1. Chapter 17 Warm-Up
Explain the contribution that Beadle and Tatum made to understanding the role of DNA.
Compare and contrast DNA to RNA.
What is the difference between replication, transcription and translation?

2. Chapter 17 Warm-Up Describe the steps in transcription.
Contrast transcription in prokaryotes vs. eukaryotes.
How many nucleotides are in an mRNA molecule to code for a protein with 200 amino acids?

3. Chapter 17 Warm-Up How does mRNA differ from pre-mRNA?
What is the difference between introns and exons?
Describe how spliceosomes modify mRNA.

4. Chapter 17 Warm-Up Describe the steps of translation.
If the DNA sequence is: 3’ T A C G A T C A G 5’
the cDNA would be:
the mRNA is:
the tRNA is:
the amino acid sequence is:
How does the cell determine the ultimate destination of a polypeptide being synthesized?

5. Chapter 17 Warm-Up
What is a frameshift mutation? How can they impact protein synthesis?
Contrast a missense vs. nonsense mutation.

6. Chapter 17 Warm-Up
Refer to page 327. Fill in the chart comparing prokaryotic and eukaryotic gene expression:
Prokaryotes
Eukaryotes

7. From Gene to Protein
Chapter 17

8. What you need to know:
The key terms: gene expression, transcription, and translation.
The major events of transcription.
How eukaryotic cells modify RNA after transcription.
The steps to translation.
How point mutations can change the amino acid sequence of a protein.

9. Concept 17.1: Genes specify proteins via transcription and translation

10. Gene Expression: process by which DNA directs the synthesis of proteins (or RNAs)
Old idea: one gene-one enzyme hypothesis
Archibald Garrod –genes dictate phenotypes via enzymes
Proposed by Beadle & Tatum – mutant mold experiments
Function of a gene = dictate production of specific enzyme
Newer idea: one gene-one polypeptide hypothesis
Most accurate: one gene-one RNA molecule (which can be translated into a polypeptide) = one gene-one polypeptide

11. Flow of genetic information
Central Dogma: DNA  RNA  protein
Transcription: DNA  RNA
Translation: RNA  protein
Ribosome = site of translation
RNA is the bridge between genes and the protiens for which they code

12. Flow of Genetic Information in Prokaryotes vs. Eukaryotes
In a eukaryotic cell, the nuclear envelope separates transcription from translation
Eukaryotic RNA transcripts are modified through RNA processing to yield the finished mRNA
Eukaryotes: can translation & transcription occur at same time? Why/not?
Prokaryotes: translation of mRNA can begin before transcription has finished

13. one gene = one RNA molecule
DNA
RNA
Nucleic acid composed of nucleotides
Single-stranded
Ribose=sugar
Uracil
Many different roles!
Nucleic acid composed of nucleotides
Double-stranded
Deoxyribose=sugar
Thymine
Template for individual

14. RNA plays many roles in the cell
pre-mRNA=precursor to mRNA, newly transcribed and not edited
mRNA= the edited version; carries the code from DNA that specifies amino acids
tRNA= carries a specific amino acid to ribosome based on its anticodon to mRNA codon
rRNA= makes up 60% of the ribosome; site of protein synthesis
snRNA=small nuclear RNA; part of a spliceosome. Has structural and catalytic roles
srpRNA=a signal recognition particle that binds to signal peptides
RNAi= interference RNA; a regulatory molecule
ribozyme= RNA molecule that functions as an enzyme

15. The Genetic Code
For each gene, one DNA strand is the template strand
mRNA (5’  3’) complementary to template
mRNA triplets (codons) code for amino acids in polypeptide chain

16. The Genetic Code
64 different codon combinations
Redundancy: 1+ codons code for each of 20 AAs
Reading frame: groups of 3 must be read in correct groupings
This code is universal: all life forms use the same code.

