Genetics a Conceptual Approach Chapter 11

What is supercoiling?

A DNA tertiary structure when DNA helix is subject to overwinding or underwinding of DNA to compact it.

Difference between negative and positive supercoiling?

Negative = under winding in the right hand direction , helps strand separation during replication and transcription(most common); Positive = overwinding, occurs ahead of replication forks.

What enzyme controls supercoiling

Topoisomerases (Type I cuts one strand, Type II cuts both strands).

Nucleoid

bacterial DNA confined to a definite region of the cytoplasm

Bacterial Genomes

contained on a single chromosome made from circular double-stranded DNA not attached to histone proteins

Eukaryotic chromosomes

extremely long linear molecule of DNA very condensed

Euchromatin vs heterochromatin?

both are chromatins(complex of DNA and proteins)

Euchromatin = undergoes normal process of condensation and decodensation where most transcription take place

Heterochromatin = remains highly condensed at the centromeres and telomeres, inactive.

What role do histones play?

proteins that have a positive charge that attracts negative charge on phosphates of DNA

What is a nucleosome?

basic repeating unit of chramatin consisting of a core of 8 histone proteins

When is DNA is more sensitive to DNase I

unbound DNA is more sensitive to DNase I

What role does histone H1 play

binds where the DNA joins and leaves the histone core and helps lock the DNA into place acting as a clamp around the nucleosome

What is chromatin remodeling?

ATP-dependent or chemical modifications to make DNA more or less accessible.

What is a centromere?

a constricted region of the chromosome, is the attachment site for the kinetochore and for spindle microtubules; this chromosome structure is necessary for proper chromosome movement in mitosis and meiosis

What is a telomere?

Repetitive DNA at chromosome ends protecting from degradation. telomeres in most somatic cells shorten each time the cell divides

What is telomerase?

An enzyme that adds telomeric repeats, maintaining chromosome ends.

C-Value

amount of DNA per cell in an organism

Denaturation

studies in which double-stranded DNA was separated and then allowed to reassociate. When double-stranded DNA in solution is heated, the hydrogen bonds that hold the two nucleotide strands together are weakened, and with enough heat, the two strands separate completely

What are transposable elements?

DNA sequences that can move in the genome.

How does mitochondrial DNA (mtDNA) differ from nuclear DNA?

Smaller, circular, few genes, no histones, mainly oxidative phosphorylation. mitochondrial genome typically encodes only a few proteins and a few rRNA and tRNA molecules needed for mitochondrial protein synthesis

What is the endosymbiotic theory?

Mitochondria and chloroplasts originated as free-living bacteria engulfed by early eukaryotes. sequences in mtDNA and cpDNA are more closely related to sequences in the genes of bacteria than they are to those found in the eukaryotic nucleus. All of this evidence indicates that mitochondria and chloroplasts are more closely related to bacterial cells than they are to the eukaryotic cells in which they are now found.

How is organelle DNA inherited?

Typically maternally (from the egg cytoplasm).

Heteroplasmy

Presence of two or more distinct variants of DNA within the cytoplasm of a single cell.

Homoplasy

The presence in multiple groups of a trait that is not inherited from the common ancestor of those groups. Can result from convergent evolution, evolutionary reversal, or parallel evolution.

How does chloroplast DNA (cpDNA) compare to mtDNA?

Larger, circular, encodes more genes (e.g. photosynthesis), often with introns.

Why do mtDNA mutations affect energy-demanding tissues?

Because they impair ATP production, especially in muscles & neurons.

Why is mtDNA used in evolutionary studies?

It is maternally inherited, mutates quickly, and lacks recombination.