1. Ch 10: Protein Synthesis DNA to RNA to Proteins
Same two steps produce all proteins:
1) DNA is transcribed (copied) to form RNA
Occurs in the nucleus
RNA moves into cytoplasm
2) RNA is translated (read) to form polypeptide chains, which fold to form proteins

2. Three Classes of RNAs Messenger RNA (mRNA) Ribosomal RNA (rRNA)
Carries protein-building instruction
Ribosomal RNA (rRNA)
Major component of ribosomes
Transfer RNA (tRNA)
Reads mRNA and delivers amino acids to ribosomes

3. 1. TRANSCRIPTION
To start you must remember that DNA is made up of nucleotides (A,T,G, C)
These letters are in a specific order because they are “instructions” for how to make proteins
RNA will “decode” the instructions

4. Transcription
Start: mRNA is produced by reading DNA inside the nucleus and using the base pairing rules.
RNA nucleotides = A, U, C , G
A pairs w/ U : C pairs w/ G
DNA= AGGTTA
mRNA= UCCAAU

5. Transcription Only small stretch is a template
RNA polymerase catalyzes nucleotide addition
Product is a single strand of RNA

6. How do we start to make mRNA?
Promoter region is a base sequence in the DNA that signals the start of a gene to be read (to make mRNA)
For transcription to occur, RNA polymerase (an enzyme!) must first bind to a promoter
mRNA continues to build until it reaches the “code” for STOP. It is then released
promoter region

7. When the DNA is transcribed it is called Precursor mRNA (or Pre mRNA)
It is filled with introns and exons
Introns: intervening nucleotide (space holders)
Exons: expressed segments of a gene

8. mRNA is made up of introns and exons
Introns are then excised (cut) from the premRNA to form Mature mRNA
Exons stay and are expressed!
Mature mRNA is what then moves onto step 2 (translation)
Introns and Exons

9. Messenger RNA (mRNA) Each codon, is specific for an amino acid.
Made up of codons: sequence of three bases: exp AUG - methionine.
Each codon, is specific for an amino acid.

10. Genetic Code Set of 64 base triplets: Codons 61 specify amino acids
Nucleotide bases read in blocks of three
61 specify amino acids
3 stop translation

11. Code Is Redundant
Twenty kinds of amino acids are specified by 61 codons
Most amino acids can be specified by more than one codon
Exp: Six codons specify leucine
UUA, UUG, CUU, CUC, CUA, CUG

12. Near-Universal Genetic Code

13. Near-Universal Genetic Code

14. Meet the other two players needed for Translation
tRNA
rRNA (Ribosome)

15. Three Stages of Translation
Initiation: All three RNA molecules meet up
Elongation: mRNA is read by the tRNA. tRNA delivers the amino acids to the growing protein (polypeptide chain)
Termination: A stop codon is read and the process is complete

16. Elongation: how does the tRNA know what amino acid to bring?
~ Each tRNA contains a 3 base anticodon ~ In order to deliver the correct amino acid, the codon and the anticodon must match up using the complimentary base pair rules!

17. As the tRNA delivers the correct amino acids ~ the amino acids will begin to link together with a peptide bond ~ the tRNA will release the it and go off to find another amino acid to keep the process going.

18. Termination 1: STOP codon is reached
2: release the mRNA and polypeptide chain
from the ribosome.
(is free to join the pool of proteins in the cytoplasm or to enter rough ER)
The two ribosomal subunits now separate

19. Polysome A cluster of many ribosomes translating one mRNA transcript
Transcript threads through the multiple ribosomes like the thread of bead necklace
Allows rapid synthesis of proteins

20. 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

21. Gene Mutations Base-Pair Substitutions
Silent mutation: no amino acid change; redundancy in code
Missense: change amino acid
Nonsense: change to stop codon

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

23. Chromosome Mutations
Transposons: DNA segments that move spontaneously about the genome
(When they insert into a gene region, they usually inactivate that gene)
1.) Inversion
2.) Translocation
3.) Deletion
4.) Duplication

24. Prokaryote vs. Eukaryote genes
Prokaryotes
DNA in cytoplasm
circular chromosome
naked DNA
no introns
Transcription & translation are simultaneous in bacteria
Eukaryotes
DNA in nucleus
linear chromosomes
DNA wound on histone proteins
RNA polymerase requires transcription factor
introns vs. exons
Walter Gilbert hypothesis:
Maybe exons are functional units and introns make it easier for them to recombine, so as to produce new proteins with new properties through new combinations of domains.
Introns give a large area for cutting genes and joining together the pieces without damaging the coding region of the gene…. patching genes together does not have to be so precise.
intron = noncoding (inbetween) sequence
eukaryotic
DNA
exon = coding (expressed) sequence