North Carolina Biology EOC: Molecular Genetics - a complete overview of DNA, protein synthesis, the cell cycle, gene expression, mutations, and biotechnology

What the molecular genetics content demands

The molecular genetics content sits in the Heredity strand and runs from the molecule that stores information (DNA) through how that information is used (protein synthesis), how cells divide (the cell cycle) and specialize (gene expression), how the information changes (mutations), and how we manipulate it (biotechnology). The recurring crosscutting concepts are structure and function (DNA and proteins) and cause and effect (gene to protein to trait).

This guide ties together the matching topic pages, each with its own practice questions: DNA structure and replication, protein synthesis: transcription and translation, the cell cycle and mitosis, gene expression and cell differentiation, mutations and genetic variation, and biotechnology and DNA technology.

DNA structure and replication

DNA is a double helix of two strands of nucleotides (a sugar, a phosphate, and a base). The bases pair by A-T and C-G, so the strands are complementary. The order of bases is the genetic code. DNA copies itself by semiconservative replication: the strands separate and each acts as a template for a new complementary strand, giving two identical molecules. Base pairing makes the copy accurate.

Protein synthesis

A gene's code becomes a protein in two steps. Transcription (in the nucleus) copies DNA into mRNA (RNA uses uracil for thymine). Translation (at the ribosome) reads the mRNA in codons of three bases; tRNA brings the amino acid matching each codon, building the protein. To count amino acids, divide the number of mRNA bases by three.

The cell cycle and mitosis

The cell cycle is mostly interphase (growth and DNA copying), then mitosis (dividing the nucleus) and cytokinesis (dividing the cytoplasm). The result is two genetically identical daughter cells with the full chromosome number, used for growth, repair, and replacing cells. Uncontrolled division, when the cell-cycle controls fail, is cancer.

Gene expression and differentiation

Every body cell has the same DNA, but cells differ because different genes are expressed in each. Expressed genes make proteins that give a cell its structure and function. The process of becoming a specialized cell is differentiation, and stem cells are unspecialized cells that can divide and differentiate. Loss of control over the cell cycle links back to cancer.

Mutations

A mutation is a change in the DNA base sequence: substitution, insertion, or deletion. Insertions and deletions cause a frameshift that changes every codon after them, so they are often more damaging. A mutation can be harmful, beneficial, or neutral, depending partly on the environment. Only gamete mutations are inherited, and mutations are the only source of new alleles, the raw material for evolution.

Biotechnology

Genetic engineering transfers a gene between organisms, creating a GMO (bacteria making human insulin is the classic case, possible because the genetic code is universal). Gel electrophoresis separates DNA fragments by size, used in DNA fingerprinting. Selective breeding and cloning are older and newer tools, and CRISPR edits DNA precisely. The standard asks you to weigh benefits against ethical and safety concerns.

Check your knowledge

A mix of recall and reasoning questions covering the molecular genetics content. Attempt them under timed conditions, then check against the solutions.

1. State the base-pairing rule in DNA. (1 mark)
2. Write the complementary DNA strand to A T C G G A. (1 mark)
3. State what transcription produces and where it occurs. (2 marks)
4. A piece of mRNA has 9 bases. State how many amino acids it codes for and why. (2 marks)
5. State the outcome of mitosis (number of cells, genetic content). (2 marks)
6. Explain how two cells with the same DNA can be different cell types. (2 marks)
7. Name the three types of point mutation and state which cause a frameshift. (2 marks)
8. State what gel electrophoresis separates DNA fragments by. (1 mark)
9. Bacteria are given the human insulin gene. Name the biotechnology used and give one benefit. (2 marks)