Chromosomes Flashcards
homologous recombination
DNA segments that are similar to each other break and rejoin to form a new combination
site specific recombination
nonhomologous DNA segments are recombined at specific sites
transposable elements
small segments of DNA that move themselves to multiple locations within chromosomal DNA
harlequin chromosome
reveals recombination after BrdU staining between sister chromatids
holliday junction
the mechanism of crossing over between two homologous chromosomes
viral integration
some virus integrate DNA into host chromsome by site specific recombination
antibody recombination
site specific recombination of v and j regions for light chain; v, d, and j regions for heavy chain variable
recombination signal
recognition site for site specific recombination between the v and j regions
NHEJ proteins
non-homologous end-joining proteins; connection phase of V(D)J recombination
homologous chromosomes
homologs - the maternal and paternal chromosomes of a pair
human karyotype
cytogeneticists use the 46 human chromosomes displayed at mitosis to view abnormalities
human genes
approximately 25,000
Avg gene size
27,000 nucleotide pairs or 9,000 amino acids
Avg # exons/gene
10
nuclease
breaks down DNA by cutting between the nucleosomes
histone octamer
two molecules each of H2A, H2B, H3, and H4
Histone
high salt dissociates the ionic (salt) linkages between DNA and histones
histone deacetylase complex
HDAC-removes acetyl groups (COCH3) from lysine and removing gene expression proteins
histone acetyl transferase
HAT-commonly adds acetyl group to lysine on histones and recruits proteins that turn on gene expression. Also adds acetyl to transcription factors
histone methyl transferase
adds methyl groups
acetylation vs methylation
A methylated lysine cannot be acetylated and vice versa
histone covalent modifications
acetylation+methylation of lysines, phosphorylation of serine+threonine, methylation of arginine, ubiquityl+sumoyl+biotin of lysine
Histone synthesis
synthesized during S phase
histone variants
synthesized during interphase binding to specific chromatin sites
histone code potential
signals that stretch of chromatin is newly replicated, chromatin damaged or needs repair
reader-writer complex
A gene regulatory protein will recruit a histone modifying enzyme, which attracts a code reader protein causing a repetitive effect
barrier sequence
cluster of proteins such as histone acetylase enzymes blocks chromatin condensing
lampbrush chromosomes
extended meiotically paired chromosomes in amphibian oocytes allows viewing of interphase chromosomes
polytene chromosome
all homologous chromosomes are side by side and allow viewing of dark heterochromatin DNA bands; first seen drosophila
Chromosome puff
duirng transcription, the DNA puffs out on a polytene chromosome
Heterochromatin types
different types of heterochromatin allow different levels of compaction
nucleus subcompartments
cajal bodies, nucleolus, and repair factories create specialized environments in nucleus
homologous gene
genes similar in nucleotide sequence and function because of common ancestry
pseudogene
one copy of a duplicated gene can be seen to have become irreversibly inactivated by multiple mutations
Globin gene duplications
The globin gene family has duplicated and diverged over eveolution from a single globin to variety of globins during development
point mutation
change in a single base pair within the DNA
base substitution
one base is substituted for another base
transition mutation
base substitution where a pyrimidine is substituted for a pyrimidine or purine for a purine
transversion mutation
base substitution where a pyrimidine is substituted for a purine
silent mutation
base mutation that does not alter the amino acid sequence even though the nucleotide has changed
missense mutation
base substitution where amino acid sequence changes from one amino acid to another with one nucleotide change
nonsense mutation
change from a normal codon to a stop codon
operon polarity
nonsense mutation occurs in a bacterial operon it might inhibit downstream gene expression
frameshift mutation
addition or deletion of a number of nucleotides not divisible by 3
neutral mutation
silent mutation and when a missense mutation has not detectable effect on protein
wild type genotype
relatively prevalent genotype and if multiple alleles could have mutliple wild type alleles
mutant allele
a rare mutation that changes the wild type genotype by altering DNA gene sequence
conditional mutants
affect the phenotype under a defined set of conditions such as temperature sensitivity
suppressor mutations
a second mutation that affect the phenotype expression of the first mutation by affecting protein
intragenic suppressor
when the second mutation is within the same gene (such as LacY) as the first mutation
intergenic suppressor
suppressor mutation the is in a different gene from first mutation
promoter mutations
up promoter or down promoter mutations affect transcription
splice mutation
mutations in eukaryotic genes can alter splice junctions and affect the order and/or number of exons that are contained within mRNA
trinucleotide repeat expansion
repeated sequence of 3 nucleotides can readily increase in number from one generation to the next
position effect mutation
Genes may be moved next to regulatory sequences such as promoters or heterochromatin regions
genetic mosaic mutation
somatic regions that are genotypically different from each other
spontaneous mutation
changes in DNA structure that result from abnormalities in biological processes
induced mutation
abnormalities caused by environmental agents
spontaneous mutation cause
molecular change in DNA caused by depurination, deamination, tautomeric shift
depurination
removal of a purine (adenine, guanine) from DNA which breaks covalent bond between deoxyribose and purine causing apurinic site
deamination
removal of an amino group from cytosine which produces uracil or changes 5-methylcytosine to thymine
T+G tautomers
common form is keto form and rare is enol form
A+C tautomers
common form is amino form and rare is imino form
tautomeric shift
if the base tautomers shift right before DNA replication a mutation can occur
deamination mutagen
nitrous acid replaces amino groups with keto groups in bases
hypoxanthine
deamination of adenine. hypoxanthine pairs with cytosine
5-bromouracil
base analogue that has tautomeric shifts commonly
UV mutagen
thymine dimers between bases in DNA
photolyase
in plants and yeast thymine dimers are split
alkyltransferase
protein removes methyl or ethyl groups from guanine bases mutated by alkylating agents
base excision repair
enzyme DNA glycosylase that recognizes abnormal bases and cleaves the bond to sugar
nucleotide excision repair
direct repair of nucleotides
homologous recombination repair
repairs double stranded breaks by exchanging DNA between broken and unbroken sister chromatids during S and G2 phase
nonhomologous end joining
repairs double stranded breaks by filling DNA gaps and ligates them together
bacteria origin of replication
bacterial chromosomes have a single origin of replication and proceeds bidirectionally
