Nucleic Acids

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शिक्षकों के लिए: Nucleic Acids (Biology, HL) के लिए इस्तेमाल के लिए तैयार लेसन स्लाइड्स, रिवीज़न नोट्स — इन्हें अपने लेसन में इस्तेमाल करें, या टॉपिक को एक इंटरैक्टिव क्लास एक्टिविटी की तरह चलाएं जिसे आपके शिक्षार्थी लाइव गेम की तरह खेलें।

लेसन नोट्स

DNA and RNA as Genetic Material

DNA (deoxyribonucleic acid) carries the genetic code in all living organisms, making the genetic code universal.
DNA is mainly found in the nucleus where it forms chromosomes, and is also found in chloroplasts and mitochondria of eukaryotic cells.
RNA (ribonucleic acid) is the main component of ribosomes and plays an important role in protein synthesis; some RNA is also found in the nucleus and cytoplasm.
Certain viruses (such as SARS-CoV-2) contain RNA as their genetic material instead of DNA, causing diseases such as COVID-19, Ebola, mumps and influenza.
Viruses are not considered living because they cannot replicate by themselves, depend on other living cells, and lack a cellular structure.

From cell to gene

Nucleotide Components

Both DNA and RNA are polymers made of repeating units called nucleotides.
Each nucleotide is formed from a pentose sugar (5 carbon atoms), a nitrogen-containing organic base (1 or 2 rings), and a phosphate group (acidic and negatively charged).
The base and phosphate group are both covalently bonded to the sugar.
The nitrogenous bases in DNA are adenine (A), guanine (G), cytosine (C) and thymine (T); RNA shares the same bases except thymine is replaced by uracil (U).
Adenine and guanine are purine bases; cytosine, thymine and uracil are pyrimidine bases.

The sugar-phosphate backbone

Drawing Nucleotides and Polynucleotides

Simple shapes can represent nucleotide components: pentagons for pentose sugars, circles for phosphates (often with P inside), and rectangles for bases.
Covalent bonds can be shown with solid lines; hydrogen bonds with dashed lines or complementary shapes that fit together.
Nucleotides join in chains when the phosphate group of one nucleotide forms a covalent bond to the pentose sugar of the next, forming a large polymer.
These polymers are called nucleic acids or polynucleotides; the linkage forms a sugar-phosphate backbone with a base linked to each sugar.
The polymer of nucleotides is known as a strand; DNA is double-stranded, RNA is usually single-stranded.
There are just 4 separate bases that can be joined in any combination/sequence because the sugar and phosphate are the same in every nucleotide.

RNA Structure

RNA molecules are relatively short (a hundred to a few thousand nucleotides) and usually form a single-stranded polynucleotide with ribose as the pentose sugar.
RNA nucleotides contain adenine, guanine, cytosine and uracil (instead of thymine).
The carbon atoms in nucleotides are numbered from the right in a clockwise direction, indicating the orientation of the polynucleotide.
Different types of RNA: mRNA (formed in the nucleus, transported to ribosomes), tRNA (transports amino acids to ribosomes), and rRNA (forms part of ribosomes).
Adjacent RNA nucleotides are linked by condensation reactions, releasing a molecule of water and forming a phosphodiester bond between the pentose sugar of one nucleotide and the phosphate group of the next.

DNA Structure and Complementary Base Pairing

DNA is a double helix made of two antiparallel strands of nucleotides linked by hydrogen bonding between complementary base pairs.
Each DNA polynucleotide strand has alternating deoxyribose sugars and phosphate groups forming the sugar-phosphate backbone, with a 3' end and a 5' end.
Because the strands run in opposite directions, one is the 5' to 3' strand and the other is the 3' to 5' strand.
The nitrogenous bases project out from the backbone towards the interior of the double-stranded DNA molecule.
Adenine (A) always pairs with thymine (T) via two hydrogen bonds; guanine (G) always pairs with cytosine (C) via three hydrogen bonds — this is complementary base pairing.
The base pairings A–T and C–G are equal in length, so the DNA helix has the same 3D structure regardless of base sequence; purines are larger than pyrimidines due to their two carbon ringed structure.

