NESA Biology DNA and Polypeptide Synthesis

This describes the function of DNA polymerase, the enzyme responsible for synthesizing new DNA strands, not histones.

Initiating replication involves specific initiator proteins and the origin recognition complex, whereas histones are primarily structural proteins involved in packaging.

Joining amino acids to form polypeptides is the function of ribosomes during translation, not histones.

This is incorrect because the sequence clearly contains nucleotides, meaning it must contain codons.

This is incorrect. Three is the number of nucleotides that make up a single codon, not the total number of codons in the given sequence.

This is incorrect. Twelve is the total number of individual nucleotides in the sequence, not the number of three-nucleotide codons.

Carbohydrates, such as glucose, are the substrates being broken down during metabolism, not the catalysts driving the reactions.

Nucleotides are the building blocks of DNA and RNA or act as energy carriers like ATP, rather than functioning as metabolic enzymes.

Lipids are primarily used for long-term energy storage and forming cell membranes, not for catalyzing biochemical reactions.

Ribosomes are the site of protein synthesis and are composed of ribosomal RNA (rRNA) and proteins, not DNA.

Prokaryotic cells lack a membrane-bound nucleus; their DNA is instead located in an irregularly shaped region called the nucleoid.

Vacuoles are organelles primarily used for storage, waste disposal, and maintaining turgor pressure; they do not contain DNA.

An insertion would add a base to the sequence. The comparison shows that a nucleotide has been removed (deleted) rather than added, as the sequence has shifted to the left.

A substitution replaces one nucleotide with another without changing the length of the sequence. The observed change is a frameshift mutation caused by a deletion, which alters the reading frame of all subsequent codons.

This describes a substitution mutation. However, the sequences show that a base was removed entirely, causing the downstream sequence to shift, which characterizes a deletion mutation rather than a substitution.

While thalassemia affects haemoglobin, Tay-Sachs disease is caused by a mutation affecting the enzyme beta-hexosaminidase A, which is unrelated to haemoglobin.

Thalassemia is a genetic disorder affecting haemoglobin, but malaria is an infectious disease caused by a parasite, not a genetic mutation in the haemoglobin protein.

Sickle cell anaemia is caused by a mutation in haemoglobin, but malaria is a parasitic infection, not a genetic disorder found in the amino acid sequence of haemoglobin.

Incorrect. While the nucleus contains the majority of the cell's genetic material, plant cells also have DNA in other semi-autonomous organelles.

Incorrect. This option correctly identifies the nucleus and chloroplasts but incorrectly omits mitochondria, which are present in plant cells and contain their own DNA.

Incorrect. Ribosomes are the cellular machinery for protein synthesis and are composed of ribosomal RNA (rRNA) and proteins, not DNA.

A polygenic trait is controlled by multiple genes, but the prompt specifies that this trait is determined by alleles of a single gene (the $C$ gene).

While the $c^h$ allele may be recessive to other alleles, the temperature-dependent change in fur color specifically demonstrates how the environment affects the expression of the trait, not its dominance or recessiveness.

The scenario describes the effect of temperature on a single gene's product, not an interaction between two different genes (epistasis).

Incorrect. Regulating gene expression is primarily the role of regulatory proteins, such as transcription factors, rather than structural proteins.

Incorrect. Transmitting information between cells is the function of signaling proteins, such as hormones, and receptor proteins.

Incorrect. Catalyzing metabolic reactions is the specific function of enzymes, which are catalytic proteins rather than structural ones.

Nitrite ($NO_2^-$) is an intermediate formed during the reduction of nitrate; it is generally toxic to plants in high concentrations and is not the primary source absorbed for protein synthesis.

While nitrogen is incorporated into organic molecules as ammonium ($NH_4^+$), free ammonia ($NH_3$) is toxic to plant cells, and nitrate is the predominant form of nitrogen available in and absorbed from the soil.

Plants cannot directly utilize atmospheric nitrogen ($N_2$) because they lack the enzyme nitrogenase required to break the strong triple bond between nitrogen atoms; they rely on nitrogen-fixing bacteria or soil nutrients.

Incorrect. While some proteins like collagen provide structural support, enzymes specifically function as biological catalysts rather than structural components.

Incorrect. Transport proteins, such as channel or carrier proteins, move molecules across membranes, whereas enzymes are primarily responsible for catalyzing reactions.

Incorrect. Receptor proteins bind to signaling molecules to transmit signals into the cell, which is a distinct function from the catalytic role of enzymes.

While nuclear chromosomes are linear, the DNA molecule is highly coiled and condensed, meaning the uncoiled DNA is much longer than the chromosome itself.

Nuclear chromosomes are linear, not circular (circular chromosomes are typically found in prokaryotes or organelles), and the uncoiled DNA molecule is longer than the chromosome.

Although the DNA molecule is longer than the condensed chromosome, nuclear chromosomes are linear, not circular.

Mature mRNA has already undergone splicing to remove introns, so it would only contain exons.

Copy DNA (cDNA) is synthesized from mature mRNA using reverse transcriptase, meaning it lacks introns.

While genomic DNA contains both exons and introns, it is typically a double-stranded molecule, whereas the molecule described is single-stranded.

Cells produce thousands of different proteins, such as enzymes, structural proteins, and receptors, so they are not all identical.

While some proteins have a quaternary structure consisting of multiple polypeptide chains, many functional proteins consist of only a single polypeptide chain.

Gene expression is highly regulated in cells; genes are turned on and off in response to the cell's needs rather than being expressed continuously.