17. Concept 17.2: Transcription is the DNA-directed synthesis of RNA

18. Transcription
Transcription unit: stretch of DNA that codes for a polypeptide or RNA (eg. tRNA, rRNA)
RNA polymerase:
Separates DNA strands and transcribes mRNA
mRNA elongates in 5’  3’ direction
Uracil (U) replaces thymine (T) when pairing to adenine (A)
Attaches to promoter (start of gene) and stops at terminator (end of gene)

19. 1. Initiation
Bacteria: RNA polymerase binds directly to promoter in DNA

20. 1. Initiation Eukaryotes:
TATA box = DNA sequence (TATAAAA) upstream from promoter
Transcription factors must recognize TATA box before RNA polymerase can bind to DNA promoter

21. 2. Elongation
RNA polymerase adds RNA nucleotides to the 3’ end of the growing chain (A-U, G-C)

22. 2. Elongation
As RNA polymerase moves, it untwists DNA, then rewinds it after mRNA is made

23. 3. Termination
RNA polymerase transcribes a terminator sequence in DNA, then mRNA and polymerase detach.
It is now called pre-mRNA for eukaryotes.
Prokaryotes = mRNA ready for use

24. Flow of Genetic Information in Prokaryotes vs. Eukaryotes

25. Concept 17.3: Eukaryotic cells modify RNA after transcription

26. Additions to pre-mRNA:
5’ cap (modified guanine) and 3’ poly-A tail ( A’s) are added
Help export from nucleus, protect from enzyme degradation, attach to ribosomes

27. RNA Splicing
Pre-mRNA has introns (noncoding sequences) and exons (codes for amino acids)
Splicing = introns cut out, exons joined together

28. Ribozyme = RNA acts as enzyme
RNA Splicing
small nuclear ribonucleoproteins = snRNPs
snRNP = snRNA + protein
Pronounced “snurps”
Recognize splice sites
snRNPs join with other proteins to form a spliceosome
Spliceosomes catalyze the process of removing introns and joining exons
Ribozyme = RNA acts as enzyme

29. Why have introns? Some regulate gene activity
Alternative RNA Splicing: produce different combinations of exons
One gene can make more than one polypeptide!
20,000 genes  100,000 polypeptides

30. Concept 17.4: Translation is the RNA-directed synthesis of a polypeptide

31. Components of Translation
mRNA = message
tRNA = interpreter
Ribosome = site of translation

32. tRNA Transcribed in nucleus Specific to each amino acid
Transfer AA to ribosomes
Anticodon: pairs with complementary mRNA codon
Base-pairing rules between 3rd base of codon & anticodon are not as strict. This is called wobble.

33. tRNA
Aminoacyl-tRNA-synthetase: enzyme that binds tRNA to specific amino acid

34. Ribosomes
Ribosome = rRNA + proteins
made in nucleolus
2 subunits

35. Ribosomes Active sites: A site: holds AA to be added
P site: holds growing polypeptide chain
E site: exit site for tRNA

36. Translation: 1. Initiation
Small subunit binds to start codon (AUG) on mRNA
tRNA carrying Met attaches to P site
Large subunit attaches

37. 2. Elongation

38. 2. Elongation
Codon recognition: tRNA anticodon matches codon in A site

39. 2. Elongation
Peptide bond formation: AA in A site forms bond with peptide in P site

40. 2. Elongation
Translocation: tRNA in A site moves to P site; tRNA in P site moves to E site (then exits)

41. 2. Elongation
Repeat over and over

42. 3.Termination Stop codon reached and translation stops
Release factor binds to stop codon; polypeptide is released
Ribosomal subunits dissociate

43. Polyribosomes
A single mRNA can be translated by several ribosomes at the same time

44. Protein Folding
During synthesis, polypeptide chain coils and folds spontaneously
Chaperonin: protein that helps polypeptide fold correctly

45. Types of Ribosomes
Free ribosomes: synthesize proteins that stay in cytosol and function there
Bound ribosomes (to ER): make proteins of endomembrane system (nuclear envelope, ER, Golgi, lysosomes, vacuoles, plasma membrane) & proteins for secretion
Uses signal peptide to target location

46. Cellular “Zip Codes”
Signal peptide: 20 AA at leading end of polypeptide determines destination
Signal-recognition particle (SRP): brings ribosome to ER

47. Application: Intro to Differentiation Dr Sam Rhine Genetics Conference

48. Quick Review of RNA
RNA Polymerase: is the enzyme that reads a gene on DNA to produce mRNA
Double helix of DNA must be unwound in order to be copied
Helicase is the enzyme that is responsible for disconnecting the strands of DNA
RNA Polymerase acts like Helicase on small sections of DNA
ALL polymerase must read DNA in 3’-5’ direction so RNA can be written in 5’-3’ direction
At this point DNA and RNA are antiparallel for now
Remember in translation: mRNA is read 5’-3’ when making polypeptide
Modifications after mRNA is made
Splice out introns, keep the exons
5’ cap at 5’ end, poly A tail at 3’ end