The DNA double helix

Basis of the Genetic Code

DNA molecules carry the genetic code as a sequence of nitrogenous bases (A, G, C, T) in the nucleotides.
One strand carries the base sequence read by enzymes — the coding strand; the sequence of bases forming genes determines the order of amino acids in synthesised proteins.
The code is read as a triplet of bases called a codon, with each sequence of three bases coding for one amino acid; there are 20 different amino acids.
The sequence of amino acids determines the shape and function of the protein synthesised from the code.
The genetic code is universal — almost every organism uses the same code (with rare minor exceptions), so the same triplet codes code for the same amino acids in all living things.
The universal nature of the genetic code is why genetic engineering is possible and provides evidence for a universal common ancestor.
Conserved sequences are coding and non-coding sequences that have remained unchanged in all organisms; highly conserved sequences are usually found in genes for proteins involved in transcription and translation, and in histone proteins.

DNA vs RNA Comparison

Pentose sugar: DNA contains deoxyribose; RNA contains ribose.
Bases: DNA contains A, C, G, T; RNA contains A, C, G, U (uracil instead of thymine).
Number of strands: DNA is double-stranded (double helix); RNA is single-stranded.
RNA polynucleotide chains are relatively short compared to DNA.
Complementary base pairing means the base sequence on one DNA strand determines the sequence of the other — one strand acts as a template of the other.
This allows DNA to be copied very precisely during DNA replication, ensuring the genetic code is accurately copied and expressed in newly formed cells.

DNA as an Information Storage Molecule

Despite only four bases (A, T, C, G), they can combine to form a very diverse range of DNA base sequences in molecules of different lengths.
DNA therefore has an almost limitless capacity for storing genetic information.
Storage capacity can be measured by the number of genes; even the most simplistic forms of life may contain several thousand genes.
Examples of approximate gene numbers: Human 20 000, Dog 19 000, Water flea 31 000, Bacterium (E. coli) 4 300, Rice plant 41 500.
Storage capacity can also be measured in base pairs; the DNA in a human cell nucleus contains about 3.2 gigabases (about 10⁹ DNA base pairs).
These base pairs are contained in DNA with a length of about 2 meters, fitting within the nucleus of each human cell — an indication of how incredibly well packaged this genetic information is.

Nucleosomes and Molecular Visualisation Software

Unlike most prokaryotic DNA which is 'naked', eukaryotic nuclear DNA is associated with proteins called histones to form chromatin.
A nucleosome consists of a strand of DNA coiled around a core of eight histone proteins (octamer) to form a bead-like structure.
DNA takes two turns around the histone core and is held in place by an additional histone protein attached to linker DNA; the DNA continues to wind around a series of nucleosomes forming a 'string of beads'.
Nucleosomes help to supercoil the DNA, resulting in a compact structure that saves space within the nucleus; they also help to protect DNA and facilitate movement of chromosomes during cell division.
Nucleosomes can be tagged with proteins to promote or suppress transcription.
Molecular visualisation software allows macromolecules (protein, DNA, RNA, complex carbohydrates) to be visualised as 3-D structures, relating primary sequence information to structure and function.
Macromolecules can be represented as ball and stick atom models or simplified ribbon representations; most software is freely available online or through bioinformatics repositories such as the Protein Data Bank (PDB).
In the PDB, searching for 6T79 (human nucleosome) and selecting '3D view' in Mol×shows the DNA double helix surrounding the histone proteins, with the DNA making two loops around the histone octamer core and histone tails projecting from the core.

The Hershey & Chase Experiment

DNA was identified in 1869 but many scientists assumed protein was the heritable material, owing to there being 20 amino acids and only 4 nucleotide bases.
In the 1950s, Alfred Hershey and Martha Chase showed that DNA, not protein, is the factor of heredity responsible for carrying genetic information from one generation to another.
They used viruses that infect bacteria (T2 bacteriophage infecting E. coli) as they consist only of DNA encapsulated by a protein coat.
Their method relied on a chemical difference: DNA contains phosphorus but no sulfur, while proteins contain sulfur but no phosphorus, allowing a radioactive isotope of each element to label one biomolecule without labelling the other.
Step 1: Bacteria were grown in media containing either radioactive sulfur (³⁵S) or radioactive phosphorus (³²P), then infected with viruses; progeny viruses took up the radioactive atoms, giving ³⁵S-labelled protein coats or ³²P-labelled DNA.
Step 2: Fresh, unlabelled bacteria were infected separately with each type of labelled virus; whichever biomolecule entered the bacteria must be the heritable material.
Step 3: A blender detached the viral coats from the bacterial cells, and centrifugation separated them — viruses are small and remained in the supernatant; bacteria are larger and formed a pellet.
Results: With ³²P-labelled viruses, radioactivity was found in the pellet (viral DNA had entered the bacteria); with ³⁵S-labelled viruses, radioactivity remained in the supernatant (protein coats had stayed outside).
Conclusion: DNA, not protein, is the hereditary material — providing unequivocal proof.
NOS: The availability of radioisotopes as research tools (made available at the end of the Second World War) made the Hershey-Chase experiment possible.

