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Biology HL - IB > Nucleic acid > Flashcards

Nucleic acid Flashcards

1
Q

What is the primary genetic material of living organisms?

A

Deoxyribose nucleic acid (DNA) carries the genetic code in all living organisms.

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2
Q

Why is the genetic code considered universal?

A

The genetic code applies to all forms of life, indicating that it is universal.

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3
Q

Where is DNA primarily located?

A

DNA is mainly found in the nucleus, forming chromosomes, and also in chloroplasts and mitochondria of eukaryotic cells.

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4
Q

What role does RNA play in cells?

A

RNA is the main component of ribosomes, which are crucial for protein synthesis.

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5
Q

In what form can RNA be found in viruses?

A

Certain viruses, such as SARS-CoV-2, contain RNA as their genetic material instead of DNA.

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6
Q

Why are viruses not considered living organisms?

A

Viruses cannot replicate by themselves and depend on living cells for replication and survival.

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7
Q

What are the components of a nucleotide?

A

A nucleotide consists of a pentose sugar, a nitrogen-containing organic base, and a phosphate group.

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8
Q

What type of sugar is present in nucleotides?

A

The sugar in nucleotides is a pentose sugar, which has five carbon atoms.

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9
Q

What are the nitrogenous bases found in DNA?

A

The nitrogenous bases in DNA are Adenine (A), Guanine (G), Cytosine (C), and Thymine (T).

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10
Q

How does RNA differ from DNA regarding nitrogenous bases?

A

RNA contains uracil (U) instead of thymine (T), which is found in DNA.

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11
Q

What distinguishes purines from pyrimidines?

A

Adenine and Guanine are purines; Cytosine, Thymine (in DNA), and Uracil (in RNA) are pyrimidines.

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12
Q

How are nucleotides linked to form nucleic acids?

A

Nucleotides join together through covalent bonds to form chains that create DNA or RNA strands.

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13
Q

What forms the sugar-phosphate backbone of nucleic acids?

A

The phosphate group of one nucleotide forms a covalent bond with the pentose sugar of another nucleotide.

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14
Q

What type of bond links adjacent nucleotides together?

A

Adjacent nucleotides are linked by phosphodiester bonds formed through condensation reactions.

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15
Q

Describe the structure of RNA.

A

RNA usually forms a single-stranded polynucleotide with ribose as the pentose sugar.

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16
Q

What types of RNA exist within cells?

A

Types include messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA).

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17
Q

How do adjacent RNA nucleotides bond?

A

They bond through condensation reactions that release a molecule of water, forming phosphodiester bonds.

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18
Q

Describe the structure of DNA.

A

DNA is a double helix made of two antiparallel strands linked by hydrogen bonds between complementary base pairs.

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19
Q

How many strands does DNA consist of?

A

DNA consists of two polynucleotide strands running in opposite directions, known as antiparallel strands.

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20
Q

What defines the ends of a DNA strand?

A

Each DNA strand has a 3’ end and a 5’ end based on which carbon atom on the pentose sugar can bond with another nucleotide.

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21
Q

How do hydrogen bonds function in DNA structure?

A

Hydrogen bonds form between complementary base pairs: Adenine pairs with Thymine (two hydrogen bonds) and Guanine pairs with Cytosine (three hydrogen bonds).

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22
Q

Explain complementary base pairing.

A

Complementary base pairing ensures that specific bases pair together: A with T and C with G, allowing for accurate DNA replication.

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23
Q

What is meant by “antiparallel” strands in DNA?

A

Antiparallel strands refer to two strands running in opposite directions, one oriented from 5’ to 3’ and the other from 3’ to 5’.

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24
Q

Describe the three-dimensional shape of DNA.

A

DNA forms a three-dimensional structure known as a double helix.

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25
Q

How is genetic information encoded in DNA?

A

Genetic information is encoded as sequences of nitrogenous bases, with each triplet called a codon coding for an amino acid.

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26
Q

What determines the order of amino acids in proteins?

A

The sequence of bases on the coding strand determines the order of amino acids during protein synthesis.

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27
Q

Define codon.

A

A codon is a sequence of three nitrogenous bases that codes for one amino acid.

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28
Q

How many different amino acids can be coded for by codons?

A

There are 20 different amino acids that can be coded for by various codons.

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29
Q

Explain the conservation of the genetic code.

A

The genetic code is universal; nearly all organisms use the same triplet codes for amino acids, allowing for genetic engineering across species.

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30
Q

What evidence supports the idea of a universal common ancestor?

A

The similarity in genetic codes across species suggests shared ancestry among all living organisms on Earth.

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31
Q

Differentiate between coding and non-coding sequences.

A

Coding sequences code for proteins, while non-coding sequences do not but may have regulatory functions or structural roles.

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32
Q

What are conserved sequences?

A

Conserved sequences are regions that have remained unchanged across different organisms, often found in essential genes involved in transcription and translation.

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33
Q

Compare properties between DNA and RNA.

