Ch 17 - Transcription, Translation: From Genotype to Phenotype - Key Concepts

genetics Ch 17

What is the difference between genotype and phenotype? Provide an example of how a specific genotype can lead to a specific phenotype.

Genotype is the genetic makeup of an organism, while phenotype is the observable characteristics or traits.

• i.e., having the genotype for sickle cell anemia (two recessive alleles for the beta-globin gene) can result in the phenotype of misshapen red blood cells and poor oxygen transport

Explain the concepts of redundancy in the genetic code and its significance.

Redundancy in the genetic code means that multiple codons can code for the same amino acid. This provides a buffer against mutations, as a change in the third nucleotide of a codon may not always alter the amino acid produced.

Describe the role of RNA polymerase in transcription. How does it differ in prokaryotes versus eukaryotes?

RNA polymerase is the enzyme that synthesizes mRNA by using DNA as a template. In prokaryotes, RNA polymerase binds directly to the promoter, while in eukaryotes, transcription factors must first bind the promoter to recruit RNA polymerase II.

Outlines the steps involved in the formation of the RNA polymerase II initiation complex in eukaryotes.

• Formation of the RNA polymerase II initiation complex begins with the binding of TFIID to the TATA box via the TATA binding protein (TBP).

• This creates a pre-initiation complex that allows RNA polymerase II to recognize the transcription start site, along with the help of transcription activation factors (TAFs) and coactivators like the enhanceosome.

What are the functions of the 5’ cap and poly-A tail in mRNA processing?

• The 5’ cap is a modified guanine nucleotide added to the 5’ end of mRNA, protecting it from degradation and helping the ribosome bind.

• The poly-A tail is a string of adenine nucleotides added to the 3’ end, promoting mRNA stability and aiding in export from the nucleus.

Explain the process of splicing, including the roles of introns and exons.

• Splicing is the process of removing introns (non-coding regions) from the pre-mRNA and joining exons (coding regions) together to form mature mRNA.

• This process is facilitated by spliceosomes, which are composed of small nuclear RNAs (snRNAs) and proteins.

Describe the structure and function of tRNA in translation.

• tRNA is a type of RNA that binds to specific amino acids and delivers them to the ribosome during translation.

• Each tRNA has an anticodon that is complementary to a specific codon on the mRNA, ensuring that the correct amino acid is added to the polypeptide chain.

Outline the three main steps of translation: initiation, elongation, and termination.

Initiation

• involves the mRNA binding to the small ribosomal subunit, followed by the binding of the initiator tRNA (methionine) to the start codon (AUG).

Elongation

• involves the addition of amino acids to the growing polypeptide chain, as the ribosome moves along the mRNA

Termination

• occurs when the ribosome encounters a stop codon (UAA, UGA, or UAG), releasing the polypeptide chain

Explain the difference between missense, nonsense, and frameshift mutations.

Missense

• changes one amino acid in the polypeptide sequence

Nonsense

• introduces premature stop codon, resulting in a shortened polypeptide

Frameshift

• insertion or deletion of nucleotides, altering the reading frame and changing all subsequent amino acids

How does the mutation that causes sickle cell anemia affect the structure and function of hemoglobin?

• point mutation changes glutamic acid to valine at the 6th amino acid in the beta-globin chain

• hydrophobic valine causes hemoglobin molecules to stick together, leading to misshapen red blood cells that clog capillaries