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DZI Biology and Health Education study materials
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DZI Biology and Health Education practice questions

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Question 1Cell Biology and Molecular Biology

Which organelle is the primary site of ATP synthesis by oxidative phosphorylation in a eukaryotic cell?

  1. Mitochondrion Correct answer.
  2. Golgi apparatus
  3. Smooth endoplasmic reticulum
  4. Lysosome

Explanation

The inner mitochondrial membrane houses the electron transport chain and ATP synthase, which together couple proton gradient dissipation to ATP production. Other organelles perform different roles such as modification, degradation, or lipid synthesis.

Question 2Cell Biology and Molecular Biology

During DNA replication, which enzyme adds nucleotides to the growing strand by matching them to the template?

  1. DNA polymerase Correct answer.
  2. DNA ligase
  3. Helicase
  4. Topoisomerase

Explanation

DNA polymerase reads the template strand and catalyzes phosphodiester bond formation between the incoming nucleotide and the growing chain, using base complementarity to select the correct nucleotide.

Question 3Cell Biology and Molecular Biology

A cell placed in a hypertonic solution will most likely undergo which change?

  1. Swelling and lysis
  2. Shrinking as water leaves Correct answer.
  3. No net water movement
  4. Active pumping of solutes inward

Explanation

In a hypertonic environment the solute concentration outside exceeds that inside, so water moves out of the cell by osmosis down its concentration gradient. Loss of water reduces cell volume and causes shrinkage.

Question 4Cell Biology and Molecular Biology

Which molecule serves as the immediate energy currency of the cell for most metabolic work?

  1. NADH
  2. Pyruvate
  3. Glucose
  4. ATP Correct answer.

Explanation

ATP hydrolysis releases free energy that drives endergonic cellular processes, and ATP is regenerated continuously. It is the direct donor of phosphate groups in most energy-requiring reactions.

Question 5Cell Biology and Molecular Biology

Which phase of the cell cycle is characterized by DNA replication?

  1. S phase Correct answer.
  2. G1 phase
  3. M phase
  4. G2 phase

Explanation

S phase is the synthesis phase in which chromosomal DNA is duplicated so each daughter cell can receive a complete genome. G1 and G2 are gap phases, and M phase is when chromosomes are segregated and the cell divides.

Question 6Cell Biology and Molecular Biology

In a diploid organism, a somatic cell that has completed meiosis II in a gamete-producing lineage would contain which chromosome complement?

  1. Diploid and unreplicated
  2. Diploid and replicated
  3. Haploid and replicated
  4. Haploid and unreplicated Correct answer.

Explanation

Meiosis reduces the chromosome number by half, and the second division separates sister chromatids so each resulting gamete carries single, unreplicated chromosomes. The haploid state is restored at fertilization.

Question 7Cell Biology and Molecular Biology

Which statement best describes the role of the sodium-potassium pump in maintaining membrane potential?

  1. It moves sodium and potassium down their gradients without energy input
  2. It transports only potassium ions across the membrane
  3. It imports three sodium ions and exports two potassium ions per ATP hydrolyzed
  4. It exports three sodium ions and imports two potassium ions per ATP hydrolyzed Correct answer.

Explanation

The pump hydrolyzes ATP to move three sodium ions out and two potassium ions in against their gradients, producing a net outward current that contributes to the resting potential. This electrogenic stoichiometry helps maintain the steep sodium and potassium gradients.

Question 8Cell Biology and Molecular Biology

A mutation changes a codon from UAC to UAA in the middle of an mRNA. What is the most likely consequence for the protein?

  1. Premature termination of translation Correct answer.
  2. No change because the codons are synonymous
  3. A single amino acid substitution
  4. A frameshift affecting all downstream codons

Explanation

UAA is a stop codon, so the ribosome will terminate translation at that position and release a truncated polypeptide. This is a nonsense mutation, distinct from a missense or frameshift change.

Question 9Cell Biology and Molecular Biology

Which feature distinguishes prokaryotic from eukaryotic gene expression?

  1. Prokaryotes use RNA polymerase for transcription
  2. Prokaryotes export mRNA to the cytoplasm before translation
  3. Prokaryotes couple transcription and translation in the same compartment Correct answer.
  4. Prokaryotes splice introns before translation

Explanation

Because prokaryotes lack a nuclear envelope, ribosomes can bind nascent mRNA and begin translation while transcription is still ongoing. Eukaryotes separate these processes spatially by the nuclear membrane.

