Nucleic acids are important information-carrying molecules
Scientists investigated the cell cycle in Arabidopsis thaliana root tips. They measured the percentage of cells undergoing mitosis and DNA replication at different distances from the root cap.
Their results are shown in Table 1.
Table 1
| Distance from root cap / μm\mu\text{m}μm | Percentage of cells undergoing mitosis | Percentage of cells undergoing DNA replication |
|---|---|---|
| 100 | 18.2 | 12.4 |
| 400 | 8.5 | 5.2 |
| 800 | 1.2 | 0.4 |
| 1500 | 0.0 | 0.0 |
Describe and explain the data in Table 1.
The scientists determined the percentage of cells undergoing DNA replication by using a chemical called BrdU. Cells use BrdU instead of nucleotides containing thymine during DNA replication.
Describe how BrdU would be incorporated into new DNA during semi-conservative replication.
Cells with BrdU in their DNA are detected using an anti-BrdU antibody with an enzyme attached.
Use your knowledge of the ELISA test to suggest and explain how the scientists identified the cells that have BrdU in their DNA.
Scientists investigated the cell cycle in neoblasts (stem cells) of planarian flatworms (Dugesia tigrina) undergoing regeneration after amputation. Neoblast activity was measured at 6, 24, 48, and 72 hours post-amputation.
Their results are shown in Table 1.
Table 1
| Time post-amputation / hours | Percentage of neoblasts undergoing mitosis | Percentage of neoblasts undergoing DNA replication |
|---|---|---|
| 666 | 0.40.40.4 | 2.12.12.1 |
| 242424 | 5.25.25.2 | 18.618.618.6 |
| 484848 | 12.812.812.8 | 6.46.46.4 |
| 727272 | 1.91.91.9 | 1.11.11.1 |
Describe and explain the data in Table 1.
The scientists determined the percentage of neoblasts undergoing DNA replication by using a thymine analogue called BrdU (5-bromo-2'-deoxyuridine). Cells use BrdU instead of nucleotides containing thymine during DNA replication.
Describe how BrdU would be incorporated into new DNA during semi-conservative replication.
Cells with BrdU in their DNA are detected using an anti-BrdU antibody with an enzyme attached.
Use your knowledge of the ELISA test to suggest and explain how the scientists identified the cells that have BrdU in their DNA.
Describe the role of DNA helicase in the semi-conservative replication of DNA.
Figure 5 shows the percentage of human cells undergoing DNA replication. Some cells contained a protein called Cyclin E and some cells did not contain Cyclin E. All cells were in early interphase at time 0.
It took less time for 30% of cells with Cyclin E to be undergoing DNA replication than for 30% of cells without Cyclin E. Use Figure 5 to calculate this time difference as a percentage decrease. Show your working.
Cyclin E stimulates the phosphorylation of key replication proteins, which activates them. Describe how a protein can be phosphorylated.
Some tumour cells contain higher than normal concentrations of Cyclin E. Use Figure 5 to suggest why higher than normal concentrations of Cyclin E could result in a tumour.
Scientists investigated the cell cycle in liver cells taken from rats 5 days before their birth and then at 3, 10, and 20 days after their birth.
Their results are shown in Table 1. Age 0 days = day of birth.
Table 1
| Age / days | Percentage of liver cells undergoing mitosis | Percentage of liver cells undergoing DNA replication |
|---|---|---|
| −5-5−5 | 16.416.416.4 | 10.210.210.2 |
| 333 | 9.89.89.8 | 4.14.14.1 |
| 101010 | 2.52.52.5 | 0.50.50.5 |
| 202020 | 0.40.40.4 | 0.00.00.0 |
Describe and explain the data in Table 1.
The scientists determined the percentage of liver cells undergoing DNA replication by using a chemical called IdU. Cells use IdU instead of nucleotides containing thymine during DNA replication.
Describe how IdU would be incorporated into new DNA during semi-conservative replication.
Cells with IdU in their DNA are detected using an anti-IdU antibody with an enzyme attached.
Use your knowledge of the ELISA test to suggest and explain how the scientists identified the cells that have IdU in their DNA.
Describe the structure of a ribonucleic acid (RNA) molecule and describe three ways in which its molecular structure differs from that of a deoxyribonucleic acid (DNA) molecule.
