Molecular Unit 2

Review questions and definitions

DNA helicase

Enzyme that unqinds the DNA double helix by breaking hydrogen bonds between complementary bases during replication.

DNA ligase

Enzyme that joins DNA fragments together by sealing breaks in the sugar-phosphate backbone.

DNA polymerase

Enzyme that builds new DNA strands by adding nucleotides complementary to the template strand.

DNA repair

Cellular processes that detect and correct damaged or incorrectly copied DNA to maintain genome integrity.

DNA replication

Process of copying DNA to produce 2 identical DNA molecules before cell division.

Homologous recombination

DNA repair process that uses a homologous DNA sequence as a template to accurately repair double-strand breaks.

Lagging strand

New DNA strand synthesized discontinously in short Okazaki fragments because DNA polymerase can only synthesize 5’ to 3’.

Leading strand

New DNA strand synthesized continously in the 5’ to 3’ direction toward the replication fork.

Mismatch repair

Repair system that corrects incorrectly paired nucleotides that remain after DNA replication.

Mutation

A permanent change in the DNA nucleotide sequence that can be inherited by daughter cells.

Nonhomologous end joining (NHEJ)

DNA repair process that directly joins broken DNA ends without using a template; it can introduce small mutations.

Okazaki fragment

A short segment of newly synthesized DNA produced on the lagging strand during replication.

Primase

Enzyme that makes a short RNA primer, providing a starting point for DNA polymerase.

Proofreading

DNA polymerase’s ability to detect and correct incorrectly added nucleotides while DNA is being replicated.

Replication fork

Y-shaped region where DNA is unqound and new DNA strands are being synthesized.

Replication origin

Specific DNA sequence where DNA replication begins and replication forks form.

RNA (ribonucleic acid)

Nucleic acid usually composed of a single strand of ribonucleotides; involved in gene expression and other cellular processes.

Telomerase

Enzyme that extends telomeres by adding repetitive DNA sequences to the ends of chromosomes.

Telomere

Repetitive DNA sequence at the end of a chromosome that protects chromosome ends from damage or loss of important DNA.

Template

Existing DNA strand that provides the base sequence used to build a complementary new strand.

Proteins are folded to fit the shape that they need best. What proteins assist with this folding?

Chaperone Proteins

Which base pair creates a strong 3 hydrogen bond in DNA replication and transcription?

guanine and cytosine

New nucleotides are added to the __ end of a growing DNA strand?

3’

What forms the backbone of DNA?

sugar and phosphate

Which of the following is NOT true about telomeres?

They promotes cell growth when they become too short because the chromosome have space to keep replicating

Which of the following is a characteristic of the replication origin sequence?

multiple per chromosome

Proteins are always synthesized from their _ end toward their _ end.

N-terminal / C-terminal

What is the correct order of the levels of chrmosome packaging, from lowest (least compact) to highest (most compact)?

nucleosome, chromatin fiber, chromatin loop, mitotic chromosome

Which of the following is false regarding histone modifications?

Only a single modification can be makde, allowing minimal control over chromosome structure.

Where does the energy for DNA replication come from?

Nucelotide triphosphates are hydrolyzed to form nucleotide monophosphates.

How does base-pairing enable the information in DNA to be replicated?