1. Honors Biology Chapter 12
Molecular Genetics

2. Identify key historical findings in the pursuit of the structure of DNA.
Draw and label a diagram of the molecular structure of DNA, showing the relationships between the six essential molecules that make up DNA: deoxyribose, phosphate, adenine, cytosine, guanine, thymine.
Apply knowledge of complementary base pairing to predict a DNA strand sequence given information about the other DNA strand.

3. What IS the physical “factor” identified by Mendel?
How do “factors” produce phenotypes? What is the molecular basis for the “genetic code?”
Scientists could narrow it down to molecules found in the nucleus: DNA, RNA, or protein?
Most thought proteins, because they’re much more diverse and complex

4. Griffith’s Transformation
Working with pneumonia in 1928, Griffith transformed or changed bacteria from one form to another.

5. Avery’s Experiments What is the “transforming factor”?
Avery used enzymes to destroy molecules from the heat killed cells before transforming harmless cells.
Concluded: DNA is the transforming factor.

6. Hershey-Chase Experiment
Alfred Hershey & Martha Chase: Radioactively label viral protein vs. DNA, let the phages infect bacteria, then separate them
Bacteria had the DNA trace, not the protein trace

7. Rosalind Franklin & Photo 51
Franklin used X-ray diffraction to photograph crystallized DNA molecules.
Showed the helical shape and repeating structure of DNA

8. The Double Helix
In 1953, James Watson and Francis Crick used scientific evidence reported by other scientists to suggest a model for the DNA structure as a double helix

9. Information molecules
Nucleic Acids
Information molecules
Examples
DNA
Deoxyribonucleic Acid
RNA
Ribonucleic Acid
RNA

10. Nucleic Acids Function: genetic material stores information
blueprint for building proteins
DNA  RNA  proteins
transfers information
blueprint for new cells
blueprint for next generation
DNA
proteins

11. Nucleic acids 5 different nucleotides Building block = nucleotides
nucleotide – nucleotide – nucleotide – nucleotide
5 different nucleotides
different nitrogen bases
A, T, C, G, U
Nitrogen bases I’m the A,T,C,G or U part!
phosphate
sugar
N base

12. 4 Types of Nitrogenous Bases in DNA
Purines: have 2 rings (Adenine and Guanine)
Pyrimidines: have 1 ring (Thymine and Cytosine)

13. Complementary Base Pairing
Chargaff’s Base Pairing Rule: Chargaff determined that the amount of Adenine = amount of Thymine, and the amount of Guanine = the amount of Cytosine.
The bases are connected to each other in the double helix by hydrogen bonds.
A pairs with T
C pairs with G

14. DNA Double strand twists into a double helix
Hydrogen bonds between nitrogen bases that join the 2 strands are weak
the two strands can separate and reattach
with relative ease
It’s a helix or B sheet within a single region. Can have both in one protein but a specific region is one or another

15. Describe and model the process of DNA replication, including an explanation of why it produces identical copies of DNA.

16. Copying DNA
A dividing cell replicates (i.e. duplicates) its DNA in S phase
creates 2 copies of all DNA (sister chromatids)
separates the 2 copies to 2 daughter cells
DNA
cell
nucleus

17. Copying DNA
Matching bases allows DNA to be easily copied

18. DNA Replication Steps: DNA starts as a double-stranded molecule
matching bases (A:T, C:G)
Then the helix untwists and…

19. DNA replication Strands “unzip” at the weak bonds between bases
Done by an enzyme, helicase

20. DNA replication Enzyme DNA polymerase
DNA bases in nucleus
Enzyme DNA polymerase
matches free-floating bases to exposed strand
DNA
polymerase

21. New copies of DNA
Get 2 exact copies of DNA to split between new cells, thanks to complementary base pairing
Each copy = one original strand, one new strand
DNA
polymerase
DNA
polymerase

22. DNA Replication-Review
This process is responsible for the formation of sister chromatids, and their characteristic X shape
Copying DNA

23. double-stranded human chromosomes
ready for mitosis

24. From Gene to Protein

25. Compare and contrast DNA and RNA.
Explain and model the overall process of protein synthesis (transcription and translation).
Apply knowledge of transcription to predict an mRNA sequence given information about a DNA sequence.