A

Property: DNA RNA
Sugar: Deoxyribose Ribose
Bases: A, C, G, T A, C, G, U
Strands: Double-stranded Single-stranded

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34
Q

What is the primary genetic material of living organisms?

A

Deoxyribose nucleic acid (DNA) carries the genetic code in all living organisms.

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35
Q

Why is the genetic code considered universal?

A

The genetic code applies to all forms of life, indicating that it is universal.

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36
Q

Where is DNA primarily located in eukaryotic cells?

A

DNA is mainly found in the nucleus, where it forms chromosomes, and also in chloroplasts and mitochondria.

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37
Q

What role does RNA play in cells?

A

RNA is primarily a component of ribosomes, which are crucial for protein synthesis, and some RNA is also found in the nucleus and cytoplasm.

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38
Q

What are the components of a nucleotide?

A

A nucleotide consists of a pentose sugar (five carbon atoms), a nitrogen-containing organic base (with one or two rings), and a phosphate group (acidic and negatively charged).

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39
Q

How does RNA differ from DNA in terms of nitrogenous bases?

A

RNA has uracil (U) instead of thymine (T), which is found in DNA.

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40
Q

Classify the nitrogenous bases into purines and pyrimidines.

A

Purines: Adenine (A) and Guanine (G); Pyrimidines: Cytosine (C), Thymine (T), and Uracil (U)

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41
Q

Describe the basic structure of a nucleotide.

A

Sugar: Pentose sugar represented by a pentagon
Phosphate: Negatively charged group represented by a circle with “P”
Base: Nitrogenous base represented by a rectangle

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42
Q

How do nucleotides link to form nucleic acids?

A

Nucleotides join together through covalent bonds to form chains that create DNA or RNA strands, resulting in polynucleotides.

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43
Q

What forms the sugar-phosphate backbone of nucleic acids?

A

The phosphate group of one nucleotide forms a covalent bond with the pentose sugar of another nucleotide, creating a sugar-phosphate backbone.

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44
Q

How are adjacent RNA nucleotides linked?

A

Adjacent RNA nucleotides are linked by phosphodiester bonds formed through condensation reactions that release a molecule of water.

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45
Q

Describe the structure of RNA.

A

RNA typically forms a single-stranded polynucleotide with ribose as the pentose sugar and contains adenine, guanine, cytosine, and uracil as nitrogenous bases.

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46
Q

Explain how mRNA functions.

A

mRNA is synthesized in the nucleus and transports genetic information from DNA to ribosomes for protein synthesis.

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47
Q

What role does tRNA play during protein synthesis?

A

tRNA transports specific amino acids to ribosomes during translation, matching them with corresponding codons on mRNA.

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48
Q

What is ribosomal RNA (rRNA)?

A

rRNA forms part of ribosomes and plays a crucial role in synthesizing proteins by facilitating the binding of mRNA and tRNA.

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49
Q

Describe the structure of DNA.

A

DNA consists of two antiparallel strands forming a double helix, linked by hydrogen bonds between complementary base pairs.

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50
Q

How do hydrogen bonds function in DNA structure?

A

Hydrogen bonds form between complementary base pairs: Adenine pairs with Thymine (two hydrogen bonds) and Guanine pairs with Cytosine (three hydrogen bonds).

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51
Q

Explain complementary base pairing.

A

Complementary base pairing ensures that specific bases pair together: A with T and C with G, allowing for accurate DNA replication.

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52
Q

What defines antiparallel strands in DNA?

A

Antiparallel strands refer to two strands running in opposite directions; one strand runs from 5’ to 3’ while the complementary strand runs from 3’ to 5’.

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53
Q

What is meant by “coding strand” in DNA?

A

The coding strand carries the base sequence that will be read by enzymes during transcription to synthesize mRNA.

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54
Q

Define “template strand”.

A

The template strand serves as a guide for synthesizing mRNA during transcription based on complementary base pairing.

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55
Q

How many different amino acids can be coded for by codons?

A

There are 20 different amino acids that can be coded for by various triplet codons in mRNA.

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56
Q

Explain how genetic information is encoded in DNA.

A

Sequence: The sequence of nitrogenous bases encodes genetic information.
Codon: Each triplet of bases codes for one amino acid.

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57
Q

Why is the genetic code considered universal?

A

Almost every organism uses the same triplet codes for amino acids, allowing for genetic engineering across species.

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58
Q

What evidence supports common ancestry among organisms?

A

Genetic Code: Similarities in coding sequences across species suggest shared ancestry.
Conserved Sequences : Highly conserved sequences indicate evolutionary relationships.

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59
Q

Describe mutations’ impact on genetic sequences.

A

Beneficial: May enhance survival or reproductive success.
Harmful: Can disrupt normal functions or lead to disease.

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60
Q

Describe how nucleotides form nucleic acids.

A

Nucleotides join together to form chains that create DNA or RNA strands through covalent bonding between the phosphate group of one nucleotide and the pentose sugar of another.

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61
Q

What does the genetic code consist of?