Chargaff's Data and the Problem of Induction

Erwin Chargaff analysed the DNA composition of different organisms during the 1930s and 1940s and discovered that the number of purine bases equals the number of pyrimidine bases.
He also found that the number of adenine bases equals the number of thymine bases, while the number of guanine bases equals the number of cytosine bases.
This means a purine base can only pair with a pyrimidine base between the sugar-phosphate backbone, since they have different sizes — forming the foundation of complementary base pairing in DNA.
The inductive scientific method starts with observations and raw data, then formulates a hypothesis tested by investigation; using past data to predict the future assumes the future will be the same.
It is impossible to prove a hypothesis generated by inductive reasoning as absolutely true — this is the problem of induction, the main reason most scientific theories are considered tentative.
Even if several investigations support a hypothesis, it can still be falsified in the future as new discoveries are made; Karl Popper suggested new scientific knowledge is gained by the falsification of existing hypotheses rather than by inductive steps.
Phoebus Levene discovered the pentose sugars of DNA and RNA in the early 1900s and suggested the tetranucleotide hypothesis — that nucleic acid structure was a repeating tetramer unit called a nucleotide.
At the time, limitations to analytic techniques made it difficult to determine the relative amounts of nucleotides present in nucleic acids.
The tetranucleotide hypothesis was falsified by Chargaff's data in the late 1940s, which showed the organism-specificity of nucleic acids; when the structure of DNA was determined in the 1950s, it further proved the repeating tetramer unit would not be suitable for carrying genetic information from one generation to the next.

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फ्री प्रीव्यू — 60 में से 8 सवाल। सभी देखने के लिए साइन अप करें।

1.Which of the following correctly lists the three components of a nucleotide?
Easy
- AA pentose sugar, a nitrogen-containing base and a phosphate group
- BA hexose sugar, an amino acid and a phosphate group
- CA pentose sugar, a nitrogen-containing base and a sulfate group
- DA deoxyribose sugar, a protein and a phosphate group
2.The diagram represents a nucleotide. Which row correctly identifies components 1, 2 and 3?
Easy
- A1 = Phosphate group, 2 = Pentose sugar, 3 = Adenine
- B1 = Adenine, 2 = Pentose sugar, 3 = Phosphate group
- C1 = Pentose sugar, 2 = Phosphate group, 3 = Adenine
- D1 = Phosphate group, 2 = Adenine, 3 = Pentose sugar
3.Which of the following statements apply to RNA? (select all that apply)
Medium
- AThe molecule is in the shape of a double helix, with antiparallel strands
- BThe four bases are adenine, cytosine, guanine, thymine
- CRibose is present as the pentose sugar in its nucleotides
- DIt is a polymer formed by the linkage of many nucleotides
- EIt is usually single-stranded
4.The diagram shows a section of a DNA molecule. Which of these base pairs are not correct?
Medium
- ANone
- B1
- C2
- D3
5.Which of the following statements correctly describes a nucleosome?
Easy
- AA strand of DNA coiled around a central core of eight histone proteins.
- BA strand of DNA wrapped around a central core of four histone proteins.
- CA section of supercoiled DNA.
- DA strand of DNA wrapped around a central core of eight chromatin proteins.
6.A short piece of DNA 19 base pairs long was analysed to find the number of nucleotide bases in each of the polynucleotide strands. Some of the results are shown below. Number of nucleotide bases A T G C Strand 1 8 - - - Strand 2 - 8 3 4 How many nucleotides containing adenine (A) were present in strand 2?
Medium
- A2
- B4
- C6
- D8
7.Which of the following would be a result of analysing a DNA molecule?
Medium
- AAn equal ratio of pentose sugars to phosphates and an equal ratio of thymine to adenine bases.
- BTwice as many pentose sugars as phosphates and an equal ratio of guanine to cytosine bases.
- CAn equal ratio of hexose sugars to phosphates and an equal ratio of thymine to cytosine bases.
- DTwice as many hexose sugars as phosphates and an equal ratio of guanine to adenine bases.
8.DNA is described as a double-helix, antiparallel structure. Which of the following statements best explains the term 'antiparallel'?
Medium
- AOne strand possesses deoxyribose sugar, the opposite strand possesses ribose sugars.
- BThe nitrogenous bases invert their orientation on the sense strand versus the antisense strand.
- CThe alignment of the sugar-phosphate backbone of each strand runs in opposite directions.
- DThe alignment of the two strands of nucleotides runs in opposite directions.

