CH7: DNA STRUCTURE & GENE FUNCTION

What evidence shows that DNA is the genetic material?

Experiments by Griffith, Avery, and Hershey-Chase demonstrated that DNA, not proteins, carries genetic information.

What are the components of DNA and its three-dimensional structure?

DNA is made of nucleotides (composed of a sugar, phosphate group, and nitrogenous base). The structure is a double helix.

What is Chargaff’s rule?

A = T and C = G (Adenine pairs with Thymine, Cytosine pairs with Guanine).

What evidence helped Watson and Crick discover DNA's structure?

Rosalind Franklin’s X-ray diffraction images provided key data that led to the discovery of DNA’s double-helix structure.

How do hydrogen bonds contribute to DNA’s structure?

Hydrogen bonds form between complementary nitrogenous bases (A-T and C-G), stabilizing the double helix structure.

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

DNA stores genetic information; RNA is transcribed from DNA and carries the message for protein synthesis; Proteins are synthesized according to RNA’s instructions.

Describe the structural and functional differences between RNA and DNA.

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.

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

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.

Where in the cell does transcription occur?

Transcription occurs in the nucleus in eukaryotes.

What is the role of RNA polymerase in transcription?

RNA polymerase synthesizes RNA from the DNA template strand.

What happens during each stage of transcription?

Initiation: RNA polymerase binds to the promoter region; Elongation: RNA polymerase adds nucleotides to the growing RNA strand; Termination: RNA polymerase reaches the terminator, releasing the RNA transcript.

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

The promoter signals the start of transcription, binding RNA polymerase; the terminator signals the end of transcription, releasing the RNA.

How is mRNA processed after transcription in eukaryotic cells?

5’ capping, Poly-A tail addition, and splicing of introns and exons.

Define the genetic code.

The genetic code is the set of rules by which mRNA is translated into an amino acid sequence in proteins.

Where in the cell does translation occur?

Translation occurs in the cytoplasm at the ribosome.

What happens in each stage of translation?

Initiation: mRNA, tRNA, and ribosomal subunits assemble; Elongation: tRNA brings amino acids to the ribosome; Termination: The ribosome reaches a stop codon.

List the sequence of mRNA transcribed from the following DNA template: A G G C A T A C C T G A G T C.

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.

How do bacterial cells use operons to regulate gene expression?

Bacterial operons allow genes to be regulated together, often via a repressor or activator protein.

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

Chromatin structure, transcriptional control, RNA processing, translation regulation, post-translational modifications.

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

Substitution changes one nucleotide; insertion shifts the reading frame; deletion also causes a frameshift.