A

The genetic code consists of sequences of nitrogenous bases in DNA, read as triplets called codons, each coding for one amino acid.

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62
Q

What role does RNA play in cells?

A

RNA is a main component of ribosomes, which are crucial for protein synthesis, and some RNA is also found in the nucleus and cytoplasm.

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63
Q

What type of genetic material do certain viruses contain?

A

Certain viruses, such as SARS-CoV-2, contain RNA as their genetic material instead of DNA.

63
Q

Why are viruses not considered living organisms?

A

Viruses cannot replicate by themselves and depend on host cells for replication and survival; they also lack cellular structure.

64
Q

What are the components of a nucleotide?

A

A nucleotide consists of a pentose sugar (five carbon atoms), a nitrogen-containing organic base (with one or two rings), and a phosphate group (acidic and negatively charged).

65
Q

How does RNA differ from DNA regarding nitrogenous bases?

A

RNA contains uracil (U) instead of thymine (T), which is found in DNA.

66
Q

Describe the basic structure of a nucleotide.

A

Sugar: Pentose sugar represented by a pentagon
Phosphate: Negatively charged group represented by a circle with “P”
Base: Nitrogenous base represented by a rectangle

67
Q

How do nucleotides link to form nucleic acids?

A

Nucleotides join together through covalent bonds to form chains that create DNA or RNA strands, resulting in polynucleotides.

68
Q

What forms the sugar-phosphate backbone of nucleic acids?

A

The phosphate group of one nucleotide forms a covalent bond with the pentose sugar of another nucleotide, creating a sugar-phosphate backbone.

69
Q

What role does tRNA play during protein synthesis?

A

tRNA transports specific amino acids to ribosomes during translation, matching them with corresponding codons on mRNA.

70
Q

How do hydrogen bonds function in DNA structure?

A

Hydrogen bonds form between complementary base pairs: Adenine pairs with Thymine (two hydrogen bonds) and Guanine pairs with Cytosine (three hydrogen bonds).

71
Q

Describe the structure of DNA.

A

DNA consists of two antiparallel strands forming a double helix, linked by hydrogen bonds between complementary base pairs.

72
Q

Define “template strand”.

A

The template strand serves as a guide for synthesizing mRNA during transcription based on complementary base pairing.

73
Q

Explain how genetic information is encoded in DNA.

A

Sequence: The sequence of nitrogenous bases encodes genetic information.
Codon: Each triplet of bases codes for one amino acid.

74
Q

Describe how nucleotides form polynucleotides.

A

Nucleotides join together through covalent bonds between their phosphate groups and pentose sugars, forming long chains known as polynucleotides.

75
Q

Define “sugar-phosphate backbone”.

A

The sugar-phosphate backbone consists of alternating sugar and phosphate groups that provide structural support to nucleic acid molecules

76
Q

How do condensation reactions contribute to nucleotide bonding?

A

Condensation reactions link nucleotides by forming phosphodiester bonds while releasing water molecules during bond formation.

77
Q

What distinguishes RNA from DNA regarding structure?

A

Property DNA RNA
Strands: Double-stranded Single-stranded
Length Longer Shorter
Sugar Deoxyribose Ribose
Base A, T, C, G A, U, C, G

78
Q

What is DNA and why is it considered the genetic material of living organisms?

A

What is DNA and why is it considered the genetic material of living organisms?
Back: DNA (Deoxyribonucleic Acid) is the genetic material of all living organisms. It contains the instructions for the development and functioning of all known living organisms. DNA is a long, double-stranded molecule that carries genetic information in the form of a code made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T). The sequence of these bases determines the information available for building and maintaining an organism.

79
Q

How does DNA store and transmit genetic information?

A

DNA stores genetic information in its base sequence. The order of A, T, G, and C bases along the DNA strand encodes specific instructions for making proteins. This information is transmitted through the processes of replication (copying DNA) and transcription (converting DNA information into RNA). During cell division, DNA is replicated and passed on to daughter cells, ensuring genetic continuity. The ability of DNA to store, replicate, and transmit genetic information makes it the fundamental basis of inheritance in living organisms.

80
Q

Why are viruses not considered living organisms despite some using RNA as genetic material?

A

Viruses are not considered living organisms because they lack several key characteristics of life:
- They cannot reproduce independently, requiring a host cell’s machinery.
- They do not carry out their own metabolism.
- They cannot maintain homeostasis on their own.
- They do not grow or develop.
- While some viruses use RNA as their genetic material, this alone is not sufficient to classify them as living. The use of RNA instead of DNA is just one of many unique features of viruses that set them apart from living organisms.

81
Q

How does the genetic material in viruses differ from that in living organisms?

A

While all living organisms use DNA as their genetic material, viruses can use either DNA or RNA. Some viruses, like influenza and HIV, use RNA as their genetic material. This RNA can be single-stranded or double-stranded. In contrast, living organisms universally use double-stranded DNA. The viral genetic material, whether DNA or RNA, is typically much simpler and smaller than that of living organisms. It often encodes only the essential information needed for viral replication and assembly, relying heavily on the host cell’s machinery for these processes.

