1. RNA and Protein Synthesis
Chapter 12
RNA and Protein Synthesis

2. RNA Objectives: Define: How does RNA differ from DNA?
How does the cell make RNA?
Define:
RNA
Messenger RNA
Ribosomal RNA
Transfer RNA
Transcription
RNA polymerase
Promoter
Intron
exon

3. I. The Role of RNA
Double-helix structure  DNA copied by separating 2 strands, then use base pairing to make a new complementary strand
Structure did not explain how a gene worked
Explained by discovery of RNA
RNA – nucleic acid – involved in putting genetic code into action

4. A. Comparing RNA and DNA
DNA & RNA – nucleotides made of 5-carbon sugar, phosphate group, nitrogenous base
3 important differences:
Sugar in RNA is ribose instead of deoxyribose
RNA is single-stranded instead of double-stranded
RNA contains uracil in place of thymine
Differences make it easy for enzymes to tell the DNA and RNA apart

5. DNA = master plan – stays safely in nucleus
RNA = blue prints – go to protein-building sites in cytoplasm (ribosomes)

6. B. Functions of RNA Disposable copy of a segment of DNA
Working facsimile of a single gene
Most only have 1 job = protein synthesis
Controls assembly of amino acids into proteins
3 types of RNA & each has specific job in making proteins

7. 1. Messenger RNA
Genes contain instructions for assembling amino acids into proteins
Messenger RNA carries copies of instructions from DNA to other parts of cell

8. 2. Ribosomal RNA Proteins assembled on ribosomes
Ribosomes composed of 2 subunits
Subunits made up of several ribosomal RNA molecules and as many as 80 different proteins
Ribosomal RNA forms an important part of both subunits of ribosome

9. 3. Transfer RNA
Transfers each amino acid to ribosome as it is specified by coded messages in mRNA
Carries amino acids to ribosomes
Matches amino acids to coded mRNA message

10. II. RNA Synthesis
Cells invest large amounts of raw material and energy into making RNA molecules
If we understand how cells do this, we can understand more about how genes work

11. A. Transcription
Transcription – segments of DNA serve as templates to produce complementary RNA molecules
Prokaryotes – RNA synthesis and protein synthesis occur in cytoplasm
Eukaryotes – RNA produced in nucleus  moves to cytoplasm to produce protein

12. Transcription in Eukaryotes
Requires RNA polymerase (Enzyme) –binds to DNA & separates DNA strands
Uses one strand of DNA as a template to assemble complementary strand of RNA
Ability to copy a single strand of DNA into RNA makes it possible for a single gene to produce hundreds or thousands of RNA molecules

13. B. Promoters RNA polymerase doesn’t bind just anywhere on DNA
RNA polymerase only binds to promoters
Promoters – regions of DNA that have specific base sequences
Are signals to DNA molecule that show RNA polymerase exactly where to begin making RNA
Similar signals in DNA cause transcription to stop when new RNA molecules is completed

14. C. RNA Editing
Sometimes require editing before ready to be read (like a 1st, rough draft)
Pre-mRNA molecules have bits and pieces cut out of them before they go into action
Introns – portions cut out and discarded
Taken out of pre-mRNA while still in nucleus
Exons – remaining pieces
Spliced back together to form final mRNA

15. READING DNA TO MAKING A PROTEIN
DNA : TTA GCG AGC GTT (base Triplets) holds instructions
mRNA: AAU CGC UCG CAA (Codons) each codon codes for an amino acid that builds a protein.
tRNA: UUA GCG AGC GUU (anti-codons) these are the tRNA letters that go out and find the correct amino acid for the protein

16. Take DNA and Transcribe it into mRNA and tRNA
DNA Strand: TAC GGC TAT ACT
mRNA:
tRNA:

17. Exit Ticket What are the 3 types of RNA?
What are the 3 major differences between RNA and DNA?

18. Do Now What are the three major differences between DNA and RNA?
What are the 3 types of RNA and what job does each complete in the body?
Transcribe the following DNA sequence:
ATAGCTGATCGA

