DNA & Chromosomes Flashcards
define genetic library
where most genes in a cell are contained
what is a nuclear membrane; what is another name for it
2 concentric membranes that separates the nucleus from the cytoplasm; nuclear envelope
define nuclear pores
selective channels through the nuclear envelope, allowing some substances thru
define nucleolus
the site of ribosomal RNA synthesis and assembly to ribosomal subunits
chromosomes
long strand of DNA and protein which can divide
DNA replication
provides a “mechanism for heredity” and cell division
gene expression
process of converting gene’s nucleotide sequence to amino acid sequence
what is The Genome
complete set of info in an organism’s DNA
what composes a nucleotide
- pentose sugar
- phosphate group
- nitrogenous base
how many nucleotides make a DNA molecule
2
what are some properties of DNA
- sugar-phosphate backbone
- chemical polarity
- complementary base pairing
- antiparallel strands
- double-helix
describe the bonding of purines with pyramidines
- a pairs with t using 2 h bonds
- g pairs with c using 3 h bonds
what direction do the nitrogenous bases point on DNA structure
toward centre of helix
define mitotic chromosomes
chromosomes in their most compressed form
what are challenges chromosomes face
- packaging (greater length of DNA per human cell than diameter of cell nucleus)
- accessibility
are DNA strands always tightly packed?
only during cell division (mitosis)
what do chromosomes do that helps cells to condense them
chromosomes wrap around specialized proteins
How do eukaryotic cells manage to package DNA molecules into compact chromosomes – yet still keep it accessible for replication?
thru formation of chromatin, which can change structure when needed
what are histones
- proteins that are responsible for first level of DNA packing in chromatin
- they tightly ionically bind to DNA
what is a nucleosome; what is it a basic unit of
- DNA wrapped around histone proteins
- basic unit of chromatin structure
are nucleosomes inside nucleotides, or the other way around
nucleosomes include ~200 nucleotide DNA pairs
what type of a charge does DNA have and how does that affect the proteins it wraps around
- negative charge (b/c of P groups in backbone)
- will wrap around positively charged proteins (amino acids like lysine, arginine)
describe steps of DNA packing with chromosomes
- short region of DNA double helix condenses into string for chromatin
- chromatin beads on a string pack into each other to make nucleosomes (interphase)
- packs into chromosome in extended form
- this condenses into a section of chromosome
- this condenses into spot on centromere
what are 3 ways that make chromatin dynamic
- protein assemblies (chromatin remodeling complexes)
- histone tail modifications
- histone (de)acetylation
describe histone acetylation
- acetyl group added to positive amino acids in histone tails
- the charge neutralizes and prevents binding to neighboring nucleosomes
- relaxation of chromatin structure to activate transcription
describe histone deacetylation
- acetyl group is removed from histone tails
- becomes charged and allows for binding to neighboring nucleosomes
- chromatin structure condenses and transcription is inhibited
define telomere
repeated DNA sequence on ends of chromosomes which allows for them to be replicated and protection
define replication origin
where the replication of the chromosome begins
define centromere
DNA sequence that allows attachment to mitotic spindles
how are DNA strands read
from 5’ to 3’ ends