Question 10Cell Biology and Molecular Biology

Which property of the genetic code allows a single amino acid to be specified by more than one codon?

  1. Degeneracy Correct answer.
  2. Specificity
  3. Universality
  4. Non-overlapping nature

Explanation

Degeneracy means that multiple codons can encode the same amino acid, which buffers some mutations against changing the protein. Specificity refers to a codon determining one amino acid, while universality describes shared usage across organisms.

Question 11Cell Biology and Molecular Biology

In a cross between two heterozygous individuals for a single gene with complete dominance, what is the expected phenotypic ratio among offspring?

  1. 1:1
  2. 9:3:3:1
  3. 1:2:1
  4. 3:1 Correct answer.

Explanation

A monohybrid cross of Aa by Aa yields genotypes in a 1:2:1 ratio, but with complete dominance the heterozygotes resemble the dominant homozygotes, giving a 3:1 phenotypic ratio.

Question 12Cell Biology and Molecular Biology

Which component of the cytoskeleton forms the mitotic spindle and serves as tracks for vesicle transport?

  1. Microtubules Correct answer.
  2. Keratin fibers
  3. Microfilaments
  4. Intermediate filaments

Explanation

Microtubules are hollow polymers of tubulin that assemble into the spindle apparatus and serve as rails for motor proteins moving cargo. Microfilaments and intermediate filaments serve different structural roles.

Question 13Cell Biology and Molecular Biology

An enzyme's reaction rate increases with substrate concentration and then plateaus. What does the plateau indicate?

  1. The enzyme has denatured
  2. All active sites are saturated with substrate Correct answer.
  3. The reaction has become endergonic
  4. The substrate is being consumed faster than supplied

Explanation

At high substrate concentrations the enzyme reaches maximal velocity because essentially all active sites are occupied, so adding more substrate cannot increase the rate. This plateau defines Vmax in Michaelis-Menten kinetics.

Question 14Cell Biology and Molecular Biology

Which process produces genetic variation through exchange of segments between homologous chromosomes?

  1. Crossing over during prophase I Correct answer.
  2. Mitotic crossing over
  3. Independent assortment
  4. Cytokinesis

Explanation

During prophase I of meiosis, homologous chromosomes pair and exchange reciprocal segments at chiasmata, creating new combinations of alleles on a chromosome. Independent assortment shuffles chromosomes but not segments within them.

Question 15Cell Biology and Molecular Biology

A drug blocks the electron transport chain. Which immediate consequence is expected in a mitochondrion?

  1. Increased proton gradient across the inner membrane
  2. Decreased ATP synthesis by ATP synthase Correct answer.
  3. Enhanced glycolysis in the cytosol
  4. Increased oxygen consumption

Explanation

Blocking electron transport prevents protons from being pumped into the intermembrane space, so the proton-motive force collapses and ATP synthase cannot drive ATP production. Oxygen consumption also falls because it is the terminal electron acceptor.

Question 16Cell Biology and Molecular Biology

Which statement about the structure of the plasma membrane is most accurate?

  1. It consists primarily of cellulose and protein
  2. It is a fluid mosaic in which proteins and lipids can move laterally Correct answer.
  3. It is a static bilayer of phospholipids with proteins fixed in place
  4. It is a rigid layer of cholesterol only

Explanation

The fluid mosaic model describes the membrane as a dynamic phospholipid bilayer in which proteins and lipids diffuse laterally. Cholesterol modulates fluidity but does not form the membrane alone.

Question 17Cell Biology and Molecular Biology

Which level of protein structure is defined by the overall three-dimensional shape formed by folding of a single polypeptide chain?

  1. Tertiary structure Correct answer.
  2. Secondary structure
  3. Primary structure
  4. Quaternary structure

Explanation

Tertiary structure describes the folding of the entire polypeptide into a functional three-dimensional conformation stabilized by hydrophobic, ionic, and disulfide interactions. Secondary structure refers to local motifs such as helices and sheets.

Question 18Cell Biology and Molecular Biology

In the lac operon, what happens when lactose is present and glucose is absent?