82
Q

What is the significance of DNA being the universal genetic material in living organisms?

A

The universality of DNA as the genetic material in all living organisms is significant for several reasons:
- It suggests a common ancestor for all life on Earth.
- It allows for genetic information to be transferred between different species (horizontal gene transfer).
- It enables the use of common molecular biology techniques across different organisms.
- It provides a basis for understanding evolution and the relationships between different species.
- It allows for the development of universal genetic technologies, such as DNA sequencing and genetic engineering, that can be applied across various organisms.
- This universality underscores the fundamental unity of life on Earth, despite its incredible diversity.

83
Q

What are the three main components of a nucleotide?

A

A nucleotide consists of three main components:
- A phosphate group
- A pentose sugar (either ribose in RNA or deoxyribose in DNA)
- A nitrogenous base
- These components are covalently bonded together to form the nucleotide structure. The phosphate group is attached to the 5’ carbon of the sugar, while the nitrogenous base is attached to the 1’ carbon of the sugar.

84
Q

How should nucleotides be represented in diagrams?

A

In diagrams, nucleotides should be represented using specific shapes for each component:
- Circles for phosphate groups
- Pentagons for pentose sugars
- Rectangles for nitrogenous bases
- This simplified representation helps to clearly show the relative positions of each component within the nucleotide structure.

85
Q

What are the differences between DNA and RNA nucleotides?

A

The main differences between DNA and RNA nucleotides are:
- Sugar: DNA has deoxyribose, while RNA has ribose
- Bases: DNA uses thymine, while RNA uses uracil instead
- Structure: DNA is typically double-stranded, while RNA is usually single-stranded
- In diagrams, these differences would be represented by slight variations in the pentagon (sugar) and rectangle (base) components.

86
Q

What are the five types of nitrogenous bases found in nucleic acids?

A

The five types of nitrogenous bases found in nucleic acids are:
- Adenine (A)
- Guanine (G)
- Cytosine (C)
- Thymine (T) - in DNA only
- Uracil (U) - in RNA only
- These bases are represented by rectangles in nucleotide diagrams. Adenine and guanine are purines (larger, double-ring structures), while cytosine, thymine, and uracil are pyrimidines (smaller, single-ring structures).

87
Q

How does the phosphate group contribute to nucleic acid structure?

A

The phosphate group plays a crucial role in nucleic acid structure:
- It forms the backbone of the DNA/RNA strand by linking nucleotides together.
- It contributes to the overall negative charge of nucleic acids.
- It forms a phosphodiester bond between the 3’ carbon of one sugar and the 5’ carbon of the next.
In diagrams, the phosphate group is represented by a circle, typically shown at the top of the nucleotide structure to indicate its position in the 5’ to 3’ orientation of the nucleic acid strand.

88
Q

What is the sugar-phosphate backbone in DNA and RNA?

A

The sugar-phosphate backbone is a continuous chain of covalently bonded atoms that forms the structural framework of DNA and RNA molecules. It consists of alternating sugar (deoxyribose in DNA, ribose in RNA) and phosphate groups. This backbone runs along the length of the nucleic acid molecule, providing strength and stability to the overall structure.

89
Q

How are sugar and phosphate groups bonded in the backbone?

A

Sugar and phosphate groups are connected through phosphodiester bonds. The 5’ carbon of one sugar molecule is linked to the 3’ carbon of the next sugar molecule via a phosphate group. This creates a repeating pattern of sugar-phosphate-sugar-phosphate along the length of the nucleic acid strand. These covalent bonds are strong, contributing to the stability of the DNA or RNA molecule.

90
Q

Why is the sugar-phosphate backbone important for nucleic acid structure?

A

The sugar-phosphate backbone is crucial for nucleic acid structure because:
- It provides structural integrity to the molecule.
- It creates a consistent, repeating pattern that allows for the regular spacing of nitrogenous bases.
- It contributes to the overall negative charge of DNA and RNA, influencing their interactions with other molecules.
- It determines the directionality of the nucleic acid strand (5’ to 3’).

91
Q

How does the sugar-phosphate backbone contribute to the double helix structure of DNA?

A

In DNA’s double helix structure, the sugar-phosphate backbones of two complementary strands run antiparallel to each other on the outside of the helix. This arrangement:
- Provides structural support for the double helix.
Allows the nitrogenous bases to face inward, facilitating base pairing.
- Creates major and minor grooves in the helix, which are important for protein interactions.
- The strong covalent bonds in the backbone maintain the integrity of each strand, while the weaker hydrogen bonds between base pairs allow for easy separation during processes like replication and transcription.

92
Q

How does the sugar-phosphate backbone differ between DNA and RNA?

A

While the basic structure of the sugar-phosphate backbone is similar in DNA and RNA, there are key differences:
- Sugar type: DNA uses deoxyribose, while RNA uses ribose (which has an additional hydroxyl group on the 2’ carbon).
- Structure: DNA typically forms a double-stranded helix with two backbones, while RNA is usually single-stranded with one backbone.
- Stability: The absence of the 2’ hydroxyl group in DNA makes its backbone more stable than RNA’s, contributing to DNA’s role as the primary genetic material in most organisms.

