Ib Bio Topic 7 Nucleic Acids

What is the composition of the backbone of DNA?

• Alternating sugar and phosphate molecules

• Complementary base pairs

• Alternating sugar and base molecules

• A polysaccharide

What is a difference between the sense and antisense strands of DNA?

• Nucleotides are linked to the sense strand by hydrogen bonding during transcription, but not to the antisense strand.

• The sense strand has the same base sequence as tRNA, but the antisense strand does not.

• Nucleotides are linked to the antisense strand by hydrogen bonding during transcription, but not to the sense strand.

• The antisense strand has the same base sequence as mRNA but the sense strand does not.

The diagram below represents a DNA nucleotide.

What could the part labelled X represent?

• Adenosine

• Deoxryribose

• Phosphate

• Guanine

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NGSS.HS-LS1-1

In the structure of DNA which one of the following binds with cytosine?

• Deoxyribose

• Thymine

• Ribose

• Adenine

What are the components of a DNA nucleotide?

• Deoxyribose, a phosphate and one of the bases: adenine, cytosine, guanine or thymine

• Ribose, a phosphate and one of the bases: adenine, cytosine, guanine or uracil

• Deoxyribose, a nitrate and one of the bases: adenine, cytosine, guanine or thymine

• Ribose, a nitrate and one of the bases: adenine, cytosine, guanine or thymine

The percentage of thymine in the DNA of an organism is approximately 30%.

What is the percentage of guanine?

• 70%

• 30%

• 40%

• 20%

Which molecule is found in both DNA and RNA?

• Ribose

• Uracil

• Amino acid

• Phosphate

Which molecules form the nucleotide marked in the diagram?

• phosphate, deoxyribose and nitrogenous base

• phosphorus, ribose and nitrogenous base

• phosphorus, deoxyribose and guanosine

• phosphate, ribose and guanine

The graph below shows the effect of temperature on the separation of the strands in DNA to form single strands. The temperature at which 50% of the DNA is single-stranded is called the melting temperature (TM).

What do the results show?

• When the temperature reaches 85°C there are no more double-stranded DNA molecules.

• When the temperature reaches 85°C the DNA strands start separating rapidly.

• A TM of 85°C means that DNA is not stable at room temperature (25°C).

• The separation of the DNA strands is directly proportional to the increase in temperature.

The base ratios in the DNA and RNA for an onion (Allium cepa) are shown in the tables.

What is the reason for the difference between these figures?

• DNA is only found in the nucleus but RNA is found throughout the cell.

• DNA is made entirely of double helix but RNA is not.

• In DNA, bases A and T are complementary but in RNA, bases A and C are complementary.

• RNA comes in three forms but DNA only comes in one form.

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