In a prokaryotic cell, the single chromosome sits in a region of the cytoplasm without a membrane called the nucleoid.
Missing Word
nucleoid
The nucleoid is the part of a prokaryotic cell's cytoplasm where its chromosome is concentrated. Unlike a nucleus, it is not enclosed by a membrane.
Category: DNA Structure
Question 2
In eukaryotes, DNA wraps around small, positively charged proteins called histones to form a beads-on-a-string structure.
Missing Word
histones
Histones are the proteins that DNA winds around to form nucleosomes. Their positive charge attracts the negatively charged phosphate backbone of DNA.
Category: DNA Structure
Question 3
The five-carbon sugar in the backbone of a DNA strand is deoxyribose.
Missing Word
deoxyribose
Deoxyribose is the pentose sugar of DNA. It lacks the hydroxyl group on the 2' carbon that is present in ribose, the sugar of RNA.
Category: DNA Structure
Question 4
The monomer of DNA, built from a phosphate group, a five-carbon sugar and a nitrogenous base, is called a nucleotide.
Missing Word
nucleotide
A nucleotide is the building block of nucleic acids. In DNA, the four nucleotides differ only in their base: adenine, thymine, guanine or cytosine.
Category: DNA Structure
Question 5
On the lagging strand, new DNA is made as a series of short pieces known as Okazaki fragments.
Missing Word
Okazaki
Okazaki fragments form because DNA polymerase works only in the 5' to 3' direction, which on the lagging strand means moving away from the fork. Each fragment starts with its own RNA primer.
Category: Replication and Repair
Question 6
The enzyme primase synthesizes the short RNA starter sequences that DNA polymerase extends during replication.
Missing Word
primase
Primase builds short RNA primers that supply the free 3' end DNA polymerase needs. The primers are later removed and replaced with DNA.
Category: Replication and Repair
Question 7
The repetitive, noncoding sequences that cap the ends of linear eukaryotic chromosomes are called telomeres.
Missing Word
telomeres
Telomeres are protective repeated sequences at chromosome ends. They shorten a little with each round of replication unless the enzyme telomerase rebuilds them.
Category: Replication and Repair
Question 8
A permanent change in the base sequence of DNA is called a mutation.
Missing Word
mutation
A mutation is any lasting change in the DNA sequence. Many arise from replication errors or damage that repair systems fail to fix.
Category: Replication and Repair
Question 9
When DNA polymerase checks each newly added base and removes a wrong one before moving on, it is carrying out proofreading.
Missing Word
proofreading
Proofreading is the error-checking activity built into DNA polymerase itself. It catches most copying mistakes as they happen, before mismatch repair is needed.
Category: Replication and Repair
Question 10
The process that copies the information in a gene into a molecule of messenger RNA is called transcription.
Missing Word
transcription
Transcription is the first step of gene expression, carried out by RNA polymerase. It proceeds through initiation, elongation and termination.
Category: Transcription and Processing
Question 11
The step of mRNA processing that cuts out intervening sequences and joins the coding sequences together is called splicing.
Missing Word
splicing
Splicing removes introns and links exons into a continuous coding sequence. It must be precise, because even one extra or missing nucleotide would shift the reading frame.
Category: Transcription and Processing
Question 12
The three-base sequence on a transfer RNA that pairs with a matching mRNA codon is called its anticodon.
Missing Word
anticodon
The anticodon is complementary to a codon on the mRNA. This pairing ensures that each tRNA delivers its amino acid to the right place in the growing chain.
Category: Translation
Question 13
The start codon AUG also specifies the amino acid methionine.
Missing Word
methionine
AUG both marks where translation begins and codes for methionine, so new polypeptides start with this amino acid. The initial methionine is often removed after translation.
Category: Translation
Question 14
In eukaryotic cells, ribosomal RNA is made and assembled into ribosome subunits in a dense region of the nucleus called the nucleolus.
Missing Word
nucleolus
The nucleolus is the site of rRNA synthesis and ribosome subunit assembly. The subunits then leave the nucleus to carry out translation in the cytoplasm.
Category: Translation
Question 15
A cluster of bacterial genes transcribed together under the control of a single promoter and operator, such as the lac genes, is called an operon.
Missing Word
operon
An operon groups related genes so they can be switched on or off together. The lac operon, for example, controls the genes a bacterium needs to take up and use lactose.
Category: Gene Regulation