93
Q

What are the nitrogenous bases found in DNA?

A

The nitrogenous bases found in DNA are adenine (A), guanine (G), cytosine (C), and thymine (T). These bases form the genetic code by pairing specifically: adenine pairs with thymine (A-T) and guanine pairs with cytosine (G-C). This complementary base pairing is crucial for DNA’s double-helix structure and its ability to store genetic information.

94
Q

What are the nitrogenous bases found in RNA?

A

The nitrogenous bases found in RNA are adenine (A), guanine (G), cytosine (C), and uracil (U). Unlike DNA, RNA uses uracil instead of thymine. In RNA, adenine pairs with uracil (A-U) during processes like transcription, while guanine still pairs with cytosine (G-C).

95
Q

How are nitrogenous bases classified?

A

Nitrogenous bases are classified into two groups:
- Purines: Adenine (A) and guanine (G), which have a larger, double-ring structure.
- Pyrimidines: Cytosine (C), thymine (T), and uracil (U), which have a smaller, single-ring structure.
This classification is important because purines always pair with pyrimidines to maintain a consistent width in the DNA double helix.

96
Q

What is the role of nitrogenous bases in the genetic code?

A

Nitrogenous bases form the basis of the genetic code by their specific sequences along a DNA or RNA strand. Groups of three bases, called codons, correspond to specific amino acids during protein synthesis. For example, the codon AUG codes for methionine, which is also the start codon for translation. The sequence of these bases determines the structure and function of proteins.

97
Q

How do base-pairing rules differ between DNA and RNA?

A

In DNA, base-pairing follows these rules:
- Adenine pairs with thymine (A-T) via two hydrogen bonds.
- Guanine pairs with cytosine (G-C) via three hydrogen bonds.
- In RNA, thymine is replaced by uracil, so adenine pairs with uracil (A-U). The other pairing, guanine-cytosine (G-C), remains unchanged. These pairing rules ensure accurate replication and transcription of genetic material.

98
Q

Why is complementary base pairing important for nucleic acids?

A

Complementary base pairing is important because it ensures accurate replication of DNA during cell division and proper transcription of RNA from a DNA template. The specific pairing of A-T (or A-U in RNA) and G-C allows for error-checking mechanisms and maintains the integrity of genetic information across generations. It also stabilizes the double-helix structure of DNA.

99
Q

What are the components of an RNA nucleotide?

A

An RNA nucleotide consists of three parts:
- A phosphate group
- A ribose sugar (pentose)
- One of four nitrogenous bases: adenine (A), guanine (G), cytosine (C), or uracil (U)

100
Q

How is an RNA polymer formed?

A

An RNA polymer is formed through condensation reactions between nucleotides. The 3’ hydroxyl group of one nucleotide’s ribose sugar reacts with the 5’ phosphate group of the next nucleotide, releasing a water molecule and forming a phosphodiester bond.

101
Q

How should RNA structure be represented in diagrams?

A

In diagrams, RNA structure is typically shown as:
- Circles for phosphate groups
- Pentagons for ribose sugars
- Rectangles for nitrogenous bases
- The sugar-phosphate backbone forms a continuous chain, with bases extending from it.

102
Q

What are the key differences between RNA and DNA structure?

A

Key differences between RNA and DNA structure:
- RNA uses ribose sugar instead of deoxyribose
- RNA contains uracil (U) instead of thymine (T)
- RNA is usually single-stranded, unlike double-stranded DNA

103
Q

What are the characteristics of an RNA polymer?

A

Characteristics of an RNA polymer:
- The sugar-phosphate backbone provides structural support
- The sequence of bases carries genetic information
RNA strands have a 5’ to 3’ directionality, determined by the orientation of the sugar-phosphate backbone
- RNA is typically single-stranded but can form secondary structures through base pairing

104
Q

What is the basic structure of DNA?

A

DNA is a double helix made of two antiparallel strands of nucleotides. The two strands are linked by hydrogen bonding between complementary base pairs. Each strand has a sugar-phosphate backbone with nitrogenous bases extending inward.

105
Q

How are the two strands of DNA oriented?

A

The two strands of DNA are antiparallel, meaning they run in opposite directions. One strand runs in the 5’ to 3’ direction, while the complementary strand runs in the 3’ to 5’ direction.

106
Q

What are the complementary base pairs in DNA?

A

In DNA, adenine (A) pairs with thymine (T), and guanine (G) pairs with cytosine (C). These specific pairings are crucial for maintaining the structure and function of DNA.

107
Q

How are the complementary base pairs held together in DNA?

A

Complementary base pairs in DNA are held together by hydrogen bonds. Adenine forms two hydrogen bonds with thymine, while guanine forms three hydrogen bonds with cytosine.

108
Q

What is the significance of the complementary base pairing in DNA?