19. Section 13.2 Ribosomes and Protein Synthesis
Objectives:
What is the genetic code, and how is it read?
What role does the ribosome play in assembling proteins?
What is the “central dogma” of molecular biology?
Define:
Polypeptide
Genetic code
Codon
Translation
Anticodon
Gene expression

20. I. The Genetic Code
Step 1 = transcribe nucleotide base sequence from DNA to RNA
Transcribed info contains code for making proteins
Proteins made by joining amino acids together = polypeptides
20 amino acids

21. RNA contains 4 bases: adenine, cytosine, guanine, uracil
4 letters form a language = genetic code
The genetic code is read 3 letters at a time
Codon – each 3-letter “word” in mRNA – consists of 3 bases that specify a single amino acid

22. A. How to Read Codons 64 possible 3-base codons from 4 letters
Genetic code table (start at center of circle, move outward through 2 more rings, read amino acid name)

24. B. Start and Stop Codons Punctuation marks for messages
Methionine = AUG = initiation (“start”) codon for protein synthesis
mRNA is read (3 bases at a time)
“Stop” codon – ends translation
Polypeptide is complete

25. Do Now Transcribe the following DNA sequence:
ATGCTAGCTAAT
What DNA sequence indicates a start codon? Stop Codon?
What is the difference between an intron and exon?
How do you read the genetic table chart?

26. II. Translation
Sequence of nucleotide bases in mRNA = set of instructions that gives order amino acids
Once complete  polypeptide folds into final shape to become a functional protein
Ribosomes use sequence of codons in mRNA to assemble amino acids
Translation – process of decoding an mRNA message into a protein

27. A. Steps in Translation Transcription in nucleus
Translation in ribosomes
Ribosome attaches to mRNA
Each codon passes through ribosome
tRNAs bring proper amino acids into ribosome
Ribosome attaches amino acids one at a time to growing chain
Each tRNA carries only 1 kind of amino acid
Each tRNA has 3 unpaired bases (anticodon – complementary to one mRNA codon)
Next tRNA brings next amino acid w/ anticodon

28. Ribosome helps form peptide bond b/w first and second amino acids
At same time bond holding first tRNA molecule to its amino acid is broken
tRNA moves into 3rd binding site  exits ribosome
Ribosome moves to 3rd codon  tRNA brings amino acid for 3rd codon

29. - ribosome releases both newly formed polypeptide & mRNA
Polypeptide chain continues to grow until ribosome reaches “stop” codon on mRNA
- ribosome releases both newly formed polypeptide & mRNA
Translation process complete

30. READING DNA TO MAKING A PROTEIN
DNA : TTA GCG AGC GTT (base Triplets) holds instructions
mRNA: AAU CGC UCG CAA (Codons) each codon codes for an amino acid that builds a protein.
tRNA: UUA GCG AGC GUU (anti-codons) these are the tRNA letters that go out and find the correct amino acid for the protein

31. Take DNA and Transcribe it into mRNA and tRNA
DNA Strand: TAC GGC TAT ACT
mRNA:
tRNA:

32. B. The Roles of tRNA and rRNA in Translation
All 3 types come together in ribosome during translation
mRNA – carries coded message that directs the process
tRNA – deliver exactly the right amino acid called for by each codon on mRNA
Enable ribosome to “read” mRNA message
rRNA – help hold ribosomal proteins in place & help locate beginning of mRNA message
May carry out chemical reactions that joins amino acids together

33. III. The Molecular Basis of Heredity
Most genes contain nothing more than instructions for assembling proteins
Many proteins = enzymes that catalyze and regulate chemical reactions
Gene codes for enzyme to produce pigment that controls color of flower
Another gene produces proteins that regulate patterns of tissue growth in a leaf
Proteins = microscopic tools  each specifically designed to build or operate a component of a living cell

34. Molecular biology – seeks to explain living organisms by studying them at the molecular level (DNA and RNA)
“Central dogma” of molecular biology is that information is transferred from DNA to RNA to protein
Many exceptions: viruses (transfer info in opposite direction)
Gene expression – way in which DNA, RNA and proteins are involved in putting genetic information into action in living cells

35. Discovery – near-universal nature of genetic code
Some organisms w/ slight variations in amino acids assigned to particular codons
Code is always read 3 bases at a time
Always “read” in same direction
Despite enormous diversity in form and function, living organisms display remarkable unity in molecular biology of genes

36. Exit Ticket DNA  _______  _________ What is transcription?
What is Translation?
What is a codon?
What does a codon determine?

