CH7: DNA STRUCTURE & GENE FUNCTION

CHAPTER 7: DNA STRUCTURE & GENE FUNCTION

Q: What evidence shows that DNA is the genetic material?
A: Experiments by Griffith, Avery, and Hershey-Chase demonstrated that DNA, not proteins, carries genetic information.

Q: What are the components of DNA and its three-dimensional structure?
A: DNA is made of nucleotides (composed of a sugar, phosphate group, and nitrogenous base). The structure is a double helix.

Q: What is Chargaff’s rule?
A: A = T and C = G (Adenine pairs with Thymine, Cytosine pairs with Guanine).

Q: What evidence helped Watson and Crick discover DNA's structure?
A: Rosalind Franklin’s X-ray diffraction images provided key data that led to the discovery of DNA’s double-helix structure.

Q: How do hydrogen bonds contribute to DNA’s structure?
A: Hydrogen bonds form between complementary nitrogenous bases (A-T and C-G), stabilizing the double helix structure.

Q: What are the roles of DNA, RNA, and protein in the central dogma?
A:

• DNA stores genetic information.

• RNA is transcribed from DNA and carries the message for protein synthesis.

• Proteins are synthesized according to RNA’s instructions.

Q: Describe the structural and functional differences between RNA and DNA.
A:

• DNA is double-stranded, contains deoxyribose sugar, and uses thymine as a base.

• RNA is single-stranded, contains ribose sugar, and uses uracil instead of thymine.

Q: What are the three types of RNA, and how do they contribute to protein synthesis?
A:

• mRNA: carries the genetic code from DNA to the ribosome for translation.

• tRNA: transfers amino acids to the ribosome during protein synthesis.

• rRNA: is a major component of the ribosome, facilitating protein synthesis.

Q: Where in the cell does transcription occur? What is the role of RNA polymerase in transcription? What happens during each stage of transcription?
A:

• Transcription occurs in the nucleus in eukaryotes.

• RNA polymerase synthesizes RNA from the DNA template strand.

• Stages:

  1. Initiation: RNA polymerase binds to the promoter region.

  2. Elongation: RNA polymerase adds nucleotides to the growing RNA strand.

  3. Termination: RNA polymerase reaches the terminator, releasing the RNA transcript.

Q: What are the roles of the promoter and terminator sequences in transcription?
A:

• The promoter signals the start of transcription, binding RNA polymerase.

• The terminator signals the end of transcription, releasing the RNA.

Q: How is mRNA processed after transcription in eukaryotic cells?
A:

• 5’ capping: a cap is added to the mRNA’s 5’ end.

• Poly-A tail: a tail of adenine nucleotides is added to the 3’ end.

• Splicing: introns are removed, and exons are joined together.

Q: Define the genetic code.
A: The genetic code is the set of rules by which mRNA is translated into an amino acid sequence in proteins, with codons specifying which amino acid is added.

Q: Where in the cell does translation occur? What happens in each stage of translation?
A: Translation occurs in the cytoplasm at the ribosome.
Stages:

1. Initiation: mRNA, tRNA, and ribosomal subunits assemble.

2. Elongation: tRNA brings amino acids to the ribosome, which links them into a polypeptide.

3. Termination: The ribosome reaches a stop codon, and the polypeptide is released.

Q: List the sequence of mRNA transcribed from the following DNA template:
DNA template: A G G C A T A C C T G A G T C
A) How many codons are in the mRNA?
B) Translate the mRNA and list the amino acid sequence of the resulting polypeptide.

A:

• The mRNA sequence is: U C C G U A U G G A C U C A G

• There are 5 codons in the mRNA.

B:

• The corresponding amino acid sequence (using the codon chart) is: Serine - Valine - Tryptophan - Threonine - Glutamine

Q: How do bacterial cells use operons to regulate gene expression?
A: Bacterial operons allow genes to be regulated together, often via a repressor or activator protein that controls the operon’s transcription in response to environmental signals.

Q: Describe the points at which eukaryotic cells can regulate gene expression.
A:

• Chromatin structure (e.g., DNA methylation, histone modification)

• Transcriptional control (e.g., transcription factors)

• RNA processing (e.g., alternative splicing, mRNA stability)

• Translation regulation (e.g., initiation factors, microRNAs)

• Post-translational modifications (e.g., protein folding, phosphorylation)

Q: Compare and contrast how substitution, insertion, and deletion mutations can alter a protein.
A:

• Substitution: Changes one nucleotide, potentially altering one amino acid in the protein (may or may not affect function).

• Insertion: Adds one or more nucleotides, shifting the reading frame (frameshift mutation), often altering the entire protein structure.

• Deletion: Removes one or more nucleotides, also causing a frameshift and likely altering protein function.