Biology · Unit 6 · Paper 3

Gene Expression & Regulation unit test

A test on this unit alone, marked as a percentage and a letter grade — for the test your class is actually sitting, rather than for May. Answer everything, then submit once: seeing the answer to question 3 before attempting question 4 makes the final percentage meaningless.

Paper 1 Paper 2 Paper 3

Each paper is built from this unit’s 40 terms and is the same for everyone, so a teacher can assign “Unit 6, Paper 3” and every student sits the identical test. Multiple choice is marked objectively; the written sections you mark yourself against the model answer and rubric.

Suggested time 31 min 28 points0/17 attempted

PCR

Start and stop codons

lac operon

Alternative splicing

Topoisomerase

Plasmid

Universality of the genetic code

Point mutation types

Promoter and TATA box

trp operon

RNA processing

Origin of replication

Short answer 1. Define or explain: Regulatory vs structural genes

3 pts

Short answer 2. Define or explain: Homeotic genes

3 pts

Short answer 3. Define or explain: DNA polymerase

3 pts

Short answer 4. Define or explain: Translation

3 pts

Free response

4 pts

Scientists can quantify the rate of translation as ribosomes move along an mRNA from one codon to the next. Using ribosome profiling, they measured how long a ribosome remains stationary at each codon. The average translation rate across all codons is 5.2 amino acids per second, but the average rate for a specific codon in different mRNA sequences can vary widely, and those variations are thought to help the protein fold correctly. The rate at which three codons were translated was measured in 100 different mRNAs. FIGURE 1. DISTRIBUTION OF TRANSLATION RATES (number of times each rate was recorded) Rate (ms/codon) 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 900 950 (A) GAC 3 18 20 14 14 14 9 3 1 0 1 0 1 0 0 0 0 0 (B) AUU 11 35 32 10 4 3 2 2 1 0 0 0 0 0 0 0 0 0 (C) UGG 1 3 5 12 12 11 13 9 10 9 4 4 4 3 1 1 1 1 A longer time per codon means a slower rate of translation.

(a) Using the data in Figure 1, graph A, identify the rate (in ms/codon) that was recorded the greatest number of times for the GAC codon.

(b) Using the data in Figure 1, graphs B and C, describe the variation in translation rate of the AUU codon compared with that of the UGG codon.

(c) Scientists hypothesize that tRNA molecules that bind to UGG codons are available in lower abundance than are tRNAs that bind to AUU codons. Support the scientists’ hypothesis using the data in Figure 1.

(d) Amino acids can be encoded by multiple codons, and in many organisms certain codons for the same amino acid occur more frequently in an mRNA than others. Based on the data provided, explain why the use of one codon over another for the same amino acid might result in increased levels of protein production from a particular mRNA.