37. Do Now What process involves RNA getting the instructions from DNA?
What process involves the assembling of a protein?
What join together to form the protein?
Where are proteins assembled?

38. Section 13.3 Mutations Objectives: Define: What are mutations?
How do mutations affect genes?
Define:
Mutation
Point mutation
Frameshift mutation
Mutagen
polyploidy

39. I. Types of Mutations Cells make mistakes in copying DNA
Mutations – heritable changes in genetic information
Gene mutations: produce changes in a single gene
Chromosomal mutations: produce changes in whole chromosome

40. A. Gene Mutations
Point mutation – involve changes in one or a few nucleotides; occur at a single point in DNA sequence
Occur during replication
Can be passed on to every cell that develops from original mutated cell

41. 1. Substitutions One base changed to a different base
Affect no more than single amino acid
Sometimes have no effect at all
Changed mRNA from CCC to CCA = no effect
Changed CCC to ACC = proline replaced with threonine

42. 2. Insertions and Deletions
One base inserted or removed from DNA sequence
Effects can be dramatic
Code read 3 bases at a time
If nucleotide is added or deleted  bases still read in groups of 3  groupings shift in every codon that follows mutation
Frameshift mutation – shift “reading frame” of genetic message
Can change every amino acid that follows the point of mutation
Can alter a protein so much that is unable to perform its normal function

43. B. Chromosomal Mutations
Involve changes in number or structure of chromosomes
Can change location of genes on chromosomes
Can change number of copies of some genes
4 types:
Deletion – loss of all or part of a chromosome
Duplication – produces extra copy of all or part of a chromosome
Inversion – reverses direction of parts of a chromosome
Translocation – part of one chromosome breaks off and attaches to another

44. II. Effects of Mutations
Genes can be altered by natural events or artificial means
Mutations may or many not affect organism
Some mutations that affect an individual can also affect a species or ecosystem
Many produced by errors in genetic processes
Errors during DNA replication: inserts incorrect base 1 in 10million bases
Small changes can accumulate over time
Stressful environmental conditions cause bacteria to increase mutation rates
Can be helpful: ability to consume new food source or resist poison

45. A. Mutagens Mutagen – chemical or physical agents in environment
Chemical: Pesticides, natural plant alkaloids, tobacco smoke, environmental pollutants
Physical: electromagnetic radiation; interact w/ DNA & produce high rates of mutation
Cells can repair some damage
When they cannot  DNA sequence changes permanently
Some=interfere w/ base-pairing  increases error rate of DNA replication
Some=weaken DNA strand  breaks & inversions create chromosomal mutations

46. B. Harmful and Helpful Mutations
Effects of mutations on genes vary widely
Some have little or no effect and some produce beneficial variations
Some negatively disrupt gene function
Depends on how its DNA changes relative to the organism’s situation
Without mutations  organisms could not evolve  mutations are source of genetic variability in a species

47. 1. Harmful Effects
Most harmful – dramatically change protein structure or gene activity
Defective proteins can disrupt normal biological activities  result in genetic disorders (cancers) (sickle-cell disease)

48. 2. Beneficial Effects
Mutations often produce proteins with new or altered functions that can be useful to organisms in different or changing environments
Insects resist chemical pesticides (mosquitoes)
Humans increase bone strength/density; increase resistance to HIV
Plant/animal breeders take advantage of “good” mutations
Polyploidy – multiple sets of chromosomes in gametes b/c chromosomes failed to separate during meiosis
Polyploidy plants – often larger and stronger than diploid plants (bananas/limes)

49. Exit Ticket What is a mutation? What is a point mutation?
What types of point mutations are there?
How can a mutation be a good thing?
How can a mutation be bad for the organism?
What is a mutagen?