Question

holt mcdougal biology chapter 8 section 6 pages 234 - 237

1. what is the difference between promoters and operators?
2. explain how the lac operon is turned on and off like a switch.
3. describe how gene expression is regulated at many points in eukaryotic cells.
4. name two internal and two external factors that affect gene expression.

holt mcdougal biology chapter 8 section 7 pages 238 - 241

1. differentiate between a point mutation and a frameshift mutation.
2. how are phenotypes impacted by mutations?
3. why arent mutations in body cells passed on to offspring?

Explanation:

• binding sites for RNA polymerase to start transcription. Operators are DNA regions where repressor proteins bind to regulate transcription.

1. In the lac operon, when lactose is present, it binds to the repressor, changing its shape so it can't bind to the operator, turning the operon on. When lactose is absent, the repressor binds to the operator, turning the operon off.
2. In eukaryotic cells, gene expression is regulated at DNA - packing level, transcription initiation, mRNA processing, mRNA transport, translation, and post - translation modification.
3. Internal factors: transcription factors, hormones. External factors: light, temperature.
4. A point mutation changes a single nucleotide. A frameshift mutation occurs when nucleotides are inserted or deleted, shifting the reading frame of the genetic code.
5. Mutations can change the amino acid sequence of a protein, which may alter the protein's structure and function, thus impacting the phenotype.
6. Offspring inherit genetic material from gametes (sperm and egg). Mutations in body (somatic) cells are not present in gametes, so they are not passed on to offspring.

Answer:

1. Promoters are binding sites for RNA polymerase to start transcription; operators are binding sites for repressors to regulate transcription.
2. Lactose presence/absence determines binding of repressor to operator, turning the lac operon on/off.
3. Regulated at DNA - packing, transcription, mRNA processing, transport, translation, and post - translation.
4. Internal: transcription factors, hormones. External: light, temperature.
5. Point mutation: single - nucleotide change. Frameshift mutation: insertion/deletion shifts reading frame.
6. Mutations can change protein structure/function, impacting phenotype.
7. Somatic cell mutations are not in gametes, so not passed to offspring.