1. GENE EXPRESSION CH 17 http://www.youtube.com/watch?v=88kMwpC7CCg

2. I. Basic principles of gene expression
A. General characteristics

3. process by which genetic info in DNA is converted to protein
DNA → RNA is transcription
RNA → protein is translation
RNA is the bridge between proteins and genes that code for them
The concept of gene is universal to all domains of life
The general process of gene expression is also universal
The genetic code is also universal

5. B. The genetic code

6. Language of DNA and RNA are nucleotides
Language of proteins are amino acids
The nucleotide sequence must be translated into amino acid sequence
Nucleotide sequence is read in groups of 3 nucleotides called codons
The genetic code is redundant

7. II. Transcription
Process by which the genetic info in DNA is copied into RNA
Occurs at specific regions of DNA called genes
the basic structure of genes are the same in all domains

8. Promotor: where transcription starts.
Coding sequence: what is transcribed to RNA
Terminator: where transcription stops

9. A. The process of transcription
Only one strand of the DNA is transcribed into RNA, the template strand
RNA strand is complementary to DNA strand copied
Enzyme is RNA polymerase

10. Three stages: initiation, elongation, termination
Initiation: RNA polymerase binds to promoter with the help of various transcription factors and unzips DNA.

11. Elongation: RNA polymerase reads template stand of DNA making RNA
Termination: transcription stops

12. B. Post-transcriptional processing of mRNA in eukaryotes
Before mRNA is usable it must be processed
5’ CAP and 3’ poly A tail put on
Purpose of CAP and tail: help RNA leave nucleus, prevent its degradation, and help ribosome bind to 5’end
Splicing out of introns

13. snRNPs binds to intron/exon junction
Introns: segments of gene that are transcribed into mRNA but don’t code for protein
Must be cut out
snRNPs binds to intron/exon junction
snRNPs attract each other looping out the introns
introns are cut out and exons are glued together

14. III. Translation
Process by which genetic information carried in the mRNA is converted into protein
Requires the help of tRNA which transfers amino acids to growing protein in the ribosome

15. A. The structure of a tRNA
Anticodon: a group of 3 nucleotides complementary to a codon in mRNA
CCA site: place where amino acid is attached

17. Accurate translation requires 2 steps:
There must be a correct match between tRNA and amino acid which is done by aminoacyl tRNA synthase
There must be a correct match between anticodon and codon

18. B. Ribosomes Where translation occurs
Facilitates interaction of tRNA and mRNA
Made of 2 subunits of rRNA
Overall structure of bacterial and eukaryotic ribosomes are similar but many antibiotics target bacterial ribosomes without affecting eukaryotic ribosomes

19. Ribosomes have 3 binding sites for tRNA
P site: holds the tRNA that carries growing polypeptide chain
A site: holds the tRNA carrying the next amino acid to be added to growing chain
E site: exit site where free tRNAs leave

20. C. The Process of Translation
Occurs at the ribosome and is fundamentally the same in prokaryotes and eukaryotes but eukaryotic ribosomes are larger
occurs in 3 stages: initiation, elongation, termination

21. 1. Initiation
mRNA interacts with a ribosome such that 1st AUG sits in the P site
initiator tRNA binds to the FIRST AUG codon in mRNA

22. 2. Elongation and translocation
2nd tRNA with the correct anticodon binds to the 2nd codon in mRNA in the A site
The 2 adjacent amino acids are linked via dehydration reaction
Ribosome moves down 3 nucleotides
1st tRNA leaves thru the E site
This process continues

23. 3. Termination At the stop codon:
At the stop codon:
Release factor binds to stop codon in the A site
Translation stops and protein leaves

24. If a protein is destined for another location like the cell membrane or is to be secreted, it has a signal sequence that brings the ribosome to the RER

25. Many ribosomes can translate mRNA at the same time forming polyribosome. Can make a lot of protein quickly

26. Protein can be modified after translation to make the functional protein:
2 or more protein chains interact to form the functional protein (quaternary structure)
Small carbohydrate chains can be added to some proteins

27. IV. Mutations Changes in the DNA sequence
Can be a product of mistakes made during replication, transcription, or DNA repair
Most are caused by mutagens: agents that damage DNA
Most change the way the protein folds, affecting its function

28. Two types of small scale mutations: substitution mutations and frameshift mutation

29. Silent: no effect on protein due to redundancy in genetic code
Base substitution mutation: a single nucleotide is changed. Can be silent, missense, nonsense
Silent: no effect on protein due to redundancy in genetic code

30. Missense: mutation results in a different amino acid

31. Nonsense: amino acid changed to stop codon

32. Insertion /deletion mutations: loss or addition of nucleotides and are most often disastrous

33. http://highered. mcgraw-hill

34. V. Evolutionary significance of Mutations
Mutation rate is relatively low. Keeps genome constant from generation to generation
DNA repair mechanisms
DNA polymerase proofreads
Double strandedness and coiling of DNA protect it
However, mutations do occur. Mutations provide genetic variation for evolution to act on.