Chapter 5 - DNA and Chromosomes Flashcards
A
A-T base pair
B
G-C base pair
C
deoxyribose
D
phosphodiester bonds
E
purine base
F
pyrimidine base
A DNA strand has a polarity because its two ends contain different bases.
False
G-C base pairs are more stable than A-T base pairs.
True
- The two polynucleotide chains in the DNA double helix are held together by ____________ between the bases on the different strands. All the bases are therefore on the outside/ inside of the double helix, with the sugar-phosphate backbones on the outside/ inside.
hydrogen bonds; inside; outside
A ____________ is often defined as a segment of DNA that contains the instructions for making a particular protein or RNA molecule.
gene
______________is the total amount of genetic information carried in the complete set of chromosomes in an organism.
genome
Each DNA molecule is packaged in a separate ___________________ and the total genetic information stored in the chromosomes of an organism is said to constitute its __________.
chromosome; genome
Each chromosome contains a single long DNA molecule. True or False?
True
Each human cell contains about _________ of DNA; yet the cell nucleus is only _________ in diameter. Tucking all this material into such a small space is the equivalent of trying to fold 40km (24miles) of extremely fine thread into a tennis ball.
2m; 5-8 um
Two copies of each of H2A, H2B, H3, and H4 form a ______ around which the double-stranded DNA helix is twice.
nucleosome core particle
Histones are relatively small proteins with a very high proportion of positively charged amino acids: positive charge helps the histones bind tightly to DNA. True or False?
True
In living cells nucleosomes are packed upon one another to generate regular arrays in which the DNA is more highly condensed, usually in the form of a 30nm fiber. True or false?
True
By light microscopy there are two types of chromatin in interphase nuclei of higher eukaryotic cells: a highly condensed form called _______________ and all the rest, which is less condensed, called __________________
heterochromatin; eurochromatin
During interphase, the chromosomes are extended as long, thin, tangled threads of DNA in the nucleus and cannot be easily distinguished in the light microscope. We refer to chromosomes in this extended state as _________________.
interphase
Chromosomes from nearly all cells are visible during mitosis, where they coil up to form much more condensed structures , called __________________
mitotic chromosome
In eukaryotic _______, DNA is complexed with proteins to form ____. The paternal and maternal copies of human Chromosome 1 are _____, whereas the paternal copy of Chromosome 1 and the maternal copy of Chromosome 3 are nonhomologous chromosomes. Cytogeneticists can determine large-scale chromosomal abnormalities by looking at a patient’s ______.
chromosomes; chromatin; homologous; karyotype
The display of the 46 human chromosomes at mitosis is called the human ___
karyotype
- Given the sequence of one strand of a DNA helix (below), provide the sequence of the complementary strand and label the 5′ and 3′ ends.
5′-GCATTCGTGGGTAG-3′
5′-CTACCCACGAATGC-3′
Be careful with the polarity!
The human genome comprises 23 pairs of chromosomes found in nearly every cell in the body.
How many centromeres are in each cell? What is the main function of the centromere?
46; distribution of chromosomes to daughter cells via mitosis
The human genome comprises 23 pairs of chromosomes found in nearly every cell in the body.
How many telomeres are in each cell? What is their main function?
92; protection and enable completion replication
The human genome comprises 23 pairs of chromosomes found in nearly every cell in the body.
How many replication origins are in each cell? What is their main function?
>200; these DNA sequences direct the initiation of DNA synthesis needed to replicate chromosomes.
Each chromosome is a single molecule of ____ whose extraordinarily long length can be compacted by as much as ___-fold during ___ and tenfold more during _____.
DNA; 1000; interphase; mitosis
This is accomplished by binding to ______ that help package the DNA in an orderly manner so it can fit in the small space delimited by the ______.
proteins; nuclear envelope
The structure of the DNA–protein complex, called __________, is highly ________ over time.
chromatin; dynamic
A cell can regulate its chromatin structure- temporarily decondensing or condensing particular regions of its chromosomes – using ____ and enzymes that ________ histone tails in various ways.
chromatin remodeling complex; modify
The loosing of chromatin to a more decondensed state allows proteins involved in _____, ________, and _______ to gain access to the necessary DNA sequences.
gene expression; DNA replication; DNA repair
Some forms of chromatin have a pattern of histone tail modification that causes the DNA to become so highly condensed that its genes cannot be expressed to produce RNA; such condensation occurs on all chromosomes during mitosis and in the _______________ of interphase chromosomes.
heterochromatin
Interphase chromosomes contain both darkly staining _____and more lightly staining ____.
heterochromatin; euchromatin
Genes that are being transcribed are thought to be packaged in a ____ condensed type of euchromatin.
less
Nucleosome core particles are separated from each other by stretches of ____ DNA.
linker
A string of nucleosomes coils up with the help of _______ to form the more compact structure of the ___ .
histone H1; 30-nm fiber
A __________ model describes the structure of the 30-nm fiber.
zigzag
The 30 nm chromatin fiber is further compacted by the formation of ____ that emanate from a central ______.
loops; axis
Describe the mechanism by which heterochromatin can spread, once it has been established in one region of the chromosome.
Once the initial H3 lysine 9 methylation is established on core histone octamers in one region, the modification attracts a specific set of proteins and other histone-methylating enzymes. These enzymes create the same modification on adjacent histone octamers, which continue to recruit more heterochromatin-specific proteins and enzymes, creating a wave of heterochromatin spreading along the chromosome.
Methylation and acetylation are common changes made to histone H3, and the specific combination of these changes is sometimes referred to as the “histone code.” Which of the following patterns will probably lead to gene silencing?
lysine 9 methylation
DNA and its associated proteins
chromatin
basic unit of chromatin packing
nucleosomes
Nucleosomes consist of ____ pairs of histones, which is ___ total.
4; 8
____ are highly conserved, small, positively charged proteins.
Histones
Histones are ___ bp of DNA.
147
____ chromosomes are the most condensed.
mitotic
___ chromosomes are the less condensed.
interphase
Nucleosomes are further packed into 30 nm fibers via what two ways?
1- Interactions between histone tails;
2- Binding of histone H1
Histone-modifying enzymes work in concert with the chromatin-remodeling complexes to ____ and ____ stretches of chromatin, allowing local chromatin structure to change rapidly according to the needs of the cell.
condense; relax
The pattern of histone modification indicates the status of the nearby ____.
chromatin
What are the two levels of interphase chromatin condensation?
Heterochromatin; Euchromatin
2 co-centric lipid bi-layers
nuclear envelope
allows exchange between cytoplasm and nucleus
nuclear pores
the mesh of intermediate filaments that support the nucleus
nuclear lamina
example of “biochemical neighborhood”
nucleolus
What contains the genes that encode ribosomal RNAs?
nucleolus
The process of sorting human chromosome pairs by size and morphology is called karyotyping. A modern method employed for karyotyping is called chromosome painting. How are individual chromosomes “painted”?
Chromosome painting relies on the specificity of DNA complementarity. Because unique sequences for each chromosome are known, short DNA molecules matching a set of these sites can be designed for each chromosome. Each set is labeled with a specific combination of fluorescent dyes and then allowed to hybridize (form base pairs) with the two homologous chromosomes that contain the unique sequences being targeted
One of the two X chromosomes is inactivated in the cells of mammalian females by ______________ formation
heterochromatin
Each female cell contains two X chromosomes, whereas male cells contain one X and one Y. Because a double dose of X-chromosome products would be lethal, one of these two chromosomes becomes condensed into ______________early in embryonic development. Thereafter, the condensed and inactive state of that X chromosome is inherited in all of the many descendants of those cells.
heterochromatin