और सवाल

9.The approximate angle of orientation ('twist') of one nucleotide in respect to its neighbouring nucleotide in a given strand of DNA is between 35 and 40°. How many base pairs are required for the double-helix to twist by one whole turn?
Medium
- A5
- B8
- C10
- D12
10.The simplified diagram represents a section of DNA in 2D form. How many mistakes are there in this diagram?
Medium
- A0
- B2
- C3
- D4
11.Which of the following drawings best represents the structure of a section of DNA?
Medium
- AA drawing showing two antiparallel strands with complementary base pairs and hydrogen bonds
- BA drawing showing two parallel strands with identical base sequences
- CA drawing showing a single strand with alternating sugars and bases
- DA drawing showing two strands with ribose sugars and uracil bases
12.Which of the following statements about the genetic code are correct? (select all that apply)
Medium
- AA single DNA base will always be transcribed and translated in eukaryotic organisms.
- BA single DNA base can be part of genes that overlap each other.
- CThe genetic code allows multiple triplet codons to code for a single amino acid.
- DThe genetic code in a eukaryotic organism's genome stays the same throughout the organism's life.
13.Which of the following are correct statements about nucleosomes? (select all that apply)
Medium
- AThey contain histone proteins
- BThey help supercoil the DNA to form a compact structure
- CThey are found in both eukaryotes and prokaryotes
- DThey consist of both DNA and chromatin
14.In the 1950s, Hershey and Chase demonstrated that DNA, not protein, is a factor of heredity responsible for carrying genetic information from one generation to another. They used viruses that were labelled with either radioactive sulphur (35S) or radioactive phosphorus (32P) to infect bacteria. Which of these statements correctly describes the results of their experiment?
Medium
- AOnly bacteria infected by 32P labelled viruses were shown to be radioactive
- B32P was only detected in the supernatant
- COnly bacteria infected by 35S labelled viruses were shown to be radioactive
- D35S was detected in the pellet after centrifugation
15.Which of the following statements about molecular visualisation software are correct? (select all that apply)
Medium
- ACan help relate structure to chemical or biological behaviour.
- BCan support the design of pharmaceutically active compounds.
- CCan be used to study the interactions between proteins.
- DIs primarily used to identify if a DNA sequence encodes for a gene.
16.Which of the following would be the result of analysing a DNA molecule 14 000 base pairs in length?
Hard
- A28 000 pentose sugars, 14 000 phosphate groups, an equal ratio of cytosine to thymine bases and an equal ratio of guanine to adenine bases
- B28 000 pentose sugars, 28 000 phosphate groups, an equal ratio of cytosine to guanine bases and an equal ratio of thymine to adenine bases
- C14 000 pentose sugars, 28 000 phosphate groups, an equal ratio of cytosine to thymine bases and an equal ratio of guanine to adenine bases
- D28 000 pentose sugars, 28 000 phosphate groups, an equal ratio of cytosine to thymine bases and an equal ratio of guanine to adenine bases
17.Which of the following would not be considered an advantage of complementary base pairing in DNA?
Hard
- AIt enables each DNA strand to act as a template for the formation of a new strand during replication
- BHydrogen bonding between complementary bases stabilises the structure of the DNA molecule
- CIt ensures genetic continuity between generations of cells so that they all contain the same genetic information as the parent cells
- DIt plays an important role in maintaining the covalent bonds within the DNA molecule
18.The genetic code is universal, meaning that almost every organism uses the same code.
Easy
True or false?
19.RNA nucleotides contain the pentose sugar deoxyribose.
Easy
True or false?
20.Match each nitrogenous base with its correct classification.
Medium
- Adenine
- Guanine
- Cytosine
- Thymine
- Purine
- Pyrimidine
21.Place the steps of the Hershey and Chase experiment in the correct order.
Medium
- Bacteria grown in radioactive media and infected with viruses
- Labelled viruses infect unlabelled bacteria
- Blender detaches viral coats from bacterial cells
- Centrifugation separates viruses (supernatant) from bacteria (pellet)
22.A DNA molecule contains 30% adenine. What percentage of its bases are guanine?
Medium
- A20%
- B30%
- C40%
- D70%
23.Nucleosomes are found in prokaryotic cells.
Easy
True or false?
24.Which of the following are differences between DNA and RNA? (select all that apply)
Medium
