Chapter 5 Flashcards
Linear sequence of nucleotides
ATGC
Structure of DNA
double helix composed of antiparallel DNA strands held by hydrogen bonds between G-C and A-T base pairs
G is paired with
C
A is paired with
T
Genetic material of a eukaryotic cell is contained in a
set of chromosomes
When a gene is expressed, part of its nucleotide sequence is
transcribed into RNA, which are translated to make proteins
In eukaryotic chromosomes, the DNA is
tightly folded
What makes eukaryotic DNA tightly folded
Set of histone proteins and nonhistone chromosomal proteins
pack the DNA into a repeating array of DNA–protein par-ticles called nucleosomes
Histones
The loosening of chromatin to a more decondensed state allows
proteins in gene expression, DNA replication, and DNA repair to gain access to necessary DNA sequences
a high degree of condensation occurs on all chromosomes during
Mitosis and in the heterochromatin of interphase chromosomes
Building block of DNA is
phosphate + sugar (deoxyribose) +base
Four different kinds of bases
Purines: A and G
Pyrimidines: T and C
Bases in DNA are linked together in one strand by
covalent bonds between the 3’-hydroxyl (-OH) group of
one sugar and the 5’-phosphate of another
G-C base pairs use how many hydrogen bonds
3
A-T base pairs use how many hydrogen bonds
2
Which base pairs are more stable
G-C because they require higher temps to melt
The base pairs are located __ the double helix and the phosphate groups on the sugar phosphate backbone are __ charged on the __
inside, negatively, outside
Each strand of the double helix contains a sequence that is
exactly complementary to its partner strand
DNA encodes information in the order or sequence of its nucleotides
A T C G
How do four nucleotides specify the sequence of twenty different amino acids
A two base pair code could only specify 16 (4 x 4) amino acids, A three base pair code could specify 64 (4 x 4 x 4) amino acids
process by which the DNA nucleotide sequence of a gene is transcribed into an RNA nucleotide sequence and then translated into the amino acid sequence of a protein.
Gene expression
The complete set of information in an organism’s DNA is called its
genome
The complex of DNA and protein
chromatin
In interphase chromatin, the DNA is compacted
~500-fold
In humans, __nucleotide base pairs are distributed into _ chromosomes
3.2 x 10^9
24
Homologous chromosomes known as
autosomes
There are how many homologous chromosomes
2 sets of 22
How many sex chromosomes
2, XX or XY
Each human chromosome can be identified using
chromsome painting
- A display of the full set of 46 chromosomes
karyotype
Cytogeneticists use __ to identify chromosomal abnormalities due to chromosome loss or
rearrangements
karyotypes
Approximately how many genes in humans
25,000
Cell replication occurs in
interphase
Chromosome duplication requires __ origins of replication per chromosome
multiple
Proper duplication of the two ends of the chromosome requires
two telomeres
The duplicated chromosomes (chromatids) are held together by their
centromeres
What happens in the M phase or mitosis
the chromosomes become even more compacted to form mitotic chromsomes
The nuclear envelope breaks down and the chromosomes attach to…
the microtubules of the miotic spindle by their kinetochores
centromeric DNA plus specialized centromere binding proteins
kinetochores
What type of DNA occupies discrete territories in the nucleus
Interphase
The genes encoding __ are located on different chromosomes
but these regions cluster together in the __
ribosomal RNAs (rRNAs), nucleolus
site of rRNA synthesis and packaging with ribosomal proteins
Nucleolus
Proteins have two classes in chromosome packing
Histones and non-histone chromosomal proteins
What protein is very abundant and highly basic
Histones (Lysines and arginines)
1st level of chromosome packing is done by the
nucleosome
Nucleosomes are composed of a
Histone octamer
Histone octamer contain
two copies of H2A, H2B, H3, and H4
There are how many turns of DNA/nucleosome in chromosome packing
1.7
Mild treatments that partially unfold DNA reveal
“beads on a string”
To isolare histone octamers…
treat core particles with high salt
What histone tail extends from the core particle
N-terminal
2nd level of chromosome packing is done by
Histone H1
Chromatin are packed
nucleosome
8 protein histone molecules attach to DNA, forming a compact tight loop
Nucleosome
Chromatin remodeling involves what two strategies
ATP-dependent chromatin remodeling complexes and histone modifying enzymes
What chromatin remodeling process repositions the DNA around the nucleosome
ATP-dependent chromatin remodeling complexes
Histone modifying enzymes remodel chromatin by
covalently modify amino acids on the histone tails
Covalent modifications of histones include
addition and/or removal of acetyl, methyl, or
phosphate groups to specific amino acids
Regions of chromosomes that contain active genes are
more extended and seen as euchromatin
Regions of chromosomes with inactive or silent genes are
more compacted and seen as heterochromatin
Example of epigenetic inheritance
one X chromosome is
randomly inactivated by heterochromatin formation in each cell; pattern of X-chromosome inactivation is inherited by daughter cells. Tissues in adult female end up as mosaics
Epigenetic changes allow long lived cells to..