  1. The operon is expressed only if a mutation occurs in the promoter
  2. The operon is repressed because the repressor binds the operator
  3. The operon is partially expressed because the repressor remains bound
  4. The operon is fully expressed because the repressor is inactivated and cAMP levels are high Correct answer.

Explanation

Lactose binds the repressor and releases it from the operator, while low glucose raises cAMP that activates CAP to stimulate transcription. Together these signals produce strong expression of the operon.

Question 19Cell Biology and Molecular Biology

A cell has a mutation in a tumor suppressor gene that eliminates its function. What is the likely effect on cell cycle control?

  1. Chromosome replication is completely blocked
  2. Apoptosis is triggered in every cell
  3. Checkpoint control is weakened and cells may proliferate abnormally Correct answer.
  4. The cell cycle is arrested at checkpoints

Explanation

Tumor suppressor proteins normally restrain progression through checkpoints or promote repair and apoptosis. Loss of function removes this brake, allowing damaged cells to continue dividing and increasing cancer risk.

Question 20Cell Biology and Molecular Biology

Which experimental observation best supports the semi-conservative model of DNA replication?

  1. Each daughter molecule contains one parental and one newly synthesized strand Correct answer.
  2. Replication occurs only on the leading strand
  3. Each daughter molecule consists entirely of new DNA
  4. Parental DNA is degraded before replication begins

Explanation

The semi-conservative model predicts that each replication product retains one original strand paired with a new one, which was demonstrated in density-shift experiments. This distinguishes it from conservative and dispersive models.

Question 21Cell Biology and Molecular Biology

Which mechanism explains why a single gene can produce multiple distinct protein isoforms in eukaryotic cells?

  1. Random codon reassignment
  2. Replication of the gene multiple times
  3. Alternative splicing of pre-mRNA Correct answer.
  4. Simultaneous transcription and translation

Explanation

Alternative splicing allows different combinations of exons to be joined, so one pre-mRNA can yield several mature mRNAs encoding different isoforms. This expands proteome diversity without requiring additional genes.

Question 22Cell Biology and Molecular Biology

In a signal transduction cascade, what is the principal advantage of a multi-step kinase cascade?

  1. It prevents any signal from reaching the nucleus
  2. It amplifies the signal at each step Correct answer.
  3. It slows the response so cells can recover
  4. It eliminates the need for receptors

Explanation

Each activated kinase can phosphorylate many downstream targets, so a small number of receptor-bound ligands can produce a large cellular response. Amplification also allows regulatory control at multiple nodes.

Question 23Cell Biology and Molecular Biology

Which statement about the relationship between genotype and phenotype is correct?

  1. Environmental factors can influence how a genotype is expressed Correct answer.
  2. Phenotype always equals the dominant allele
  3. Phenotype is determined solely by genotype
  4. Genotype changes as the environment changes

Explanation

Phenotype results from the interaction between genotype and environmental conditions, so the same genotype can produce different phenotypes. Environmental effects on gene expression explain this variation.

Question 24Cell Biology and Molecular Biology

What is the function of ribosomes during gene expression?

  1. They splice introns from pre-mRNA
  2. They replicate DNA before division
  3. They transcribe DNA into mRNA
  4. They translate mRNA into polypeptide chains Correct answer.

Explanation

Ribosomes bind mRNA and use tRNA-delivered amino acids to assemble polypeptides according to the codon sequence. They are the site of translation, not transcription or splicing.

Question 25Cell Biology and Molecular Biology

A cell is treated with a drug that prevents the formation of the mitotic spindle. Which outcome is most likely?

  1. Cells complete mitosis faster than normal
  2. Cells fail to separate chromosomes and division is arrested Correct answer.
  3. Cells fuse their nuclei into one polyploid nucleus
  4. Cells undergo replication without dividing

Explanation

Without a functional spindle, chromosomes cannot attach to microtubules and align at the metaphase plate, so the spindle assembly checkpoint halts progression. This is the basis for several anti-cancer drugs that target microtubules.

Question 26Cell Biology and Molecular Biology

Which enzyme is responsible for adding the RNA primer during DNA replication?