- ADNA contains deoxyribose; RNA contains ribose
- BDNA is double-stranded; RNA is usually single-stranded
- CDNA contains thymine; RNA contains uracil
- DDNA is found only in the nucleus; RNA is found only in the cytoplasm
- EDNA is a polymer; RNA is not a polymer
25.Which of the following correctly describes the directionality of DNA strands?
Hard
- ABoth strands run from 5' to 3' in the same direction
- BOne strand runs from 5' to 3' and the other runs from 3' to 5'
- CBoth strands run from 3' to 5' in the same direction
- DThe directionality alternates along each strand
26.Which of the following statements about the genetic material of viruses are correct? (select all that apply)
Medium
- ASome viruses, such as SARS-CoV-2, contain RNA as their genetic material instead of DNA
- BViruses are able to replicate independently without a host cell
- CViruses lack a cellular structure
- DAll viruses contain DNA as their genetic material
- EViruses depend on other living cells for replication and survival
27.Which of the following statements about the components of a nucleotide are correct? (select all that apply)
Medium
- AThe pentose sugar contains five carbon atoms
- BThe phosphate group is basic and positively charged
- CThe nitrogenous base may contain one or two rings of atoms
- DThe base and phosphate group are both covalently bonded to the sugar
- EThe pentose sugar contains six carbon atoms
28.Which of the following statements about the sugar-phosphate backbone of a polynucleotide strand are correct? (select all that apply)
Medium
- AThe phosphate group of one nucleotide forms a covalent bond to the pentose sugar of the next nucleotide
- BThe covalent bonds between nucleotides are formed by condensation reactions that release water
- CThe bases are linked directly to each other along the backbone
- DThe backbone consists of alternating pentose sugars and phosphate groups
- EHydrogen bonds form the main links between adjacent nucleotides within one strand
29.Which of the following statements about the types of RNA found in cells are correct? (select all that apply)
Medium
- Amessenger RNA (mRNA) is formed in the nucleus and transported to ribosomes in the cytoplasm
- Btransfer RNA (tRNA) transports amino acids to ribosomes during protein synthesis
- Cribosomal RNA (rRNA) forms part of ribosomes
- DmRNA forms part of the ribosome structure
- EtRNA carries the genetic code out of the nucleus
30.Match each type of RNA with its correct role in the cell.
Medium
- messenger RNA (mRNA)
- transfer RNA (tRNA)
- ribosomal RNA (rRNA)
- transports amino acids to ribosomes during protein synthesis
- forms part of the structure of ribosomes
- is formed in the nucleus and transported to ribosomes in the cytoplasm
31.Place the following steps of the Hershey and Chase experiment in the correct order.
Medium
- Bacteria were grown in media containing either radioactive sulfur (35S) or radioactive phosphorus (32P), then infected with viruses
- Progeny viruses took up the radioactive atoms, producing labelled protein coats or labelled DNA
- Fresh, unlabelled bacteria were infected separately with each type of labelled virus
- A blender detached the viral coats from the bacterial cells, and centrifugation separated them
- Radioactivity was detected in the pellet for 32P and in the supernatant for 35S
32.Place the following stages in the correct sequence for the flow of genetic information from DNA to protein.
Medium
- The coding strand of DNA is transcribed into a strand of mRNA
- The template strand is read in the 3' to 5' direction to synthesise mRNA in the 5' to 3' direction
- mRNA moves into the cytoplasm of the cell
- Ribosomes translate the transcribed code in the 5' to 3' direction
- The base sequence determines the specific order of amino acids in the polypeptide chain
33.The phosphate group of a nucleotide is acidic and negatively charged.
Easy
True or false?
34.In DNA, the purine adenine always pairs with the pyrimidine thymine, forming three hydrogen bonds.
Medium
True or false?
35.The base pairings A–T and C–G are equal in length, so the DNA helix has the same 3D structure regardless of the base sequence.
Medium
True or false?
36.Chargaff's data showed that in DNA the number of purine bases equals the number of pyrimidine bases, and that adenine equals thymine while guanine equals cytosine.
Medium
True or false?
37.Which of the following best describes the term 'double helix' in relation to DNA?
Medium
- ATwo antiparallel polynucleotide strands held together by hydrogen bonds between complementary bases, forming a three-dimensional twisted shape
- BTwo parallel polynucleotide strands held together by covalent bonds between complementary bases