26. DNA  Proteins  Cells  Bodies
DNA gets all the glory, Proteins do all the work

27. What do we know? DNA Proteins DNA = instructions for proteins
proteins run living organisms
enzymes
all chemical reactions in living organisms are controlled by enzymes (proteins)
structure
all living organisms are built out of proteins

28. Protein Synthesis: Part 1
So… How does the cell get the instructions
from the nucleus to the ribosomes?
CELL
CYTOPLASM
NUCLEUS
RIBOSOMES – where proteins are made
DNA – stores info to make proteins
mRNA
Where are the instructions to make proteins?
Where are proteins made?
It makes a copy to send called – messenger RNA

29. Flow of Genetic Information
1. A gene or segment of DNA is located on a chromosome
2. The cell uses transcription to copy the gene into a piece of mRNA
3. The mRNA leaves the nucleus and goes to a ribosome
4. The ribosome uses translation to direct the assembly of a protein
5. Gene is now expressed in the cell

30. RNA = Ribonucleic Acid Structure: Types:
Made of a single strand of nucleotides
Nucleotides use Ribose instead of Deoxyribose
Nitrogen base thymine is replaced by Uracil
Types:
Messenger RNA (mRNA): single stranded- used to carry DNA code out of nucleus “working copy”
Transfer RNA (tRNA): binds to specific amino acids, used to build proteins
Ribosomal RNA (rRNA): makes up ribosomes along with proteins

31. DNA vs. RNA DNA RNA deoxyribose sugar nitrogen bases double stranded
G, C, A, T
T = thymine
T : A
C : G
double stranded
RNA
ribose sugar
nitrogen bases
G, C, A, U
U = uracil
U : A
C : G
single stranded

32. DNA vs. RNA
DNA
RNA
DNA

33. Transcription Making mRNA from DNA
DNA strand is the template (pattern)
match bases
U : A
G : C
Enzyme
RNA polymerase

34. Matching bases of DNA & RNA
Double stranded DNA unzips T G G T A C A G C T A G T C A T C G T A C C G T

35. Matching bases of DNA & RNA
Double stranded DNA unzips T G G T A C A G C T A G T C A T C G T A C C G T

36. Matching bases of DNA & RNA
Match RNA bases to DNA bases on one of the DNA strands C U G A G U G U C U G C A A C U A A G C
RNA
polymerase U A G A C C T G G T A C A G C T A G T C A T C G T A C C G T

37. Matching bases of DNA & RNA
U instead of T is matched to A
TACGCACATTTACGTACGCGG
DNA
AUGCGUGUAAAUGCAUGCGCC
mRNA

38. Transcription Steps
RNA Polymerase binds to the promoter (specific place for polymerase to bind) on the DNA and begins transcription
DNA strands separate or unzip.
One of the original strands serves as a template. RNA polymerase binds new RNA nucleotides to the template strand following base pairing rules. (A-U, C-G)
mRNA leaves the nucleus and carries the instructions to the ribosomes. The DNA “re-zips”.
A – T C – G G – C A – T C – G T – A
A T C G G C A T C G T A
A - U T C - G G G - C C A - U T C - G G T - A A
A – T U C – G G G – C C A – T U C – G G T – A A 1 2
3 - 4 5

39. Explain and model the overall process of protein synthesis (transcription and translation).
Apply knowledge of translation to predict a tRNA sequence given information about an mRNA sequence.
Apply knowledge of translation to predict an amino acid sequence given information about a tRNA sequence.

40. How do you convert from one language to another?
RNA to protein
But… building blocks are mismatched.
RNA “language” = 4 bases. Protein “language” = 20 amino acids.
How do you convert from one language to another?
mRNA A C C A U G U C G A U C A G U A G C A U G G C A aa aa aa aa aa aa aa aa

41. But there’s still the 4 to 20 problem…
TACGCACATTTACGTACGCGG
DNA
AUGCGUGUAAAUGCAUGCGCC
mRNA ?
Met Arg Val Asn Ala Cys Ala
protein

42. Solution: mRNA codes for proteins in triplets
TACGCACATTTACGTACGCGG
DNA
codons
AUGCGUGUAAAUGCAUGCGCC
mRNA
AUGCGUGUAAAUGCAUGCGCC
mRNA ?
Met Arg Val Asn Ala Cys Ala
protein
Codon
block of 3 mRNA nucleotides that “codes” for one amino acid

43. Now, how are the codons matched to amino acids?
TACGCACATTTACGTACGCGG
DNA
AUGCGUGUAAAUGCAUGCGCC
mRNA
codon
UAC
Met
GCA
Arg
tRNA
CAU
Val
anti-codon
amino acid

44. mRNA to protein = Translation
The message -> mRNA
The reader  ribosome
The transporter  transfer RNA (tRNA)
The product -> polypeptide/protein
ribosome
mRNA A C C A U G U C G A U C A G U A G C A U G G C A U G G aa
tRNA U A C aa
tRNA G A aa
tRNA C
tRNA aa A G U aa aa

