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2.1 Structure of RNA and DNA ASA AQ Biology B2 Nucleic Acids Kerboodle Answers
Q1.Ans Nucleotide is made up of three components:
- Sugar: A pentose sugar.
- Phosphate group
- A nitrogen-containing organic base. Adenine (A), Cytosine (C), Thymine (T), Uracil (U), and Guanine (G).
Q 2 Ans Base pairing occurs between complementary bases. Adenine is complementary to thymine and guanine is to cytosine. This is why base pairing cannot occur between adenine & cytosine and guanine & thymine. Other reason could be that The bases are linked by hydrogen bonds. The molecular structures could be such that hydrogen bonds do no form between adenine and cytosine and between guanine and thymine.
Q 3 Ans Base sequence on other strand will be ACCTCTGA.
Q 4 Ans If 19.9% is guanine then, as guanine always pairs with cytosine, it also makes up 19.9% of the bases in the DNA. So together they make up 39.8%. This means the remaining 60.2% of DNA must be adenine and thymine in equal amounts. So half of this 30.1%. That means adenine is 30.1% in human DNA.
Unravelling the role of DNA:
Q 1 Ans It is important to validate the current theory rather than automatically accepting it. Because sometimes, the theories are not true.
Q 2 Ans A hypothesis is an idea or proposition that can be tested by observations or experiments, about the natural world. In order to be considered scientific, hypotheses are subject to scientific evaluation and must be falsifiable, which means that they are worded in such a way that they can be proven to be incorrect.
Q 3 Ans To discount the first explanation one can minimize experimental errors by carefully performing experiments.
Q 4 Ans Mutations happen very rarely so changes caused due to mutation were also rare and their repeatability is not there. With the help of this fact second explanation can discounted.
Q 5 Ans it is necessary for society to analyse the risks and benefits of these discoveries before they are developed. Because new discoveries will be released and will have greater impact on surrounding.
A prime location:
Q 1 Ans: In vivo means inside the cell.
Q 2 Ans DNA polymerases can only add nucleotides to the 3′ end of an existing DNA strand. They use the free -OH group found at the 3′ end as a “hook,” adding a nucleotide to this group in the polymerization reaction.
2.2 DNA replication: ASA AQ Biology B2 Nucleic Acids Kerboodle Answers
Q 1 Ans TCAGATGC
Q 2 Ans The process of DNA replication is described as semi-conservative because newly formed DNA has one strand of original DNA and one strand is newly synthesised.
Q 3 Ans Function of DNA polymerase is to join the complementary nucleotides on the new strand. If inhibitor of DNA polymerase is added it will affect the joining of nucleotide on the synthesising strand of DNA.
Evidence for semi-conservative replication:
Q 1 Ans Organic bases such as Adenine, cytosine, thymine or guanine.
Q 2 Ans due to the semi-conservative replication of DNA, after one generation all the DNA is made up of one parent strand and one new strand. Parent DNA has
15N where as new strand has
14N.
Q 3 Ans-
Q 4 Ans
Q 5 Ans 75% of DNA will be made up of
14N only after three generations.
2.3 Energy and ATP: ASA AQ Biology B2 Nucleic Acids Kerboodle Answers
Q 1 Ans Phosphate groups are the key to how ATP stores energy. These bonds between phosphate groups have low activation energy and are unstable thus can be broken easily. When these bonds break considerable amount of energy is released. This energy can be further used in many other reactions.
Q 2 Ans During the conversion of ATP to ADP inorganic phosphate is released which can be used in phosphoryation other compounds in order to make them reactive. By this way activation energy in enzyme-catalysed reactions is lowered.
Q 3 Ans Three roles of ATP in plant cells are as following:
- Metabolic process: ATP provides the energy required to build up macromolecules from their basic units. For example, making starch from glucose or polypeptides from amino acids.
- Active transport: During the active transport, energy is required to change the shape of carrier proteins in plasma membranes. Required energy is provided by ATP.
- Activation of molecules: During the conversion of ATP to ADP inorganic phosphate is released which can be used in phosphoryation other compounds in order to make them reactive. By this way activation energy in enzyme-catalysed reactions is lowered. For example: addition of phosphate to glucose molecule at the start of glycolysis.
2.4 Water and its functions ASA AQ Biology B2 Nucleic Acids Kerboodle Answers
1.Ans a=Polar; b=charge; c=hydrogen bonds; d=surface tension; e=hydrolysis; f=photosyntheis
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Practice questions:
Q 1 (a)(i) Ans F is pentose sugar which forms a part of nucleotide.
(iiAns 18% adenine that means thymine percentage is also 18% in the DNA. Both adenine and thymine constitute 36% of DNA that means remaining 64% will be of guanine and cytosine. So half of 64% will be 32%. 32% part of DNA is made up of guanine.
(b) (i)Ans 9000 base pairs are there in human. For every 1000 base pairs DNA is 2 µm long. 20,000 per 1,000 base pairs. 20,000 x 9 = 180,000m. That means 180,000 m long is human DNA.
(ii) Ans The ration is lower in case of E.coli because it is smaller and contains fewer genes and no introns. So numbers of base pairs are less as compared to human,
Q 2 (a) Ans R= pentose sugar
Q= Phosphate
(b) Ans Hydrogen bond
(c) Ans Including the START and STOP codon total number of DNA base will be 127*3=381+3+3= 387.
(d) Ans
| Gln |
Met |
Met |
Arg |
Arg |
Arg |
Asn |
(e) Ans e. DNA base sequence guided the amino acids sequence on the polypeptide chain. Change in DNA base sequence will directly affect the amino acid sequence. Amino acid sequence in protein that could be an enzyme, will determine its structure and function. Any abnormality in amino acid sequence due to DNA base sequence change will result in abnormal, non-functional enzyme.
Q 3 (a) Ans Due to hydrogen bonding in between it is not easily compressed thus provides support such as in case of hydrostatic skeleton of animals such as the earthworm and turgor pressure in herbaceous plants. It is transparent and therefore aquatic plants and animals can live easily in water bodies. Light which is required for photosynthesis can easily reach to them.
(b) Ans Two inorganic ions within human body and their function:
- pH of any solution is determined by hydrogen ions and this will affect functioning of enzymes.
- Sodium ions are also important. They play major role during transport of glucose and amino acids across plasma membranes.
(c) Ans ATP is a nucleotide and has three phosphate groups.
- Phosphate groups are the key to how ATP stores energy.
- These bonds between phosphate groups have low activation energy and are unstable thus can be broken easily.
- When these bonds break considerable amount of energy is released. This energy can be further used in many other reactions.
ATP + H
2O à ADP + P
i + E
Adenosine triphosphate water Adenosine diphosphate inorganic phosphate Energy
For this reaction ATP hydrolase enzyme is required. Because water is used in this reaction it is known as hydrolysis.
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References:
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AQA GCSE Science Kerboodle textbook
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