49. Quick Review of RNA
mRNA is translated multiple times before being broken down:
Read 1 gene to 1 mRNA 1 time  at least1 polypeptide/1protien
Read 5 times  at least 5 proteins

50. Quick Review of making a polypeptide
Ch5 p86 fig 5.25
In the _______
DNA transcribed or translated
Making ______
mRNA is modified. ___ out ___ keep, add the _____ and ___
mRNA is sent out of __ to the ___
mRNA is read by the __
Using the help of _____ work together with the ____ to build the polypeptide.
In the nucleus. DNA Transcribed. Making mRNA. Interons out, exons kept, add 5’ cap, add poly A tail, mRNA is sent out the nuclear pore to the cytoplasm, mRNA is read by the ribosomes, using the help of tRNA work together with the ribosome to build the polypeptide.
DNA  mRNA  Protein
is misleading???

51. Quick Review of Genes Genes can be read many times periods of times
Min: 60 days
Max: life of organism depending on type of cell
Certain cells only read certain set of genes
Every cell in body are identical
There are 225 different types of cells in body

52. Differentiation ex: Pancreas
Accessory organ that facilitates digestion, made of 3 parts, is located centrally behind the stomach, controls blood sugar by use of 2 enzymes: insulin and glucogan to regulate sugar levels
Pancreas has both beta and alpha cells
but only beta cells of the pancreas produce insulin
All cells in your body are ______
so all cells have the gene for insulin
So why aren’t all cells reading all sets of genes?
Why are the beta cells of the pancreas the only cells that are reading insulin?

53. What happens in Pancreas
Eat Sugar  insulin levels spike instantly
How does insulin go from slightly detectable levels to high immediately
Beta cells of the pancreas read the insulin gene multiple times
Make transcript
Read the transcript multiple times
Remember mRNA can be translated multiple times
producing many instances of that polypeptide

54. Pancreatic Cancer as an example
Is one of the most deadly cancers
Whipple Procedure = Pancreadectomy
Remove part of the pancreas, part of the small intestines, all the gall blatter, and part of the stomach to remove the tumor
Pancreatic Cancer patients are not eligible for this procedure
This as an illustration of why
Research Paper on Whipple Procedure
Read in the Journal of Medical Procedures, take notes, write report from notes
You cant submit a page from the journal as the research paper. You have to make notes
Same with make proteins. mRNA doesn’t just become the protein. There is still mRNA that must be broken down later.
DNA  mRNA  Protein
is misleading???

55. Concept 17.5: Point mutations can affect protein structure and function

56. The Central Dogma
Mutations happen here
Effects play out here

57. Mutations = changes in the genetic material of a cell
Large scale mutations: chromosomal; always cause disorders or death
nondisjunction, translocation, inversions, duplications, large deletions
Point mutations: alter 1 base pair of a gene
Base-pair substitutions – replace 1 with another
Missense: different amino acid
Nonsense: stop codon, not amino acid
Frameshift – mRNA read incorrectly; nonfunctional proteins
Caused by insertions or deletions

58. Substitution = Missense

59. Substitution = Nonsense

60. Substitution = Silent (no effect)

61. Insertion = Frameshift Mutation

62. Deletion = Extensive missense, premature termination

63. Pulmonary hypertension
Sickle Cell Disease
Symptoms
Anemia
Pain
Frequent infections
Delayed growth
Stroke
Pulmonary hypertension
Organ damage
Blindness
Jaundice
gallstones
Caused by a genetic defect
Carried by 5% of humans
Carried by up to 25% in some regions of Africa
Life expectancy
42 in males 48 in females

64. Sickle-Cell Disease = Point Mutation

65. Mutation occurs in the beta chain – have them look at their amino acid structures and think about why the change may be important

66. Sickle cell hemoglobin forms long, inflexible chains

68. Comparison: Prokaryotes vs. Eukaryotes

69. Prokaryote vs. Eukaryote

70. Prokaryotes vs. Eukaryotes
Transcription and translation both in cytoplasm
DNA/RNA in cytoplasm
RNA poly binds directly to promoter
Transcription makes mRNA (not processed)
No introns
Transcription in nucleus; translation in cytoplasm
DNA in nucleus, RNA travels in/out nucleus
RNA poly binds to TATA box & transcription factors
Transcription makes pre- mRNA  RNA processing  final mRNA
Exons, introns (cut out)

71. A Summary of Protein Synthesis (p. 348)
Most current definition for a gene: A region of DNA whose final product is either a polypeptide or an RNA molecule