6.1. Structure of nucleic acids and replication of DNA
A subsection of Biology, 9700, through 6. Nucleic acids and protein synthesis
Listing 10 of 244 questions
Two sets of bacteria were grown using different types of nitrogen-containing growth media. One set was grown in a medium containing the ‘heavy’ isotope of nitrogen, 15N, until all the DNA was labelled. The other set was grown in a medium containing the ‘light’ isotope of nitrogen, 14N, until all the DNA was labelled. The DNA from each set of bacteria was extracted and centrifuged. The diagram shows the position in the centrifuge tubes of this DNA. DNA with 14N DNA with 15N Bacteria with 15N labelled DNA were transferred to a medium containing 14N and allowed to reproduce once. The DNA of the new generation of bacteria was extracted and centrifuged. Which tube shows the position of DNA from this new generation of bacteria?
9700_w17_qp_12
MCQ
2017
Paper 1, Variant 2
View
Meselson and Stahl investigated DNA in bacteria. They grew bacteria in a medium with only heavy nitrogen, 15N, until all of the bacterial DNA was heavy. These bacteria were moved from a heavy nitrogen medium and cultured in a medium with only light nitrogen, 14N. A sample of bacteria was collected from the first generation and their DNA analysed. Hybrid DNA contains heavy DNA and light DNA. Which row shows the percentage of light DNA strands and the percentage of hybrid DNA molecules in the first generation produced in the medium containing light nitrogen?
9700_w19_qp_13
MCQ
2019
Paper 1, Variant 3
View
Outline the role of DNA polymerase in the replication of DNA. Floxuridine is a drug used to treat cancer. Floxuridine inhibits DNA replication. Suggest why the inhibition of DNA replication is an effective treatment for cancer. Floxuridine prevents thymine nucleotides being produced. Explain why floxuridine does not affect transcription. is a scanning electron micrograph of a lung cancer cell in a stage of the cell cycle. Name the stage of the cell cycle occurring in . Explain why smoking tobacco increases the risk of developing lung cancer.
9700_w19_qp_21
THEORY
2019
Paper 2, Variant 1
View
Carbohydrates, proteins and nucleic acids are types of biological molecule. Within each type, there are examples of molecules that can be described as polymers. A polymer is a large molecule composed of smaller repeating molecules known as monomers. Complete Table 4.1 to produce a summary of some named biological polymers. Table 4.1 polymer constituent monomer type of bond between monomers amylose glucose cellulose glucose collagen peptide DNA DNA nucleotide glycogen glycosidic Explain why an amylose molecule and a cellulose molecule have very different structures, even though they both have glucose as the constituent monomer. Polymerisation of DNA nucleotides occurs during the semi-conservative replication of a molecule of DNA during interphase. Describe the semi-conservative replication of DNA.
9700_w19_qp_22
THEORY
2019
Paper 2, Variant 2
View
Human cytomegalovirus (HCMis a common virus affecting humans. In people with a fully functioning immune system, infection by HCMV usually causes no, or only mild, symptoms. A is a diagram of a section through HCMV. In B, only the outer part of HCMV is sectioned. glycoprotein double-stranded DNA tegument proteins S A B T The viral DNA shown in contains genes that code for proteins important in viral replication and viral structure, including viral DNA polymerase and proteins known as tegument proteins. Viruses can only replicate in host cells as they need to use processes and contents of the host cell. Complete viral particles that are released from the host cell are known as virions. Structure S in A is a subunit of structure T in B. Name the chemical compound used to make structure S and name structure T. S T The actual diameter of the HCMV shown in is 0.17 micrometres (µm). Calculate the actual diameter of the virus in nanometres . Suggest the role of viral DNA polymerase within the host cell. The virus in is drawn as a spherical shape. Structure T is always the same shape. However, electron micrographs show that HCMV virions are not all the same shape. Suggest how HCMV virions can be of different shapes. With reference to A, state one similarity and one difference between the genetic material of HCMV and the genetic material of a typical bacterial cell. HCMV is known to infect some types of human cell that carry out the mitotic cell cycle. Studies have shown that in the presence of one tegument protein, UL69, the cell cycle stops in the G1 stage. Outline the effects the presence of UL69 will have on the normal activity of the mitotic cell cycle. After a person has been infected with HCMV, the virus remains in a dormant state in the body for life. If the virus becomes active again , the virus will only cause serious illness if the person has a weak immune system at that time. Explain why the response to reactivation of HCMV is more likely to cause serious illness in a person who has a weak immune system.
9700_w22_qp_22
THEORY
2022
Paper 2, Variant 2
View
Meselson and Stahl investigated DNA in bacteria. They grew bacteria in a medium with only heavy nitrogen, 15N, until all of the bacterial DNA contained only heavy nitrogen. These bacteria were then moved from the heavy nitrogen medium and cultured in a medium with only light nitrogen, 14N. Some bacteria were collected from each of the next three generations and their DNA was analysed. Hybrid DNA contains both heavy and light nitrogen. Which row shows the correct DNA of the first and third generations?
9700_m17_qp_12
MCQ
2017
Paper 1, Variant 2
View
The gene for the enzyme catalase is on chromosome 11 in humans. Explain the meaning of the term gene. Two enzymes, DNA polymerase and DNA ligase, are involved in the replication of DNA. shows the replication of part of human chromosome 11 by DNA polymerase. The arrows show the direction of synthesis of the new polynucleotides by DNA polymerase. G G C A G A T T T G C C T G C T G A G G A A A C G G A C G A C T C C C C G T G A T T T G C C T G C T G A C T A A A C G G A C G A C C C T A A C A T T G T 5' 5' 3' 3' A T T A A G A C C C T G C C DNA polymerase DNA polymerase Describe the roles of DNA polymerase and DNA ligase in the replication of DNA. State the name of the stage of interphase in the cell cycle when DNA replication occurs. is a diagram of chromosome 11 at metaphase of mitosis. A B State the names and functions of structures A and B. structure A function structure B function Complete to show what happens to chromosome 11 in anaphase, so that the daughter nuclei are genetically identical. cell surface membrane
9700_s23_qp_21
THEORY
2023
Paper 2, Variant 1
View
Questions Discovered
244