Chapter 11 lecture 11 Flashcards
what are shortened telomeres associated with?
shorter life span
- increase incidence of disease
proof: Romanian orphans in orphanages has shorter telomeres than children who grew up with foster parents of biological parents
Topoisomerase
enzyme responsible for adding and removing turns in the coil
supercoiling
one types of DNA tertiary structure
- takes place when the DNA helix is subjected to strain by being overwound or underwound
Positive supercoiling
models of DNA that are overrotated
negative supercoiling
molecules of DNA that are underrotated
A DNA molecule 300 bp long has 20 complete rotation. This DNA is:
a. positively supercoiled
b. negatively supercoiled
c. relaxed
b. negatively supercoiled
DNA has approx. 10 bp per turn
so 100 BP would have 10 turns
plasmid
small circular DNA molecule within a bacterial cell that is physically separate from the chromosomal DNA and replicated independently
- bacteria use them to shuttle genes around
How does bacterial DNA differ from eukaryotic DNA?
Bacterial DNA is not complexed to histone proteins and is circular
Euchromatin
- undergoes the normal process of condensation and decondensation in the cell cycle
- looseley condensed
- replicated throughout S phase
- often transcribed
common crossover
heterochromatin
remains highly condensed state throughout the cell cycle
- at centromeres and telomeres
- replicated late S phase
- cross over not common
histones
small, positively charged proteins of 5 major types
- have high % of Arg and Lys
- package and order the DNA
nucleosome core
basic unit of DNA packaging in eukaryotes consisting of a segment of DNA wound in sequence around 8 core histone proteins
- fundamental repeating unit of chromatin
chromatosome
a histone octamer, 1 molecule of linker histone, and 166 bp of DNA
- the linker histone (H1) is a binding agent, acting like a finger holding down the DNA preventing its release
linker DNA
double-stranded DNA inbetween 2 nucleosome cores that, in association with histone H1, holds the cores together
-30-40 bp
Chromatin
DNA + protein
H1 is the LOCK
how long is the DNA wrapped around the nucleosome?
145-147 bp
Neutralizing their positive charges would have which effect on the histone proteins?
a. they would bind DNA tighter
b. they would separate from the DNA
c. they would no longer be attracted to each other
d. they would cause supercoiling of the DNA
B. they would separate from the DNA
What 2 things help to compartmentalize the genome into domains of different transcriptional potentials?
DNA Methylation
and
Histone modification
Methylation of DNA
tightens it forming heterochromatin
thus low methylation = euchromatin
How many copoes of H2B histon would be found in chromatin containing 50 nucleosomes?
a. 5
b. 10
c. 50
d. 100
d. 100
there are 2 in every nucleosome
polytene chromosome
created by repeated rounds of DNA replication with no cell division
- often in insect salivary gland cells
Chromosomal puffs
regions of relaxed chromatin where active transcription is taking place
- localized swellings of the chromosome
DNase I sensitivity
correlates with gene activity
- an enzyme that digests DNA but function to digest depends on chromatin structure
- more sensitive to unbound DNA
Epigenetic changes
methylation ; capable of being reversed and often due to environmental factors
epigenetics
a heritable alteration of phenotype because of altered chromatin structure (histone modification) or the modification of DNA (methylation) without changing the DNA sequence
- NO DNA SEQUENCE CHANGE
Acetylation of DNA
tends to loosen the DNA
- leads to unwinding
- changes their ability and compliance
centromere structure
region of the chromosome in which spindles attach
- surrounded by heterochromatin, essential for chromosome separation
- acts as site of assembly of the kinetochore
telomere structure
a region of repetitive nucleotide sequences at each end of a chromosome, which protects the end of the chromosome from deterioration or from fusion with neighboring chromosomes
- G-rich strand at the telomere is longer than the C-rich strand
- in mammals the G-rich strand folds over and pairs with a short stretch of DNA to form a t-loop
Human telomere sequence
5’- (TTAGGG)n -3’
-
kinetochore
highly complex multiprotein structure that is responsible for the actual events of chromosome segregation
i.e. binding microtubules and signaling to the cell machinery
What s a characteristic of DNA sequences at the telomeres?
a. one strand consists of guanine and adenine (or thymine) nucleotides
b. they consist of repeated sequences
c. one strand protrudes beyond the other, creating some single-stranded DNA at the end.
d. all of the above
d all the above
What happens to a chromosome that loses it’s centromere?
It will not segregate into the nucleus in mitosis and is usually lost
C value
the amount of DNA per cell
- a quantity termed in eukarotic organisms
denaturation
melting point
renaturation
when slowly cooled single-stranded DNA will collide and hydrogen bonds will form again between complementary base pairs to form dsDNA
Unique sequence DNA
sequences that are present only once or at most a few times in the genome
moderately repetitive DNA
typically consist of DNA sequences from 150-300 bp in length that are repeated many thousands of times
tandem repeat sequeces
type of moderately repetitive DNA
- appear one after another and tend to be clustered at particular locations on the chromosome
interspersed repeat sequences
are scattered throughout the genome
type of moderately repetitive DNA
- remnantants of transposable elements
SINES
short interspersed elements
ex alu sequences
- short sequences that are remnants of retroviruses
LINES
long interspersed elements
ex L1
highly repetitive DNA
short sequences often
most of the genes that encode proteins are found in?
a. unique sequence DNA
b. moderately repetitive DNA
c. highly repetitive DNA
d. all of the above
a. unique sequence DNA
Microsatellite DNA
consists of a tract of tandemly repeated (i.e. adjacent) DNA motifs that range in length from two to five nucleotides, and are typically repeated 5-50 times.
- ex. TATATATATATA
- used for mapping location within the genome
- each person has a unique “fingerprint” of microsatellites which is useful in forensics
endosymbiotic theory
proposes that mitochondria and chloroplasts were once free living bacteria that became internal inhabitants of early eukaryotic cells . over time many of original gene lost because nuclear genes existed or were transferred to the nucleus
What evidence supports the endosymbiotic theory?
- many modern protists are hosts to endosymbiotic bacteria
- mitochondria are similar in size to eubacteria and have their own DNA and ribosomes
- antibiotics tha tinhibit protein synthesis in eubacteria also inhibit protein synthesis in mitochondria
- gene sequences in mtDNA and cpDNA are most similat to eubacterial DNA sequences
Uniparental inheritance
of organelle-encoded traits
animal mtDNA inherited almost exclusively from female parent
replicative segregation
in heteroplasmic cells: organelles segregate randomly into the two progeny cells
in a few organisms, trains encoded by mtDNA can be inherited from either parent. This observation indicated that in these organisms
a. mitochondria do not exhibit replicative segregation
b. heteroplasmy is present
c. both sperm and eggs contribute cytoplasm to the zygote
d. there are multiple copies of mtDNA in each cell
c. both sperm and eggs contribute cytoplasm to the zygote
in its organization, chloroplast DNA is most similar to
a. eubacteria
b. archaea
c. nuclear DNA of plants
d. nuclear DNA of primitive eukaryotes
a. eubacteria
