1. Honors Biology Chapter 12
Molecular Genetics

2. From Gene to Protein

3. 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.

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

5. 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

6. Flow of Genetic Information
1. Chromosomes have regions called genes
2. The cell uses transcription to copy a gene by building a piece of mRNA
3. The mRNA leaves the nucleus and goes to a ribosome
4. The ribosome reads the mRNA and uses translation to direct the assembly of a protein
5. Gene is now expressed in the cell

7. 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

8. 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

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

10. 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

11. 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

12. 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

13. Matching bases of DNA & RNA
U instead of T is matched to A
TACGCACATTTACGTAC
DNA
mRNA
AUGCGUGUAAAUGCAUG

14. 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

15. http://highered. mheducation

16. 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.

17. 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?
Translate!
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

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

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

20. 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

21. 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

22. 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)

23. In Animated Format

24. 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

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

26. 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.

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

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

29. Mutations

30. 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

31. 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

32. Example: Sickle cell anemia

33. 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

34. 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)

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

36. 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.

38. 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)
Beneficial vs. detrimental is determined by the environment! (ex: sickle cell anemia protects against malaria)