A

Complementary base pairing in DNA is essential for several reasons:
- It maintains the double helix structure.
- It allows for accurate DNA replication.
- It enables the process of transcription for gene expression.
- It provides a mechanism for DNA repair.

109
Q

What is the difference in the number of strands between DNA and RNA?

A

DNA is typically double-stranded, forming a double helix structure. RNA is usually single-stranded, though it can form secondary structures through base pairing.

110
Q

How do the nitrogenous bases differ between DNA and RNA?

A

DNA contains adenine (A), guanine (G), cytosine (C), and thymine (T). RNA uses uracil (U) instead of thymine, along with A, G, and C.

111
Q

What is the difference in pentose sugar between DNA and RNA?

A

DNA contains deoxyribose, while RNA contains ribose. The key difference is that ribose has a hydroxyl (-OH) group on the 2’ carbon, while deoxyribose lacks this group.

112
Q

Sketch the difference between ribose and deoxyribose.

A

Ribose (in RNA):
O
|
HO-C-H
|
H-C-OH
|
H-C-OH
|
H-C-OH
|
CH2OH

Deoxyribose (in DNA):
O
|
HO-C-H
|
H-C-H
|
H-C-OH
|
H-C-OH
|
CH2OH

113
Q

What are some examples of nucleic acids?

A

Examples of nucleic acids include:
- DNA: Found in chromosomes, mitochondria, and chloroplasts
- mRNA: Messenger RNA, carries genetic information from DNA to ribosomes
- tRNA: Transfer RNA, brings amino acids to ribosomes during protein synthesis
- rRNA: Ribosomal RNA, forms part of the ribosome structure

114
Q

What contributes to the diversity of possible DNA base sequences?

A

The diversity of possible DNA base sequences is due to:
- Variable length of DNA molecules
- Four different nucleotide bases (A, T, G, C) that can be arranged in any order
- No restrictions on the sequence of bases

115
Q

How does DNA demonstrate a limitless capacity for storing information?

A

DNA demonstrates a limitless capacity for storing information because:
- There is no theoretical limit to the length of a DNA molecule
- Each position in the sequence can be any of the four bases
- The number of possible combinations increases exponentially with length
- This allows for an enormous number of possible gene sequences and genetic information to be stored.

116
Q

Why is DNA considered an economical method of information storage?

A

DNA is considered an economical method of information storage because:
- It uses only four different bases to encode vast amounts of information
- The double-helix structure allows for compact storage
- Information is stored at the molecular level, requiring minimal physical space
- The base-pairing mechanism allows for easy replication and transcription of stored information

117
Q

How does the base sequence diversity relate to genetic variation?

A

The base sequence diversity relates to genetic variation by:
- Allowing for a vast number of possible alleles for each gene
- Enabling the encoding of a wide variety of proteins with different functions
- Providing the raw material for evolution through mutations and genetic recombination
- Supporting the diversity of life forms observed in nature

118
Q

What is the significance of DNA’s information storage capacity in modern biotechnology?

A

The significance of DNA’s information storage capacity in modern biotechnology includes:
- Enabling the development of genetic engineering techniques
- Supporting the field of genomics and personalized medicine
- Allowing for the creation of genetically modified organisms
- Inspiring new methods of data storage using DNA as a medium
- Facilitating the study of evolutionary relationships between species through comparative genomics

119
Q

What is complementary base pairing in DNA?

A

Complementary base pairing in DNA refers to the specific hydrogen bonding between nucleotide bases. Adenine pairs with thymine via two hydrogen bonds, while guanine pairs with cytosine via three hydrogen bonds. This pairing is crucial for the structure and function of DNA.

120
Q

How does complementary base pairing enable DNA replication?

A

During DNA replication, the double helix unwinds and each strand serves as a template. Complementary bases are added to each template strand according to the base pairing rules. This process ensures that genetic information is accurately copied and passed on to daughter cells, maintaining genetic continuity.

121
Q

What role does complementary base pairing play in transcription?

A

In transcription, complementary base pairing allows RNA polymerase to create an mRNA strand complementary to the DNA template strand. The mRNA sequence is determined by the DNA sequence, ensuring that genetic information is accurately transferred from DNA to RNA for protein synthesis.

122
Q

How does complementary base pairing contribute to translation?

A

During translation, complementary base pairing occurs between mRNA codons and tRNA anticodons. This pairing ensures that the correct amino acids are brought to the ribosome in the proper sequence, allowing for accurate protein synthesis based on the genetic information.

123
Q

What is the importance of complementary base pairing in DNA repair?

A

Complementary base pairing is essential for DNA repair mechanisms. When errors occur in DNA replication or due to damage, repair enzymes can identify mismatches by recognizing non-complementary base pairs. The correct base can then be inserted based on the complementary strand, maintaining the integrity of genetic information.

124
Q

What is the genetic code and how is it conserved across life forms?