- CA single polynucleotide strand folded into a twisted shape by hydrogen bonds
- DTwo antiparallel polynucleotide strands held together by covalent bonds between the sugar-phosphate backbones
38.A DNA molecule contains 22% guanine. What percentage of its bases are adenine?
Medium
- A22%
- B28%
- C44%
- D56%
39.Which of the following correctly describes the directionality of the two strands in a DNA molecule?
Medium
- AOne strand runs 5' to 3' while the other runs 3' to 5', so the strands are antiparallel
- BBoth strands run 5' to 3' in the same direction, so the strands are parallel
- COne strand runs 5' to 3' while the other also runs 5' to 3', so the strands are antiparallel
- DOne strand contains deoxyribose while the other contains ribose, so the strands are antiparallel
40.A DNA molecule 14 000 base pairs in length was analysed. Which of the following would be a result of this analysis?
Hard
- A28 000 pentose sugars, 28 000 phosphate groups, and an equal ratio of adenine to thymine bases
- B14 000 pentose sugars, 28 000 phosphate groups, and an equal ratio of adenine to thymine bases
- C28 000 pentose sugars, 14 000 phosphate groups, and an equal ratio of adenine to thymine bases
- D28 000 pentose sugars, 28 000 phosphate groups, and an equal ratio of adenine to guanine bases
41.Name the nitrogenous base found in RNA that replaces thymine.
Easy
42.Name the type of bond that forms between the phosphate group of one nucleotide and the pentose sugar of the next nucleotide in a polynucleotide strand.
Medium
43.Complete the sentence about the structure of DNA.
Easy
The two strands of DNA are held together by ____ bonds between complementary base pairs.
44.Complete the table comparing DNA and RNA by filling in the missing pentose sugars.
Medium
DNA contains the pentose sugar ____, while RNA contains the pentose sugar ____.
45.A DNA molecule has 200 adenine bases. How many thymine bases does it have?
Medium
46.Complete the sentence about Chargaff's data.
Medium
Chargaff's data showed that the number of purine bases equals the number of ____ bases, and that the number of adenine bases equals the number of ____ bases.
47.What is the name of the bond that forms between complementary bases in DNA?
Easy
48.A DNA molecule contains 18% cytosine. What percentage of its bases are guanine?
Medium
49.A DNA molecule is 5000 base pairs in length. How many phosphate groups are present in the molecule?
Hard
50.The approximate angle of orientation (twist) of one nucleotide with respect to its neighbouring nucleotide in a strand of DNA is between 35 and 40°. Using 36° per nucleotide, how many base pairs are required for the double helix to twist by one whole turn?
Medium
51.Complete the sentence about the linkage of nucleotides.
Easy
The phosphate group of one nucleotide is linked to the pentose sugar of the next one by a ____ reaction, releasing a molecule of ____.
52.Complete the sentence about the structure of a nucleosome.
Medium
A nucleosome consists of a strand of DNA coiled around a core of ____ histone proteins, and the DNA takes ____ turns around this core.
53.Hershey and Chase carried out an experiment to determine whether the molecule of heredity was protein or DNA; their results after centrifugation are shown below. Note the following: Extracellular material is found in the supernatant. The y-axis shows the percentage of each radioactive element present in the supernatant; the remainder of each element ends up in the pellet. Which radioactive element would be found in the pellet and why?
Hard
54.Explain how the structure of DNA relates to its function in storing genetic information.
Hard
55.Explain how the results of the Hershey and Chase experiment provided evidence that DNA, not protein, is the heritable material.
Hard
56.Explain how Chargaff's data falsified the tetranucleotide hypothesis.
Hard
57.A DNA molecule has 200 adenine bases. How many thymine bases does it have?
Medium
- A200 bases
- B220 bases
- C180 bases
- D240 bases
58.A DNA molecule contains 18% cytosine. What percentage of its bases are guanine?
Medium
- A19 %
- B18 %
- C17 %
- D20 %
59.A DNA molecule is 5000 base pairs in length. How many phosphate groups are present in the molecule?
Hard
- A12000 phosphate groups
- B9000 phosphate groups
- C10000 phosphate groups
- D11000 phosphate groups
60.The approximate angle of orientation (twist) of one nucleotide with respect to its neighbouring nucleotide in a strand of DNA is between 35 and 40°. Using 36° per nucleotide, how many base pairs are required for the double helix to twist by one whole turn?
Medium
- A11 base pairs
- B10 base pairs
- C9 base pairs
- D12 base pairs

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