Study Guide 13
Last revised: Thursday, October 11, 2001

Topic: RNA, protein synthesis, and the genetic code

Chapter 17

1. How much DNA is there in a bacterial cell? a human cell? How many proteins could be encoded if all this DNA coded for protein sequences? Approximately what % of this DNA actually codes for proteins sequences?
2. What is meant by “transcription”? What molecules are needed for this to occur?
3. What is a promoter?
4. What are the 3 types of RNA, and what role does each play?
5. What is meant by “translation”? Where does this occur in the cell? What molecules are needed for this to occur?
6. A molecule of m–RNA has the following structure:
   ...... A A A U G G G G G U C U U U G U G C U A G G G U G A U U G .......
   
   
   
   Write the sequence of the translated protein (use the genetic code below)
   Note: where is the “start” codon? Does this protein have a “stop” codon?
   
   
   
   The Genetic Code
   
   

   	U	C	A	G
   U	UUU – phe UUC – phe UUA – leu UUG – leu	UCU – ser UCC – ser UCA – ser UCG – ser	UAU – tyr UAC – tyr UAA – stop UAG – stop	UGU – cys UGC – cys UGA – stop UGG – trp	U C A G
   C	CUU – leu CUC – leu CUA – leu CUG – leu	CCU – pro CCC – pro CCA – pro CCG – pro	CAU – his CAC – his CAA –gln CAG –gln	CGU – arg CGC – arg CGA – arg CGG – arg	U C A G
   A	AUU – ileu AUC – ileu AUA – ileu AUG – start/met	ACU – thr ACC – thr ACA – thr ACG – thr	AAU – asn AAC – asn AAA – lys AAG – lys	AGU – ser AGC – ser AGA – arg AGG – arg	U C A G
   G	GUU – val GUC – val GUA – val GUG – val	GCU – ala GCC – ala GCA – ala GCG – ala	GAU – asp GAC – asp GAA – glu GAG – glu	GGU – gly GGC – gly GGA – gly GGG – gly	U C A G

   
   
   
   
7. What is the role of a ribosome? Where are they found? Are there different ribosomes to make different proteins?
8. What do activating enzymes (technically, “aminoacyl tRNA synthetases) accomplish? Approximately how many of them are there?
9. “Codons” represent a series of 3 bases in DNA or RNA that specify a single amino acid. “Anticodons” are found on transfer RNA molecules. Theoretically, if there are 64 different codons, how many anticodons must there be?
10. Note that the “start” codon AUG is also the first amino acid of a protein, methionine (abbreviated met). Does this mean that every protein should start with met?
11. Note that the “stop” codons do not specify any amino acid but instead cause termination of protein growth. What are the 3 stop codons?
12. The process of protein synthesis is pretty complicated, and is normally discussed in 3 steps: initiation, elongation, and termination — see Figs. 17.15-17. mRNA attaches to a ribosome; tRNA molecules bring amino acids into the ribosome, match up their anticodons with appropriate codons on the mRNA, and locate amino acids at the appropriate positions. Note that there are only two sites on the ribosome at which tRNA can bind. Why are these called A and P? What binds to each of these two sites?
13. Besides ribosomes, m-RNAs and AA-tRNAs, what other factors are required for protein synthesis? What is a termination factor? When is it required?
14. What is a polyribosome?
15. How is protein synthesis different between prokaryotes and eukaryotes?
16. What is an exon? an intron? a spliceosome? Be sure you understand Fig. 17.10.
17. What is a ribozyme? Give two examples.
18. What is a mutation? Give an example of a point mutation, an insertion, and a deletion mutation.
19. What are some common causes of mutations?
20. In the following list, identify which components are required for DNA replication (label “1”), transcription (label “2”), and translation (label “3”).
    

(a) DNA polymerase	(b) t–RNA	(c) elongation factors
(d) m–RNA	(e) ribosomes	(f) primase
(g) helicase	(h) “AUG” codon	(i) RNA polymerase
(j) ATP, CTP, GTP, UTP	(k) amino acids	(l) initiation factor
(m) dATP, dCTP, dGTP, dTTP	(n) release factor	(o) promoter

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