Lecture 2: DNA, Chromosomes and Genomes 2 Flashcards
Understand regulation of chromatin structure Understand how chromatin structure relates to gene expression and cell cycle changes
What is heterochromatin?
- very condensed chromatin
- late replicating and genetically inactive
- highly concentrated at centromeres and telomeres
- contains very few genes, those that are present are resistant to gene expression
What is position effect?
Activity of a gene depends on position on chromosome. For example, if near heterochromatin, the gene may be silenced
What is euchromatin?
less condensed chromatin that has gene expression
What are the three types of histone modifications?
acetylation of lysines
mono, di, tri- methylation of lysines
phosphorylation of serines
What happens in the acetylation of lysine?
loosens chromatin structure, added by histone acetyl tranferases (HATs); removed by histone deacetylase complexes (HDACs)
What happens in the methylation of lysine?
tightens the chromatin structure, added by methyl transferases; removed by histone remethylases
What is a variant histone protein?
synthesized during interphase and inserted into already formed chromatin
exits for each core histone except H4 and are less well conserved
Creates diversity
What is the histone code read by?
The code reader complex, involves joint recognition of histone tail and covalent modifications
What halts the spread of of chromatin modification?
barrier sequences
What are types of barrier sequences?
physical or enzymatic
What is the HS4 region?
protects the Beta globin locus from silencing, contains a cluster of histone acetylase binding sites
What do centromere sequences consist of?
short repetitive DNA called alpha satellite DNA
Centromeric heterochromatin is defined by ________, not ______
assembly of proteins, DNA sequence
What happens to chromatin during gene transcription?
decondensation, “chromosome puffs”
What happens to the location during gene expression?
actively transcribed genes extend out of its area on an extended chromosome loop
True of false: mitotic chromosomes are highly condensed.
True
What is the purpose of condensation?
disentanglement of sister chromatids to allow separation in cell division and protection of fragile DNA molecule as separation occurs
What does condensin do?
use ATP hydrolysis to coil DNA molecules into chromatids
What are homologues?
genes that are similar in both sequence and function due to common ancestry
How do genomic changes occur?
occur as mistakes in DNA replication and repair
What type of genomic changes can occur?
- base pair substitutions
- duplications
- deletions
- inversions
- translocations
What are reasons for sequence conservation?
not having enough time for mutations since lineage separation
purifying selection
What is purifying selection?
elimination of mutations that interfere with important gene functions
What are pseudogenes?
duplicated gene that has become irreversibly inactive by multiple mutations
Explain the evolution of the globin gene family
- duplication and mutation gave rise to beta and alpha genes
- translocation moved alpha to separate chromosomes
- further duplication and mutation resulted in more specialized beta molecules
By how much do human sequences vary from one another?
0.1%
what are SNPs?
- Single-nucleotide polymorphin.
- points in the genome where one group has one nucleotide and another group has another
- high variation rate
What are CNVs?
- copy number variants
- presence of many duplications and deletions of large blocks of DNA