A

The genetic code is the set of rules by which DNA sequences are translated into proteins. It is highly conserved across all known life forms, from bacteria to humans, using a nearly identical system of three-nucleotide codons to specify amino acids and start/stop signals.

125
Q

How does the conservation of the genetic code support the idea of universal common ancestry?

A

The near-universal nature of the genetic code suggests that all living organisms descended from a single common ancestor that possessed this code. The consistency across diverse life forms, including archaea, bacteria, and eukaryotes, indicates an ancient origin predating the divergence of these major domains of life.

126
Q

Are there any variations in the genetic code, and how do they relate to common ancestry?

A

While the genetic code is highly conserved, minor variations exist, such as alternative stop codons in some organisms. These variations actually reinforce the idea of common ancestry by demonstrating how the code has been slightly modified in some lineages over billions of years of evolution.

127
Q

How does the conservation of the genetic code impact molecular biology and biotechnology?

A

The conservation of the genetic code allows genes from one organism to be expressed in another, a principle fundamental to genetic engineering. This interchangeability of genetic material between vastly different species underscores the deep evolutionary connections between all life forms.

128
Q

How does the universality of the genetic code relate to the RNA world hypothesis?

A

The universality of the genetic code supports the RNA world hypothesis, suggesting that RNA may have preceded DNA as the primary genetic material in early life forms. This hypothesis provides a potential explanation for how the current DNA-based genetic system evolved from a common ancestral form.

129
Q

What is the directionality of DNA and RNA strands?

A

DNA and RNA strands have a specific directionality, running from the 5’ end to the 3’ end. This directionality is determined by the orientation of the sugar-phosphate backbone, where the 5’ carbon of one nucleotide is linked to the 3’ carbon of the next nucleotide via a phosphodiester bond.

130
Q

How does the 5’ to 3’ directionality affect DNA replication?

A

During DNA replication, new strands are always synthesized in the 5’ to 3’ direction. This means that one strand (the leading strand) can be synthesized continuously, while the other strand (the lagging strand) must be synthesized in short fragments called Okazaki fragments, which are later joined together.

131
Q

What is the significance of 5’ to 3’ directionality in transcription?

A

In transcription, RNA polymerase reads the DNA template strand in the 3’ to 5’ direction and synthesizes the complementary RNA strand in the 5’ to 3’ direction. This ensures that the resulting mRNA has the correct sequence and orientation for subsequent translation.

132
Q

How does the 5’ to 3’ directionality impact translation?

A

During translation, ribosomes read the mRNA from the 5’ end to the 3’ end. This directionality ensures that the protein is synthesized from the N-terminus to the C-terminus, which is crucial for proper protein folding and function.

133
Q

Why is the 5’ to 3’ directionality important for the stability of nucleic acids?

A

The 5’ to 3’ directionality provides stability to nucleic acids. The 5’ end typically has a phosphate group, while the 3’ end has a hydroxyl group. This arrangement helps protect the molecule from degradation by exonucleases, which typically work in a specific direction.

134
Q

What is purine-to-pyrimidine bonding in DNA?

A

Purine-to-pyrimidine bonding in DNA refers to the specific base pairing between purines (adenine and guanine) and pyrimidines (thymine and cytosine). Adenine pairs with thymine, and guanine pairs with cytosine. This specific pairing contributes to the stability of the DNA double helix structure.

135
Q

How does purine-to-pyrimidine bonding contribute to DNA helix stability?

A

Purine-to-pyrimidine bonding contributes to DNA helix stability by ensuring consistent spacing between the two strands of DNA. The adenine-thymine (A-T) pair forms two hydrogen bonds, while the cytosine-guanine (C-G) pair forms three hydrogen bonds. This consistent bonding pattern helps maintain the overall structure and stability of the DNA molecule.

136
Q

Why do A-T and C-G base pairs have equal length?

A

A-T and C-G base pairs have equal length because purines (A and G) always pair with pyrimidines (T and C). This consistent pairing ensures that the distance between the sugar-phosphate backbones remains constant along the entire length of the DNA molecule, regardless of the specific base sequence.

137
Q

How does the equal length of base pairs affect the DNA helix structure?

A

The equal length of A-T and C-G base pairs ensures that the DNA helix maintains the same three-dimensional structure regardless of the base sequence. This consistent structure is crucial for the proper functioning of DNA, including replication, transcription, and protein-DNA interactions.

138
Q

What would happen to the DNA structure if purine-to-pyrimidine bonding was not maintained?

A

If purine-to-pyrimidine bonding was not maintained, the DNA structure would be irregular and unstable. Unequal base pair lengths would cause distortions in the double helix, potentially leading to problems with DNA replication, transcription, and other cellular processes that rely on the consistent structure of DNA.

139
Q

What is a nucleosome?

A

A nucleosome is the basic unit of DNA packaging in eukaryotes, consisting of a segment of DNA wrapped around a core of histone proteins. It is the first level of chromatin organization and plays a crucial role in compacting DNA within the nucleus.

140
Q

What is the composition of the histone core in a nucleosome?