The gene coding for the DNA polymerase enzyme in a newly isolated marine bacteriophage is 8.568 kilobases8.568\text{ kilobases}8.568 kilobases in length. In this bacteriophage, the DNA double helix makes one complete helical turn every 10.2 base pairs10.2\text{ base pairs}10.2 base pairs. Every complete helical turn is 3.4 nm3.4\text{ nm}3.4 nm in length.
Use this information to calculate the length in micrometres (μm\mu\text{m}μm) of this DNA polymerase-coding gene. Give your answer to 3 significant figures.
State the names of two enzymes directly involved in synthesizing or joining DNA strands during DNA replication and repair.
In response to cellular stress, an enzyme called PKA phosphorylates a transcription factor called CREB. This phosphorylation allows CREB to bind to specific promoter sequences on DNA and initiate gene transcription.
Use your knowledge of protein structure to explain how the phosphorylation of CREB allows it to bind to DNA.
The synthesis of a new DNA strand requires nucleoside triphosphates (such as dATP) rather than nucleoside monophosphates.
Explain, in terms of energy changes, why nucleoside triphosphates are required for this polymerisation reaction.
Double-strand DNA breaks are normally detected by a sensor protein called ATM. Upon activation, ATM phosphorylates p53, which upregulates the inhibitor p21 to arrest the cell cycle at the G1/S G_1/S\,G1/S checkpoint, allowing time for DNA repair. A mutation could result in a person having a non-functional form of the ATM gene.
Predict the biological consequences of having a homozygous mutation that produces a completely non-functional ATM protein.
The diagram shows a short section of a single-stranded nucleic acid polymer.
Using your knowledge of nucleic acid structure:
Describe how the nucleotides in this polymer are joined together to form the backbone of the molecule.
Describe three ways in which the molecular structure of a ribonucleic acid (RNA) molecule differs from that of a deoxyribonucleic acid (DNA) molecule.
Name two enzymes directly involved in synthesizing and joining DNA segments on the lagging strand during semi-conservative DNA replication.
When DNA double-strand breaks occur, an enzyme called ATM kinase phosphorylates a histone protein variant called H2AX. This phosphorylation enables H2AX to bind to a mediator protein called MDC1, which recruits DNA repair machinery.
Use your knowledge of protein structure to suggest how the phosphorylation of H2AX enables it to bind to MDC1.
The synthesis of a new DNA strand requires nucleotides to be in their activated triphosphate form (such as dGTP) rather than their monophosphate form (dGMP).
Use your knowledge of energy changes in chemical reactions to suggest why nucleotides must be in the triphosphate form.
Single-stranded DNA damage during replication is recognized by a ring-shaped protein complex called the 9-1-1 complex (comprising Rad9, Rad1, and Hus1). When bound to damaged DNA, the 9-1-1 complex recruits the ATR kinase, which halts the cell cycle at the S-phase checkpoint to allow time for DNA repair before replication continues. A mutation can result in a person producing a non-functional version of the Rad9 protein.
Predict the potential consequences of having a non-functional Rad9 protein on both the cellular level and the whole organism.
Describe the role of DNA helicase in the semi-conservative replication of DNA.
Figure 5 shows the percentage of eukaryotic cells in S-phase (undergoing DNA replication) over time. Some cells contained a high concentration of active CDK2 protein, and some cells contained a low concentration of active CDK2 protein. All cells were synchronised at the start of interphase at time 0.
It took less time for 50% of cells with a high CDK2 concentration to be in S-phase than for 50% of cells with a low CDK2 concentration.
Use Figure 5 to calculate this time difference as a percentage decrease. Show your working.
CDK2 is a kinase that activates replication proteins by phosphorylating them.
Describe how a protein can be phosphorylated.
Overexpression of CDK2 is frequently observed in human lung cancers.
Use Figure 5 to suggest why a higher than normal concentration of active CDK2 could result in a tumour.
Nucleic acids are important information-carrying molecules Questions
Practise AQA A Level Biology Nucleic acids are important information-carrying molecules with exam-style questions for A Level Biology. 14 questions covering Structure of DNA and RNA and DNA replication, matched to the AQA A Level Biology (7402) specification and written in Paper 1, Paper 2 and Paper 3 style. Every question includes a full worked solution and mark scheme, so you can see where marks are awarded rather than just whether you got the answer right.