  1. Helicase
  2. Primase Correct answer.
  3. Ligase
  4. DNA polymerase III

Explanation

Primase synthesizes a short RNA primer that provides a free 3'-OH group for DNA polymerase to begin adding deoxyribonucleotides. DNA polymerase cannot initiate synthesis without this primer, so primase is essential for both leading and lagging strand synthesis. Helicase unwinds the DNA, and ligase joins Okazaki fragments later.

Question 27Cell Biology and Molecular Biology

Which cellular process directly requires the hydrolysis of GTP for its progression?

  1. Fatty acid synthesis
  2. Glycolysis
  3. Translation elongation Correct answer.
  4. DNA mismatch repair

Explanation

During translation elongation, GTP hydrolysis is required for the binding of aminoacyl-tRNA to the A site of the ribosome and for the translocation step. These GTP-dependent steps ensure the accuracy and directionality of protein synthesis. Glycolysis and fatty acid synthesis primarily use ATP or NADPH, and mismatch repair uses ATP.

Question 28Cell Biology and Molecular Biology

A cell is placed in a hypertonic solution. Which immediate response is expected to maintain cell volume?

  1. Increased activity of aquaporins to enhance water influx
  2. Breakdown of glycogen to increase intracellular osmoles
  3. Inhibition of ion channels to prevent ion loss
  4. Activation of Na+/K+ pumps to increase intracellular ion concentration Correct answer.

Explanation

In a hypertonic environment, water tends to leave the cell, causing shrinkage. To counteract this, cells can activate ion pumps such as the Na+/K+ ATPase to accumulate ions intracellularly, which increases intracellular osmolarity and draws water back in. This regulatory volume increase helps maintain cell volume and function.

Question 29Cell Biology and Molecular Biology

In eukaryotic cells, alternative splicing can generate multiple protein isoforms from a single gene. Which outcome best explains how this contributes to proteomic diversity?

  1. The mRNA is edited to change individual nucleotides
  2. The gene is duplicated, creating paralogs with new functions
  3. Different exon combinations produce proteins with altered domains and functions Correct answer.
  4. Post-translational modifications create distinct protein variants

Explanation

Alternative splicing joins different combinations of exons, leading to mRNA variants that encode proteins with different domain compositions. This allows one gene to produce multiple protein isoforms with distinct functions, localizations, or regulatory properties. Gene duplication and post-translational modifications are separate mechanisms that also increase diversity but do not directly result from alternative splicing.

Question 30Cell Biology and Molecular Biology

A mutation in the gene encoding a DNA repair enzyme eliminates its activity. Which long-term consequence is most likely for the cell?

  1. Enhanced ability to repair other types of DNA damage
  2. Accumulation of mutations and increased risk of cancer Correct answer.
  3. Immediate cell cycle arrest and apoptosis
  4. Increased rate of DNA replication and cell division

Explanation

DNA repair enzymes correct damage and replication errors; without their activity, mutations accumulate over successive cell divisions. This genomic instability can lead to activation of oncogenes or inactivation of tumor suppressors, increasing cancer risk. The other outcomes are either not direct consequences or contrary to the loss of repair function.

Question 31Genetics and Evolution

Which process produces gametes with half the chromosome number of the parent cell?

  1. Mitosis
  2. Meiosis Correct answer.
  3. Binary fission
  4. Fertilization

Explanation

Meiosis is a reductive division in which a diploid cell undergoes two successive divisions, yielding four haploid gametes. This halving is essential so that fertilization restores the diploid number. Mitosis and binary fission instead conserve the chromosome number.

Question 32Genetics and Evolution

A child has blood type O while both parents have blood type A. Which genotype combination best explains this?

  1. Both parents are heterozygous AO Correct answer.
  2. Both parents are homozygous BB
  3. Both parents are homozygous AA
  4. One parent is AB and the other is AO

Explanation

Type O requires two recessive i alleles, so each parent must contribute one i allele. Parents who are both AO have type A blood yet can pass on i, giving a 25% chance of an O child. Homozygous AA parents cannot transmit i at all.

Question 33Genetics and Evolution

In a population at Hardy-Weinberg equilibrium, the frequency of a recessive allele is 0.3. What proportion of the population is expected to be heterozygous carriers?

  1. 0.42 Correct answer.
  2. 0.21
  3. 0.09
  4. 0.49

Explanation

The carrier frequency is 2pq, where q equals 0.3 and p equals 0.7. Multiplying 2 × 0.7 × 0.3 gives 0.42, so 42% of individuals are expected carriers. The value q² (0.09) describes affected homozygotes, not carriers.

