Exam 2 Review
Supplemental Instruction
Iowa State University
Leader:
Course:
Instructor:
Date:
Lilli Howard
BIOL/GEN 313
Dr. Vollbrecht
02/23/14
1. RNA Functions
a. What are some characteristics of introns?
-located in primary transcript
-much larger than exons
-removed by RNA splicing: SPLICING REACTION
b. What is the function of the Shine-Dalgarno consensus sequence?
-signals where coding region starts in prokaryotes
c. How is the poly(A) tail added to pre-mRNA? What is the purpose of the poly(A) tail?
-added with poly(A) polymerase and catalyzed by ATP
- increases half-life of mRNA
d. Describe the basic structure of ribosomes in bacterial and eukaryotic cells.
-Bacteria: 70S  30S (21 proteins) and 50S (31 proteins)
-Eukaryotes: 80S  60S (49) and 40S (33)
e. What are the four types of pre-mRNA posttranscriptional modifications? What are
their purposes?
-addition of 5’cap: binds to ribosomes, stabilizes mRNA, enhances splicing
-addition of poly(A) tail: stabilizes mRNA, binds to ribosomes
-RNA splicing: removes introns, facilitates export to cytoplasm, alternative splicing
-RNA editing: alters nucleotide structure of mRNA
2. Protein Structure & Genetic Code
a. What are isoaccepting tRNAs?
-different tRNAs with different anticodons specify the same amino acid
b. The following triplets constitute anticodons found on a series of tRNAs. Name the
amino acid carried by each of these tRNAs.
a. 5’-UUU-3’  3’-AAA-5’ or 3’-GAA-5’  Lys
b. 5’-GAC-3’  3’-CUG-5’  Val
c. 5’-UUG-3’ 3’-AAC-5’  Gln
d. 5’-CAG-3’ 3’-GUC-5’  Leu
c. Describe the four levels of structure of a protein. What primarily determines the
secondary and tertiary structures of a protein?
-Primary: amino acid sequence
-Secondary: regular folding of aa’s such as alpha helix and beta sheets
-Tertiary: higher order folding of aa’s to form overall 3D shape of molecule
-Quaternary: interaction of 2 or more polypeptides to form functional protein
d. Through wobble, a single anticodon can pair with more than one codon.
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e. What does tRNA charging refer to?
-Attachment of the correct amino acid to the corresponding tRNA
-Amino acids linked to 3’-OH of tRNA by an ester bond
-Amino-acyl tRNA synthetase enzymes catalyze attachment of amino acid
3. Translation
a. What role do initiation factors play in protein synthesis?
-IF-1: dissociates large and small subunits of ribosome
-IF-2: forms complex with GTP and charged initiatior tRNA and delivers it to complex
-IF-3: binds to small subunit of ribosome: prevents binding of large unit during initiation
b. Arrange the following components of translation in the approximate order in which
they would appear or be used in protein synthesis:
i.
70S initiation complex (4)
ii.
30S initiation complex (2)
iii.
Release factor 1 (7)
iv.
Elongation factor G (6)
v.
Initiation factor 3 (1)
vi.
Elongation factor Tu (5)
vii.
fMet-tRNAfMet (3)
c. What are the requirements for translation?
-Ribosomes with 2 subunits
-Charged tRNAs
-mRNA with initiation codon AUG
-accessory proteins
-GTP (energy source)
d. What are the three RNA binding sites and what are their purposes?
-A: acceptor: charged tRNA enter here; peptide bond forms between aa’s in A and P
-P: growing peptide chain attached here: tRNA releases amino acid
-E: exit
e. What kind of bonds are found in the polypeptide chain?
-Peptide bonds: catalyzed by rRNA
f. What are the differences between prokaryotic and eukaryotic translation?
-Prokaryotes: find AUG start codon by hybridizing mRNA and rRNA: can initiate
translation when transcription is still going
-Eukaryotes: ribosome binds to 5’ cap and scans for AUG: must complete
transcription, editing
4. Mitosis
a. What defines a diploid cell? Has 2 sets of chromosomes
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b. What would be the result if a chromosome did not have a kinetochore?
-The kinetochore is the point at which spindle microtubules attach to the
chromosome. The chromosome would not be drawn into the nucleus and the
resulting cells would be missing a chromosome
c. What are the main steps and checkpoints of the cell cycle?
Figure 2.9 page 21
d. What are the main steps and defining features of mitosis?
Figure 2.10 page 23
5. Meiosis
a. What are the steps and end products of meiosis?
Figure 2.15 page 28-28
Table 2.2 page 27
b. When does crossing over take place? Why is it important?
-prophase 1
-genetic variation
(random distribution of chromosomes)
c. What is an example of a reductional division? Equational division?
Anaphase I of Meiosis vs Anaphase of Mitosis
d. If an organism has a diploid number of 8, how many possible gametes does it have?
24 = 16
6. Mendelian Principles
a. Describe a monohybrid cross. Make an example Punnett square or branch diagram.
-a cross between two individuals that differ in a single characteristic
(AA x aa) (Aa x Aa)
b. Describe a di-hybrid cross. Make an example Punnett square or branch diagram.
-a cross between two individuals that differ in two characteristics
(AA BB x aa bb) (Aa Bb x Aa Bb
c. What is the principle of segregation?
d. Describe the sum and multiplication rules and when to use them.
-sum = or
- multiplication = and
e. What is a test cross and when do we use one?
-a cross between an individual with an unkown genotype and a homozygous recessive
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7. Sex Determination & Sex Linkage
a. Describe the following:
i. Dioecious: only male or only female reproductive structures in each
organism
ii. Monoecious: both male and female reproductive structures in the same
organism
iii. Hermaphroditism: an individual possesses both male and female
reproductive structures; produce both male and female gametes
iv.
Heterogametic: sex that produces two types of gametes ex: X and Y
v.
Homogametic: sex that produces gametes that are all alike
vi.
Barr body: inactivated X chromosome found in female placental animals
b. What is the pseudoautosomal region? How does the inheritance of genes in this
region differ from the inheritance of other Y-linked characteristics?
-small region of the X and Y chromosome that contain homologous gene
sequences allowing them to be considered a homologous pair
-genes are inherited similar to autosomal genes whereas Y linked traits are passed
only from father to son
c. What characteristics are exhibited by a Y-linked trait?
-appear only in mails; always transmitted from father to son
d. In drosphila, yellow body is an X-linked gene that is recessive to the gene for the
gray body.
i. A homozygous gray female is crossed with a yellow male. The F1 are
intercrossed to produce F2. Give the genotypes and phenotypes, along with
the expected proportions of the F1 and F2 progeny.
-F1: ½ XY (gray males) ½ X’X (gray females)
-F2: ¼ XY (gray males) ¼ X’Y (yellow males) ¼ XX (gray females) ¼
X’X (gray females)
1060 Hixson-Lied Student Success Center  515-294-6624  sistaff@iastate.edu  http://www.si.iastate.edu