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Q-bank Biochemistry II


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*ol 2067


*ol 2065


*OL 1095





*0.19, 0.14

*OL 2062

*Abnormal parent-specific methylation pattern

*Rest of explanation:

--Choice D:
Microsatellite instability is characteristic of individuals with loss-of-function mutations in the mismatch repair genes (hMLH, hMSH). Areas of DNA with dinucleotide repeats (an example of microsatellites) are often associated with strrand slippage during DNA replication that can change the number of repeats on the newly synthesized strand (microsatellite instability). This replication error is normally corrected by the mismatch repair enzymes. Loss of mismatch repair is associated with a form of colon cancer (HNPCC), endometrial cancer, and microsatellite instability in the tumor cells.

--Choice E:
T-cell immunodeficiency is characteristic of DiGeorge anomaly, often associated with a deletion at 22q.11.2. The anomaly is characterized by structural/functional defects of the thymus, hypoparathyroidism, and secondary hypocalcemia. DiGeorge anomaly is associated, in some cases, with palate abnormalities and a characteristic facial appearance.


*Introducing negative supercoils into DNA to stabilize an underwound DNA helix.



*ol 1513


*ol 1093

*Three bands of 222, 126, and 96 bp

*ol 320

*nonsense mutation



*OL 1664


*OL 331



Northern blotting, the RNA counterpart to Southern blotting, will determine the size and abundance of mRNA of a specific gene in a given sample of RNA. RNA is NOT able to be cleaved by restriction enzymes the way the DNA can; however, RNA molecules for different proteins are of different lengths. The sample is separated by agarose gel electrophoresis, transferred to a nitrocellulose membrane, and probed with a specific, labeled probe. This will be expsoed to film and the bands will appear, revealing the size and the abundance of specific mRNAs.

Western blotting is the protein counterpart of Southern and Northern blotting. Proteins are isolated from the cell type of interest and separated by size on a polyacrylamide gel, then transferred to a nitrocellulose membrane. The filter is then incubated with antibodies that specifically react with the protein of interest, then it is incubated with a labeled antibody (e.g., radioactive) that reacts with the first antibody. After this has been washed off, the membrane is espoxed to film and bands characteristic of the protein being studied will appear. This is useful to determine whether a protein is present or absent in a patient or if it is the wrong size, indicating an error in the DNA for this protein.

*ol 1064

*A two base pair addition resulted in the elimination of a stop codon in the beta-chain.


A point mutation is the result of a single base pair change, which is NOT the case here. A point mutation resulting in the insertion of a new stop codon is called a nonsense mutation, and it would result in a shorter-than-normal protein.

A two base pair deletion is NOT evidence by the coding sequence given in the stem. It would also cause a frameshift in the reading frame, with the possible result of a longer or shorter protein, most likely with abnormal function due to the change in primary structure (amino acid sequence.).

Since the hemoglobin Cranston beta-chain is clearly longer than thenormal beta-chain, choices A, C, and E, which would produce a shorter chain, can be eliminated immediately.

*ol 1860


*OL 1667


*OL 2120



--G0 is the differentiated phase; it lies outside the cycle, and as long as cells remain in the G0 phase, they cannot divide. With respect to the G0 phase, there are three general types of mammalian cells: permanent, stabile, and labile. Permanent cells such as neurons, skeletal, and cardiac muscle cells and erthrocytes differentiate, and then cease dividing; these cells remain in the G0 phase until they die; their replacement is by stem cell division and maturation. Stable cells such as hepatocytes and lymphocytes will stay in the G0 phase until stimulated to leave; they then reenter the cycle at G1 and start dividing. Labile cells do not enter the G0 phase and divide at relatively constant rates. Labile cels include the hematopoietic stem cells (bone marrow), the epithelial cells that line the gut and body surface, hair folicles, and most neoplastic cells. It is these labile cells that are most susceptible to antimetabolites.

W is the mitotic phase because it precedes the G1 phase. This represents the time interval during which the cell divides to form two daughter cells. Since this is the phase in which cell division occurs, all the other phases in the cycle are part of the interphase.

X, as noted from its relation to the G0 phase, is the G1 phase. This is the time period during which the cell prepares for entry into the S phase. Specific members of a group of proteins called cyclins control entry into the S phase. One such protein, cyclin D, working in conjunction with other regulatory factors, is a serine protein kinase that phosphorylates the retinoblastoma (Rb) protein. Mutations in the Rb protein cause retinoblastoma, the most prevalent childhood cancer of the eye.

Z represents the G2 phase that follows the S phase. During this time period, the cell prepares for mitosis. Cyclin B controls entry into the M phase.

*ol 1658

*Genetic test for a trinucleotide repeat expansion.

*ol 1666




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