Question 34Genetics and Evolution

Which structural feature of DNA most directly enables semiconservative replication?

  1. The sugar deoxyribose in each nucleotide
  2. The antiparallel orientation of the helix alone
  3. Presence of phosphate groups in the backbone
  4. Complementary base pairing between the two strands Correct answer.

Explanation

Because adenine pairs only with thymine and guanine only with cytosine, each strand carries the information needed to template its partner. This complementarity lets each parental strand direct synthesis of a new strand. The other features are structural but do not specify the sequence.

Question 35Genetics and Evolution

A mutation changes a codon from GAA to GAG, and the resulting protein is unchanged. What type of mutation is this?

  1. Nonsense mutation
  2. Frameshift mutation
  3. Silent mutation Correct answer.
  4. Missense mutation

Explanation

GAA and GAG both code for glutamic acid, so the amino acid sequence is preserved and the mutation is silent. This is possible because the genetic code is degenerate, with several codons per amino acid. Missense and nonsense changes would alter the protein product.

Question 36Genetics and Evolution

Which observation from the fossil record provides the strongest evidence that whales evolved from land-dwelling ancestors?

  1. Whale fossils are found in marine sediments worldwide
  2. Whales have a streamlined body shape
  3. Pelvic bones persist in modern whales without a walking function Correct answer.
  4. Modern whales communicate with complex songs

Explanation

Vestigial pelvic and hind-limb bones in modern whales are remnants of ancestors that used hind limbs for walking. Such reduced structures are best explained by descent with modification from terrestrial mammals. The other observations describe ecology or function but do not indicate ancestry.

Question 37Genetics and Evolution

In a small island population, a hurricane randomly kills most individuals regardless of their traits. Which evolutionary mechanism does this illustrate?

  1. Natural selection
  2. Gene flow
  3. Assortative mating
  4. Genetic drift Correct answer.

Explanation

Genetic drift is a random change in allele frequencies caused by chance events, and its effects are strongest in small populations. Because survival here is unrelated to heritable traits, selection is not acting. Bottlenecks of this kind reduce genetic variation.

Question 38Genetics and Evolution

Two species of lizard live in the same desert but one is active at dawn and the other at midday, and they never interbreed. Which reproductive barrier is involved?

  1. Mechanical isolation
  2. Temporal isolation Correct answer.
  3. Geographic isolation
  4. Hybrid inviability

Explanation

Temporal isolation occurs when species breed or are active at different times, preventing gamete exchange. Here the differing activity schedules keep the populations reproductively separate despite shared habitat. Geographic isolation would require physical separation.

Question 39Genetics and Evolution

A trait shows continuous variation in a population and is influenced by many genes plus environment. Which pattern of inheritance is this?

  1. Polygenic inheritance Correct answer.
  2. Codominance at one locus
  3. Sex-linked inheritance
  4. Complete dominance at a single locus

Explanation

Polygenic traits are controlled by many genes whose effects add up, producing a smooth bell-shaped distribution. Environmental input further smooths the phenotype. Single-locus patterns give discrete classes rather than continuous ranges.

Question 40Genetics and Evolution

A woman is a carrier of an X-linked recessive disorder. Her partner is unaffected. What is the probability that a son will be affected?

  1. 50% Correct answer.
  2. 100%
  3. 25%
  4. 0%

Explanation

Sons inherit their single X chromosome from the mother, and half of her eggs carry the mutant allele. Therefore each son has a 50% chance of being affected. Daughters instead receive a normal X from the father and are at most carriers.

Question 41Genetics and Evolution

Which statement correctly describes the relationship between genotype and phenotype?

  1. Phenotype is determined solely by genotype
  2. Phenotype always reveals the underlying genotype
  3. Genotype changes whenever phenotype changes
  4. Environment can influence how a genotype is expressed Correct answer.

Explanation

Phenotype results from genotype interacting with environmental factors such as nutrition and temperature. Identical genotypes can therefore produce different phenotypes. Genotype also cannot always be read from appearance when dominance or environmental effects mask it.

Question 42Genetics and Evolution

During protein synthesis, which molecule delivers amino acids to the ribosome in the order specified by the mRNA codons?

