AIDS is caused by a virus whose genetic material is
- A.single stranded circular DNA
- B.double stranded DNA
- C.single stranded RNA
- D.double stranded RNA
Correct answer
Explanation
The correct answer is C, single stranded RNA. AIDS is caused by HIV, a retrovirus whose genome is two copies of single-stranded RNA.
After HIV enters a helper T-cell (CD4 cell), its enzyme reverse transcriptase copies the viral RNA into DNA, which is then built into the host cell's own DNA. The infected cell makes new viruses and is destroyed, so the T-cell count falls and the immune system weakens; this late stage is AIDS (Acquired Immuno Deficiency Syndrome). Reverse transcription, RNA to DNA, is why HIV is called a retrovirus, and the ELISA test is used to detect infection.
A is wrong because single-stranded circular DNA is found in small viruses such as the plant geminiviruses.
B is wrong because double-stranded DNA is the genome of viruses such as herpes and smallpox.
D is wrong because double-stranded RNA is found in viruses such as the rotavirus.
Exam tip: HIV = retrovirus, ssRNA, reverse transcriptase, attacks helper T-cells; detected by ELISA.
Practice Questions
View allWhich one of the following cell organelles contains DNA?
- A.Golgi apparatus
- B.Mitochondrion
- C.Lysosome
- D.Endoplasmic reticulum
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Mitochondria carry their own small, circular DNA and their own ribosomes. Mitochondria are the powerhouses of the cell, where aerobic respiration makes ATP.
Read the full explanation →Which set of vegetables is underground stem or modified stem of a plant?
- A.Potato, artichoke, round gourd
- B.Onion, garlic, carrot
- C.Potato, onion, garlic
- D.Potato, garlic, turnip
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All three are underground modified stems: the potato is a stem tuber, and onion and garlic are bulbs. A stem can be told from a root by its nodes and buds.
Read the full explanation →A sound wave having frequency of 300 Hz is travelling in an unknown medium. Its wavelength is not known. It travels a distance equal to 150 times its wavelength in time t. The value of t is :
- A.0.5 s
- B.1 s
- C.1.5 s
- D.2 s
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A wave moves forward by one wavelength in each cycle, so 150 wavelengths take 150 cycles, and 150 cycles at 300 per second take half a second.
Read the full explanation →A body floats in a liquid if the buoyant force is :
- A.equal to its weight.
- B.less than its weight.
- C.greater than its weight.
- D.zero.
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A floating body is in equilibrium, so the upward buoyant force exactly balances its weight. By Archimedes' principle, a body in a liquid is pushed up by a force equal to the weight of the liquid it displaces.
Read the full explanation →Which of the following are the different parts of a human brain ?
- A.Forefront brain, Standard brain and Hind brain
- B.Fore brain, Median brain and Rear brain
- C.Fore brain, Mid brain and Hind brain
- D.Precursor brain, Mean brain and Hind brain
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These are the three main divisions of the human brain. The fore brain is the largest part.
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