1. Chapter 10: DNA and RNA

2. DNA Deoxyribonucleic acid Structure of DNA
Made up of four subunits called nucleotides
Each nucleotide is made up of a sugar, a phosphate and a base

3. Four Bases Two Purines Two pyrimidines Adenine (A) Guanine (G)
Cytosine (C)
Thymine (T)

4. DNA Double Helix
DNA is made of two nucleotide strands that wrap around each other in the shape of a double helix.

5. DNA Structure Bonds Hold DNA Together
Nucleotides along each DNA strand are linked by covalent bonds.
Complementary nitrogenous bases are bonded by hydrogen bonds.

6. Chargaff
Amount of adenine equals the amount of thymine and the amount of cytosine equals the amount of guanine
A=T
C=G

7. But what does DNA look like?
Rosalind Franklin
Working in Wilkin’s lab created x-ray pictures of DNA
Wilkins shared this information with another pair of scientists without Franklin’s consent

8. Watson and Crick
Watson and Crick discovered that DNA resembles a twisted ladder shape: double helix

9. DNA Structure
Two side of the ladder are made up of alternating sugar and phosphate molecules
The rungs of the ladder are pairs of bases (A with T, and G with C): Base pair rule
Rungs are anti-parallel (5’->3’ and 3’ ->5’)

10. Drawing DNA Draw one side of the rung 5’ -> 3’
Start with the sugar
Add the phosphate and the base to form your nucleotide
Continue adding bases to the 3’ end
Determine the matching base for next side
When finishing each nucleotide, be sure to draw in the 3’ -> 5’ direction

11. Making copies: Replication
DNA can “unzip” when it needs to replicate (helicase)
Occurs prior to cell division so each new cell gets the correct information

12. Replication DNA molecule separates into two strands
Complementary strands form on the template of each of the original sides of the DNA
Each new DNA has one old and one new strand (semiconservative replication)

13. Replication enzymes Helicase Primase DNA polymerase Ligase Unwinds DNA
Adds an RNA primer on unzipped DNA
DNA polymerase
Add new bases to the 3’ end of previous base
Ligase
Seals fragments after RNA primer removed

14. Steps of DNA Replication
Replication begins with the separation of the DNA strands by helicases.
Then, primase adds an RNA primer where replication will occur
DNA polymerases form new strands by adding complementary nucleotides to each of the original strands.
The new segments of DNA are sealed by ligase

15. See it in action: http://www.johnkyrk.com/DNAreplication.html
See it in action:

16. DNA Replication

17. DNA Replication
Each new DNA molecule is made of one strand of nucleotides from the original DNA molecule and one new strand. This is called semi-conservative replication.

18. Replication Forks Increase the Speed of Replication

19. Replication DNA polymerase can only add to a 3’ end Leading strand
Runs 5’->3’
Lagging strand
Runs 3’->5’ SO can’t add directly
Have to replicate in fragments called Okazaki fragments
Ligase bonds the fragments together

20. Single-strand binding protein Overall directions of replication
DNA Replication
Overview
Origin of replication
Leading strand
Lagging strand
Leading strand
Lagging strand
Single-strand binding protein
Overall directions of replication
Helicase
Leading strand 5
DNA pol III 3 3
Primer
Primase 5
Parental DNA 3
Figure A summary of bacterial DNA replication
DNA polymerase
Lagging strand 5
DNA polymerase
DNA ligase 4 3 5 3 2 1 3 5

21. Replication animation

22. Central Dogma
Has its exceptions, but gives us a basic idea of how DNA does its job

23. RNA Single stranded nucleic acid Made up of nucleotides Sugar: Ribose
Thymine instead of Uracil
Shorter: length of one gene

24. RNA Structure and Function
Types of RNA
Cells have three major types of RNA:
messenger RNA (mRNA)
ribosomal RNA (rRNA)
transfer RNA (tRNA)

25. Activity
In pairs, create a chart that will fit in your foldable (no more than 1/8th size of construction paper) that compares and contrasts the different forms of RNA
Be sure to include:
Name
Structure
Function
Picture

26. RNA Structure and Function
mRNA carries the genetic “message” from the nucleus to the cytosol.
rRNA is the major component of ribosomes.
tRNA carries specific amino acids, helping to form polypeptides.

27. Making proteins
Cells use a two step process to read each gene and produce the amino acid chain that becomes a protein.
These processes are:
Transcription
Translation

28. Gene 2 Gene 1 Gene 3 DNA template strand mRNA Codon TRANSLATION
Fig. 17-4
Gene 2
DNA
molecule
Gene 1
Gene 3
DNA
template
strand
TRANSCRIPTION
Figure 17.4 The triplet code
mRNA
Codon
TRANSLATION
Protein
Amino acid

29. Transcription The process of building an RNA copy of a DNA sequence
DNA is too big to leave the nucleus
mRNA is a copy of the DNA sequence

30. mRNA Also known as messenger RNA
Takes the code out into the cell for protein synthesis

31. Steps of Transcription
Initiation
RNA polymerase binds to a promoter (specific nucleotide sequence: TATA box)
Elongation
RNA polymerase adds free RNA nucleotides that are complementary to the DNA strand
Termination
RNA polymerase releases at a termination sequence

32. Steps of Transcription

33. Completed RNA transcript
Promoter
Transcription unit 5 3 3 5
DNA
Start point
RNA polymerase 1
Initiation 5 3 3 5
RNA
transcript
Template strand
of DNA
Unwound
DNA 2
Elongation
Rewound
DNA 5 3 3 3 5
Figure 17.7 The stages of transcription: initiation, elongation, and termination 5
RNA
transcript 3
Termination 5 3 3 5 5 3
Completed RNA transcript

34. Genetic Code
The nearly universal genetic code identifies the specific amino acids coded for by each three-nucleotide mRNA codon.

35. Translation Steps of Translation
During translation, amino acids are assembled from information encoded in mRNA.
As the mRNA codons move through the ribosome, tRNAs add specific amino acids to the growing polypeptide chain.
The process continues until a stop codon is reached and the newly made protein is released.

36. Ribosome Amino acids tRNA with amino acid attached Ribosome tRNA
Polypeptide
tRNA with
amino acid
attached
Ribosome
Trp
Phe
Gly
Figure Translation: the basic concept
tRNA
Anticodon 5
Codons 3
mRNA

37. Translation: Assembling Proteins

38. DNA Errors in Replication
Changes in DNA are called mutations.
DNA proofreading and repair prevent many replication errors.
DNA Replication and Cancer
Unrepaired mutations that affect genes that control cell division can cause diseases such as cancer.

39. The Human Genome
The entire gene sequence of the human genome, the complete genetic content, is now known.
To learn where and when human cells use each of the proteins coded for in the approximately 30,000 genes in the human genome will take much more analysis.