1. RNA and PROTEIN SYNTHESIS
CHAPTER 13
RNA and PROTEIN SYNTHESIS

2. What is the genetic material responsible for our physical traits?
DNA

3. What are the functions of DNA?
Copying information
Storing information
Transmitting information

4. How does DNA store and transmit information?
Genes contain coded DNA instructions for making proteins
DNA stored in nucleus
Proteins are made in the cytoplasm by ribosomes
PROBLEM…how to get the code to the machinery?
Another nucleic acid, RNA, translates the DNA message into protein

5. Central Dogma of Molecular Biology
Describes flow of information from DNA to protein
transcription
translation
RNA
DNA
Protein
RNA is the link between DNA and proteins.

6. Analogy for central dogma
The master plan has all the information needed to construct a building.

7. Analogy for central dogma
But builders never bring a valuable master plan to the building site where it might be damaged or lost.

8. Analogy for central dogma
Instead, builders work from blueprints, inexpensive disposable copies of the master plan.

9. Analogy for central dogma
Master plan = DNA
Building site = ribosomes (in cytoplasm)
Blueprint copies = RNA

10. Comparison of DNA and RNA
Consists of nucleotides
Double stranded
Deoxyribose as sugar
Bases = A, C, T and G
RNA
Consists of nucleotides
Single stranded
Ribose as sugar
Uracil (U) replaces T

11. RNA Builds Protein
Messenger RNA – carries the instructions from DNA to cytoplasm on how to make the protein
Ribosomal RNA – form ribosomes in cytoplasm to help build the protein
Transfer RNA – delivers the amino acids needed to build the protein

12. Transcription (RNA synthesis)
DNA  RNA
Occurs in the nucleus
Requires RNA polymerase
Builds RNA strand
Uses one strand of DNA as template
Involves single gene
Produces MANY RNA copies

13. Transcription (RNA Synthesis)
How does RNA polymerase know where to start and stop?
Sequences mark the start (promoter) and end (terminator) of a gene. RNA polymerase recognizes these sequences.

14. Transcription (RNA Synthesis)
RNA editing: non-coding sections of the mRNA transcript (introns) are cut out. Remaining pieces (exons) are spliced together.
What do you think would happen if introns were not removed from the pre-mRNA?
Why do cells use energy to make a large RNA moelcule and then cut it up and throw pieces (introns) away? Biologists still don’t have a complete answer. But current understanding is that mRNA can be cut and spliced in different ways in different tissues making it possible for a single gene to produce severl different forms of RNA. Introns and exons may also play a role in evolution.

15. RNAi Video

16. Replication vs Transcription
Replication copies the entire DNA
Transcription only copies one gene
Replication only makes one copy
Transcription makes many copies
BOTH involve complex enzymes
BOTH follow complementary base pairing
BOTH occur in the nucleus

17. If you were given the sequence of a DNA strand, could you figure out the sequence of the mRNA strand? Remember, U instead of T in RNA!!!
For example:
DNA T A C G C C C T A T T G A T
mRNA ?? A U G C G G G A UA AC U A

18. RIBOSOMES and PROTEIN SYNTHESIS
13.2
RIBOSOMES and PROTEIN SYNTHESIS

19. Translation a.k.a. Protein Synthesis
RNA  Protein

20. The language of protein synthesis
Language of RNA = nucleotides
Language of protein = amino acids
20 different amino acids found in proteins
Sequence of amino acids influences the shape of the protein which determines its function
Triplet code: three mRNA bases (codon) code for one amino acid

21. How is the order of bases in DNA and RNA translated into a particular order of amino acids in a protein?
Genetic Code
(mRNA codon translated into amino acid)

22. Genetic Code:
Codon = a group of three nucleotide bases in the mRNA that codes for a particular amino acid
RNA contains 4 bases
Bases form a language with just four letters in the alphabet
RNA is translated three “letters” at a time so that each “word” is three bases long and corresponds to one amino acid
Each three letter “word” = codon

23. Genetic Code: (mRNA codon to amino acid)
RNA contains 4 bases
Bases form a language with just four letters in the alphabet
RNA is translated three “letters” at a time so that each “word” is three bases long and corresponds to one amino acid
Each three letter “word” = codon

24. Genetic Code: punctuation
START codon signals the start of translation
AUG
also codes for methionine
STOP codons signal stop of translation
UGA, UAA, UAG
Do not code for any amino acid

25. Genetic Code = common language
UNIVERSAL – shared by all organisms
REDUNDANT – more than one codon may code for the same amino acid
Allows flexibility if mistakes are made

26. Quick Check A certain gene has the following base sequence:
GACAAGTCCAATC
Write the sequence of the mRNA molecule transcribed from this gene
Divide you mRNA sequence into codons
How many codons?
What amino acid does each codon code for?
How many amino acids?

27. The role of ribosomes in translation…
Ribosomes use the sequence of codons in mRNA to assemble amino acids into protein chains

28. The role of transfer RNA (tRNA) in translation…
Each tRNA molecule carries one kind of amino acid
Anticodon on tRNA recognizes complementary codon on mRNA
For example, tRNA for methionine has the anticodon UAC which pairs with the methionine codon (AUG)

29. Process of Translation
Ribosome binds to mRNA
mRNA codons attract complementary tRNA anticodons
Ribosome forms a peptide bond between amino acids then breaks bond holding the amino acid to the tRNA
Empty tRNA leaves; the ribosome pulls the mRNA exposing the next codon

30. QUICK CHECK… Remember, U instead of T in RNA!!!
For example:
DNA T A C G C C C T A T T G A T A
mRNA ??
Amino acids
tRNA

31. Central Dogma of Molecular Biology
Describes flow of information from DNA to protein
transcription
translation
RNA
DNA
Protein
RNA is the link between DNA and proteins.

32. 13.3
MUTATIONS

33. Mutations are changes in the DNA
Gene mutations (single gene)
Chromosomal mutations (multiple genes involved)
mutated
base

34. 1. Gene Mutations
Also known as point mutations because they occur at a single point in the DNA sequence
Occur during replication
Different types
Substitutions
Insertions and deletions

35. A. Substitutions One base is changed to a different base
Only affect one amino acid
Sometimes have no effect (silent)
EX: changing mRNA codon from CCC to CCA
Codon still specifies proline; SILENT
EX: changing mRNA codon from CCC to ACC
Replaces proline with threonine

36. B. Insertions and Deletions
Frameshift mutations – “shift” the reading frame
Effects are dramatic
Can change every amino acid after the mutation

37. Frameshift Mutations

39. 2. Chromosome mutations Changes in number or structure of chromosomes
Occur during meiosis
Four types
Deletion (loss of all or part of a chromosome)
Duplication (extra copy)
Inversion (reverse in the direction of a chromosome)
Translocation (one chromosome attaches to another)

41. Mutagens
Chemical or physical agents in the environment that can cause mutations in DNA
Include
Pesticides, tobacco, environmental pollutants, UV light, X-rays

42. Harmful and Helpful Mutations
Mutations can be harmful if…
They cause drastic changes in the protein that is produced
Defective proteins can disrupt normal function
Ex: sickle cell anemia, some cancer
The effects of mutations on genes vary widely. Some have little or no effect; and some produce beneficial variations. Some negatively disrupt gene function.

43. Harmful and Helpful Mutations
Beneficial effects
Variation produced by mutations can be highly advantageous to organisms in different or changing environments
Responsible for evolution
EX: pesticide resistance (bad news for humans but good news for mosquitoes)
EX: human resistance to HIV
The effects of mutations on genes vary widely. Some have little or no effect; and some produce beneficial variations. Some negatively disrupt gene function.