In a cell with a diploid number of 28, how many chromatids are present at prophase of mitosis?
A. 14
B. 28
C. 56
D. 112
Answer: Your understanding of ploidy and the stages of the cell cycle is tested by this question. There are
two main keys to answering this question. The first is that ploidy describes the number of sets of
chromosomes in a cell. Haploid cells have one set of chromosomes and diploid cells have two
sets of chromosomes. Another way to describe this is that the chromosomes in diploid cells are
present in homologous pairs. The second key is understanding that chromosomes are replicated
during S phase because both daugher cells produced by mitosis must have identical genomes.
A cell with a diploid number of 28 has two sets of 14 chromosomes. This falsifies choice A
because 14 is the haploid number of the cell. Chromatids are identical copies of replicated
chromosomes. All mitotic phases occur after DNA has been replicated during S phase. A cell
that has 28 chromosomes when it enters S phase, will have 56 sister chromatids after replication
during S phase. Sister chromatids will remain together throughout G2 and mitosis, until daughter
cells are formed by cytokinesis. This falsifies choice B and supports choice C. A cell with 112
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chromatids would have a diploid number of 56. This falsifies choice D and confirms choice C as
the best answer
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The 3' end of DNA
A. refers to the end that has a hydroxyl group attached to the number 3 carbon of deoxyribose. B. attaches to the 5' phosphate group of the incoming nucleotide. C. always has thymine attached to it. D. usually has guanine attached to it. E. refers to the end that has a hydroxyl group attached to the number 3 carbon of deoxyribose AND attaches to the 5' phosphate group of the incoming nucleotide.
Answer the following statements true (T) or false (F)
1. Catabolic and anabolic reactions in living cells involve the transfer of electrons from one molecule to another in reduction-oxidation reactions. 2. Metabolism refers to only those reactions that release energy. 3. The half-life of a molecule is the time it takes for 50% of the molecule to be broken down and recycled. 4. Autophagy is an important process that removes worn-out organelles, recycles components, then releases them into the cytosol.
A plasmid is a
a. small segment of DNA that is often isolated from virus chromosomes for cloning purposes. b. large linear segment of DNA that is often isolated from bacterial chromosomes for cloning purposes. c. small circular segment of DNA in bacteria that is linked by hydrogen bonds to the main bacterial chromosome. d. large circular segment of DNA in bacteria that is completely separated with the chromosome. e. small circular segment of DNA in bacteria that is completely separated from the chromosome.
A method used to link genetic markers with specific genes on chromosomes is called ____________________. Fill in the blank(s) with the appropriate word(s)