45. Transfer RNA Transfer RNA (tRNA)
A folded RNA chain, with three exposed bases (anticodon) and an amino acid
Which amino acid it carries depends solely on the anticodon
Function: Carry amino acids to ribosome, assemble them in correct order

46. Translation Steps
Initiation: Ribosome attaches to the mRNA at the start codon (AUG)
tRNA with the complementary anti-codon (UAC) binds to the mRNA codon, bringing the amino acid methionine with it.
Ribosome shifts down the mRNA to the next codon.
Elongation: Another tRNA with the complementary anti-codon binds to the mRNA codon. The amino acid from the tRNA binds to methionine.
The ribosome shifts again, another tRNA brings another amino acid to bind to the growing amino acid chain.
Termination: Process continues until the ribosome reads a stop codon, at which time it releases the finished amino acid chain (AKA: protein)

47. In Animated Format

48. Genetic Code All life on Earth uses the same code Code is redundant
Due to common origin
Code is redundant
several codons for each amino acid
“mutation insurance!”
Strong evidence for a single origin in evolutionary theory.
Start codon
AUG
methionine
Stop codons
UGA, UAA, UAG

49. The Genetic Code
A map of CODONS, not ANTIcodons

50. Recap of Protein Synthesis
A gene = a region of the chromosome that codes for one protein
mRNA is made in the nucleus using DNA as a template. (TRANSCRIPTION) mRNA travels to ribosome.
Protein is made at the ribosome by matching tRNA to mRNA. (TRANSLATION)
Amino acid sequence determines protein’s shape, protein shape determines its function.

51. transcription
translation
“Central Dogma” of Molecular Genetics DNA -> RNA -> Protein -> Trait Expanded version: DNA -> mRNA -> tRNA -> amino acid sequence -> protein shape -> protein function -> trait

52. Mutations

53. Distinguish between point/substitution and frameshift/insertion/deletion mutations, and predict their effects on an amino acid sequence.

54. Mutations
Mutations are changes in DNA sequences, usually as errors in replication
different DNA order = different RNA order = different protein = different trait
Human germ cell line averages 35 mutations per generation BB Bb bb

55. Mutations Point or Substitution mutations single base change
Ex: T instead of C
Can be:
silent mutation
no amino acid change due to redundancy in code
missense
change amino acid
nonsense
change to stop codon

56. Example: Sickle cell anemia

57. Sickle cell anemia Autosomal codominant/recessive inheritance pattern
Strikes 1 in 3 Subsaharan Africans, 1 in 500 African Americans
Sickle-shaped red blood cells carry less oxygen, easily “clog” blood vessels

58. Mutations Frameshift shift in the reading frame insertions deletions
changes everything “downstream”
Tends to have more profound effects than point mutations
insertions
adding base(s)
deletions
losing base(s)

59. Frameshift mutations (Point) THE RAT AND THE CAT ATE THE RED BAT
THE RTA NDT HEC ATA TET HER EDB AT
THE RAA TAN DTH ECA TAT ETH ERE DBA T
(Point)
THE RQT AND THE CAT ATE THE RED BAT

60. Example: Cystic fibrosis
Primarily Northern and Western European descent
strikes 1 in 2500 births
1 in 25 white Europeans are carriers (Aa)
normal allele codes for a membrane protein
mutant channel limits movement of Cl- (& H2O) across cell membrane
thicker & stickier mucus coats cells in lungs, pancreas, digestive tract
without treatment children die before 5; with treatment can live past their late 20s
Cystic fibrosis is an inherited disease that is relatively common in the U.S. Cystic fibrosis affects multiple parts of the body including the pancreas, the sweat glands, and the lungs. When someone has cystic fibrosis, they often have lots of lung problems. The cause of their lung problems is directly related to basic problems with diffusion and osmosis in the large airways of the lungs.
People without cystic fibrosis have a small layer of salt water in the large airways of their lungs. This layer of salt water is under the mucus layer which lines the airways. The mucus layer in the airways helps to clear dust and other inhaled particles from the lungs.

62. Mutations Mutation = not necessarily bad.
As a phenomenon, is essential to genetic diversity. And individual mutations…
can be beneficial (ex: a fur color protein that more closely matches environment)
can be neutral (ex: silent mutations)
can be detrimental (ex: cystic fibrosis)
can be beneficial and detrimental! (ex: sickle cell anemia protects against malaria)