNA
Only 1 type 3 types
Deoxyribose ribose
A,C,G,T A,C,G,U
In nucleus in nucleus & cytoplasm
Made by replication made by transcription-mRNA
DNA codons RNA codons & anticodons

44. Review of the whole process