1. DNA and RNA
Chapter 12

2. Genetic facts in 1900:
Both female and male organisms have identical chromosomes except for one pair.
Genes are located on chromosomes
All organisms have two types of chromosomes:
Sex chromosomes
Autosomes

3. Chargaff’s rules
The relative amounts of adenine and thymine are the same in DNA
The relative amounts of cytosine and guanine are the same.
Named after Erwin Chargaff

4. Rosalind Franklin
Used X-Ray diffraction to get information about the structure of DNA:

5. Structure of DNA Discovered in 1953 by two scientists:
James Watson (USA)
Francis Crick (GBR)
Known as the double-helix model.

7. WARM UP
Write the complementary sequence to the following DNA sequence: The first three have been written for you. (Chargaff’s Rule)
T A T T G C A G A T A A C T G
A T A
Write the complementary sequence to the following RNA sequence: The first three have been written for you.
G A T T G C A G A T A A C T G
C U A

8. Homework Write definitions for: DNA replication DNA helicase
replication fork
DNA polymerase

9. The double-helix
A twisted ladder with two long chains of alternating phosphates and sugars. The nitrogenous bases act as the “rungs” joining the two strands. DNA is called the blueprint of life

10. How long is the DNA molecule?

11. Chromosomes & DNA replication
The nucleus of one human cell contains approximately 1 meter of DNA.
Histones = DNA tightly wrapped around a protein
Nucleosome:

12. Chromosome structure:

13. DNA replication Must occur before a cell divides.
Each new cell needs a copy of the information in order to grow.

14. DNA replication. Why needed?
Before DNA strand can be replicated or copied it must be “unzipped”
Helicase (enzyme that unzips) DNA Polymerase
Starts at many different points. Why?

15. Completing the replication
After the DNA molecule comes apart, bases of free nucleotides in the nucleus join their complimentary bases.

16. Proteins carry out the process of replication.
DNA serves only as a template.
Enzymes and other proteins do the actual work of replication.
Enzymes unzip the double helix.
Free-floating nucleotides form hydrogen bonds with the template strand.
nucleotide
The DNA molecule unzips in both directions.

17. DNA polymerase enzymes bond the nucleotides together to form the double helix.
Polymerase enzymes form covalent bonds between nucleotides in the new strand.
DNA polymerase
new strand
nucleotide

18. DNA replication is semiconservative.
Two new molecules of DNA are formed, each with an original strand and a newly formed strand.
DNA replication is semiconservative.
original strand
new strand
Two molecules of DNA

19. Replication is fast and accurate.
DNA replication starts at many points in eukaryotic chromosomes.
There are many origins of replication in eukaryotic chromosomes.
DNA polymerases can find and correct errors.

20. Complete the complimentary base pairings

21. Review
A twisted ladder with two long chains of alternating phosphates and sugars. The nitrogenous bases act as the “rungs” joining the two strands. DNA is called the blueprint of life

22. Before DNA strand can be replicated or copied it must be “unzipped”
Helicase (enzyme that unzips)

23. Completing the replication
After the DNA molecule comes apart, bases of free nucleotides in the nucleus join their complimentary bases by DNA Polymerase

24. DNA MODELS
15mins

25. Due Dates Genetics Quiz - Unit 2 test – Nov 17th/18th
DNA Projects – Nov 28th

26. PROTEIN SYNTHESIS

27. Pop Quiz
20 mins

28. RNA Very similar to DNA. Exceptions: Ribose is the 5-carbon sugar
Uracil replaces thymine
Single-stranded

29. mRNA (messenger) Copies genetic code of DNA by matching bases.
Occurs in the nucleus.
DNA changing to RNA

30. TRANSCRIPTION DNA is copied into mRNA with the aid of RNA polymerase.
The RNA polymerase will bind to promoters that act as signals in the DNA sequence to make RNA.

31. Transcription continued:

32. Exons and Introns EXONS
A segment of DNA in eukaryotic organisms that codes for a specific amino acid
INTRONS
A segment of DNA that does NOT code for an amino acid.

33. Confusing genetic terms:
Polypeptide = a chain of amino acids.
Protein = a complex structure composed of polypeptides
Amino acids = smallest structural unit of a polypeptide.
Gene = a distinct unit of material found on a chromosome

34. Reading the genetic code
The genetic code is responsible for building all the proteins in the body using 20 different amino acids.
How many 3 letter words can you make from the letters A,T,G and C?
Answer: 64

35. Codons
A three letter “word” that specifies an amino acid.

36. Genetic code:

37. Practice

38. tRNA (transfer) approx. 80 nucleotides in length. Cross-like shape
At one end an amino acid is attached
At the other end there is an anticodon
Acts like a truck

39. Polypeptide assembly
Translation = reading or “translating” the RNA code to form a chain of amino acids.
Known as protein synthesis
Occurs in the cytoplasm. (p.304)

40. Mutations The source of variation in a genetic sequence.
Can be either gene or chromosomal mutations.
Point mutations = a change in a single nucleotide in a sequence of DNA.

41. Frameshift Mutation
Inserting an extra nucleotide which, in turn, shifts the entire sequence one way or the other.

42. Chromosomal mutations
Involves a change in the number or structure of the chromosomes.
Deletion : when a piece of a chromosome breaks off and is lost.
Duplication : when a segment of a chromosome is repeated
Inversion : when a segment of a chromosome is reversed.

43. More chromosomal mutations
Translocation : when part of a chromosome breaks off and is attached to a non-homologous chromosome.

44. Control of gene expression
Genes are often like light switches that can be turned off and on.
Operon = occur in prokaryotes. (bacteria) different genes that work together to activate gene functions

45. Factors:
Overall gene control is more difficult for eukaryotes because functional genes may be on different chromosomes.
Environmental such as chemicals and temperature.