DNA and polypeptide synthesis + Genetic variation

What is a plasmid?

A small, separate ring of non-chromosomal DNA found in prokaryotes that often carries useful genes, like antibiotic resistance, which are not strictly required for everyday survival.

What is the main difference between how DNA is packaged in prokaryotes and eukaryotes?

Prokaryotic DNA is circular, supercoils, and loops around a central scaffold protein to form a nucleoid. Eukaryotic DNA is linear and wraps tightly around histone proteins to form bead-like structures called nucleosomes.

Why does mitochondrial DNA only trace maternal ancestral lines?

During fertilization, the sperm contributes almost no cytoplasm. The egg cell supplies all the cytoplasm and its organelles, including the mitochondria, so your mitochondrial DNA comes entirely from your mother.

A scientist discovers a new animal that has twice as many unique proteins as it has genes. How does alternative splicing explain this scenario?

When pre-mRNA is processed, its coding segments can be stitched together in different combinations. This allows a single gene to code for multiple distinct variations of a protein.

What is gene expression?

The process where the instructions in a gene's DNA sequence are switched on and used to create a functional cellular product, like a protein.

What is the main difference between introns and exons?

Exons are the coding sequences of DNA that get expressed as proteins, while introns are non-coding segments that are cut out before translation.

What is the underlying mechanism behind epigenetics?

Chemical tags like methyl or acetyl groups attach to DNA or histones, changing how tightly the DNA is wound. This controls whether genes are accessible for transcription without changing the actual DNA sequence.

A pink-flowered hydrangea plant is moved from a garden with alkaline soil to a garden with highly acidic soil. How will this environmental change affect the plant's phenotype?

The plant will start producing blue flowers because the soil's acidity changes how its flower color genes are expressed.

What is the main difference between the effects of DNA methylation and DNA acetylation?

Methylation packs DNA tightly around histones to turn off gene expression, while acetylation loosens the DNA to make it accessible for transcription.

What is a polypeptide?

A linear chain of many amino acids linked together by peptide bonds that forms the basic structural unit of a protein.

Why does a single amino acid substitution, like the one in sickle cell anemia, completely change how a protein functions?

Changing an amino acid alters the chemical bonding forces, which disrupts how the polypeptide chain folds into its specific three-dimensional shape.

An Arctic fox has a gene for dark fur, but its coat turns white during winter. How does this happen if its genotype hasn't changed?

Environmental factors like temperature or daylight interact with the fox's genotype, switching its fur pigment genes on or off to change its physical appearance.

What is the main difference between fibrous and globular proteins?

Fibrous proteins are long, water-insoluble, and provide structural support like hair and skin. Globular proteins are spherical, water-soluble, and perform functional tasks like transport or catalysis.

Why does crossing over during meiosis lead to genetic variation?

Homologous chromosomes pair up and physically swap pieces of genetic material, which breaks up linked genes and creates brand new combinations of maternal and paternal alleles.

If a mutation occurs in a person's skin cell during their lifetime, why won't their future children inherit this mutation?

The mutation happened in a somatic body cell, not a germline cell undergoing meiosis, so it cannot be passed down through gametes during fertilization.

What is the main difference between primary and secondary protein structure?

Primary structure is the basic linear sequence of amino acids in a chain. Secondary structure is the local folding, like a spiral helix or pleated sheet, formed by hydrogen bonding.