1. Protein Synthesis

2. DNA  RNA  Protein

3. 2 Major Steps
Transcription – DNA is transcribed (copied!) into single stranded mRNA (DNA code transcribed into RNA code)
Translation – mRNA is translated into protein (amino acids)

4. Transcription Occurs in nucleus (where the DNA is located!)
Generally divided into three steps – initiation, elongation, termination

5. A. Initiation
RNA polymerase (enzyme) attaches to promoter regions of DNA at TATA box
RNAP requires TATA box and other transcription factors to be present

6. B. Elongation
RNAP can only add nucleotides to the 3’ of the growing mRNA strand; thus mRNA is synthesized in the 5’ 3’ direction

7. C. Termination
Transcription ends when mRNA polymerase reaches a specific STOP sequence:
ATT
ATC
ACT

8. mRNA processing
After transcription, mRNA must be modified so that it can exit the nucleus
1. GTP cap added to 5’ end of mRNA (stability & attachment point for ribosome down the road)
2. Poly-A tail added to 3’ end of mRNA (stability & guidance so mRNA goes from nucleus to ribosome)
3. Removal of introns

9. Introns vs. Exons
Exons – sequences that contain the code for a polypeptide (protein); exons are expressed
Introns – non-coding sequences of mRNA

10. Original, unprocessed mRNA contains both introns and exons
Before mRNA exits nucleus for translation at ribosome, snRNPs (small nuclear ribonucleoproteins) remove introns and splice exons together

13. Translation
Occurs in cytoplasm where processed mRNA meets ribosome and is translated into protein
Steps:
Initiation
Elongation
Termination

14. For translation to occur, you need…
Activated tRNA
-tRNA in cytoplasm finds the correct amino acid
-Attachment (activation) requires 1 ATP and enzyme

15. Ribosomes consist of 2 subunits (small and large)
2. Ribosomal subunits
Ribosomes consist of 2 subunits (small and large)
Each subunit is made of rRNA and protein
Each is built separately in nucleolus
The two subunits exit nucleolus and form the ribosome in the cytoplasm when translation starts

16. The Genetic Code Codon – triplets of bases
mRNA makes a template strand (from DNA) that is translated into protein via a triplet code
Every three base pairs codes for a particular aa

18. 1. Initiation
Brings together mRNA (from nucleus), tRNA (in cytoplasm), and ribosomal subunits (from nucleolus)
Small ribosomal subunit binds to mRNA and a specific tRNA (methionine)
Small subunit scans mRNA until it finds AUG (start codon)
Large subunit attaches the complex

20. 2. Elongation
Begins with the next tRNA arriving at the P site of the ribosome

22. Polyribosome

23. 3. Termination
Occurs when the ribosome encounters one of three STOP codons located on mRNA
At this point, polypeptide synthesis is complete and the ribosome detaches from the polypeptide

25. Point Mutations Chemical changes in just one base pair of a gene
2 general types:
Base pair substitutions
Base pair insertions or deletions

26. 1. Base pair substitutions
Substitution of one base pair with another
Often silent mutations because they don’t have an effect on encoded protein due to redundancy of genetic code:
DNA: CCG  CCA
mRNA: GGC  GGU
AA: gly  gly

27. Example: Sickle Cell Anemia
Results from a single point mutation in a gene that codes for one of the polypeptide chains that form hemoglobin
Fatigue, paleness, rapid heart rate, shortness of breath, jaundice

28. 2. Insertions & Deletions
Additions or deletions of nucleotide base pairs
BAD NEWS… these are often called frameshift mutations because they literally shift the reading frame of the mRNA  protein

29. Example: Tay-Sachs Disease
Inherited frameshift mutation on chromosome 15
Mutation results in malformation of hexoaminidase A, a protein that breaks down a particular chemical in gangliosides (nerve tissue)
Deafness, blindness, dementia, paralysis, slow growth, mental retardation etc

30. Mutagens
Spontaneous mutations – errors that result from cellular machinery malfunction
Environmental mutations – damage to DNA caused by environment
Mutagens – chemical agents that interact with DNA and cause problems
X-rays, UV light, various drugs (seriously)