108
CASE FILES: BIOCHEMISTRY
C O M P R E H E N SIO N Q U E ST IO N S
[11.1] Hereditary retinoblastoma is a genetic disease that is inherited as an auto-
somal dominant trait. Patients with hereditary retinoblastoma develop
tumors of the retina early in life, usually in both eyes. The affected gene
(RB1)
was the first tumor suppressor gene to be identified. Which of the
following best describes the function of the protein encoded by the
RB1
gene?
A. It binds transcription factors required for expression of DNA repli-
cation enzymes.
B. It allosterically inhibits DNA polymerase.
C. It binds to the promoter region of DNA and prevents transcription.
D. It phosphorylates signal-transduction proteins.
[11.2] Mutations in the tumor suppressor gene
BRCA1
are transmitted in an
autosomal dominant fashion. When a cell is transformed to a tumor
cell in individuals who have inherited one mutant allele of this tumor
suppressor gene, which of the following most likely occurs?
A. A transcription factor is over expressed.
B. Deletion or mutation of the normal gene on the other chromosome.
C. Chromosomal translocation.
D. Gene duplication of the mutant gene.
[11.3] Women who inherit one mutant
BRCA1
gene have a 60 percent chance
of developing breast cancer by the age of 50. The protein produced by
the
BRCA1
gene has been found to be involved in the repair of DNA
double-strand breaks. Which of the following processes is most likely
to be adversely affected by a deficiency in the
BRCA1
protein?
A. Removal of thymine dimers
B. Removal of RNA primers
C. Removal of carcinogen adducts
D. Homologous recombination
E. Correction of mismatch errors
A nsw ers
[11.1]
A. The
RB1
protein binds to E2F transcription factors, preventing
them from activating transcription of the genes encoding enzymes
required for DNA replication, such as DNA polymerase. The RB1-E2F
complex acts as a transcription repressor. Midway through G1 phase,
RB1
is phosphorylated by cyclin-dependent kinases, releasing E2F to
activate transcription. A deficiency of
RB1
leads to unregulated tran-
scription of DNA replicatory enzymes and DNA synthesis.
previous page 122 Case Files   Biochemistry read online next page 124 Case Files   Biochemistry read online Home Toggle text on/off