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Biology
Grade 11-12
Molecular Genetics and Gene Expression Cheat Sheet
A printable reference covering DNA structure, replication, transcription, translation, mutations, gene regulation, and biotechnology for grades 11-12.
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Molecular genetics explains how DNA stores information, copies itself, and directs the production of proteins. Students need this cheat sheet to connect DNA structure, gene expression, and inheritance at the molecular level. It is especially useful for reviewing replication, transcription, translation, mutations, and gene regulation before tests or labs.
Key Facts
- DNA is made of nucleotides, and each nucleotide contains a phosphate group, a deoxyribose sugar, and one nitrogen base.
- Base-pairing rules in DNA are A pairs with T and C pairs with G, while in RNA A pairs with U and C pairs with G.
- During DNA replication, each original strand acts as a template, so the result is two DNA molecules that each contain one old strand and one new strand.
- DNA polymerase builds new DNA only in the 5' to 3' direction by adding nucleotides to the 3' end.
- Transcription copies a gene from DNA into mRNA using the template strand, and RNA polymerase builds RNA in the 5' to 3' direction.
- Translation reads mRNA codons in groups of three bases, and each codon specifies one amino acid or a stop signal.
- The central dogma is DNA to RNA to protein, which means genetic information is usually transcribed into RNA and translated into a polypeptide.
- Gene expression can be regulated at transcription, RNA processing, translation, or protein modification, allowing cells with the same DNA to perform different functions.
Vocabulary
- Gene
- A gene is a segment of DNA that contains instructions for making a functional RNA or protein product.
- Codon
- A codon is a three-base sequence on mRNA that codes for an amino acid or a stop signal during translation.
- Transcription
- Transcription is the process of making an RNA copy of a DNA sequence.
- Translation
- Translation is the process in which ribosomes use mRNA instructions to assemble amino acids into a polypeptide.
- Mutation
- A mutation is a change in the nucleotide sequence of DNA that may affect RNA, protein structure, or gene regulation.
- Promoter
- A promoter is a DNA sequence where RNA polymerase and transcription factors bind to begin transcription.
Common Mistakes to Avoid
- Confusing replication with transcription is wrong because replication copies the entire DNA molecule, while transcription copies only a gene or region into RNA.
- Writing RNA with thymine is wrong because RNA uses uracil instead of thymine, so A pairs with U during transcription.
- Reading codons from the DNA template strand is wrong because codons are usually written and interpreted from the mRNA sequence.
- Assuming every mutation changes a protein is wrong because some mutations are silent, occur outside coding regions, or do not affect protein function.
- Forgetting directionality is wrong because DNA and RNA polymerases build new strands only in the 5' to 3' direction.
Practice Questions
- 1 A DNA coding strand has the sequence 5'-ATG GCT TAA-3'. What is the mRNA sequence transcribed from this gene region?
- 2 An mRNA sequence is 5'-AUG UUU GGC UGA-3'. How many amino acids are coded before translation stops?
- 3 If a DNA molecule contains 28% adenine, what percentages of thymine, cytosine, and guanine does it contain?
- 4 Two liver cells and two nerve cells in the same person have the same DNA. Explain why they can produce different proteins and have different functions.