The enzyme that is responsible for replicating molecules of DNA by attaching complementary bases in the correct sequence is called ____________________ ____________________. 27. Enzymes called ____________________ are responsible for unwinding the DNA double helix by breaking the hydrogen bonds that hold the complementary strands together. 28. Errors in nucleotide sequences are called ____________________.
Controlling the Code: molecules at work The lac operon 2. (a) Write a description of the role of the operator in B-gal production. • What is the operator? The operator is a segment of DNA located between the promoter and the enzyme genes. It acts as a switch by determining whether RNA polymerase can attach to the promoter and start transcribing.
a. A small ribosomal subunit binds to mRNA with the codon AUG. A tRNA with the anticodon UAC binds to the AUG codon. b. A second tRNA docks at the ribosome and peptide bonds form between the amino acids. c. The ribosome moves on down the mRNA, making room for the next incoming tRNA and amino acid.
Marshall Nirenberg and Heinrich Matthaei used mRNA made up of repeating uracil nucleotides in a cell free extract. They obtained amino acid chains consisting of phenylalanine. What did they learn when they asked the question, ”What happens when mRNA made up of only cytosine, alanine, and guanine are placed in a cell free extract?” 10. Explain how the structure of tRNA helps it to deliver the correct amino acid to the corresponding mRNA codon at the ribosome. Sketch the structure of a tRNA molecule, making sure to label the amino acid and the
7. The figure to the right shows that injection of M-phase cytoplasm into an oocyte triggers the cell to enter mitosis. What would be the expected effect on cell division if cytoplasm from a G2-phase cell were injected into an M-phase cell? A. DNA replication would begin again. B. activation of all cyclin-CDK complex in the cell.
The smaller plasmids make use of the host cell’s own DNA replicative enzymes in order to make copies of themselves, whereas some of the larger ones carry genes that code for special enzymes that are specific for plasmid replication. Size and copy number of plasmid is an important feature of plasmids for cloning purpose e.g. plasmid ranging from 6-10 Kb is very suitable for cloning and having copy number as many as 50. Plasmid may be of following type: • F-Plasmid: having ability to promote conjugal transfer of plasmid e.g. F-Plasmid of E.coli • R-Plasmid: responsible for providing resistance to host against foreign bodies such as anti bacterial resistance e.g.
[pic] For each of the cells labelled B and C, identify the type of cell division, which has occurred to produce the cell. In each case give a reason for your answer. (2) 4. Read through the following passage on the cell cycle and mitosis, then write on the dotted lines the most appropriate word or words to complete the passage. (6) In the cell cycle, replication of DNA takes place during .......................a.............................. At the beginning of prophase the chromosomes become visible and can be seen to consist of two ..................b...........................joined at the ......................c...............................