Chapter 5 Flashcards
what is a nucleotide composed of?
a sugar-phosphate covalently linked to a base
how are nucleotides linked?
covalently linked together into a polynucleotide chain, with sugar-phosphate backbone from which the bases extent
what is a DNA molecule composed of?
2 polynucleotide chains (DNA strands)
how are DNA strands held together?
by hydrogen bonds between paired bases
how many h-bonds are formed between A & T?
2
how many h-bonds are formed between G & C?
3
how many rings do purines have?
2
how many rings do pyrimidines have?
single
what is a base pair?
purine-pyrimidine pair
the 3’ end carries what?
an unlinked -OH group attached to 3’ position on sugar ring
the 5’ end carries what?
a free phosphate group attached to 5’ position on sugar sing
how many base pair per turn?
10
what is chromatin?
combination of DNA and proteins that make up the contents of the nucleus of a cell
what does chromosome painting do?
expose to a collection of fluorescent dye-labeled DNA
what is a karyotype?
homologous chromosomes that are numbered and arranged in pairs
what is inherited ataxia?
a disease that deteriorates motor skill
what does ataxia do to chromosome 12?
one normal and one abnormal, longer with material from chromosome 4
what strand encodes the information to make protein of RNA molecules?
coding strand, can be either strand
in humans majority of chromosome don’t carry critical info
junk DNA
what happens during interphase?
cell is actively expressing genes and DNA is replicated
what happens during M phase?
chromosomes condense, gene expression ceases, and mitotic spindle forms from microtubules and other proteins.
what is a nuclear envelope?
it forms around each chromosome set and the cell divides to produce 2 daughter cells in final step of M phase
where are the multiple origins of replication on a chromosome?
1 centromere, and 2 telomeres
during interphase, DNA replicates at the origin of replication in which direction?
bi-directionally from the origins across the chromosome
what do telomeres contain? why?
repeated nucleotide sequences that enable the ends of chromosomes to be replicated, also cap the end.
why do telomeres cap the end of chromosomes?
prevent it from being mistaken by the cell as broken DNA in need repair
how is the nuclear envelope supported?
by the nuclear lamina
what is the nuclear lamina?
network of protein filaments that form a thin layer underlying the inner nuclear membrane
what is the chromatin that appears as a mass with dense chromosomal regions called?
heterochromatin (dark region)
what is heterochromatin?
is chromatin expressing little to no genes, and located under the nuclear envelope
what is the large dark region inside the nucleus?
nucleolus
what does the nucleolus contain?
contain the genes fro ribosomal RNA
where is rRNA located?
on multiple chromosome, but clustered together in the nucleolus
what are the proteins on eukaryotic chromosomes?
histones nad nonhistone chromosome proteins
nucleosomes contain DNA wrapped around a core of how many histone modules?
8
how many histones make up the nucleosome core.
4 small proteins with high proportion of + charged amino acids
how does the + charge help the nucleosome?
helps the histone bind tightly to the - charged sugar-phosphate backbone of DNA
what pulls nucleosomes together into the 30-nm fiber?
a linker histone (H1)
what does Histon H1 consist of?
a globular region plus a pair of long tails at its c-terminal and n-terminal ends
what does the globular region do?
constrains an additional 20 base pairs of DNA where it exits from the nucleosome core.
why is the globular region important?
for the formation of the 30 nm fiber
what are the two ways chromatin structure differ with degrees of extension or condensation?
heterochromatin and euchromatin
heterochromatin is more condensed than what?
euchromatin
what does the chromatin-remodeling complex do?
repositions the DNA wrapped around the nucleosome
how does the chromatin-remodeling complex work?
protein machine that uses the energy of ATP hydrolysis to change the position of DNA
what happens when the tightly bound DNA moves along the complex?
loosen the underlying DNA, making it more accessible to other protein
multiple rounds of nucleosome sliding does what?
decondense chromatin
what can dictate how to stretch of chromatin is treated by the cells?
the pattern of modification of histone tails
histones can be modified by the covalent attachment of a # of different chemical groups:
acetyl group, methyl group, phosphate
where do most modifications go on the tail?
n-terminal tails of histone
different combinations of histone tail modifications can confer what?
a specific meaning on the stretch of chromatin on which they occur
heterochromatin-specific modifications allow what?
heterochromatin to form and spread
what can repressive modifications to the histone tail do?
attract heterochromatin-specific proteins that reproduce the same modifications on neighboring proteins
repressive modifications allow heterochromatin to spread until?
it encounters a DNA barrier sequence that prevents heterochromatin spread
how can an expression of a gene be altered?
by moving it to another location in the genome
what is the position effect?
activity of a gene depends on its position along a chromosome
how can an X chromosome be inactivated?
by heterochromatin formation
