1. From DNA to Proteins
Chapter 14

2. Marvelous Mussel Adhesive
Mussel binds itself to rocks with threads coated with the protein bysuss
Gene for bysuss has been put into yeast
Yeast synthesize the protein based on the instructions in the mussel DNA

3. Steps from DNA to Proteins
Same two steps produce all proteins:
1) DNA is transcribed to form RNA
Occurs in the nucleus
RNA moves into cytoplasm
2) RNA is translated to form polypeptide chains, which fold to form proteins

4. Three Classes of RNAs Messenger RNA Ribosomal RNA Transfer RNA
Carries protein-building instruction
Ribosomal RNA
Major component of ribosomes
Transfer RNA
Delivers amino acids to ribosomes

5. A Nucleotide Subunit of RNA
uracil (base)
phosphate group
sugar
(ribose)
Figure 14.2 Page 228

6. Base Pairing during Transcription
DNA
G C A T
RNA
G C A U
DNA
C G T A
DNA
C G T A
base pairing in DNA replication
base pairing in transcription

7. Transcription & DNA Replication
Like DNA replication
Nucleotides added in 5’ to 3’ direction
Unlike DNA replication
Only small stretch is template
RNA polymerase catalyzes nucleotide addition
Product is a single strand of RNA

8. Promoter A base sequence in the DNA that signals the start of a gene
For transcription to occur, RNA polymerase must first bind to a promoter

9. Gene Transcription DNA to be transcribed DNA winds up again
transcribed unwinds
transcribed DNA winds up again
mRNA
transcript
RNA polymerase
Figure 14.4c Page 229

10. Adding Nucleotides 5’ growing RNA transcript 3’ 5’ 3’
direction of transcription
Figure 14.4d Page 229

11. Transcript Modification
unit of transcription in a DNA strand 3’
exon
intron
exon
intron
exon 5’
transcription into pre-mRNA
poly-A
tail
cap 5’ 3’
snipped out
snipped out 5’ 3’
Figure 14.5 Page 229
mature mRNA transcript

12. Genetic Code Set of 64 base triplets Codons 61 specify amino acids
3 stop translation
Figure 14.7 Page 230

13. tRNA Structure codon in mRNA anticodon amino-acid attachment siteOH
Figure 14.8 Page 231

14. Ribosomes small ribosomal subunit large ribosomal subunit
tunnel
small ribosomal subunit
large ribosomal subunit
intact ribosome
Figure 14.9b,c Page 231

15. Three Stages of Translation
Initiation
Elongation
Termination

16. Initiation Initiator tRNA binds to small ribosomal subunit
Small subunit/tRNA complex attaches to mRNA and moves along it to an AUG “start” codon
Large ribosomal subunit joins complex
Fig a-c Page 232

17. Binding Sites binding site for mRNA A (second binding site for tRNA)
P (first binding site for tRNA)
Figure 14.10d Page 232

18. Elongation mRNA passes through ribosomal subunits
tRNAs deliver amino acids to the ribosomal binding site in the order specified by the mRNA
Peptide bonds form between the amino acids and the polypeptide chain grows

19. Elongation
Fig e-g Page 233

20. Termination Stop codon into place No tRNA with anticodon
Release factors bind to the ribosome
mRNA and polypeptide are released
mRNA
new
polypeptide
chain
Fig j-k Page 233

21. What Happens to the New Polypeptides?
Some just enter the cytoplasm
Many enter the endoplasmic reticulum and move through the cytomembrane system where they are modified

22. Overview Transcription Translation mRNA rRNA tRNA
Mature mRNA transcripts
ribosomal subunits
mature tRNA
Translation

23. Base-Pair Substitutions
Gene Mutations
Base-Pair Substitutions
Insertions
Deletions

24. Base-Pair Substitution
a base substitution within the triplet (red)
original base triplet in a DNA strand
During replication, proofreading
enzymes make a substitution
possible outcomes: or
original, unmutated sequence
a gene mutation
Figure Page 234

25. Frameshift Mutations Insertion Deletion Both shift the reading frame
Extra base added into gene region
Deletion
Base removed from gene region
Both shift the reading frame
Result in many wrong amino acids

26. Frameshift Mutation mRNA parental DNA arginine glycine tyrosine
tryptophan
asparagine
amino acids
altered mRNA
DNA with
base insertion
arginine
glycine
leucine
leucine
glutamate
altered amino-
acid sequence
Figure Page 234

27. Transposons DNA segments that move spontaneously about the genome
When they insert into a gene region, they usually inactivate that gene

28. Mutation Rates Each gene has a characteristic mutation rate
Average rate for eukaryotes is between 10-4 and 10-6 per gene per generation
Only mutations that arise in germ cells can be passed on to next generation

29. Mutagens Ionizing radiation (X rays) Nonionizing radiation (UV)
Natural and synthetic chemicals