A

The histone core of a nucleosome is composed of eight histone proteins. Specifically, it contains two copies each of histones H2A, H2B, H3, and H4, forming an octamer around which the DNA is wrapped.

141
Q

How is DNA wrapped around the histone core in a nucleosome?

A

In a nucleosome, approximately 147 base pairs of DNA are wrapped around the histone octamer core. The DNA makes about 1.65 turns around the core, forming a left-handed superhelix.

142
Q

What is the role of the additional histone protein in a nucleosome?

A

An additional histone protein, known as H1 or the linker histone, is attached to the linker DNA between nucleosomes. This histone helps to stabilize the nucleosome structure and plays a role in higher-order chromatin compaction.

143
Q

What is linker DNA in the context of nucleosomes?

A

Linker DNA refers to the segment of DNA that connects adjacent nucleosomes. It is not wrapped around the histone core and varies in length between different cell types and species. The linker histone H1 binds to this region.

144
Q

How can students study the structure of a nucleosome using molecular visualization software?

A

Students can use molecular visualization software to examine the three-dimensional structure of a nucleosome. This allows them to observe the association between the histone proteins and the DNA, visualize how the DNA wraps around the histone core, and understand the spatial arrangement of the nucleosome components.

145
Q

What was the Hershey-Chase experiment?

A

The Hershey-Chase experiment, conducted in 1952 by Alfred Hershey and Martha Chase, was a pivotal study that provided evidence that DNA, not protein, is the genetic material. The experiment used bacteriophages (viruses that infect bacteria) to determine whether DNA or protein carried genetic information.

146
Q

How was the Hershey-Chase experiment designed?

A

The experiment involved labeling the DNA of some bacteriophages with radioactive phosphorus (32P) and the protein coats of others with radioactive sulfur (35S). These labeled phages were then allowed to infect bacteria. By tracking the radioactivity, the researchers could determine which component (DNA or protein) entered the bacterial cells.

147
Q

What were the key findings of the Hershey-Chase experiment?

A

The experiment showed that when bacteriophages infected bacteria, the radioactive phosphorus (associated with DNA) entered the bacterial cells, while most of the radioactive sulfur (associated with protein) remained outside. This indicated that DNA, not protein, was the genetic material being transferred to the host cells.

148
Q

How did the results of the Hershey-Chase experiment support the conclusion that DNA is the genetic material?

A

The results supported DNA as the genetic material because:
- Only DNA consistently entered the bacterial cells during infection.
- The progeny phages produced contained radioactive phosphorus, indicating that the parental DNA was used to produce new phages.
- Most of the protein coat remained outside the bacterial cells, suggesting it was not essential for genetic inheritance.

149
Q

What technological development made the Hershey-Chase experiment possible?

A

The availability of radioisotopes as research tools made the Hershey-Chase experiment possible. The use of radioactive phosphorus (32P) to label DNA and radioactive sulfur (35S) to label proteins allowed the researchers to track these molecules precisely during the infection process.

150
Q

How does the Hershey-Chase experiment demonstrate the nature of science?

A

The Hershey-Chase experiment demonstrates that technological developments can open up new possibilities for scientific investigations. The availability of radioisotopes as research tools enabled scientists to design and conduct experiments that were previously impossible, leading to significant advancements in our understanding of genetic material.

151
Q

Who was Erwin Chargaff and what did he discover?

A

Erwin Chargaff was a biochemist who discovered that the amount of adenine (A) equals thymine (T), and the amount of guanine (G) equals cytosine (C) in DNA across various species. This became known as Chargaff’s rules.

152
Q

What are Chargaff’s rules?

A

Chargaff’s rules state that in DNA:
- The amount of adenine (A) equals the amount of thymine (T)
- The amount of guanine (G) equals the amount of cytosine (C)
- The ratio of purines (A+G) to pyrimidines (C+T) is always close to 1:1

153
Q

How did Chargaff’s data contribute to our understanding of DNA structure?

A

Chargaff’s data provided crucial evidence that DNA composition was not random. It suggested a complementary base pairing system, which later helped Watson and Crick develop their double helix model of DNA structure.

154
Q

What is the “tetranucleotide hypothesis” and how did Chargaff’s data falsify it?

A

The tetranucleotide hypothesis proposed that DNA consisted of a repeating sequence of the four bases (A, T, G, C). Chargaff’s data showed that the base composition varied between species, falsifying the idea of a universal repeating sequence.

155
Q

How does Chargaff’s work relate to the “problem of induction” and the “certainty of falsification”?

A

The “problem of induction” refers to the difficulty of proving a universal statement true. However, Chargaff’s work demonstrates the “certainty of falsification” by disproving the tetranucleotide hypothesis, showing that even a single contradictory observation can disprove a theory.

156
Q

What is the significance of Chargaff’s rules being consistent across diverse life forms?

A

The consistency of Chargaff’s rules across diverse species suggests a fundamental principle in DNA structure and supports the idea of a common ancestor for all life forms. It also indicates the universality of the genetic code.

Biology HL - IB (29 decks)

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