Bio 224 - Chapter 12

Describe the key features of bacterial chromosomes

- Most are circular (some are linear) - Usually one type of chromosomes, but may have multiple copies - Average size ~1 Mbp - Have a few thousand genes - Have one origin of replication - Presence of repetitive sequences

Describe the general features and organization of eukaryotic chromosomes

- Typically linear - Multiple kinds, may occur in sets - ~10s Mbp to 100s Mbp - 100s to > 1,000 genes per chromosome - Multiple origins of replication - Centromere - Telomeres - Repetitive sequences

Define euchromatin

Actively transcribed, loosley compacted (appear as non-stained regions in the nucleus)

What are the components of a single nucleosome? A. About 146 bp of DNA and four histone proteins. B. About 146 bp of DNA and eight histone proteins. C. About 200 bp of DNA and four histone proteins. D. About 200 bp of DNA and eight histone proteins.

B. About 146 bp of DNA and eight histone proteins.

Negative supercoiling may enhance activities like transcription and DNA replication because it A. allows the binding of proteins to the major groove B. promotes DNA strand separation C. makes the DNA more compact D. all of the above

B. promotes DNA strand separation

Define chromatin

Complex of DNA and protein found in eukaryotic cells

The compaction leading to a metaphase chromosome involves which of the following? A. The formation of nucleosomes B. The formation of a 30-nm fiber C. Anchoring and further compaction of the radial loops D. All of the above

D. All of the above

A bacterial chromosome typically contains A. a few thousand genes B. one origin of replication C. some repetitive sequences D. all of the above

D. all of the above

Mechanisms that make the bacterial chromosome more compact include A. the formation of loop domains B. DNA supercoiling C. crossing over D. both A and B

D. both A and B

The chromosomes of Eukaryotes typically contain A. a few hundred to several thousand different genes B. multiple origins of replication C. a centromere D. telomeres at their ends E. all of the above

E. all of the above

Define nucleoid

Each chromosome is highly folded and coiled, and occupies its own space within the cytoplasm of the cell. This region containing the chromosome is called the nucleoid.

Define heterochromatin

Non-active, tightly compacted (appear as darkly-stained region in the nucleus)

Define supercoiling, and describe the general consequences of supercoiling

The formation of additional coils due to twisting forces. Underwinding and overwinding can induce supercoiling. Underwinding can cause fewer turns and the formation of a negative supercoil. Overwinding can cause more turns and the formation of a positive supercoil. Supercoiling makes DNA more compact and decreases the size of the bacterial chromosome, affects DNA function by creating tension on the DNA strands that may be released by DNA strand separation, and may promote DNA strand separation in small regions

Describe the general structure of a nucleosome and 30-nm fiber

The solenoid model proposes that the nucleosomes are stacked symmetrically, while the zigzag model proposes a more irregular, and twisted arrangement of the nucleosomes