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IB Biology SL/Notes/A1.2 Nucleic acids

IB Biology SLA1.2 Nucleic acidsNotes

Locate Genetic Material

DNA is the genetic material of living organisms. In eukaryotes it is found mainly in chromosomes, with extra DNA in mitochondria and chloroplasts. Some viruses use RNA, but the syllabus does not treat viruses as living organisms.

DNA is the genetic material of all living organisms.
DNA occurs in chromosomes and also in mitochondria and chloroplasts.
Some viruses use RNA, but viruses are not considered living organisms.

Which statement is safest for this syllabus?

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Build a Scoring Nucleotide

A nucleotide scores as three named parts: phosphate group, pentose sugar, and nitrogenous base. In the diagram, the sugar is the hub joined to the phosphate and the base.

After naming the three parts, use the sugar and base set to separate DNA from RNA.

DNA nucleotides use deoxyribose and the bases A, T, G, and C.
RNA nucleotides use ribose and the bases A, U, G, and C.
Purines are A and G; pyrimidines are C, T, and U.

Label the nucleotide before choosing whether it belongs to DNA or RNA.

Label
Labels
5

Use this when a question asks for nucleotide structure, DNA/RNA comparison, or base classification.

A nucleotide has a phosphate group, pentose sugar, and nitrogenous base.
DNA uses deoxyribose and thymine; RNA uses ribose and uracil.
A and G are purines; C, T, and U are pyrimidines.

Use this when a question asks for nucleotide structure, DNA/RNA comparison, or base classification.

Calling a nitrogenous base a nucleotide, or forgetting the phosphate group.

Link Nucleotides Into a Backbone

Nucleotides become a polynucleotide by condensation. The sugar of one nucleotide bonds to the phosphate of the next, forming a continuous covalent sugar-phosphate backbone. The bases project from that backbone, so their order can carry information.

Condensation reactions link nucleotides by sugar-phosphate bonds.
The sugar-phosphate backbone is a continuous covalent chain.
Bases project from the backbone and carry sequence information.

The backbone gives structural continuity; the base order carries the code.

Match each structural part to what it does.

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Reasons
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Match each structural part to what it does.

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condensation reaction
sugar-phosphate backbone
nitrogenous bases

Use Bases as a Code

Practice

The code is in the order of bases, not the repeating backbone. DNA uses A, T, G, and C; RNA uses A, U, G, and C. Protein synthesis reads bases in triplets called codons, and RNA molecules carry out different jobs in that process.

Genetic information lies in the order of nitrogenous bases.
DNA uses A, T, G, C; RNA uses A, U, G, C.
RNA is a single-stranded polynucleotide formed by condensation.
RNA contains ribose and the bases A, U, G, and C.
mRNA, tRNA, and rRNA have different roles in protein synthesis.

The code comes from base order, and different RNA molecules help the cell read that code into protein.

Match each RNA/code term to its role.

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Reasons
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Match each RNA/code term to its role.

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base sequence
triplet codon
mRNA
tRNA
rRNA

Fix DNA Model Errors

DNA is two antiparallel polynucleotide strands in a double helix. Bases point inward from the sugars and pair by hydrogen bonds: A with T, and G with C. When drawing the model, attach bases to sugars, not phosphates.

DNA has two antiparallel polynucleotide strands in a double helix.
Complementary bases pair by hydrogen bonding: A-T and G-C.
Draw bases attached to sugars, not phosphates.

A correct SL model shows where bases attach and which bases pair.

A student draws bases attached to phosphate groups and says any two bases can pair. Spot the two errors.

Spot Errors

A student draws bases attached to phosphate groups and says any two bases can pair. Spot the two errors.

Choose
Bases are attached to phosphate groups.
Any two bases can pair.
The two DNA strands are antiparallel.

Distinguish DNA From RNA

Practice

DNA and RNA are both nucleic acids, but the exam contrast is simple: strand number, sugar, base, and typical length. DNA is usually double-stranded, uses deoxyribose and thymine, and is longer. RNA is usually single-stranded, uses ribose and uracil, and is shorter.

DNA is usually double-stranded; RNA is usually single-stranded.
DNA uses deoxyribose and thymine; RNA uses ribose and uracil.
RNA molecules are usually much shorter than DNA molecules.

Sort each statement into DNA, RNA, or both.

Sort
Unsorted
5
DNA
0
RNA
0
both
0

Apply Complementary Base Pairing

Practice

Complementary base pairing is the copying rule. In DNA, A pairs with T and C pairs with G. In RNA, A pairs with U and C pairs with G. Because one strand predicts its partner, base pairing supports DNA replication, transcription, and translation.

A pairs with T in DNA and U in RNA; C pairs with G.
Complementary base pairing enables accurate DNA replication.
It also enables transcription and translation in gene expression.

A DNA template contains A-C-G. Which complementary RNA sequence fits the rule?

Choose

Explain DNA Information Capacity

DNA stores enormous information because base sequences can vary in length and order. Genome size and gene number vary widely, so they should not be treated as a simple scale of organism complexity.

DNA can vary in length and in base sequence.
Genome size and gene number vary widely between organisms.
Base-sequence diversity gives DNA enormous information-storage capacity.

DNA sequences can vary enormously, but the code used to read most codons is conserved across life.

The 64 codons have nearly the same meanings across life.
Conserved genes for transcription, translation, and ribosomes support common ancestry.
Synonymous mutations can preserve amino acid sequences.

The genetic code is also conserved. The 64 codons have nearly the same meanings across life, and conserved genes for transcription, translation, and ribosomes support common ancestry. Synonymous mutations can preserve amino acid sequences.

The 64 codons have nearly the same meanings across life.
Conserved genes for transcription, translation, and ribosomes support common ancestry.
Synonymous mutations can preserve amino acid sequences.

Match the claim to the evidence or reason.

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Reasons
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Match the claim to the evidence or reason.

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DNA has huge information capacity
Genome size is not a simple complexity scale
Genetic code supports common ancestry
Some mutations do not change the protein

Retrieve The Core Rules

Review

The core chain is: nucleotides have three parts; condensation builds the sugar-phosphate backbone; base order stores information; complementary pairing lets DNA copy and express that information.

Nucleotide parts: phosphate, pentose sugar, nitrogenous base.
Polymer rule: condensation forms a sugar-phosphate backbone.
Code rule: base order stores information and triplet codons specify amino acids.
Pairing rule: A-T or A-U, and C-G, enables replication and gene expression.
DNA/RNA contrast: DNA uses deoxyribose/T and is usually double-stranded; RNA uses ribose/U and is usually single-stranded.

Match each core rule to what it explains.

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Reasons
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Use this when a question asks how nucleic acid structure stores or transmits genetic information.

Name nucleotide parts and the sugar-phosphate backbone.
Explain that base order stores information.
Use complementary base pairing to explain copying or expression.
Contrast DNA and RNA only when the question asks for it.

Use this when a question asks how nucleic acid structure stores or transmits genetic information.

Nucleic acids are polymers of nucleotides, each with a phosphate, pentose sugar, and nitrogenous base. Condensation links nucleotides into a sugar-phosphate backbone, while the order of bases stores genetic information. Complementary base pairing, such as A-T in DNA and C-G, allows accurate replication and supports transcription and translation.

The common loss is listing parts without explaining how base order or base pairing stores and transfers information.