Knowledge Organiser
Part of DNA Genome · GCSE GCSE Biology revision
This topic summary covers Knowledge Organiser within DNA Genome for GCSE Biology. DNA structure, function, and the human genome It is section 12 of 13 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 12 of 13
Practice
25 questions
Recall
25 flashcards
Knowledge Organiser
Key Terms
- DNA — double-stranded helix made of nucleotides; carries genetic information
- Gene — a section of DNA that codes for a specific sequence of amino acids to make a protein
- Chromosome — long, coiled DNA molecule found in the nucleus; humans have 46 (23 pairs)
- Genome — all of the genetic material of an organism
- Complementary base pairing — A pairs with T; C pairs with G (always, no exceptions)
- mRNA — single-stranded messenger molecule copied from DNA in the nucleus; uses uracil (U) instead of thymine (T)
- Mutation — a change in the DNA base sequence
Must-Know Facts
- Humans have 46 chromosomes in 23 pairs
- Four DNA bases: A, T, C, G (RNA replaces T with U)
- A pairs with T; C pairs with G (always)
- Genes code for the sequence of amino acids in a protein
- The sequence of amino acids determines the protein's 3D shape, which determines its function
- mRNA leaves the nucleus through nuclear pores and travels to the ribosome
- Human Genome Project — completed 2003; sequenced all ~3.2 billion base pairs
- Most cells in the body contain the same genome (identical DNA)
Protein Synthesis
- Transcription (nucleus): DNA unzips → one strand used as template → mRNA strand built using complementary bases → mRNA leaves nucleus through nuclear pores
- Translation (ribosome): ribosome reads mRNA in triplets (codons) → each codon specifies one amino acid → amino acids joined in sequence → protein chain folds into 3D shape
- Mutation effect chain: base change → altered codon → different amino acid → different protein shape → protein may no longer function correctly
- Most mutations are neutral (genetic code is degenerate — many codons code for the same amino acid)
Common Marks Lost
- Confusing gene and genome: A gene is one section of DNA coding for one protein; the genome is ALL the genetic material of the organism — never use them interchangeably
- Wrong base pairs: students write A–G or T–C — only A–T and C–G are correct
- Saying mRNA is "the same as DNA": mRNA is single-stranded, uses uracil not thymine, and is a copy of only one gene, not the whole chromosome
- Not stating location: always write "transcription occurs in the nucleus" and "translation occurs at the ribosome" — missing either location loses a mark
- Stopping the mutation chain too early: writing "mutation changes the protein" scores 1/3 marks — the full chain needed is: base change → different amino acid → different protein shape → changed/lost function
- Saying all mutations are harmful: most are neutral because the genetic code is degenerate (multiple codons for the same amino acid)
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Practice Questions for DNA Genome
Which of the following base pairing rules is correct for DNA?
What are the four nitrogenous bases found in DNA?
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