1. Chapter 11 (Part 3) Translation
From Gene to Protein
Honors Biology
Ms. Gaynor
Lecture for 3/24/09

2. mRNA  polypeptide (protein)
REVIEW… Translation
mRNA  polypeptide (protein)

3. Brings message from DNA (DNA instructions) to ribosome to make protein
Type of RNA
Function Job
Picture
mRNA
(messenger RNA)
Brings message from DNA (DNA instructions) to ribosome to make protein
tRNA
(transfer RNA)
Transfers/moves amino acids to ribosomes
rRNA
(ribosomal RNA)
Makes up ribosomes along with proteins

4. tRNA
A cell translates mRNA message into protein with help from transfer RNA (tRNA)
Type of RNA
~80 nucleotides
“t” shape
Carries amino acids
Matches codons to
anticodons

5. tRNA Molecules of tRNA are not all identical
Each carries a specific amino acid
Each has an specific anticodon on the other end
Aminoactyl Synthase (enzyme) puts tRNA together with it amino acid

6. Aminoactyl tRNA Synthase
tRNA Assembly
Aminoactyl tRNA Synthase
ACTIVATED tRNA

7. Ribosomes
Help bind tRNA anticodons with mRNA codons during translation
Found on ROUGH Endoplasmic Reticulum RER (“bound”) or in cytoplasm (“free”)
Anticodon (tRNA) = codon (mRNA)

8. AMINO ACIDS
tRNA
(with anticodons)
mRNA
(with codons)

9. REVIEW…The Genetic Code
It’s a table used that TRANSLATES RNA nucleotides called CODONS (or mRNA “letters”) into one of the 20 amino acids
3 letter mRNA “word” = 1 amino acid
There are 4 different RNA “letters” that can be used
A, U, C, and G

10. THE GENETIC CODE

11. Ribosomes There are 2 ribosomal subunits
Constructed of proteins and ribosomal RNA or rRNA

12. Binding Sites in a Ribosome
The ribosome has three binding sites for tRNA
The P site
The A site
The E site
P site (Peptide Bond-tRNA
binding site)
E site
(Exit site)
mRNA
binding site
A site (Amino acid-
tRNA binding site)
Large
subunit
Small E P A

13. tRNA mRNA Growing polypeptide Amino acid Next amino acid
to be added to
polypeptide chain
tRNA
mRNA
Codons 3 5 \

14. Building a Polypeptide
Translation can be divided into 3 phases
Initiation
Elongation
Termination

15. Initiation of Translation
initiation stage brings together
mRNA
tRNA bearing 1st amino acid (“start”) called MET
2 subunits of a ribosome come together

16. Translation initiation complex
Large
ribosomal
subunit
Initiator tRNA
mRNA
mRNA binding site
Small
Translation initiation complex
P site
GDP
GTP
Start codon
Met U A C G E 3 5
Figure 17.17

17. Elongation
Amino acids are added one by one to the preceding amino acid
Peptide bonds are formed
Amino acid

19. Termination of Translation
When the ribosome reaches a stop codon on the mRNA
There are 3 stop codons
UAA, UAG, and UGA
Release factor (protein) binds to stop codon in A site (NOT tRNA)  polypeptide released

20. Termination of Translation
Release
factor
Free
polypeptide
Stop codon
(UAG, UAA, or UGA) 5 3

21. Phe tRNA Anticodon 5 3 Amino acids “EMPTY” tRNA tRNA with amino acid
TRANSCRIPTION
TRANSLATION
DNA
mRNA
Ribosome
Polypeptide
Amino
acids
tRNA with
amino acid
attached
tRNA
Anticodon
Trp
Phe
Gly A G C U
Codons 5 3
“EMPTY”
tRNA
Figure 17.13

22. Polypeptide  3D Protein
Primary Structure
Amino acids is a row (LINEAR)
Secondary Structure
Amino Acids BEND and FOLD towards each other
Tertiary Structure
Amino acids BIND to each other
3D shape made
Quartnary structure (only some)
2 or more polypeptides BIND to each other

23. 1 2 4 3

24. Translation (Protein Synthesis) Animation

25. Chapter 11 (Part 7) Translation & Mutations
From Gene to Protein
Honors Genetics
Ms. Gaynor

26. Review…

27. Review…

28. Review… DNA Template (Gene) TAC GGG CTC AAA TAC ACG ACT
What is the mRNA transcript?
5’ AUG CCC GAG UUU AUG UGC UGA 3’
What is the amino acid sequence?
START- Pro- Glu-Phe- Met-Cys-STOP

29. Mutations
Mutations
Are changes in the genetic material (DNA) of a cell
2 TYPES
1. Point mutations can affect protein structure and function
Are changes in just one base pair of a gene

30. POINT MUTATIONS
The change of a single nucleotide in the DNA’s template strand
Can lead to the production of
an abnormal protein or…
the same protein

31. Point Mutations Point mutations within a gene can are called
Base-pair substitutions
Can results in a mutation (change) that is
harmful
neutral (not harmful or helpful)
beneficial

32. Substitutions 2 TYPES missense (wrong aa)
1 wrong aa is added to polypeptide
nonsense (prematurely STOP)
The change in DNA leads to an early STOP codon  polypeptide is SHORTEN!!

33. POINT MUTATION ANALOGY…
TEMPLATE: THE CAT ATE THE RAT
POINT MUTATION: THE CAT ATE THE RAT
THE CAT ATE THE BAT  What kind of point mutation is this?
MISSENSE
THE CAT ATE THE XAT  What kind of point mutation is this?
NONSENSE

34. What is the “wobble” effect?
The last base (nucleotide) in a codon is said to be in the WOBBLE position.
codon mutation may encode the same amino acid
Leads to NEUTRAL or SILENT mutations
Not harmful or helpful
SILENT MUTATIONS
Mutation does not change “end result”…change in DNA still makes the SAME amino acid
NO noticeable change occurs
a change from AUU to AUC will still encode Isoleucine

35. What is a neutral mutation?
May or may not affect the resulting protein.
For example, if the codon AAA is mutated to AGA, arginine would be used in the resulting protein instead of lysine
These amino acids are chemically similar and may not have a large effect in the protein or its function
IF this change cause the protein to not function (and be LETHAL to organism) then it is not a neutral mutation but rather a missense mutation

36. 2. Frameshift Mutations Insertions and deletions
Are additions or losses of nucleotide pairs in a gene
produce frameshift mutations
2 TYPES
Insertions
Deletions

37. FRAMESHIFT MUTATION ANALOGY…
TEMPLATE: THE CAT ATE THE RAT
ADDITION of “B” MUTATION: THE CAT ATE THE RAT
THE CAT BAT ETH ERA T  What kind of frameshift mutation is this?
INSERTION
SUBTRACTION of “A” MUTATION: THE CAT ATE THE RAT
THE CAT TET HER AT  What kind of frameshift mutation is this?
DELETION

38. Which is more harmful?
Typically, frameshift mutations are more harmful BUT some point mutations can be LETHAL
Ex: Tay Sachs and Cystic Fibrosis

39. Other Types of Mutations
Inversions
“Flip Flops”
Nucleotides trade places on each strand
Deletions (2+ nucleotides)
Many nucleotides are deleted at once

40. Causes of Mutations Inherited mutations From mom and dad
Spontaneous mutations
occurs during DNA replication
Environmental mutations (Mutagens)
physical or chemical agents that can cause mutations
Ex: Sun, viruses, chemicals