Lecture 14 Flashcards
What is a telomere and what is its function?
Region of repetitive nucleotide sequences at each end of a chromosome that protects the end of the chromosome from deterioration or from fusion with neighboring chromosomes
What is the human telomere sequence?
(TTAGGG)n; n = about 2500 at birth
What happens to a telomere as chromosomes are replicated over and over again?
In each duplication, the telomere is shortened; this rate of shortening is greater in men than in women; this is associated with a shorter life span and an increased incidence of disease
What is a centromere and what is its function?
Constricted region of a chromosome where spindle fibers attach, surrounded by heterochromatin, essential for chromosome separation; provides genome stability and is the site of assembly for kinetochore
In a telomere, which strand is longer? The C rich strand or the G rich strand? What does the longer strand do in a chromosome?
G rich strand is longer; it folds over and pairs with a short stretch of DNA to form a t-loop
What is a kinetochore?
Complex of proteins associated with the centromere of a chromosome, to which the microtubules of the spindle attach during cell division
What is a centriole?
Small, cylindrical cell organelle, located near the nucleus in the cytoplasm of most eukaryotic cells, that divides in perpendicular fashion during mitosis
What is topoisomerase?
Enzyme responsible for adding and removing turns in the coil
What is positive supercoiling?
Occurs when DNA is overrotated; the helix twists on itself
What is negative supercoiling?
Occurs when DNA is underrotated; the helix twists on itself in the opposite direction
What are histones and what is their function?
Highly alkaline proteins found in eukaryotic cell nuclei that package and order DNA; histones have a positive charge and DNA is negatively charged, so that’s why they are attracted
What is the nucleosome?
Basic unit of DNA packaging in eukaryotes, consisting of a segment of DNA wound in sequence around eight core histone proteins; fundamental repeating unit of chromatin
What is linker DNA?
Double-stranded DNA in between two nucleosome cores that, in association with histone H1, holds the cores together
Compare and contrast euchromatin vs heterochromatin
Euchromatin: less condensed, found on arms of chromosomes, contain many genes, replicate throughout S phase, transcribed often, and crossing over occurs often
Heterochromatin: more condensed, found at centromeres and other places, contain few genes, replicate in late S phase, not transcribed often, and crossing over is uncommon
Neutralizing their positive charges would have which effect on the histone proteins?
They would separate from DNA and they would no longer be attracted to each other
What is DNase I sensitivity?
Correlates with gene activity/expression
What are epigenetic changes?
Changes capable of being reversed and often due to environmental factors; don’t change the sequence of the DNA (acetylation, methylation, etc.)
What are chromosomal puffs?
Regions of relaxed chromatin where active transcription is taking place
What is a gene family?
Similar but not identical copies of unique DNA sequences that arose through duplication of an existing gene
What is repetitive DNA and how does it impact the genome?
Stretches of DNA that repeat themselves throughout a genome, either in tandem or interspersed along the genome; can comprise 50% or more of an organisms DNA; includes transposable elements and related sequences vital to the organism
What is microsatellite DNA, what is its function, and how can they be used in forensics?
Consists of a tract of tandemly repeated (adjacent) DNA motifs that range in length from 2-5 nucleotides, and are typically repeated 5-50 times; used for mapping locations within the genome; very useful in forensics because each person has a unique “fingerprint” of microsatellites