alter their patterns of gene expression from environmental changes.
The pattern of modification of histone tails can determine…
how a stretch of chromatin is handled by the cell
Structure of DNA
Nucleotides, phosphodiester bonds, base pairing
A nucleotide consists of a
Nitrogen base, 5C sugar, and phosphate Groups
The subunits of nucleic acids
Nucleotides
Deoxyribose lacks the __
2’ OH group
From 5’ to 3’: order of nucleotides
GCAT
The helix is __ handed
Right
The negatively charged phosphate groups are
Outside the helix
Bases pair form
Hydrogen bonds inside
Each chromosome has
1 double stranded DNA molecules
Identify individual chromosomes using
DNA hybridization
Chromosome painting enables
Detection of some chromosomal abnormalities
In cancer cells, segments
of chromosomes are
Frequently swapped
Chromosomes are packaged & organized in discrete territories inside the
Nucleus
__ DNA sequence elements are required for chromosome duplication and segregation
3
Each chromosome has what elements
1 centromere
2 telomeres
Multiple origins of replications
the __ attaches the chromosome to the mitosis spindle
Centromere
Chromosome packaging occurs at multiple levels: first three levels
- DNA wraps around nucleosome
- H1 histone packages nucleosomes into fiber
- Non histone chromatin proteins fold the fiber into loops
basic units of chromosome structure
Nucleosokes
__ are conserved, basic (positively charged) proteins
Histones
Binding is a DNA sequence specific: T or F
False
N-terminal tails of the histones in the octamer…
Extend outward
Histones are what charges
Positive
binds linker DNA to change its path as it
exits the nucleosome core particle
H1 histone
What proteins fold the chromatin into a series of loops
Specialized non histone chromosomal proteins
The chromatin loops are further condensed to produce
Interphase chromosome
Changes in chromatin structure allow access to DNA: what two processes
• Chromatin Remodeling Complexes
• Histone Modification
Changes in chromatin structure alter
Gene expression
Changes in chromatin structure can be
Inherited by daughter cells
Interphase chromosomes contain
Euchromatin and Heterochromatin
Compact chromosomes, transcription is inactive in
Heterochromatin
Less compact chromatins, transcription is active in….
Euchromatin
Chromatin remodeling complexes use
ATP
Regulate condensation of
chromatin by locally
Altering the arrangement of nucleosomes on the DNA
Regulating condensation of chromatin makes the DNA either
More or less accessible to dna binding proteins
Modification of amino acids in histone tails create a
Histone code
Modifications often serve as
Protein binding site
highly condensed form of chromatin that is
concentrated at telomeres and centromeres
Heterochromatin
Genes located in regions of heterochromatin are
Inactive or silenced
Euchromatin is associated with
Active genes
Chromatin structure changes with
Differentiation and cell type
Condensed chromatin (heterochromatin) is __ darkly stained than
less condensed chromatin (euchromatin).
More
Changed s in chromatin structure can be
Inherited
Example of change in chromatin structure
X chromosome inactivation in females
As DNA is replicated, Histones…
Form new nucleosomes
Modified histones recruit __ to modify new nucleosomes
enzymes
How can chromatin structure be inherited?
- Parental nucleosomes with modified Histones
- 1/2 of the daughter nucleosomes have modified Histones.
- Parental pattern of histone modification re-established by proteins that recognize the same modifications they catalyze
Nucleotides are joined together by
Phosphodiester bonds
