Covering Lessons 09-12: DNA in prokaryotes and eukaryotes, transcription, translation, roles of mRNA and tRNA, protein function, and how genotype plus environment influence phenotype.
DNA organisation affects where and how the genetic code is used, transcription copies the code into mRNA, translation converts that code into a polypeptide, and protein function contributes to phenotype.
Do not blur transcription and translation together. mRNA carries codons; tRNA brings amino acids with anticodons.
Environment can influence phenotypic expression without normally changing genotype during ordinary development.
Which statement best describes DNA in most prokaryotic cells?
Why is mRNA important in eukaryotic cells?
Which statement correctly compares mRNA and tRNA?
What directly ensures that amino acids are added in the sequence specified by the mRNA?
Why can a change in amino acid sequence affect phenotype?
Which statement best explains how environment influences phenotype?
Which sequence best represents the pathway from genotype to phenotype in this module?
Which organism-feature pair is correctly matched?
If the DNA template strand has adenine at one position, which base appears in the mRNA formed during transcription?
Which statement best explains why polypeptide synthesis matters biologically?
Compare DNA organisation in prokaryotic and eukaryotic cells, referring to the main DNA form and location. (4 marks)
In most prokaryotic cells, the main DNA is usually one circular chromosome located in the nucleoid region rather than inside a membrane-bound nucleus (1 mark). Many prokaryotes also contain plasmids, which are small circular DNA molecules separate from the main chromosome (1 mark). In eukaryotic cells, DNA is arranged as multiple linear chromosomes (1 mark). These chromosomes are located inside a membrane-bound nucleus and are associated with proteins as chromatin when less condensed (1 mark).
Explain how transcription and translation together allow a gene to influence protein production. In your answer, refer to mRNA, tRNA and the ribosome. (5 marks)
During transcription, a gene is copied from a DNA template strand into mRNA, creating a temporary copy of the coded information (1 mark). The mRNA carries codons that represent the message from the gene (1 mark). In translation, the mRNA is read by a ribosome (1 mark). tRNA molecules with complementary anticodons bring the matching amino acids to the ribosome (1 mark). The ribosome then joins these amino acids into a polypeptide, allowing the information in the gene to influence protein production (1 mark).
Evaluate the statement: "Phenotype depends on genotype, but genes alone do not fully determine phenotype." Use protein function and one environmental example in your answer. (5 marks)
The statement is correct because genotype influences which proteins are produced and how those proteins function (1 mark). Protein function then contributes to phenotype, so genes affect observable characteristics through the effects of proteins rather than directly becoming traits (1 mark). If protein structure changes, function may also change, which can alter phenotype (1 mark). However phenotype is not determined by genes alone because environmental factors can influence how a characteristic is expressed (1 mark). For example, nutrition can influence adult height even when genotype remains the same, showing that phenotype reflects both genotype and environment (1 mark).
Checkpoint 3 complete - IQ3 DNA and Polypeptide Synthesis