DNA as the Genetic Material (Ch. 16)
What experiment showed that DNA, not protein, is the molecule of heredity?
The Hershey–Chase experiment demonstrated that only DNA enters bacterial cells during viral infection..
What model explains how DNA replicates so that each new molecule contains one original strand and one new strand?
The semiconservative model of replication.
Which proteins does DNA wrap around to form nucleosomes?
Histones.
What are the three-letter sequences on mRNA that specify amino acids called?
Codons.
What two modifications are added to eukaryotic mRNA before it leaves the nucleus?
A 5′ cap and a poly-A tail.
If a DNA molecule contains 30% adenine, what percentage is cytosine?
Cytosine makes up 20% of the DNA.
Which enzyme unwinds the DNA double helix during replication?
Helicase.
How many histone proteins form the core of a nucleosome?
Eight histone proteins.
What amino acid is coded by the mRNA codon AUG?
Methionine.
What are the coding and noncoding regions of a eukaryotic gene called?
Exons are coding regions, and introns are noncoding regions removed during RNA splicing.
What is the structure of DNA according to the Watson–Crick model?
DNA is a double helix made of two antiparallel strands with complementary base pairing (A–T and G–C).
What did the Meselson–Stahl experiment prove about DNA replication?
DNA replication is semiconservative, meaning each new molecule has one old and one new strand.
Which histone protein helps fold nucleosomes into a thicker 30-nm fiber?
Histone H1.
Which enzyme synthesizes RNA from a DNA template?
RNA polymerase.
What are the three main types of RNA and their functions?
mRNA carries the genetic code.
tRNA brings amino acids to the ribosome.
rRNA forms ribosomes and catalyzes protein synthesis.
What are the three components of a DNA nucleotide?
A phosphate group, a deoxyribose sugar, and a nitrogenous base.
What is one main difference between DNA replication in prokaryotes and eukaryotes?
Prokaryotes have one origin of replication, while eukaryotes have multiple origins along each chromosome.
What is the difference between euchromatin and heterochromatin?
Euchromatin is loosely packed and active in transcription; heterochromatin is tightly packed and inactive.
What is the function of the promoter region and TATA box in transcription?
They help RNA polymerase and transcription factors bind to DNA to start transcription.
What are the three stages of translation?
Initiation, elongation, and termination.
How does complementary base pairing allow DNA to replicate accurately?
Each base pairs only with its complement (A–T, G–C), ensuring identical copies during replication.
Which four main enzymes are involved in DNA replication, and what does each do?
Helicase unwinds DNA.
Primase adds RNA primers.
DNA polymerase builds new strands.
DNA ligase joins Okazaki fragments.
Why must DNA be both compacted and accessible?
DNA must fit inside the nucleus but remain accessible for replication and transcription.
What are the three stages of transcription, and what happens in each?
Initiation – RNA polymerase binds the promoter.
Elongation – RNA nucleotides are added to the growing strand.
Termination – RNA polymerase releases the completed RNA transcript.
What are two key differences in protein synthesis between prokaryotes and eukaryotes?
In prokaryotes, transcription and translation occur simultaneously in the cytoplasm.
In eukaryotes, transcription occurs in the nucleus and mRNA is processed before translation.