  1. Messenger RNA
  2. DNA polymerase
  3. Transfer RNA Correct answer.
  4. Ribosomal RNA

Explanation

Transfer RNA molecules carry specific amino acids and match their anticodons to mRNA codons at the ribosome. This pairing ensures amino acids are added in the sequence the mRNA specifies. Ribosomal RNA forms the ribosome itself rather than delivering amino acids.

Question 43Genetics and Evolution

A gene is inserted into a bacterium using a plasmid vector. Which component of the plasmid allows researchers to identify bacteria that took up the plasmid?

  1. Origin of replication
  2. Promoter for the inserted gene
  3. Multiple cloning site
  4. Selectable marker gene Correct answer.

Explanation

A selectable marker, often an antibiotic-resistance gene, lets transformed bacteria survive on selective medium while non-transformants die. This makes successful uptake identifiable. The origin of replication and cloning site serve other functions.

Question 44Genetics and Evolution

Which condition is necessary for a population to remain in Hardy-Weinberg equilibrium?

  1. Strong natural selection
  2. Frequent mutation
  3. Small population size
  4. Random mating Correct answer.

Explanation

Hardy-Weinberg equilibrium requires random mating plus a large population, no mutation, no migration, and no selection. Random mating ensures alleles combine independently of phenotype. The other listed conditions all drive allele frequencies to change.

Question 45Genetics and Evolution

In chickens, a black-feathered bird crossed with a white-feathered bird produces offspring with both black and white feathers on the same bird. Which inheritance pattern is shown?

  1. Epistasis
  2. Complete dominance
  3. Incomplete dominance
  4. Codominance Correct answer.

Explanation

Codominance occurs when both alleles are fully expressed in the heterozygote, so both colors appear side by side. Incomplete dominance would instead blend the traits into an intermediate shade. The patchy dual expression is the key distinguishing feature.

Question 46Genetics and Evolution

A karyotype shows three copies of chromosome 21. Which term describes this condition?

  1. Monosomy
  2. Polyploidy
  3. Deletion
  4. Trisomy Correct answer.

Explanation

Trisomy means three copies of a particular chromosome instead of the usual two, as in trisomy 21. It usually arises from nondisjunction during meiosis. Polyploidy would involve extra sets of all chromosomes rather than one extra copy.

Question 47Genetics and Evolution

A population of insects develops resistance to an insecticide after several years of use. Which explanation best fits evolutionary theory?

  1. Resistant individuals already existed and survived to reproduce Correct answer.
  2. Insects learned to detoxify the chemical during their lifetime
  3. The insecticide was diluted over time, reducing its effect
  4. The insecticide caused mutations that made individual insects resistant

Explanation

Variation in resistance exists before the insecticide is applied, and selection favors those individuals that survive and reproduce. Resistance alleles therefore increase in frequency over generations. Mutation is random and not directed by the chemical.

Question 48Genetics and Evolution

Which type of RNA carries genetic information from DNA in the nucleus to the ribosome in the cytoplasm?

  1. Ribosomal RNA
  2. Messenger RNA Correct answer.
  3. Small nuclear RNA
  4. Transfer RNA

Explanation

Messenger RNA is transcribed from DNA and transports the encoded sequence to the ribosome for translation. Its codons specify the amino acid order. Transfer RNA brings amino acids, while ribosomal RNA builds the ribosome.

Question 49Genetics and Evolution

A couple, each with a sibling affected by an autosomal recessive disorder, are both found to be carriers. What is the probability that their child will be affected?

  1. 25% Correct answer.
  2. 0%
  3. 50%
  4. 75%

Explanation

Two carrier parents each pass the mutant allele with probability one-half, so the chance of an affected homozygous child is one-half times one-half, or 25%. Three-quarters of children are expected to be unaffected, with half of all children being carriers. The sibling history does not change the calculation once carrier status is known.

Question 50Genetics and Evolution

Which feature of the genetic code allows a single amino acid to be specified by more than one codon?

  1. It is non-overlapping
  2. It is universal
  3. It is read in triplets
  4. It is degenerate Correct answer.

Explanation

Degeneracy means several codons can encode the same amino acid, which buffers some mutations. For example, GAA and GAG both specify glutamic acid. Universality and triplet reading are separate properties of the code.